Go gRPC Gateway

1. gRPC 回顾总结

1.1 gRPC

go get -u google.golang.org/grpc

• 强大的 IDL，使用 Protocol Buffers 作为数据交换格式
• 跨语言、跨平台
• 支持HTTP2，双向传输、多路复用、认证等

grpc下常用包：

• metadata: 提供方法对 grpc 元数据结构MD 进行获取和处理
• credentials: 封装了客户端对服务端进行身份验证所需的所有状态，并做出各种断言
• codes: grpc 标准错误码

1.2 Protoc Plugin

编译插件

go get -u github.com/golang/protobuf/protoc-gen-go

1.3 Protocol Buffers v3

Google 推出的一种数据描述语言，支持多语言、跨平台，二进制格式。

1.4 protoc

Protocol Buffers 运用程序

wget https://github.com/google/protobuf/releases/download/v3.5.1/protobuf-all-3.5.1.zip
unzip protobuf-all-3.5.1.zip
cd protobuf-3.5.1/
./configure
make
make install

生成 golang 源文件：

protoc --go_out=plugins=grpc,import_path=mypkg:. *.proto

2. gRPC-Gateway

grpc-gateway 是proto的一个插件，它读取gRPC服务定义，并生成一个反向代理服务器，将RESTful JSON API转换为gRPC.

2.1 安装

go get -u github.com/grpc-ecosystem/grpc-gateway/protoc-gen-grpc-gateway

2.2 proto文件

2.2.1 google.api

google 官方提供的 api 描述文件，主要针对 grpc-gateway 的 http 转换支持，定义了 Protocol Buffer 所扩展的 HTTP Option

1) annotations.proto

// Copyright (c) 2015, Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

syntax = "proto3";

package google.api;

import "google/api/http.proto";
import "google/protobuf/descriptor.proto";

option java_multiple_files = true;
option java_outer_classname = "AnnotationsProto";
option java_package = "com.google.api";

extend google.protobuf.MethodOptions {
  // See `HttpRule`.
  HttpRule http = 72295728;
}

2) http.proto

// Copyright 2016 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

syntax = "proto3";

package google.api;

option cc_enable_arenas = true;
option java_multiple_files = true;
option java_outer_classname = "HttpProto";
option java_package = "com.google.api";


// Defines the HTTP configuration for a service. It contains a list of
// [HttpRule][google.api.HttpRule], each specifying the mapping of an RPC method
// to one or more HTTP REST API methods.
message Http {
  // A list of HTTP rules for configuring the HTTP REST API methods.
  repeated HttpRule rules = 1;
}

