refactor: add ssh sniff support and improve protocol sniffing error handling

src/internal/rewrite/rewriter.go

@@ -157,15 +157,17 @@ func (r *Rewriter) Process(dst net.Conn, src net.Conn, destAddr string, srcAddr
 		}
 	}()
 
-	if strings.HasSuffix(destAddr, "443") && sniff.SniffTLSClientHello(reader) {
-		r.Cache.Add(destAddr, struct{}{})
-		log.LogInfoWithAddr(srcAddr, destAddr, "tls client hello detected, added to cache")
-		statistics.AddConnection(&statistics.ConnectionRecord{
-			Protocol: sniff.HTTPS,
-			SrcAddr:  srcAddr,
-			DestAddr: destAddr,
-		})
-		return
+	if strings.HasSuffix(destAddr, "443") {
+		if isTLS, _ := sniff.SniffTLS(reader); isTLS {
+			r.Cache.Add(destAddr, struct{}{})
+			log.LogInfoWithAddr(srcAddr, destAddr, "tls client hello detected, added to cache")
+			statistics.AddConnection(&statistics.ConnectionRecord{
+				Protocol: sniff.HTTPS,
+				SrcAddr:  srcAddr,
+				DestAddr: destAddr,
+			})
+			return
+		}
 	}
 
 	var isHTTP bool
@@ -177,7 +179,7 @@ func (r *Rewriter) Process(dst net.Conn, src net.Conn, destAddr string, srcAddr
 	if !isHTTP {
 		r.Cache.Add(destAddr, struct{}{})
 		log.LogInfoWithAddr(srcAddr, destAddr, "sniff first request is not http, added to cache, switching to raw proxy")
-		if sniff.SniffTLSClientHello(reader) {
+		if isTLS, _ := sniff.SniffTLS(reader); isTLS {
 			statistics.AddConnection(&statistics.ConnectionRecord{
 				Protocol: sniff.TLS,
 				SrcAddr:  srcAddr,

src/internal/sniff/sniff.go

@@ -16,10 +16,24 @@ const (
 	HTTPS     Protocol = "HTTPS"
 	TLS       Protocol = "TLS"
 	WebSocket Protocol = "WebSocket"
+	SSH       Protocol = "SSH"
 )
 
 var ErrPeekTimeout = errors.New("peek timeout")
 
+func SniffProtocol(reader *bufio.Reader) (Protocol, error) {
+	if isTLS, _ := SniffTLS(reader); isTLS {
+		return TLS, nil
+	}
+	if isHTTP, _ := SniffHTTP(reader); isHTTP {
+		return HTTP, nil
+	}
+	if isSSH, _ := SniffSSH(reader); isSSH {
+		return SSH, nil
+	}
+	return TCP, nil
+}
+
 // peekLineSlice reads a line from bufio.Reader without consuming it.
 // returns the line bytes (without CRLF) or error.
 func peekLineSlice(br *bufio.Reader, maxSize int) ([]byte, error) {

src/internal/sniff/ssh.go

@@ -0,0 +1,14 @@
+package sniff
+
+import "bufio"
+
+func SniffSSH(reader *bufio.Reader) (bool, error) {
+	header, err := reader.Peek(4)
+	if err != nil {
+		return false, err
+	}
+	if string(header) == "SSH-" {
+		return true, nil
+	}
+	return false, nil
+}

src/internal/sniff/tls.go

@@ -2,24 +2,24 @@ package sniff
 
 import "bufio"
 
-func SniffTLSClientHello(reader *bufio.Reader) bool {
+func SniffTLS(reader *bufio.Reader) (bool, error) {
 	header, err := reader.Peek(3)
 	if err != nil {
-		return false
+		return false, err
 	}
 	// TLS record type 0x16 = Handshake
 	if header[0] != 0x16 {
-		return false
+		return false, nil
 	}
 	// TLS version
 	versionMajor := header[1]
 	versionMinor := header[2]
 	if versionMajor != 0x03 {
-		return false
+		return false, nil
 	}
 	if versionMinor < 0x01 || versionMinor > 0x04 {
-		return false
+		return false, nil
 	}
 
-	return true
+	return true, nil
 }

src/internal/sniff/websocket.go

@@ -1,8 +1,11 @@
 package sniff
 
-func SniffWebSocket(header []byte) bool {
-	if len(header) < 2 {
-		return false
+import "bufio"
+
+func SniffWebSocket(reader *bufio.Reader) (bool, error) {
+	header, err := reader.Peek(2)
+	if err != nil {
+		return false, err
 	}
 
 	b0 := header[0]
@@ -14,21 +17,21 @@ func SniffWebSocket(header []byte) bool {
 
 	// requested frames from client to server must be masked
 	if mask == 0 {
-		return false
+		return false, nil
 	}
 	// Control frames must have FIN set
 	if rsv != 0 {
-		return false
+		return false, nil
 	}
 	// opcode must be in valid range
 	if opcode > 0xA {
-		return false
+		return false, nil
 	}
 	// payload length
 	payloadLen := b1 & 0x7F
 	if payloadLen > 0 && payloadLen <= 125 {
-		return true
+		return true, nil
 	}
 
-	return true
+	return true, nil
 }