Re: Downloading from generated mirror

[Valentin David <valentin david codethink co uk>]

On Mon, 2018-04-30 at 16:48 +0100, Jonathan Maw wrote:
> On 2018-04-30 12:56, Valentin David wrote:
> >  2. Multiple directories
> >  -----------------------
> >
> > For some plugins, in #330, there is an extra component in the path.
> > It
> > is a number incrementing from 0. There are some plugins that might
> > get
> > new incompatible repositories or files for a same URL. And when we
> > detect this, we create a new directory.
> >
> >  - ostree and git should not suffer of this problem, because we can
> > just compose repositories and collisions are unlikely.
> >  - zip and tar need it when the file is changed.
> >  - bzr needs it, when we detect that remote repository does not
> > contain
> > at least all the commits we have locally.
> >
> > The loop that tries mirrors should retry while counting on the last
> > path component for those plugins requiring it.
> >
> > There must be now two exceptions raised from source plugins:
> >  - one that says the URL works but the reference is not available,
> >  - another one for any other error.
> > The loop should count until it find the second error.
>
> Hi Valentin,
>
> Looking at this, the Source.fetch() method currently expects a 
> SourceError
> to be raised whenever there's a network error or if the source
> reference
> couldn't be matched.
>
> Do you think it would help backwards-compatibility if we keep to 
> returning
> SourceErrors, but distinguish between the two cases based on the
> error's
> "reason" field?
>
> e.g. in GitSource we extend assert_ref to have the reason "no-ref",
> and 
> use
> any other SourceError when fetching as a reason to stop looping and
> try
> another alias mapping.

I was thinking of creating a class that inherits SourceError so we can
write:

except RefNotFound:
  # Next path
except SourceError:
  # Next mirror

And still be backwards-compatible.