cmd/apigw/main.go

Source

Package: main
File: cmd/apigw/main.go
GitHub: https://github.com/theroutercompany/api_router/blob/main/cmd/apigw/main.go

Overview

What:

CLI entrypoint for operating the gateway.

This command is the primary user-facing interface for:

running the gateway (run)
validating config (validate)
generating a sample config (init)
managing a background daemon (daemon)
calling the control-plane admin endpoints (admin)
snapshotting env-based config into YAML (convert-env)

Why:

The gateway is designed to be both embeddable and operable. A thin CLI makes it easy to run locally, integrate with deployment scripts, and manage long-running processes without forcing a specific process manager.

How:

main() dispatches based on the first CLI argument. Each subcommand parses its own flags and then calls into shared packages:

pkg/gateway/config for config loading/validation
pkg/gateway/runtime for runtime lifecycle (including reload callback)
pkg/gateway/daemon for PID-file based daemon management

Notes: The CLI does not attempt to hide secrets beyond what the admin endpoints do. Avoid printing full configs with secrets to logs/terminals in production.

Imports
Constants
Functions and Methods
Related docs

Imports

`import` block 1

cmd/apigw/main.go#L3
import (
	"context"
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"os/exec"
	"os/signal"
	"path/filepath"
	"strconv"
	"strings"
	"syscall"
	"time"

	"github.com/fsnotify/fsnotify"
	"gopkg.in/yaml.v3"

	gatewayconfig "github.com/theroutercompany/api_router/pkg/gateway/config"
	gatewaydaemon "github.com/theroutercompany/api_router/pkg/gateway/daemon"
	gatewayruntime "github.com/theroutercompany/api_router/pkg/gateway/runtime"
)

Constants

`const` block 1

cmd/apigw/main.go#L223
const daemonChildEnv = "APIGW_DAEMON_CHILD"

`daemonChildEnv`

What: Environment variable used to mark a background daemon child process.

Why: Prevents recursive respawning when apigw daemon start --background launches a child that should run in the foreground.

How: The parent sets APIGW_DAEMON_CHILD=1 on the child process environment; the child checks it to decide whether to spawn again.

`const` block 2

cmd/apigw/main.go#L599
const sampleConfigYAML = `# Gateway configuration for the API router.
version: ""

http:
  port: 8080
  shutdownTimeout: 15s

readiness:
  timeout: 2s
  userAgent: api-router-gateway/readyz
  upstreams:
    - name: trade
      baseURL: https://trade.example.com
      healthPath: /health
      tls:
        enabled: false
        insecureSkipVerify: false
        caFile: ""
        clientCertFile: ""
        clientKeyFile: ""
    - name: task
      baseURL: https://task.example.com
      healthPath: /health
      tls:
        enabled: false
        insecureSkipVerify: false
        caFile: ""
        clientCertFile: ""
        clientKeyFile: ""

auth:
  secret: replace-me
  issuer: router
  audiences:
    - api

cors:
  allowedOrigins:
    - https://app.example.com

rateLimit:
  window: 60s
  max: 120

metrics:
  enabled: true
`

`sampleConfigYAML`

What: Embedded sample YAML used by the init command.

Why: Provides a quick starting point without requiring users to copy files from the repo.

How: Writes this string to disk in initCommand (optionally overwriting via --force).

Functions and Methods

`main`

What: Program entrypoint that dispatches to subcommands.

Why: Keeps the CLI simple and avoids a large framework for a small command surface.

How: Switches on os.Args[1], calls the matching command function, and exits non-zero on error.

cmd/apigw/main.go#L28
func main() {
	if len(os.Args) < 2 {
		usage()
		os.Exit(1)
	}

	var err error
	switch os.Args[1] {
	case "run":
		err = runCommand(os.Args[2:])
	case "validate":
		err = validateCommand(os.Args[2:])
	case "init":
		err = initCommand(os.Args[2:])
	case "daemon":
		err = daemonCommand(os.Args[2:])
	case "admin":
		err = adminCommand(os.Args[2:])
	case "convert-env":
		err = convertEnvCommand(os.Args[2:])
	default:
		usage()
		os.Exit(1)
	}

	if err != nil {
		log.Fatalf("apigw %s: %v", os.Args[1], err)
	}
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L29: if len(os.Args) < 2 { usage() os.Exit(1) }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L30: usage()
    - What: Calls usage.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
  - L31: os.Exit(1)
    - What: Calls os.Exit.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
L34: var err error
- What: Declares local names.
- Why: Introduces variables or types used later in the function.
- How: Executes a Go declaration statement inside the function body.
L35: switch os.Args[1] { case "run": err = runCommand(os.Args[2:]) case "validate": err = validateCommand(os.Args[2:]) case "init": err = initCo…
- What: Selects a branch from multiple cases.
- Why: Keeps multi-case branching readable and explicit.
- How: Evaluates the switch expression and executes the first matching case.
- Nested steps:
  - L36: case "run":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L37: err = runCommand(os.Args[2:])
        
        What: Assigns err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L38: case "validate":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L39: err = validateCommand(os.Args[2:])
        
        What: Assigns err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L40: case "init":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L41: err = initCommand(os.Args[2:])
        
        What: Assigns err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L42: case "daemon":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L43: err = daemonCommand(os.Args[2:])
        
        What: Assigns err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L44: case "admin":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L45: err = adminCommand(os.Args[2:])
        
        What: Assigns err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L46: case "convert-env":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L47: err = convertEnvCommand(os.Args[2:])
        
        What: Assigns err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L48: default:
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L49: usage()
        
        What: Calls usage.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
      - L50: os.Exit(1)
        
        What: Calls os.Exit.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
L53: if err != nil { log.Fatalf("apigw %s: %v", os.Args[1], err) }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L54: log.Fatalf("apigw %s: %v", os.Args[1], err)
    - What: Calls log.Fatalf.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.

`runCommand`

What: Implements apigw run to start the gateway runtime and optionally hot-reload on config changes.

Why: Provides the primary "run the gateway locally/in containers" workflow with an optional file watcher.

How: Loads config, builds a runtime with a reload callback, optionally starts a config watcher, and loops handling OS signals, runtime exit, watcher errors, and reload requests by stopping and restarting the runtime with rt.Reload.

cmd/apigw/main.go#L58
func runCommand(args []string) error {
	fs := flag.NewFlagSet("run", flag.ExitOnError)
	configPath := fs.String("config", "", "Path to gateway configuration file")
	watch := fs.Bool("watch", false, "Watch the config file for changes and hot-reload")
	if err := fs.Parse(args); err != nil {
		return err
	}

	opts := []gatewayconfig.Option{}
	if *configPath != "" {
		opts = append(opts, gatewayconfig.WithPath(*configPath))
	}

	cfg, err := gatewayconfig.Load(opts...)
	if err != nil {
		return fmt.Errorf("load config: %w", err)
	}

	reloadRequests := make(chan gatewayconfig.Config, 1)
	enqueueReload := func(cfg gatewayconfig.Config) {
		select {
		case reloadRequests <- cfg:
		default:
			go func() { reloadRequests <- cfg }()
		}
	}

	reloadFunc := func() (gatewayconfig.Config, error) {
		cfg, err := gatewayconfig.Load(opts...)
		if err != nil {
			return gatewayconfig.Config{}, err
		}
		enqueueReload(cfg)
		return cfg, nil
	}

	rt, err := gatewayruntime.New(cfg, gatewayruntime.WithReloadFunc(reloadFunc))
	if err != nil {
		return fmt.Errorf("build runtime: %w", err)
	}

	ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer cancel()

	var (
		watchErrCh  <-chan error
		watchCancel context.CancelFunc
	)
	if *watch {
		if *configPath == "" {
			return errors.New("--config is required when --watch is enabled")
		}
		watchReloadCh, errCh, cancelWatch, err := watchConfig(ctx, *configPath, opts)
		if err != nil {
			return fmt.Errorf("watch config: %w", err)
		}
		watchErrCh = errCh
		watchCancel = cancelWatch
		go func() {
			for cfg := range watchReloadCh {
				enqueueReload(cfg)
			}
		}()
	}
	defer func() {
		if watchCancel != nil {
			watchCancel()
		}
	}()

	runCtx, runCancel := context.WithCancel(ctx)
	runDone := make(chan error, 1)
	go func() {
		runDone <- rt.Run(runCtx)
	}()

	for {
		select {
		case err := <-runDone:
			runCancel()
			if err != nil && !errors.Is(err, context.Canceled) {
				return err
			}
			return nil
		case cfg := <-reloadRequests:
			runCancel()
			if err := <-runDone; err != nil && !errors.Is(err, context.Canceled) {
				return err
			}
			if err := rt.Reload(cfg); err != nil {
				return fmt.Errorf("reload config: %w", err)
			}
			runCtx, runCancel = context.WithCancel(ctx)
			runDone = make(chan error, 1)
			go func() {
				runDone <- rt.Run(runCtx)
			}()
			log.Printf("configuration reloaded")
		case err, ok := <-watchErrCh:
			if !ok {
				watchErrCh = nil
				continue
			}
			if err != nil {
				log.Printf("config watch error: %v", err)
			}
		case <-ctx.Done():
			runCancel()
		}
	}
}

Walkthrough

Expand walkthrough (84 steps)

The list below documents the statements inside the function body, including nested blocks and inline closures.

