grpc-unary-client.go

package main

import (
	"bytes"
	"context"
	"crypto/tls"
	"encoding/binary"
	"fmt"
	"io"
	"net"
	"net/http"
	"strconv"

	"github.com/taoso/foo/hello"
	"golang.org/x/net/http2"
	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/protobuf/proto"
)

var plainTextH2Transport = &http2.Transport{
	AllowHTTP: true,
	DialTLS: func(network, addr string, cfg *tls.Config) (net.Conn, error) {
		return net.Dial(network, addr)
	},
}

type grpcClient struct {
	http.Client
}

func NewGrpcClient() grpcClient {
	return grpcClient{http.Client{Transport: plainTextH2Transport}}
}

func (c *grpcClient) DoUnary(ctx context.Context, api string, in, out proto.Message) (resp *http.Response, err error) {
	pb, err := proto.Marshal(in)
	if err != nil {
		return
	}

	// https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests
	bs := make([]byte, 5)
	// 第一个字节默认为0，表示不压缩
	// 后四个字节保存 pb 消息长度
	binary.BigEndian.PutUint32(bs[1:], uint32(len(pb)))

	body := io.MultiReader(bytes.NewReader(bs), bytes.NewReader(pb))

	req, err := http.NewRequest("POST", api, body)
	if err != nil {
		return
	}

	req = req.WithContext(ctx)

	req.Header.Set("trailers", "TE")
	req.Header.Set("content-type", "application/grpc+proto")

	if resp, err = c.Do(req); err != nil {
		return
	}
	defer resp.Body.Close()

	if pb, err = io.ReadAll(resp.Body); err != nil {
		return
	}

	// Unary 调用出错不会返回 body
	// 此时 grpc-status 跟 http 状态码一同返回
	// 不能通过 Trailer 读取
	if status := resp.Header.Get("grpc-status"); status != "" {
		var c int
		if c, err = strconv.Atoi(status); err != nil {
			return
		}
		err = grpc.Errorf(codes.Code(c), resp.Header.Get("grpc-message"))
		return
	}

	// 因为是 Unary，可以直接跳过前五个字节
	err = proto.Unmarshal(pb[5:], out)

	return
}

func main() {
	c := NewGrpcClient()

	in := &hello.HelloRequest{Name: "涛叔"}
	out := &hello.HelloReply{}
	api := "http://127.0.0.1:8080/hello.Greeter/SayHello"

	resp, err := c.DoUnary(context.Background(), api, in, out)
	if err != nil {
		panic(err)
	}

	fmt.Println(out.Message, resp.Trailer.Get("trace-bin"))
}