firmware/btc: return struct in BTCSign and BTCSignMessage

Better clarity and composes better with generic functions returning a
single value.

Author: benma

api/firmware/btc.go

@@ -542,18 +542,27 @@ func (device *Device) BTCRegisterScriptConfig(
 	return nil
 }
 
+type BTCSignMessageResult struct {
+	// Signature is the 64 byte raw signature.
+	Signature []byte
+	// RecID is the recoverable ID.
+	RecID byte
+	// ElectrumSig65 is the 65 byte signature in Electrum format.
+	ElectrumSig65 []byte
+}
+
 // BTCSignMessage signs a Bitcoin message. The 64 byte raw signature, the recoverable ID and the 65
 // byte signature in Electrum format are returned.
 func (device *Device) BTCSignMessage(
 	coin messages.BTCCoin,
 	scriptConfig *messages.BTCScriptConfigWithKeypath,
 	message []byte,
-) (raw []byte, recID byte, electrum65 []byte, err error) {
+) (*BTCSignMessageResult, error) {
 	if isTaproot(scriptConfig) {
-		return nil, 0, nil, errp.New("taproot not supported")
+		return nil, errp.New("taproot not supported")
 	}
 	if !device.version.AtLeast(semver.NewSemVer(9, 2, 0)) {
-		return nil, 0, nil, UnsupportedError("9.2.0")
+		return nil, UnsupportedError("9.2.0")
 	}
 
 	supportsAntiklepto := device.version.AtLeast(semver.NewSemVer(9, 5, 0))
@@ -564,7 +573,7 @@ func (device *Device) BTCSignMessage(
 		var err error
 		hostNonce, err = generateHostNonce()
 		if err != nil {
-			return nil, 0, nil, err
+			return nil, err
 		}
 		hostNonceCommitment = &messages.AntiKleptoHostNonceCommitment{
 			Commitment: antikleptoHostCommit(hostNonce),
@@ -583,14 +592,14 @@ func (device *Device) BTCSignMessage(
 	}
 	response, err := device.queryBTC(request)
 	if err != nil {
-		return nil, 0, nil, err
+		return nil, err
 	}
 
 	var signature []byte
 	if supportsAntiklepto {
 		signerCommitment, ok := response.Response.(*messages.BTCResponse_AntikleptoSignerCommitment)
 		if !ok {
-			return nil, 0, nil, errp.New("unexpected response")
+			return nil, errp.New("unexpected response")
 		}
 		response, err := device.queryBTC(&messages.BTCRequest{
 			Request: &messages.BTCRequest_AntikleptoSignature{
@@ -600,12 +609,12 @@ func (device *Device) BTCSignMessage(
 			},
 		})
 		if err != nil {
-			return nil, 0, nil, err
+			return nil, err
 		}
 
 		signResponse, ok := response.Response.(*messages.BTCResponse_SignMessage)
 		if !ok {
-			return nil, 0, nil, errp.New("unexpected response")
+			return nil, errp.New("unexpected response")
 		}
 		signature = signResponse.SignMessage.Signature
 		err = antikleptoVerify(
@@ -614,12 +623,12 @@ func (device *Device) BTCSignMessage(
 			signature[:64],
 		)
 		if err != nil {
-			return nil, 0, nil, err
+			return nil, err
 		}
 	} else {
 		signResponse, ok := response.Response.(*messages.BTCResponse_SignMessage)
 		if !ok {
-			return nil, 0, nil, errp.New("unexpected response")
+			return nil, errp.New("unexpected response")
 		}
 		signature = signResponse.SignMessage.Signature
 	}
@@ -628,5 +637,9 @@ func (device *Device) BTCSignMessage(
 	// See https://github.com/spesmilo/electrum/blob/84dc181b6e7bb20e88ef6b98fb8925c5f645a765/electrum/ecc.py#L521-L523
 	const compressed = 4 // BitBox02 uses only compressed pubkeys
 	electrumSig65 := append([]byte{27 + compressed + recID}, sig...)
-	return sig, recID, electrumSig65, nil
+	return &BTCSignMessageResult{
+		Signature:     sig,
+		RecID:         recID,
+		ElectrumSig65: electrumSig65,
+	}, nil
 }

api/firmware/btc_test.go

@@ -161,7 +161,7 @@ func TestSimulatorBTCSignMessage(t *testing.T) {
 
 		pubKey := simulatorPub(t, device, keypath...)
 
-		sig, _, _, err := device.BTCSignMessage(
+		result, err := device.BTCSignMessage(
 			coin,
 			&messages.BTCScriptConfigWithKeypath{
 				ScriptConfig: NewBTCScriptConfigSimple(messages.BTCScriptConfig_P2WPKH_P2SH),
@@ -171,7 +171,7 @@ func TestSimulatorBTCSignMessage(t *testing.T) {
 		)
 		require.NoError(t, err)
 		sigHash := chainhash.DoubleHashB([]byte("\x18Bitcoin Signed Message:\n\x07message"))
-		require.True(t, parseECDSASignature(t, sig).Verify(sigHash, pubKey))
+		require.True(t, parseECDSASignature(t, result.Signature).Verify(sigHash, pubKey))
 	})
 }
 
@@ -352,7 +352,7 @@ func TestBTCSignMessage(t *testing.T) {
 		generateHostNonce = func() ([]byte, error) {
 			return hostNonce, nil
 		}
-		sig, recID, electrumSig65, err := env.device.BTCSignMessage(
+		result, err := env.device.BTCSignMessage(
 			messages.BTCCoin_BTC,
 			&messages.BTCScriptConfigWithKeypath{
 				ScriptConfig: NewBTCScriptConfigSimple(messages.BTCScriptConfig_P2WPKH_P2SH),
@@ -362,9 +362,9 @@ func TestBTCSignMessage(t *testing.T) {
 		)
 		if env.version.AtLeast(semver.NewSemVer(9, 2, 0)) {
 			require.NoError(t, err)
-			require.Equal(t, expectedSig[:64], sig)
-			require.Equal(t, byte(0), recID)
-			require.Equal(t, electrumSig65, append([]byte{31}, expectedSig[:64]...))
+			require.Equal(t, expectedSig[:64], result.Signature)
+			require.Equal(t, byte(0), result.RecID)
+			require.Equal(t, result.ElectrumSig65, append([]byte{31}, expectedSig[:64]...))
 		} else {
 			require.EqualError(t, err, UnsupportedError("9.2.0").Error())
 		}