On 04/11/2012 05:55 PM, Zulfiqar Malik wrote:
I am trying to write a very small shell client for some automation
related things and am running into problems with libssh2_channel_read.
Here are the two scenarios (application has to be single threaded.):
1. Blocking mode: libssh2_channel_read blocks if there's no data and
never returns. Its impossible to use this function reliably.
2. Non-blocking mode: libssh2_channel_read doesn't block but keeps on
returning -37 (LIBSSH2_ERROR_EAGAIN) and I end up with essentially the
same problem i.e. stuck in an infinite loop. To top it off
libssh2_channel_eof doesn't work and always returns 0.
You don't say what's happening at the other end. Can we assuming it's
something like:
libssh2_channel_exec(channel, "cat foo");
and that you want to exit when the contents of foo have been returned?
Is is possible, for example, that your channel is not returning eof
because it isn't eof?
I don't know what's wrong or what needs to be done but I cannot seem to
find a way through this problem. I have tried libssh2 v 1.3.1 and the
latest one 1.4.1 with the same result. Given below is my readOutput
method which reads the output:
for (;;count++)
{
/* loop until we block */
int rc;
do {
char buffer[1024];
rc = libssh2_channel_read(channel, buffer, sizeof(buffer));
if (rc > 0) {
bytecount += rc;
buffer[rc] = '\0';
Probably not related, but ^^^ corrupts the stack if libssh2_channel_read
returns a full buffer. If you're going to explicitly null terminate the
buffer, you need:
rc = libssh2_channel_read(channel, buffer, sizeof(buffer) - 1);
fprintf(stderr, "%s", buffer);
count = 0;
}
else {
if (rc != LIBSSH2_ERROR_EAGAIN)
fprintf(stderr, "libssh2_channel_read returned
%d\n", rc);
}
if (libssh2_channel_eof(channel)) {
rc = 0;
break;
}
}
while(rc > 0);
//::Sleep(3);
/* this is due to blocking that would occur otherwise so we loop on
this condition */
if(rc == LIBSSH2_ERROR_EAGAIN)
{
::Sleep(5);
//waitsocket(sock, sshSession);
I'm assuming this references something like the waitsocket() example at
http://www.libssh2.org/examples/ssh2_exec.html. Why the sleep instead?
}
else
break;
}
Matt
--
Matthew Booth, RHCA, RHCSS
Red Hat Engineering, Virtualisation Team
GPG ID: D33C3490
GPG FPR: 3733 612D 2D05 5458 8A8A 1600 3441 EA19 D33C 3490
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