I prefer the alternative method you mentioned - if you could update your PR that'd be great - thanks!

I'm also curious... in those instances where realpath returns false and chdir returns true can you post the output of $sftp->getLastSFTPError() and of getServerIdentification()? Like when I try to change to a non existent directory with chmod $sftp->getLastSFTPError() returns this:

NET_SFTP_STATUS_NO_SUCH_FILE: No such file

None of that changes the merit of your PR (which is sound). None-the-less I'm curious!

@terrafrost done.

Apologies I think I messed up my initial report. It's quite a hard issue to diagnose because of where the code is and the fact I can't replicate it locally at all. I'll write out the issue in case you have any insight.

The code was basically:

$sftp->chdir($directory);
if ( !$sftp->put( $destinationFilename, $sourceFilename, 1 ) ) {
    $error = "Failed to upload to SFTP: " . $sftp->getLastSFTPError() . " copying " . $sourceFilename . " to " . $destinationFilename;
    return false;
}

Note at first we weren't checking the return value of chdir.
$directory is user configurable so values tend to vary "/directory", "directory" etc. In the case I'm looking at the $directory is "reports".
Sometimes the put() fails with 'Please close the channel (256) before trying to open it again', this was because pwd was false which triggered reconnection. When the failed upload is retried (hours later, different php process) it succeeds.

Yesterday I changed the code so we check the result of chdir() and pwd before the put(). It now reliably fails and getLastSFTPError() set to NET_SFTP_STATUS_NO_SUCH_FILE: /reports does not exist.

I can't run getServerIdentification() easily, but the servers are OpenSSH8.9 and Azure Blob Storage SFTP.

I cherry picked this into the 1.0 branch and then merged that into the 2.0, 3.0 and master branches:

857245e