Add module generator option (#1400)

* Add module generator option

* Feedback from code review

protoc-gen-grpc-gateway/internal/gengateway/generator.go

@@ -32,11 +32,12 @@ type generator struct {
 	useRequestContext  bool
 	registerFuncSuffix string
 	pathType           pathType
+	modulePath         string
 	allowPatchFeature  bool
 }
 
 // New returns a new generator which generates grpc gateway files.
-func New(reg *descriptor.Registry, useRequestContext bool, registerFuncSuffix, pathTypeString string, allowPatchFeature bool) gen.Generator {
+func New(reg *descriptor.Registry, useRequestContext bool, registerFuncSuffix, pathTypeString, modulePathString string, allowPatchFeature bool) gen.Generator {
 	var imports []descriptor.GoPackage
 	for _, pkgpath := range []string{
 		"context",
@@ -84,6 +85,7 @@ func New(reg *descriptor.Registry, useRequestContext bool, registerFuncSuffix, p
 		useRequestContext:  useRequestContext,
 		registerFuncSuffix: registerFuncSuffix,
 		pathType:           pathType,
+		modulePath:         modulePathString,
 		allowPatchFeature:  allowPatchFeature,
 	}
 }
@@ -105,9 +107,10 @@ func (g *generator) Generate(targets []*descriptor.File) ([]*plugin.CodeGenerato
 			glog.Errorf("%v: %s", err, code)
 			return nil, err
 		}
-		name := file.GetName()
-		if g.pathType == pathTypeImport && file.GoPkg.Path != "" {
-			name = fmt.Sprintf("%s/%s", file.GoPkg.Path, filepath.Base(name))
+		name, err := g.getFilePath(file)
+		if err != nil {
+			glog.Errorf("%v: %s", err, code)
+			return nil, err
 		}
 		ext := filepath.Ext(name)
 		base := strings.TrimSuffix(name, ext)
@@ -121,6 +124,27 @@ func (g *generator) Generate(targets []*descriptor.File) ([]*plugin.CodeGenerato
 	return files, nil
 }
 
+func (g *generator) getFilePath(file *descriptor.File) (string, error) {
+	name := file.GetName()
+	switch {
+	case g.modulePath != "" && g.pathType != pathTypeImport:
+		return "", errors.New("cannot use module= with paths=")
+
+	case g.modulePath != "":
+		trimPath, pkgPath := g.modulePath+"/", file.GoPkg.Path+"/"
+		if !strings.HasPrefix(pkgPath, trimPath) {
+			return "", fmt.Errorf("%v: file go path does not match module prefix: %v", file.GoPkg.Path, trimPath)
+		}
+		return filepath.Join(strings.TrimPrefix(pkgPath, trimPath), filepath.Base(name)), nil
+
+	case g.pathType == pathTypeImport && file.GoPkg.Path != "":
+		return fmt.Sprintf("%s/%s", file.GoPkg.Path, filepath.Base(name)), nil
+
+	default:
+		return name, nil
+	}
+}
+
 func (g *generator) generate(file *descriptor.File) (string, error) {
 	pkgSeen := make(map[string]bool)
 	var imports []descriptor.GoPackage

protoc-gen-grpc-gateway/internal/gengateway/generator_test.go

@@ -1,6 +1,7 @@
 package gengateway
 
 import (
+	"errors"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -100,9 +101,11 @@ func TestGenerateServiceWithoutBindings(t *testing.T) {
 
