Mini gRPC Project (1): Creating a Simple Increment API on Go
Tags: go
Published: 2020-10-15 09:48:50

# Objectives

To create an api function that increments the given argument.

```
$ curl "http://localhost:8080/increment?val=3"
{"val":4} //the api returns 4
$ curl "http://localhost:8080/increment?val=10"
{"val":11} //the api returns 11
```


# Prerequisites

- MacOS Catalina
- Already have gopaths configured


# Download necessary packages

```
$ go get -u github.com/golang/protobuf/protoc-gen-go
$ go get -u github.com/grpc-ecosystem/go-grpc-middleware/logging/zap
$ go get -u go.uber.org/zap
```


# Create folders

```
micro-prac$ tree
.
├── proto
│   ├── calc.proto
│   └── gen
│       └── calc.pb.go # will be created using command
└── src
    ├── backend
    │   └── main.go
    └── frontend
        └── main.go

5 directories, 4 files
```

# Create proto files

## `proto/calc.proto`

```
// proto/calc.proto

syntax = "proto3";

service Calc {
    rpc Increment(NumRequest) returns (NumResponse) {}
}

message NumRequest {
    int64 val = 1;
}

message NumResponse {
    int64 val = 1;
}
```

Use the following command in your path (I got some warning but it worked okay).

```
//create gen folder for string pb.proto files
proto$ mkdir gen

proto$ protoc --go_out=plugins=grpc:gen calc.proto
2020/10/15 18:04:20 WARNING: Missing 'go_package' option in "calc.proto",
  1 package main
please specify it with the full Go package path as
a future release of protoc-gen-go will require this be specified.
```

