[FFmpeg-devel] http: honor response headers in redirect caching

[Eran Kornblau]

> 
> 
> Hi,
> 
> On Mon, Jan 17, 2022 at 7:10 AM Ronald S. Bultje <rsbultje at gmail.com> wrote:
> 
> > Hi,
> >
> > On Tue, Jan 11, 2022 at 9:43 AM Eran Kornblau 
> > <eran.kornblau at kaltura.com>
> > wrote:
> >
> >> Hi all,
> >>
> >> Recently I’ve submitted a patch that adds a config option to disable 
> >> the caching of http redirects.
> >> We planned this as a workaround to the fact there’s a limit on the 
> >> expiration that can be set on S3 pre-signed URLs.
> >> The idea was to have a service that generates signed S3 URLs and 
> >> redirects to them, ffmpeg would hit this service on every 
> >> seek/disconnect, and get a fresh S3 URL.
> >>
> >> We found that in some cases, ffmpeg seeks on every frame (probably 
> >> due to some gap between the positions of video/audio frames in the 
> >> file). In these cases, completely disabling the redirect caching 
> >> becomes quite inefficient - our S3 signing service gets called ~20 
> >> times/sec by a single encoding task.
> >>
> >> The attached patch provides a more complete/correct implementation of 
> >> redirect caching – the decision whether to cache/for how long is now 
> >> determined according to the response from the server - status code 
> >> (e.g. 301 vs 302), expires header & cache-control header. The 
> >> behavior (detailed in the comment of the commit) is more aligned with 
> >> how browsers handle it.
> >>
> >> In high level, these are the changes that were implemented in the 
> >> patch –
> >>
> >>   1.  Added a dictionary on HTTPContext for keeping the cache – since 
> >> I need to save both the target URL and the expiration, I’m formatting 
> >> them together on a single string
> >> (“expiry;target-url”)
> >>   2.  Added a string on HTTPContext to save the value of the location 
> >> header – this makes the existing flags new_location/location_changed 
> >> redundant, and they were removed
> >>   3.  Added functions for parsing Cache-Control/Expires – for Expires 
> >> I used the existing function for parsing cookie expiration time. The 
> >> result is saved on a new integer on HTTPContent - a zero value means 
> >> that no such header was encountered yet, a negative value means the 
> >> response should not be cached.
> >> Once this patch is merged, IMHO we can remove the flag that I added 
> >> in the previous patch (=always treat it as 0, and have the caching 
> >> work based on the new dictionary). I will happily submit another 
> >> patch for this.
> >>
> >> Thank you!
> >>
> >
> > Will merge this in 1-2 days if there's no further comments.
> >
> 
> Merged.
> 
> Ronald

Ronald, thank you for your continued support on this one!

As promised, sending another patch to remove the `cache_redirect` option, as it seems to be no longer needed.

Thanks

Eran
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