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package sctp
import (
"encoding/binary"
"errors"
"fmt"
"hash/crc32"
)
// Create the crc32 table we'll use for the checksum
var castagnoliTable = crc32.MakeTable(crc32.Castagnoli) // nolint:gochecknoglobals
// Allocate and zero this data once.
// We need to use it for the checksum and don't want to allocate/clear each time.
var fourZeroes [4]byte // nolint:gochecknoglobals
/*
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
)
var (
errPacketRawTooSmall = errors.New("raw is smaller than the minimum length for a SCTP packet")
errParseSCTPChunkNotEnoughData = errors.New("unable to parse SCTP chunk, not enough data for complete header")
errUnmarshalUnknownChunkType = errors.New("failed to unmarshal, contains unknown chunk type")
errChecksumMismatch = errors.New("checksum mismatch theirs")
)
func (p *packet) unmarshal(raw []byte) error {
if len(raw) < packetHeaderSize {
return fmt.Errorf("%w: raw only %d bytes, %d is the minimum length", errPacketRawTooSmall, 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 fmt.Errorf("%w: offset %d remaining %d", errParseSCTPChunkNotEnoughData, offset, len(raw))
}
var c chunk
switch chunkType(raw[offset]) {
case ctInit:
c = &chunkInit{}
case ctInitAck:
c = &chunkInitAck{}
case ctAbort:
c = &chunkAbort{}
case ctCookieEcho:
c = &chunkCookieEcho{}
case ctCookieAck:
c = &chunkCookieAck{}
case ctHeartbeat:
c = &chunkHeartbeat{}
case ctPayloadData:
c = &chunkPayloadData{}
case ctSack:
c = &chunkSelectiveAck{}
case ctReconfig:
c = &chunkReconfig{}
case ctForwardTSN:
c = &chunkForwardTSN{}
case ctError:
c = &chunkError{}
case ctShutdown:
c = &chunkShutdown{}
case ctShutdownAck:
c = &chunkShutdownAck{}
case ctShutdownComplete:
c = &chunkShutdownComplete{}
default:
return fmt.Errorf("%w: %s", errUnmarshalUnknownChunkType, 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 fmt.Errorf("%w: %d ours: %d", errChecksumMismatch, 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) (sum uint32) {
// Fastest way to do a crc32 without allocating.
sum = crc32.Update(sum, castagnoliTable, raw[0:8])
sum = crc32.Update(sum, castagnoliTable, fourZeroes[:])
sum = crc32.Update(sum, castagnoliTable, raw[12:])
return sum
}
// 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 += fmt.Sprintf("Chunk %d:\n %s", i, chunk)
}
return res
}
