Tsung code to extract a random link using xpath

Tsung is a tool for load testing. Though Tsung has an official document, it is very concise. There is not much resource regarding to advanced features, so it took me quite a while to figure out how to get a random link from a page.

Code snippet:

<request> 
	<dyn_variable name='all_item' xpath="/html/body/div/div[2]/div[*]/div/a/@href"/>
	<http url='/bid_items' version='1.1' method='GET'></http>
</request>

<setdynvars sourcetype="eval"
	code='fun({Pid,DynVars})->
	    {ok,Val}=ts_dynvars:lookup(all_item,DynVars),
	    random:seed(now()),
	    lists:nth(random:uniform(length(Val)), Val) end.' >
	<var name="nth_item" />
</setdynvars>

<request subst="true">    
    <http url='%%_nth_item%%' version='1.1' method='GET'></http>
</request>

Explaination:

This snippet mimics a user going to the bid_items index page, then randomly follows one item link to view its detail.

It first uses xpath to capture all items’ links into variable all_item. Please note the usage of div[*], which captures all links matching this pattern.

In the setdynvars section, Tsung evaluates a segment of erlang code, and stores its value into variable nth_item. Within the code segment is an anonymous function, which takes in two Tsung arguments. The function returns a random entry in the list all_item.