You should see a `calc.pb.go` file created in the `gen` folder.

```
proto/gen$ cat calc.pb.go
// Code generated by protoc-gen-go. DO NOT EDIT.
// versions:
// 	protoc-gen-go v1.25.0-devel
// 	protoc        v3.13.0
// source: calc.proto

package calc

import (
	context "context"
	proto "github.com/golang/protobuf/proto"
	grpc "google.golang.org/grpc"
	codes "google.golang.org/grpc/codes"
	status "google.golang.org/grpc/status"
	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
	reflect "reflect"
	sync "sync"
)

const (
	// Verify that this generated code is sufficiently up-to-date.
	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
	// Verify that runtime/protoimpl is sufficiently up-to-date.
	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
)

// This is a compile-time assertion that a sufficiently up-to-date version
// of the legacy proto package is being used.
const _ = proto.ProtoPackageIsVersion4

type NumRequest struct {
	state         protoimpl.MessageState
	sizeCache     protoimpl.SizeCache
	unknownFields protoimpl.UnknownFields

	Val int64 `protobuf:"varint,1,opt,name=val,proto3" json:"val,omitempty"`
}

func (x *NumRequest) Reset() {
	*x = NumRequest{}
	if protoimpl.UnsafeEnabled {
		mi := &file_calc_proto_msgTypes[0]
		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
		ms.StoreMessageInfo(mi)
	}
}

func (x *NumRequest) String() string {
	return protoimpl.X.MessageStringOf(x)
}

func (*NumRequest) ProtoMessage() {}

func (x *NumRequest) ProtoReflect() protoreflect.Message {
	mi := &file_calc_proto_msgTypes[0]
	if protoimpl.UnsafeEnabled && x != nil {
		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
		if ms.LoadMessageInfo() == nil {
			ms.StoreMessageInfo(mi)
		}
		return ms
	}
	return mi.MessageOf(x)
}

// Deprecated: Use NumRequest.ProtoReflect.Descriptor instead.
func (*NumRequest) Descriptor() ([]byte, []int) {
	return file_calc_proto_rawDescGZIP(), []int{0}
}

func (x *NumRequest) GetVal() int64 {
	if x != nil {
		return x.Val
	}
	return 0
}

type NumResponse struct {
	state         protoimpl.MessageState
	sizeCache     protoimpl.SizeCache
	unknownFields protoimpl.UnknownFields

	Val int64 `protobuf:"varint,1,opt,name=val,proto3" json:"val,omitempty"`
}

func (x *NumResponse) Reset() {
	*x = NumResponse{}
	if protoimpl.UnsafeEnabled {
		mi := &file_calc_proto_msgTypes[1]
		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
		ms.StoreMessageInfo(mi)
	}
}

func (x *NumResponse) String() string {
	return protoimpl.X.MessageStringOf(x)
}

func (*NumResponse) ProtoMessage() {}

func (x *NumResponse) ProtoReflect() protoreflect.Message {
	mi := &file_calc_proto_msgTypes[1]
	if protoimpl.UnsafeEnabled && x != nil {
		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
		if ms.LoadMessageInfo() == nil {
			ms.StoreMessageInfo(mi)
		}
		return ms
	}
	return mi.MessageOf(x)
}

// Deprecated: Use NumResponse.ProtoReflect.Descriptor instead.
func (*NumResponse) Descriptor() ([]byte, []int) {
	return file_calc_proto_rawDescGZIP(), []int{1}
}

func (x *NumResponse) GetVal() int64 {
	if x != nil {
		return x.Val
	}
	return 0
}

var File_calc_proto protoreflect.FileDescriptor

var file_calc_proto_rawDesc = []byte{
	0x0a, 0x0a, 0x63, 0x61, 0x6c, 0x63, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x22, 0x1e, 0x0a, 0x0a,
	0x4e, 0x75, 0x6d, 0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x12, 0x10, 0x0a, 0x03, 0x76, 0x61,
	0x6c, 0x18, 0x01, 0x20, 0x01, 0x28, 0x03, 0x52, 0x03, 0x76, 0x61, 0x6c, 0x22, 0x1f, 0x0a, 0x0b,
	0x4e, 0x75, 0x6d, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x12, 0x10, 0x0a, 0x03, 0x76,
	0x61, 0x6c, 0x18, 0x01, 0x20, 0x01, 0x28, 0x03, 0x52, 0x03, 0x76, 0x61, 0x6c, 0x32, 0x30, 0x0a,
	0x04, 0x43, 0x61, 0x6c, 0x63, 0x12, 0x28, 0x0a, 0x09, 0x49, 0x6e, 0x63, 0x72, 0x65, 0x6d, 0x65,
	0x6e, 0x74, 0x12, 0x0b, 0x2e, 0x4e, 0x75, 0x6d, 0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x1a,
	0x0c, 0x2e, 0x4e, 0x75, 0x6d, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x22, 0x00, 0x62,
	0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
}

var (
	file_calc_proto_rawDescOnce sync.Once
	file_calc_proto_rawDescData = file_calc_proto_rawDesc
)

func file_calc_proto_rawDescGZIP() []byte {
	file_calc_proto_rawDescOnce.Do(func() {
		file_calc_proto_rawDescData = protoimpl.X.CompressGZIP(file_calc_proto_rawDescData)
	})
	return file_calc_proto_rawDescData
}

var file_calc_proto_msgTypes = make([]protoimpl.MessageInfo, 2)
var file_calc_proto_goTypes = []interface{}{
	(*NumRequest)(nil),  // 0: NumRequest
	(*NumResponse)(nil), // 1: NumResponse
}
var file_calc_proto_depIdxs = []int32{
	0, // 0: Calc.Increment:input_type -> NumRequest
	1, // 1: Calc.Increment:output_type -> NumResponse
	1, // [1:2] is the sub-list for method output_type
	0, // [0:1] is the sub-list for method input_type
	0, // [0:0] is the sub-list for extension type_name
	0, // [0:0] is the sub-list for extension extendee
	0, // [0:0] is the sub-list for field type_name
}

func init() { file_calc_proto_init() }
func file_calc_proto_init() {
	if File_calc_proto != nil {
		return
	}
	if !protoimpl.UnsafeEnabled {
		file_calc_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
			switch v := v.(*NumRequest); i {
			case 0:
				return &v.state
			case 1:
				return &v.sizeCache
			case 2:
				return &v.unknownFields
			default:
				return nil
			}
		}
		file_calc_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
			switch v := v.(*NumResponse); i {
			case 0:
				return &v.state
			case 1:
				return &v.sizeCache
			case 2:
				return &v.unknownFields
			default:
				return nil
			}
		}
	}
	type x struct{}
	out := protoimpl.TypeBuilder{
		File: protoimpl.DescBuilder{
			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
			RawDescriptor: file_calc_proto_rawDesc,
			NumEnums:      0,
			NumMessages:   2,
			NumExtensions: 0,
			NumServices:   1,
		},
		GoTypes:           file_calc_proto_goTypes,
		DependencyIndexes: file_calc_proto_depIdxs,
		MessageInfos:      file_calc_proto_msgTypes,
	}.Build()
	File_calc_proto = out.File
	file_calc_proto_rawDesc = nil
	file_calc_proto_goTypes = nil
	file_calc_proto_depIdxs = nil
}

// Reference imports to suppress errors if they are not otherwise used.
var _ context.Context
var _ grpc.ClientConnInterface

// This is a compile-time assertion to ensure that this generated file
// is compatible with the grpc package it is being compiled against.
const _ = grpc.SupportPackageIsVersion6

// CalcClient is the client API for Calc service.
//
// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://godoc.org/google.golang.org/grpc#ClientConn.NewStream.
type CalcClient interface {
	Increment(ctx context.Context, in *NumRequest, opts ...grpc.CallOption) (*NumResponse, error)
}

type calcClient struct {
	cc grpc.ClientConnInterface
}

func NewCalcClient(cc grpc.ClientConnInterface) CalcClient {
	return &calcClient{cc}
}

func (c *calcClient) Increment(ctx context.Context, in *NumRequest, opts ...grpc.CallOption) (*NumResponse, error) {
	out := new(NumResponse)
	err := c.cc.Invoke(ctx, "/Calc/Increment", in, out, opts...)
	if err != nil {
		return nil, err
	}
	return out, nil
}

// CalcServer is the server API for Calc service.
type CalcServer interface {
	Increment(context.Context, *NumRequest) (*NumResponse, error)
}

// UnimplementedCalcServer can be embedded to have forward compatible implementations.
type UnimplementedCalcServer struct {
}

func (*UnimplementedCalcServer) Increment(context.Context, *NumRequest) (*NumResponse, error) {
	return nil, status.Errorf(codes.Unimplemented, "method Increment not implemented")
}

func RegisterCalcServer(s *grpc.Server, srv CalcServer) {
	s.RegisterService(&_Calc_serviceDesc, srv)
}

func _Calc_Increment_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
	in := new(NumRequest)
	if err := dec(in); err != nil {
		return nil, err
	}
	if interceptor == nil {
		return srv.(CalcServer).Increment(ctx, in)
	}
	info := &grpc.UnaryServerInfo{
		Server:     srv,
		FullMethod: "/Calc/Increment",
	}
	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
		return srv.(CalcServer).Increment(ctx, req.(*NumRequest))
  1 // this file is sample for client
	}
	return interceptor(ctx, in, info, handler)
}

var _Calc_serviceDesc = grpc.ServiceDesc{
	ServiceName: "Calc",
	HandlerType: (*CalcServer)(nil),
	Methods: []grpc.MethodDesc{
		{
			MethodName: "Increment",
			Handler:    _Calc_Increment_Handler,
		},
	},
	Streams:  []grpc.StreamDesc{},
  1 // this file is sample for client
	Metadata: "calc.proto",
}

