Represent fingerprint internally as byte array

common/messages/client.go

@@ -5,6 +5,7 @@ package messages
 
 import (
 	"bytes"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 
@@ -105,6 +106,9 @@ func DecodeClientPollRequest(data []byte) (*ClientPollRequest, error) {
 	if message.Fingerprint == "" {
 		message.Fingerprint = defaultBridgeFingerprint
 	}
+	if hex.DecodedLen(len(message.Fingerprint)) != 20 {
+		return nil, fmt.Errorf("cannot decode fingerprint")
+	}
 
 	switch message.NAT {
 	case "":

common/messages/messages_test.go

@@ -344,6 +344,12 @@ func TestEncodeClientPollRequests(t *testing.T) {
 				defaultBridgeFingerprint,
 				nil,
 			},
+			{
+				"unknown",
+				"fake",
+				"123123",
+				fmt.Errorf(""),
+			},
 		} {
 			req1 := &ClientPollRequest{
 				NAT:         test.natType,