ssh2-sftp-client crashes Node process with no error and exit code 0

[LEQADA]

I have an issue which looks exactly like this one #49

I'm using:

• Node.js 12
• ssh2-sftp-client 4.1.0

Here is a minimal reproducible code

const Client = require('ssh2-sftp-client')
const inspect = require('util').inspect

const sftpClient = new Client();

sftpClient.on('error', (err) => {
  console.log('SFTP client emitted ERROR: ' + inspect(err))
})
sftpClient.on('end', () => {
  console.log('SFTP client emitted END')
})
sftpClient.on('finish', () => {
  console.log('SFTP client emitted FINISH')
})
sftpClient.on('close', () => {
  console.log('SFTP client emitted CLOSE')
})

const options = {
  host: '',
  port: '22',
  username: '',
  password: ''
};

// below infinite loop is to simulate large number of 
// connections in my production code
(async () => {
  while (true) {
    try {
      await new Promise(resolve => setTimeout(() => resolve(sftpClient.connect(options)), 1000))
    } catch {
      console.log('boom')
    }
  }
})()

process.on('exit', code => console.log(`Catched!. Exit code: ${code}`))

process.on('uncaughtException', (err, origin) => {
  console.error('Unhandled exception. Please handle!', err.stack || err)
  console.error(`Origin: ${JSON.stringify(origin)}`)
})

process.on('unhandledRejection', (err, promise) => {
  console.error('Unhandled promise rejection. Please handle!', promise, err.stack || err)
})

process.on('warning', (warning) => {
  console.warn(warning.name)
  console.warn(warning.message)
  console.warn(warning.stack)
})

process.on('rejectionHandled', (promise) => {
  console.log('rejectionHandled event triggered')
})

As you can see, it shouldn't escape the infinite loop unless there is an Error. And it in fact does not for some iterations but eventually it escapes (usually after <10 iterations). And the only log I see is

SFTP client emitted END
Catched!. Exit code: 0

On the SFTP server side I have the following limitations in the sshd_config file

MaxSessions 1
MaxStartups 1

I don't know how is it possible to exit with code 0 without any error trace without actually calling process.exit(0). This makes investigation even harder, because I don't know what to look for.

[theophilusx]

I'll need to look at this closer. However, I do see a problem with your code. You are using the same client object to try and make all the connections. You can't do that. You need to create a new Client() object for each connection or you need to end each connection before trying to open another one.

[theophilusx]

Not 100% sure, but I think your code is faulty. Apart from the mentioned issue of trying to do multiple connections with the same client concurrently, I suspect that errors are not able to bubble up from the connect promise due to how you are calling them. It looks to me like you are resolving the promise you wrap the call to connect with immediately, so there is nothing waiting on the connect promise itself.

With the below code, errors are created when the remote server starts rejecting the connections. If I don't limit the while loop, I end up just getting memory and gc errors from node (which would be expected).

There is one minor issue though. The close listener should be getting a boolean passed to it which states whether the connection was closed due to errors or just after a normal request. For some reason, it is getting undefined, so I need to look at that.

'use strict';

const dotenvPath = __dirname + '/../.env';

require('dotenv').config({path: dotenvPath});

const Client = require('../src/index');
const inspect = require('util').inspect;

const config = {
  host: process.env.SFTP_SERVER,
  username: process.env.SFTP_USER,
  password: process.env.SFTP_PASSWORD,
  port: process.env.SFTP_PORT || 22
};

let clients = [];
let promises = [];
let count = 0;

function makeConnection() {
  count++;
  let c = new Client();
  c.on('error', err => {
    console.log('SFTP client emitted ERROR: ' + inspect(err));
  });
  c.on('end', () => {
    console.log('SFTP client emitted END');
  });
  c.on('finish', () => {
    console.log('SFTP client emitted FINISH');
  });
  c.on('close', hadError => {
    console.log(`SFTP client emitted CLOSE: Had Error: ${hadError}`);
  });
  clients.push(c);
  promises.push(c.connect(config));
  console.log(`Connection ${count} requested`);
}

process.on('exit', code => console.log(`Catched!. Exit code: ${code}`));

