Show HN: A Chrome extension that prevents duplicate downloads | Hacker News Reader

Show HN: A Chrome extension that prevents duplicate downloads

chrome.google.com

30 pointsyefim32316 comments

Can't wait to try this out. Some of the course files on my university's website are in .docx format instead of .pdf and I always forget I've downloaded them before, so by the end of the semester I end up with 7 copies of the same file.

As an aside, one of the problems I've had with certain Chrome Extensions is that the Chrome Webstore is telling me that "This application is not supported on this computer. Installation has been disabled." I started noticing this when I upgraded to Win 8 from my Win 7, and when I looked it up it was something about NPAPI plugins being disabled for Chrome on Windows 8. However this [1] and [2] make it seem that this is only for Chrome in metro mode, but I've been getting this message in Desktop mode as well. Now I don't know anything about Chrome extensions and file system access, but it would be great if it can be coded using some other kind of plugin. There is a workaround for Chrome/Win8 [3] but it does require a bit of work and it will put people off from installing it if they have to jump through those hoops.

[1] (https://groups.google.com/forum/#!topic/tincr-for-chrome-dev...)

[2] (http://blog.chromium.org/2012/07/npapi-plug-ins-in-windows-8...)

[3] ()http://blog.chromium.org/2012/07/npapi-plug-ins-in-windows-8...

I apologize for the lack of support. Chrome's download API (https://developer.chrome.com/dev/extensions/downloads.html) is very flaky and has just been added full support in Chrome 27.0.1448.0 dev-m according to http://stackoverflow.com/questions/15451313/closed-uncaught-...

Oh don't worry about it. Kinda saw it coming as I had that problem before. And that's great! Been meaning to switch to the dev channel for a while now.

Ah, that explains a lot. This looks useful because I often have an itchy trigger finger and download more than one copy. But you know what I really miss in Chrome would be a decent download manager that lets me select multiple files from one page instead of DLing them one at a time. Last time I looked the only extension for this practically announced itself as malware.

Funnily enough, this extension exists as a sample extension in the Chrome extension docs. Apparently, you can't link to specific samples, so just go to https://developer.chrome.com/dev/extensions/samples.html and filter by "downloads." The extension you're looking for is "Download Selected Links."

It looks like this: http://i.imgur.com/XF6S0mu.png

+20 internets to you - that's a serious time-saver for me!

Source is up here: https://github.com/yefim323/Have-I-Downloaded-This-Before

It's a good idea, but downloading something from the same URL (or filename fragment from an URL) does not necessarily imply that it's a duplicate. Would be interesting to see something similar to this extension that uses attributes sent at the start of an HTTP response - e.g. entity tag or content length - for duplicate checking.

I was thinking of also checking for the same file size. Would that improve the accuracy of detecting duplicates?

It would, but you'd have to first download the whole file to check which is probably counter productive. Consider storing some http header values such as a reference to the Etag header if provided, and checking that value before saving twice. Also consider storing Cache-Control headers, and Expires headers. The Content-Length header would be a way to detect same file size before transferring the whole file, but for large file downloads which used chunked encoding.

Some resources:

http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

http://en.wikipedia.org/wiki/Chunked_transfer_encoding

http://en.wikipedia.org/wiki/HTTP_ETag

I'm glad you're addressing this problem! I always end up with file(1).zip in my downloads folder.

I don't want a choice! I want it to do the right thing.

What happens if I've deleted the file from my downloads folder? Is that considered to be "downloaded before"?

Nope, it doesn't count. The Chrome downloads API allows me to makes sure the file exists on disk.

What's the point? I don't mind downloading it right there again at all...

It's a passive way of notifying you that you already have this file on disk. You can resume the download if you want to keep the second file.

How about one that just keeps it from closing when there is a download in progress? So frustrating when that happens.

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