> On Thur, 25 May 2017, Daniel Stenberg wrote:

> You mean like when handle Y reaches state X, start transfer Z ? Where X
> would be more or less those different states.
>
> That just feels like a very niche feature that we've had very little requests
> for. And I suspect it would also lead to many more things needed for it to be
> really usable to applications; like what if it doesn't reach the state within a
> certain time or what if it ends before it reaches the state how would that be
> signalled back to the application? Tricky.

Yes I see the problem there.

>
> Another approach would be to offer a callback for state changes so that
> applications can get told when the transfer state changes and then they
> could do whatever they want with that info. A callback seems better to me
> than just a getinfo, since if you want to do something special when libcurl
> reaches a particular state it's impractical to keep polling the state to detect
> it...
>
> Of course, even with callbacks we have the problem for when a certain state
> isn't reached at all but instead get skipped etc.
>

With my Statechart hat on, it sounds like you're proposing triggering "new" events on state entry. That does indeed sound better than polling but I wonder if a simpler approach might just be to emit the "old" events that triggered the libcurl state transition. In practice, libcurl and the application would have their own independent state chart models; these could be very similar, or very different. The benefit is that libcurl's internal state remains hidden and avoids some problems. However, I'm sure there are difficulties with this approach too :)

Lucas

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Received on 2017-05-25