forked from pion/webrtc
/
packet.go
169 lines (143 loc) · 4.8 KB
/
packet.go
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package sctp
import (
"encoding/binary"
"fmt"
"hash/crc32"
"github.com/pkg/errors"
)
/*
Packet represents an SCTP packet, defined in https://tools.ietf.org/html/rfc4960#section-3
An SCTP packet is composed of a common header and chunks. A chunk
contains either control information or user data.
SCTP Packet 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk #n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
SCTP Common Header 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Value Number | Destination Value Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Verification Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/
type packet struct {
sourcePort uint16
destinationPort uint16
verificationTag uint32
chunks []chunk
}
const (
packetHeaderSize = 12
)
func (p *packet) unmarshal(raw []byte) error {
if len(raw) < packetHeaderSize {
return errors.Errorf("raw only %d bytes, %d is the minimum length for a SCTP packet", len(raw), packetHeaderSize)
}
p.sourcePort = binary.BigEndian.Uint16(raw[0:])
p.destinationPort = binary.BigEndian.Uint16(raw[2:])
p.verificationTag = binary.BigEndian.Uint32(raw[4:])
offset := packetHeaderSize
for {
// Exact match, no more chunks
if offset == len(raw) {
break
} else if offset+chunkHeaderSize > len(raw) {
return errors.Errorf("Unable to parse SCTP chunk, not enough data for complete header: offset %d remaining %d", offset, len(raw))
}
var c chunk
switch chunkType(raw[offset]) {
case INIT:
c = &chunkInit{}
case INITACK:
c = &chunkInitAck{}
case ABORT:
c = &chunkAbort{}
case COOKIEECHO:
c = &chunkCookieEcho{}
case COOKIEACK:
c = &chunkCookieAck{}
case HEARTBEAT:
c = &chunkHeartbeat{}
case PAYLOADDATA:
c = &chunkPayloadData{}
case SACK:
c = &chunkSelectiveAck{}
default:
return errors.Errorf("Failed to unmarshal, contains unknown chunk type %s", chunkType(raw[offset]).String())
}
if err := c.unmarshal(raw[offset:]); err != nil {
return err
}
p.chunks = append(p.chunks, c)
chunkValuePadding := getPadding(c.valueLength())
offset += chunkHeaderSize + c.valueLength() + chunkValuePadding
}
theirChecksum := binary.LittleEndian.Uint32(raw[8:])
ourChecksum := generatePacketChecksum(raw)
if theirChecksum != ourChecksum {
return errors.Errorf("Checksum mismatch theirs: %d ours: %d", theirChecksum, ourChecksum)
}
return nil
}
func (p *packet) marshal() ([]byte, error) {
raw := make([]byte, packetHeaderSize)
// Populate static headers
// 8-12 is Checksum which will be populated when packet is complete
binary.BigEndian.PutUint16(raw[0:], p.sourcePort)
binary.BigEndian.PutUint16(raw[2:], p.destinationPort)
binary.BigEndian.PutUint32(raw[4:], p.verificationTag)
// Populate chunks
for _, c := range p.chunks {
chunkRaw, err := c.marshal()
if err != nil {
return nil, err
}
raw = append(raw, chunkRaw...)
paddingNeeded := getPadding(len(raw))
if paddingNeeded != 0 {
raw = append(raw, make([]byte, paddingNeeded)...)
}
}
// Checksum is already in BigEndian
// Using LittleEndian.PutUint32 stops it from being flipped
binary.LittleEndian.PutUint32(raw[8:], generatePacketChecksum(raw))
return raw, nil
}
func generatePacketChecksum(raw []byte) uint32 {
rawCopy := make([]byte, len(raw))
copy(rawCopy, raw)
// Clear existing checksum
for offset := 8; offset <= 11; offset++ {
rawCopy[offset] = 0x00
}
return crc32.Checksum(rawCopy, crc32.MakeTable(crc32.Castagnoli))
}
// String makes packet printable
func (p *packet) String() string {
format := `Packet:
sourcePort: %d
destinationPort: %d
verificationTag: %d
`
res := fmt.Sprintf(format,
p.sourcePort,
p.destinationPort,
p.verificationTag,
)
for i, chunk := range p.chunks {
res = res + fmt.Sprintf("Chunk %d:\n %s", i, chunk)
}
return res
}