[SFTP Adapter (phpseclib v3)] Retry mechanism doesn't work

[lcobucci]

Bug Report

Q	A
BC Break	no
Version	2.4.4

Summary

In phpseclibv3 we have exceptions when dealing with unreliable connections, which isn't handled well by SftpConnectionProvider and cause the retry mechanism to be bypassed.

flysystem/src/PhpseclibV3/SftpConnectionProvider.php

Lines 114 to 153 in 29eb78c

	public function provideConnection(): SFTP
	{
	$tries = 0;
	start:
	$connection = $this->connection instanceof SFTP
	? $this->connection
	: $this->setupConnection();
	if ( ! $this->connectivityChecker->isConnected($connection)) {
	$connection->disconnect();
	$this->connection = null;
	if ($tries < $this->maxTries) {
	$tries++;
	goto start;
	}
	throw UnableToConnectToSftpHost::atHostname($this->host);
	}
	return $this->connection = $connection;
	}
	private function setupConnection(): SFTP
	{
	$connection = new SFTP($this->host, $this->port, $this->timeout);
	$connection->setPreferredAlgorithms($this->preferredAlgorithms);
	$connection->disableStatCache();
	try {
	$this->checkFingerprint($connection);
	$this->authenticate($connection);
	} catch (Throwable $exception) {
	$connection->disconnect();
	throw $exception;
	}
	return $connection;
	}

How to reproduce

Testing and reproducing this requires a flaky connection, here's a snippet that isolates the problem: https://3v4l.org/KmXsL

[lcobucci]

@frankdejonge a possible solution would be catching the exceptions and relying on null. Would be nice to have your input before sending a PR :)

[lcobucci]

Closing here as #1451 has been released 👍
Thanks @frankdejonge