feat(osiris): add TCP and TLS fingerprinting

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

internal/fingerprint/tcp.go

@@ -0,0 +1,46 @@
+package fingerprint
+
+import (
+	"fmt"
+	"net/http"
+	"strings"
+)
+
+// JA4T represents a TCP fingerprint
+type JA4T struct {
+	Window      uint32
+	Options     []uint8
+	MSS         uint16
+	WindowScale uint8
+}
+
+func (j JA4T) String() string {
+	var sb strings.Builder
+
+	// Start with the window size
+	fmt.Fprintf(&sb, "%d", j.Window)
+
+	// Append each option
+	for i, opt := range j.Options {
+		if i == 0 {
+			fmt.Fprint(&sb, "_")
+		} else {
+			fmt.Fprint(&sb, "-")
+		}
+		fmt.Fprintf(&sb, "%d", opt)
+	}
+
+	// Append MSS and WindowScale
+	fmt.Fprintf(&sb, "_%d_%d", j.MSS, j.WindowScale)
+
+	return sb.String()
+}
+
+// GetTCPFingerprint extracts TCP fingerprint from HTTP request context
+func GetTCPFingerprint(r *http.Request) *JA4T {
+	ptr := r.Context().Value(tcpFingerprintKey{})
+	if fpPtr, ok := ptr.(*JA4T); ok && ptr != nil && fpPtr != nil {
+		return fpPtr
+	}
+	return nil
+}