I’m creating something that includes a file upload service of sorts, and I need to store data compressed with zlib’s compress() function. I send it across the internet already compressed, but I need to know the uncompressed file size on the remote server. Is there any way I can figure out this information without uncompress()ing the data on the server first, just for efficiency? That’s how I’m doing it now, but if there’s a shortcut I’d love to take it.
By the way, why is it called uncompress? That sounds pretty terrible to me, I always thought it would be decompress…
The zlib format doesn’t have a field for the original input size, so I doubt you will be able to do that without simulating a decompression of the data. The gzip format has a “input size” (
ISIZE) field, that you could use, but maybe you want to avoid changing the compression format or having the clients sending the file size.But even if you use a different format, if you don’t trust the clients you would still need to run a more expensive check to make sure the uncompressed data is the size the client says it is. In this case, what you can do is to make the uncompress-to-/dev/null process less expensive, making sure zlib doesn’t write the output data anywhere, as you just want to know the uncompressed size.