proxy: support standalone mode

Signed-off-by: Koichi Shiraishi <zchee.io@gmail.com>

proxy/proxy.go

@@ -6,6 +6,7 @@ package proxy
 
 import (
 	"fmt"
+	"path/filepath"
 	"sort"
 
 	"github.com/iancoleman/strcase"
@@ -22,6 +23,8 @@ const (
 	grpcPackage  = protogen.GoImportPath("google.golang.org/grpc")
 )
 
+var pbPackage protogen.GoImportPath
+
 // FileNameSuffix is the suffix added to files generated by deepcopy
 const FileNameSuffix = "_proxy.pb.go"
 
@@ -31,39 +34,63 @@ type Config struct {
 	Out        string
 }
 
-// GenerateFile generates DeepCopyInto() and DeepCopy() functions for .pb.go types.
+// GenerateFile generates RPC service proxy from .pb.go types.
 func GenerateFile(p *protogen.Plugin, f *protogen.File, cfg *Config) *protogen.GeneratedFile {
 	if len(f.Services) == 0 {
 		return nil
 	}
 
 	filename := f.GeneratedFilenamePrefix + FileNameSuffix
 	goImportPath := f.GoImportPath
-
+	if cfg.Standalone && cfg.Out != "" {
+		goImportPath = protogen.GoImportPath(cfg.Out)
+	}
 	g := p.NewGeneratedFile(filename, goImportPath)
 
-	g.QualifiedGoIdent(contextPackage.Ident(""))
-	g.QualifiedGoIdent(errorsPackage.Ident(""))
-	g.QualifiedGoIdent(netPackage.Ident(""))
-	g.QualifiedGoIdent(grpcPackage.Ident(""))
-	g.QualifiedGoIdent(emptyPackage.Ident(""))
+	g.QualifiedGoIdent(contextPackage.Ident("Context"))
+	g.QualifiedGoIdent(errorsPackage.Ident("New"))
+	g.QualifiedGoIdent(netPackage.Ident("Addr"))
+	g.QualifiedGoIdent(grpcPackage.Ident("CallOption"))
+	g.QualifiedGoIdent(emptyPackage.Ident("Empty"))
+	if cfg.Standalone {
+		pbPackage = protogen.GoImportPath(f.GoImportPath)
+		g.QualifiedGoIdent(pbPackage.Ident(""))
+	}
 
 	g.P(`// Code generated by protoc-gen-proxy. DO NOT EDIT.`)
 	g.P()
 	g.P(`package `, f.GoPackageName)
 	g.P()
-
+	g.P()
 	g.P(`var _ `, emptyPackage.Ident("Empty"))
+	g.P()
 	for _, service := range f.Services {
 		serviceName := service.GoName
 		lowerServiceName := strcase.ToLowerCamel(serviceName)
 		serverName := lowerServiceName + "Server"
 
 		methods := make(map[string]string)
+		idStr := pbPackage.String()
+		importPath := filepath.Base(idStr[1 : len(idStr)-1])
+		registerServerName := fmt.Sprintf("Register%sServer", serviceName)
+		if cfg.Standalone {
+			registerServerName = importPath + "." + registerServerName
+		}
+
 		for _, method := range service.Methods {
 			input := method.Input.GoIdent.GoName
 			output := method.Output.GoIdent.GoName
 
+			if cfg.Standalone {
+				// handle emptypb
+				if input != "Empty" {
+					input = importPath + "." + input
+				}
+				if output != "Empty" {
+					output = importPath + "." + output
+				}
+			}
+
 			// handle emptypb
 			if input == "Empty" {
 				input = "emptypb.Empty"
@@ -72,7 +99,11 @@ func GenerateFile(p *protogen.Plugin, f *protogen.File, cfg *Config) *protogen.G
 				output = "emptypb.Empty"
 			}
 
-			methods[method.GoName] = fmt.Sprintf(`(ctx context.Context, req *%s) (*%s, error)`, input, output)
+			args := fmt.Sprintf(`(ctx context.Context, req *%s) (*%s, error)`, input, output)
+			if cfg.Standalone && method.Desc.IsStreamingServer() {
+				args = fmt.Sprintf(`(req *%s, srv %s_%sServer)`, input, importPath+"."+serviceName, method.GoName)
+			}
+			methods[method.GoName] = args
 		}
 
 		// sort RPC methods
@@ -114,7 +145,7 @@ func GenerateFile(p *protogen.Plugin, f *protogen.File, cfg *Config) *protogen.G
 		g.P(`// Serve starts serving the proxy server on the given listener with the specified options.`)
 		g.P(`func (p *Proxy) Serve(l net.Listener, opts ...grpc.ServerOption) error {`)
 		g.P(`	srv := grpc.NewServer(opts...)`)
-		g.P(`	Register`, serviceName, `Server(srv, &`, serverName, `{proxy: p})`)
+		g.P(`	`, registerServerName, `(srv, &`, serverName, `{proxy: p})`)
 		g.P()
 		g.P(`	return srv.Serve(l)`)
 		g.P(`}`)