 func TestGenerateOutputPath(t *testing.T) {
 	cases := []struct {
-		file     *descriptor.File
-		pathType pathType
-		expected string
+		file          *descriptor.File
+		pathType      pathType
+		modulePath    string
+		expected      string
+		expectedError error
 	}{
 		{
 			file: newExampleFileDescriptorWithGoPkg(
@@ -142,13 +145,79 @@ func TestGenerateOutputPath(t *testing.T) {
 			pathType: pathTypeSourceRelative,
 			expected: ".",
 		},
+		{
+			file: newExampleFileDescriptorWithGoPkg(
+				&descriptor.GoPackage{
+					Path: "example.com/path/root",
+					Name: "example_pb",
+				},
+			),
+			modulePath: "example.com/path/root",
+			expected:   ".",
+		},
+		{
+			file: newExampleFileDescriptorWithGoPkg(
+				&descriptor.GoPackage{
+					Path: "example.com/path/to/example",
+					Name: "example_pb",
+				},
+			),
+			modulePath: "example.com/path/to",
+			expected:   "example",
+		},
+		{
+			file: newExampleFileDescriptorWithGoPkg(
+				&descriptor.GoPackage{
+					Path: "example.com/path/to/example/with/many/nested/paths",
+					Name: "example_pb",
+				},
+			),
+			modulePath: "example.com/path/to",
+			expected:   "example/with/many/nested/paths",
+		},
+
+		// Error cases
+		{
+			file: newExampleFileDescriptorWithGoPkg(
+				&descriptor.GoPackage{
+					Path: "example.com/path/root",
+					Name: "example_pb",
+				},
+			),
+			modulePath:    "example.com/path/root",
+			pathType:      pathTypeSourceRelative, // Not allowed
+			expectedError: errors.New("cannot use module= with paths="),
+		},
+		{
+			file: newExampleFileDescriptorWithGoPkg(
+				&descriptor.GoPackage{
+					Path: "example.com/path/rootextra",
+					Name: "example_pb",
+				},
+			),
+			modulePath:    "example.com/path/root",
+			expectedError: errors.New("example.com/path/rootextra: file go path does not match module prefix: example.com/path/root/"),
+		},
 	}
 
 	for _, c := range cases {
-		g := &generator{pathType: c.pathType}
+		g := &generator{
+			pathType:   c.pathType,
+			modulePath: c.modulePath,
+		}
 
 		file := c.file
 		gots, err := g.Generate([]*descriptor.File{crossLinkFixture(file)})
+
+		// If we expect an error response, check it matches what we want
+		if c.expectedError != nil {
+			if err == nil || err.Error() != c.expectedError.Error() {
+				t.Errorf("Generate(%#v) failed with %v; wants error of: %v", file, err, c.expectedError)
+			}
+			return
+		}
+
+		// Handle case where we don't expect an error
 		if err != nil {
 			t.Errorf("Generate(%#v) failed with %v; wants success", file, err)
 			return

protoc-gen-grpc-gateway/main.go

@@ -30,6 +30,7 @@ var (
 	allowDeleteBody            = flag.Bool("allow_delete_body", false, "unless set, HTTP DELETE methods may not have a body")
 	grpcAPIConfiguration       = flag.String("grpc_api_configuration", "", "path to gRPC API Configuration in YAML format")
 	pathType                   = flag.String("paths", "", "specifies how the paths of generated files are structured")
+	modulePath                 = flag.String("module", "", "specifies a module prefix that will be stripped from the go package to determine the output directory")
 	allowRepeatedFieldsInBody  = flag.Bool("allow_repeated_fields_in_body", false, "allows to use repeated field in `body` and `response_body` field of `google.api.http` annotation option")
 	repeatedPathParamSeparator = flag.String("repeated_path_param_separator", "csv", "configures how repeated fields should be split. Allowed values are `csv`, `pipes`, `ssv` and `tsv`.")
 	allowPatchFeature          = flag.Bool("allow_patch_feature", true, "determines whether to use PATCH feature involving update masks (using google.protobuf.FieldMask).")
@@ -81,7 +82,7 @@ func main() {
 		}
 	}
 
-	g := gengateway.New(reg, *useRequestContext, *registerFuncSuffix, *pathType, *allowPatchFeature)
+	g := gengateway.New(reg, *useRequestContext, *registerFuncSuffix, *pathType, *modulePath, *allowPatchFeature)
 
 	if *grpcAPIConfiguration != "" {
 		if err := reg.LoadGrpcAPIServiceFromYAML(*grpcAPIConfiguration); err != nil {