```


# Create frontend files

## `src/frontend/main.go`

```
# src/frontend/main.go
// this file is sample for client
package main

import (
	"context"
	"encoding/json"
	"log"
	"net/http"
	"os"
	"strconv"

	"github.com/grpc-ecosystem/go-grpc-middleware/logging/zap"
	"go.uber.org/zap"
	"google.golang.org/grpc"

	pb "../../proto/gen"
)

func main() {
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		log.Println("health check")
	})
	http.HandleFunc("/increment", incrementHandler)
	log.Fatal(http.ListenAndServe(":8080", nil))
	log.Println("listen started")
}

func incrementHandler(w http.ResponseWriter, r *http.Request) {
	logger, err := zap.NewDevelopment()
	if err != nil {
		log.Fatalf("failed to create logger :%v", err)
	}
	var servName string
	if s := os.Getenv("BACKEND_SERVICE_NAME"); s != "" {
		servName = s
	} else {
		servName = "127.0.0.1"
	}
	logger.Debug("go", zap.String("servName", servName))
	conn, err := grpc.Dial(servName+":8000", grpc.WithInsecure(), grpc.WithUnaryInterceptor(
		grpc_zap.UnaryClientInterceptor(logger),
	))
	grpc_zap.ReplaceGrpcLogger(logger)
	if err != nil {
		log.Fatalf("failed to connect :%v", err)
	}
	defer conn.Close()

	val, err := strconv.Atoi(r.URL.Query().Get("val"))
	if err != nil {
		logger.Error("got value error", zap.Error(err))
	}
	client := pb.NewCalcClient(conn)
	ctx := context.Background()
	res, err := client.Increment(ctx, &pb.NumRequest{Val: int64(val)})
	if err != nil {
		logger.Error("got error from server", zap.Error(err))
	}
	logger.Info("got response", zap.Int64("value", res.Val))
	b, err := json.Marshal(res)
	if err != nil {
		logger.Error("json parse error", zap.Error(err))
	}
	w.Write(b)
}
```

