multi: surface grpc error codes from server to client

client.go

@@ -15,6 +15,7 @@ import (
 	"github.com/lightninglabs/loop/loopdb"
 	"github.com/lightninglabs/loop/swap"
 	"github.com/lightninglabs/loop/sweep"
+	"google.golang.org/grpc/status"
 )
 
 var (
@@ -610,3 +611,17 @@ func (s *Client) LoopInTerms(ctx context.Context) (
 
 	return s.Server.GetLoopInTerms(ctx)
 }
+
+// wrapGrpcError wraps the non-nil error provided with a message providing
+// additional context, preserving the grpc code returned with the original
+// error. If the original error has no grpc code, then codes.Unknown is used.
+func wrapGrpcError(message string, err error) error {
+	// Since our error is non-nil, we don't need to worry about a nil
+	// grpcStatus, we'll just get an unknown one if no code was passed back.
+	grpcStatus, _ := status.FromError(err)
+
+	return status.Error(
+		grpcStatus.Code(), fmt.Sprintf("%v: %v", message,
+			grpcStatus.Message()),
+	)
+}

client_test.go

@@ -17,6 +17,8 @@ import (
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 )
 
 var (
@@ -372,3 +374,39 @@ func testSuccess(ctx *testContext, amt btcutil.Amount, hash lntypes.Hash,
 
 	ctx.finish()
 }
+
+// TestWrapGrpcError tests grpc error wrapping in the case where a grpc error
+// code is present, and when it is absent.
+func TestWrapGrpcError(t *testing.T) {
+	tests := []struct {
+		name         string
+		original     error
+		expectedCode codes.Code
+	}{
+		{
+			name: "out of range error",
+			original: status.Error(
+				codes.OutOfRange, "err string",
+			),
+			expectedCode: codes.OutOfRange,
+		},
+		{
+			name:         "no grpc code",
+			original:     errors.New("no error code"),
+			expectedCode: codes.Unknown,
+		},
+	}
+
+	for _, testCase := range tests {
+		testCase := testCase
+
+		t.Run(testCase.name, func(t *testing.T) {
+			err := wrapGrpcError("", testCase.original)
+			require.Error(t, err, "test only expects errors")
+
+			status, ok := status.FromError(err)
+			require.True(t, ok, "test expects grpc code")
+			require.Equal(t, testCase.expectedCode, status.Code())
+		})
+	}
+}

loopin.go

@@ -9,11 +9,10 @@ import (
 	"sync"
 	"time"
 
-	"github.com/btcsuite/btcutil"
-
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/mempool"
 	"github.com/btcsuite/btcd/wire"
+	"github.com/btcsuite/btcutil"
 	"github.com/lightninglabs/lndclient"
 	"github.com/lightninglabs/loop/labels"
 	"github.com/lightninglabs/loop/loopdb"
@@ -86,7 +85,7 @@ func newLoopInSwap(globalCtx context.Context, cfg *swapConfig,
 	// request that we send to the server.
 	quote, err := cfg.server.GetLoopInQuote(globalCtx, request.Amount)
 	if err != nil {
-		return nil, fmt.Errorf("loop in terms: %v", err)
+		return nil, wrapGrpcError("loop in terms", err)
 	}
 
 	swapFee := quote.SwapFee
@@ -172,7 +171,7 @@ func newLoopInSwap(globalCtx context.Context, cfg *swapConfig,
 	)
 	probeWaitCancel()
 	if err != nil {
-		return nil, fmt.Errorf("cannot initiate swap: %v", err)
+		return nil, wrapGrpcError("cannot initiate swap", err)
 	}
 
 	// Because the context is cancelled, it is guaranteed that we will be

loopin_test.go

@@ -4,15 +4,14 @@ import (
 	"context"
 	"testing"
 
+	"github.com/btcsuite/btcd/wire"
+	"github.com/btcsuite/btcutil"
 	"github.com/lightninglabs/loop/loopdb"
 	"github.com/lightninglabs/loop/swap"
 	"github.com/lightninglabs/loop/test"
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/stretchr/testify/require"
-
-	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btcutil"
 )
 
 var (

loopout.go

@@ -128,7 +128,7 @@ func newLoopOutSwap(globalCtx context.Context, cfg *swapConfig,
 		receiverKey, request.SwapPublicationDeadline, request.Initiator,
 	)
 	if err != nil {
-		return nil, fmt.Errorf("cannot initiate swap: %v", err)
+		return nil, wrapGrpcError("cannot initiate swap", err)
 	}
 
 	err = validateLoopOutContract(

release_notes.md

@@ -19,3 +19,7 @@ This file tracks release notes for the loop client.
 #### Breaking Changes
 
 #### Bug Fixes
+* Grpc error codes returned by the swap server when swap initiation fails are 
+  now surfaced to the client. Previously these error codes would be returned
+  as a string.
+