commit 65e214248fc8e29f5c4c74075b2a74c9d10232a5
parent 0cf1dfb386ded8d8b966ebeca50bbca10bb82d11
Author: Oliver Lowe <o@olowe.co>
Date: Sun, 16 Jun 2024 16:09:31 +1000
rtp: add header decoding
Not complete or properly tested but it's a start!
Diffstat:
| A | rtp/rtp.go | | | 112 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
1 file changed, 112 insertions(+), 0 deletions(-)
diff --git a/rtp/rtp.go b/rtp/rtp.go
@@ -0,0 +1,112 @@
+// Package rtp implements the Real-Time Transport Protocol as
+// specified in RFC 3550.
+package rtp
+
+import (
+ "encoding/binary"
+ "errors"
+ "fmt"
+)
+
+type Packet struct {
+ Header Header
+ Payload []byte
+}
+
+type Header struct {
+ Version uint8
+ // TODO(otl): do we store padding bytes? how many?
+ padding bool
+ Marker bool
+ Type PayloadType
+ Sequence uint16
+ Timestamp uint32
+ SyncSource uint32
+ ContribSource []uint32
+ Extension *Extension
+}
+
+const VersionRFC3550 uint8 = 2
+const VersionDraft uint8 = 1
+
+type PayloadType uint8
+
+const (
+ PayloadMP2T PayloadType = 33
+ // ...
+)
+
+type Extension struct {
+ Profile [2]byte
+ Data []byte
+}
+
+var ErrNoPayload = errors.New("no payload")
+
+func Unmarshal(data []byte, p *Packet) error {
+ // version (2), padding (1), ext (1), contribcount (4)
+ // marker (1), type (7)
+ // sequence (16)
+ // timestamp (32)
+ // syncsource (32)
+ need := 1 + 1 + 2 + 4 + 4
+ if len(data) < need {
+ return fmt.Errorf("need %d bytes, have %d", need, len(data))
+ }
+
+ p.Header.Version = uint8(data[0] & 0b11000000)
+ p.Header.padding = data[0]&0b00100000 > 0
+ // extension bit, ignore til later, 0b00010000
+ cc := data[0] & 0b00001111
+ if cc > 0 {
+ p.Header.ContribSource = make([]uint32, cc)
+ }
+
+ // m t t t t t t t
+ p.Header.Marker = data[1]&0x80 > 0
+ p.Header.Type = PayloadType(uint8(data[1] & 0x7f))
+
+ p.Header.Sequence = binary.BigEndian.Uint16(data[2:4])
+ p.Header.Timestamp = binary.BigEndian.Uint32(data[4:8])
+ p.Header.SyncSource = binary.BigEndian.Uint32(data[8:12])
+
+ if len(data) == 12 {
+ return ErrNoPayload
+ }
+ data = data[12:]
+
+ if data[0]&0b00010000 > 0 {
+ if len(data) < 4 {
+ return fmt.Errorf("header extension: %d bytes after header, need %d", len(data), 4)
+ }
+ ext := &Extension{}
+ copy(ext.Profile[:], data[:2])
+ length := int(binary.BigEndian.Uint16(data[2:4]))
+ if len(data) < length {
+ return fmt.Errorf("header extension: reports length %d bytes, only have %d", length, len(data))
+ }
+ if length > 0 {
+ ext.Data = data[4 : 4+length]
+ data = data[4+length:]
+ } else {
+ data = data[4:]
+ }
+ p.Header.Extension = ext
+ }
+
+ need = len(p.Header.ContribSource) * 4 // 32-bit uints * 4 for number of bytes needed
+ if len(data) < need {
+ return fmt.Errorf("contribution sources: need %d bytes, only have %d", need, len(data))
+ }
+ var n int
+ for i := range p.Header.ContribSource {
+ p.Header.ContribSource[i] = binary.BigEndian.Uint32(data[n : n+4])
+ n += 4
+ }
+
+ if len(data[n:]) == 0 {
+ return ErrNoPayload
+ }
+ p.Payload = data[n:]
+ return nil
+}
