Bypassing The Browse File / Upload File Dialog

I am building a Chrome extension for internal use, and at one step, the user can upload a file. This is always the same file, and I would like to skip the browse dialog and directl

Solution 1:

If your goal is to send a file to the server then trying to select it in an <input> field is the wrong way - you can create a FormData object directly and send it via XMLHttpRequest. Note that you can also create a FormData object from an existing form. This works both in Firefox and Chrome and even from a web page (usual same-origin restrictions apply of course).

The tricky part is getting a File object that you can add to the form data. From all I know, Chrome extensions don't have direct file system access other than by using an NPAPI plugin - so they cannot get a file from user's disk drive, they can merely create a blob with some data. Firefox extensions however have the File constructor that allows them to create a File object by path.

So in Firefox you would do something like this:

var formdata = new FormData();
formdata.append("file", new File("file://C:/random.txt"));

var request = new XMLHttpRequest();
request.open("POST", "http://my.server/submitFile");
request.send(formdata);

Solution 2:

Firefox:

What you want seems to be possible according to this answer, but I haven't investigated it closely.

Chrome:

Outside of an NPAPI plugin, this is definitely not possible. Your browser cannot access the filesystem except when the user explicitly asks it to do so via a file dialog. If any page on the Web were able to programmatically set a filepath and then fetch the file when the user clicks a form button, that would raise massive security concerns.

So, a normal webpage certainly can't do it, obviously. If a Chrome extension could do it (i.e. read any file in the filesystem) then it would at the bare minimum require a special permission. The list of permissions does not include filesystem access, so that's out of the question.

The only option, as I mentioned in the beginning, would be to develop an NPAPI plugin to the read the file for you, which would be like building a hospital to treat a pimple. NPAPI has a pretty steep development learning curve, and it introduces significant security concerns (since your extension can now act the local user, the cost of a security compromise is much higher).

If you're willing to place the file on the browser's virtual HTML5 filesystem, then you could do that. Without specific knowledge of your needs, I can't say if that will be appropriate for you.