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376 lines
15 KiB
376 lines
15 KiB
# 说明
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gRPC暴露了两个拦截器接口，分别是：
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* `grpc.UnaryServerInterceptor`服务端拦截器
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* `grpc.UnaryClientInterceptor`客户端拦截器
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基于两个拦截器可以针对性的定制公共模块的封装代码，比如`warden/logging.go`是通用日志逻辑。
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# 分析
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## 服务端拦截器
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让我们先看一下`grpc.UnaryServerInterceptor`的声明，[官方代码位置](https://github.com/grpc/grpc-go/blob/master/interceptor.go)：
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```go
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// UnaryServerInfo consists of various information about a unary RPC on
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// server side. All per-rpc information may be mutated by the interceptor.
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type UnaryServerInfo struct {
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// Server is the service implementation the user provides. This is read-only.
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Server interface{}
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// FullMethod is the full RPC method string, i.e., /package.service/method.
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FullMethod string
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}
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// UnaryHandler defines the handler invoked by UnaryServerInterceptor to complete the normal
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// execution of a unary RPC. If a UnaryHandler returns an error, it should be produced by the
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// status package, or else gRPC will use codes.Unknown as the status code and err.Error() as
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// the status message of the RPC.
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type UnaryHandler func(ctx context.Context, req interface{}) (interface{}, error)
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// UnaryServerInterceptor provides a hook to intercept the execution of a unary RPC on the server. info
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// contains all the information of this RPC the interceptor can operate on. And handler is the wrapper
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// of the service method implementation. It is the responsibility of the interceptor to invoke handler
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// to complete the RPC.
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type UnaryServerInterceptor func(ctx context.Context, req interface{}, info *UnaryServerInfo, handler UnaryHandler) (resp interface{}, err error)
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```
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看起来很简单包括：
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* 一个`UnaryServerInfo`结构体用于`Server`和`FullMethod`字段传递，`Server`为`gRPC server`的对象实例，`FullMethod`为请求方法的全名
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* 一个`UnaryHandler`方法用于传递`Handler`，就是基于`proto`文件`service`内声明而生成的方法
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* 一个`UnaryServerInterceptor`用于拦截`Handler`方法，可在`Handler`执行前后插入拦截代码
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为了更形象的说明拦截器的执行过程，请看基于`proto`生成的以下代码[代码位置](https://github.com/go-kratos/kratos-demo/blob/master/api/api.pb.go)：
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```go
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func _Demo_SayHello_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
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in := new(HelloReq)
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if err := dec(in); err != nil {
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return nil, err
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}
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if interceptor == nil {
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return srv.(DemoServer).SayHello(ctx, in)
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}
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info := &grpc.UnaryServerInfo{
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Server: srv,
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FullMethod: "/demo.service.v1.Demo/SayHello",
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}
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handler := func(ctx context.Context, req interface{}) (interface{}, error) {
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return srv.(DemoServer).SayHello(ctx, req.(*HelloReq))
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}
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return interceptor(ctx, in, info, handler)
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}
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```
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这个`_Demo_SayHello_Handler`方法是关键，该方法会被包装为`grpc.ServiceDesc`结构，被注册到gRPC内部，具体可在生成的`pb.go`代码内查找`s.RegisterService(&_Demo_serviceDesc, srv)`。
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* 当`gRPC server`收到一次请求时，首先根据请求方法从注册到`server`内的`grpc.ServiceDesc`找到该方法对应的`Handler`如：`_Demo_SayHello_Handler`并执行
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* `_Demo_SayHello_Handler`执行过程请看上面具体代码，当`interceptor`不为`nil`时，会将`SayHello`包装为`grpc.UnaryHandler`结构传递给`interceptor`
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这样就完成了`UnaryServerInterceptor`的执行过程。那么`_Demo_SayHello_Handler`内的`interceptor`是如何注入到`gRPC server`内，则看下面这段代码[官方代码位置](https://github.com/grpc/grpc-go/blob/master/server.go)：
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```go
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// UnaryInterceptor returns a ServerOption that sets the UnaryServerInterceptor for the
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// server. Only one unary interceptor can be installed. The construction of multiple
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// interceptors (e.g., chaining) can be implemented at the caller.
