Re: Need help, channel_read() blocks forever before EOF

["Paulo R. Panhoto" <paulo.panhoto@xxxxxxxxx>]

Hello,

Your loop is not checking for SSH_ERROR. Perhaps you should change it to 
if(... && channel_poll(channel, 0) > 0).

Your stacktrace shows that you are reading on a socket that has no data. 
Why don't you try channel_read_nonblocking() instead?

    -- Paulo

On 16/05/11 10:39, Zhang Qian wrote:
> Hi,
>
> I wrote a program in a RHEL linux machine which tries to execute a 
> powershell script remotely on a Windows 2008 server, and get the 
> result back. In the Windows 2008 server, I have WinSSHD installed and 
> running.
>
> I found my program will always hang at channel_read(), see  the 
> following callstack:
> (gdb) bt
> #0  0x000000381f4d4755 in recv () from /lib64/libc.so.6
> #1  0x00002aaaaaaca2cc in ssh_socket_unbuffered_read (s=0x605720, 
> buffer=0x60b430, len=16) at socket.c:135
> #2  0x00002aaaaaaca338 in ssh_socket_completeread (s=0x605720, 
> buffer=0x60b430, len=16) at socket.c:197
> #3  0x00002aaaaaacaa63 in ssh_socket_wait_for_data (s=0x605720, 
> session=0x605050, len=<value optimized out>) at socket.c:297
> #4  0x00002aaaaaac3ea9 in packet_read2 (session=0x605050) at packet.c:66
> #5  0x00002aaaaaab92e0 in channel_read (channel=0x60b9b0, 
> buffer=0x60ac60, bytes=498, is_stderr=<value optimized out>)
>     at channels.c:850
> #6  0x0000000000401e74 in helper_SSHChannelGets (sessionRec=0x605010, 
> maxBytesToRead=498, result=0x7fffffffe478, timeout_in_sec=0)
>     at sshutils.c:323
> #7  0x0000000000402827 in helper_SSHGets (sessionRec=0x605010, 
> resultSize=513,
>     result=0x7fffffffe530 " <Property 
> Name=\"VMName\">Test_VM</Property>\r\n", timeout_in_sec=0) at 
> sshutils.c:686
> #8  0x0000000000402bfa in SSHGets (sessionRec=0x605010, resultSize=513,
>     result=0x7fffffffe530 " <Property 
> Name=\"VMName\">Test_VM</Property>\r\n") at sshutils.c:826
> #9  0x0000000000401499 in main () at main.c:25
>
> I am sure the EOF did not happen, so why did channel_read() block 
> there and never return? Only about 1/3 result can be returned back.
>
> In my program, I call channel_request_exec() to execute the powershell 
> script remotely, and then call channel_read() in a while loop to get 
> the stdout of that script:
>     ...
>     /* The following code are in a while loop */
>     if (channel_is_open(channel) &&  channel_poll(channel,0)) {
>         curr_bytes=channel_read(channel,readbuf, bytes_to_read, 0);
>         ...
>
> Is there any mistakes in my program? Or any configurations I should do 
> in WinSSHD? Or try another SSH daemon for Windows?
>
> Any help will be really appreciated, thanks!
>
>
>
> Regards,
> Qian