# Create backend files

## `src/backend/main.go`

```
package main

import (
	"fmt"
	"github.com/grpc-ecosystem/go-grpc-middleware/logging/zap"
	"go.uber.org/zap"
	"google.golang.org/grpc"
	"log"
	"net"
	pb "../../proto/gen"
	context "golang.org/x/net/context"
)

func main() {
	port := 8000
	logger, err := zap.NewDevelopment()
	if err != nil {
		log.Fatalf("failed to create logger :%v", err)
	}
	lis, err := net.Listen("tcp", fmt.Sprintf(":%d", port))
	if err != nil {
		logger.Fatal("failed to listen", zap.Error(err))
	}
	server := grpc.NewServer(grpc.UnaryInterceptor(
		grpc_zap.UnaryServerInterceptor(logger),
	))
	grpc_zap.ReplaceGrpcLogger(logger)
	pb.RegisterCalcServer(server, &CalcService{})
	server.Serve(lis)
}

type CalcService struct{}

func (s *CalcService) Increment(ctx context.Context, req *pb.NumRequest) (*pb.NumResponse, error) {
	req.Val++
	return &pb.NumResponse{Val: req.Val}, nil
}

```

Run the `go run main.go` in both backend and frontend.

When you use curl, you should be able to get a response.

## Run the curl commands

```
$ curl "http://localhost:8080/increment?val=10"
{"val":11}
```


## Results on frontend side

```
frontend$ go run main.go
2020-10-15T18:21:11.609+0900	DEBUG	frontend/main.go:39	go	{"servName": "127.0.0.1"}
2020-10-15T18:21:11.610+0900	INFO	zap/grpclogger.go:46	[core]Subchannel picks a new address "127.0.0.1:8000" to connect	{"system": "grpc", "grpc_log": true}
2020-10-15T18:21:11.610+0900	INFO	zap/grpclogger.go:46	[core]Channel Connectivity change to CONNECTING	{"system": "grpc", "grpc_log": true}
2020-10-15T18:21:11.612+0900	INFO	zap/grpclogger.go:46	[core]Subchannel Connectivity change to READY	{"system": "grpc", "grpc_log": true}
2020-10-15T18:21:11.613+0900	INFO	zap/grpclogger.go:46	[core]pickfirstBalancer: UpdateSubConnState: 0xc0001ac6e0, {READY <nil>}	{"system": "grpc", "grpc_log": true}
2020-10-15T18:21:11.613+0900	INFO	zap/grpclogger.go:46	[core]Channel Connectivity change to READY	{"system": "grpc", "grpc_log": true}
2020-10-15T18:21:11.616+0900	DEBUG	zap/options.go:203	finished client unary call	{"system": "grpc", "span.kind": "client", "grpc.service": "Calc", "grpc.method": "Increment", "grpc.code": "OK", "grpc.time_ms": 6.538000106811523}
```

## Results on backend

```
$ go run main.go
2020-10-15T18:21:11.615+0900	INFO	zap/options.go:203	finished unary call with code OK	{"grpc.start_time": "2020-10-15T18:21:11+09:00", "system": "grpc", "span.kind": "server", "grpc.service": "Calc", "grpc.method": "Increment", "grpc.code": "OK", "grpc.time_ms": 0.21799999475479126}
2020-10-15T18:21:11.617+0900	INFO	zap/grpclogger.go:46	[transport]transport: loopyWriter.run returning. connection error: desc = "transport is closing"	{"system": "grpc", "grpc_log": true}
2020-10-15T18:21:15.505+0900	INFO	zap/options.go:203	finished unary call with code OK	{"grpc.start_time": "2020-10-15T18:21:15+09:00", "system": "grpc", "span.kind": "server", "grpc.service": "Calc", "grpc.method": "Increment", "grpc.code": "OK", "grpc.time_ms": 0.023000000044703484}
2020-10-15T18:21:15.506+0900	INFO	zap/grpclogger.go:46	[transport]transport: loopyWriter.run returning. connection error: desc = "transport is closing"	{"system": "grpc", "grpc_log": true}
```

## Next: Deployment on GKE

We will deploy this simple gRPC API on GKE here: [Mini gRPC Project (2): Deploying the gRPC API on k8s](https://dev.to/greenteabiscuit/mini-grpc-project-deploying-the-grpc-api-on-k8s-4h15)