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