L59: fs := flag.NewFlagSet("run", flag.ExitOnError)
- What: Defines fs.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L60: configPath := fs.String("config", "", "Path to gateway configuration file")
- What: Defines configPath.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L61: watch := fs.Bool("watch", false, "Watch the config file for changes and hot-reload")
- What: Defines watch.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L62: if err := fs.Parse(args); err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L62: err := fs.Parse(args)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L63: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L66: opts := []gatewayconfig.Option{}
- What: Defines opts.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L67: if *configPath != "" { opts = append(opts, gatewayconfig.WithPath(*configPath)) }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L68: opts = append(opts, gatewayconfig.WithPath(*configPath))
    - What: Assigns opts.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L71: cfg, err := gatewayconfig.Load(opts...)
- What: Defines cfg, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L72: if err != nil { return fmt.Errorf("load config: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L73: return fmt.Errorf("load config: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L76: reloadRequests := make(chan gatewayconfig.Config, 1)
- What: Defines reloadRequests.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L77: enqueueReload := func(cfg gatewayconfig.Config) { select { case reloadRequests <- cfg: default: go func() { reloadRequests <- cfg }() } }
- What: Defines enqueueReload.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
- Nested steps:
  - L77: func(cfg gatewayconfig.Config) { select { case reloadRequests <- cfg: default: go func() { reloadRequests <- cfg }() } }
    - What: Defines an inline function (closure).
    - Why: Encapsulates callback logic and may capture variables from the surrounding scope.
    - How: Declares a func literal and uses it as a value (for example, as an HTTP handler or callback).
    - Nested steps:
      - L78: select { case reloadRequests <- cfg: default: go func() { reloadRequests <- cfg }() }
        
        What: Selects among concurrent operations.
        
        Why: Coordinates channel operations without blocking incorrectly.
        
        How: Executes a select statement and runs one ready case.
        
        Nested steps:
        
        L79: case reloadRequests <- cfg:
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        L80: default:
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        Nested steps:
        
        L81: go func() { reloadRequests <- cfg }()
        
        What: Starts a goroutine.
        
        Why: Runs work concurrently.
        
        How: Invokes the function call asynchronously using go.
        
        Nested steps:
        
        L81: func() { reloadRequests <- cfg }
        
        What: Defines an inline function (closure).
        
        Why: Encapsulates callback logic and may capture variables from the surrounding scope.
        
        How: Declares a func literal and uses it as a value (for example, as an HTTP handler or callback).
        
        Nested steps:
        
        L81: reloadRequests <- cfg
        
        What: Sends a value on a channel.
        
        Why: Communicates with another goroutine.
        
        How: Executes a channel send operation.
L85: reloadFunc := func() (gatewayconfig.Config, error) { cfg, err := gatewayconfig.Load(opts...) if err != nil { return gatewayconfig.Config{},…
- What: Defines reloadFunc.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
- Nested steps:
  - L85: func() (gatewayconfig.Config, error) { cfg, err := gatewayconfig.Load(opts...) if err != nil { return gatewayconfig.Config{}, err } enqueue…
    - What: Defines an inline function (closure).
    - Why: Encapsulates callback logic and may capture variables from the surrounding scope.
    - How: Declares a func literal and uses it as a value (for example, as an HTTP handler or callback).
    - Nested steps:
      - L86: cfg, err := gatewayconfig.Load(opts...)
        
        What: Defines cfg, err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
      - L87: if err != nil { return gatewayconfig.Config{}, err }
        
        What: Branches conditionally.
        
        Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L88: return gatewayconfig.Config{}, err
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
      - L90: enqueueReload(cfg)
        
        What: Calls enqueueReload.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
      - L91: return cfg, nil
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
L94: rt, err := gatewayruntime.New(cfg, gatewayruntime.WithReloadFunc(reloadFunc))
- What: Defines rt, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L95: if err != nil { return fmt.Errorf("build runtime: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L96: return fmt.Errorf("build runtime: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L99: ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
- What: Defines ctx, cancel.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L100: defer cancel()
- What: Defers a call for cleanup.
- Why: Ensures the deferred action runs even on early returns.
- How: Schedules the call to run when the surrounding function returns.
L102: var ( watchErrCh <-chan error watchCancel context.CancelFunc )
- What: Declares local names.
- Why: Introduces variables or types used later in the function.
- How: Executes a Go declaration statement inside the function body.
L106: if *watch { if *configPath == "" { return errors.New("--config is required when --watch is enabled") } watchReloadCh, errCh, cancelWatch, e…
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L107: if *configPath == "" { return errors.New("--config is required when --watch is enabled") }
    - What: Branches conditionally.
    - Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
    - How: Evaluates the condition and executes the matching branch.
    - Nested steps:
      - L108: return errors.New("--config is required when --watch is enabled")
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L110: watchReloadCh, errCh, cancelWatch, err := watchConfig(ctx, *configPath, opts)
    - What: Defines watchReloadCh, errCh, cancelWatch, err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L111: if err != nil { return fmt.Errorf("watch config: %w", err) }
    - What: Branches conditionally.
    - Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
    - How: Evaluates the condition and executes the matching branch.
    - Nested steps:
      - L112: return fmt.Errorf("watch config: %w", err)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L114: watchErrCh = errCh
    - What: Assigns watchErrCh.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L115: watchCancel = cancelWatch
    - What: Assigns watchCancel.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L116: go func() { for cfg := range watchReloadCh { enqueueReload(cfg) } }()
    - What: Starts a goroutine.
    - Why: Runs work concurrently.
    - How: Invokes the function call asynchronously using go.
    - Nested steps:
      - L116: func() { for cfg := range watchReloadCh { enqueueReload(cfg) } }
        
        What: Defines an inline function (closure).
        
        Why: Encapsulates callback logic and may capture variables from the surrounding scope.
        
        How: Declares a func literal and uses it as a value (for example, as an HTTP handler or callback).
        
        Nested steps:
        
        L117: for cfg := range watchReloadCh { enqueueReload(cfg) }
        
        What: Iterates over a collection.
        
        Why: Processes multiple elements with the same logic.
        
        How: Executes a for ... range loop.
        
        Nested steps:
        
        L118: enqueueReload(cfg)
        
        What: Calls enqueueReload.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
L122: defer func() { if watchCancel != nil { watchCancel() } }()
- What: Defers a call for cleanup.
- Why: Ensures the deferred action runs even on early returns.
- How: Schedules the call to run when the surrounding function returns.
- Nested steps:
  - L122: func() { if watchCancel != nil { watchCancel() } }
    - What: Defines an inline function (closure).
    - Why: Encapsulates callback logic and may capture variables from the surrounding scope.
    - How: Declares a func literal and uses it as a value (for example, as an HTTP handler or callback).
    - Nested steps:
      - L123: if watchCancel != nil { watchCancel() }
        
        What: Branches conditionally.
        
        Why: Handles different execution paths based on runtime state.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L124: watchCancel()
        
        What: Calls watchCancel.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
L128: runCtx, runCancel := context.WithCancel(ctx)
- What: Defines runCtx, runCancel.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L129: runDone := make(chan error, 1)
- What: Defines runDone.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L130: go func() { runDone <- rt.Run(runCtx) }()
- What: Starts a goroutine.
- Why: Runs work concurrently.
- How: Invokes the function call asynchronously using go.
- Nested steps:
  - L130: func() { runDone <- rt.Run(runCtx) }
    - What: Defines an inline function (closure).
    - Why: Encapsulates callback logic and may capture variables from the surrounding scope.
    - How: Declares a func literal and uses it as a value (for example, as an HTTP handler or callback).
    - Nested steps:
      - L131: runDone <- rt.Run(runCtx)
        
        What: Sends a value on a channel.
        
        Why: Communicates with another goroutine.
        
