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}