ETag support with pre-gzipped content stored in static variables

[JosePineiro]

willmmiles commented about ETag support form FS files:

Very cool! In WLED we've got similar logic being applied to statically linked resources, ie. pre-gzipped content stored in static variables and served via beginResponse(200, contentType, data_ptr, data_size). We do it this way so the web UI can be updated with a regular firmware OTA, without having to make a copy of the content to the filesystem. Perhaps there's room to add a send_gzip() function that invokes the same code for compiled-in static content?

I assume the function you're using is beginResponse(int code, const char *contentType, const uint8_t *content, size_t len, AwsTemplateProcessor callback).
The simplest option would be to use the void send(int code, const char *contentType, const uint8_t *content, size_t len, AwsTemplateProcessor callback = nullptr) function.
The strategy might be to check if the content has the GZIP Magic number (to make sure it is a gz content). If so, use eTag and disable AwsTemplateProcessor callback.
This way, it wouldn't be necessary to create new functions, and the improvement would work in the existing code.