Hello,
I am actually using SFTP class to log into AWS Tranfer Family in a long running process that need to upload files.
After a while AWS seems like to disconnect the user and phpseclib does not detect it.

In order to check if the connection is still open I call isConnected method but it always return true and then after I try to upload a file it leads to the following error;
Connection closed prematurely

I tried a different approach using ping() and now the error is :
At least one byte needs to be present for successful C / b decodes

This is the logs:
`-> NET_SSH2_MSG_REQUEST_FAILURE (since last: 0.0001, network: 0s)

<- NET_SSH2_MSG_DEBUG (since last: 0, network: 0s)
00000000 00:00:00:00:4e:53:46:54:50:3a:20:6b:65:79:20:6f ....NSFTP: key o
00000010 70:74:69:6f:6e:73:3a:20:61:67:65:6e:74:2d:66:6f ptions: agent-fo
00000020 72:77:61:72:64:69:6e:67:20:70:6f:72:74:2d:66:6f rwarding port-fo
00000030 72:77:61:72:64:69:6e:67:20:70:74:79:20:75:73:65 rwarding pty use
00000040 72:2d:72:63:20:78:31:31:2d:66:6f:72:77:61:72:64 r-rc x11-forward
00000050 69:6e:67:00:00:00:00 ing....

<- NET_SSH2_MSG_DEBUG (since last: 0, network: 0s)
00000000 00:00:00:00:4e:53:46:54:50:3a:20:6b:65:79:20:6f ....NSFTP: key o
00000010 70:74:69:6f:6e:73:3a:20:61:67:65:6e:74:2d:66:6f ptions: agent-fo
00000020 72:77:61:72:64:69:6e:67:20:70:6f:72:74:2d:66:6f rwarding port-fo
00000030 72:77:61:72:64:69:6e:67:20:70:74:79:20:75:73:65 rwarding pty use
00000040 72:2d:72:63:20:78:31:31:2d:66:6f:72:77:61:72:64 r-rc x11-forward
00000050 69:6e:67:00:00:00:00 ing....

<- NET_SSH2_MSG_UNIMPLEMENTED (since last: 0.004, network: 0.004s)
00000000 00:00:00:06 ....

At least one byte needs to be present for successful C / b decodes
0 /var/www/html/vendor/phpseclib/phpseclib/phpseclib/Net/SSH2.php(2664): phpseclib3\Common\Functions\Strings::unpackSSH2('C', false)
1 /var/www/html/vendor/phpseclib/phpseclib/phpseclib/Net/SSH2.php(2334): phpseclib3\Net\SSH2->privatekey_login('xxxxx', Object(phpseclib3\Crypt\RSA\PrivateKey))
2 /var/www/html/vendor/phpseclib/phpseclib/phpseclib/Net/SSH2.php(2279): phpseclib3\Net\SSH2->login_helper('xxxxx', Object(phpseclib3\Crypt\RSA\PrivateKey))
3 /var/www/html/vendor/phpseclib/phpseclib/phpseclib/Net/SSH2.php(2191): phpseclib3\Net\SSH2->sublogin('xxxxx', Object(phpseclib3\Crypt\RSA\PrivateKey))
4 /var/www/html/vendor/phpseclib/phpseclib/phpseclib/Net/SSH2.php(3386): phpseclib3\Net\SSH2->login('xxxxx', Object(phpseclib3\Crypt\RSA\PrivateKey))
5 /var/www/html/vendor/phpseclib/phpseclib/phpseclib/Net/SSH2.php(3368): phpseclib3\Net\SSH2->reconnect()`

I am using the version 3.0.33, tried also 3.0.34, but got the same errors

Other logs I got :
SSH_MSG_GLOBAL_REQUEST: hostkeys-00@openssh.com
SSH_MSG_DEBUG: SFTP: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
SSH_MSG_DEBUG: SFTP: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
SSH_MSG_GLOBAL_REQUEST: hostkeys-00@openssh.com
SSH_MSG_DEBUG: SFTP: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
SSH_MSG_DEBUG: SFTP: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
SSH_MSG_DISCONNECT: NET_SSH2_DISCONNECT_PROTOCOL_ERROR
data packet referred to nonexistent channel 0