HTTP Post request to a PHP server

2007-02-19T00:19:52Z

Grid Wise: /* Introduction */

== Introduction ==

LSL now offer the ability to request HTTP page from any website.

You can use different methods to access your webserver.
The most obvious is GET, the get method allows any number of parameters.

The syntax is :

http://www.yourwebsite.com/pay.php?user=Corto+Maltese&amount=100

In the example above the page pay.php is requested with 2 parameters param1 and param2.
The issue with GET is that if someone manage to sniff or guess your webpage, he could potentially take any webbrowser and type :

http://www.yourwebsite.com/pay.php?param1=Joe+Blog&amount=1000000

And your web server will have little idea that this request is bogus.

This is where my library comes into action.

The LSL library takes every character in your HTTP request and compute a security HashCode.
The library will then add this extra security hash parameter to your request like that:

http://www.yourwebsite.com/pay.php?user=Corto+Maltese&amount=100&hash=edabcc1792b33e7d6055cc4c8e69912c

When the server receive the request, it will be able to check that the hash provided is correct.
If the request was tempered, the hash will not be correct, the server will therefore ignore the request and not allow Job Blog to pretend he has paid L$ 1,000,000.

Also the library uses a POST method, the POST method is not very different from GET but allow slightly more input parameters than GET, The POST method is also a bit more secure as the parameters do not appears in the cache statistics or similar tools.

== Syntax ==

The main LSL function is called xrequest

xrequest(string Url, List Parameters)

Url :
is the address of your webpage. for example "http://www.yoursite.com/sl.php"

Parameters :
is a list of string, the list must be set in pairs using this format:
[variable_name_1, variable_value_1, variable_name_2, variable_value_2, ...]

In the example below the script request a page using the parameters a=1, b=2 and c=3.
<code>
default
{
touch_start(integer total_number)
{
xrequest("http://www.yoursite.com/sl.php",["a","1","b","2","c","3"]);
}

http_response(key request_id, integer status, list metadata, string body)
{
if (request_id == http_request_id)
{
llSetText(body, <0,0,1>, 1);
}
}

}
</code>

Here is the code of the xrequest function.
Note that you should change the SECRET_NUMBER to any number of your choice but preferably something rather large and random up to 2,000,000,000.

<code>
integer SECRET_NUMBER=123456789;

xrequest(string url, list l)
{
integer i;
integer len=llGetListLength(l) & 0xFFFE; // makes the list count even
string body;

for (i=0;i<len;i+=2)
{
string varname=llList2String(l,i);
string varvalue=llList2String(l,i + 1);
if (i>0) body+="&";
body+=llEscapeURL(varname)+"="+llEscapeURL(varvalue);
}
string hash=llMD5String(body,SECRET_NUMBER);
http_request_id = llHTTPRequest(url+"?hash="+hash,[HTTP_METHOD,"POST",HTTP_MIMETYPE,"application/x-www-form-urlencoded"],body);
}
</code>

On the server side here is the PHP function which will allow your server to check the securty hash:

<code>
<?php
function checkHash()
{
$hash=$_GET["hash"];
$body="";
$cpt=0;
$SECRET_NUMBER=123456789;
foreach ($_POST as $name => $value) {
if ($cpt++>0) $body.="&";
$body.=urlencode($name)."=".urlencode($value);
}
$calcHash=md5("$body:$SECRET_NUMBER");
if ($hash!=$calcHash)
{
//sleep(2); // slow down the requests
echo "result=FAIL\nMSG=Invalid hash";
die;
}
}

checkHash();
// You can use the parameters here by simply using $_POST["parameter_name"]
echo "OK";
?>
</code>

This library could be improved, to treat output parameter too.
It doesn't do anything in this area yet.

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HTTP Post request to a PHP server