148 lines
5.1 KiB
Go
148 lines
5.1 KiB
Go
package sctp
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import (
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"encoding/binary"
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"errors"
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"fmt"
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)
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/*
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chunkSelectiveAck represents an SCTP Chunk of type SACK
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This chunk is sent to the peer endpoint to acknowledge received DATA
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chunks and to inform the peer endpoint of gaps in the received
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subsequences of DATA chunks as represented by their TSNs.
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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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| Type = 3 |Chunk Flags | Chunk Length |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Cumulative TSN Ack |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Advertised Receiver Window Credit (a_rwnd) |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Number of Gap Ack Blocks = N | Number of Duplicate TSNs = X |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Gap Ack Block #1 Start | Gap Ack Block #1 End |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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/ /
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\ ... \
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/ /
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Gap Ack Block #N Start | Gap Ack Block #N End |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Duplicate TSN 1 |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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/ /
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\ ... \
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/ /
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Duplicate TSN X |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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type gapAckBlock struct {
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start uint16
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end uint16
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}
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var (
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errChunkTypeNotSack = errors.New("ChunkType is not of type SACK")
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errSackSizeNotLargeEnoughInfo = errors.New("SACK Chunk size is not large enough to contain header")
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errSackSizeNotMatchPredicted = errors.New("SACK Chunk size does not match predicted amount from header values")
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)
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// String makes gapAckBlock printable
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func (g gapAckBlock) String() string {
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return fmt.Sprintf("%d - %d", g.start, g.end)
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}
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type chunkSelectiveAck struct {
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chunkHeader
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cumulativeTSNAck uint32
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advertisedReceiverWindowCredit uint32
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gapAckBlocks []gapAckBlock
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duplicateTSN []uint32
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}
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const (
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selectiveAckHeaderSize = 12
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)
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func (s *chunkSelectiveAck) unmarshal(raw []byte) error {
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if err := s.chunkHeader.unmarshal(raw); err != nil {
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return err
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}
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if s.typ != ctSack {
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return fmt.Errorf("%w: actually is %s", errChunkTypeNotSack, s.typ.String())
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}
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if len(s.raw) < selectiveAckHeaderSize {
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return fmt.Errorf("%w: %v remaining, needs %v bytes", errSackSizeNotLargeEnoughInfo,
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len(s.raw), selectiveAckHeaderSize)
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}
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s.cumulativeTSNAck = binary.BigEndian.Uint32(s.raw[0:])
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s.advertisedReceiverWindowCredit = binary.BigEndian.Uint32(s.raw[4:])
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s.gapAckBlocks = make([]gapAckBlock, binary.BigEndian.Uint16(s.raw[8:]))
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s.duplicateTSN = make([]uint32, binary.BigEndian.Uint16(s.raw[10:]))
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if len(s.raw) != selectiveAckHeaderSize+(4*len(s.gapAckBlocks)+(4*len(s.duplicateTSN))) {
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return errSackSizeNotMatchPredicted
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}
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offset := selectiveAckHeaderSize
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for i := range s.gapAckBlocks {
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s.gapAckBlocks[i].start = binary.BigEndian.Uint16(s.raw[offset:])
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s.gapAckBlocks[i].end = binary.BigEndian.Uint16(s.raw[offset+2:])
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offset += 4
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}
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for i := range s.duplicateTSN {
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s.duplicateTSN[i] = binary.BigEndian.Uint32(s.raw[offset:])
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offset += 4
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}
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return nil
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}
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func (s *chunkSelectiveAck) marshal() ([]byte, error) {
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sackRaw := make([]byte, selectiveAckHeaderSize+(4*len(s.gapAckBlocks)+(4*len(s.duplicateTSN))))
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binary.BigEndian.PutUint32(sackRaw[0:], s.cumulativeTSNAck)
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binary.BigEndian.PutUint32(sackRaw[4:], s.advertisedReceiverWindowCredit)
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binary.BigEndian.PutUint16(sackRaw[8:], uint16(len(s.gapAckBlocks)))
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binary.BigEndian.PutUint16(sackRaw[10:], uint16(len(s.duplicateTSN)))
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offset := selectiveAckHeaderSize
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for _, g := range s.gapAckBlocks {
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binary.BigEndian.PutUint16(sackRaw[offset:], g.start)
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binary.BigEndian.PutUint16(sackRaw[offset+2:], g.end)
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offset += 4
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}
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for _, t := range s.duplicateTSN {
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binary.BigEndian.PutUint32(sackRaw[offset:], t)
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offset += 4
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}
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s.chunkHeader.typ = ctSack
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s.chunkHeader.raw = sackRaw
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return s.chunkHeader.marshal()
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}
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func (s *chunkSelectiveAck) check() (abort bool, err error) {
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return false, nil
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}
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// String makes chunkSelectiveAck printable
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func (s *chunkSelectiveAck) String() string {
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res := fmt.Sprintf("SACK cumTsnAck=%d arwnd=%d dupTsn=%d",
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s.cumulativeTSNAck,
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s.advertisedReceiverWindowCredit,
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s.duplicateTSN)
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for _, gap := range s.gapAckBlocks {
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res = fmt.Sprintf("%s\n gap ack: %s", res, gap)
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}
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return res
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}
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