拦截器

gRPC拦截器（interceptor）是一种函数，它可以在gRPC调用之前和之后执行一些逻辑，例如认证、授权、日志记录、监控和统计等。拦截器函数是gRPC中非常重要的概念，它允许我们在服务端和客户端添加自定义逻辑，以满足业务需求和运维需求。

在gRPC中，拦截器函数通常通过实现grpc.UnaryServerInterceptor和grpc.StreamServerInterceptor接口来定义。UnaryServerInterceptor用于拦截一元RPC请求，而StreamServerInterceptor用于拦截流式RPC请求。在客户端中，我们可以使用grpc.UnaryClientInterceptor和grpc.StreamClientInterceptor来拦截gRPC调用。

在gRPC中，拦截器函数可以被链接起来，形成一个拦截器链。在这个拦截器链中，每个拦截器函数都可以处理请求并将其转发给下一个拦截器函数，或者直接返回响应。因此，我们可以在拦截器函数中编写不同的逻辑，例如实现认证、授权、监控和统计等。
以下是一些常见的gRPC拦截器：

• 认证和授权拦截器：用于对gRPC调用进行身份验证和权限控制，例如检查token、验证用户名和密码、检查访问控制列表等；
• 日志记录拦截器：用于记录gRPC调用的日志，例如记录请求的方法、参数、响应状态等；
• 监控和统计拦截器：用于监控gRPC调用的性能和吞吐量，例如记录调用次数、响应时间、错误率等；
• 缓存拦截器：用于在服务端或客户端缓存一些数据，例如缓存计算结果、缓存数据库查询结果等。

服务端拦截器

一元拦截器

package main

import (
	"context"
	"flag"
	"log"
	"time"

	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials/insecure"
	pb "mygrpc/proto/hello" // 引入编译生成的包
)

const (
	defaultName = "world"
)

var (
	addr = flag.String("addr", "localhost:50051", "the address to connect to")
	name = flag.String("name", defaultName, "Name to greet")
)

func main() {
	flag.Parse()
	// 与服务建立连接.
	conn, err := grpc.Dial(*addr, grpc.WithTransportCredentials(insecure.NewCredentials()))
	if err != nil {
		log.Fatalf("did not connect: %v", err)
	}
	defer conn.Close()
	// 创建指定服务的客户端
	c := pb.NewGreeterClient(conn)

	// 连接服务器并打印出其响应。
	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
	defer cancel()
	// 调用指定方法
	r, err := c.SayHello(ctx, &pb.HelloRequest{Name: *name})
	if err != nil {
		log.Fatalf("could not greet: %v", err)
	}
	log.Printf("Greeting: %s", r.GetMessage())
}

结果

2023/12/07 14:52:55 ======= [Server Interceptor]  /hello.Greeter/SayHello
2023/12/07 14:52:55  Pre Proc Message : name:"world"
2023/12/07 14:52:55 Received: world
2023/12/07 14:52:55  Post Proc Message : message:"Hello world"

流拦截器

流式拦截器需要对grpc.ServerStream进行包装，重新实现RecvMsg和SendMsg方法。

func (s *server) SearchOrders(req *pb.HelloRequest, stream pb.Greeter_SearchOrdersServer) error {
	log.Printf("Recved %v", req.GetName())
	// 具体返回多少个response根据业务逻辑调整
	for i := 0; i < 10; i++ {
		// 通过 send 方法不断推送数据
		err := stream.Send(&pb.HelloReply{})
		if err != nil {
			log.Fatalf("Send error:%v", err)
			return err
		}
	}
	return nil
}

type wrappedStream struct {
	// 包装器流
	grpc.ServerStream
}
// 接受信息拦截器
func (w *wrappedStream) RecvMsg(m interface{}) error {
	log.Printf("====== [Server Stream Interceptor Wrapper] Receive a message (Type: %T) at %s", m, time.Now().Format(time.RFC3339))
	return w.ServerStream.RecvMsg(m)
}
// 发送消息拦截器
func (w *wrappedStream) SendMsg(m interface{}) error {
	log.Printf("====== [Server Stream Interceptor Wrapper] Send a message (Type: %T) at %v", m, time.Now().Format(time.RFC3339))
	return w.ServerStream.SendMsg(m)
}

func newWrappedStream(s grpc.ServerStream) grpc.ServerStream {
	return &wrappedStream{s}
}

func orderServerStreamInterceptor(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
	// 前置处理
	log.Println("====== [Server Stream Interceptor] ", info.FullMethod)