        How: Executes a channel send operation.
L134: for { select { case err := <-runDone: runCancel() if err != nil && !errors.Is(err, context.Canceled) { return err } return nil case cfg := …
- What: Runs a loop.
- Why: Repeats logic until a condition is met or the loop terminates.
- How: Executes a for loop statement.
- Nested steps:
  - L135: select { case err := <-runDone: runCancel() if err != nil && !errors.Is(err, context.Canceled) { return err } return nil case cfg := <-relo…
    - What: Selects among concurrent operations.
    - Why: Coordinates channel operations without blocking incorrectly.
    - How: Executes a select statement and runs one ready case.
    - Nested steps:
      - L136: case err := <-runDone:
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        Nested steps:
        
        L137: runCancel()
        
        What: Calls runCancel.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
        
        L138: if err != nil && !errors.Is(err, context.Canceled) { return err }
        
        What: Branches conditionally.
        
        Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L139: return err
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
        
        L141: return nil
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
      - L142: case cfg := <-reloadRequests:
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        Nested steps:
        
        L143: runCancel()
        
        What: Calls runCancel.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
        
        L144: if err := <-runDone; err != nil && !errors.Is(err, context.Canceled) { return err }
        
        What: Branches conditionally.
        
        Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L144: err := <-runDone
        
        What: Defines err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
        
        L145: return err
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
        
        L147: if err := rt.Reload(cfg); err != nil { return fmt.Errorf("reload config: %w", err) }
        
        What: Branches conditionally.
        
        Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L147: err := rt.Reload(cfg)
        
        What: Defines err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
        
        L148: return fmt.Errorf("reload config: %w", err)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
        
        L150: runCtx, runCancel = context.WithCancel(ctx)
        
        What: Assigns runCtx, runCancel.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
        
        L151: runDone = make(chan error, 1)
        
        What: Assigns runDone.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
        
        L152: go func() { runDone <- rt.Run(runCtx) }()
        
        What: Starts a goroutine.
        
        Why: Runs work concurrently.
        
        How: Invokes the function call asynchronously using go.
        
        Nested steps:
        
        L152: func() { runDone <- rt.Run(runCtx) }
        
        What: Defines an inline function (closure).
        
        Why: Encapsulates callback logic and may capture variables from the surrounding scope.
        
        How: Declares a func literal and uses it as a value (for example, as an HTTP handler or callback).
        
        Nested steps:
        
        L153: runDone <- rt.Run(runCtx)
        
        What: Sends a value on a channel.
        
        Why: Communicates with another goroutine.
        
        How: Executes a channel send operation.
        
        L155: log.Printf("configuration reloaded")
        
        What: Calls log.Printf.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
      - L156: case err, ok := <-watchErrCh:
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        Nested steps:
        
        L157: if !ok { watchErrCh = nil continue }
        
        What: Branches conditionally.
        
        Why: Handles different execution paths based on runtime state.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L158: watchErrCh = nil
        
        What: Assigns watchErrCh.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
        
        L159: continue
        
        What: Executes a statement.
        
        Why: Advances the function logic.
        
        How: Runs this statement as part of the function body.
        
        L161: if err != nil { log.Printf("config watch error: %v", err) }
        
        What: Branches conditionally.
        
        Why: Handles different execution paths based on runtime state.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L162: log.Printf("config watch error: %v", err)
        
        What: Calls log.Printf.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
      - L164: case <-ctx.Done():
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        Nested steps:
        
        L165: runCancel()
        
        What: Calls runCancel.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.

`validateCommand`

What: Implements apigw validate to check config validity without starting the server.

Why: Useful in CI and in deployment pipelines to fail fast before rollout.

How: Loads config via gatewayconfig.Load (optionally with --config) and prints a success message on completion.

cmd/apigw/main.go#L170
func validateCommand(args []string) error {
	fs := flag.NewFlagSet("validate", flag.ExitOnError)
	configPath := fs.String("config", "", "Path to gateway configuration file")
	if err := fs.Parse(args); err != nil {
		return err
	}

	opts := []gatewayconfig.Option{}
	if *configPath != "" {
		opts = append(opts, gatewayconfig.WithPath(*configPath))
	}

	if _, err := gatewayconfig.Load(opts...); err != nil {
		return fmt.Errorf("validate config: %w", err)
	}

	fmt.Println("configuration valid")
	return nil
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L171: fs := flag.NewFlagSet("validate", flag.ExitOnError)
- What: Defines fs.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L172: configPath := fs.String("config", "", "Path to gateway configuration file")
- What: Defines configPath.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L173: if err := fs.Parse(args); err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L173: err := fs.Parse(args)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L174: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L177: opts := []gatewayconfig.Option{}
- What: Defines opts.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L178: if *configPath != "" { opts = append(opts, gatewayconfig.WithPath(*configPath)) }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L179: opts = append(opts, gatewayconfig.WithPath(*configPath))
    - What: Assigns opts.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L182: if _, err := gatewayconfig.Load(opts...); err != nil { return fmt.Errorf("validate config: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L182: _, err := gatewayconfig.Load(opts...)
    - What: Defines _, err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L183: return fmt.Errorf("validate config: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L186: fmt.Println("configuration valid")
- What: Calls fmt.Println.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L187: return nil
- What: Returns from the current function.
- Why: Ends the current execution path and hands control back to the caller.
- How: Executes a return statement (possibly returning values).

`initCommand`

What: Implements apigw init to write a sample configuration file.

Why: Reduces friction for first-time setup and local development.

How: Writes sampleConfigYAML to --path (default apigw.yaml) and refuses to overwrite unless --force is set.

cmd/apigw/main.go#L190
func initCommand(args []string) error {
	fs := flag.NewFlagSet("init", flag.ExitOnError)
	outputPath := fs.String("path", "apigw.yaml", "Destination path for generated config")
	force := fs.Bool("force", false, "Overwrite existing file")
	if err := fs.Parse(args); err != nil {
		return err
	}

	if !*force {
		if _, err := os.Stat(*outputPath); err == nil {
			return fmt.Errorf("config file %s already exists (use --force to overwrite)", *outputPath)
		}
	}

	if err := os.WriteFile(*outputPath, []byte(sampleConfigYAML), 0o644); err != nil {
		return fmt.Errorf("write config: %w", err)
	}

	fmt.Printf("configuration written to %s\n", *outputPath)
	return nil
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L191: fs := flag.NewFlagSet("init", flag.ExitOnError)
- What: Defines fs.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L192: outputPath := fs.String("path", "apigw.yaml", "Destination path for generated config")
- What: Defines outputPath.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L193: force := fs.Bool("force", false, "Overwrite existing file")
- What: Defines force.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L194: if err := fs.Parse(args); err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L194: err := fs.Parse(args)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L195: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L198: if !*force { if _, err := os.Stat(*outputPath); err == nil { return fmt.Errorf("config file %s already exists (use --force to overwrite)", …
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L199: if _, err := os.Stat(*outputPath); err == nil { return fmt.Errorf("config file %s already exists (use --force to overwrite)", *outputPath) }
    - What: Branches conditionally.
    - Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
    - How: Evaluates the condition and executes the matching branch.
    - Nested steps:
      - L199: _, err := os.Stat(*outputPath)
        
        What: Defines _, err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
      - L200: return fmt.Errorf("config file %s already exists (use --force to overwrite)", *outputPath)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
L204: if err := os.WriteFile(*outputPath, []byte(sampleConfigYAML), 0o644); err != nil { return fmt.Errorf("write config: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L204: err := os.WriteFile(*outputPath, []byte(sampleConfigYAML), 0o644)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L205: return fmt.Errorf("write config: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L208: fmt.Printf("configuration written to %s\n", *outputPath)
- What: Calls fmt.Printf.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L209: return nil
- What: Returns from the current function.
- Why: Ends the current execution path and hands control back to the caller.
- How: Executes a return statement (possibly returning values).

`usage`

What: Prints CLI usage text.

Why: Provides a quick help message when the CLI is invoked incorrectly.

How: Writes a static usage block to stderr.

cmd/apigw/main.go#L212
func usage() {
	fmt.Fprintf(os.Stderr, "Usage: apigw <command> [options]\n")
	fmt.Fprintf(os.Stderr, "Commands:\n")
	fmt.Fprintf(os.Stderr, "  run       Start the gateway using the provided config\n")
	fmt.Fprintf(os.Stderr, "  validate  Validate configuration without starting the gateway\n")
	fmt.Fprintf(os.Stderr, "  init      Generate a config skeleton\n")
	fmt.Fprintf(os.Stderr, "  daemon    Manage the gateway as a background process\n")
	fmt.Fprintf(os.Stderr, "  admin     Invoke admin control-plane endpoints (status/reload)\n")
	fmt.Fprintf(os.Stderr, "  convert-env  Snapshot environment variables into a YAML config\n")
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L213: fmt.Fprintf(os.Stderr, "Usage: apigw <command> [options]\n")
- What: Calls fmt.Fprintf.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L214: fmt.Fprintf(os.Stderr, "Commands:\n")
- What: Calls fmt.Fprintf.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L215: fmt.Fprintf(os.Stderr, " run Start the gateway using the provided config\n")
- What: Calls fmt.Fprintf.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L216: fmt.Fprintf(os.Stderr, " validate Validate configuration without starting the gateway\n")
- What: Calls fmt.Fprintf.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L217: fmt.Fprintf(os.Stderr, " init Generate a config skeleton\n")
- What: Calls fmt.Fprintf.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L218: fmt.Fprintf(os.Stderr, " daemon Manage the gateway as a background process\n")
- What: Calls fmt.Fprintf.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L219: fmt.Fprintf(os.Stderr, " admin Invoke admin control-plane endpoints (status/reload)\n")
- What: Calls fmt.Fprintf.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L220: fmt.Fprintf(os.Stderr, " convert-env Snapshot environment variables into a YAML config\n")
- What: Calls fmt.Fprintf.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.

