pub type ImageFetcher = fn(&str, Box<dyn FnOnce(Result<Vec<u8>, String>) + Send>);Expand description
The image stores and the two things a host has to name: a decoder is chosen by the
images feature, and the fetcher is registered by whoever has a network. See
Image::network.
Hands the bytes at url to the callback, once, from wherever suits the platform.
A function pointer and not a closure: this is registered once for the process, and
a plain fn needs no allocation, no lifetime and no Sync wrapper to store.