File Download and Client Disconnection?

Question

Given the following code:

async function (req, res, next) {
  const fd = await fs.open("myfile.txt")
  fs.createReadStream(null, { fd, autoClose: false })
    .on('error', next)
    .on('end', () => fs.close(fd))
    .pipe(res)
}

What happens if the client disconnects before downloading the entire file? ie will end still be called or is the file descriptor leaked, and if so how can I fix it? If `end´ is called does that mean that the entire file is read even though the client no longer listens for it?

Note, I know I could do this without fd but this is a simplification of more complex code.

Answer 1

It looks like file will not be closed, or at least your end event handler will not be called.

You can create test for that, but here's mine:

const http = require('http');
const fs   = require('fs');

var server = http.createServer(function (req, res) {
    console.log('server request received');
    const fd = fs.openSync('myfile.txt', 'r');
    fs.createReadStream(null, { fd, autoClose: false })
        .on('error', err => {
            console.error('file error', err);
        })
        .on('end', () => {
            console.log('file end');
            fs.close(fd);
        })
        .on('close', () => {
            console.log('file closed');
        })
        .pipe(res)
            .on('error', err => console.error('server stream error', err))
            .on('end', () => console.log('server stream end'))
            .on('close', () => console.log('server stream closed'))
    ;
});

server.listen(0, 'localhost', () => {
    const address = server.address();

    var req = http.request({port: address.port}, function (res) {
        res.on('data', data => {
            console.log('response data');
            // Comment next line to read whole file.
            req.abort();
        });
        res.on('end', () => {
            console.log('response ended');
            setTimeout(() => server.close(), 1000);
        });
        req.once('abort', () => {
            console.log('request aborted');
        });
    });

    req.end(() => {
        console.log('request sent');
    });
});

I removed async/wait for simplicity of running test.

When req.abort() is called, i get following output:

request sent
server request received
response data
request aborted
response ended
server stream closed

After commenting that line, and allowing code to read whole file:

request sent
server request received
response data
response data
response data
response data
response data
response data
file end
response data
response ended

To create test myfile.txt i used following command:

dd if=/dev/zero of=myfile.txt bs=1k count=200