NodeJS deserialization from a stream - json

Question

I am having an issue deserializing from a stream in node (specifically the pricing feed from the Bitcoin GOX exchange). Basically a chunk arrives which is well formed complete and verified JSON. Here is the code:
var gox = require('goxstream');
var fs = require('fs');
var options = {
currency: 'AUD',
ticker: true,
depth: false
};
var goxStream = gox.createStream(options);
goxStream.on('data', function(chunk) {
console.log(JSON.parse(chunk));
});
When trying to parse it I get the following
undefined:0
^
SyntaxError: Unexpected end of input
Any ideas? I have included a sample chunk:
> {"channel": "eb6aaa11-99d0-4f64-9e8c-1140872a423d", "channel_name":
> "ticker.BTCAUD", "op": "private", "origin": "broadcast", "private":
> "ticker", "ticker": {
> "high": {
> "value": "121.51941",
> "value_int": "12151941",
> "display": "AU$121.51941",
> "display_short": "AU$121.52",
> "currency": "AUD"
> },
> "low": {
> "value": "118.00001",
> "value_int": "11800001",
> "display": "AU$118.00001",
> "display_short": "AU$118.00",
> "currency": "AUD"
> },
> "avg": {
> "value": "119.58084",
> "value_int": "11958084",
> "display": "AU$119.58084",
> "display_short": "AU$119.58",
> "currency": "AUD"
> },
> "vwap": {
> "value": "119.80280",
> "value_int": "11980280",
> "display": "AU$119.80280",
> "display_short": "AU$119.80",
> "currency": "AUD"
> },
> "vol": {
> "value": "249.73550646",
> "value_int": "24973550646",
> "display": "249.73550646\u00a0BTC",
> "display_short": "249.74\u00a0BTC",
> "currency": "BTC"
> },
> "last_local": {
> "value": "118.50000",
> "value_int": "11850000",
> "display": "AU$118.50000",
> "display_short": "AU$118.50",
> "currency": "AUD"
> },
> "last_orig": {
> "value": "108.99500",
> "value_int": "10899500",
> "display": "$108.99500",
> "display_short": "$109.00",
> "currency": "USD"
> },
> "last_all": {
> "value": "118.79965",
> "value_int": "11879965",
> "display": "AU$118.79965",
> "display_short": "AU$118.80",
> "currency": "AUD"
> },
> "last": {
> "value": "118.50000",
> "value_int": "11850000",
> "display": "AU$118.50000",
> "display_short": "AU$118.50",
> "currency": "AUD"
> },
> "buy": {
> "value": "118.50000",
> "value_int": "11850000",
> "display": "AU$118.50000",
> "display_short": "AU$118.50",
> "currency": "AUD"
> },
> "sell": {
> "value": "119.99939",
> "value_int": "11999939",
> "display": "AU$119.99939",
> "display_short": "AU$120.00",
> "currency": "AUD"
> },
> "item": "BTC",
> "now": "1376715241731341" }}
You can verify it here: http://jsonlint.com
Also it is probably worth mentioning I have already tried parsing and removing the escaped characters. Also have tried a couple of different serializers with the same results

Answer 1

You are getting the data chunk by chunk. Chunks themselves may not be complete JSON objects. Either buffer all of the data, or use something to do it for you (say the request module), or if you need to parse a long stream take a look at the JSONparse module.

Answer 2

You are getting two separate chunks (or at least: that's what I am getting when re-creating your issue). One (the first) is a valid JSON object, while the other (the second) is "almost empty": it is a 1-byte string containing just an LF (ASCII 0x0a).
The second one fails parsing, of course.
Read my first answer: this is exactly such a case. If you concat the two chunks together you get a complete JSON object with a trailing LF, easily passing JSON.parse(). If you try to parse the chunks separately, though, however, the first one succeeds (a trailing LF is not a mandatory) while the second one fails (an LF by itself is not a valid JSON object).
For your case, you would have to:
1) Either assume Mt.Gox always sends data "this way", ignore those "almost empty" chunks, and parse only the "non empty" chunks.
2) Or use JSONparse which parses JSON streams.