Magento headers already sent

Sometime while working with Magento, especially while browsing the site with Google Chrome, you may get the following error:

Duplicate headers received from server
The response from the server contained duplicate headers. This problem is generally the result of a misconfigured website or proxy. Only the website or proxy administrator can fix this issue.
Error 349 (net::ERR_RESPONSE_HEADERS_MULTIPLE_CONTENT_DISPOSITION): Multiple Content-Disposition headers received. This is disallowed to protect against HTTP response splitting attacks.

This will be fixed in Magento 1.7.x, but until then, if you like to fix it you need to duplicate a core file in the app/code/local/ folder modifying few lines.

The file you need is app/code/core/Mage/Core/Controller/Varien/Action.php, and you need to modify the method _prepareDownloadResponse, in particular this code:


$this->getResponse()
->setHttpResponseCode(200)
->setHeader('Pragma', 'public', true)
->setHeader('Cache-Control', 'must-revalidate, post-check=0, pre-check=0', true)
->setHeader('Content-type', $contentType, true)
->setHeader('Content-Length', is_null($contentLength) ? strlen($content) : $contentLength)
->setHeader('Content-Disposition', 'attachment; filename="'.$fileName.'"')
->setHeader('Last-Modified', date('r'));


into:


$this->getResponse()
->setHttpResponseCode(200)
->setHeader('Pragma', 'public', true)
->setHeader('Cache-Control', 'must-revalidate, post-check=0, pre-check=0', true)
->setHeader('Content-type', $contentType, true)
->setHeader('Content-Length', is_null($contentLength) ? strlen($content) : $contentLength, true)
->setHeader('Content-Disposition', 'attachment; filename="'.$fileName.'"', true)
->setHeader('Last-Modified', date('r'), true);


As said before, you have to duplicate this file before modifying, messing with the core files is always bad!
Your new file will be /app/code/local/Mage/core/Controller/Varien/Action.php.

If you plan to upgrade to Magento 1.7.x keep in mind that it is better to remove this patched file!

Enjoy!

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