上两篇文章简单讲解了一下 gRPC 的使用，但是外界根本无法调用我们的代码，我们也不知道外界如何访问，假设另一个客户端要访问，要么就把 proto 文件发给他，然后去生成客户端代码进行调用，这样可能就显得非常麻烦，那么有没有更好地方案呢？就是今天要说的 gRPC-Gateway

什么是gRPC-Gateway

那么什么是 gRPC-Gateway ? 根据 官方文档 的描述：

gRPC-Gateway is a plugin of protoc. It reads a gRPC service definition and generates a reverse-proxy server which translates a RESTful JSON API into gRPC. This server is generated according to custom options in your gRPC definition.

gRPC-Gateway 是 protoc 的一个插件，它能够读取Protobuf的服务定义，生成一个反向代理服务器，将 RESTful JSON API 转换为gRPC

换句话说就是：就是将 gRPC 转为 RESTful HTTP API

好了，废话不多说了，直接开干吧

本文所需的环境

• Protobuf
• gRPC
• gRPC-Gateway

关于 Protobuf 和 gRPC 已经在 Go 语言 gRPC 的简单使用 中介绍过了，本文就不涉及了，

之前的两篇文章分别为： Go 语言 gRPC 的简单使用 和 Go 语言 gRPC 四种通信方式的简单使用

安装 gRPC-Gateway

go install github.com/grpc-ecosystem/grpc-gateway/v2/protoc-gen-grpc-gateway@latest

老规矩新建 proto 文件 api/simple_getway/simple_getway.proto

syntax = "proto3";
option go_package = "api/simple_getway;simple_getway";

package simple_getway;

import "google/api/annotations.proto";

service HttpService {
  rpc Get(GetRequest) returns (GetResponse) {
    option (google.api.http) = {
      get: "/v1/get"
    };
  }
  rpc Post(PostRequest) returns (PostResponse) {
    option (google.api.http) = {
      post: "/v1/post"
      body: "*"
    };
  }
}
message GetRequest {
  string name = 1;
}
message GetResponse {
  int32 code = 1;
  string message = 2;
  string body = 3;
}
message PostRequest {
  string name = 1;
}
message PostResponse {
  int32 code = 1;
  string message = 2;
  string body = 3;
}

其中 service 包含两个方法，我这里叫 get 、post 了，名字随意哈。在方法体中 有一个 option ，这个格式几乎是固定的，就这么写就可以了

接下来需要到 [googleapis]去拷贝两个 proto 文件,分别是 annotations.proto 和 http.proto 。直接放在 api/google/api 文件夹下

如果你打不开。那就直接复制我代码吧。

annotations.proto 文件内容：

// Copyright 2015 Google LLC
//
// 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 go_package = "google.golang.org/genproto/googleapis/api/annotations;annotations";
option java_multiple_files = true;
option java_outer_classname = "AnnotationsProto";
option java_package = "com.google.api";
option objc_class_prefix = "GAPI";

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

http.proto 文件内容:

// Copyright 2015 Google LLC
//
// 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 go_package = "google.golang.org/genproto/googleapis/api/annotations;annotations";
option java_multiple_files = true;
option java_outer_classname = "HttpProto";
option java_package = "com.google.api";
option objc_class_prefix = "GAPI";

// Defines the HTTP configuration for an API 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 configuration rules that apply to individual API methods.
  //
  // **NOTE:** All service configuration rules follow "last one wins" order.
  repeated HttpRule rules = 1;

  // When set to true, URL path parameters will be fully URI-decoded except in
  // cases of single segment matches in reserved expansion, where "%2F" will be
  // left encoded.
  //
  // The default behavior is to not decode RFC 6570 reserved characters in multi
  // segment matches.
  bool fully_decode_reserved_expansion = 2;
}

