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

[Vic Lee <llyzs@xxxxxxx>]

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