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Posted to dev@mina.apache.org by GitBox <gi...@apache.org> on 2022/11/03 23:31:05 UTC
[GitHub] [mina-sshd] tomaswolf opened a new issue, #266: Race condition causes ScpTest.testScpNativeOnMultipleFiles() to fail (flaky test)
tomaswolf opened a new issue, #266:
URL: https://github.com/apache/mina-sshd/issues/266
The ultimate problem is a general one concerning ChannelExecs:
If
* there is a communication protocol implemented between the client and the remote command via the stdin/stdout streams,
* and if the protocol is such that the remote command can return an error code _in this application protocol_,
* and the client uses the default inverted output stream to read that error code,
* and the client then decides to close the channel (even gracefully),
then it is possible that the `AbstractClientChannel`'s `out` stream is closed between lines [436](https://github.com/apache/mina-sshd/blob/a85d0743/sshd-core/src/main/java/org/apache/sshd/client/channel/AbstractClientChannel.java#L436) and 437, and then the `flush()`call on the `ChannelPipedOutputStream` may fail, causing the whole session to go down.
This can happen in the `ScpTest`at line [343](https://github.com/apache/mina-sshd/blob/a85d0743e/sshd-scp/src/test/java/org/apache/sshd/scp/client/ScpTest.java#L343), which tests an scp upload command that should fail. The scp server sends back an ERROR ack, which the client reads (on an I/O thread) and forwards in `AbstractClientChannel`. The client reads this though the `ChannelPipedInputStream` (on the main thread) and throws an exception, which then causes the channel to be closed at the end of `DefaultScpClient.runUpload()` (still on the main thread). Only then does the I/O thread call `flush()`, which then fails with an exception.
So in short we have
1. I/O thread: receive data
2. I/O thread: write data to `ChannelPipedOutputStream`
3. Main thread: read data from `ChannelPipedInputStream`
4. Main thread: close channel
5. I/O thread: call `ChannelPipedOutputStream.flush()` and fail.
This is all the more infuriating since `ChannelPipedOutputStream.flush()` is essentially a no-op. Moreover: an exception when a channel has received data and tries to forward it should not take down the whole session but only this channel.
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[GitHub] [mina-sshd] tomaswolf closed issue #266: Race condition causes ScpTest.testScpNativeOnMultipleFiles() to fail (flaky test)
Posted by GitBox <gi...@apache.org>.
tomaswolf closed issue #266: Race condition causes ScpTest.testScpNativeOnMultipleFiles() to fail (flaky test)
URL: https://github.com/apache/mina-sshd/issues/266
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