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README.md

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-# [WIP] protoc-gen-go-dubbo
+# protoc-gen-go-dubbo
+
+## Prerequisites
+Before using `protoc-gen-go-dubbo`, make sure you have the following prerequisites installed on your system:
+- Go (version 1.17 or higher)
+- Protocol Buffers (version 3.0 or higher)
+
+## Installation
+To install `protoc-gen-go-dubbo`, you can use `go install`:
+```shell
+go install github.com/dubbogo/protoc-gen-go-dubbo
+```
+
+Or you can clone this repository and build it manually:
+```shell
+git clone github.com/dubbogo/protoc-gen-go-dubbo
+cd protoc-gen-go-dubbo
+go build
+```
+
+## Usage
+To generate dubbo code using `protoc-gen-go-dubbo`, you can use the following command:
+```shell
+protoc -I ./ \
+  --go-dubbo_out=./ --go-dubbo_opt=paths=source_relative \
+  ./greet.proto
+```
+The `--go-dubbo_out` option specifies the output directory for the generated code,
+and `--go-dubbo_opt=paths=source_relative` sets the output path to be relative to the source file.
+
+## Example
+To generate Dubbo code, you can create a `.proto` file with the following content:
+```protobuf
+syntax = "proto3";
+
+package greet;
+
+option go_package = "some_path/greet;greet";
+
+import "unified_idl_extend/unified_idl_extend.proto";
+
+message GreetRequest {
+  string name = 1;
+
+  option (unified_idl_extend.message_extend) = {
+    java_class_name: "org.apache.greet.GreetRequest";
+  };
+}
+
+message GreetResponse {
+  string greeting = 1;
+
+  option (unified_idl_extend.message_extend) = {
+    java_class_name: "org.apache.greet.GreetResponse";
+  };
+}
+
+service GreetService {
+  rpc Greet(GreetRequest) returns (GreetResponse) {
+    option (unified_idl_extend.method_extend) = {
+      method_name: "greet";
+    };
+  }
+}
+```
+Note that you need to import the `unified_idl_extend` package to use the `method_extend` options to extend the service.
+And Dubbo protocol must be used with Hessian2 serialization, so you need to use the `message_extend` options to extend 
+the message.
+
+Then, you can run the following command to generate the Dubbo and Hessian2 code:
+```shell
+protoc -I ./ \
+  --go-hessian2_out=./ --go-hessian2_opt=paths=source_relative \
+  --go-dubbo_out=./ --go-dubbo_opt=paths=source_relative \
+  ./greet.proto
+```
+This will generate the `greet.dubbo.go` and `greet.hessian2.go` file in the same directory as your `greet.proto` file:
+```shell
+.
+├── greet.hessian2.go
+├── greet.dubbo.go
+├── greet.proto
+└── unified_idl_extend
+    ├── unified_idl_extend.pb.go
+    └── unified_idl_extend.proto
+```
+
+The content of the `greet.hessian2.go` file will be:
+```go
+// Code generated by protoc-gen-go-dubbo. DO NOT EDIT.
+
+// Source: greet.proto
+// Package: greet
+
+package greet
+
+import (
+	"context"
+
+	"dubbo.apache.org/dubbo-go/v3"
+	"dubbo.apache.org/dubbo-go/v3/client"
+	"dubbo.apache.org/dubbo-go/v3/common"
+	"dubbo.apache.org/dubbo-go/v3/common/constant"
+	"dubbo.apache.org/dubbo-go/v3/server"
+)
+
+const (
+	// GreetServiceName is the fully-qualified name of the GreetService service.
+	GreetServiceName = "greet.GreetService"
+
+	// These constants are the fully-qualified names of the RPCs defined in this package. They're
+	// exposed at runtime as procedure and as the final two segments of the HTTP route.
+	//
+	// Note that these are different from the fully-qualified method names used by
+	// google.golang.org/protobuf/reflect/protoreflect. To convert from these constants to
+	// reflection-formatted method names, remove the leading slash and convert the remaining slash to a
+	// period.
+	// GreetServiceGreetProcedure is the fully-qualified name of the GreetService's Greet RPC.'
+	GreetServiceGreetProcedure = "/greet.GreetService/greet"
+)
+
+var (
+	_ GreetService = (*GreetServiceImpl)(nil)
+)
+
+type GreetService interface {
+	Greet(ctx context.Context, req *GreetRequest, opts ...client.CallOption) (*GreetResponse, error)
+}
+
+// NewGreetService constructs a client for the greet.GreetService service
+func NewGreetService(cli *client.Client, opts ...client.ReferenceOption) (GreetService, error) {
+	conn, err := cli.DialWithInfo("greet.GreetService", &GreetService_ClientInfo, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return &GreetServiceImpl{
+		conn: conn,
+	}, nil
+}
+
+func SetConsumerService(srv common.RPCService) {
+	dubbo.SetConsumerServiceWithInfo(srv, &GreetService_ClientInfo)
+}
+
+// GreetServiceImpl implements GreetService
+type GreetServiceImpl struct {
+	conn *client.Connection
+}
+
+func (c *GreetServiceImpl) Greet(ctx context.Context, req *GreetRequest, opts ...client.CallOption) (*GreetResponse, error) {
+	resp := new(GreetResponse)
+	if err := c.conn.CallUnary(ctx, []interface{}{req}, resp, "greet", opts...); err != nil {
+		return nil, err
+	}
+	return resp, nil
+}
+
+var GreetService_ClientInfo = client.ClientInfo{
+	InterfaceName: "greet.GreetService",
+	MethodNames: []string{
+		"greet",
+	},
+	ConnectionInjectFunc: func(dubboCliRaw interface{}, conn *client.Connection) {
+		dubboCli := dubboCliRaw.(*GreetServiceImpl)
+		dubboCli.conn = conn
+	},
+}
+
+// GreetServiceHandler is an implementation of the greet.GreetService service.
+type GreetServiceHandler interface {
+	Greet(ctx context.Context, req *GreetRequest) (*GreetResponse, error)
+}
+
+func RegisterGreetServiceHandler(srv *server.Server, hdlr GreetServiceHandler, opts ...server.ServiceOption) error {
+	return srv.Register(hdlr, &GreetService_ServiceInfo, opts...)
+}
+
+func SetProviderService(srv common.RPCService) {
+	dubbo.SetProviderServiceWithInfo(srv, &GreetService_ServiceInfo)
+}
+
+var GreetService_ServiceInfo = server.ServiceInfo{
+	InterfaceName: "greet.GreetService",
+	ServiceType:   (*GreetServiceHandler)(nil),
+	Methods: []server.MethodInfo{
+		{
+			Name: "greet",
+			Type: constant.CallUnary,
+			ReqInitFunc: func() interface{} {
+				return new(GreetResponse)
+			},
+			MethodFunc: func(ctx context.Context, args []interface{}, handler interface{}) (interface{}, error) {
+				req := args[0].(*GreetRequest)
+				res, err := handler.(GreetServiceHandler).Greet(ctx, req)
+				return res, err
+			},
+		},
+	},
+}
+```