`daemonCommand`

What: Implements apigw daemon subcommand dispatch (start/stop/status).

Why: Groups daemon lifecycle operations under a single top-level command.

How: Selects a subcommand (default start) and delegates to daemonStart, daemonStop, or daemonStatus.

cmd/apigw/main.go#L225
func daemonCommand(args []string) error {
	subcommand := "start"
	if len(args) > 0 && !strings.HasPrefix(args[0], "-") {
		subcommand = args[0]
		args = args[1:]
	}

	switch subcommand {
	case "start":
		return daemonStart(args)
	case "stop":
		return daemonStop(args)
	case "status":
		return daemonStatus(args)
	default:
		return fmt.Errorf("unknown daemon subcommand %q", subcommand)
	}
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L226: subcommand := "start"
- What: Defines subcommand.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L227: if len(args) > 0 && !strings.HasPrefix(args[0], "-") { subcommand = args[0] args = args[1:] }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L228: subcommand = args[0]
    - What: Assigns subcommand.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L229: args = args[1:]
    - What: Assigns args.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L232: switch subcommand { case "start": return daemonStart(args) case "stop": return daemonStop(args) case "status": return daemonStatus(args) de…
- What: Selects a branch from multiple cases.
- Why: Keeps multi-case branching readable and explicit.
- How: Evaluates the switch expression and executes the first matching case.
- Nested steps:
  - L233: case "start":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L234: return daemonStart(args)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L235: case "stop":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L236: return daemonStop(args)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L237: case "status":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L238: return daemonStatus(args)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L239: default:
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L240: return fmt.Errorf("unknown daemon subcommand %q", subcommand)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).

`daemonStart`

What: Starts the gateway daemon, optionally in background mode.

Why: Supports running the gateway as a managed process with PID/log files without requiring external tooling.

How: If --background and not already a child, spawns a child apigw daemon start process; otherwise calls gatewaydaemon.Run with config/pid/log options and a signal-cancelled context.

cmd/apigw/main.go#L244
func daemonStart(args []string) error {
	rawArgs := append([]string(nil), args...)
	fs := flag.NewFlagSet("daemon start", flag.ExitOnError)
	configPath := fs.String("config", "", "Path to gateway configuration file")
	pidPath := fs.String("pid", "apigw.pid", "Path to write the PID file")
	logPath := fs.String("log", "", "Path to write daemon logs")
	background := fs.Bool("background", false, "Run the daemon in the background")
	if err := fs.Parse(args); err != nil {
		return err
	}

	isChild := os.Getenv(daemonChildEnv) == "1"
	if *background && !isChild {
		childArgs := []string{"daemon", "start"}
		for _, arg := range rawArgs {
			if strings.HasPrefix(arg, "--background") {
				continue
			}
			childArgs = append(childArgs, arg)
		}
		cmd := exec.Command(os.Args[0], childArgs...)
		cmd.Stdout = os.Stdout
		cmd.Stderr = os.Stderr
		cmd.Env = append(os.Environ(), daemonChildEnv+"=1")
		if err := cmd.Start(); err != nil {
			return fmt.Errorf("start background daemon: %w", err)
		}
		fmt.Fprintf(os.Stdout, "daemon started (pid %d)\n", cmd.Process.Pid)
		return nil
	}

	os.Unsetenv(daemonChildEnv)
	ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer cancel()

	options := gatewaydaemon.Options{
		ConfigPath: *configPath,
		PIDFile:    *pidPath,
		LogFile:    *logPath,
	}

	return gatewaydaemon.Run(ctx, options)
}

Walkthrough

Expand walkthrough (30 steps)

The list below documents the statements inside the function body, including nested blocks and inline closures.

L245: rawArgs := append([]string(nil), args...)
- What: Defines rawArgs.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L246: fs := flag.NewFlagSet("daemon start", flag.ExitOnError)
- What: Defines fs.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L247: configPath := fs.String("config", "", "Path to gateway configuration file")
- What: Defines configPath.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L248: pidPath := fs.String("pid", "apigw.pid", "Path to write the PID file")
- What: Defines pidPath.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L249: logPath := fs.String("log", "", "Path to write daemon logs")
- What: Defines logPath.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L250: background := fs.Bool("background", false, "Run the daemon in the background")
- What: Defines background.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L251: if err := fs.Parse(args); err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L251: err := fs.Parse(args)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L252: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L255: isChild := os.Getenv(daemonChildEnv) == "1"
- What: Defines isChild.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L256: if *background && !isChild { childArgs := []string{"daemon", "start"} for _, arg := range rawArgs { if strings.HasPrefix(arg, "--background…
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L257: childArgs := []string{"daemon", "start"}
    - What: Defines childArgs.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L258: for _, arg := range rawArgs { if strings.HasPrefix(arg, "--background") { continue } childArgs = append(childArgs, arg) }
    - What: Iterates over a collection.
    - Why: Processes multiple elements with the same logic.
    - How: Executes a for ... range loop.
    - Nested steps:
      - L259: if strings.HasPrefix(arg, "--background") { continue }
        
        What: Branches conditionally.
        
        Why: Handles different execution paths based on runtime state.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L260: continue
        
        What: Executes a statement.
        
        Why: Advances the function logic.
        
        How: Runs this statement as part of the function body.
      - L262: childArgs = append(childArgs, arg)
        
        What: Assigns childArgs.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L264: cmd := exec.Command(os.Args[0], childArgs...)
    - What: Defines cmd.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L265: cmd.Stdout = os.Stdout
    - What: Assigns cmd.Stdout.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L266: cmd.Stderr = os.Stderr
    - What: Assigns cmd.Stderr.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L267: cmd.Env = append(os.Environ(), daemonChildEnv+"=1")
    - What: Assigns cmd.Env.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L268: if err := cmd.Start(); err != nil { return fmt.Errorf("start background daemon: %w", err) }
    - What: Branches conditionally.
    - Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
    - How: Evaluates the condition and executes the matching branch.
    - Nested steps:
      - L268: err := cmd.Start()
        
        What: Defines err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
      - L269: return fmt.Errorf("start background daemon: %w", err)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L271: fmt.Fprintf(os.Stdout, "daemon started (pid %d)\n", cmd.Process.Pid)
    - What: Calls fmt.Fprintf.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
  - L272: return nil
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L275: os.Unsetenv(daemonChildEnv)
- What: Calls os.Unsetenv.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L276: ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
- What: Defines ctx, cancel.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L277: defer cancel()
- What: Defers a call for cleanup.
- Why: Ensures the deferred action runs even on early returns.
- How: Schedules the call to run when the surrounding function returns.
L279: options := gatewaydaemon.Options{ ConfigPath: *configPath, PIDFile: *pidPath, LogFile: *logPath, }
- What: Defines options.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L285: return gatewaydaemon.Run(ctx, options)
- What: Returns from the current function.
- Why: Ends the current execution path and hands control back to the caller.
- How: Executes a return statement (possibly returning values).

`daemonStop`

What: Stops the daemon process by sending a signal and waiting for exit.

Why: Provides a controlled shutdown path and cleans up stale PID files.