// # gRPC Transcoding
//
// gRPC Transcoding is a feature for mapping between a gRPC method and one or
// more HTTP REST endpoints. It allows developers to build a single API service
// that supports both gRPC APIs and REST APIs. Many systems, including [Google
// APIs](https://github.com/googleapis/googleapis),
// [Cloud Endpoints](https://cloud.google.com/endpoints "Cloud Endpoints"), [gRPC
// Gateway](https://github.com/grpc-ecosystem/grpc-gateway),
// and [Envoy](https://github.com/envoyproxy/envoy "Envoy") proxy support this feature
// and use it for large scale production services.
//
// `HttpRule` defines the schema of the gRPC/REST mapping. The mapping specifies
// how different portions of the gRPC request message are mapped to the URL
// path, URL query parameters, and HTTP request body. It also controls how the
// gRPC response message is mapped to the HTTP response body. `HttpRule` is
// typically specified as an `google.api.http` annotation on the gRPC method.
//
// Each mapping specifies a URL path template and an HTTP method. The path
// template may refer to one or more fields in the gRPC request message, as long
// as each field is a non-repeated field with a primitive (non-message) type.
// The path template controls how fields of the request message are mapped to
// the URL path.
//
// Example:
//
//     service Messaging {
//       rpc GetMessage(GetMessageRequest) returns (Message) {
//         option (google.api.http) = {
//             get: "/v1/{name=messages/*}"
//         };
//       }
//     }
//     message GetMessageRequest {
//       string name = 1; // Mapped to URL path.
//     }
//     message Message {
//       string text = 1; // The resource content.
//     }
//
// This enables an HTTP REST to gRPC mapping as below:
//
// HTTP | gRPC
// -----|-----
// `GET /v1/messages/123456`  | `GetMessage(name: "messages/123456")`
//
// Any fields in the request message which are not bound by the path template
// automatically become HTTP query parameters if there is no HTTP request body.
// For example:
//
//     service Messaging {
//       rpc GetMessage(GetMessageRequest) returns (Message) {
//         option (google.api.http) = {
//             get:"/v1/messages/{message_id}"
//         };
//       }
//     }
//     message GetMessageRequest {
//       message SubMessage {
//         string subfield = 1;
//       }
//       string message_id = 1; // Mapped to URL path.
//       int64 revision = 2;    // Mapped to URL query parameter `revision`.
//       SubMessage sub = 3;    // Mapped to URL query parameter `sub.subfield`.
//     }
//
// This enables a HTTP JSON to RPC mapping as below:
//
// HTTP | gRPC
// -----|-----
// `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 URL query parameters must have a
// primitive type or a repeated primitive type or a non-repeated message type.
// In the case of a repeated type, the parameter can be repeated in the URL
// as `...?param=A&param=B`. In the case of a message type, each field of the
// message is mapped to a separate parameter, such as
// `...?foo.a=A&foo.b=B&foo.c=C`.
//
// For HTTP methods that allow a request body, the `body` field
// specifies the mapping. Consider a REST update method on the
// message resource collection:
//
//     service Messaging {
//       rpc UpdateMessage(UpdateMessageRequest) returns (Message) {
//         option (google.api.http) = {
//           patch: "/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 | gRPC
// -----|-----
// `PATCH /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:
//
//     service Messaging {
//       rpc UpdateMessage(Message) returns (Message) {
//         option (google.api.http) = {
//           patch: "/v1/messages/{message_id}"
//           body: "*"
//         };
//       }
//     }
//     message Message {
//       string message_id = 1;
//       string text = 2;
//     }
//
//
// The following HTTP JSON to RPC mapping is enabled:
//
// HTTP | gRPC
// -----|-----
// `PATCH /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 when
// 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:
//
//     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 | gRPC
// -----|-----
// `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
//
// 1. Leaf request fields (recursive expansion nested messages in the request
//    message) are classified into three categories:
//    - Fields referred by the path template. They are passed via the URL path.
//    - Fields referred by the [HttpRule.body][google.api.HttpRule.body]. They are passed via the HTTP
//      request body.
//    - All other fields are passed via the URL query parameters, and the
//      parameter name is the field path in the request message. A repeated
//      field can be represented as multiple query parameters under the same
