add traffic sniffing for handler

internal/util/sniffing/sniff.go

@@ -0,0 +1,55 @@
+package sniffing
+
+import (
+	"bufio"
+	"context"
+	"crypto/tls"
+	"encoding/binary"
+	"net/http"
+	"strings"
+
+	dissector "github.com/go-gost/tls-dissector"
+)
+
+const (
+	ProtoHTTP = "http"
+	ProtoTLS  = "tls"
+	ProtoSSH  = "ssh"
+)
+
+func Sniff(ctx context.Context, r *bufio.Reader) (proto string, err error) {
+	hdr, err := r.Peek(dissector.RecordHeaderLen)
+	if err != nil {
+		return
+	}
+
+	// try to sniff TLS traffic
+	tlsVersion := binary.BigEndian.Uint16(hdr[1:3])
+	if hdr[0] == dissector.Handshake &&
+		(tlsVersion >= tls.VersionTLS10 && tlsVersion <= tls.VersionTLS13) {
+		return ProtoTLS, nil
+	}
+
+	// try to sniff HTTP traffic
+	if isHTTP(string(hdr[:])) {
+		return ProtoHTTP, nil
+	}
+
+	if string(hdr) == "SSH-2" {
+		return ProtoSSH, nil
+	}
+
+	return
+}
+
+func isHTTP(s string) bool {
+	return strings.HasPrefix(http.MethodGet, s[:3]) ||
+		strings.HasPrefix(http.MethodPost, s[:4]) ||
+		strings.HasPrefix(http.MethodPut, s[:3]) ||
+		strings.HasPrefix(http.MethodDelete, s) ||
+		strings.HasPrefix(http.MethodOptions, s) ||
+		strings.HasPrefix(http.MethodPatch, s) ||
+		strings.HasPrefix(http.MethodHead, s[:4]) ||
+		strings.HasPrefix(http.MethodConnect, s) ||
+		strings.HasPrefix(http.MethodTrace, s)
+}