Don't forget Content-Type

After two months of disappointment and frustration, things are finally looking up for us Mets fans, aren’t they? Bryce might disagree though.

This isn’t so much a code tip as it is a friendly reminder to remember to specify your Content-Type header when making a HTTP request. Due to this, I recently ran into a interesting little issue at work.

We have a small web-based tool that allows developers to upload HTML5 games and test them against a dummy API. Over the past few days I was tasked with recreating the tool in Node.js (it’s an old PHP-based page that needed some fixing up – I reached the conclusion it would be much simpler to redo it). At certain points during play, the game would send a JSON request with various details: event type, token, game data, etc. To receive and process the request, I had a pretty standard-looking express route using a JSON parser:

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var express = require('express');
var bodyParser = require('body-parser');
var app = express();
app.use(bodyParser.json());
//...
app.post('/events', function(req, res) {
  log(req.body);
  processEvent(req.body);
  res.end();
});

However, every time I triggered the appropriate action in the provided HTML5 game to send the request, req.body was empty! As an intermediate Node.js programmer I thought I had missed something simple or perhaps was using some deprecated parsing functionality by mistake. I checked the request payload to see if it was syntactically incorrect, but to no avail. After about a half hour of futility it occured to me to double check the request headers:

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Accept: */*
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.8
Connection: keep-alive
Content-Length: 93
Content-Type: text/plain;charset=UTF-8
Cookie: connect.sid=s%3AsLygHHEcLKxITLJugl
Host: localhost

The game was not setting the Content-Type header to application/json – instead it was text/plain. This made the bodyParser unable to parse it correctly.

In a perfect world this would be corrected in the game itself by setting the header correctly, but this being reality I knew I would not be able to fix the other hundreds of games that had the same issue. So, I had to settle for parsing the request in its raw form:

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function getRequestPayload(req) {
  return new Promise(function(resolve, reject) {
    var str = '';
    req.on('data', function(buf) {
      str += buf;
    });
    req.on('end', function() {
      resolve(str);
    });
  });
}
app.post('/events', function(req, res) {
  getRequestPayload(req)
    .then(function(json) {
      var json = JSON.parse(json);
      log(json);
      processEvent(json);
      res.end();
    })
    .catch(function(err) {
      log(err);
      res.end();
    });
});

If you’re not familiar with promises you should definitely check them out. In this particular instance I’m using the Bluebird promise library.

Hopefully this reminder will spare another developer the expense of having to work around this.