From: Mykyta Dorokhin <kit-d_at_ukr.net>
Date: Fri, 31 Dec 2010 10:43:04 +0200

('binary' encoding is not supported, stored as-is) ('binary' encoding is not supported, stored as-is)  Hello curl team,

   Here is my situation. I use curl_easy interface for uploading data
   from the GSM/CDMA modem (ARM, Linux) to the HTTPS server. I
   implemented a retry logic based on a set of timeouts: CURLOPT_TIMEOUT,
   CURLOPT_CONNECTTIMEOUT. In addition I have implemented an inactivity
   timer which goes off if number of uploaded bytes not is not changing
   during configured time (I used curl_progress_callback).

   Now the problem. Once my inactivity timer goes off I return non-zero
   value from curl_progress_callback and curl_easy_perform returns
   CURLE_ABORTED_BY_CALLBACK code. In this case libcurl closes the
   connection, by, I assume, calling close(sock). Close() call returns
   immediately and my retry logic algorithm proceed with additional
   attempts. If there is an unsent data in the TCP socket buffer then, as
   I understand, TCP FIN segments will not be sent immediately. Taking
   into account that TCP uses 1,2,4,8,... retransmission intervals then
   it is possible that the connection quality is acceptable already but
   the data is still not being sent for, say 16 or more seconds. It means
   that the connection will remain open on the server for quite a long
   time even though there is no need in it.
   So, I think I could take advantage of SO_LINGER socket option since it
   seems may be used to force TCP/IP stack to sent the connection reset
   state to the server immediately. It least this can lower the number of
   stale connections on the server.

   The questions are:
   1) Does my reasoning makes sense?
   2) How can I set SO_LINGER option to the socket?
   3) Is it possible to set SO_LINGER option just before closing the
   connection? Not sure if it is safe to use the options form all
   communications I have,

   BTW, I use curl-7.20.0 + openssl-0.9.8.l

   Thanks,
   Nikita

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Received on 2010-12-31