mirror of
https://github.com/pion/webrtc.git
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51e669e1d8
* Make sure errors in SCTP make it all the way back * Move structs into files with proper names in SCTP * Add String() for AssociationState enum * Add callbacks to Association to that we can handle DATA in the DataChannel package and send outbound SCTP
113 lines
3.5 KiB
Go
113 lines
3.5 KiB
Go
package sctp
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import (
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"encoding/binary"
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"hash/crc32"
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"github.com/pkg/errors"
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)
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/*
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Packet represents an SCTP packet, defined in https://tools.ietf.org/html/rfc4960#section-3
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An SCTP packet is composed of a common header and chunks. A chunk
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contains either control information or user data.
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SCTP Packet Format
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0 1 2 3
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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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Common Header |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Chunk #1 |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| ... |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Chunk #n |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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SCTP Common Header Format
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0 1 2 3
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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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Source Port Number | Destination Port Number |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Verification Tag |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Checksum |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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type Packet struct {
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SourcePort uint16
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DestinationPort uint16
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VerificationTag uint32
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Chunks []Chunk
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}
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const (
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packetHeaderSize = 12
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)
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// Unmarshal populates a Packet from a raw buffer
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func (p *Packet) Unmarshal(raw []byte) error {
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if len(raw) < packetHeaderSize {
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return errors.Errorf("raw only %d bytes, %d is the minimum length for a SCTP packet", len(raw), packetHeaderSize)
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}
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p.SourcePort = binary.BigEndian.Uint16(raw[0:])
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p.DestinationPort = binary.BigEndian.Uint16(raw[2:])
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p.VerificationTag = binary.BigEndian.Uint32(raw[4:])
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offset := packetHeaderSize
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for {
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// Exact match, no more chunks
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if offset == len(raw) {
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break
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} else if offset+chunkHeaderSize > len(raw) {
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return errors.Errorf("Unable to parse SCTP chunk, not enough data for complete header: offset %d remaining %d", offset, len(raw))
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}
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var c Chunk
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switch ChunkType(raw[offset]) {
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case INIT:
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c = &Init{}
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default:
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return errors.Errorf("Failed to unmarshal, contains unknown chunk type %d", raw[offset])
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}
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if err := c.Unmarshal(raw[offset:]); err != nil {
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return err
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}
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p.Chunks = append(p.Chunks, c)
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chunkValuePadding := c.valueLength() % 4
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offset += chunkHeaderSize + c.valueLength() + chunkValuePadding
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}
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theirChecksum := binary.LittleEndian.Uint32(raw[8:])
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ourChecksum := generatePacketChecksum(raw)
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if theirChecksum != ourChecksum {
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return errors.Errorf("Checksum mismatch theirs: %d ours: %d", theirChecksum, ourChecksum)
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}
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return nil
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}
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// Marshal populates a raw buffer from a packet
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func (p *Packet) Marshal() ([]byte, error) {
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return nil, errors.Errorf("Unimplemented")
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}
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func generatePacketChecksum(raw []byte) uint32 {
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rawCopy := make([]byte, len(raw))
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copy(rawCopy, raw)
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// Clear existing checksum
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for offset := 8; offset <= 11; offset++ {
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rawCopy[offset] = 0x00
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}
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return crc32.Checksum(rawCopy, crc32.MakeTable(crc32.Castagnoli))
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}
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