HTTP cache for thumbnails, pages, dimensions

[Leeingnyo]

Use ETag header for HTTP caching

• thumbnails and pages
  • hashing image data with SHA1 (strong validation)
  • Resolve [Feature Request] HTTP cache for thumbnails and pages #213
• dimensions
  • It took so long times for big manga files, since it requires to read an entire zip file. For the device that has a bad I/O performance, It would be helped.
  • I use a zip_path of an entry and its mtime for hashing (SHA1), set ETag for weak validation

[Leeingnyo]

Should I use browser cache, too?

Cache-Control: public, max-age=#{seconds}

the above response header makes images cached into a memory or a disk.
It make the browser skip a HTTP request for the images.
but I can't set a value of max-age for caching

[hkalexling]

Thanks a lot for the PR! I took a quick look and it looks good. Let me spend more time and test it tomorrow :)

[hkalexling]

Regarding the max-age value, I think for the pages and dimensions we can be more aggressive and set it to something like 86400 seconds (which is 24 hours) or even higher. But for the thumbnail we should probably disable browser cache, because the user can upload a custom thumbnail whenever they want.

[Leeingnyo]

okay! I'll add max-age header for pages and dimensions API

[hkalexling]

LGTM. Thanks!