lib/protocol: Avoid panic in DeviceIDFromBytes (#6714)

lib/protocol/deviceid.go

@@ -46,13 +46,13 @@ func DeviceIDFromString(s string) (DeviceID, error) {
 	return n, err
 }
 
-func DeviceIDFromBytes(bs []byte) DeviceID {
+func DeviceIDFromBytes(bs []byte) (DeviceID, error) {
 	var n DeviceID
 	if len(bs) != len(n) {
-		panic("incorrect length of byte slice representing device ID")
+		return n, fmt.Errorf("incorrect length of byte slice representing device ID")
 	}
 	copy(n[:], bs)
-	return n
+	return n, nil
 }
 
 // String returns the canonical string representation of the device ID

lib/protocol/deviceid_test.go

@@ -99,8 +99,10 @@ func TestShortIDString(t *testing.T) {
 
 func TestDeviceIDFromBytes(t *testing.T) {
 	id0, _ := DeviceIDFromString(formatted)
-	id1 := DeviceIDFromBytes(id0[:])
-	if id1.String() != formatted {
+	id1, err := DeviceIDFromBytes(id0[:])
+	if err != nil {
+		t.Fatal(err)
+	} else if id1.String() != formatted {
 		t.Errorf("Wrong device ID, got %q, want %q", id1, formatted)
 	}
 }
@@ -150,7 +152,10 @@ func TestNewDeviceIDMarshalling(t *testing.T) {
 
 	// Verify it's the same
 
-	if DeviceIDFromBytes(msg2.Test) != id0 {
+	id1, err := DeviceIDFromBytes(msg2.Test)
+	if err != nil {
+		t.Fatal(err)
+	} else if id1 != id0 {
 		t.Error("Mismatch in old -> new direction")
 	}
 }