How: Parses a signal, calls gatewaydaemon.Stop, then polls gatewaydaemon.Status until the process exits or the wait timeout expires.

cmd/apigw/main.go#L288
func daemonStop(args []string) error {
	fs := flag.NewFlagSet("daemon stop", flag.ExitOnError)
	pidPath := fs.String("pid", "apigw.pid", "Path to PID file")
	signalName := fs.String("signal", "SIGTERM", "Signal to send (name or number)")
	wait := fs.Duration("wait", 5*time.Second, "Time to wait for shutdown")
	if err := fs.Parse(args); err != nil {
		return err
	}

	sig, err := parseSignal(*signalName)
	if err != nil {
		return err
	}

	status, err := gatewaydaemon.Stop(*pidPath, sig)
	if errors.Is(err, os.ErrNotExist) {
		fmt.Fprintln(os.Stdout, "daemon not running (no pid file)")
		return nil
	}
	if err != nil {
		return fmt.Errorf("stop daemon: %w", err)
	}

	if !status.Running {
		fmt.Fprintln(os.Stdout, "daemon already stopped")
		_ = os.Remove(*pidPath)
		return nil
	}

	deadline := time.Now().Add(*wait)
	waitDur := *wait
	for {
		time.Sleep(200 * time.Millisecond)
		st, err := gatewaydaemon.Status(*pidPath)
		if errors.Is(err, os.ErrNotExist) {
			fmt.Fprintln(os.Stdout, "daemon stopped")
			_ = os.Remove(*pidPath)
			return nil
		}
		if err != nil {
			return fmt.Errorf("check status: %w", err)
		}
		if !st.Running {
			fmt.Fprintln(os.Stdout, "daemon stopped")
			_ = os.Remove(*pidPath)
			return nil
		}
		if time.Now().After(deadline) {
			return fmt.Errorf("daemon pid %d did not stop within %s", st.PID, waitDur)
		}
	}
}

Walkthrough

Expand walkthrough (37 steps)

The list below documents the statements inside the function body, including nested blocks and inline closures.

L289: fs := flag.NewFlagSet("daemon stop", flag.ExitOnError)
- What: Defines fs.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L290: pidPath := fs.String("pid", "apigw.pid", "Path to PID file")
- What: Defines pidPath.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L291: signalName := fs.String("signal", "SIGTERM", "Signal to send (name or number)")
- What: Defines signalName.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L292: wait := fs.Duration("wait", 5*time.Second, "Time to wait for shutdown")
- What: Defines wait.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L293: if err := fs.Parse(args); err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L293: err := fs.Parse(args)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L294: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L297: sig, err := parseSignal(*signalName)
- What: Defines sig, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L298: if err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L299: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L302: status, err := gatewaydaemon.Stop(*pidPath, sig)
- What: Defines status, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L303: if errors.Is(err, os.ErrNotExist) { fmt.Fprintln(os.Stdout, "daemon not running (no pid file)") return nil }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L304: fmt.Fprintln(os.Stdout, "daemon not running (no pid file)")
    - What: Calls fmt.Fprintln.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
  - L305: return nil
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L307: if err != nil { return fmt.Errorf("stop daemon: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L308: return fmt.Errorf("stop daemon: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L311: if !status.Running { fmt.Fprintln(os.Stdout, "daemon already stopped") _ = os.Remove(*pidPath) return nil }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L312: fmt.Fprintln(os.Stdout, "daemon already stopped")
    - What: Calls fmt.Fprintln.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
  - L313: _ = os.Remove(*pidPath)
    - What: Assigns _.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L314: return nil
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L317: deadline := time.Now().Add(*wait)
- What: Defines deadline.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L318: waitDur := *wait
- What: Defines waitDur.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L319: for { time.Sleep(200 * time.Millisecond) st, err := gatewaydaemon.Status(*pidPath) if errors.Is(err, os.ErrNotExist) { fmt.Fprintln(os.Stdo…
- What: Runs a loop.
- Why: Repeats logic until a condition is met or the loop terminates.
- How: Executes a for loop statement.
- Nested steps:
  - L320: time.Sleep(200 * time.Millisecond)
    - What: Calls time.Sleep.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
  - L321: st, err := gatewaydaemon.Status(*pidPath)
    - What: Defines st, err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L322: if errors.Is(err, os.ErrNotExist) { fmt.Fprintln(os.Stdout, "daemon stopped") _ = os.Remove(*pidPath) return nil }
    - What: Branches conditionally.
    - Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
    - How: Evaluates the condition and executes the matching branch.
    - Nested steps:
      - L323: fmt.Fprintln(os.Stdout, "daemon stopped")
        
        What: Calls fmt.Fprintln.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
      - L324: _ = os.Remove(*pidPath)
        
        What: Assigns _.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
      - L325: return nil
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L327: if err != nil { return fmt.Errorf("check status: %w", err) }
    - What: Branches conditionally.
    - Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
    - How: Evaluates the condition and executes the matching branch.
    - Nested steps:
      - L328: return fmt.Errorf("check status: %w", err)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L330: if !st.Running { fmt.Fprintln(os.Stdout, "daemon stopped") _ = os.Remove(*pidPath) return nil }
    - What: Branches conditionally.
    - Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
    - How: Evaluates the condition and executes the matching branch.
    - Nested steps:
      - L331: fmt.Fprintln(os.Stdout, "daemon stopped")
        
        What: Calls fmt.Fprintln.
        
        Why: Performs side effects or delegates work to a helper.
        
        How: Executes the expression statement.
      - L332: _ = os.Remove(*pidPath)
        
        What: Assigns _.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
      - L333: return nil
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L335: if time.Now().After(deadline) { return fmt.Errorf("daemon pid %d did not stop within %s", st.PID, waitDur) }
    - What: Branches conditionally.
    - Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
    - How: Evaluates the condition and executes the matching branch.
    - Nested steps:
      - L336: return fmt.Errorf("daemon pid %d did not stop within %s", st.PID, waitDur)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).

`daemonStatus`

What: Reports daemon status based on the PID file.

Why: Allows scripts and operators to check whether the managed process is running.

How: Calls gatewaydaemon.Status and prints daemon running, daemon stopped, or daemon not running depending on the PID/state.

cmd/apigw/main.go#L341
func daemonStatus(args []string) error {
	fs := flag.NewFlagSet("daemon status", flag.ExitOnError)
	pidPath := fs.String("pid", "apigw.pid", "Path to PID file")
	if err := fs.Parse(args); err != nil {
		return err
	}

	status, err := gatewaydaemon.Status(*pidPath)
	if err != nil {
		return fmt.Errorf("status: %w", err)
	}
	if status.PID == 0 {
		fmt.Fprintln(os.Stdout, "daemon not running")
		return nil
	}
	if status.Running {
		fmt.Fprintf(os.Stdout, "daemon running (pid %d)\n", status.PID)
	} else {
		fmt.Fprintf(os.Stdout, "daemon stopped (stale pid %d)\n", status.PID)
	}
	return nil
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L342: fs := flag.NewFlagSet("daemon status", flag.ExitOnError)
- What: Defines fs.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L343: pidPath := fs.String("pid", "apigw.pid", "Path to PID file")
- What: Defines pidPath.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L344: if err := fs.Parse(args); err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L344: err := fs.Parse(args)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L345: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L348: status, err := gatewaydaemon.Status(*pidPath)
- What: Defines status, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L349: if err != nil { return fmt.Errorf("status: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L350: return fmt.Errorf("status: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L352: if status.PID == 0 { fmt.Fprintln(os.Stdout, "daemon not running") return nil }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L353: fmt.Fprintln(os.Stdout, "daemon not running")
    - What: Calls fmt.Fprintln.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
  - L354: return nil
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L356: if status.Running { fmt.Fprintf(os.Stdout, "daemon running (pid %d)\n", status.PID) } else { fmt.Fprintf(os.Stdout, "daemon stopped (stale …
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L357: fmt.Fprintf(os.Stdout, "daemon running (pid %d)\n", status.PID)
    - What: Calls fmt.Fprintf.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
  - L359: fmt.Fprintf(os.Stdout, "daemon stopped (stale pid %d)\n", status.PID)
    - What: Calls fmt.Fprintf.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
L361: return nil
- What: Returns from the current function.
- Why: Ends the current execution path and hands control back to the caller.
- How: Executes a return statement (possibly returning values).

`parseSignal`

What: Parses a signal name or number into a syscall.Signal.

Why: Allows daemon stop to accept both human-friendly names and numeric values.

