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Kevin Wan
Kevin Wan

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5 minutes to add RESTful APIs for your gRPC services

gRPC service with HTTP interface?

While go-zero brought an excellent RESTful and gRPC service development experience to the developers, more expectations arised.

  • I want to write code only once
  • I want both the gRPC and HTTP interfaces

It makes sense! You see what users say.

User A: a set of logic, HTTP and gRPC together.

User B: if go-zero can simplify this step I feel it will become the the best microservices framework, ever.

So I fell into a deep thought: the user is never wrong, but do we want to provide it?

Here comes the article.

Let's write gRPC service first

We are too familiar with this service. Create a new directory, let's call it grpc-restufl, and put a sum.proto file in it

syntax = "proto3";

package sum;
option go_package="./pb";

message SumRequest {
    int64 a = 1;
    int64 b = 2;
}

message SumResponse {
    int64 result = 1;
}

service Sum {
    rpc Add(SumRequest) returns (SumResponse) {}
}
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One-click generation, you know.

$ goctl rpc protoc --go_out=. --go-grpc_out=. --zrpc_out=. sum.proto
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See what you get

.
β”œβ”€β”€ etc
β”‚ └── sum.yaml
β”œβ”€β”€ go.mod
β”œβ”€β”€ internal
β”‚ β”œβ”€β”€ config
β”‚ β”‚ └── config.go
β”‚ β”œβ”€β”€ logic
β”‚ β”‚ └── addlogic.go
β”‚ β”œβ”€β”€ server
β”‚ β”‚ └── sumserver.go
β”‚ └── svc
β”‚ └── servicecontext.go
β”œβ”€ pb
β”‚ β”œβ”€β”€ sum.pb.go
β”‚ └── sum_grpc.pb.go
β”œβ”€ sum
β”‚ └── sum.go
β”œβ”€β”€ sum.go
└── sum.proto
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To implement the business logic, modify the Add method in internal/logic/addlogic.go as follows.

func (l *AddLogic) Add(in *pb.SumRequest) (*pb.SumResponse, error) {
    return &pb.SumResponse{
        Result: in.A+in.B,
    }, nil
}
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You can run it, and the business logic is there (although it is very simple, for demo purpose.)

$ go mod tidy && go run sum.go
Starting rpc server at 127.0.0.1:8080...
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For those who are familiar with go-zero, there is no highlight (new knowledge) here, let's go ahead ~

Provide HTTP interface

Update go-zero

First, let's update go-zero to v1.4.0 version,

$ go get -u github.com/zeromicro/go-zero@latest
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Modify the proto file

Modify sum.proto, I created a new sum-api.proto, as follows

syntax = "proto3";

package sum;
option go_package="./pb";

import "google/api/annotations.proto";

message SumRequest {
    int64 a = 1;
    int64 b = 2;
}

message SumResponse {
    int64 result = 1;
}

service Sum {
    rpc Add(SumRequest) returns (SumResponse) {
        option (google.api.http) = {
            post: "/v1/sum"
            body: "*"
        };
    }
}
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Generate proto descriptor file

protoc --include_imports --proto_path=. --descriptor_set_out=sum.pb sum-api.proto
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Modify the configuration file

The modified internal/config/config.go looks like this (partially)

type Config struct {
    zrpc.RpcServerConf
    Gateway gateway.GatewayConf
Gateway.GatewayConf }
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The modified etc/sum.yaml is as follows

Gateway:
  Name: gateway
  Port: 8081
  Upstreams:
    - Grpc:
        Endpoints:
          - localhost:8080
      ProtoSets:
        - sum.pb
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Modify the main function

Create gateway and use ServiceGroup to manage gRPC server and gateway server, part of the code is as follows.

    gw := gateway.MustNewServer(c.Gateway)
    group := service.NewServiceGroup()
    group.Add(s)
    group.Add(gw)
    defer group.Stop()

    fmt.Printf("Starting rpc server at %s... \n", c.ListenOn)
    fmt.Printf("Starting gateway at %s:%d... \n", c.Gateway.Host, c.Gateway.Port)
    group.Start()
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Great job!

Let's start the service

$ go run sum.go
Starting rpc server at 127.0.0.1:8080...
Starting gateway at 0.0.0.0:8081...
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Test it with curl

$ curl -i -H "Content-Type: application/json" -d '{"a":2, "b":3}' localhost:8081/v1/sum
HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Traceparent: 00-ad5b7df7a834a1c05ee64999e3310811-195ba1f4f9956cc4-00
Date: Mon, 18 Jul 2022 14:33:11 GMT
Content-Length: 20

{
  "result": "5"
}
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And look at the link information in our gateway and gRPC logs that corresponds to what the client received, awesome!

{"@timestamp": "2022-07-18T22:33:11.437+08:00", "caller": "serverinterceptors/statinterceptor.go:76", "content": "127.0.0.1:61635 - /sum. Sum/Add - {\"a\":2,\"b\":3}", "duration": "0.0ms", "level": "info", "span": "b3c85cd32a76f8c9", "trace":" ad5b7df7a834a1c05ee64999e3310811"}
{"@timestamp": "2022-07-18T22:33:11.438+08:00", "caller": "handler/loghandler.go:197", "content":"[HTTP] 200 - POST /v1/sum - 127.0.0.1: 61662 - curl/7.79.1", "duration": "0.7ms", "level": "info", "span": "195ba1f4f9956cc4", "trace": "ad5b7df7a834a1c05ee64999e3310811"}
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Conclusion

You see, adding the HTTP interface to our gRPC service is very easy? Isn't it?

Also, don't underestimate this simple gateway, the configuration will automatically load balance if it is docked to the gRPC service found behind it, and you can also customize the middleware to control it whatever you want.

By the way, the full code for this example is at.

https://github.com/kevwan/grpc-restful

Project address

https://github.com/zeromicro/go-zero

Feel free to use go-zero and star to support us!

Top comments (2)

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jakewca profile image
Jake

This really conflates REST and HTTP. gRPC doesn’t require transferring a state, but REST does. These are semantic differences, not syntactic ones, so a lot more domain knowledge is required.

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faysou profile image
faysou

Very interesting. It would maybe be interesting if gozero could support code generation from openapi and asyncapi specs.

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