访问grpc流变量以在Node中长时间运行进程

Question

I am using Node.js to connect to a server using gRPC that performs a long running task.

The server sends a unidirectional stream to the client (the Node.js app) while the job is in progress. I need to implement a Stop button and am told that closing the gRPC stream will stop the job in progress.

This is currently my code:

let express = require('express'),
    router = express.Router(),
    grpc = require('grpc'),
    srv = grpc.load(__dirname + '/job_handler.proto').ns;

let startJob = (jobID, parameters) => srv.createJob(jobID, parameters);

router.post('/jobs', (req, res) => {
    let lengthyOperation = startJob(jobID, parameters);
    lengthyOperation.on('data', (data) => {
        console.log(`Data from lengthy operation: ${data}`);
    });

    lengthyOperation.on('end', () =>
        console.log('Lengthy operation completed');
    });

    res.setHeader('Location', `/jobs/${jobID}`);
    res.status(202).send();
});

As you can see, I send an HTTP 202 response to the client upon creating the job and it continues asynchronously in the background.

Questions:

1. How do I close the stream?
2. How do I access the lengthyOperation variable to do so?

Answer 1

The lengthyOperation object has a cancel method that cancels the call. So, when you want to stop the stream, just call lengthyOperation.cancel() .

Note that when you do this, it will cause the call to end with an error. I would recommend adding a lengthyOperation.on('error', ...) handler to handle that error.