HTTP ranges

What if the client only wants the first 200 bytes out of a remote
resource or perhaps 300 bytes somewhere in the middle? The HTTP protocol
allows a client to ask for only a specific data range. The client asks the
server for the specific range with a start offset and an end offset. It can even
combine things and ask for several ranges in the same request by just listing a
bunch of pieces next to each other. When a server sends back multiple
independent pieces to answer such a request, you will get them separated with
mime boundary strings and it will be up to the user application to handle that
accordingly. curl will not further separate such a response.

However, a byte range is only a request to the server. It does not have to
respect the request and in many cases, like when the server automatically
generates the contents on the fly when it is being asked, it will simply refuse
to do it and it then instead respond with the full contents anyway.

You can make libcurl ask for a range with CURLOPT_RANGE. Like if you want
the first 200 bytes out of something:

curl_easy_setopt(curl, CURLOPT_RANGE, "0-199");

Or everything in the file starting from index 200:

curl_easy_setopt(curl, CURLOPT_RANGE, "200-");

Get 200 bytes from index 0 and 200 bytes from index 1000:

curl_easy_setopt(curl, CURLOPT_RANGE, "0-199,1000-199");