String to Zipped Stream in php

Question

I have a processing server with my database and a serving database to serve up files with a low bandwidth cost. On the processing server, php is not able to create files so everything must be done with streams and/or stay in memory before being sent over to another server for download. A few days ago I found out about the stream abstraction with 'php://memory' and that I can do something like

$fp=fopen('php://memory','w+');
fwrite($fp,"Hello world");
fseek($fp,0,SEEK_SET);

//make a ftp connection here with $conn_id
$upload = ftp_fput($conn_id,"targetpath/helloworld.txt",$fp,FTP_BINARY);

to make the file in memory and then allow me to ftp it over to my other server. This is exactly what I want, except I also want to zip the data before sending it -- preferably using only native parts of php like ziparchive and not additional custom classes for special stream manipulation. I know that I am very close with the following...

$zip = new ZipArchive();
if($zip->open('php://memory', ZIPARCHIVE::CREATE)) {
  $zip->addFromString('testtext.txt','Hello World!');
  $fp = $zip->getStream('test'); if(!$fp) print "no filepointer";

  //make a ftp connection here with $conn_id
  $upload = ftp_fput($conn_id,"targetpath/helloworld.zip",$fp,FTP_BINARY);
} else print "couldn't open a zip like that";

The point at which this fails is the call to getStream (which always returns false although I think I am using correctly). It appears that the zip is fine making the file in 'php://memory' but for some reason getStream still fails although perhaps I don't sufficiently understand how ZipArchive makes zips...

How can I go from the string to the zipped filepointer so that I can ftp the zip over to my other server? Remember I can't make any files or else I would just make the zip file then ftp it over.

EDIT: based on skinnynerd's suggestions below I tried the following

$zip = new ZipArchive();
if($zip->open('php://memory', ZIPARCHIVE::CREATE)) {
  $zip->addFromString('testtext.txt','Hello World!');
  $zip->close(); 

  $fp = fopen('php://memory','r+');
  fseek($fp,0,SEEK_SET);

  //connect to ftp
  $upload = ftp_fput($conn_id,"upload/transfer/helloworld.zip",$fp,FTP_BINARY);
}

This does make a zip and send it over but the zip is 0 bytes large so I don't think that 'php://memory' works the way I thought... it actually fails at the close step -- the $zip->close() returns false which makes me wonder if I can open zips into 'php://memory' at all. Does anyone know what I can try along these line to get the zip?

Answer 1

Does it have to be a Zip archive? Since you're trying to save bandwith it could be a gzip too.

<?php
 $ftp_credentials = "ftp://USER:PASSWORD@HOST/helloworld.gz";
 $gz = gzencode("Hello World!", 9);
 $options = array('ftp' => array('overwrite' => true));
 $stream_context = stream_context_create($options);
 file_put_contents($ftp_credentials, $gz, 0, $stream_context);
?>