How: Accepts integers and a small set of common names (TERM, KILL, INT, QUIT), returning an error for unsupported values.

cmd/apigw/main.go#L364
func parseSignal(value string) (syscall.Signal, error) {
	if value == "" {
		return syscall.SIGTERM, nil
	}
	if n, err := strconv.Atoi(value); err == nil {
		return syscall.Signal(n), nil
	}

	switch strings.ToUpper(value) {
	case "TERM", "SIGTERM":
		return syscall.SIGTERM, nil
	case "KILL", "SIGKILL":
		return syscall.SIGKILL, nil
	case "INT", "SIGINT":
		return syscall.SIGINT, nil
	case "QUIT", "SIGQUIT":
		return syscall.SIGQUIT, nil
	default:
		return 0, fmt.Errorf("unsupported signal %q", value)
	}
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L365: if value == "" { return syscall.SIGTERM, nil }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L366: return syscall.SIGTERM, nil
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L368: if n, err := strconv.Atoi(value); err == nil { return syscall.Signal(n), nil }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L368: n, err := strconv.Atoi(value)
    - What: Defines n, err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L369: return syscall.Signal(n), nil
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L372: switch strings.ToUpper(value) { case "TERM", "SIGTERM": return syscall.SIGTERM, nil case "KILL", "SIGKILL": return syscall.SIGKILL, nil cas…
- What: Selects a branch from multiple cases.
- Why: Keeps multi-case branching readable and explicit.
- How: Evaluates the switch expression and executes the first matching case.
- Nested steps:
  - L373: case "TERM", "SIGTERM":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L374: return syscall.SIGTERM, nil
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L375: case "KILL", "SIGKILL":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L376: return syscall.SIGKILL, nil
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L377: case "INT", "SIGINT":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L378: return syscall.SIGINT, nil
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L379: case "QUIT", "SIGQUIT":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L380: return syscall.SIGQUIT, nil
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L381: default:
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L382: return 0, fmt.Errorf("unsupported signal %q", value)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).

`adminCommand`

What: Implements the apigw admin subcommand (status/config/reload).

Why: Provides a simple way to query or trigger control-plane behavior from scripts and terminals.

How: Parses flags (base URL, token, timeout) and dispatches to adminGET or adminPOST based on subcommand.

cmd/apigw/main.go#L386
func adminCommand(args []string) error {
	subcommand := "status"
	if len(args) > 0 && !strings.HasPrefix(args[0], "-") {
		subcommand = args[0]
		args = args[1:]
	}

	fs := flag.NewFlagSet("admin "+subcommand, flag.ExitOnError)
	baseURL := fs.String("url", "http://127.0.0.1:9090", "Base URL for the admin server")
	token := fs.String("token", "", "Bearer token for admin requests")
	timeout := fs.Duration("timeout", 5*time.Second, "HTTP request timeout")
	if err := fs.Parse(args); err != nil {
		return err
	}

	client := &http.Client{Timeout: *timeout}
	base := strings.TrimRight(*baseURL, "/")

	switch subcommand {
	case "status":
		return adminGET(client, base+"/__admin/status", *token)
	case "config":
		return adminGET(client, base+"/__admin/config", *token)
	case "reload":
		return adminPOST(client, base+"/__admin/reload", *token)
	default:
		return fmt.Errorf("unknown admin subcommand %q", subcommand)
	}
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L387: subcommand := "status"
- What: Defines subcommand.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L388: if len(args) > 0 && !strings.HasPrefix(args[0], "-") { subcommand = args[0] args = args[1:] }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L389: subcommand = args[0]
    - What: Assigns subcommand.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L390: args = args[1:]
    - What: Assigns args.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L393: fs := flag.NewFlagSet("admin "+subcommand, flag.ExitOnError)
- What: Defines fs.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L394: baseURL := fs.String("url", "http://127.0.0.1:9090", "Base URL for the admin server")
- What: Defines baseURL.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L395: token := fs.String("token", "", "Bearer token for admin requests")
- What: Defines token.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L396: timeout := fs.Duration("timeout", 5*time.Second, "HTTP request timeout")
- What: Defines timeout.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L397: if err := fs.Parse(args); err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L397: err := fs.Parse(args)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L398: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L401: client := &http.Client{Timeout: *timeout}
- What: Defines client.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L402: base := strings.TrimRight(*baseURL, "/")
- What: Defines base.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L404: switch subcommand { case "status": return adminGET(client, base+"/__admin/status", *token) case "config": return adminGET(client, base+"/__…
- What: Selects a branch from multiple cases.
- Why: Keeps multi-case branching readable and explicit.
- How: Evaluates the switch expression and executes the first matching case.
- Nested steps:
  - L405: case "status":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L406: return adminGET(client, base+"/__admin/status", *token)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L407: case "config":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L408: return adminGET(client, base+"/__admin/config", *token)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L409: case "reload":
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L410: return adminPOST(client, base+"/__admin/reload", *token)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
  - L411: default:
    - What: Selects a switch case.
    - Why: Makes multi-branch control flow explicit and readable.
    - How: Runs this case body when the switch value matches (or when default is selected).
    - Nested steps:
      - L412: return fmt.Errorf("unknown admin subcommand %q", subcommand)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).

`adminGET`

What: Performs an admin GET request and prints the JSON response body.

Why: Shared helper for admin status and admin config.

How: Builds an HTTP request, optionally sets bearer token header, checks for 200 OK, and prints the response body.

cmd/apigw/main.go#L416
func adminGET(client *http.Client, url, token string) error {
	req, err := http.NewRequest(http.MethodGet, url, nil)
	if err != nil {
		return err
	}
	if token != "" {
		req.Header.Set("Authorization", "Bearer "+token)
	}
	resp, err := client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return fmt.Errorf("admin request failed: %s", strings.TrimSpace(string(body)))
	}
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return err
	}
	fmt.Println(string(body))
	return nil
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L417: req, err := http.NewRequest(http.MethodGet, url, nil)
- What: Defines req, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L418: if err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L419: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L421: if token != "" { req.Header.Set("Authorization", "Bearer "+token) }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L422: req.Header.Set("Authorization", "Bearer "+token)
    - What: Calls req.Header.Set.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
L424: resp, err := client.Do(req)
- What: Defines resp, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L425: if err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L426: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L428: defer resp.Body.Close()
- What: Defers a call for cleanup.
- Why: Ensures the deferred action runs even on early returns.
- How: Schedules the call to run when the surrounding function returns.
L429: if resp.StatusCode != http.StatusOK { body, _ := io.ReadAll(resp.Body) return fmt.Errorf("admin request failed: %s", strings.TrimSpace(stri…
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L430: body, _ := io.ReadAll(resp.Body)
    - What: Defines body, _.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L431: return fmt.Errorf("admin request failed: %s", strings.TrimSpace(string(body)))
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L433: body, err := io.ReadAll(resp.Body)
- What: Defines body, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L434: if err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L435: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L437: fmt.Println(string(body))
- What: Calls fmt.Println.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L438: return nil
- What: Returns from the current function.
- Why: Ends the current execution path and hands control back to the caller.
- How: Executes a return statement (possibly returning values).

`adminPOST`

What: Performs an admin POST request and prints the response body (or a fallback message).

Why: Shared helper for admin reload.

How: Builds an HTTP POST request, optionally sets bearer token header, checks for 202 Accepted, and prints the response body or "reload requested".

cmd/apigw/main.go#L441
func adminPOST(client *http.Client, url, token string) error {
	req, err := http.NewRequest(http.MethodPost, url, nil)
	if err != nil {
		return err
	}
	if token != "" {
		req.Header.Set("Authorization", "Bearer "+token)
	}
	resp, err := client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusAccepted {
		body, _ := io.ReadAll(resp.Body)
		return fmt.Errorf("admin reload failed: %s", strings.TrimSpace(string(body)))
	}
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return err
	}
	if len(strings.TrimSpace(string(body))) > 0 {
		fmt.Println(string(body))
	} else {
		fmt.Println("reload requested")
	}
	return nil
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L442: req, err := http.NewRequest(http.MethodPost, url, nil)
- What: Defines req, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L443: if err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L444: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L446: if token != "" { req.Header.Set("Authorization", "Bearer "+token) }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L447: req.Header.Set("Authorization", "Bearer "+token)
    - What: Calls req.Header.Set.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
L449: resp, err := client.Do(req)
- What: Defines resp, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L450: if err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L451: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L453: defer resp.Body.Close()
- What: Defers a call for cleanup.
- Why: Ensures the deferred action runs even on early returns.
- How: Schedules the call to run when the surrounding function returns.
L454: if resp.StatusCode != http.StatusAccepted { body, _ := io.ReadAll(resp.Body) return fmt.Errorf("admin reload failed: %s", strings.TrimSpace…
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L455: body, _ := io.ReadAll(resp.Body)
    - What: Defines body, _.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L456: return fmt.Errorf("admin reload failed: %s", strings.TrimSpace(string(body)))
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L458: body, err := io.ReadAll(resp.Body)
- What: Defines body, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L459: if err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L460: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L462: if len(strings.TrimSpace(string(body))) > 0 { fmt.Println(string(body)) } else { fmt.Println("reload requested") }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L463: fmt.Println(string(body))
    - What: Calls fmt.Println.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
  - L465: fmt.Println("reload requested")
    - What: Calls fmt.Println.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
L467: return nil
- What: Returns from the current function.
- Why: Ends the current execution path and hands control back to the caller.
- How: Executes a return statement (possibly returning values).

