abstract : during a phone call treated by a voicexml client application using 7.38.0 libcurl version, we experiencea 15 seconds delay in the reception of the answer to a POST request. 
We use libcurl in a C++ voicexml application developped around OpenVXI software. At some point in the course of a phone callusing this application there is a 15 seconds delay between an POST sent and the libcurl treatment of the answer. In the tcpdumptrace the answer is fast, but in the code this delay is experienced between curl_easy_perform() and the next line. The CURLOPT_HEADERFUNCTION function is called directly at the reception of the answer, while CURLOPT_WRITEFUNCTION is called 15 seconds later.
the behavior was the same with libcurl 7.26.0, we have upgraded to 7.38.0 without improvement.
Physical server ProLiant DL360p Gen8   (S/N: CZJ33100X9)Hardware :  1 processor, 4 coeurs : Intel Xeon CPU E5-2609 0 @ 2.40GHz  8 Gb RAM  4 Ethernet interfaces (d8:9d:67:25:7e:74 d8:9d:67:25:7e:75 d8:9d:67:25:7e:76 d8:9d:67:25:7e:77)  1 ATA disk :    sda: modele LOGICAL VOLUME  , capacite 279 Go.System :  Linux, version 3.2.0-4-amd64  Architecture : x86_64 (Debian : amd64)  Distribution Debian : 7.10 (Wheezy)
ii  curl                                  7.38.0-4+deb8u4.1Prosod amd64                   command line tool for transferring data with URL syntaxii  gnupg-curl                            1.4.12-7+deb7u7         amd64                   GNU privacy guard - a free PGP replacement (cURL)ii  libcurl3:amd64                        7.38.0-4+deb8u4.1Prosod amd64                   easy-to-use client-side URL transfer library (OpenSSL flavour)ii  libcurl3-gnutls:amd64                 7.38.0-4+deb8u4.1Prosod amd64                   easy-to-use client-side URL transfer library (GnuTLS flavour)ii  libcurl4-openssl-dev:amd64            7.38.0-4+deb8u4.1Prosod amd64                   development files and documentation for libcurl (OpenSSL flavour)
CURLOPT_HEADERFUNCTION log:09/08/2016 10:16:02 curlWriteHeader key=server val=Microsoft-IIS/7.509/08/2016 10:16:02 curlWriteHeader key=cache-control val=no-cache09/08/2016 10:16:02 curlWriteHeader key=pragma val=no-cache09/08/2016 10:16:02 curlWriteHeader key=content-length val=422709/08/2016 10:16:02 curlWriteHeader key=content-type val=text/html; charset=utf-809/08/2016 10:16:02 curlWriteHeader key=x-aspnet-version val=2.0.5072709/08/2016 10:16:02 curlWriteHeader key=x-powered-by val=ASP.NET
CURLOPT_WRITEFUNCTION log:09/08/2016 10:16:17 curlWriteCallback rsize=1731 tsize=4227
included files : delay_tcpdump.pcap (POST at 10:16:02.671184), delay_strace.pcap, delay_debug.txt

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