Example grpc chat client-server

gRPC uses HTTP/2 for transport and protocol Buffers as the interface description language. HTTP/2 is multiplexed and it can support multiple requests in parallel over a single TCP connection.

With gRPC we can define our service once in a .proto file and implement clients and servers.

Protocol buffers allow serialization and deserialization of structured data, with the goal to provide a faster way to make systems communicate due to optimized serialization and deserialization

Protobuf is a binary message format, and because it is in binary, serialization and de-serialization is fast and the size of the message is lower than JSON & XML.

Once you've defined your messages, you run the protocol buffer compiler for your application's language on your .proto file to generate data access classes for the client and server

Installation:

 go get github.com/golang/protobuf/protoc-gen-go  
 export PATH="$PATH:$(go env GOPATH)/bin" 

Working with grpc:

1. Define the datastructures(protocol buffer message types) and APIs required in the proto file

2. Once you've defined your messages, you run the protocol buffer compiler

To compile the proto file and generate code:
    * install protoc-gen
    * create a directory (chat) where we want the files generated by protoc to go into.
    * Run the command to compile chat.proto and generate code
    
        protoc --go_out=plugins=grpc:chat chat.proto
        
        General syntax : protoc -I=$SRC_DIR --go_out=$DST_DIR $SRC_DIR/chat.proto

3 Implement the chat service

chat.go in package chat is the implementation of the ChatServer, the apis defined in proto file Uses the interface methods, register chat methods with grpc server

4. Start the grpc server to provide handlers for the services (apis) defined above (server.go)

   Start grpc server 
   In server.go -> 
       The grpc server is started
       Listeners are added for chat service (register the chat service defined in the proto file)
       
   

5. Send messages to the server from a client:

client.go initializes a client and sends a message using the method defined in the proto file (sayHello) (Refer chat.pb.go for available methods and data structures)

6. Streaming is possible using the multiplexing capability provided by http2

Server Streaming RPC: The client sends a single request and the server can send back multiple responses (Ex: The server fetches data in parts and returns it to client soon as it is available) Client Streaming RPC: Where the client sends multiple requests and the server only sends back a single response ( Ex. client uploads a large file in parts to the server) Bidirectional Streaming RPC: Where both the client and server send messages to each other at the same time without waiting for a response.

References

• https://tutorialedge.net/golang/go-grpc-beginners-tutorial/
• https://developers.google.com/protocol-buffers/docs/gotutorial