ddtrace/opentracer: translate Datadog errors to OpenTracing errors

This change fixes so that the OpenTracing implementation returns standard errors
defined in opentracing-go, as opposed to returning errors defined in ddtrace/tracer.

Fixes #998

ddtrace/opentracer/tracer.go

@@ -73,7 +73,7 @@ func (t *opentracer) Inject(ctx opentracing.SpanContext, format interface{}, car
 	}
 	switch format {
 	case opentracing.TextMap, opentracing.HTTPHeaders:
-		return t.Tracer.Inject(sctx, carrier)
+		return translateError(t.Tracer.Inject(sctx, carrier))
 	default:
 		return opentracing.ErrUnsupportedFormat
 	}
@@ -83,7 +83,8 @@ func (t *opentracer) Inject(ctx opentracing.SpanContext, format interface{}, car
 func (t *opentracer) Extract(format interface{}, carrier interface{}) (opentracing.SpanContext, error) {
 	switch format {
 	case opentracing.TextMap, opentracing.HTTPHeaders:
-		return t.Tracer.Extract(carrier)
+		sctx, err := t.Tracer.Extract(carrier)
+		return sctx, translateError(err)
 	default:
 		return nil, opentracing.ErrUnsupportedFormat
 	}
@@ -99,3 +100,18 @@ func (t *opentracer) ContextWithSpanHook(ctx context.Context, openSpan opentraci
 	}
 	return tracer.ContextWithSpan(ctx, ddSpan.Span)
 }
+
+func translateError(err error) error {
+	switch err {
+	case tracer.ErrSpanContextNotFound:
+		return opentracing.ErrSpanContextNotFound
+	case tracer.ErrInvalidCarrier:
+		return opentracing.ErrInvalidCarrier
+	case tracer.ErrInvalidSpanContext:
+		return opentracing.ErrInvalidSpanContext
+	case tracer.ErrSpanContextCorrupted:
+		return opentracing.ErrSpanContextCorrupted
+	default:
+		return err
+	}
+}

ddtrace/opentracer/tracer_test.go

@@ -7,6 +7,7 @@ package opentracer
 
 import (
 	"context"
+	"errors"
 	"testing"
 
 	"gopkg.in/DataDog/dd-trace-go.v1/ddtrace"
@@ -37,3 +38,20 @@ func TestSpanWithContext(t *testing.T) {
 	assert.True(ok)
 	assert.Equal(got, want.(*span).Span)
 }
+
+func TestTranslateError(t *testing.T) {
+	for name, tt := range map[string]struct {
+		in, out error
+	}{
+		"nil":                     {in: nil, out: nil},
+		"unrecognized":            {in: errors.New("unrecognized"), out: errors.New("unrecognized")},
+		"ErrSpanContextNotFound":  {in: tracer.ErrSpanContextNotFound, out: opentracing.ErrSpanContextNotFound},
+		"ErrInvalidCarrier":       {in: tracer.ErrInvalidCarrier, out: opentracing.ErrInvalidCarrier},
+		"ErrInvalidSpanContext":   {in: tracer.ErrInvalidSpanContext, out: opentracing.ErrInvalidSpanContext},
+		"ErrSpanContextCorrupted": {in: tracer.ErrSpanContextCorrupted, out: opentracing.ErrSpanContextCorrupted},
+	} {
+		t.Run(name, func(t *testing.T) {
+			assert.Equal(t, tt.out, translateError(tt.in))
+		})
+	}
+}