When it comes to sending several files to a website visitor's disk, we all come to the same solution : zip the files, and send the zip.
Yes, but ...

1. many users don't actually know what to do with an archive : you lose half of the visitors
2. the zipping process with many large files is extremely resource-consuming (disk + CPU + process).

The main goal of my on-the-fly zipper is there : it is able to create a zip structure and to send it to the visitor at the same time, with the ability to predict the final file size so that the user can have a progress indication of the download !

More precisely :

1. it computes the zip file exact size considering the input files size and the structure. The zip size is sent as HTTP header to the visitor.
2. it creates a zip structure in the output buffer (the buffer that is sent to the visitor by the web server, progressively when it is filled)
3. it creates the directory entries in the structure
4. it adds the files entries in the structure with "no-compress" option, to declare that the file is actually uncompressed in the zip : this way, no heavy processing is required on the server, and the file has the same size as when it is compressed with most heavy files (photos, videos, music, programs)
5. it pushes the file itself in the output buffer
6. it computes the file CRC using the built-in most-efficient function by hashing the file in small pieces (which requires a CRC32 hack!)
7. it loops for each file, and then closes the structure. Job Done.
8. Its only restriction is the computing time allowed by the server, that is sometimes limited to 30s.

The software can run on any PHP server. The visitor just runs a usual browser : he does not see any difference with a standard zip process.

Want to see it in action? This site integrates this system to send you archives of the projects : just click any of the download icons on your left.

My software has been used since 2005 by my private website visitors.

To get a licence, please contact me at matheret@free.fr