`watchConfig`

What: Watches a config file for changes and emits reloaded gatewayconfig.Config values.

Why: Enables apigw run --watch hot reloads without external tooling.

How: Creates an fsnotify watcher on the config directory, debounces write/create/rename events, reloads config via gatewayconfig.Load, and returns channels for configs and errors plus a cancel function.

cmd/apigw/main.go#L470
func watchConfig(parent context.Context, path string, opts []gatewayconfig.Option) (<-chan gatewayconfig.Config, <-chan error, context.CancelFunc, error) {
	absPath, err := filepath.Abs(path)
	if err != nil {
		return nil, nil, nil, fmt.Errorf("resolve config path: %w", err)
	}

	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		return nil, nil, nil, err
	}
	dir := filepath.Dir(absPath)
	if err := watcher.Add(dir); err != nil {
		watcher.Close()
		return nil, nil, nil, fmt.Errorf("watch directory: %w", err)
	}

	ctx, cancel := context.WithCancel(parent)
	reloadCh := make(chan gatewayconfig.Config)
	errCh := make(chan error, 1)

	go func() {
		defer close(reloadCh)
		defer close(errCh)
		defer watcher.Close()

		var debounce <-chan time.Time
		for {
			select {
			case <-ctx.Done():
				return
			case evt, ok := <-watcher.Events:
				if !ok {
					return
				}
				if !targetsFile(evt.Name, absPath) {
					continue
				}
				if evt.Op&(fsnotify.Write|fsnotify.Create|fsnotify.Rename) == 0 {
					continue
				}
				debounce = time.After(200 * time.Millisecond)
			case <-debounce:
				cfg, err := gatewayconfig.Load(opts...)
				if err != nil {
					errCh <- err
					debounce = nil
					continue
				}
				select {
				case reloadCh <- cfg:
				case <-ctx.Done():
				}
				debounce = nil
			case err, ok := <-watcher.Errors:
				if !ok {
					return
				}
				errCh <- err
			}
		}
	}()

	return reloadCh, errCh, cancel, nil
}

Walkthrough

Expand walkthrough (47 steps)

The list below documents the statements inside the function body, including nested blocks and inline closures.

L471: absPath, err := filepath.Abs(path)
- What: Defines absPath, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L472: if err != nil { return nil, nil, nil, fmt.Errorf("resolve config path: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L473: return nil, nil, nil, fmt.Errorf("resolve config path: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L476: watcher, err := fsnotify.NewWatcher()
- What: Defines watcher, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L477: if err != nil { return nil, nil, nil, err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L478: return nil, nil, nil, err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L480: dir := filepath.Dir(absPath)
- What: Defines dir.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L481: if err := watcher.Add(dir); err != nil { watcher.Close() return nil, nil, nil, fmt.Errorf("watch directory: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L481: err := watcher.Add(dir)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L482: watcher.Close()
    - What: Calls watcher.Close.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
  - L483: return nil, nil, nil, fmt.Errorf("watch directory: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L486: ctx, cancel := context.WithCancel(parent)
- What: Defines ctx, cancel.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L487: reloadCh := make(chan gatewayconfig.Config)
- What: Defines reloadCh.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L488: errCh := make(chan error, 1)
- What: Defines errCh.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L490: go func() { defer close(reloadCh) defer close(errCh) defer watcher.Close() var debounce <-chan time.Time for { select { case <-ctx.Done(): …
- What: Starts a goroutine.
- Why: Runs work concurrently.
- How: Invokes the function call asynchronously using go.
- Nested steps:
  - L490: func() { defer close(reloadCh) defer close(errCh) defer watcher.Close() var debounce <-chan time.Time for { select { case <-ctx.Done(): ret…
    - What: Defines an inline function (closure).
    - Why: Encapsulates callback logic and may capture variables from the surrounding scope.
    - How: Declares a func literal and uses it as a value (for example, as an HTTP handler or callback).
    - Nested steps:
      - L491: defer close(reloadCh)
        
        What: Defers a call for cleanup.
        
        Why: Ensures the deferred action runs even on early returns.
        
        How: Schedules the call to run when the surrounding function returns.
      - L492: defer close(errCh)
        
        What: Defers a call for cleanup.
        
        Why: Ensures the deferred action runs even on early returns.
        
        How: Schedules the call to run when the surrounding function returns.
      - L493: defer watcher.Close()
        
        What: Defers a call for cleanup.
        
        Why: Ensures the deferred action runs even on early returns.
        
        How: Schedules the call to run when the surrounding function returns.
      - L495: var debounce <-chan time.Time
        
        What: Declares local names.
        
        Why: Introduces variables or types used later in the function.
        
        How: Executes a Go declaration statement inside the function body.
      - L496: for { select { case <-ctx.Done(): return case evt, ok := <-watcher.Events: if !ok { return } if !targetsFile(evt.Name, absPath) { continue …
        
        What: Runs a loop.
        
        Why: Repeats logic until a condition is met or the loop terminates.
        
        How: Executes a for loop statement.
        
        Nested steps:
        
        L497: select { case <-ctx.Done(): return case evt, ok := <-watcher.Events: if !ok { return } if !targetsFile(evt.Name, absPath) { continue } if e…
        
        What: Selects among concurrent operations.
        
        Why: Coordinates channel operations without blocking incorrectly.
        
        How: Executes a select statement and runs one ready case.
        
        Nested steps:
        
        L498: case <-ctx.Done():
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        Nested steps:
        
        L499: return
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
        
        L500: case evt, ok := <-watcher.Events:
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        Nested steps:
        
        L501: if !ok { return }
        
        What: Branches conditionally.
        
        Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L502: return
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
        
        L504: if !targetsFile(evt.Name, absPath) { continue }
        
        What: Branches conditionally.
        
        Why: Handles different execution paths based on runtime state.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L505: continue
        
        What: Executes a statement.
        
        Why: Advances the function logic.
        
        How: Runs this statement as part of the function body.
        
        L507: if evt.Op&(fsnotify.Write|fsnotify.Create|fsnotify.Rename) == 0 { continue }
        
        What: Branches conditionally.
        
        Why: Handles different execution paths based on runtime state.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L508: continue
        
        What: Executes a statement.
        
        Why: Advances the function logic.
        
        How: Runs this statement as part of the function body.
        
        L510: debounce = time.After(200 * time.Millisecond)
        
        What: Assigns debounce.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
        
        L511: case <-debounce:
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        Nested steps:
        
        L512: cfg, err := gatewayconfig.Load(opts...)
        
        What: Defines cfg, err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
        
        L513: if err != nil { errCh <- err debounce = nil continue }
        
        What: Branches conditionally.
        
        Why: Handles different execution paths based on runtime state.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L514: errCh <- err
        
        What: Sends a value on a channel.
        
        Why: Communicates with another goroutine.
        
        How: Executes a channel send operation.
        
        L515: debounce = nil
        
        What: Assigns debounce.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
        
        L516: continue
        
        What: Executes a statement.
        
        Why: Advances the function logic.
        
        How: Runs this statement as part of the function body.
        
        L518: select { case reloadCh <- cfg: case <-ctx.Done(): }
        
        What: Selects among concurrent operations.
        
        Why: Coordinates channel operations without blocking incorrectly.
        
        How: Executes a select statement and runs one ready case.
        
        Nested steps:
        
        L519: case reloadCh <- cfg:
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        L520: case <-ctx.Done():
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        L522: debounce = nil
        
        What: Assigns debounce.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
        
        L523: case err, ok := <-watcher.Errors:
        
        What: Selects a select-case branch.
        
        Why: Coordinates concurrent operations without blocking incorrectly.
        
        How: Runs this case body when its channel operation is ready (or runs default immediately).
        
        Nested steps:
        
        L524: if !ok { return }
        
        What: Branches conditionally.
        
        Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L525: return
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
        
        L527: errCh <- err
        
        What: Sends a value on a channel.
        
        Why: Communicates with another goroutine.
        
        How: Executes a channel send operation.
L532: return reloadCh, errCh, cancel, nil
- What: Returns from the current function.
- Why: Ends the current execution path and hands control back to the caller.
- How: Executes a return statement (possibly returning values).

`convertEnvCommand`

What: Implements apigw convert-env to snapshot the effective configuration into YAML.

Why: Helps migrate legacy env-driven deployments to YAML by producing a reproducible config file.

