How to catch http client request exceptions in node.js


Question

I've got a node.js app that I want to use to check if a particular site is up and returning the proper response code. I want to be able to catch any errors that come up as the domain name isn't resolving or the request is timing out. The problem is is that those errors cause Node to crap out. I'm new to this whole asynchronous programming methodology, so I'm not sure where to put my try/catch statements.

I have an ajax call that goes to something like /check/site1. Server side that calls a function which attempts to make a connection and then return the statusCode. It's a very simple function, and I've wrapped each line in a try/catch and it never catches anything. Here it is:

function checkSite(url){
    var site = http.createClient(80, url);
    var request = site.request('GET', '/', {'host': url});
    request.end();
    return request;
  }

Even with each of those lines wrapped in a try/catch, I will still get uncaught exceptions like EHOSTUNREACH and so on. I want to be able to catch those and return that to the ajax call.

Any recommendations on what to try next?

1
37
3/8/2016 8:16:27 PM

Accepted Answer

http.createClient has been deprecated.

Here is a quick example of how to handle errors using the new http.request:

var http = require("http");

var options = {
    host : "www.example.com"
};

var request = http.request(options, function(req) {
    ...
});
request.on('error', function(err) {
    // Handle error
});

request.end();
60
11/7/2014 3:59:48 PM

I stumbled across another solution while I was researching a similar problem. http.Client emits an 'error' event if a connection can't be established for any reason. If you handle this event then the exception won't be thrown:

var http = require('http');
var sys = require('sys');

function checkSite(url) {
    var site = http.createClient(80, url);
    site.on('error', function(err) {
        sys.debug('unable to connect to ' + url);
    });
    var request = site.request('GET', '/', {'host': url});
    request.end();
    request.on('response', function(res) {
        sys.debug('status code: ' + res.statusCode);
    });
}

checkSite("www.google.com");
checkSite("foo.bar.blrfl.org");

Of course, the connection error and the response to the request both arrive asynchronously, meaning that simply returning the request won't work. Instead, you'd have to notify the caller of the results from within the event handlers.


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