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https://issues.apache.org/jira/browse/SSHD-1262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17523026#comment-17523026
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Lyor Goldstein commented on SSHD-1262:
--------------------------------------
The log clearly shows the {{SSH_MSG_CHANNEL_OPEN_CONFIRMATION}} with the zero
size
{noformat}
2022-04-13 05:51:41:644 [sshd-SshClient[5313b03e]-nio2-thread-8] DEBUG
org.apache.sshd.client.session.ClientConnectionService -
channelOpenConfirmation(TcpipClientChannel[id=0,
recipient=-1]-ClientSessionImpl[User@/x.xxx.xx.xxx:xxxx])
SSH_MSG_CHANNEL_OPEN_CONFIRMATION sender=0, window-size=0, packet-size=65536
{noformat}
and no further window adjustments - therefore, according to the [RFC 4254
section 5.1|https://datatracker.ietf.org/doc/html/rfc4254#section-5.1]
{quote}
The 'initial window size' specifies how many bytes of channel data can be sent
to the sender of this message without adjusting the window
{quote}
which in this case is +zero+ - i.e., the client (or server) will wait until
window is expanded. There may be a special behavior that uses zero size to mean
something else using KEX extensions (see RFC-8308, 9142) however I do not see
such a request in the log file + we do not support all of these extensions (I
think {{xon/xoff}} is the relevant one to this issue)
> Unhandled SSH_MSG_CHANNEL_WINDOW_ADJUST leeds to SocketTimeoutException
> -----------------------------------------------------------------------
>
> Key: SSHD-1262
> URL: https://issues.apache.org/jira/browse/SSHD-1262
> Project: MINA SSHD
> Issue Type: Bug
> Affects Versions: 2.7.0, 2.8.0
> Reporter: Stefan Maute
> Priority: Major
> Labels: mina, sshd
> Attachments: failing-pf-trace-logs.txt
>
>
> Wanted to open a local port forwarding to an SSH server and afterwards
> connect to MQTT server over the SSh tunnel. During the MQTT connection
> attempt I encountered a SocketTimeoutException in the logs (StackTrace below).
> What I could see in the logs is that the server is sending an initial window
> size of 0 and afterwards the _waitForCondition_ method is throwing the
> SocketTimeoutException .
> After analyzing the logs I maybe have an idea what is going on here. My
> assumption is that there is some deadlock in case the initial window size is
> 0 and the SSH_MSG_CHANNEL_WINDOW_ADJUST isn't handled properly.
> I have attached the whole log file. Lines of interest are from 169 to 229.
> Tested with 2.7.0 and 2.8.0.
>
> {code:java}
> WARN org.apache.sshd.common.forward.DefaultForwarder -
> exceptionCaught(Nio2Session[local=/127.0.0.1:44259, remote=/127.0.0.1:60188])
> SocketTimeoutException:
> waitForCondition(Window[client/remote](TcpipClientChannel[id=0,
> recipient=0]-ClientSessionImpl[Admin@/x.xxx.xx.x:xxxx])) timeout exceeded:
> PT30S java.net.SocketTimeoutException:
> waitForCondition(Window[client/remote](TcpipClientChannel[id=0,
> recipient=0]-ClientSessionImpl[Admin@/x.xxx.xx.x:xxxx])) timeout exceeded:
> PT30S at
> org.apache.sshd.common.channel.Window.waitForCondition(Window.java:332)
> at org.apache.sshd.common.channel.Window.waitForSpace(Window.java:286) at
> org.apache.sshd.common.channel.ChannelOutputStream.write(ChannelOutputStream.java:154)
> at
> org.apache.sshd.client.channel.ClientChannelPendingMessagesQueue.writeMessage(ClientChannelPendingMessagesQueue.java:174)
> at
> org.apache.sshd.client.channel.ClientChannelPendingMessagesQueue.flushPendingQueue(ClientChannelPendingMessagesQueue.java:221)
> at
> org.apache.sshd.client.channel.ClientChannelPendingMessagesQueue.operationComplete(ClientChannelPendingMessagesQueue.java:206)
> at
> org.apache.sshd.client.channel.ClientChannelPendingMessagesQueue.operationComplete(ClientChannelPendingMessagesQueue.java:51)
> at
> org.apache.sshd.common.future.AbstractSshFuture.notifyListener(AbstractSshFuture.java:159)
> at
> org.apache.sshd.common.future.DefaultSshFuture.notifyListeners(DefaultSshFuture.java:215)
> at
> org.apache.sshd.common.future.DefaultSshFuture.setValue(DefaultSshFuture.java:112)
> at
> org.apache.sshd.client.future.DefaultOpenFuture.setOpened(DefaultOpenFuture.java:68)
> at
> org.apache.sshd.client.channel.AbstractClientChannel.handleOpenSuccess(AbstractClientChannel.java:360)
> at
> org.apache.sshd.common.session.helpers.AbstractConnectionService.channelOpenConfirmation(AbstractConnectionService.java:545)
> at
> org.apache.sshd.common.session.helpers.AbstractConnectionService.process(AbstractConnectionService.java:456)
> at
> org.apache.sshd.common.session.helpers.AbstractSession.doHandleMessage(AbstractSession.java:503)
> at
> org.apache.sshd.common.session.helpers.AbstractSession.handleMessage(AbstractSession.java:429)
> at
> org.apache.sshd.common.session.helpers.AbstractSession.decode(AbstractSession.java:1466)
> at
> org.apache.sshd.common.session.helpers.AbstractSession.messageReceived(AbstractSession.java:389)
> at
> org.apache.sshd.common.session.helpers.AbstractSessionIoHandler.messageReceived(AbstractSessionIoHandler.java:64)
> at
> org.apache.sshd.common.io.nio2.Nio2Session.handleReadCycleCompletion(Nio2Session.java:359)
> at
> org.apache.sshd.common.io.nio2.Nio2Session$1.onCompleted(Nio2Session.java:336)
> at
> org.apache.sshd.common.io.nio2.Nio2Session$1.onCompleted(Nio2Session.java:333)
> at
> org.apache.sshd.common.io.nio2.Nio2CompletionHandler.lambda$completed$0(Nio2CompletionHandler.java:38)
> at
> java.base/java.security.AccessController.doPrivileged(AccessController.java:318)
> at
> org.apache.sshd.common.io.nio2.Nio2CompletionHandler.completed(Nio2CompletionHandler.java:37)
> at java.base/sun.nio.ch.Invoker.invokeUnchecked(Invoker.java:129) at
> java.base/sun.nio.ch.Invoker$2.run(Invoker.java:221) at
> java.base/sun.nio.ch.AsynchronousChannelGroupImpl$1.run(AsynchronousChannelGroupImpl.java:113)
> at
> java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
> at
> java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
> at java.base/java.lang.Thread.run(Thread.java:833) {code}
>
>
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