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

["Ronald S. Bultje" <rsbultje@gmail.com>]

Hi,

On Sun, Jan 30, 2022 at 1:15 AM Eran Kornblau <eran.kornblau@kaltura.com>
wrote:

> >
> > -----Original Message-----
> > From: Eran Kornblau
> > Sent: Wednesday, 19 January 2022 9:14
> > To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
> > Subject: RE: [FFmpeg-devel] http: honor response headers in redirect
> caching
> >
> > >
> > >
> > > Hi,
> > >
> > > On Mon, Jan 17, 2022 at 7:10 AM Ronald S. Bultje <rsbultje@gmail.com>
> wrote:
> > >
> > > > Hi,
> > > >
> > > > On Tue, Jan 11, 2022 at 9:43 AM Eran Kornblau
> > > > <eran.kornblau@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
>
> Ping
>

Got it, will apply this later today. I realize this is an API change but
since the option only existed for 2 weeks, it should be OK.

Ronald
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