Add support for RFC2333, DTMF payload

src/net/rtp/payload.go

@@ -62,11 +62,14 @@ package rtp
 // 35-71     Unassigned      ?
 // 72-76     Reserved for RTCP conflict avoidance                                  [RFC3551]
 // 77-95     Unassigned      ?
-// 96-127    dynamic         ?                                                     [RFC3551]
+// 96-100    dynamic         ?                                                     [RFC3551]
+// 101       DTMF            ?                                                     [RFC2833]
+// 102-127   dynamic         ?                                                     [RFC3551]
 
 const (
 	Audio = 1
 	Video = 2
+	Event = 3
 )
 
 // PayloadFormat holds RTP payload formats.
@@ -136,5 +139,7 @@ func init() {
 	// 35-71     Unassigned      ?
 	// 72-76     Reserved for RTCP conflict avoidance
 	// 77-95     Unassigned      ?
-	// 96-127    dynamic         ?
+	// 96-100    dynamic         ?
+	PayloadFormatMap[101] = &PayloadFormat{101, Event, 8000, 0, "DTMF"}
+	// 102-127   dynamic         ?
 }

src/payload/dtmf.go

@@ -0,0 +1,88 @@
+// Copyright (C) 2021 Homin Lee
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// Authors: Homin Lee <[email protected]>
+//
+
+package payload
+
+import (
+	"encoding/binary"
+	"fmt"
+)
+
+// RFC2333, RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals
+/*
+   Payload format
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |     event     |E|R| volume    |          duration             |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+*/
+
+type DTMF []byte
+
+// IsValid checks DTMF is valid DTMF payload
+func (dp DTMF) IsValid() bool {
+	if len(dp) != 4 {
+		return false
+	}
+	// check R field
+	if (dp[1] & 0b0100_0000) != 0 {
+		return false
+	}
+
+	return true
+}
+
+// Event returns event char for received event
+func (dp DTMF) Event() byte {
+	return dp[0]
+}
+
+// ASCIIEvent returns ASCII char for received event
+func (dp DTMF) ASCIIEvent() byte {
+	switch dp[0] {
+	case 0, 1, 2, 3, 4, 5, 6, 7, 8, 9:
+		return '0' + dp[0]
+	case 10:
+		return '*'
+	case 11:
+		return '#'
+	}
+	return 0
+}
+
+// Volume returns volume of the DTMF
+func (dp DTMF) Volume() int {
+	return int(dp[1] & 0b0011_1111)
+}
+
+// Duration returns duration of the DTMF
+func (dp DTMF) Duration() int {
+	return int(binary.BigEndian.Uint16(dp[2:4]))
+}
+
+// IsEnd returns the end bit is set or not
+func (dp DTMF) IsEnd() bool {
+	return (dp[1] & 0b1000_0000) == 0b1000_0000
+}
+
+// String for Stringer interface (for debug)
+func (dp DTMF) String() string {
+	return fmt.Sprintf("DTMF[Evt=%v Vol=%v Dur=%v IsEnd=%v]",
+		dp.Event(), dp.Volume(), dp.Duration(), dp.IsEnd())
+}