// `HttpRule` defines the mapping of an RPC method to one or more HTTP
// REST APIs.  The mapping determines what portions of the request
// message are populated from the path, query parameters, or body of
// the HTTP request.  The mapping is typically specified as an
// `google.api.http` annotation, see "google/api/annotations.proto"
// for details.
//
// The mapping consists of a field specifying the path template and
// method kind.  The path template can refer to fields in the request
// message, as in the example below which describes a REST GET
// operation on a resource collection of messages:
//
// ```proto
// service Messaging {
//   rpc GetMessage(GetMessageRequest) returns (Message) {
//     option (google.api.http).get = "/v1/messages/{message_id}/{sub.subfield}";
//   }
// }
// message GetMessageRequest {
//   message SubMessage {
//     string subfield = 1;
//   }
//   string message_id = 1; // mapped to the URL
//   SubMessage sub = 2;    // `sub.subfield` is url-mapped
// }
// message Message {
//   string text = 1; // content of the resource
// }
// ```
//
// This definition enables an automatic, bidrectional mapping of HTTP
// JSON to RPC. Example:
//
// HTTP | RPC
// -----|-----
// `GET /v1/messages/123456/foo`  | `GetMessage(message_id: "123456" sub: SubMessage(subfield: "foo"))`
//
// In general, not only fields but also field paths can be referenced
// from a path pattern. Fields mapped to the path pattern cannot be
// repeated and must have a primitive (non-message) type.
//
// Any fields in the request message which are not bound by the path
// pattern automatically become (optional) HTTP query
// parameters. Assume the following definition of the request message:
//
// ```proto
// message GetMessageRequest {
//   message SubMessage {
//     string subfield = 1;
//   }
//   string message_id = 1; // mapped to the URL
//   int64 revision = 2;    // becomes a parameter
//   SubMessage sub = 3;    // `sub.subfield` becomes a parameter
// }
// ```
//
// This enables a HTTP JSON to RPC mapping as below:
//
// HTTP | RPC
// -----|-----
// `GET /v1/messages/123456?revision=2&sub.subfield=foo` | `GetMessage(message_id: "123456" revision: 2 sub: SubMessage(subfield: "foo"))`
//
// Note that fields which are mapped to HTTP parameters must have a
// primitive type or a repeated primitive type. Message types are not
// allowed. In the case of a repeated type, the parameter can be
// repeated in the URL, as in `...?param=A&param=B`.
//
// For HTTP method kinds which allow a request body, the `body` field
// specifies the mapping. Consider a REST update method on the
// message resource collection:
//
// ```proto
// service Messaging {
//   rpc UpdateMessage(UpdateMessageRequest) returns (Message) {
//     option (google.api.http) = {
//       put: "/v1/messages/{message_id}"
//       body: "message"
//     };
//   }
// }
// message UpdateMessageRequest {
//   string message_id = 1; // mapped to the URL
//   Message message = 2;   // mapped to the body
// }
// ```
//
// The following HTTP JSON to RPC mapping is enabled, where the
// representation of the JSON in the request body is determined by
// protos JSON encoding:
//
// HTTP | RPC
// -----|-----
// `PUT /v1/messages/123456 { "text": "Hi!" }` | `UpdateMessage(message_id: "123456" message { text: "Hi!" })`
//
// The special name `*` can be used in the body mapping to define that
// every field not bound by the path template should be mapped to the
// request body.  This enables the following alternative definition of
// the update method:
//
// ```proto
// service Messaging {
//   rpc UpdateMessage(Message) returns (Message) {
//     option (google.api.http) = {
//       put: "/v1/messages/{message_id}"
//       body: "*"
//     };
//   }
// }
// message Message {
//   string message_id = 1;
//   string text = 2;
// }
// ```
//
// The following HTTP JSON to RPC mapping is enabled:
//
// HTTP | RPC
// -----|-----
// `PUT /v1/messages/123456 { "text": "Hi!" }` | `UpdateMessage(message_id: "123456" text: "Hi!")`
//
// Note that when using `*` in the body mapping, it is not possible to
// have HTTP parameters, as all fields not bound by the path end in
// the body. This makes this option more rarely used in practice of
// defining REST APIs. The common usage of `*` is in custom methods
// which don't use the URL at all for transferring data.
//
// It is possible to define multiple HTTP methods for one RPC by using
// the `additional_bindings` option. Example:
//
// ```proto
// service Messaging {
//   rpc GetMessage(GetMessageRequest) returns (Message) {
//     option (google.api.http) = {
//       get: "/v1/messages/{message_id}"
//       additional_bindings {
//         get: "/v1/users/{user_id}/messages/{message_id}"
//       }
//     };
//   }
// }
// message GetMessageRequest {
//   string message_id = 1;
//   string user_id = 2;
// }
// ```
//
// This enables the following two alternative HTTP JSON to RPC
// mappings:
//
// HTTP | RPC
// -----|-----
// `GET /v1/messages/123456` | `GetMessage(message_id: "123456")`
// `GET /v1/users/me/messages/123456` | `GetMessage(user_id: "me" message_id: "123456")`
//
// # Rules for HTTP mapping
//
// The rules for mapping HTTP path, query parameters, and body fields
// to the request message are as follows:
//
// 1. The `body` field specifies either `*` or a field path, or is
//    omitted. If omitted, it assumes there is no HTTP body.
// 2. Leaf fields (recursive expansion of nested messages in the
//    request) can be classified into three types:
//     (a) Matched in the URL template.
//     (b) Covered by body (if body is `*`, everything except (a) fields;
//         else everything under the body field)
//     (c) All other fields.
// 3. URL query parameters found in the HTTP request are mapped to (c) fields.
// 4. Any body sent with an HTTP request can contain only (b) fields.
//
// The syntax of the path template is as follows:
//
//     Template = "/" Segments [ Verb ] ;
//     Segments = Segment { "/" Segment } ;
//     Segment  = "*" | "**" | LITERAL | Variable ;
//     Variable = "{" FieldPath [ "=" Segments ] "}" ;
//     FieldPath = IDENT { "." IDENT } ;
//     Verb     = ":" LITERAL ;
//
// The syntax `*` matches a single path segment. It follows the semantics of
// [RFC 6570](https://tools.ietf.org/html/rfc6570) Section 3.2.2 Simple String
// Expansion.
//
// The syntax `**` matches zero or more path segments. It follows the semantics
// of [RFC 6570](https://tools.ietf.org/html/rfc6570) Section 3.2.3 Reserved
// Expansion.
//
// The syntax `LITERAL` matches literal text in the URL path.
//
// The syntax `Variable` matches the entire path as specified by its template;
// this nested template must not contain further variables. If a variable
// matches a single path segment, its template may be omitted, e.g. `{var}`
// is equivalent to `{var=*}`.
//
// NOTE: the field paths in variables and in the `body` must not refer to
// repeated fields or map fields.
//
// Use CustomHttpPattern to specify any HTTP method that is not included in the
// `pattern` field, such as HEAD, or "*" to leave the HTTP method unspecified for
// a given URL path rule. The wild-card rule is useful for services that provide
// content to Web (HTML) clients.
message HttpRule {
  // Selects methods to which this rule applies.
  //
  // Refer to [selector][google.api.DocumentationRule.selector] for syntax details.
  string selector = 1;

