Re: channel_write will fail if large amount of data are being written (0.4 branch)

[Aris Adamantiadis <aris@xxxxxxxxxxxx>]

Hi Vic,

Could you try to get a backtrace at this place ?
I wonder why ssh_socket_nonblocking_flush is called. I put a breakpoint 
on this function and was not able to trigger it using samplessh.
Could you also check session->blocking value ? normaly it's set to 1 in 
ssh_new and I could not find any other place where it's changed.

Thanks,

Aris

Vic Lee a écrit :
> Hi,
>
> I found another bug in channel_write() which make it fail to tunnel an
> xterm over SSH.
>
> According to the description, channel_write() is a blocking write until
> all data written or until error. However, in the following call
> sequence:
>
> channel_write -> packet_send -> packet_send2 -> packet_write ->
> packet_flush (at packet.c:456), it uses a non-blocking call:
>
>   rc = packet_flush(session, 0);
>
> which will almost always return SSH_AGAIN if large amount of data are
> being flushed, and SSH_AGAIN will eventually returned by packet_send.
> However, when channel_write calls packet_send it does not check for
> SSH_AGAIN and simply think anything other than SSH_OK is an error.
>
> This bug makes it impossible to tunnel an xterm (it's funny somehow
> xterm has large data transmit). I temporarily change the packet_flush to
> a blocking call fix the issue. But I think a right patch should be on
> channel_write, checking SSH_AGAIN.
>
> Your comments?
>
> Thanks,
>
> Vic