Only set SpanStatus in error scenarios (#58)

- Only set SpanStatus when errors are non nil
- Leave SpanStatus unset for all non error scenarios
- Add test for Streaming 
- Update old tests to check SpanStatus

Fixes: https://github.com/bufbuild/connect-opentelemetry-go/issues/51

interceptor.go

@@ -290,7 +290,7 @@ func protocolToSemConv(protocol string) string {
 
 func spanStatus(err error) (codes.Code, string) {
 	if err == nil {
-		return codes.Ok, ""
+		return codes.Unset, ""
 	}
 	if connectErr := new(connect.Error); errors.As(err, &connectErr) {
 		return codes.Error, connectErr.Message()

interceptor_test.go

@@ -34,6 +34,7 @@ import (
 	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/codes"
 	"go.opentelemetry.io/otel/metric/unit"
 	"go.opentelemetry.io/otel/propagation"
 	"go.opentelemetry.io/otel/sdk/instrumentation"
@@ -952,6 +953,8 @@ func TestClientSimple(t *testing.T) {
 	if _, err := pingClient.Ping(context.Background(), requestOfSize(1, 0)); err != nil {
 		t.Errorf(err.Error())
 	}
+	require.Len(t, clientSpanRecorder.Ended(), 1)
+	require.Equal(t, clientSpanRecorder.Ended()[0].Status().Code, codes.Unset)
 	assertSpans(t, []wantSpans{
 		{
 			spanName: pingv1connect.PingServiceName + "/" + PingMethod,
@@ -999,6 +1002,8 @@ func TestHandlerFailCall(t *testing.T) {
 	if err == nil {
 		t.Fatal("expecting error, got nil")
 	}
+	require.Len(t, clientSpanRecorder.Ended(), 1)
+	require.Equal(t, clientSpanRecorder.Ended()[0].Status().Code, codes.Error)
 	assertSpans(t, []wantSpans{
 		{
 			spanName: pingv1connect.PingServiceName + "/" + FailMethod,
@@ -1049,6 +1054,8 @@ func TestClientHandlerOpts(t *testing.T) {
 		t.Errorf(err.Error())
 	}
 	assertSpans(t, []wantSpans{}, serverSpanRecorder.Ended())
+	require.Len(t, clientSpanRecorder.Ended(), 1)
+	require.Equal(t, clientSpanRecorder.Ended()[0].Status().Code, codes.Unset)
 	assertSpans(t, []wantSpans{
 		{
 			spanName: pingv1connect.PingServiceName + "/" + PingMethod,
@@ -1469,6 +1476,8 @@ func TestStreamingHandlerTracing(t *testing.T) {
 	assert.NoError(t, err)
 	assert.NoError(t, stream.CloseRequest())
 	assert.NoError(t, stream.CloseResponse())
+	require.Len(t, spanRecorder.Ended(), 1)
+	require.Equal(t, spanRecorder.Ended()[0].Status().Code, codes.Unset)
 	assertSpans(t, []wantSpans{
 		{
 			spanName: pingv1connect.PingServiceName + "/" + CumSumMethod,
@@ -1524,6 +1533,8 @@ func TestStreamingClientTracing(t *testing.T) {
 	assert.NoError(t, err)
 	assert.NoError(t, stream.CloseRequest())
 	assert.NoError(t, stream.CloseResponse())
+	require.Len(t, spanRecorder.Ended(), 1)
+	require.Equal(t, spanRecorder.Ended()[0].Status().Code, codes.Unset)
 	assertSpans(t, []wantSpans{
 		{
 			spanName: pingv1connect.PingServiceName + "/" + CumSumMethod,
@@ -1668,6 +1679,39 @@ func TestWithoutServerPeerAttributes(t *testing.T) {
 	}, spanRecorder.Ended())
 }
 
+func TestStreamingSpanStatus(t *testing.T) {
+	t.Parallel()
+	var propagator propagation.TraceContext
+	handlerSpanRecorder := tracetest.NewSpanRecorder()
+	handlerTraceProvider := trace.NewTracerProvider(trace.WithSpanProcessor(handlerSpanRecorder))
+	clientSpanRecorder := tracetest.NewSpanRecorder()
+	clientTraceProvider := trace.NewTracerProvider(trace.WithSpanProcessor(clientSpanRecorder))
+	client, _, _ := startServer(
+		[]connect.HandlerOption{WithTelemetry(
+			WithPropagator(propagator),
+			WithTracerProvider(handlerTraceProvider),
+		)}, []connect.ClientOption{
+			WithTelemetry(
+				WithPropagator(propagator),
+				WithTracerProvider(clientTraceProvider),
+			),
+		}, failPingServer())
+	stream := client.CumSum(context.Background())
+	assert.NoError(t, stream.Send(&pingv1.CumSumRequest{Number: 1}))
+	_, err := stream.Receive()
+	assert.NoError(t, err)
+	_, err = stream.Receive()
+	assert.NoError(t, err)
+	_, err = stream.Receive()
+	assert.Error(t, err)
+	assert.NoError(t, stream.CloseRequest())
+	assert.NoError(t, stream.CloseResponse())
+	assert.Equal(t, len(handlerSpanRecorder.Ended()), 1)
+	assert.Equal(t, len(clientSpanRecorder.Ended()), 1)
+	assert.Equal(t, handlerSpanRecorder.Ended()[0].Status().Code, codes.Error)
+	assert.Equal(t, clientSpanRecorder.Ended()[0].Status().Code, codes.Error)
+}
+
 // streamingHandlerInterceptorFunc is a simple Interceptor implementation that only
 // wraps streaming handler RPCs. It has no effect on unary or streaming client RPCs.
 type streamingHandlerInterceptorFunc func(connect.StreamingHandlerFunc) connect.StreamingHandlerFunc