feat(gengapic): raise Operation errors from diregapic

closes: googleapis#1320

internal/gengapic/custom_operation.go

@@ -192,8 +192,11 @@ func (g *generator) customOperationType() error {
 	p("}")
 	p("")
 	g.imports[pbinfo.ImportSpec{Path: "context"}] = true
-	g.imports[pbinfo.ImportSpec{Name: "gax", Path: "github.com/googleapis/gax-go/v2"}] = true
+	g.imports[pbinfo.ImportSpec{Path: "http"}] = true
 	g.imports[pbinfo.ImportSpec{Path: "time"}] = true
+	g.imports[pbinfo.ImportSpec{Name: "gax", Path: "github.com/googleapis/gax-go/v2"}] = true
+	g.imports[pbinfo.ImportSpec{Path: "github.com/googleapis/gax-go/v2/apierror"}] = true
+	g.imports[pbinfo.ImportSpec{Path: "google.golang.org/api/googleapi"}] = true
 
 	for _, handle := range op.handles {
 		pollingParams := op.pollingParams[handle]
@@ -204,6 +207,16 @@ func (g *generator) customOperationType() error {
 		poll := operationPollingMethod(handle)
 		pollReq := g.descInfo.Type[poll.GetInputType()].(*descriptor.DescriptorProto)
 		pollNameField := operationResponseField(pollReq, opNameField.GetName())
+		// Look up the fields for error code and error message.
+		errorCodeField := operationField(op.message, extendedops.OperationResponseMapping_ERROR_CODE)
+		if errorCodeField == nil {
+			return fmt.Errorf("field %s not found in %T", extendedops.OperationResponseMapping_ERROR_CODE, op)
+		}
+		errorCode := snakeToCamel(errorCodeField.GetName())
+		errorMessageField := operationField(op.message, extendedops.OperationResponseMapping_ERROR_MESSAGE)
+		if errorMessageField == nil {
+			return fmt.Errorf("field %s not found in %T", extendedops.OperationResponseMapping_ERROR_MESSAGE, op)
+		}
 
 		// type
 		p("// Implements the %s interface for %s.", handleInt, handle.GetName())
@@ -229,6 +242,19 @@ func (g *generator) customOperationType() error {
 		p("    return err")
 		p("  }")
 		p("  h.proto = resp")
+		p("  if resp.%s != nil && resp.Get%s() != http.StatusOK {", errorCode, errorCode)
+		p("  	aErr := googleapi.Error{")
+		p("  		Code: int(resp.Get%s()),", errorCode)
+		if hasField(op.message, "error") {
+			g.imports[pbinfo.ImportSpec{Path: "fmt"}] = true
+			p("  		Message: fmt.Sprintf(\"%%s: %%v\", resp.Get%s(), resp.GetError()),", snakeToCamel(errorMessageField.GetName()))
+		} else {
+			p("  		Message: resp.Get%s(),", snakeToCamel(errorMessageField.GetName()))
+		}
+		p("  	}")
+		p("  	err, _ := apierror.FromError(&aErr)")
+		p("  	return err")
+		p("  }")
 		p("  return nil")
 		p("}")
 		p("")
@@ -314,6 +340,17 @@ func (g *generator) customOpStatusEnumDone() string {
 	return s
 }
 
+// hasField returns true if the target DescriptorProto has the given field,
+// otherwise it returns false.
+func hasField(m *descriptor.DescriptorProto, field string) bool {
+	for _, f := range m.GetField() {
+		if f.GetName() == field {
+			return true
+		}
+	}
+	return false
+}
+
 // operationField is a helper for loading the target google.cloud.operation_field annotation value
 // if present on a field in the given message.
 func operationField(m *descriptor.DescriptorProto, target extendedops.OperationResponseMapping) *descriptor.FieldDescriptorProto {

internal/gengapic/custom_operation_test.go

@@ -154,9 +154,18 @@ func TestCustomOperationType(t *testing.T) {
 		Options: statusOpts,
 	}
 
+	errorCodeOpts := &descriptor.FieldOptions{}
+	proto.SetExtension(errorCodeOpts, extendedops.E_OperationField, extendedops.OperationResponseMapping_ERROR_CODE)
+	errorCodeField := &descriptor.FieldDescriptorProto{
+		Name:    proto.String("ERROR_CODE"),
+		Type:    descriptor.FieldDescriptorProto_TYPE_STRING.Enum(),
+		Options: errorCodeOpts,
+	}
+
 	op := &descriptor.DescriptorProto{
 		Name:     proto.String("Operation"),
 		EnumType: []*descriptor.EnumDescriptorProto{statusEnum},
+		Field:    []*descriptor.FieldDescriptorProto{errorCodeField},
 	}
 
 	inNameOpts := &descriptor.FieldOptions{}