Recipe 20.17 Resuming an HTTP GET
use LWP; $have = length($file); $response = $ua->get($URL, 'Range', "bytes=$have-"); # $response->content hold the rest of the file
The Range header lets you specify which bytes to fetch. The 0th byte is the first in the file, so the range "bytes=0-" fetches the whole file.
You can also specify a range with two endpoints: "0-25", for example, fetches the first 26 bytes of the file. If you want to fetch an interior range, use "26-99".
Some servers don't support ranges, even though they claim to understand HTTP 1.1. In this case you'll be sent the whole file, not the range you asked for. To detect this, use HEAD to see the size of the file and then use a GET with a range to fetch the rest. If the content in the GET response is the same length as the original file, your range was ignored.
Here is the full list of ranges possible in the HTTP 1.1 specification:
The HTTP specification also permits lists of ranges (e.g., "0-5,10-15,20-"). This returns a multipart response.
20.17.4 See Also
LWP documentation; the HTTP spec at http://www.ietf.org/rfc/rfc2616.txt