process.on('uncaughtException', (err, origin) => {
  console.error('Unhandled exception. Please handle!', err.stack || err);
  console.error(`Origin: ${JSON.stringify(origin)}`);
});

process.on('unhandledRejection', (err, promise) => {
  console.error(
    'Unhandled promise rejection. Please handle!',
    promise,
    err.stack || err
  );
});

process.on('warning', warning => {
  console.warn(warning.name);
  console.warn(warning.message);
  console.warn(warning.stack);
});

process.on('rejectionHandled', () => {
  console.log('rejectionHandled event triggered');
});

let conCount = 0;
let maxConn = 100;

while (conCount < maxConn) {
  try {
    conCount++;
    setTimeout(() => makeConnection(), 1000);
  } catch (err) {
    console.log(`Boom: ${err.message}`);
  }
}

[theophilusx]

There is something very odd going on, but tracking it down is difficult. I'm fairly certain it is something within the SSH2 module and it is at the networking layer. Something is causing node to exit early. The connections appear to be successful and you can even query them. However, the script just seems to exit (without any errors) before the final then block in the promise chain is completed. However, when I first run the test script, it works fine. If I then immediately run it a second time, it exits early. If I wait (until all TIME_WAIT tcp connections have expired - usually 2 minutes on most Linux systems) it runs fine.

I have made some changes to the code in the fix-error-propogation branch of the repository. I have added the ability to set a client name to be associated with each client to make it easier to see which client is throwing errors etc e.g. you can do

let client = new Client('some-name');

I have also added a check which will generate an error if you try to connect using a client which is already connected.

The test script I'm using is also in the examples directory of the repository. It is called loadup2.js and I have copied it below.

'use strict';

const dotenvPath = __dirname + '/../.env';

require('dotenv').config({path: dotenvPath});

const Client = require('../src/index');

const config = {
  host: process.env.SFTP_SERVER,
  username: process.env.SFTP_USER,
  password: process.env.SFTP_PASSWORD,
  port: process.env.SFTP_PORT || 22
};

let maxConnections = 15;
let clientCount = 0;
let clients = [];
let promises = [];

function makeConnection() {
  clientCount++;
  let c = new Client(`Client-${clientCount}`);
  c.on('error', err => {
    console.log(`${c.clientName}: Error - ${err.message}`);
  });
  clients.push(c);
  promises.push(
    c
      .connect(config)
      .then(() => {
        console.log(`${c.clientName}: Connected`);
        return c.cwd();
      })
      .then(d => {
        console.log(`${c.clientName}: ${d}`);
        return c.end();
      })
      .then(() => {
        console.log(`${c.clientName}: Connection closed`);
        return true;
      })
  );
  console.log(`Connection ${clientCount} requested`);
}

while (clientCount < maxConnections) {
  makeConnection();
}

Promise.all(promises)
  .then(vals => {
    console.log('Script Completed');
    console.dir(vals);
  })
  .catch(err => {
    console.log(`First Error: ${err.message}`);
  });

I have done a lot of checking and am fairly confident that the ssh2-sftp-module is handling errors when they are generated correctly. The problem seems to be that whatever is causing node to exit is not thorwing/rasiing any error or exception, so there is nothing to catch and respond to.

Next Steps

1. Write a script which only uses ssh2 and sshsftp-streams to see if a similar problem occurs. If it oes, we can then raise an issue against those modules.

2. Test with different node versions to see if the same issue exists for all versions.

[theophilusx]

Now have a work-around for this issue which is currently being tested.

[theophilusx]

Work-around for end() event appears to fix the issue and all tests pass.

[lojzatran]

@theophilusx can you share your workaround for this issue? I'm also experiencing it and it's quite critical for us. Thank you.

[theophilusx]

The workaround is now in the main branch of the repository. I will probably release an updated version in the next day or so. In the meantime, you can use the repository code directly. The basic workaround was to add a listener for the end event which will reject the connect promise if an end event is triggered during the connection process. See the repository for details. Lam Tran <notifications@github.com> writes:

…

@theophilusx can you share your workaround for this issue? I'm also experiencing it and it's quite critical for us. Thank you. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub, or mute the thread.

-- Tim Cross

[KshamaShrey]

Hi Team,

Even I am facing this issue.Could you please let me know how you have fixed this issue? Thanks