Add UDP Like transport mode to snowflake

server/lib/packetIDConnServer.go

@@ -0,0 +1,52 @@
+package snowflake_server
+
+import (
+	"errors"
+	"net"
+
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/turbotunnel"
+)
+
+type ConnID = turbotunnel.ClientID
+
+type packetConnIDConnServer struct {
+	// This net.Conn must preserve message boundaries.
+	net.Conn
+	connID           ConnID
+	clientIDReceived bool
+}
+
+var ErrClientIDNotReceived = errors.New("ClientID not received")
+
+func (p *packetConnIDConnServer) GetClientID() (ConnID, error) {
+	if !p.clientIDReceived {
+		return p.connID, ErrClientIDNotReceived
+	}
+	return p.connID, nil
+}
+
+func (p *packetConnIDConnServer) Read(buf []byte) (n int, err error) {
+	n, err = p.Conn.Read(buf)
+	if err != nil {
+		return
+	}
+	switch buf[0] {
+	case 0xfe:
+		p.clientIDReceived = true
+		copy(p.connID[:], buf[1:9])
+		copy(buf[0:], buf[9:])
+		return n - 9, nil
+	case 0xff:
+		copy(buf[0:], buf[1:])
+		return n - 1, nil
+	}
+	return 0, nil
+}
+
+func (p *packetConnIDConnServer) Write(buf []byte) (n int, err error) {
+	n, err = p.Conn.Write(append([]byte{0xff}, buf...))
+	if err != nil {
+		return 0, err
+	}
+	return len(buf) - 1, nil
+}