[rfc] Extending Patchwork as a GSoC project

[Ralf Ramsauer]

Hi Stephen,

On 07/05/2020 15:46, Stephen Finucane wrote:
> Welcome, Rohit.
> 
> On Thu, 2020-05-07 at 09:00 +0530, Rohit Sarkar wrote:
>>> Message IDs and patch IDs should also be stable/immutable. Message IDs,
>>> being a property of _mails_, will be the same across different patchwork
>>> instances that consume the same mail. Patch IDs, being a property of the
>>> specific database that ingested the patch, will vary from patchwork
>>> instance to patchwork instance.
>>>
>>>> Daniel, I have in mind that there is already some kind of infrastructure
>>>> in patchwork for receiving raw patches... AFAIR, Mete implemented an
>>>> export routine that eases the first initial import. Is there a
>>>> possibility to reliably "receive all new patches since my last pull"?
>>>
>>> I struggle a little bit to follow the who's importing and exporting from
>>> whom, but:
>>>
>>>   - There is now code to extract patches in one go from a patchwork
>>>     instance. I'd caution you that there are gigabytes of patches in the
>>>     databases of production instances going back over a decade, so you
>>>     might find that a challenging data set to acquire and work with.
>>>
>>>   - In terms of 'catching up': I think you're asking if Patchwork will
>>>     let you _export_ all patches since your last pull, rather than asking
>>>     if patchwork will let you import patches? I think that makes the most
>>>     sense in context. If that's the case, then the way I would do that
>>>     is:
>>>
>>>     a) observe the highest patch ID in the project you are tracking, as
>>>        patch IDs are always increasing. Note that the same cannot be said
>>>        about dates - patchwork instances, due to the quirks of email,
>>>        often get mail out-of-order. You probably want something like:
>>>
>>>        http://patchwork.ozlabs.org/api/patches/?order=-id&project=linuxppc-dev
>>>
>>>     b) Retrieve all email from your last pull to that patch ID. Bear in
>>>        mind that it is likely that more email will arrive while you are
>>>        doing this - hence why I suggest fetching the patch ID first! Be
>>>        careful also of pagination as that can also change if new patches
>>>        come in. One day we will fix this by adding cursor-based
>>>        pagination as well but we haven't done it yet. As such you
>>>        probably want to do this with a different query with the opposite
>>>        ordering, something like:
>>>
>>>        http://patchwork.ozlabs.org/api/patches/?since=2020-05-01T00%3A00%3A00&project=linuxppc-dev
>>>
>>>        (order=id is implied but wouldn't hurt to specify it, and an API
>>>        version, in your final code)
>>
>> I might be missing something, but why does it matter if more patches
>> arrive while pulling? PaStA can pull all patches since it's last pull as
>> you mentioned. 
> 
> I'll also point out the events API [1]. This would be a lighter way to
> probe for new patches. In particular, you probably care about the
> 'patch-created' event, which occurs every time we receive a new patch.
> You can poll for these like so:
> 
>     http://patchwork.ozlabs.org/api/events/?category=patch-created&since=2020-05-01T00%3A00%3A00&project=linuxppc-dev
> 
> Also, this doesn't exist yet, but it would be quite easy to add the
> concept of webhooks. With a webhook infrastructure, you'd be able to
> configure Patchwork to POST a JSON payload to an arbitrary URL every
> time we e.g. receive a new patch. This would allow Patchwork to push

Uh, does that scale?

> things to you instead of having to poll. You would have to wait for a
> future 3.0 release for this though, assuming you wanted to run against
> a public instance.

Both approaches, webhooks and events are synchronous methods that only
work if there are no interruptions. I'd rather prefer asynchronous methods.

Thanks
  Ralf

> 
> Stephen
> 
> [1] https://patchwork.readthedocs.io/en/latest/api/rest/schemas/v1.2/#get--api-1.2-events-
>