Basic IRCv3 message parser

1 files changed, 125 insertions, 0 deletions

diff --git a/message.go b/message.go
new file mode 100644
index 0000000..190c198
--- /dev/null
+++ b/message.go
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: Copyright (c) 2018-2024 luk3yx <https://luk3yx.github.io>
+// SPDX-FileCopyrightText: Copyright (c) 2025 Runxi Yu <https://runxiyu.org>
+
+package irc
+
+import (
+	"bytes"
+)
+
+type Message struct {
+	Command string
+	Source  *Source
+	Tags    map[string]string
+	Args    []string
+}
+
+// All strings returned are borrowed from the input byte slice.
+func Parse(raw []byte) (msg Message, err error) {
+	sp := bytes.Split(raw, []byte{' '}) // TODO: Use bytes.Cut instead here
+
+	if bytes.HasPrefix(sp[0], []byte{'@'}) { // TODO: Check size manually
+		if len(sp[0]) < 2 {
+			err = ErrMalformedMsg
+			return
+		}
+		sp[0] = sp[0][1:]
+
+		msg.Tags, err = tagsToMap(sp[0])
+		if err != nil {
+			return
+		}
+
+		if len(sp) < 2 {
+			err = ErrMalformedMsg
+			return
+		}
+		sp = sp[1:]
+	} else {
+		msg.Tags = nil // TODO: Is a nil map the correct thing to use here?
+	}
+
+	if bytes.HasPrefix(sp[0], []byte{':'}) { // TODO: Check size manually
+		if len(sp[0]) < 2 {
+			err = ErrMalformedMsg
+			return
+		}
+		sp[0] = sp[0][1:]
+
+		source := parseSource(sp[0])
+		msg.Source = &source
+
+		if len(sp) < 2 {
+			err = ErrMalformedMsg
+			return
+		}
+		sp = sp[1:]
+	}
+
+	msg.Command = bytesToString(sp[0])
+	if len(sp) < 2 {
+		return
+	}
+	sp = sp[1:]
+
+	for i := 0; i < len(sp); i++ {
+		if len(sp[i]) == 0 {
+			continue
+		}
+		if sp[i][0] == ':' {
+			if len(sp[i]) < 2 {
+				sp[i] = []byte{}
+			} else {
+				sp[i] = sp[i][1:]
+			}
+			msg.Args = append(msg.Args, bytesToString(bytes.Join(sp[i:], []byte{' '})))
+			// TODO: Avoid Join by not using sp in the first place
+			break
+		}
+		msg.Args = append(msg.Args, bytesToString(sp[i]))
+	}
+
+	return
+}
+
+var ircv3TagEscapes = map[byte]byte{
+	':': ';',
+	's': ' ',
+	'r': '\r',
+	'n': '\n',
+}
+
+func tagsToMap(raw []byte) (tags map[string]string, err error) {
+	tags = make(map[string]string)
+	for rawTag := range bytes.SplitSeq(raw, []byte{';'}) {
+		key, value, found := bytes.Cut(rawTag, []byte{'='})
+		if !found {
+			err = ErrInvalidIRCv3Tag
+			return
+		}
+		if len(value) == 0 {
+			tags[bytesToString(key)] = ""
+		} else {
+			if !bytes.Contains(value, []byte{'\\'}) {
+				tags[bytesToString(key)] = bytesToString(value)
+			} else {
+				valueUnescaped := bytes.NewBuffer(make([]byte, 0, len(value)))
+				for i := 0; i < len(value); i++ {
+					if value[i] == '\\' {
+						i++
+						byteUnescaped, ok := ircv3TagEscapes[value[i]]
+						if !ok {
+							byteUnescaped = value[i]
+						}
+						valueUnescaped.WriteByte(byteUnescaped)
+					} else {
+						valueUnescaped.WriteByte(value[i])
+					}
+				}
+				tags[bytesToString(key)] = bytesToString(valueUnescaped.Bytes())
+			}
+		}
+	}
+	return
+}