How to Replace Parameters in a URL Request

Consider the example where an application creates a session ID when a user logs on. This session ID is required in each request after the logon page. To implement this scenario, you have to capture the session ID when it is first generated, and then use that value in each subsequent request.

You start by using the process described in How to Capture Web Application Recording to capture the logon and subsequent actions. The recorded session for logging on to the application and performing some actions might look similar to the following example.

http://www.myapp.com/home.aspx
http://www.myapp.com/search.aspx?query=testing&sessionid=32793279321721
http://www.myapp.com/results.aspx?sessionid=32793279321721
http://www.myapp.com/submit.aspx?sessionid=32793279321721

In this request sequence, the session ID is created by the first request and used in the second, third, and fourth requests. When you run this monitor, it fails because the first request generates a new session ID that could not match the session ID that was used when the session was captured.

To configure this request sequence with parameter replacement, you have to create an extraction rule on the first request to create a context parameter for the session ID. The extraction rule inspects the body of the request to locate the value for the sessionid variable. You would then modify the subsequent requests to use this parameter instead of the value for the session ID.

The modified requests look similar to the following example.

http://www.myapp.com/home.aspx
http://www.myapp.com/search.aspx?query=testing&sessionid=$ParametersContext/sessionID$
http://www.myapp.com/results.aspx?sessionid=$ParametersContext/sessionID$
http://www.myapp.com/submit.aspx?sessionid=$ParametersContext/sessionID$

Context parameters are collected by an extraction rule, and each extraction rule collects a single context parameter. You create an extraction rule in the Properties dialog box of the request that initially generates the required data. To identify the value to extract, you must view the body of the response returned from the particular request. You can either view the source of the page returned in the browser or use a tool that lets you inspect the details of HTTP responses. You cannot view the text by using the Web Application Editor.

When you have identified the request that contains the information you have to extract, you view the Extraction Rules tab in the properties of that request and create one or more extraction rules. The details of each extraction rule are shown in the following table.

You use a parameter in a request by replacing the explicit value with a variable representing the parameter. The format of the variable is $ParametersContext/<ContextParameterName>$. When the request is run, the variable is replaced with the data extracted by the parameter.

You can insert the variable into the request by using one of the two following methods:

• In the Request Properties dialog box, click the General tab, and then click Request URL to modify the request URL for the request.

• In the Request Properties dialog box, click the General tab, and then click the Insert parameter button. Use the Insert Parameter dialog box for the request. This is accessed from the Insert parameter button on the General tab in the Request Properties dialog box for the request.

The following procedure provides an example of using parameter extraction in a web application. This example performs a query for the first entry in the Popular Now section of the Bing home page. Because this value changes regularly, you have to first connect to the main page and collect the search term from the body of the response. You then use this term to build the request to perform the actual search.

The main Bing page is shown below with the Popular Now section highlighted.

To determine where in the response body the search term appears, you can view the source of the page. A portion of the source is shown below with the HTML code of the Popular Now section. In this HTML code, you only need the search string which is highlighted in the following illustration. The request is formed from https://www.bing.com followed by this string.

You could just pull out the term itself, but it is more straightforward to include the entire string in the parameter. This string is preceded by the characters <h3>Popular now</h3><ul><li><a href=" and ends with the next occurrence of ". Those are the values that you will use when you define the parameter extraction.