	// 包装器流调用 流RPC
	err := handler(srv, newWrappedStream(ss))
	if err != nil {
		log.Printf("RPC failed with error %v", err)
	}
	return err
}
func main() {
	flag.Parse()
	lis, err := net.Listen("tcp", fmt.Sprintf(":%d", *port))
	if err != nil {
		log.Fatalf("failed to listen: %v", err)
	}
	// 开启rpc
	s := grpc.NewServer(grpc.StreamInterceptor(orderServerStreamInterceptor))
	// 注册服务
	pb.RegisterGreeterServer(s, &server{})
	log.Printf("service listening at %v", lis.Addr())
	if err := s.Serve(lis); err != nil {
		log.Fatalf("failed to serve: %v", err)
	}
}

结果

GOROOT=D:\software\Go #gosetup
GOPATH=D:\software\golibrary #gosetup
D:\software\Go\bin\go.exe build -o C:\Users\29071\AppData\Local\JetBrains\GoLand2023.3\tmp\GoLand\___go_build_mygrpc_service_steamInterceptorservice.exe mygrpc/service/steamInterceptorservice #gosetup
C:\Users\29071\AppData\Local\JetBrains\GoLand2023.3\tmp\GoLand\___go_build_mygrpc_service_steamInterceptorservice.exe
2023/12/07 15:07:48 service listening at [::]:50051
2023/12/07 15:08:07 ====== [Server Stream Interceptor]  /hello.Greeter/searchOrders
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Receive a message (Type: *hello.HelloRequest) at 2023-12-07T15:08:07+08:00
2023/12/07 15:08:07 Recved 开始服务端rpc流测试
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Send a message (Type: *hello.HelloReply) at 2023-12-07T15:08:07+08:00
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Send a message (Type: *hello.HelloReply) at 2023-12-07T15:08:07+08:00
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Send a message (Type: *hello.HelloReply) at 2023-12-07T15:08:07+08:00
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Send a message (Type: *hello.HelloReply) at 2023-12-07T15:08:07+08:00
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Send a message (Type: *hello.HelloReply) at 2023-12-07T15:08:07+08:00
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Send a message (Type: *hello.HelloReply) at 2023-12-07T15:08:07+08:00
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Send a message (Type: *hello.HelloReply) at 2023-12-07T15:08:07+08:00
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Send a message (Type: *hello.HelloReply) at 2023-12-07T15:08:07+08:00
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Send a message (Type: *hello.HelloReply) at 2023-12-07T15:08:07+08:00
2023/12/07 15:08:07 ====== [Server Stream Interceptor Wrapper] Send a message (Type: *hello.HelloReply) at 2023-12-07T15:08:07+08:00
Process finished with the exit code -1073741510 (0xC000013A: interrupted by Ctrl+C)

客户端拦截器

一元拦截器

func orderUnaryClientInterceptor(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
	// 前置处理逻辑
	log.Println("Method : " + method)

	// 调用invoker 执行远程方法
	err := invoker(ctx, method, req, reply, cc, opts...)

	// 后置处理逻辑
	log.Println(reply)
	return err
}

func main() {
	flag.Parse()
	// 与服务建立连接.
	conn, err := grpc.Dial(*addr, grpc.WithTransportCredentials(insecure.NewCredentials()),
		grpc.WithUnaryInterceptor(orderUnaryClientInterceptor)) //添加拦截器
	if err != nil {
		log.Fatalf("did not connect: %v", err)
	}
	defer conn.Close()
	// 创建指定服务的客户端
	c := pb.NewGreeterClient(conn)

	// 连接服务器并打印出其响应。
	ctx, cancel := context.WithTimeout(context.Background(), time.Second) // 设置超时时间为一秒
	defer cancel()
	// 调用指定方法
	r, err := c.SayHello(ctx, &pb.HelloRequest{Name: *name})
	if err != nil {
		log.Fatalf("could not greet: %v", err)
	}
	log.Printf("Greeting: %s", r.GetMessage())
}

结果

2023/12/07 16:37:28 Method : /hello.Greeter/SayHello
2023/12/07 16:37:28 message:"Hello world"
2023/12/07 16:37:28 Greeting: Hello worl

