[web-devel] [Yesod] Re: Next version of WAI: cleaning house

[Michael Snoyman]

I think Greg and davean are saying something similar here. If I may
paraphrase (please correct me if I'm wrong): some information may not be
derivable by the WAI handler (e.g. Warp) itself, but with a little bit of
help from the user, that information could be included in the WAI standard.

If that's what you're getting at, I disagree. This would essentially mean
we require users to provide information to Warp, so that Warp can provide
that information to user applications. Warp (or any other handler) is just
a dumb transport mechanism then. And since we can't rely on that
information being present, we'd wrap it up with Maybe values, and therefore
end up losing type safety.

The prime example of all this is application root. I still strongly believe
that Yesod did this the right way: if the user needs to provide the
information, then ask the user to provide the information to the
application itself, and the WAI handler needn't know anything about it.

Is there some kind of data that the WAI handler could do a better job of
passing onto the application than the user can do?


On Tue, Jul 23, 2013 at 11:58 PM, Greg Weber <greg at gregweber.info> wrote:

> In Rack most of these things are known. In some cases this requires users
> to configure the proxy to send headers.
>
> One solution would be having the user state what values are being depended
> on and having Warp fail on startup with an error message if it can't
> collect them.
> It is possible to expect some of these values to not change (and require a
> reboot of warp when they do) and have them be part of Warp rather than WAI.
>
> But just wrapping these values in a Maybe could be another approach.
>
>
> On Tue, Jul 23, 2013 at 1:13 PM, Michael Snoyman <michael at snoyman.com>wrote:
>
>> The reason we'd be removing those is that there *still* isn't any way to
>> know this. If Warp is sitting behind a reverse proxy (which is virtually
>> always the case, whether Amazon ELB, Nginx, Keter, or something else)
>> there's no way to know what the actual server name, server port, or scheme
>> are.
>>
>>
>> On Tue, Jul 23, 2013 at 6:37 PM, Federico Mastellone <fmaste at gmail.com>wrote:
>>
>>> Hi,
>>>
>>> Without isSecure and serverPort, will Applications be able to handle
>>> requests to different ports and HTTP or HTTPS in different ways? I won't be
>>> able to know if the login is made over HTTP and redirect to HTTPS with any
>>> Wai server.
>>>
>>> On 23/07/2013, at 07:04, Michael Snoyman <michael at snoyman.com> wrote:
>>>
>>> Some of you may have seen the brief interchange between Kazu and myself
>>> regarding ResourceT in WAI. Let me give a very brief synopsis of the
>>> situation:
>>>
>>>    - In order to allow WAI applications to acquire scarce resources
>>>    like file handles in an exception-safe way, WAI actions all live in a
>>>    `ResourceT IO` monad, instead of just `IO`.
>>>    - Kazu has mentioned to me in the past that, based on his profiling,
>>>    monadic bind for ResourceT may currently be a bottleneck in WAI.
>>>    - I made an experimental change to WAI so that, instead of actions
>>>    living in `ResourceT IO`, the WAI Request value contains a ResourceT
>>>    InternalState value, which can be used to accomplish the exact same thing
>>>    as living in ResourceT (see [1]).
>>>    - Kazu checked out the performance difference of this new branch,
>>>    and it allows for some better optimizations.
>>>
>>> If this was purely a performance optimization, I would probably just
>>> optimize Warp and not bother changing WAI. However, I think that this
>>> change makes WAI itself better as well, and therefore am in favor of making
>>> this as a breaking change, releasing it as WAI 2.0[2]. Firstly, are there
>>> any objections to this move?
>>>
>>> So as long as we're making a breaking change, the question arises: what
>>> other changes should we be making to WAI? I know Kazu had mentioned adding
>>> fields to avoid the need for lookups, can you clarify that request a bit?
>>> Here are some other changes I can think of:
>>>
>>>    - Remove the deprecated isSecure field from the Request data type.
>>>    - Remove the misleading fields serverName and serverPort fields as
>>>    well.
>>>    - Possibly: hide the Request constructor so that new fields can be
>>>    added without breaking backwards compatibility.
>>>
>>> If anyone else has some ideas, please bring them up.
>>>
>>> [1]
>>> http://haddocks.fpcomplete.com/fp/7.4.2/20130704-120/resourcet/Control-Monad-Trans-Resource.html#g:10
>>> [2] For the Yesod community: the change is minor enough that Yesod 1.2
>>> can have some conditional compilation to support both the current WAI 1.4
>>> and WAI 2.0, so this shouldn't affect most Yesod users at all.
>>>
>>> _______________________________________________
>>> web-devel mailing list
>>> web-devel at haskell.org
>>> http://www.haskell.org/mailman/listinfo/web-devel
>>>
>>>
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