TDI and HTTP POST

Tuesday, 26 May 2015
I was recently asked how to successfully perform an HTTP POST request using TDI's HTTP Client Connector. NULL values kept being processed by the web server and there seemed to be no obviously documented way to perform the task.

On the face of it, this seems like a straightforward piece of functionality, but the truth is that it is not quite as straightforward as it seems.

To understand how to pass parameters to a web server via HTTP POST using TDI, it would help to understand what is actually happening when using a standard web form.

Consider the following:

<html>
<head />
<body>
<form action="result.php" method="post">
User Name<br />
<input type="text" name="uname">
<br />
Password<br />
<input type="password" name="pass">
<br />
<input type="submit" value="submit">
</form>
</body>
</html>

The submit button on this form will cause the browser to send an HTTP request to the web server with a CONTENT-TYPE of: "application/x-www-form-urlencoded". This is the key to unlocking our problem!

The values for the attributes requested in the form will be passed in the BODY of the request rather like the query string you might see in HTTP GET requests:

uname=x&pass=y

So to mimic form submission using the POST method via TDI, all you need to do is follow these steps:

  • Set the Mode to CallReply (if you want to see what the web server has done with your request)
  • Set the Request method to POST
  • Set the http.Content-Type to "application/x-www-form-urlencoded"
  • Set the http.body to name/value pairs in query string format

Hopefully that will see your TDI Assembly Lines behaving themselves when acting as HTTP Client and attempting to use the POST method to transfer information.