Go中的 Interceptor 拦截器

前言

在编写 golang 的gRPC服务时，想要使用类似于laravel框架中的 middleware 中间件的功能，恰巧原生的代码中并没有相关中间件的功能，在翻阅了一些大量文档后，发现有一个和中间件功能很相识的东西，就是 Interceptor 拦截器。

拦截器详解

grpc服务端提供了interceptor功能，可以在服务端接收到请求时优先对请求中的数据做一些处理后再转交给指定的服务处理并响应，功能类似middleware，很适合在这里处理验证、日志等流程。

普通拦截器(UnaryServerInterceptor)

• 拦截普通的一次请求一次响应的rpc服务

流式拦截器(StreamServerInterceptor)

• 拦截流式的rpc服务

用法

这里主要讲解 普通拦截器(UnaryServerInterceptor) 的使用方法，我们打开 go 的源码，查看 UnaryServerInterceptor 的相关代码，，如下：

/*
 *
 * Copyright 2016 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package grpc

import (
	"context"
)

// UnaryInvoker is called by UnaryClientInterceptor to complete RPCs.
type UnaryInvoker func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, opts ...CallOption) error

// UnaryClientInterceptor intercepts the execution of a unary RPC on the client. invoker is the handler to complete the RPC
// and it is the responsibility of the interceptor to call it.
// This is an EXPERIMENTAL API.
type UnaryClientInterceptor func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, invoker UnaryInvoker, opts ...CallOption) error

// Streamer is called by StreamClientInterceptor to create a ClientStream.
type Streamer func(ctx context.Context, desc *StreamDesc, cc *ClientConn, method string, opts ...CallOption) (ClientStream, error)

// StreamClientInterceptor intercepts the creation of ClientStream. It may return a custom ClientStream to intercept all I/O
// operations. streamer is the handler to create a ClientStream and it is the responsibility of the interceptor to call it.
// This is an EXPERIMENTAL API.
type StreamClientInterceptor func(ctx context.Context, desc *StreamDesc, cc *ClientConn, method string, streamer Streamer, opts ...CallOption) (ClientStream, error)

// UnaryServerInfo consists of various information about a unary RPC on
// server side. All per-rpc information may be mutated by the interceptor.
type UnaryServerInfo struct {
	// Server is the service implementation the user provides. This is read-only.
	Server interface{}
	// FullMethod is the full RPC method string, i.e., /package.service/method.
	FullMethod string
}

// UnaryHandler defines the handler invoked by UnaryServerInterceptor to complete the normal
// execution of a unary RPC. If a UnaryHandler returns an error, it should be produced by the
// status package, or else gRPC will use codes.Unknown as the status code and err.Error() as
// the status message of the RPC.
type UnaryHandler func(ctx context.Context, req interface{}) (interface{}, error)

// UnaryServerInterceptor provides a hook to intercept the execution of a unary RPC on the server. info
// contains all the information of this RPC the interceptor can operate on. And handler is the wrapper
// of the service method implementation. It is the responsibility of the interceptor to invoke handler
// to complete the RPC.
type UnaryServerInterceptor func(ctx context.Context, req interface{}, info *UnaryServerInfo, handler UnaryHandler) (resp interface{}, err error)

// StreamServerInfo consists of various information about a streaming RPC on
// server side. All per-rpc information may be mutated by the interceptor.
type StreamServerInfo struct {
	// FullMethod is the full RPC method string, i.e., /package.service/method.
	FullMethod string
	// IsClientStream indicates whether the RPC is a client streaming RPC.
	IsClientStream bool
	// IsServerStream indicates whether the RPC is a server streaming RPC.
	IsServerStream bool
}

// StreamServerInterceptor provides a hook to intercept the execution of a streaming RPC on the server.
// info contains all the information of this RPC the interceptor can operate on. And handler is the
// service method implementation. It is the responsibility of the interceptor to invoke handler to
// complete the RPC.
type StreamServerInterceptor func(srv interface{}, ss ServerStream, info *StreamServerInfo, handler StreamHandler) error

可以看出 UnaryInterceptor 函数的唯一参数是一个 UnaryServerInterceptor ， UnaryInterceptor 返回的 ServerOption 作为 grpc.NewServer 的参数。而 UnaryServerInterceptor 是一个函数类型，其中四个参数分别是

• ctx: 当前请求的Context
• req：当前请求的参数
• info：当前请求的服务端信息
• handler：服务端处理这次请求的handler

那么我们如何去实现一个拦截器呢？代码如下：

// SentryUnaryServerInterceptor 实现xxx拦截器
func SentryUnaryServerInterceptor() grpc.UnaryServerInterceptor {
	//ctx context.Context：请求上下文
	//req interface{}：RPC 方法的请求参数
	//info *UnaryServerInfo：RPC 方法的所有信息
	//handler UnaryHandler：RPC 方法本身
	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (_ interface{}, err error) {

		// 可以在这里收集请求日志，响应日志，做token校验等等。。

		return handler(ctx, req)
	}
}

我们只需要在方法内实现一个拦截器的闭包，返回一个 grpc.UnaryServerInterceptor 实例，在外部接收并使用到到 grpc.NewServer 中去，即可使用该拦截器了。

结语

PHPer 的转 go 的辛酸路0.0