From: Allan Bonadio <unsure@...>
Date: 2010-08-28T11:09:55+09:00
Subject: Re: how to detect used protocol (SOAP, JSON, XML etc.)

jeljer te Wies wrote:
> The problem is that I can't figure out how to check what protocol is
> used. (the only thing i can figure out is to just try to transform it
> with every known "protocol" until it doesn't return an error anymore.

Silly wabbit!  Just take a look at the JSON, XML and SOAP files you are 
(or would be) getting.  Pretty easy for a human to tell at a distance 
which.  And not hard to do a decent job in your server code.

XML, strictly formatted, always starts with a specific line that says 
it's XML.  Here's three examples I got by randomly searching the web:

<?xml version="1.0" encoding="ISO-8859-1"?>
<?xml version="1.0" encoding=UTF-8"?>
<?xml version="1.0"?>
Must be the first line.  Therefore the first six characters in the whole 
file should be '<?xml '.  So like this:
if (datastring.substr(0, 6) == '<?xml ') ...

sorry I'm writing in JS today.

XML, sloppily formatted, might blow this off.  At any rate, it consists 
of <tags> just like HTML.  So the first character (after maybe some 
whitespace) should be <.  You're not supposed to do sloppy XML, but my 
boss does.  If you have to accept sloppy xml, like this:
if (datastring.search(/^\s*</) >= 0) ....

SOAP is a dialect of XML, I don't know much about it but probably 
there's some clues close to the start; look at some files and/or read 
some SOAP docs.

JSON usually starts with an object at the root, which almost always 
starts with a quoted fieldname like this:
{"qleft":5.5,"qright":-22.01}

IF it doesn't, chances are it has an array at the root like this:
[{"qleft":5.5,"qright":-22.01},{"qleft":6.5, "qright":-202.01}]

If your JSON is tight, like it often is, you can just look for one of 
these two like this:
if (datastring.substr(0, 2) == '{"' || datastring.substr(0, 1) == '[') 
...

In fact, if you look at your protocol, it's very possible it'll ALWAYS 
start with an object at top, even simpler.  so you can blow off starting 
[s.

But of course you can legally stick in spaces so you could use this 
regex:
if (datastring..search(/^\s*[\[|\{]/) >= 0) ....

easy!
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