Server Streaming API

In server streaming API the client will send one request to the server and in response will receive many responses from the server.

We will develop:

A streaming server which will take ONE GreetManyTimesRequest that contains a Greeting
It will return many GreetManyTimesResponse that contains a result string

Step 1 – Creating proto files and compiling it

compiling

GRPC_TOOLS_PLUGIN="$HOME/AppData/Roaming/npm/grpc_tools_node_protoc_plugin.cmd" && C:/Users/deepak.sood/Downloads/protoc-3.13.0-win64/bin/protoc.exe -I=. ./protos/greet.proto --js_out=import_style=commonjs,binary:./server --grpc_out=./server --plugin=protoc-gen-grpc=$GRPC_TOOLS_PLUGIN

Step 2 – implementing server

var greets = require('../server/protos/greet_pb');
var service = require('../server/protos/greet_grpc_pb');

var grpc = require('grpc');

/*
Implementing the greet RPC method
*/

// this should be the same name as our API as present in greet_grpc_pb file
function greet(call, callback) {

    // creating the actual greeting response
    var greeting = new greets.GreetResponse();

    //now we have our greet response, so let's now construct the response
    // call is used as it will have all the information from line 11 when called
    //getGreeting is from the GreetRequest object
    greeting.setResult(
        "Hello" + call.request.getGreeting().getFirstName()
    )

    callback(null, greeting); // passed in the greeting to be passed on to the client 


}


function greetManyTimes(call, callback) {
    // in order to get the streaming we need to get the firstName
    var firstName = call.request.getGreeting().getFirstName();

    let count = 0, intervalID = setInterval(function () {
        //greet many times response
        var greetmanyTimesResponse = new greets.GreetManyTimesResponse();
        greetmanyTimesResponse.setResult(firstName);

        //setup streaming
        call.write(greetmanyTimesResponse);
        if(++count>9){
            clearInterval(intervalID)
            call.end(); // we have sent all messages
        }
        
    })

}

function main() {
    var server = new grpc.Server();
    server.addService(service.GreetServiceService, { greet: greet, greetManyTimes: greetManyTimes })
    server.bind("127.0.0.1:50051", grpc.ServerCredentials.createInsecure());
    server.start();

    console.log("Server running on port 127.0.0.1:50051")
}

main();

Let’s test this

Step 3 – Implementing Client

function callGreetManyTimes(){
    var client = new service.GreetServiceClient(
        'localhost:50051',
        grpc.credentials.createInsecure()
    )

    var request = new greets.GreetManyTimesRequest();

    var greeting = new greets.Greeting();
    greeting.setFirstName("Deepak")
    greeting.setLastName("Sood")

    request.setGreeting(greeting);

    //passing empty functions as I expect nothing
    //equating it to the client so that I can invoke certain methods
    var call = client.greetManyTimes(request, () =>{})

    call.on('data', (response) =>{
        console.log('client streaming response ', response.getResult());
    })

    call.on('status', (status) =>{
        console.log(status);
    })

    call.on('error', (error) =>{
        console.error(error);
    })

    call.on('end', () =>{
        console.error('Streaming Ended !');
    })

}


callGreetManyTimes()

And that’s how it works !!

About the author

Deepak Sood