Bug#636871: provide a command-line switch to prefer IPv6 or IPv4

[Julian Andres Klode <jak@debian.org>]

On Tue, Oct 10, 2017 at 11:12:16PM +0200, Ludens wrote:
> On Sat, 7 Oct 2017 23:28:57 +0200 Julian Andres Klode <jak@debian.org>
> wrote:
> > JFTR: I wrote an implementation of parts of happy eyeballs for another
> > bug we should probably merge in here, but it fails the test suite on
> > CI: https://github.com/julian-klode/apt/commits/bugfix/happy-eyeballs
> >
> > I started a rewrite of that in another local branch, but it's not
> > done yet.
> 
> Hi,
> 
> I started some work on this without knowing about the code that was
> there. The patch attached implements Happy Eyeballs in (roughly) the
> following way:
> 
> In ConnectToHostname, if the first DoConnect does not complete within
> 300ms, another DoConnect is performed with an address of a different IP
> family. So, if the first DoConnect used IPv6, the second will use IPv4
> and vice versa. Of these two connection attempts, the first one that
> completes will be used. The precedence ordering of getaddrinfo is also
> taken into account. Hopefully, this is helpful.

I looked at the patch, but it did not look very neatly structured to
me - more like the rest of the code... ;). My second attempt now is:

  https://github.com/Debian/apt/compare/master...julian-klode:pu/happy-eyeballs?expand=1

It's basically building lists of Connection objects and waiting on these,
using the first successful connection (and waiting only 300 ms after adding
a preferred connection, and then waiting the specified time out after optionally
adding a non-preferred connection family).

That said, I do not have a system with broken IPv6 routing, so
I can't really test it. It's also not entirely neat yet either...

-- 
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