CODEWITHSUNDEEP
node.jshttpkoa
MattG
MattG

Reputation: 6445

Detect client disconnection in Koa

How can my node.js Koa server detect and log that a client has disconnected before a response can be sent.

Normally the sequence is:

  1. node.js koa server starts
  2. client sends http request
  3. node.js koa server spends some time servicing the request
  4. node.js koa server sends response to client

If the client disconnects after 2 is finished, but before 4 is complete, can node.js Koa detect and log this?

I have tested using this simple script and running curl from another terminal, then during the 10 second delay for node.js to sleep, I terminate (ctrl-c) the curl command. 

const Koa = require('koa');
const app = new Koa();

/**
 * synchronously delay/sleep/block for time ms
 */
const delay = time => new Promise(res=> {
    console.log(`About to sleep for ${time} ms`)
    setTimeout(res,time)
});

app.on('error', (err, ctx) => {
    console.error('server error', err, ctx)
});

app.use(async ctx => {
  ctx.req.on('close', () => {
    console.log('Request closed');
  });

  console.log('Hello World Started')

  await delay(10000)

  console.log('Hello World Ended');
  ctx.body = 'Hello World !!!';

});

app.listen(3000, () => console.log('running on port 3000'));

The ctx.req.on('close' event is emitted a single time in both cases:

  1. Client disconnects before response sent.
  2. Server responds to client which is still connected, waiting for response.

I am using:

node --version
v13.8.0

Discussion on when different versions of node emit req.on('close') event here: https://github.com/nodejs/node/issues/31394.

Assuming there is no specific "the client has disconnected before you have sent a response" event, what is the best pattern, to detect that situation in general, so I can log it.

Upvotes: 1

Views: 1383

Answers (1)

Kiru
Kiru

Reputation: 11

We could use a variable to assess this. Code mentioned below logs the error message when client is closed before the request processing is complete. This is kind of a dirty fix, but it works 

const Koa = require('koa');
const app = new Koa();

/**
 * synchronously delay/sleep/block for time ms
 */
const delay = time => new Promise(res=> {
    console.log(`About to sleep for ${time} ms`)
    setTimeout(res,time)
});

app.on('error', (err, ctx) => {
    console.error('server error', err, ctx)
});

app.use(async ctx => {
  let requestProcessingCompleted = false    
  ctx.req.on('close', () => {
    console.log('Request closed');
    if(!requestProcessingCompleted){
        console.log("Client connection closed before request processing completed")
    }
  });

  console.log('Hello World Started')

  await delay(10000)

  console.log('Hello World Ended');
  ctx.body = 'Hello World !!!';
  requestProcessingCompleted = true
});

app.listen(3000, () => console.log('running on port 3000'));

Upvotes: 1

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