Warning: Undefined array key 2 in SSH2 initShell

[simPod]

Sometimes, I get Warning: Undefined array key 2

phpseclib/phpseclib/Net/SSH2.php

Line 2863 in bff58b0

$this->server_channels[self::CHANNEL_SHELL],

I don't know why it happens but having an exception would be better, WDYT?

[terrafrost]

Normally that'd be set here:

phpseclib/phpseclib/Net/SSH2.php

Lines 3939 to 3947 in bff58b0

	switch ($this->channel_status[$channel]) {
	case MessageType::CHANNEL_OPEN:
	switch ($type) {
	case MessageType::CHANNEL_OPEN_CONFIRMATION:
	list(
	$this->server_channels[$channel],
	$window_size,
	$this->packet_size_client_to_server[$channel]
	) = Strings::unpackSSH2('NNN', $response);

Since it isn't.... can you post your full SSH logs? You can get them by doing define('NET_SSH2_LOGGING', 2) at the top of your file and echo $ssh->getLog() after the error.

Thanks!

[simPod]

There's something wrong with my cisco devices.

I have no problem with having the error but it should be handled with exception rather than php warning.

[terrafrost]

Can you get me the information I asked for?

Errors and exceptions behave fundamentally differently. Exceptions, even if caught, will prevent the rest of the function from executing. Errors won't. Now, speaking abstractly, if the PHP error isn't a fatal error, then maybe the code should be written in such a way not to cause that error to appear, whilst still executing.

What the best fix is ultimately depends on the context, and I would like to better understand what is happening.

[simPod]

Just to keep the thread going, I've sent logs to @terrafrost.

[mewejo]

Did you make any progress with this @simPod?

[simPod]

No, there's nothing we can do until some exception is thrown.

[mewejo]

This is a weird one.

It only happens on some servers. But those it does happen on, it always happens.

The first connection to the server will consistently fail. The second will succeed. But if I restart a Laravel Tinker session (a PHP shell in production), the issue happens again. Something is cached, and it's not the SSH2 instance, it must be something at the PHP level or lower.

After a lot of debugging, adding a sleep(1) after login(), and before calling read() seems to consistently fix the issue. I don't like adding a sleep() but, right now, it seems the only viable solution.

The same issue doesn't happen with exec(). Maybe because the time it's taking to run the command is mimicking the benefit of the sleep() above...

Does this help at all with a theory @terrafrost ?

[terrafrost]

@mewejo - Calling write() too quickly can result in unexpected behavior as discussed here:

http://phpseclib.com/docs/commands#gotcha-writing-without-first-reading

But it's not clear to me why read() wouldn't work if called too quickly.

Could you post your SSH2 logs with and without the sleep(1)? You can get define('NET_SSH2_LOGGING', 2) at top and then echo $ssh->getLog() after you run the command.