  // Determines the URL pattern is matched by this rules. This pattern can be
  // used with any of the {get|put|post|delete|patch} methods. A custom method
  // can be defined using the 'custom' field.
  oneof pattern {
    // Used for listing and getting information about resources.
    string get = 2;

    // Used for updating a resource.
    string put = 3;

    // Used for creating a resource.
    string post = 4;

    // Used for deleting a resource.
    string delete = 5;

    // Used for updating a resource.
    string patch = 6;

    // Custom pattern is used for defining custom verbs.
    CustomHttpPattern custom = 8;
  }

  // The name of the request field whose value is mapped to the HTTP body, or
  // `*` for mapping all fields not captured by the path pattern to the HTTP
  // body. NOTE: the referred field must not be a repeated field.
  string body = 7;

  // Additional HTTP bindings for the selector. Nested bindings must
  // not contain an `additional_bindings` field themselves (that is,
  // the nesting may only be one level deep).
  repeated HttpRule additional_bindings = 11;
}

// A custom pattern is used for defining custom HTTP verb.
message CustomHttpPattern {
  // The name of this custom HTTP verb.
  string kind = 1;

  // The path matched by this custom verb.
  string path = 2;
}

2.2.2 hello.proto

syntax = "proto3";

package proto;

import "google/api/annotations.proto";

service HelloWorld {
    rpc SayHelloWorld(HelloWorldRequest) returns (HelloWorldResponse) {
        option (google.api.http) = {
            post: "/hello_world"
            body: "*"
        };
    }
}

message HelloWorldRequest {
    string referer = 1;
}

message HelloWorldResponse {
    string message = 1;
}

2.3 编译 proto

# 编译google.api
protoc -I . --go_out=plugins=grpc,Mgoogle/protobuf/descriptor.proto=github.com/golang/protobuf/protoc-gen-go/descriptor:. google/api/*.proto

# 编译hello_http.proto为hello_http.pb.proto
protoc -I . --go_out=plugins=grpc,Mgoogle/api/annotations.proto=go-grpc-example/proto/google/api:. ./hello.proto

# 编译hello_http.proto为hello_http.pb.gw.proto
protoc --grpc-gateway_out=logtostderr=true:. ./hello.proto

3. 命令行模块

3.1 安装Cobra命令行工具

go get -u github.com/spf13/cobra

1) root.go

var rootCmd = &cobra.Command{
	Use:   "grpc",
	Short: "Run the gRPC hello-world server",
}

func Execute() {
	if err := rootCmd.Execute(); err != nil {
		log.Fatalf("rootCmd.Execute err: %v", err)
	}
}

2) server.go

var serverCmd = &cobra.Command{
	Use:   "server",
	Short: "Run the gRPC hello-world server",
	Run: func(cmd *cobra.Command, args []string) {
		defer func() {
			if err := recover(); err != nil {
				log.Println("Recover error: %v", err)
			}
		}()

		server.Serve()
	},
}

func init() {
	serverCmd.Flags().StringVarP(&server.ServerPort, "port", "p", "9005", "server port")
	serverCmd.Flags().StringVarP(&server.CertPath, "cert", "c", "../../certs/server.pem", "cert path")
	serverCmd.Flags().StringVarP(&server.KeyPath, "key", "k", "../../certs/server.key", "key path")
	serverCmd.Flags().StringVarP(&server.CertName, "name", "n", "go-grpc-example", "server hostname")

	rootCmd.AddCommand(serverCmd)
}