feat: added error unwrapping

Signed-off-by: Martin Chodur <m.chodur@seznam.cz>

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+* Support for error unwrapping. (Supported for `github.com/pkg/errors` and native wrapping added in go1.13)
+
 ## [1.2.0](https://github.com/grpc-ecosystem/go-grpc-prometheus/releases/tag/v1.2.0) - 2018-06-04
 
 ### Added

makefile

@@ -1,5 +1,3 @@
-SHELL="/bin/bash"
-
 GOFILES_NOVENDOR = $(shell go list ./... | grep -v /vendor/)
 
 all: vet fmt test

packages/grpcstatus/grpcstatus.go

@@ -0,0 +1,57 @@
+package grpcstatus
+
+import (
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+type gRPCStatus interface {
+	GRPCStatus() *status.Status
+}
+
+func unwrapPkgErrorsGRPCStatus(err error) (*status.Status, bool) {
+	type causer interface {
+		Cause() error
+	}
+
+	// Unwrapping the github.com/pkg/errors causer interface, using `Cause` directly could miss some error implementing
+	// the `GRPCStatus` function so we have to check it on our selves.
+	unwrappedCauser := err
+	for unwrappedCauser != nil {
+		if s, ok := unwrappedCauser.(gRPCStatus); ok {
+			return s.GRPCStatus(), true
+		}
+		cause, ok := unwrappedCauser.(causer)
+		if !ok {
+			break
+		}
+		unwrappedCauser = cause.Cause()
+	}
+	return nil, false
+}
+
+// Since error can be wrapped and the `FromError` function only checks for `GRPCStatus` function
+// and as a fallback uses the `Unknown` gRPC status we need to unwrap the error if possible to get the original status.
+// pkg/errors and Go native errors packages have two different approaches so we try to unwrap both types.
+// Eventually should be implemented in the go-grpc status function `FromError`. See https://github.com/grpc/grpc-go/issues/2934
+func GrpcStatusFromError(err error) (s *status.Status, ok bool) {
+	s, ok = status.FromError(err)
+	if ok {
+		return s, true
+	}
+
+	// Try to unwrap `github.com/pkg/errors` wrapped error
+	s, ok = unwrapPkgErrorsGRPCStatus(err)
+	if ok {
+		return s, true
+	}
+
+	// Try to unwrap native wrapped errors using `fmt.Errorf` and `%w`
+	s, ok = unwrapNativeWrappedGRPCStatus(err)
+	if ok {
+		return s, true
+	}
+
+	// We failed to unwrap any GRPSStatus so return default `Unknown`
+	return status.New(codes.Unknown, err.Error()), false
+}

packages/grpcstatus/grpcstatus1.13+_test.go

@@ -0,0 +1,28 @@
+// +build go1.13
+// Copyright 2016 Michal Witkowski. All Rights Reserved.
+// See LICENSE for licensing terms.
+
+package grpcstatus
+
+import (
+	"fmt"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+	"testing"
+)
+
+func TestNativeErrorUnwrapping(t *testing.T) {
+	gRPCCode := codes.FailedPrecondition
+	gRPCError := status.Errorf(gRPCCode, "Userspace error.")
+	expectedGRPCStatus, _ := status.FromError(gRPCError)
+	testedErrors := [...]error{
+		fmt.Errorf("go native wrapped error: %w", gRPCError),
+	}
+
+	for _, e := range testedErrors {
+		resultingStatus, ok := GrpcStatusFromError(e)
+		require.True(t, ok)
+		require.Equal(t, expectedGRPCStatus, resultingStatus)
+	}
+}

packages/grpcstatus/grpcstatus_test.go

@@ -0,0 +1,38 @@
+// Copyright 2016 Michal Witkowski. All Rights Reserved.
+// See LICENSE for licensing terms.
+
+package grpcstatus
+
+import (
+	"github.com/pkg/errors"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+	"testing"
+)
+
+// Own implementation of pkg/errors withStack to avoid additional dependency
+type wrappedError struct {
+	cause error
+	msg   string
+}
+
+func (w *wrappedError) Error() string { return w.msg + ": " + w.cause.Error() }
+
+func (w *wrappedError) Cause() error { return w.cause }
+
+func TestErrorUnwrapping(t *testing.T) {
+	gRPCCode := codes.FailedPrecondition
+	gRPCError := status.Errorf(gRPCCode, "Userspace error.")
+	expectedGRPCStatus, _ := status.FromError(gRPCError)
+	testedErrors := [...]error{
+		gRPCError,
+		errors.Wrap(gRPCError, "pkg/errors wrapped error: "),
+	}
+
+	for _, e := range testedErrors {
+		resultingStatus, ok := GrpcStatusFromError(e)
+		require.True(t, ok)
+		require.Equal(t, expectedGRPCStatus, resultingStatus)
+	}
+}

packages/grpcstatus/native_unwrap1.12-.go

@@ -0,0 +1,11 @@
+// +build !go1.13
+
+package grpcstatus
+
+import (
+	"google.golang.org/grpc/status"
+)
+
+func unwrapNativeWrappedGRPCStatus(err error) (*status.Status, bool) {
+	return nil, false
+}

packages/grpcstatus/native_unwrap1.13+.go

@@ -0,0 +1,17 @@
+// +build go1.13
+
+package grpcstatus
+
+import (
+	"errors"
+	"google.golang.org/grpc/status"
+)
+
+func unwrapNativeWrappedGRPCStatus(err error) (*status.Status, bool) {
+	// Unwrapping the native Go unwrap interface
+	var unwrappedStatus gRPCStatus
+	if ok := errors.As(err, &unwrappedStatus); ok {
+		return unwrappedStatus.GRPCStatus(), true
+	}
+	return nil, false
+}

server_metrics.go

@@ -2,10 +2,10 @@ package grpc_prometheus
 
 import (
 	"context"
-
+	"github.com/grpc-ecosystem/go-grpc-prometheus/packages/grpcstatus"
 	prom "github.com/prometheus/client_golang/prometheus"
+
 	"google.golang.org/grpc"
-	"google.golang.org/grpc/status"
 )
 
 // ServerMetrics represents a collection of metrics to be registered on a
@@ -106,7 +106,7 @@ func (m *ServerMetrics) UnaryServerInterceptor() func(ctx context.Context, req i
 		monitor := newServerReporter(m, Unary, info.FullMethod)
 		monitor.ReceivedMessage()
 		resp, err := handler(ctx, req)
-		st, _ := status.FromError(err)
+		st, _ := grpcstatus.GrpcStatusFromError(err)
 		monitor.Handled(st.Code())
 		if err == nil {
 			monitor.SentMessage()
@@ -120,7 +120,7 @@ func (m *ServerMetrics) StreamServerInterceptor() func(srv interface{}, ss grpc.
 	return func(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
 		monitor := newServerReporter(m, streamRPCType(info), info.FullMethod)
 		err := handler(srv, &monitoredServerStream{ss, monitor})
-		st, _ := status.FromError(err)
+		st, _ := grpcstatus.GrpcStatusFromError(err)
 		monitor.Handled(st.Code())
 		return err
 	}