//      name.
//  2. If [HttpRule.body][google.api.HttpRule.body] is "*", there is no URL query parameter, all fields
//     are passed via URL path and HTTP request body.
//  3. If [HttpRule.body][google.api.HttpRule.body] is omitted, there is no HTTP request body, all
//     fields are passed via URL path and URL query parameters.
//
// ### Path template syntax
//
//     Template = "/" Segments [ Verb ] ;
//     Segments = Segment { "/" Segment } ;
//     Segment  = "*" | "**" | LITERAL | Variable ;
//     Variable = "{" FieldPath [ "=" Segments ] "}" ;
//     FieldPath = IDENT { "." IDENT } ;
//     Verb     = ":" LITERAL ;
//
// The syntax `*` matches a single URL path segment. The syntax `**` matches
// zero or more URL path segments, which must be the last part of the URL path
// except the `Verb`.
//
// The syntax `Variable` matches part of the URL path as specified by its
// template. A variable template must not contain other variables. If a variable
// matches a single path segment, its template may be omitted, e.g. `{var}`
// is equivalent to `{var=*}`.
//
// The syntax `LITERAL` matches literal text in the URL path. If the `LITERAL`
// contains any reserved character, such characters should be percent-encoded
// before the matching.
//
// If a variable contains exactly one path segment, such as `"{var}"` or
// `"{var=*}"`, when such a variable is expanded into a URL path on the client
// side, all characters except `[-_.~0-9a-zA-Z]` are percent-encoded. The
// server side does the reverse decoding. Such variables show up in the
// [Discovery
// Document](https://developers.google.com/discovery/v1/reference/apis) as
// `{var}`.
//
// If a variable contains multiple path segments, such as `"{var=foo/*}"`
// or `"{var=**}"`, when such a variable is expanded into a URL path on the
// client side, all characters except `[-_.~/0-9a-zA-Z]` are percent-encoded.
// The server side does the reverse decoding, except "%2F" and "%2f" are left
// unchanged. Such variables show up in the
// [Discovery
// Document](https://developers.google.com/discovery/v1/reference/apis) as
// `{+var}`.
//
// ## Using gRPC API Service Configuration
//
// gRPC API Service Configuration (service config) is a configuration language
// for configuring a gRPC service to become a user-facing product. The
// service config is simply the YAML representation of the `google.api.Service`
// proto message.
//
// As an alternative to annotating your proto file, you can configure gRPC
// transcoding in your service config YAML files. You do this by specifying a
// `HttpRule` that maps the gRPC method to a REST endpoint, achieving the same
// effect as the proto annotation. This can be particularly useful if you
// have a proto that is reused in multiple services. Note that any transcoding
// specified in the service config will override any matching transcoding
// configuration in the proto.
//
// Example:
//
//     http:
//       rules:
//         # Selects a gRPC method and applies HttpRule to it.
//         - selector: example.v1.Messaging.GetMessage
//           get: /v1/messages/{message_id}/{sub.subfield}
//
// ## Special notes
//
// When gRPC Transcoding is used to map a gRPC to JSON REST endpoints, the
// proto to JSON conversion must follow the [proto3
// specification](https://developers.google.com/protocol-buffers/docs/proto3#json).
//
// While the single segment variable follows the semantics of
// [RFC 6570](https://tools.ietf.org/html/rfc6570 "RFC 6570") Section 3.2.2 Simple String
// Expansion, the multi segment variable **does not** follow RFC 6570 Section
// 3.2.3 Reserved Expansion. The reason is that the Reserved Expansion
// does not expand special characters like `?` and `#`, which would lead
// to invalid URLs. As the result, gRPC Transcoding uses a custom encoding
// for multi segment variables.
//
// The path variables **must not** refer to any repeated or mapped field,
// because client libraries are not capable of handling such variable expansion.
//
// The path variables **must not** capture the leading "/" character. The reason
// is that the most common use case "{var}" does not capture the leading "/"
// character. For consistency, all path variables must share the same behavior.
//
// Repeated message fields must not be mapped to URL query parameters, because
// no client library can support such complicated mapping.
//
// If an API needs to use a JSON array for request or response body, it can map
// the request or response body to a repeated field. However, some gRPC
// Transcoding implementations may not support this feature.
message HttpRule {
  // Selects a method 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 {
    // Maps to HTTP GET. Used for listing and getting information about
    // resources.
    string get = 2;

