Sequential execution of requests

Question

How can I call functions one-by-one after completing? I have code like that, which must be executed continuously.

For example, I have:

var Connection = require('ssh2');

var c = new Connection();
c.on('connect', function() {
  console.log('Connection :: connect');
});
c.on('ready', function() {
  console.log('Connection :: ready');
  c.exec('uptime', function(err, stream) {
    if (err) throw err;
    stream.on('data', function(data, extended) {
      console.log((extended === 'stderr' ? 'STDERR: ' : 'STDOUT: ')
                  + data);
    });
    stream.on('end', function() {
      console.log('Stream :: EOF');
    });
    stream.on('close', function() {
      console.log('Stream :: close');
    });
    stream.on('exit', function(code, signal) {
      console.log('Stream :: exit :: code: ' + code + ', signal: ' + signal);
      c.end();
    });
  });
});
c.on('error', function(err) {
  console.log('Connection :: error :: ' + err);
});
c.on('end', function() {
  console.log('Connection :: end');
});
c.on('close', function(had_error) {
  console.log('Connection :: close');
});
c.connect({
  host: '192.168.100.100',
  port: 22,
  username: 'frylock',
  privateKey: require('fs').readFileSync('/here/is/my/key')
});

In what way can I call several functions one-by-one? When the connection to the ssh2 server is established, and the first request is executed, I have to parse the output of this request and send another request with data from the previous request.

I have functions which can do all this; the only problem is how to make another request after the first one is completed.

score 0 · Accepted Answer · edited May 23 '17 at 12:28

You can use nested callbacks. In the 'end' handler of each request, create a new connection and setup its end handler. Nest until needed. Similar to:

c.on('end', function() {
    // after c is done, create newC
    var newC = new Connection();
    newC.on('end', function() {
         // more if needed.
    });
});

Another approach is to use some library for promises, like Q, which clears up the syntax a lot.

You can also take a look at this question: Understanding promises in node.js

score 0 · Answer 2 · answered Oct 25 '13 at 01:09

0

From the sounds of it, you might want to look into a control flow node module such as async. Also you shouldn't need to tear down the connection just to execute another command on the same server.

answered Oct 25 '13 at 01:09

mscdex

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Sequential execution of requests

2 Answers2