Add a way for them to inject their camo images

[notriddle]

Fixes #95

[kornelski]

Well, you were first! But this solves proxying of images with absolute URLs, but not images with relative URLs. So at minimum it'd be good to have it as a preprocessing step, so it can see relative image URLs.

[notriddle]

Well, you were first! But this solves proxying of images with absolute URLs, but not images with relative URLs. So at minimum it'd be good to have it as a preprocessing step, so it can see relative image URLs.

If your URL base is http://example.com/ and you're given a document like <img src="/image.png"> <img src="http://example.com/image.png">, wouldn't you want to give both images the same camo URL?

I'm basically imagining URL processing as a pipeline, where the first step converts relative URLs to absolute ones, and the second step (which, since it happens after URL resolution, can be simplified to only deal with absolute URLs) converts direct image URLs to camo image URLs.

If it doesn't work for your needs, though, we can probably just merge both 😄

[kornelski]

I'm rendering readmes from GitHub, so my URL base is https://github.com/user/repo/ and links need to use this as a base, but I want to rewrite image.png to something like https://github.com/user/repo/blob/raw/image.png (because the usual base URL is for an HTML page about the image). And if an image is https://thirdparty.example.com/image.png, I want to rewrite it to https://my-proxy/https://thirdparty.example.com/image.png.

So if the base URL is applied first, I'll have to strip it later when deciding how to handle images.

In your PR I like the idea of it being a generic attribute tranformer. There's no need to limit it to URLs.

[notriddle]

Good point. Let's merge both, then.

[kornelski]

I've renamed url_filter_map to attribute_filter to generalize it :)