Add arbitrary request headers to EhttpLoader

[frnsys]

• Closes Add a User-Agent header to HTTP image loader #4491
• I have followed the instructions in the PR template

Lets you create an EhttpLoader with arbitrary headers like so:

cc.egui_ctx.add_bytes_loader(std::sync::Arc::new(
    egui_extras::loaders::http_loader::EhttpLoader::default().with_headers(&[
        ("User-Agent", "foo"),
    ])
));

I'm not sure if there are any problems with installing a second
EhttpLoader (in addition to the one installed by default when using
egui_extras::install_image_loaders(&cc.egui_ctx). But I wasn't
sure how else to pass in configuration options to
install_image_loaders.

[github-actions]

Preview available at https://egui-pr-preview.github.io/pr/8121-http-loader-headers
Note that it might take a couple seconds for the update to show up after the preview_build workflow has completed.

View snapshot changes at kitdiff

[lucasmerlin]

If someone wanted to use this for authentication, they'd have to ensure they only ever load images from trusted endpoints, so their token is not exposed to any third partys.
Maybe instead we could have a request_template closure arg? Then one could do something like this:

cc.egui_ctx.add_bytes_loader(std::sync::Arc::new(
    egui_extras::loaders::http_loader::EhttpLoader::default().with_request_template(|url| {
		let mut request = ehttp::Request::get(url);
		if url.starts_with("https://my-api.com") {
		    request = request.with_headers(&[
        		("User-Agent", "foo"),
    		])
		}
		request
	})
));

[frnsys]

If someone wanted to use this for authentication, they'd have to ensure they only ever load images from trusted endpoints, so their token is not exposed to any third partys. Maybe instead we could have a request_template closure arg? Then one could do something like this:

cc.egui_ctx.add_bytes_loader(std::sync::Arc::new(
    egui_extras::loaders::http_loader::EhttpLoader::default().with_request_template(|url| {
		let mut request = ehttp::Request::get(url);
		if url.starts_with("https://my-api.com") {
		    request = request.with_headers(&[
        		("User-Agent", "foo"),
    		])
		}
		request
	})
));

Yes that's a good point. I updated the PR to do basically what you suggested. But I pass in the prepared Request instead of the url in case for whatever reason the Request ends up being more complicated to construct.

[lucasmerlin]

Awesome!