Monday, May 28, 2012

php-webdriver bindings for selenium: how to add time-outs

Not all webpages finish loading. In particular I've a page that keeps streaming data back to the client, and never finishes. (For instance it might be used from an ajax call.) I want to test this from Selenium, but have been hitting problems. The main problem is Selenium's get() function, which is used to fetch a fresh URL, does not return until the page has finished loading [1]. In my case that meant never, and so my test script locked up!

However all is not lost; you can specify a page load timeout. It is hidden in the protocol docs, but I've added it to the php webdriver library I use (v0.9). See the three functions below [2]; just paste them in to the bottom of WebDriver.php.

I also needed one bug fix in WebDriver.php's public function get($url). It currently ends with:
    $response=curl_exec($session);

Just after that line you should add this:
    return $this->extractValueFromJsonResponse($response);


The time-out, and that bug fix, can be used like this:

require_once "/usr/local/src/selenium/php-webdriver-bindings-0.9.0/phpwebdriver/WebDriver.php";
$webdriver = new WebDriver("localhost", "4444");
$webdriver->connect("firefox");
$webdriver->setPageLoadTimeout(2000);   //2 seconds
$url="http://example.com/forever.php"; //A page that never finishes loading
$obj=$webdriver->get($url);
if($obj===null){
    $current_url=$webdriver->getCurrentUrl();
    if(!$current_url){
        //Selenium-server not running
        }
    else{
        //It worked! (it completed loading in under two seconds)
        }
    }
elseif($obj->class=='org.openqa.selenium.TimeoutException'){
    //It timed out
    }
elseif($obj->class=='org.openqa.selenium.remote.UnreachableBrowserException'){
    //Browser was closed (or selenium-server was shutdown)
    }
else{
    echo "FAILED:";print_r($obj);
    }

This is useful stuff. There is still one problem left for me: I wanted to load two seconds worth of data and then look at it. But I cannot. The browser refuses to listen to selenium while it is loading a page! So though get() returned control to my script after two seconds, I cannot do anything with that control (except close the browser window), because the URL is still actually loading. And it will do that forever!!  (I've played with an interesting alternative approach, which also fails, but suggests that a solution is possible. But that is out of the scope of this post, which is to show how to add the time limit functions to php-webdriver-bindings.)

[1]: This is browser-specific behaviour, not by Selenium design. Firefox and Chrome, at least, behave this way.


[2]: Consider this code released, with no warranty, under the MIT license, and permission granted to use in the php-webdriver-bindings project with no attribution required.

    /**
     * Set wait for a page to load.
     *
     * This timeout is for the get() function. (Firefox and Chrome, at least, won't return from get()
     * until a page is fully loaded.  If remote server is streaming content, they would never return
     * without this time-out.)
     *
     * @param Number $timeout Number of milliseconds to wait.
     * @author Darren Cook, 2012
     * @internal http://code.google.com/p/selenium/wiki/JsonWireProtocol#/session/:sessionId/timeouts
     */
    public function setPageLoadTimeout($timeout) {
        $request = $this->requestURL . "/timeouts";       
        $session = $this->curlInit($request);
        $args = array('type'=>'page load', 'ms' => $timeout);
        $jsonData = json_encode($args);
        $this->preparePOST($session, $jsonData);
        curl_exec($session);       
    }

    /**
     * Set wait for a script to finish.
     *
     * @param Number $timeout Number of milliseconds to wait.
     * @author Darren Cook, 2012
     * @internal http://code.google.com/p/selenium/wiki/JsonWireProtocol#/session/:sessionId/timeouts
     */
    public function setAsyncScriptTimeout($timeout) {
        $request = $this->requestURL . "/timeouts";       
        $session = $this->curlInit($request);
        $args = array('type'=>'script', 'ms' => $timeout);
        $jsonData = json_encode($args);
        $this->preparePOST($session, $jsonData);
        curl_exec($session);       
    }
    /**
     * Set implict wait.
     *
     * This is for waiting for page elements to appear. Not useful for scripts or
     * waiting for the initial get() call to time out.
     *
     * @param Number $timeout Number of milliseconds to wait.
     * @author Darren Cook, 2012
     * @internal http://code.google.com/p/selenium/wiki/JsonWireProtocol#/session/:sessionId/timeouts
     */
    public function setImplicitWaitTimeout($timeout) {
        $request = $this->requestURL . "/timeouts";       
        $session = $this->curlInit($request);
        $args = array('type'=>'implicit', 'ms' => $timeout);
        $jsonData = json_encode($args);
        $this->preparePOST($session, $jsonData);
        curl_exec($session);       
    }

2 comments:

Keith said...

I wonder if Web Workers would be another approach...

Keith said...

(The following two links looked interesting:
http://ejohn.org/blog/web-workers/
http://www.html5rocks.com/en/tutorials/workers/basics/ )