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func UnaryInterceptor(i UnaryServerInterceptor) ServerOption {
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return func(o *options) {
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if o.unaryInt != nil {
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panic("The unary server interceptor was already set and may not be reset.")
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}
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o.unaryInt = i
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}
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}
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```
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请一定注意这方法的注释！！！
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> Only one unary interceptor can be installed. The construction of multiple interceptors (e.g., chaining) can be implemented at the caller.
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`gRPC`本身只支持一个`interceptor`，想要多`interceptors`需要自己实现~~所以`warden`基于`grpc.UnaryClientInterceptor`实现了`interceptor chain`，请看下面代码[代码位置](https://github.com/go-kratos/kratos/blob/master/pkg/net/rpc/warden/server.go)：
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```go
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// Use attachs a global inteceptor to the server.
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// For example, this is the right place for a rate limiter or error management inteceptor.
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func (s *Server) Use(handlers ...grpc.UnaryServerInterceptor) *Server {
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finalSize := len(s.handlers) + len(handlers)
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if finalSize >= int(_abortIndex) {
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panic("warden: server use too many handlers")
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}
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mergedHandlers := make([]grpc.UnaryServerInterceptor, finalSize)
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copy(mergedHandlers, s.handlers)
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copy(mergedHandlers[len(s.handlers):], handlers)
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s.handlers = mergedHandlers
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return s
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}
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// interceptor is a single interceptor out of a chain of many interceptors.
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// Execution is done in left-to-right order, including passing of context.
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// For example ChainUnaryServer(one, two, three) will execute one before two before three, and three
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// will see context changes of one and two.
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func (s *Server) interceptor(ctx context.Context, req interface{}, args *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
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var (
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i int
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chain grpc.UnaryHandler
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)
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n := len(s.handlers)
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if n == 0 {
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return handler(ctx, req)
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}
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chain = func(ic context.Context, ir interface{}) (interface{}, error) {
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if i == n-1 {
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return handler(ic, ir)
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}
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i++
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return s.handlers[i](ic, ir, args, chain)
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}
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return s.handlers[0](ctx, req, args, chain)
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}
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```
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很简单的逻辑：
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* `warden server`使用`Use`方法进行`grpc.UnaryServerInterceptor`的注入，而`func (s *Server) interceptor`本身就实现了`grpc.UnaryServerInterceptor`
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* `func (s *Server) interceptor`可以根据注册的`grpc.UnaryServerInterceptor`顺序从前到后依次执行
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而`warden`在初始化的时候将该方法本身注册到了`gRPC server`，在`NewServer`方法内可以看到下面代码：
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```go
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opt = append(opt, keepParam, grpc.UnaryInterceptor(s.interceptor))
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s.server = grpc.NewServer(opt...)
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```
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如此完整的服务端拦截器逻辑就串联完成。
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## 客户端拦截器
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让我们先看一下`grpc.UnaryClientInterceptor`的声明，[官方代码位置](https://github.com/grpc/grpc-go/blob/master/interceptor.go)：
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```go
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// UnaryInvoker is called by UnaryClientInterceptor to complete RPCs.
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type UnaryInvoker func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, opts ...CallOption) error
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// UnaryClientInterceptor intercepts the execution of a unary RPC on the client. invoker is the handler to complete the RPC
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// and it is the responsibility of the interceptor to call it.
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// This is an EXPERIMENTAL API.
