Node.js and Express - Strange Http Status Codes

Tue, 16 Jul 2013 16:23:43 +0000

In a Nutshell

Sending a response in Express with a call like res.send(status, body) will send body as the status code if it is numeric - ignoring status. This is due to a fudge for backwards compatibility.

The Details

As part of a project I'm working on, I'm writing a service using node.js and Express. This service exposes some entities in a MongoDB database through a REST API. Typically I hit this API through client-side Javascript, but in some places I want to hit the same API from some C# code - and I don't want to have to create classes for everything. I've got a funky library for this which I'll be publishing soon, but it helped me find a problem.

Testing the C# code showed me something that was a bit odd - GETs and POSTSs were working fine, but PUTs and DELETEs were showing an HTTP Status code of ‘1’ (which isn’t a valid code). Here’s the what I was seeing:

Checking the node server showed the same thing - DELETEs were returning status 1.

The server code is very lightweight so it’s quick to see what’s going on:

[code lang=“js”]exports.deleteUser = function(request, response) {

// Get the id.
var id = request.params.id;
// Log the user id.
console.log('Deleting user: ' + id);
// Get the users collection, delete the object.
db.collection(collectionName, function(err, collection) {
collection.remove({'_id':new BSON.ObjectID(id)}, {safe:true}, function(err, result) {
if (err) {
console.log('Error deleting user: ' + err);
response.send(400, {'error':'An error has occurred'});
} else {
console.log('' + result + ' document(s) deleted');
response.send(result);
}
});
});

}[/code]

The function is called successfully, so we hit ‘response.send’. This looks like the problem - the result object is simply the number one, checking the Express Api Documentation for send shows some examples like this:

res.send(new Buffer('whoop'));
res.send({ some: 'json' });
res.send('some html');
res.send(404, 'Sorry, we cannot find that!');
res.send(500, { error: 'something blew up' });
res.send(200);

So just like the final example, we’re sending the code 1, which is not valid. What surprised me was what happened when I changed the send call to the below:

[code lang=“js”]response.send(200, result)[/code]

I was still getting the code 1 returned. It turns out that this is a kind of undocumented oddity of Express - if you pass a numeric code and the second argument is also numeric it sends the second argument as the status.

In response.js of Express we find:

[code lang=“js”]res.send = function(body){ var req = this.req; var head = ‘HEAD’ == req.method; var len;

// allow status / body if (2 == arguments.length) { // res.send(body, status) backwards compat if (’number’ != typeof body && ’number’ == typeof arguments[1]) { this.statusCode = arguments[1]; } else { this.statusCode = body; body = arguments[1]; } }[/code]

So it seems the Express used to support a call like res.send({body}, 200) - and checks for a numeric second argument for backwards compatibility.

The workaround - don’t send numbers as any part of the response, unless it’s most definitely the status code - if you want to return the number of documents deleted, format it as json first, otherwise Express will get confused and mess with your status codes.

Json on dwmkerr.com

Node.js and Express - Strange Http Status Codes

In a Nutshell

The Details