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src/sydra/compat/wire/protocol.zig

Purpose​

Implements a minimal subset of the PostgreSQL startup negotiation plus helpers to write common backend messages.

This file is intentionally low-level: it reads/writes bytes and constructs big-endian length-prefixed pgwire frames.

Public constants​

  • pub const ssl_request_code: u32 = 80877103
  • pub const cancel_request_code: u32 = 80877102
  • pub const protocol_version_3: u32 = 3 << 16 (3.0, value 196608)

Startup types​

pub const StartupOptions​

  • allow_ssl: bool = false

When allow_ssl is false, SSL requests are explicitly declined.

pub const Parameter​

  • key: []const u8
  • value: []const u8

pub const StartupRequest​

  • protocol_version: u32
  • parameters: []Parameter = &[_]Parameter{}
  • ssl_request_seen: bool = false

Methods:

  • pub fn deinit(self: *StartupRequest, alloc) void
    • Frees param.key, param.value, and the parameters slice.
  • pub fn find(self: StartupRequest, key: []const u8) ?[]const u8
    • Linear scan over parameters.

Startup parsing​

pub fn readStartup(alloc, reader, writer, options) !StartupRequest​

Consumes the Postgres startup negotiation and returns parsed parameters.

Behavior:

  • Repeatedly reads frames of:
    • [len:u32be][body:len-4]
  • If the first 4 bytes of the body equal ssl_request_code:
    • writes a single byte response:
      • 'S' if options.allow_ssl (TLS is still “future work”)
      • 'N' otherwise (current default)
    • continues to read the next frame as the real startup packet.
  • If the protocol equals cancel_request_code:
    • returns error.CancelRequestUnsupported.
  • Validates protocol major is 3 (protocol & 0xFFFF0000 == protocol_version_3), otherwise error.UnsupportedProtocol.
  • Parses key/value parameters as NUL-terminated strings until a trailing empty key.
  • Duplicates parameter key/value strings into allocator-owned memory.

Key errors surfaced by this function:

  • error.InvalidStartupLength (len < 8)
  • error.MalformedStartupPacket (missing NUL terminators, truncation)
  • error.UnsupportedProtocol
  • error.CancelRequestUnsupported
SSL request handling loop (excerpt)
while (true) {
    const total_len = try readU32(reader);
    if (total_len < 8) return error.InvalidStartupLength;
    const body_len = total_len - 4;

    var body = try alloc.alloc(u8, body_len);
    defer alloc.free(body);
    try reader.readNoEof(body);

    const protocol = std.mem.readInt(u32, @as(*const [4]u8, @ptrCast(body[0..4].ptr)), .big);

    if (protocol == ssl_request_code) {
        try writer.writeAll(if (options.allow_ssl) "S" else "N");
        ssl_seen = true;
        continue;
    }

    if (protocol == cancel_request_code) return error.CancelRequestUnsupported;
    if ((protocol & 0xFFFF0000) != protocol_version_3) return error.UnsupportedProtocol;
    // parse key/value parameters...
    break;
}
Parameter parsing (excerpt)
var idx: usize = 4;
while (idx < body.len) {
    const key_end = std.mem.indexOfScalarPos(u8, body, idx, 0) orelse return error.MalformedStartupPacket;
    if (key_end == idx) break; // trailing NUL

    const val_start = key_end + 1;
    if (val_start >= body.len) return error.MalformedStartupPacket;
    const val_end = std.mem.indexOfScalarPos(u8, body, val_start, 0) orelse return error.MalformedStartupPacket;

    const key_slice = body[idx..key_end];
    const value_slice = body[val_start..val_end];
    try appendParameter(alloc, &params, key_slice, value_slice);
    idx = val_end + 1;
}

Message writers​

All message writers write a complete backend message in one call.

pub fn writeAuthenticationOk(writer) !void​

Writes an AuthenticationOk message:

  • Type byte: 'R'
  • Length: 8
  • Auth method: 0 (OK)

pub fn writeParameterStatus(writer, key, value) !void​

Writes:

  • Type byte: 'S'
  • Payload: key\0value\0

pub fn writeReadyForQuery(writer, status: u8) !void​

Writes:

  • Type byte: 'Z'
  • Payload: single status byte (commonly 'I' for idle)

pub fn writeCommandComplete(writer, tag: []const u8) !void​

Writes:

  • Type byte: 'C'
  • Payload: tag\0

pub fn writeEmptyQueryResponse(writer) !void​

Writes:

  • Type byte: 'I'
  • Payload length: 4 (no payload)

pub fn writeErrorResponse(writer, severity, code, message) !void​

Writes an ErrorResponse with fields:

  • S (severity)
  • C (SQLSTATE code)
  • M (message)

Each field is NUL-terminated; the entire message ends with an extra NUL byte.

writeErrorResponse framing (excerpt)
try writer.writeByte('E');
var length: u32 = 4 + 1; // length field + terminating zero
length += @intCast(severity.len + code.len + message.len + 3);

var buf: [4]u8 = undefined;
std.mem.writeInt(u32, buf[0..4], length, .big);
try writer.writeAll(buf[0..4]);

try writer.writeByte('S');
try writer.writeAll(severity);
try writer.writeByte(0);
try writer.writeByte('C');
try writer.writeAll(code);
try writer.writeByte(0);
try writer.writeByte('M');
try writer.writeAll(message);
try writer.writeByte(0);
try writer.writeByte(0);

pub fn writeNoticeResponse(writer, message) !void​

Writes a NoticeResponse with fields:

  • S = "NOTICE"
  • M = message

pub fn formatParameters(params: []Parameter, writer) !void​

Formats parameter pairs as key=value, key=value, ... (used for debugging/logging).