Join one FM-Funknetz talk group from a headset window.

The station reads ~/.funknetz.json, speaks protocol 2.0, and builds an unsigned funknetz.app.

Co-authored-by: Cursor <cursoragent@cursor.com>

station/protocol.go

@@ -0,0 +1,158 @@
+package station
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+)
+
+const (
+	tcpHeartbeat     = 1
+	tcpProtoVer      = 5
+	tcpAuthChallenge = 10
+	tcpAuthResponse  = 11
+	tcpAuthOK        = 12
+	tcpError         = 13
+	tcpServerInfo    = 100
+	tcpTalkerStart   = 104
+	tcpTalkerStop    = 105
+	tcpSelectTG      = 106
+
+	udpHeartbeat = 1
+	udpAudio     = 101
+	udpFlush     = 102
+
+	maxFrame = 32768
+)
+
+type frame struct {
+	typ  uint16
+	body []byte
+}
+
+func writeFrame(w io.Writer, typ uint16, body []byte) error {
+	payload := make([]byte, 2+len(body))
+	binary.BigEndian.PutUint16(payload[:2], typ)
+	copy(payload[2:], body)
+	var hdr [4]byte
+	binary.BigEndian.PutUint32(hdr[:], uint32(len(payload)))
+	if _, err := w.Write(hdr[:]); err != nil {
+		return err
+	}
+	_, err := w.Write(payload)
+	return err
+}
+
+func readFrame(r io.Reader) (frame, error) {
+	var hdr [4]byte
+	if _, err := io.ReadFull(r, hdr[:]); err != nil {
+		return frame{}, err
+	}
+	n := binary.BigEndian.Uint32(hdr[:])
+	if n < 2 || n > maxFrame {
+		return frame{}, fmt.Errorf("frame length %d", n)
+	}
+	buf := make([]byte, n)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return frame{}, err
+	}
+	return frame{typ: binary.BigEndian.Uint16(buf[:2]), body: buf[2:]}, nil
+}
+
+func appendU16(b []byte, v uint16) []byte {
+	var buf [2]byte
+	binary.BigEndian.PutUint16(buf[:], v)
+	return append(b, buf[:]...)
+}
+
+func appendString(b []byte, s string) []byte {
+	b = appendU16(b, uint16(len(s)))
+	return append(b, s...)
+}
+
+func appendBlob(b []byte, p []byte) []byte {
+	b = appendU16(b, uint16(len(p)))
+	return append(b, p...)
+}
+
+func parseU16(b []byte) (uint16, []byte, error) {
+	if len(b) < 2 {
+		return 0, nil, io.ErrUnexpectedEOF
+	}
+	return binary.BigEndian.Uint16(b[:2]), b[2:], nil
+}
+
+func parseU32(b []byte) (uint32, []byte, error) {
+	if len(b) < 4 {
+		return 0, nil, io.ErrUnexpectedEOF
+	}
+	return binary.BigEndian.Uint32(b[:4]), b[4:], nil
+}
+
+func parseString(b []byte) (string, []byte, error) {
+	n, rest, err := parseU16(b)
+	if err != nil {
+		return "", nil, err
+	}
+	if len(rest) < int(n) {
+		return "", nil, io.ErrUnexpectedEOF
+	}
+	return string(rest[:n]), rest[n:], nil
+}
+
+func parseBlob(b []byte) ([]byte, []byte, error) {
+	n, rest, err := parseU16(b)
+	if err != nil {
+		return nil, nil, err
+	}
+	if len(rest) < int(n) {
+		return nil, nil, io.ErrUnexpectedEOF
+	}
+	return rest[:n], rest[n:], nil
+}
+
+func parseStringList(b []byte) ([]string, []byte, error) {
+	n, rest, err := parseU16(b)
+	if err != nil {
+		return nil, nil, err
+	}
+	out := make([]string, 0, n)
+	for range int(n) {
+		s, next, err := parseString(rest)
+		if err != nil {
+			return nil, nil, err
+		}
+		out = append(out, s)
+		rest = next
+	}
+	return out, rest, nil
+}
+
+func parseServerInfo(b []byte) (uint16, []string, error) {
+	_, rest, err := parseU16(b)
+	if err != nil {
+		return 0, nil, err
+	}
+	id, rest, err := parseU16(rest)
+	if err != nil {
+		return 0, nil, err
+	}
+	_, rest, err = parseStringList(rest)
+	if err != nil {
+		return 0, nil, err
+	}
+	codecs, _, err := parseStringList(rest)
+	if err != nil {
+		return 0, nil, err
+	}
+	return id, codecs, nil
+}
+
+func hasOPUS(codecs []string) bool {
+	for _, c := range codecs {
+		if c == "OPUS" {
+			return true
+		}
+	}
+	return false
+}