Thread: [JSch-users] Bug: ChannelDirectTCPIP fails if remote side sends EOF quickly

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Hello Atsuhiko  (and other interested parties),

I tried to open a direct-tcpip channel to some TCP server which replies
with a message and immediately closes the connection. (See [0] for background.)

When trying this with the StreamForwarding example, it shows the output and
then throws an JSchException (in `.connect()`). When modifying the example
to use `getInputStream()` instead of `setOutputStream()`, it only throws
the exception and I don't get to read from the stream because of the exception.

I added quite some debugging commands to Session.run [1] to localize the problem.
At the end [2] is the output when adding the logger from the Logger example.

The same problem occurs if I use socket-forwarding (PortForwardingL), but
the PortWatcher's run() loop silently discards the exception. I added a
logging call in the catch block, see below [3] for example output (last line
shows the exception, without stack trace).

As we can see, the remote host sends an SSH_MSG_CHANNEL_EOF before our channel's
connect() method had the chance to even see that the connection is open, and thus
it throws an exception instead of simply returning.

Solution idea:

We should in the Session's packet read loop somehow treat
SSH_MSG_CHANNEL_OPEN_FAILURE differently than SSH_MSG_CHANNEL_EOF.
Now, both are calling channel.remote_eof(), and this is used by the
ChannelDirectTCPIP to tell wether the connection was successful.

Maybe the ChannelDirectTCPIP could use the exit code, or another
additional status variable instead of remote_eof for this decision.

Paŭlo

[0] Background:

I wanted to create a general SocketImpl based on JSch's ChannelDirectTCPIP, so
I can implement a SocketFactory or similar things for other libraries (like RMI
or Webservice calls).

I searched a bit for a simple enough server to test this, and finally used
a server I'm working with on my current project (the same one that got me
to JSch, and where I'm using the ProxySSH I posted some weeks ago).  Normally
this is used with "telnet localhost 2006". I think another example with similar
behaviour would be the standard Daytime service as defined in RFC 861.

When my TunnelSocketImpl not worked (same exception as described), I tried with
the official examples.

[1] I commited the latest changes to the better-examples branch of my github repository.
You can view the source here:
   <https://github.com/ePaul/jsch-documentation/blob/better-examples/src/com/jcraft/jsch/Session.java#L1300>
(I think I will move this to the master branch later.)

[2] Log output from StreamForwarding example with added logger.
    The lines starting with 10.5. are on stdout, what the remote
    host sent. The rest is logging output on stderr.

