Function ExtractAllSCIDs

internal/proxy/parser.go:198–266

ExtractAllSCIDs extracts SCIDs from all coalesced packets in a UDP datagram. QUIC allows multiple packets to be coalesced in a single datagram. The server may use different SCIDs for Initial and Handshake phases.

(datagram []byte)

// QUIC allows multiple packets to be coalesced in a single datagram.
// The server may use different SCIDs for Initial and Handshake phases.
func ExtractAllSCIDs(datagram []byte) [][]byte {
	var scids [][]byte
	seen := make(map[string]bool)

	offset := 0
	for offset < len(datagram) {
		if offset+1 > len(datagram) {
			break
		}

		// Check if Long Header (first bit = 1)
		if datagram[offset]&0x80 == 0 {
			// Short Header - no more Long Header packets possible
			break
		}

		// Parse Long Header to extract SCID and find packet length
		pkt := datagram[offset:]
		if len(pkt) < 6 {
			break
		}

		// Skip header byte (1) + version (4)
		headerOffset := 5
		dcidLen := int(pkt[headerOffset])
		headerOffset++
		headerOffset += dcidLen

		if headerOffset >= len(pkt) {
			break
		}

		scidLen := int(pkt[headerOffset])
		headerOffset++

		if headerOffset+scidLen > len(pkt) {
			break
		}

		scid := pkt[headerOffset : headerOffset+scidLen]
		scidKey := string(scid)
		if !seen[scidKey] && len(scid) > 0 {
			seen[scidKey] = true
			scidCopy := make([]byte, len(scid))
			copy(scidCopy, scid)
			scids = append(scids, scidCopy)
		}
		headerOffset += scidLen

		// Read variable-length packet length field
		if headerOffset >= len(pkt) {
			break
		}
		pktLen, lenBytes, err := readVarInt(pkt[headerOffset:])
		if err != nil || lenBytes == 0 {
			break
		}
		headerOffset += lenBytes