CODEWITHSUNDEEP
zlibcompression
mitch
mitch

Reputation: 11

zlib: Decompressed File Size?

I'm using zlib to decompress a file. I want to verify that there is enough disk space to unzip the file. Do the zip format and zlib provide facilities to determine the decompressed size of its contents?

Upvotes: 1

Views: 2254

Answers (2)

B Abali
B Abali

Reputation: 443

If your file was compressed using the gzip format (RFC1952), then the last 4 bytes, the ISIZE field indicates the uncompressed file size mod 2^32. Therefore, provided that the original file was smaller than 4GB, you can determine its size by reading the last 4 bytes. Check the man pages for gunzip.

If ZLIB or raw Deflate format was used, you will have to decompress first to determine the uncompressed size.

Upvotes: 1

Spider
Spider

Reputation: 984

Just create a simple file structure for compressing:

{
FileFormatHeader (optional) x bytes
OriginalSize (4 or 8 bytes)
CompressedSize (optional) (4 or 8 bytes)
HashSum (optional) (16 bytes or different number [depends on hash algorithm])

CompressedData
}

Now you have all the information that you need for decompressing

Upvotes: 0

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