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type UnaryClientInterceptor func(ctx context.Context, method string, req, reply interface{}, cc *ClientConn, invoker UnaryInvoker, opts ...CallOption) error
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```
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看起来和服务端拦截器并没有什么太大的区别，比较简单包括：
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* 一个`UnaryInvoker`表示客户端具体要发出的执行方法
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* 一个`UnaryClientInterceptor`用于拦截`Invoker`方法，可在`Invoker`执行前后插入拦截代码
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具体执行过程，请看基于`proto`生成的下面代码[代码位置](https://github.com/go-kratos/kratos-demo/blob/master/api/api.pb.go)：
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```go
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func (c *demoClient) SayHello(ctx context.Context, in *HelloReq, opts ...grpc.CallOption) (*google_protobuf1.Empty, error) {
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out := new(google_protobuf1.Empty)
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err := grpc.Invoke(ctx, "/demo.service.v1.Demo/SayHello", in, out, c.cc, opts...)
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if err != nil {
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return nil, err
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}
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return out, nil
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}
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```
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当客户端调用`SayHello`时可以看到执行了`grpc.Invoke`方法，并且将`fullMethod`和其他参数传入，最终会执行下面代码[官方代码位置](https://github.com/grpc/grpc-go/blob/master/call.go)：
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```go
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// Invoke sends the RPC request on the wire and returns after response is
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// received. This is typically called by generated code.
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//
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// All errors returned by Invoke are compatible with the status package.
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func (cc *ClientConn) Invoke(ctx context.Context, method string, args, reply interface{}, opts ...CallOption) error {
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// allow interceptor to see all applicable call options, which means those
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// configured as defaults from dial option as well as per-call options
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opts = combine(cc.dopts.callOptions, opts)
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if cc.dopts.unaryInt != nil {
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return cc.dopts.unaryInt(ctx, method, args, reply, cc, invoke, opts...)
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}
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return invoke(ctx, method, args, reply, cc, opts...)
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}
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```
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其中的`unaryInt`即为客户端连接创建时注册的拦截器，使用下面代码注册[官方代码位置](https://github.com/grpc/grpc-go/blob/master/dialoptions.go)：
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```go
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// WithUnaryInterceptor returns a DialOption that specifies the interceptor for
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// unary RPCs.
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func WithUnaryInterceptor(f UnaryClientInterceptor) DialOption {
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return newFuncDialOption(func(o *dialOptions) {
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o.unaryInt = f
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})
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}
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```
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需要注意的是客户端的拦截器在官方`gRPC`内也只能支持注册一个，与服务端拦截器`interceptor chain`逻辑类似`warden`在客户端拦截器也做了相同处理，并且在客户端连接时进行注册，请看下面代码[代码位置](https://github.com/go-kratos/kratos/blob/master/pkg/net/rpc/warden/client.go)：
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```go
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// Use attachs a global inteceptor to the Client.
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// For example, this is the right place for a circuit breaker or error management inteceptor.
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func (c *Client) Use(handlers ...grpc.UnaryClientInterceptor) *Client {
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finalSize := len(c.handlers) + len(handlers)
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if finalSize >= int(_abortIndex) {
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panic("warden: client use too many handlers")
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}
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mergedHandlers := make([]grpc.UnaryClientInterceptor, finalSize)
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copy(mergedHandlers, c.handlers)
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copy(mergedHandlers[len(c.handlers):], handlers)
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c.handlers = mergedHandlers
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return c
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}
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// chainUnaryClient creates a single interceptor out of a chain of many interceptors.
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//
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// Execution is done in left-to-right order, including passing of context.
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// For example ChainUnaryClient(one, two, three) will execute one before two before three.
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func (c *Client) chainUnaryClient() grpc.UnaryClientInterceptor {
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n := len(c.handlers)
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if n == 0 {
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return func(ctx context.Context, method string, req, reply interface{},
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cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
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return invoker(ctx, method, req, reply, cc, opts...)
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}
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}
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return func(ctx context.Context, method string, req, reply interface{},
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cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
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var (
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i int
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chainHandler grpc.UnaryInvoker
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)
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chainHandler = func(ictx context.Context, imethod string, ireq, ireply interface{}, ic *grpc.ClientConn, iopts ...grpc.CallOption) error {
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if i == n-1 {
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return invoker(ictx, imethod, ireq, ireply, ic, iopts...)
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}
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i++
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return c.handlers[i](ictx, imethod, ireq, ireply, ic, chainHandler, iopts...)