流拦截`

type wrappedStream struct {
	grpc.ClientStream
}

func (w *wrappedStream) RecvMsg(m interface{}) error {
	log.Printf("====== [Client Stream Interceptor] Receive a message (Type: %T) at %v", m, time.Now().Format(time.RFC3339))
	return w.ClientStream.RecvMsg(m)
}

func (w *wrappedStream) SendMsg(m interface{}) error {
	log.Printf("====== [Client Stream Interceptor] Send a message (Type: %T) at %v", m, time.Now().Format(time.RFC3339))
	return w.ClientStream.SendMsg(m)
}

func newWrappedStream(s grpc.ClientStream) grpc.ClientStream {
	return &wrappedStream{s}
}

func clientStreamInterceptor(ctx context.Context, desc *grpc.StreamDesc, cc *grpc.ClientConn, method string, streamer grpc.Streamer, opts ...grpc.CallOption) (grpc.ClientStream, error) {
	
  // 前置处理逻辑
	log.Println("======= [Client Interceptor] ", method)
  
  // 调用streamer 来获取客户端流
	s, err := streamer(ctx, desc, cc, method, opts...)
	if err != nil {
		return nil, err
	}
	return newWrappedStream(s), nil
}

func main(){
   // 注册拦截器到客户端流
 conn,err:=grpc.Dial(address,grpc.WithInsecure(),grpc.WithStreamInterceptor(clientStreamInterceptor))
	if err != nil {
		log.Fatalf("did not connect: %v", err)
	}
	defer conn.Close()
                     
	c := pb.NewOrderManagementClient(conn)
  ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
	defer cancel()
  
  // 调用客户端流RPC方法
  searchStream, _ := c.SearchOrders(ctx, &wrapper.StringValue{Value: "Google"})
	for {
		searchOrder, err := searchStream.Recv()
		if err == io.EOF {
			log.Print("EOF")
			break
		}
		if err == nil {
			log.Print("Search Result : ", searchOrder)
		}
	}
}

结果

2023/12/07 17:10:43 ====== [Client Stream Interceptor] Send a message (Type: *hello.HelloRequest) at 2023-12-07T17:10:43+08:00
2023/12/07 17:10:43 ====== [Client Stream Interceptor] Send a message (Type: *hello.HelloRequest) at 2023-12-07T17:10:43+08:00
2023/12/07 17:10:43 客户端流传输结束

多个拦截器

在grpc中默认的拦截器不可以传多个，因为在源码中，存在一些问题

func chainUnaryClientInterceptors(cc *ClientConn) {
	interceptors := cc.dopts.chainUnaryInts
	if cc.dopts.unaryInt != nil {
		interceptors = append([]UnaryClientInterceptor{cc.dopts.unaryInt}, interceptors...)
	}
	var chainedInt UnaryClientInterceptor
	if len(interceptors) == 0 {
		chainedInt = nil
	} else if len(interceptors) == 1 {
		chainedInt = interceptors[0]
	} else {
		chainedInt = func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, invoker UnaryInvoker, opts ...CallOption) error {
			return interceptors[0](ctx, method, req, reply, cc, getChainUnaryInvoker(interceptors, 0, invoker), opts...)
		}
	}
	cc.dopts.unaryInt = chainedInt
}

当存在多个拦截器时，取的就是第一个拦截器。因此结论是允许传多个，但并没有用。

如果真的需要多个拦截器，可以使用 go-grpc-middleware 提供的 grpc.UnaryInterceptor 和 grpc.StreamInterceptor 链式方法。核心方法如下

func ChainUnaryClient(interceptors ...grpc.UnaryClientInterceptor) grpc.UnaryClientInterceptor {
	n := len(interceptors)
	if n > 1 {
		lastI := n - 1
		return func(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
			var (
				chainHandler grpc.UnaryInvoker
				curI         int
			)

			chainHandler = func(currentCtx context.Context, currentMethod string, currentReq, currentRepl interface{}, currentConn *grpc.ClientConn, currentOpts ...grpc.CallOption) error {
				if curI == lastI {
					return invoker(currentCtx, currentMethod, currentReq, currentRepl, currentConn, currentOpts...)
				}
				curI++
				err := interceptors[curI](currentCtx, currentMethod, currentReq, currentRepl, currentConn, chainHandler, currentOpts...)
				curI--
				return err
			}

			return interceptors[0](ctx, method, req, reply, cc, chainHandler, opts...)
		}
	}
    ...
}

代码仓库

https://github.com/onenewcode/mygrpc.git

也可以直接下载绑定的资源。