A potentially serious bug in KIO/kio_http and a possible patch ??

Maksim Orlovich mo85 at cornell.edu
Sun Jul 18 17:01:37 BST 2010

You're right. Sorry. Should have looked at the entire context.

Anyway, this is definitely the sensible thing to do for 4.5; messing
about with KIO::Connection and the like is way too risky.

Speaking of that... You mentioned it ended in ::send --- did it take
the sendnow path, or the whole outgoingRequests queue? That second bit
looks really iffy to me, but I am not sure I am not just scapegoating
it. Anyway, it would be good if you could send me a bit more info on
what the request looks like, as I would like to debug the lower-level
KIO bits (who knows what else they might be messing up?)

As for gmail chat inside khtml, it seems to need improvements in
npruntime support in nspluginviewer/KParts::ScriptableExtension in
khtml due to the Flash bits; I can't be 100% sure of whether it's the
real cause or not, but I have to do that stuff anyway.

On 7/17/10, Dawit A <adawit at kde.org> wrote:
> On Saturday, July 17, 2010 12:19:31 Maksim Orlovich wrote:
>> This patch looks wrong to me, as even in the limited case, you could
>> potentially have the data that's already buffered fulfill the request
>> entirely, can you not?
> Nope and that is because in the limited case you already know the total size
> of the content you are downloading ; so you actually know there is still
> content left out there and readBuffered will do the right thing and send the
> total bytes read in that case. I also made sure the patch does not cause
> regression by checking if BR# 180631 works as before and it does...
> The issue that caused the bug (180631) which you provided a fix for is a
> chunked transfer where you cannot not really know you have gotten the whole
> data until you receive EOF from the socket. To be frank, the patch is
> actually
> a small performance improvement fix and not the actual bug fix for the Gmail
> chat issue. The actual bug that causes that issue is somewhere in the
> KIO::Connection class ; the point which the second portion of the send data
> message never makes past. IOW, I actually discovered what readBuffered does
> by
> accident while hunting for the source of the chat issue...
>> Will look at other stuff later in the evening... Though I must say I
>> am impressed you could trace down anything gmail-related to such a low
>> level.
> Believe me it was not by choice and if I did not have the source code to add
> a
> lot of debug statements and see what is happening, I would never ever have
> attempted this... Plus, I use Gmail chat  on occasions and nothing is more
> motivating than when something you use breaks, right ;)
> P.S. The patch I sent in the first email was incorrect. Make sure you try
> the
> second one I sent...
> Regards,
> Dawit A.
>> On 7/17/10, Dawit A <adawit at kde.org> wrote:
>> > Hi,
>> >
>> > The attached patch makes it possible for HTTPProtocol::readBuffered
>> > function to
>> > behaves differently when called from readLimited. This patch is intended
>> > to address the issue of the Gmail chat functionality no longer working
>> > in kdewebkit based browsers.
>> >
>> > Though the patch fully addresses the aforementioned bug, it really does
>> > not fix
>> > the actual cause of this bug. So what is the actual cause ?  Well when
>> > you log
>> > in to Gmail, a check is preformed to see if the chat functionality is
>> > enabled
>> > or not.  This is done through a simple GET request that returns a 20
>> > byte
>> > response. At that point kio_http has read the header and few bytes of
>> > the
>> > content as well, 3 bytes to be exact. kio_http stores these few bytes of
>> > data
>> > that are not part of the header in a buffer.
>> >
>> > It then attempts to read the content and that is where the fun starts...
>> > Because kio_http has received the actual size of the content it is
>> > supposed to
>> > read, it will use readLimited to get the content. readLimited in turn
>> > calls readBuffered which, as a result of a fix for bug 180631, always
>> > sends whatever
>> > data was read ahead while retrieving the header above. This means the 3
>> > bytes
>> > above will be sent to the client first in our case. After that kio_http
>> > retrieves and attempts to send the remaining 17 bytes. However, this
>> > last
>> > portion never ever makes it to the client application. It seems to
>> > disappear into the ether! Actually it never gets past
>> > KIO::Connection::send and at this
>> > point I cannot figure out why!
>> >
>> > So why this patch then ?  Simple. If you followed what I attempted to
>> > explain
>> > above, you would see that it is very inefficient for kio_http to split a
>> > 20 byte
>> > data especially when it already knows the final size of the content it
>> > is
>> > supposed to retrieve from the server ; so addressing that through this
>> > patch should be no brainer. The fact that the Gmail chat issue gets
>> > fixed as a result
>> > is only a bonus at this point.
>> >
>> > And hence my request...
>> >
>> > #1. Can someone using KHTML verify whether or not the Gmail chat
>> > functionality
>> > works for them ? I cannot get Gmail to work with KHTML here ; so I am
>> > unable to do this myself.
>> >
>> > #2. Can someone tell me if there is a scenario where sending two
>> > requests in rapid succession might result in one of them being dropped ?
>> >
>> > #3. Any objections, concerns, suggestions etc about the patch are
>> > welcome.
>> >
>> > Regards,
>> > Dawit A.

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