Add a User-Agent header to HTTP image loader

[MathiasYde]

Is your feature request related to a problem? Please describe.

I'm trying to make an egui program that shows images loaded from an CDN, but it requires that the request has a user agent as a header.

Describe the solution you'd like

Either hardcore the user agent header into the code handling HTTP image loading or add a way to allow passing in a custom user agent

Describe alternatives you've considered

Loading the image using reqwest as bytes and use ImageSource::Bytes in Image

Additional context

[emilk]

Sounds good - PRs welcome!

[MathiasYde]

Are we going for a hard coded user agent or a configurable one? I could take a crack at it

[MathiasYde]

I've been looking through the code a bit and found out that egui-extras uses ehttp for the http ImageLoader which has hardcoded headers of just ("Accept", "*/*")

Do you want to simply pass the headers into ehttp::Request::get function, a builder pattern? (ehttp::Request::get("http://..").with_headers(..).build()) or perhaps something else?

[MathiasYde]

So a few hours of debugging and I found out that the URL I use to fetch images has unescaped qoutes ("\"https://..\"") which caused images to fail due to calling to_string() directly on serde_json::Value instead of something like as_str().unwrap_or("null").to_string() 🙃

[emilk]

A hard-coded User-Agent: egui is a good start, but adding some way of changing it for EhttpLoader should be fairly easy.