Hello!
On 2019-04-07 at 23:51+02:00, Daniel Stenberg wrote:
On Sun, 7 Apr 2019, Nicolas Roeser via curl-library wrote:
But for now I can not understand the necessity of reading the HTTP
response body for a 302 response _at all_(*) when there is a usable
Location header field.
curl doesn't *have to*, but it choses to. Keeping the connection alive
and reading a little extra data over it, is usually much faster than
tearing down the connection and creating a new for next request.
I agree.
If this is done over HTTP/2 (or the coming HTTP/3), the 302 request
should be aborted since we can do that and still maintain the connection
but I'm pretty sure this optimization is still left to implement.
OK.
Or am I using the wrong means for accomplishing my goal described
above? Do I need to implement redirection following myself?
That could be a way to force this behavior you want, sure. But depending
on many conditions, that's not necessarily the faster way.
Agreed. I have not implemented redirection following, but still use the
logic in libcurl for that.
I had also written:
I have not tried it yet, but could think of using a header callback function which
monitors the headers for 3xx responses and for Location header fields. As soon as _both_
of them have be seen, I could set a flag which modifies the progress function logic until
a new HTTP response is seen (which starts with "HTTP/"). This will still
download the first big response payload entirely, won’t it?
I have decided to use this proposed way of implementing the code. The
progress function checks whether a redirecting resource (3xx header with
Location header field) is being handled, and if yes, raises the download
size limit.
(By the way, my progress function also peeks at a possible Content-Type
header field in order to abort the transfer if the document is not
interesting (in my case, not an HTML document) *and* is the last in a
(possible) chain of redirections.)
(*) Having thought about it a little more – is this behavior related
to keep-alive connections and not wanting to close them/open new ones?
Yes it is exactly that!
Thanks for your explanations, they were very useful!
--
Nico
Nicolas Roeser
kiz – Information Systems Department, Ulm University
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