A place for my programming projects and the occasional blog about technology related matters.
Remote Image Cache
Source code - addons.mozilla.org page - Version history
This was done as a request for someone on the Mozillazine forums. It’s in the sandbox at AMO so you’ll have to be a registered user to view it there. Here is the text from the AMO page explaining how it works:
Saves remote images from emails locally when mail is viewed for the first time. This allows you to view mails with remote images and have them display correctly even if you’re offline or the server hosting the remote images is down. The extension fully supports the remote content blocking policy of the user and won’t get the images until the user has allowed it for the given message.
So, some Q and A:
Q: How does it work?
A: Everytime you open a message with remote images, the extension will check if it has downloaded the images previously and if so it will set the src attribute of the image to the cached file, e.g. chrome://ricfiles/12345-filename.jpg. If it doesn’t have the image locally it will download it.
Q: Does it modify my emails permanently? What happens if I uninstall it?
A: The extension doesn’t modify the actual email, it only works on the DOM tree constructed when the email message is viewed. In english that basically means that if you uninstall the extensions then all your emails will be just as they were, referencing their remote images on their original servers.
Q: Can I tell it to download images for all my old messages?
A: No, sorry, as of version 1.0 it only downloads images for emails when the email is being viewed. That means that if you want to cache all images from your old emails you’ll have to view each and every one of them. Maybe in future versions I’ll add some bulk download feature, who knows.
Q: What happens if I delete an email?
A: The images for it remain in the cache, I haven’t implemented a delete feature yet.
Q: Can I view the cache?
A: Yes, all images are stored in a folder called RemoteImageCache under your profile folder.
Q: I get lots of email from the same place with the same images being referenced. Are they stored once or many times?
A: If you get the same image in 2 emails it’s stored 2 times. The filename in cache is basically messagenumber+filename. I did it like this because it’s easier to add things like deleting from cache when each message has its own unique images, but maybe I’ll change it later.
Q: If the images for a message are cached, is it guaranteed that no http requests will be made for them to the original server?
A: No. I haven’t found a way to block the requests from being made, so even if you have cached images you might also request them from the server. This extension is mostly just to make the messages display correctly when you’re offline or the original server has taken the images down.
Q: I think it’s great, but it needs feature X. Could you do it?
A: Maybe. You can send feature suggestions to remoteimagecache [at] einaregilsson.com or just leave it in the comments here. If you want to submit your own change to me you can get the latest source from http://einaregilsson.googlecode.com/svn/mozilla/remoteimagecache/trunk and then send me a patch.
Works with: 
Thunderbird: 1.5 – 2.0.0.*
Latest version: 1.0
Comment
I have two suggestions.
1. If your extension catches on and looks like it may be widely used contact Manuel Reimer, PrefBar Extension, and collaborate on creating a button to “Clear Image Cache”.
manuel.reimer@gmx.de
2. Include support for SeaMonkey Messenger, if support is available make notations in the Information Documentation.
Have a great day,
Michael Gordon
I’d like to suggest an option to specify where the RemoteImageCache directory resides. I’d probably put it in “Temp” so that the image cache isn’t cluttering up my main Thunderbird directory.
A question: if I delete images in RemoteImageCache without deleting the source email message, what happens when I later open up the message?
Hi Greg, sorry for the late reply. It’s unlikely that I’ll modify Remote Image Cache more, I don’t use Thunderbird myself anymore and this extension has not become very popular. However, you can easily modify it yourself to use the temp dir instead of the profile dir. Here’s how:
1. Open your thunderbird profile folder.
2. Go to extensions\remoteimagecache@einaregilsson.com\chrome\content
3. Edit the file remoteimagecache.js in a text editor
4. Change the line
var folder = prop.get(”ProfD”, Ci.nsIFile);
to
var folder = prop.get(”TmpD”, Ci.nsIFile);
and save the file. Restart Thunderbird and it should now use the temp folder by default.