使用 CURL 或 WGET 读取 Gzip 文件页脚

Question

I have a gzip file in the web server. I want to download the file only if there is enough disk space to decompress the file. Is it possible to know the decompress size before downloading the file?

The decompressed size is encoded in the footer of the gzip file [1] . We can extract the decompressed size with the following command

gzip -l

But, the file need to be downloaded. I want to avoid the file downloading if I could know the decompressed size.

Answer 1

You can hack your way with the HTTP Range header , but it will take many http requests and your server needs to accept the Range header.

1. Send a first request with the HEAD method, to figure out the total file size content-length
2. Send a second request with a Range header to get the last 4 bytes of the file. Compute theses bytes to know the file size
3. If you have enough size available on the disk (file-size + uncompressed size), download the full file.