examples: improve grammar in the interceptor example (#7163)

examples/features/interceptor/README.md

@@ -1,9 +1,10 @@
 # Interceptor
 
 gRPC provides simple APIs to implement and install interceptors on a per
-ClientConn/Server basis. Interceptor intercepts the execution of each RPC call.
-Users can use interceptors to do logging, authentication/authorization, metrics
-collection, and many other functionality that can be shared across RPCs.
+ClientConn/Server basis. Interceptors act as a layer between the application and
+gRPC and can be used to observe or control the behavior of gRPC. Interceptors
+can be used for logging, authentication/authorization, metrics collection, and
+other functionality that is shared across RPCs.
 
 ## Try it
 
@@ -17,102 +18,102 @@ go run client/main.go
 
 ## Explanation
 
-In gRPC, interceptors can be categorized into two kinds in terms of the type of
-RPC calls they intercept. The first one is the **unary interceptor**, which
-intercepts unary RPC calls. And the other is the **stream interceptor** which
-deals with streaming RPC calls. See
-[here](https://grpc.io/docs/guides/concepts.html#rpc-life-cycle) for explanation
-about unary RPCs and streaming RPCs. Each of client and server has their own
-types of unary and stream interceptors. Thus, there are in total four different
-types of interceptors in gRPC.
+gRPC has separate interceptors for unary RPCs and streaming RPCs. See the
+[gRPC docs](https://grpc.io/docs/guides/concepts.html#rpc-life-cycle) for an
+explanation about unary and streaming RPCs. Both the client and the server have
+their own types of unary and stream interceptors. Thus, there are four different
+types of interceptors in total.
 
 ### Client-side
 
 #### Unary Interceptor
 
-[`UnaryClientInterceptor`](https://godoc.org/google.golang.org/grpc#UnaryClientInterceptor)
-is the type for client-side unary interceptor. It is essentially a function type
-with signature: `func(ctx context.Context, method string, req, reply
-interface{}, cc *ClientConn, invoker UnaryInvoker, opts ...CallOption) error`.
-An implementation of a unary interceptor can usually be divided into three
-parts: pre-processing, invoking RPC method, and post-processing.
+The type for client-side unary interceptors is
+[`UnaryClientInterceptor`](https://godoc.org/google.golang.org/grpc#UnaryClientInterceptor).
+It is essentially a function type with signature: `func(ctx context.Context,
+method string, req, reply interface{}, cc *ClientConn, invoker UnaryInvoker,
+opts ...CallOption) error`. Unary interceptor implementations can usually be
+divided into three parts: pre-processing, invoking the RPC method, and
+post-processing.
 
 For pre-processing, users can get info about the current RPC call by examining
-the args passed in, such as RPC context, method string, request to be sent, and
-CallOptions configured. With the info, users can even modify the RPC call. For
-instance, in the example, we examine the list of CallOptions and see if call
-credential has been configured. If not, configure it to use oauth2 with token
-"some-secret-token" as fallback. In our example, we intentionally omit
-configuring the per RPC credential to resort to fallback.
+the args passed in. The args include the RPC context, method string, request to
+be sent, and the CallOptions configured. With this info, users can even modify
+the RPC call. For instance, in the example, we examine the list of CallOptions
+and check if the call credentials have been configured. If not, the interceptor
+configures the RPC call to use oauth2 with a token "some-secret-token" as a
+fallback. In our example, we intentionally omit configuring the per RPC
+credential to resort to the fallback.
 
-After pre-processing is done, use can invoke the RPC call by calling the
-`invoker`.
+After pre-processing, users can invoke the RPC call by calling the `invoker`.
 
-Once the invoker returns the reply and error, user can do post-processing of the
-RPC call. Usually, it's about dealing with the returned reply and error. In the
-example, we log the RPC timing and error info.
+Once the invoker returns, users can post-process the RPC call. This usually
+involves dealing with the returned reply and error. In the example, we log the
+RPC timing and error info.
 
-To install a unary interceptor on a ClientConn, configure `Dial` with
-`DialOption`
-[`WithUnaryInterceptor`](https://godoc.org/google.golang.org/grpc#WithUnaryInterceptor).
+To install a unary interceptor on a ClientConn, configure `Dial` with the
+[`WithUnaryInterceptor`](https://godoc.org/google.golang.org/grpc#WithUnaryInterceptor)
+`DialOption`.
 