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}
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return c.handlers[0](ctx, method, req, reply, cc, chainHandler, opts...)
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}
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}
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```
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如此完整的客户端拦截器逻辑就串联完成。
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# 实现自己的拦截器
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以服务端拦截器`logging`为例：
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```go
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// serverLogging warden grpc logging
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func serverLogging() grpc.UnaryServerInterceptor {
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return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
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// NOTE: handler执行之前的拦截代码：主要获取一些关键参数，如耗时计时、ip等
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// 如果自定义的拦截器只需要在handler执行后，那么可以直接执行handler
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startTime := time.Now()
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caller := metadata.String(ctx, metadata.Caller)
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if caller == "" {
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caller = "no_user"
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}
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var remoteIP string
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if peerInfo, ok := peer.FromContext(ctx); ok {
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remoteIP = peerInfo.Addr.String()
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}
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var quota float64
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if deadline, ok := ctx.Deadline(); ok {
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quota = time.Until(deadline).Seconds()
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}
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// call server handler
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resp, err := handler(ctx, req) // NOTE: 以具体执行的handler为分界线！！！
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// NOTE: handler执行之后的拦截代码：主要进行耗时计算、日志记录
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// 如果自定义的拦截器在handler执行后不需要逻辑，这可直接返回
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// after server response
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code := ecode.Cause(err).Code()
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duration := time.Since(startTime)
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// monitor
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statsServer.Timing(caller, int64(duration/time.Millisecond), info.FullMethod)
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statsServer.Incr(caller, info.FullMethod, strconv.Itoa(code))
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logFields := []log.D{
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log.KVString("user", caller),
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log.KVString("ip", remoteIP),
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log.KVString("path", info.FullMethod),
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log.KVInt("ret", code),
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// TODO: it will panic if someone remove String method from protobuf message struct that auto generate from protoc.
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log.KVString("args", req.(fmt.Stringer).String()),
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log.KVFloat64("ts", duration.Seconds()),
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log.KVFloat64("timeout_quota", quota),
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log.KVString("source", "grpc-access-log"),
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}
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if err != nil {
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logFields = append(logFields, log.KV("error", err.Error()), log.KV("stack", fmt.Sprintf("%+v", err)))
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}
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logFn(code, duration)(ctx, logFields...)
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return resp, err
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}
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}
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```
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# 内置拦截器
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## 自适应限流拦截器
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更多关于自适应限流的信息，请参考：[kratos 自适应限流](/doc/wiki-cn/ratelimit.md)
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```go
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package grpc
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import (
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pb "kratos-demo/api"
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"kratos-demo/internal/service"
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"github.com/go-kratos/kratos/pkg/conf/paladin"
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"github.com/go-kratos/kratos/pkg/net/rpc/warden"
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"github.com/go-kratos/kratos/pkg/net/rpc/warden/ratelimiter"
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)
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// New new a grpc server.
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func New(svc *service.Service) *warden.Server {
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var rc struct {
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Server *warden.ServerConfig
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}
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if err := paladin.Get("grpc.toml").UnmarshalTOML(&rc); err != nil {
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if err != paladin.ErrNotExist {
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panic(err)
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}
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}
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ws := warden.NewServer(rc.Server)
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// 挂载自适应限流拦截器到 warden server，使用默认配置
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limiter := ratelimiter.New(nil)
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ws.Use(limiter.Limit())
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// 注意替换这里：
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// RegisterDemoServer方法是在"api"目录下代码生成的
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// 对应proto文件内自定义的service名字，请使用正确方法名替换
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pb.RegisterDemoServer(ws.Server(), svc)
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ws, err := ws.Start()
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if err != nil {
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panic(err)
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}
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return ws
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}
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```
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# 扩展阅读
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[warden快速开始](warden-quickstart.md) [warden基于pb生成](warden-pb.md) [warden负载均衡](warden-balancer.md) [warden服务发现](warden-resolver.md)
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-------------
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[文档目录树](summary.md)
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