Question

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How Mega does to save a file to harddrive without requiring permission

rated 0 times [ 92] [ 4] / answers: 1 / hits: 19729 / 11 Years ago, thu, january 9, 2014, 12:00:00

I'm not sure if the place to ask this question so feel free to move my question elsewhere or closed it.

I have been told that Javascript can write and read from disk only when an explicit event like drag & drop happen on the browser and gave it a handle to a file.

In the case of Mega(ex upload) when you click download you are directly saving a file to disk without being asked to save it or installing any extension your browser.

Is it a feature of Javascript or HTML 5 because in my opinion it means a terrible security issue in this case.

Edit 1:
So my question is, how do Mega manage to write on disk without showing you the Save to dialog of your browser popped up and self determining where to put the file

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emerald

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1 Year ago

answered 11 Years ago monetm · Accepted Answer

It's just a matter of sending the right headers in the response - so the browser knows to save instead of open. It's nothing to do with javascript or HTML5.

For example, in PHP:

header('Content-Description: File Transfer');

header('Content-Type: application/octet-stream');

header('Content-Disposition: attachment; filename='.basename($file).''); 

header('Content-Transfer-Encoding: binary');

header('Connection: Keep-Alive');

header('Expires: 0');

header('Cache-Control: must-revalidate, post-check=0, pre-check=0');

header('Pragma: public');

header('Content-Length: ' . filesize($file));

I don't know what server-side technology Mega uses but this is the basic premise.

Edit: in response to your edited question about why the 'Save As' dialog does not appear, well, that's a browser setting. Chrome, for example, will by default save to your Downloads folder (on Windows) without prompting.