On 12/26/2013 12:54 PM, Sergey Mironov wrote:
Still, I think API should somehow highlight the fact
that channel is not an autonomous object, but a reference to a
client's slot. (according to the implementation, it is no more than a
tuple (channel_id,client_id)) Maybe, changing names would be enough
here. For me, recv associates with a function that could receive data
from any socket, which is not the case here. Another idea - add some
error-checking to the recv's code. It may raise an exception if user
passes it a channel which has client_id /= current_client_id.
I've added the error checking you suggested: an exception will be raised
on trying to read another client's channel. In the process, I also
fixed some issues with proper association of page requests with clients,
so that the error should occur less often. For now, I'm not convinced
that the API itself should change, considering the explanation in the
manual.
[1] Begin error: cannot start a transaction within a
transaction<br/>Expunge blocked by error: Error running SQL BEGIN
Higher-order bits: I think this indicates an Ur/Web bug; it should not be
possible to write Ur/Web code that does anything explicit with transactions.
It's possible that something about the non-atomic transactions of SQLite
(which I warn about in the manual) is responsible somehow, but it doesn't
seem likely to me.
I managed to reproduce the problem, which only manifested for me after a
fatal error in a page handler. It was an issue related to a
benchmark-inspired optimization I added recently, and not anything
specific to a database system or anything that only shows up under high
concurrency or weird disk configuration. It should be fixed now; let me
know if it recurs.
Looks like latest urweb can't compile channel2.ur anymore. It says
dev:[grwlf@greyblade:~/proj/urweb/tests]$ urweb -dbms sqlite channel2
:0:0: (to 0:0) Function Channel2/monitor needed for both a link and a form
Make sure that the signature of the containing module hides any form handlers.
:0:0: (to 0:0) Function Channel2/put needed for both a link and a form
Make sure that the signature of the containing module hides any form handlers.
Channel2.ur doesn't use any forms so it is probably a regression, is it?
I'm surprised if a previous Ur/Web version compiled this source code
without complaint. The behavior you're seeing is expected, for reasons
explained in Section 10 of the manual.
Executive summary: any properly typed function exported from a program's
main module is treated as accessible via GET requests. However, RFCs
say that GET requests shouldn't cause side effects. One fix is to add a
.urs file that only exposes the entry points you really intended. (As a
bonus, this should also enable you to remove [: transaction page]
annotations in the .ur file!)
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