On 23-Jan-22 05:46, Daniel Stenberg via curl-library wrote:
HEAD can be expensive for a server - at a minimum it has to do a stat on a file, but if the target is a program, it may require a lot more work just to create the headers. Even for the simple case where the resource is a plain file, locks and/or IO may be required (think content-type, content-length). In any case, absent knowledge of the server, HEAD should be assumed to cost the server as much as a GET, less the network cost of sending the body. It's an optimization primarily for the client, not necessarily for the server.On Sun, 23 Jan 2022, 白水月 wrote:What I was doing is to send keepalive requests to the server. I'm just wondering if there is a more graceful solution.TCP keepalive is rarely enough to maintain a connection. It usually also requires actual TCP traffic to go over it, which in the HTTP/2 case could be PING frames like with curl_easy_upkeep(). Sometimes it will also require HTTP requests to prevent the server from killing connections for being idle.If you're using HTTP/1 you instead can do "no-op" HTTP requests, such as HEAD or OPTIONS.
OPTIONS is a much better choice for keep-alive.If you don't own or have an arrangement with the server's operator, keep-alive in any form may be considered abuse.
Timothe Litt ACM Distinguished Engineer -------------------------- This communication may not represent the ACM or my employer's views, if any, on the matters discussed.
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