Question

107

Strange JSON.parse() error in node.js

rated 0 times [ 114] [ 7] / answers: 1 / hits: 23946 / 12 Years ago, thu, march 15, 2012, 12:00:00

I'm retrieving some stringifyed JSON via TCP in node.js an want to parse it. So my approach is similiar to this. I shortend and simplified it, so you don't have to know the surrounding logic.

socket.on(data, function(data) {

    console.log(data.toString());               // Shows the original stringifyed version

    console.log(JSON.parse(data.toString()));   // Doesn't work

});

The complete (beautified) JSON is this. As you can see, there are no errors.

{

    result: success,

    source: chat,

    success: {

        message: test,

        time: 1331770513,

        player: silvinci

    }

}

But JSON.parse(data.toString()) always throws me this dumb error:

{result:success,source:console,success:{time:1331762264,line:20

^

SyntaxError: Unexpected token {

    at Object.parse (native)

    at Socket.<anonymous> (/home/node/api.js:152:35)    // irrelevant from here on

    at Socket.emit (events.js:67:17)

    at TCP.onread (net.js:347:14)

So I thougt: What could be wrong with the JSON-String. Let's try it directly. Should not work. Surprise, Surprise! It worked. Why does it work when I directly enter the String?

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answered 12 Years ago dezmondhumbertob · Accepted Answer

Thanks to @Felix Kling I found my bug. It's very important to filter unescaped characters, especially outside the stringified JSON. I didn't and overlooked an invisible linebreak right after the stringified JSON.

This is the fix:

socket.on(data, function(data) {

    console.log(data.toString());                          // Shows the original stringified version

    console.log(JSON.parse(data.toString().slice(0, -4))); // Trim the sequence rn off the end of the string

});

Please note, that this only works for me, as I have a very specialized case. The server is always responding in lines of JSON, that are terminated with an rn - not the whitespace characters, but literally backslash r and backslash n.

Your code may (or probably) fail due to other errors. But checking the server's response is a good starting point when you get parsing errors.

As @Zack correctly pointed out, this is a more general fix for removing unintended whitespace:

JSON.parse(data.toString().trim());