node.js distinguishing errors when making http request

Question

My node.js application is using http.request to the REST API http://army.gov/launch-nukes and I need to distinguish between three possible cases:

• Success -- The server replies in the affirmative. I know my enemies are destroyed.
• Failure -- Either I have received error from the server, or was unable to connect to server. I still have enemies.
• Unknown -- After establishing a connection to the server, I have sent the request -- but not sure what happened. This could mean the request never made it to the server, or the server response to me never made it. I may or may not have just started a world war.

As you can see, it's very important for me to distinguish the Failure and Unknown case, as they have very different consequences and different actions I need to take.

I would also very much like to use http Keep-Alive -- as what can I say, I'm a bit of a war-monger and plan on making lots of requests in bursts (and then nothing for long periods of time)

--

The core of the question is how to separate a connection-error/time-out (which is a Failure) from an error/timeout that occurs after the request is put on the wire (which is an Unknown).

In psuedo-code logic I want this:

var tcp = openConnectionTo('army.gov') // start a new connection, or get an kept-alive one tcp.on('error', FAILURE_CASE); tcp.on('connectionEstablished',  function (connection) {         var req = connection.httpGetRequest('launch-nukes');        req.on('timeout', UNKNOWN_CASE);        req.on('response', /* read server response and decide FAILURE OR SUCCESS */);    } ) 

Answer 1

Here is an example:

var http = require('http');  var options = {   hostname: 'localhost',   port: 7777,   path: '/',   method: 'GET' };  var req = http.request(options, function (res) {   // check the returned response code   if (('' + res.statusCode).match(/^2\d\d$/)) {     // Request handled, happy   } else if (('' + res.statusCode).match(/^5\d\d$/))     // Server error, I have no idea what happend in the backend     // but server at least returned correctly (in a HTTP protocol     // sense) formatted response   } });  req.on('error', function (e) {   // General error, i.e.   //  - ECONNRESET - server closed the socket unexpectedly   //  - ECONNREFUSED - server did not listen   //  - HPE_INVALID_VERSION   //  - HPE_INVALID_STATUS   //  - ... (other HPE_* codes) - server returned garbage   console.log(e); });  req.on('timeout', function () {   // Timeout happend. Server received request, but not handled it   // (i.e. doesn't send any response or it took to long).   // You don't know what happend.   // It will emit 'error' message as well (with ECONNRESET code).    console.log('timeout');   req.abort(); });  req.setTimeout(5000); req.end(); 

I recommend you play with it using netcat, ie.:

$ nc -l 7777 // Just listens and does not send any response (i.e. timeout)  $ echo -e "HTTP/1.1 200 OK\n\n" | nc -l 7777 // HTTP 200 OK  $ echo -e "HTTP/1.1 500 Internal\n\n" | nc -l 7777 // HTTP 500 

(and so on...)