neoirc/internal/ircserver/parser.go

// Package ircserver implements a traditional IRC wire protocol
// listener (RFC 1459/2812) that bridges to the neoirc HTTP/JSON
// server internals.
package ircserver

import "strings"

// Message represents a parsed IRC wire protocol message.
type Message struct {
	// Prefix is the optional :prefix at the start (may be
	// empty for client-to-server messages).
	Prefix string
	// Command is the IRC command (e.g., "PRIVMSG", "NICK").
	Command string
	// Params holds the positional parameters, including the
	// trailing parameter (which was preceded by ':' on the
	// wire).
	Params []string
}

// ParseMessage parses a single IRC wire protocol line
// (without the trailing CR-LF) into a Message.
// Returns nil if the line is empty.
//
// IRC message format (RFC 1459 §2.3.1):
//
//	[":" prefix SPACE] command { SPACE param } [SPACE ":" trailing]
func ParseMessage(line string) *Message {
	if line == "" {
		return nil
	}

	msg := &Message{} //nolint:exhaustruct // fields set below

	// Extract prefix if present.
	if line[0] == ':' {
		idx := strings.IndexByte(line, ' ')
		if idx < 0 {
			// Only a prefix, no command — invalid.
			return nil
		}

		msg.Prefix = line[1:idx]
		line = line[idx+1:]
	}

	// Skip leading spaces.
	line = strings.TrimLeft(line, " ")
	if line == "" {
		return nil
	}

	// Extract command.
	idx := strings.IndexByte(line, ' ')
	if idx < 0 {
		msg.Command = strings.ToUpper(line)

		return msg
	}

	msg.Command = strings.ToUpper(line[:idx])
	line = line[idx+1:]

	// Extract parameters.
	for line != "" {
		line = strings.TrimLeft(line, " ")
		if line == "" {
			break
		}

		// Trailing parameter (everything after ':').
		if line[0] == ':' {
			msg.Params = append(msg.Params, line[1:])

			break
		}

		idx = strings.IndexByte(line, ' ')
		if idx < 0 {
			msg.Params = append(msg.Params, line)

			break
		}

		msg.Params = append(msg.Params, line[:idx])
		line = line[idx+1:]
	}

	return msg
}

// FormatMessage formats an IRC message into wire protocol
// format (without the trailing CR-LF).
func FormatMessage(
	prefix, command string,
	params ...string,
) string {
	var buf strings.Builder

	if prefix != "" {
		buf.WriteByte(':')
		buf.WriteString(prefix)
		buf.WriteByte(' ')
	}

	buf.WriteString(command)

	for i, param := range params {
		buf.WriteByte(' ')

		isLast := i == len(params)-1
		needsColon := strings.Contains(param, " ") ||
			param == "" || param[0] == ':'

		if isLast && needsColon {
			buf.WriteByte(':')
		}

		buf.WriteString(param)
	}

	return buf.String()
}