    // Maps to HTTP PUT. Used for replacing a resource.
    string put = 3;

    // Maps to HTTP POST. Used for creating a resource or performing an action.
    string post = 4;

    // Maps to HTTP DELETE. Used for deleting a resource.
    string delete = 5;

    // Maps to HTTP PATCH. Used for updating a resource.
    string patch = 6;

    // The custom pattern is used for specifying an HTTP method that is not
    // included in the `pattern` field, such as HEAD, or "*" to leave the
    // HTTP method unspecified for this rule. The wild-card rule is useful
    // for services that provide content to Web (HTML) clients.
    CustomHttpPattern custom = 8;
  }

  // The name of the request field whose value is mapped to the HTTP request
  // body, or `*` for mapping all request fields not captured by the path
  // pattern to the HTTP body, or omitted for not having any HTTP request body.
  //
  // NOTE: the referred field must be present at the top-level of the request
  // message type.
  string body = 7;

  // Optional. The name of the response field whose value is mapped to the HTTP
  // response body. When omitted, the entire response message will be used
  // as the HTTP response body.
  //
  // NOTE: The referred field must be present at the top-level of the response
  // message type.
  string response_body = 12;

  // 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;
}

Ok,接下来就可以生成 Go 代码了

protoc -I ./api \
  --go_out ./api --go_opt paths=source_relative \
  --go-grpc_out ./api --go-grpc_opt paths=source_relative \
  --grpc-gateway_out ./api --grpc-gateway_opt paths=source_relative \
  ./api/simple_getway/simple_getway.proto

可以看到我们这次添加了一个参数 --grpc-gateway_out

这次的文件内容就比较多了。可以大致进去浏览一下 tree -l api/simple_getway/

api/simple_getway/
├── simple_getway.pb.go
├── simple_getway.pb.gw.go
├── simple_getway.proto
└── simple_getway_grpc.pb.go

0 directories, 4 files

接下来就需要编写服务端代码，让其可以使用 http 的方法进行调用

编写 server/simple_getway.go

package main

import (
    "context"
    "github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
    pb "github.com/hedeqiang/grpc-demo/api/simple_getway"
    "google.golang.org/grpc"
    "google.golang.org/grpc/credentials/insecure"
    "log"
    "net"
    "net/http"
)

type SimpleGetway struct {
    pb.UnimplementedHttpServiceServer
}

func (s *SimpleGetway) Get(ctx context.Context, req *pb.GetRequest) (*pb.GetResponse, error) {
    return &pb.GetResponse{
        Code:    200,
        Message: "success get",
        Body:    req.GetName(),
    }, nil
}

func (s *SimpleGetway) Post(ctx context.Context, req *pb.PostRequest) (*pb.PostResponse, error) {
    return &pb.PostResponse{
        Code:    200,
        Message: "success post",
        Body:    req.GetName(),
    }, nil
}

func main() {
    // Create a listener on TCP port
    lis, err := net.Listen("tcp", ":8080")
    if err != nil {
        log.Fatalln("Failed to listen:", err)
    }

    // Create a gRPC server object
    s := grpc.NewServer()
    // Attach the Greeter service to the server
    pb.RegisterHttpServiceServer(s, &SimpleGetway{})
    // Serve gRPC server
    log.Println("Serving gRPC on 0.0.0.0:8080")
    go func() {
        log.Fatalln(s.Serve(lis))
    }()

    // Create a client connection to the gRPC server we just started
    // This is where the gRPC-Gateway proxies the requests
    conn, err := grpc.DialContext(
        context.Background(),
        "0.0.0.0:8080",
        grpc.WithBlock(),
        grpc.WithTransportCredentials(insecure.NewCredentials()),
    )
    if err != nil {
        log.Fatalln("Failed to dial server:", err)
    }

    gwmux := runtime.NewServeMux()

    // Register the gateway
    err = pb.RegisterHttpServiceHandler(context.Background(), gwmux, conn)
    if err != nil {
        log.Fatalln("Failed to register gateway:", err)
    }

    gwServer := &http.Server{
        Addr:    ":8090",
        Handler: gwmux,
    }

    log.Println("Serving gRPC-Gateway on http://0.0.0.0:8090")
    log.Fatalln(gwServer.ListenAndServe())
}

这样我们就分别暴露了 gRPC server 和使用 gRPC-Gateway 创建了一个 http 的服务

我们使用 postman 工具进行测试一下:

请求 post 方法试下：

更多详细用法请参考gRPC-Gateway