 #### Stream Interceptor
 
-[`StreamClientInterceptor`](https://godoc.org/google.golang.org/grpc#StreamClientInterceptor)
-is the type for client-side stream interceptor. It is a function type with
-signature: `func(ctx context.Context, desc *StreamDesc, cc *ClientConn, method
-string, streamer Streamer, opts ...CallOption) (ClientStream, error)`. An
-implementation of a stream interceptor usually include pre-processing, and
-stream operation interception.
-
-For pre-processing, it's similar to unary interceptor.
-
-However, rather than doing the RPC method invocation and post-processing
-afterwards, stream interceptor intercepts the users' operation on the stream.
-First, the interceptor calls the passed-in `streamer` to get a `ClientStream`,
-and then wraps around the `ClientStream` and overloading its methods with
-intercepting logic. Finally, interceptors returns the wrapped `ClientStream` to
-user to operate on.
-
-In the example, we define a new struct `wrappedStream`, which is embedded with a
-`ClientStream`. Then, we implement (overload) the `SendMsg` and `RecvMsg`
-methods on `wrappedStream` to intercept these two operations on the embedded
+The type for client-side stream interceptors is
+[`StreamClientInterceptor`](https://godoc.org/google.golang.org/grpc#StreamClientInterceptor).
+It is a function type with signature: `func(ctx context.Context, desc
+*StreamDesc, cc *ClientConn, method string, streamer Streamer, opts
+...CallOption) (ClientStream, error)`. An implementation of a stream interceptor
+usually includes pre-processing, and stream operation interception.
+
+The pre-processing is similar to unary interceptors.
+
+However, rather than invoking the RPC method followed by post-processing, stream
+interceptors intercept the users' operations on the stream. The interceptor
+first calls the passed-in `streamer` to get a `ClientStream`, and then wraps the
+`ClientStream` while overloading its methods with the interception logic.
+Finally, the interceptor returns the wrapped `ClientStream` to user to operate
+on.
+
+In the example, we define a new struct `wrappedStream`, which embeds a
+`ClientStream`. We then implement (overload) the `SendMsg` and `RecvMsg` methods
+on `wrappedStream` to intercept these two operations on the embedded
 `ClientStream`. In the example, we log the message type info and time info for
 interception purpose.
 
-To install the stream interceptor for a ClientConn, configure `Dial` with
-`DialOption`
-[`WithStreamInterceptor`](https://godoc.org/google.golang.org/grpc#WithStreamInterceptor).
+To install a stream interceptor for a ClientConn, configure `Dial` with the
+[`WithStreamInterceptor`](https://godoc.org/google.golang.org/grpc#WithStreamInterceptor)
+`DialOption`.
 
 ### Server-side
 
-Server side interceptor is similar to client side, though with slightly
-different provided info.
+Server side interceptors are similar to client side interceptors, with slightly
+different information provided as args.
 
 #### Unary Interceptor
 
-[`UnaryServerInterceptor`](https://godoc.org/google.golang.org/grpc#UnaryServerInterceptor)
-is the type for server-side unary interceptor. It is a function type with
-signature: `func(ctx context.Context, req interface{}, info *UnaryServerInfo,
-handler UnaryHandler) (resp interface{}, err error)`.
+The type for server-side unary interceptors is
+[`UnaryServerInterceptor`](https://godoc.org/google.golang.org/grpc#UnaryServerInterceptor).
+It is a function type with signature: `func(ctx context.Context, req
+interface{}, info *UnaryServerInfo, handler UnaryHandler) (resp interface{}, err
+error)`.
 
-Refer to client-side unary interceptor section for detailed implementation
-explanation.
+Refer to the client-side unary interceptor section for a detailed implementation
+and explanation.
 
-To install the unary interceptor for a Server, configure `NewServer` with
-`ServerOption`
-[`UnaryInterceptor`](https://godoc.org/google.golang.org/grpc#UnaryInterceptor).
+To install a unary interceptor on a Server, configure `NewServer` with the
+[`UnaryInterceptor`](https://godoc.org/google.golang.org/grpc#UnaryInterceptor)
+`ServerOption`.
 
 #### Stream Interceptor
 
-[`StreamServerInterceptor`](https://godoc.org/google.golang.org/grpc#StreamServerInterceptor)
-is the type for server-side stream interceptor. It is a function type with
-signature: `func(srv interface{}, ss ServerStream, info *StreamServerInfo,
-handler StreamHandler) error`.
+The type for server-side stream interceptors is
+[`StreamServerInterceptor`](https://godoc.org/google.golang.org/grpc#StreamServerInterceptor).
+It is a function type with the signature: `func(srv interface{}, ss
+ServerStream, info *StreamServerInfo, handler StreamHandler) error`.
 
-Refer to client-side stream interceptor section for detailed implementation
-explanation.
+Refer to the client-side stream interceptor section for a detailed
+implementation and explanation.
+
+To install a stream interceptor on a Server, configure `NewServer` with the
+[`StreamInterceptor`](https://godoc.org/google.golang.org/grpc#StreamInterceptor)
+`ServerOption`.
 
-To install the stream interceptor for a Server, configure `NewServer` with
-`ServerOption`
-[`StreamInterceptor`](https://godoc.org/google.golang.org/grpc#StreamInterceptor).