feat(relayd): ja4t fingerprinting

Signed-off-by: Xe Iaso <me@xeiaso.net>

2 files changed, 29 insertions, 11 deletions

diff --git a/cmd/relayd/fingerprint.go b/cmd/relayd/fingerprint.go
index 7ef2d13..1a30a57 100644
--- a/cmd/relayd/fingerprint.go
+++ b/cmd/relayd/fingerprint.go
@@ -41,12 +41,16 @@ func applyTLSFingerprinter(server *http.Server) {
 	}
 	server.ConnContext = func(ctx context.Context, c net.Conn) context.Context {
 		ctx = context.WithValue(ctx, tlsFingerprintKey{}, &TLSFingerprint{})
-		tcpFP, err := assignTCPFingerprint(c)
-		if err == nil {
-			ctx = context.WithValue(ctx, tcpFingerprintKey{}, tcpFP)
-		} else {
-			slog.Debug("ja4t error", "err", err)
+
+		if tc, ok := c.(*tls.Conn); ok {
+			tcpFP, err := assignTCPFingerprint(tc.NetConn())
+			if err == nil {
+				ctx = context.WithValue(ctx, tcpFingerprintKey{}, tcpFP)
+			} else {
+				slog.Debug("ja4t error", "err", err)
+			}
 		}
+
 		return ctx
 	}
 }
diff --git a/cmd/relayd/tcpfingerprint.go b/cmd/relayd/tcpfingerprint.go
index a5f611a..d88115b 100644
--- a/cmd/relayd/tcpfingerprint.go
+++ b/cmd/relayd/tcpfingerprint.go
@@ -1,9 +1,11 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
 	"net"
 	"net/http"
+	"os"
 	"strings"
 
 	"github.com/mikioh/tcp"
@@ -25,15 +27,27 @@ func assignTCPFingerprint(c net.Conn) (*JA4T, error) {
 
 	ci, ok := i.(*tcpinfo.Info)
 	if !ok {
-		return nil, fmt.Errorf("can't make %T into *tcpinfo.Info")
+		return nil, fmt.Errorf("can't make %T into *tcpinfo.Info", i)
 	}
 
+	json.NewEncoder(os.Stdout).Encode(ci)
+
 	result := &JA4T{
-		Window:      uint32(ci.Sys.SenderWindow),
-		MSS:         uint16(ci.SenderMSS),
-		WindowScale: 0,
+		Window: uint32(ci.Sys.SenderWindow),
+		MSS:    uint16(ci.SenderMSS),
+	}
+
+	for _, opt := range ci.PeerOptions {
+		switch opt.(type) {
+		case tcpinfo.WindowScale:
+			result.Options = append(result.Options, 3, uint8(opt.(tcpinfo.WindowScale)))
+			result.WindowScale = uint8(opt.(tcpinfo.WindowScale))
+		case tcpinfo.SACKPermitted:
+			result.Options = append(result.Options, 4, 1)
+		case tcpinfo.Timestamps:
+			result.Options = append(result.Options, 8, 1)
+		}
 	}
-	fmt.Println(result.String())
 
 	return result, nil
 }
@@ -61,7 +75,7 @@ func (j JA4T) String() string {
 
 	for i, opt := range j.Options {
 		fmt.Fprint(&sb, opt)
-		if i-1 != len(j.Options) {
+		if i != len(j.Options)-1 {
 			fmt.Fprint(&sb, "-")
 		}
 	}