How: Loads config (optionally merging an input YAML first), marshals to YAML, and writes to stdout or an output path (with optional --force).

cmd/apigw/main.go#L535
func convertEnvCommand(args []string) error {
	fs := flag.NewFlagSet("convert-env", flag.ExitOnError)
	configPath := fs.String("config", "", "Optional config file to merge before env overrides")
	outputPath := fs.String("output", "", "Destination path for generated YAML (stdout when empty)")
	force := fs.Bool("force", false, "Overwrite existing output file")
	if err := fs.Parse(args); err != nil {
		return err
	}

	opts := []gatewayconfig.Option{}
	if strings.TrimSpace(*configPath) != "" {
		opts = append(opts, gatewayconfig.WithPath(*configPath))
	}

	cfg, err := gatewayconfig.Load(opts...)
	if err != nil {
		return fmt.Errorf("load config from environment: %w", err)
	}

	data, err := yaml.Marshal(cfg)
	if err != nil {
		return fmt.Errorf("encode config: %w", err)
	}

	path := strings.TrimSpace(*outputPath)
	if path == "" {
		fmt.Print(string(data))
		return nil
	}

	if !*force {
		if _, err := os.Stat(path); err == nil {
			return fmt.Errorf("output file %s already exists (use --force to overwrite)", path)
		} else if err != nil && !errors.Is(err, os.ErrNotExist) {
			return fmt.Errorf("stat output file: %w", err)
		}
	}

	dir := filepath.Dir(path)
	if dir != "." && dir != "" {
		if err := os.MkdirAll(dir, 0o755); err != nil {
			return fmt.Errorf("ensure output directory: %w", err)
		}
	}

	if err := os.WriteFile(path, data, 0o644); err != nil {
		return fmt.Errorf("write output file: %w", err)
	}

	fmt.Printf("configuration written to %s\n", path)
	return nil
}

Walkthrough

Expand walkthrough (36 steps)

The list below documents the statements inside the function body, including nested blocks and inline closures.

L536: fs := flag.NewFlagSet("convert-env", flag.ExitOnError)
- What: Defines fs.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L537: configPath := fs.String("config", "", "Optional config file to merge before env overrides")
- What: Defines configPath.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L538: outputPath := fs.String("output", "", "Destination path for generated YAML (stdout when empty)")
- What: Defines outputPath.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L539: force := fs.Bool("force", false, "Overwrite existing output file")
- What: Defines force.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L540: if err := fs.Parse(args); err != nil { return err }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L540: err := fs.Parse(args)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L541: return err
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L544: opts := []gatewayconfig.Option{}
- What: Defines opts.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L545: if strings.TrimSpace(*configPath) != "" { opts = append(opts, gatewayconfig.WithPath(*configPath)) }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L546: opts = append(opts, gatewayconfig.WithPath(*configPath))
    - What: Assigns opts.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L549: cfg, err := gatewayconfig.Load(opts...)
- What: Defines cfg, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L550: if err != nil { return fmt.Errorf("load config from environment: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L551: return fmt.Errorf("load config from environment: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L554: data, err := yaml.Marshal(cfg)
- What: Defines data, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L555: if err != nil { return fmt.Errorf("encode config: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L556: return fmt.Errorf("encode config: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L559: path := strings.TrimSpace(*outputPath)
- What: Defines path.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L560: if path == "" { fmt.Print(string(data)) return nil }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L561: fmt.Print(string(data))
    - What: Calls fmt.Print.
    - Why: Performs side effects or delegates work to a helper.
    - How: Executes the expression statement.
  - L562: return nil
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L565: if !*force { if _, err := os.Stat(path); err == nil { return fmt.Errorf("output file %s already exists (use --force to overwrite)", path) }…
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L566: if _, err := os.Stat(path); err == nil { return fmt.Errorf("output file %s already exists (use --force to overwrite)", path) } else if err …
    - What: Branches conditionally.
    - Why: Handles different execution paths based on runtime state.
    - How: Evaluates the condition and executes the matching branch.
    - Nested steps:
      - L566: _, err := os.Stat(path)
        
        What: Defines _, err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
      - L567: return fmt.Errorf("output file %s already exists (use --force to overwrite)", path)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
      - L568: if err != nil && !errors.Is(err, os.ErrNotExist) { return fmt.Errorf("stat output file: %w", err) }
        
        What: Branches conditionally.
        
        Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
        
        How: Evaluates the condition and executes the matching branch.
        
        Nested steps:
        
        L569: return fmt.Errorf("stat output file: %w", err)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
L573: dir := filepath.Dir(path)
- What: Defines dir.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L574: if dir != "." && dir != "" { if err := os.MkdirAll(dir, 0o755); err != nil { return fmt.Errorf("ensure output directory: %w", err) } }
- What: Branches conditionally.
- Why: Handles different execution paths based on runtime state.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L575: if err := os.MkdirAll(dir, 0o755); err != nil { return fmt.Errorf("ensure output directory: %w", err) }
    - What: Branches conditionally.
    - Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
    - How: Evaluates the condition and executes the matching branch.
    - Nested steps:
      - L575: err := os.MkdirAll(dir, 0o755)
        
        What: Defines err.
        
        Why: Keeps intermediate state available for later steps in the function.
        
        How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
      - L576: return fmt.Errorf("ensure output directory: %w", err)
        
        What: Returns from the current function.
        
        Why: Ends the current execution path and hands control back to the caller.
        
        How: Executes a return statement (possibly returning values).
L580: if err := os.WriteFile(path, data, 0o644); err != nil { return fmt.Errorf("write output file: %w", err) }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L580: err := os.WriteFile(path, data, 0o644)
    - What: Defines err.
    - Why: Keeps intermediate state available for later steps in the function.
    - How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
  - L581: return fmt.Errorf("write output file: %w", err)
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L584: fmt.Printf("configuration written to %s\n", path)
- What: Calls fmt.Printf.
- Why: Performs side effects or delegates work to a helper.
- How: Executes the expression statement.
L585: return nil
- What: Returns from the current function.
- Why: Ends the current execution path and hands control back to the caller.
- How: Executes a return statement (possibly returning values).

`targetsFile`

What: Checks whether a filesystem watcher event refers to the target config file.

Why: fsnotify emits directory-level events; this filters down to the single config file we care about.

How: Resolves the event path to an absolute path and compares it to the expected absolute config path.

cmd/apigw/main.go#L588
func targetsFile(eventPath, target string) bool {
	if eventPath == "" {
		return false
	}
	abs, err := filepath.Abs(eventPath)
	if err != nil {
		return false
	}
	return abs == target
}

Walkthrough

The list below documents the statements inside the function body, including nested blocks and inline closures.

L589: if eventPath == "" { return false }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L590: return false
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L592: abs, err := filepath.Abs(eventPath)
- What: Defines abs, err.
- Why: Keeps intermediate state available for later steps in the function.
- How: Evaluates the right-hand side expressions and stores results in the left-hand variables.
L593: if err != nil { return false }
- What: Branches conditionally.
- Why: Short-circuits early when a precondition is not met or an error/edge case is detected.
- How: Evaluates the condition and executes the matching branch.
- Nested steps:
  - L594: return false
    - What: Returns from the current function.
    - Why: Ends the current execution path and hands control back to the caller.
    - How: Executes a return statement (possibly returning values).
L596: return abs == target
- What: Returns from the current function.
- Why: Ends the current execution path and hands control back to the caller.
- How: Executes a return statement (possibly returning values).

Source​

Overview​

Contents​

Imports​

import block 1​

Constants​

const block 1​

daemonChildEnv​

const block 2​

sampleConfigYAML​

Functions and Methods​

main​

Walkthrough​

runCommand​

Walkthrough​

validateCommand​

Walkthrough​

initCommand​

Walkthrough​

usage​

Walkthrough​

daemonCommand​

Walkthrough​

daemonStart​

Walkthrough​

daemonStop​

Walkthrough​

daemonStatus​

Walkthrough​

parseSignal​

Walkthrough​

adminCommand​

Walkthrough​

adminGET​

Walkthrough​

adminPOST​

Walkthrough​

watchConfig​

Walkthrough​

convertEnvCommand​

Walkthrough​

targetsFile​

Walkthrough​

Related docs​

Start Here​

Guides​

Reference​

Neighboring source​

Source

Overview

Contents

Imports

`import` block 1

Constants

`const` block 1

`daemonChildEnv`

`const` block 2

`sampleConfigYAML`

Functions and Methods

`main`

Walkthrough

`runCommand`

Walkthrough

`validateCommand`

Walkthrough

`initCommand`

Walkthrough

`usage`

Walkthrough

`daemonCommand`

Walkthrough

`daemonStart`

Walkthrough

`daemonStop`

Walkthrough

`daemonStatus`

Walkthrough

`parseSignal`

Walkthrough

`adminCommand`

Walkthrough

`adminGET`

Walkthrough

`adminPOST`

Walkthrough

`watchConfig`

Walkthrough

`convertEnvCommand`

Walkthrough

`targetsFile`

Walkthrough

Related docs

Start Here

Guides

Reference

Neighboring source