INFO: Connecting to 141.20.23.223 port 22
INFO: Connection established
INFO: Remote version string: SSH-2.0-dropbear_0.52
INFO: Local version string: SSH-2.0-JSCH-0.1.44
INFO: CheckCiphers: aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,3des-ctr,arcfour,arcfour128,arcfour256
INFO: SSH_MSG_KEXINIT sent
INFO: SSH_MSG_KEXINIT received
INFO: kex: server->client aes128-ctr hmac-md5 none
INFO: kex: client->server aes128-ctr hmac-md5 none
INFO: SSH_MSG_KEXDH_INIT sent
INFO: expecting SSH_MSG_KEXDH_REPLY
INFO: ssh_rsa_verify: signature true
WARN: Permanently added '141.20.23.223' (RSA) to the list of known hosts.
INFO: SSH_MSG_NEWKEYS sent
INFO: SSH_MSG_NEWKEYS received
INFO: SSH_MSG_SERVICE_REQUEST sent
INFO: SSH_MSG_SERVICE_ACCEPT received
INFO: Authentications that can continue: publickey,keyboard-interactive,password
INFO: Next authentication method: publickey
INFO: Authentications that can continue: password
INFO: Next authentication method: password
INFO: Authentication succeeded (password).
System.{in,out} will be forwarded to localhost:2006.
DEBUG: waiting for channel reply ...
DEBUG: packet received, type: 91
INFO: SSH_MSG_CHANNEL_OPEN_CONFIRMATION received, channel: 0
DEBUG: packet received, type: 94
INFO: SSH_MSG_CHANNEL_DATA received, channel: 0, len: 772
10.7.205.149,1353052,5242911,37,2,0
10.5.59.109,1353031,5242920,1000,1,0
10.5.58.253,1353072,5242964,36,2,0
10.7.205.151,1353009,5243308,51,2,0
10.5.59.93,1353008,5242896,86,2,0
10.7.205.153,1353333,5243057,60,2,0
10.5.59.150,1353085,5242948,74,2,0
10.5.70.9,1352998,5243159,55,2,0
10.5.59.159,1353108,5242965,55,2,0
10.5.70.16,1353094,5242978,52,2,0
10.5.70.8,1353145,5243099,51,2,0
10.5.59.151,1353205,5242922,86,2,0
10.5.59.142,1352973,5242900,58,2,0
10.5.59.147,1353018,5242996,41,2,0
10.5.70.54,1353130,5242946,33,2,0
10.5.59.161,1353426,5243212,59,2,0
10.5.70.12,1353128,5242955,71,2,0
10.5.59.117,1353091,5242902,103,2,0
10.5.59.111,1353086,5242954,14,2,0
10.5.59.153,1353032,5242921,56,2,0
10.7.205.14,1353035,5242951,1000,1,0
10.5.58.251,1353129,5242940,1000,1,0
DEBUG: packet received, type: 96
INFO: SSH_MSG_CHANNEL_EOF received, channel: 0
DEBUG: packet received, type: 97
INFO: SSH_MSG_CHANNEL_CLOSE received, channel: 0
DEBUG: ... finished waiting for channel reply
Exception in thread "main" com.jcraft.jsch.JSchException: channel is not opened: remote EOF
        at com.jcraft.jsch.ChannelDirectTCPIP.connect(ChannelDirectTCPIP.java:127)
        at StreamForwarding.main(StreamForwarding.java:60)

-----------

[3]  Logging output from PortForwardingL example with added logger.

INFO: Connecting to 141.20.23.223 port 22
INFO: Connection established
INFO: Remote version string: SSH-2.0-dropbear_0.52
INFO: Local version string: SSH-2.0-JSCH-0.1.44
INFO: CheckCiphers: aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,3des-ctr,arcfour,arcfour128,arcfour256
INFO: SSH_MSG_KEXINIT sent
INFO: SSH_MSG_KEXINIT received
INFO: kex: server->client aes128-ctr hmac-md5 none
INFO: kex: client->server aes128-ctr hmac-md5 none
INFO: SSH_MSG_KEXDH_INIT sent
INFO: expecting SSH_MSG_KEXDH_REPLY
INFO: ssh_rsa_verify: signature true
WARN: Permanently added '141.20.23.223' (RSA) to the list of known hosts.
INFO: SSH_MSG_NEWKEYS sent
INFO: SSH_MSG_NEWKEYS received
INFO: SSH_MSG_SERVICE_REQUEST sent
INFO: SSH_MSG_SERVICE_ACCEPT received
INFO: Authentications that can continue: publickey,keyboard-interactive,password
INFO: Next authentication method: publickey
INFO: Authentications that can continue: password
INFO: Next authentication method: password
INFO: Authentication succeeded (password).
localhost:2007 -> localhost:2006
DEBUG: waiting for channel reply ...
DEBUG: packet received, type: 91
INFO: SSH_MSG_CHANNEL_OPEN_CONFIRMATION received, channel: 0
DEBUG: packet received, type: 94
INFO: SSH_MSG_CHANNEL_DATA received, channel: 0, len: 774
DEBUG: packet received, type: 96
INFO: SSH_MSG_CHANNEL_EOF received, channel: 0
DEBUG: packet received, type: 97
INFO: SSH_MSG_CHANNEL_CLOSE received, channel: 0
DEBUG: ... finished waiting for channel reply
WARN: com.jcraft.jsch.JSchException: channel is not opened: remote EOF

Thread: [JSch-users] Bug: ChannelDirectTCPIP fails if remote side sends EOF quickly

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