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From:	"Lavrentiev, Anton (NIH/NLM/NCBI) [C] via cygwin" <cygwin AT cygwin DOT com>
Reply-To:	"Lavrentiev, Anton (NIH/NLM/NCBI) [C]" <lavr AT ncbi DOT nlm DOT nih DOT gov>
To:	"'cygwin AT cygwin DOT com'" <cygwin AT cygwin DOT com>
Subject:	TCP_CORK (aka TCP_NOPUSH) does not work
Date:	Tue, 30 Jul 2019 21:30:41 +0000
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X-MIME-Autoconverted:	from quoted-printable to 8bit by delorie.com id x6ULVS3n020700

Hi,

Consider the following code:

$ cat cork.c
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>

#if defined(TCP_NOPUSH)  &&  !defined(TCP_CORK)
#  define TCP_CORK  TCP_NOPUSH
#endif


int main(int argc, const char* argv[])
{
    union {
        struct sockaddr_in in;
        struct sockaddr    sa;
    } addr;
    int sock, cork = 1;

    memset(&addr, 0, sizeof(addr));
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0)
        perror("socket");
    addr.in.sin_family = AF_INET;
    addr.in.sin_addr.s_addr = inet_addr(argv[1]);
    addr.in.sin_port = htons((unsigned short) atoi(argv[2]));
    if (connect(sock, &addr.sa, sizeof(addr.in)) < 0)
        perror("connect");
    if (setsockopt(sock, IPPROTO_TCP, TCP_CORK, (char*) &cork, sizeof(cork)) != 0)
        perror("cork");
    return 0;
}

When compiled and run under Cygwin, the last syscall, setsockopt(), returns an error, Protocol not available:

gcc cork.c
./a.exe 8.8.8.8 443
cork: Protocol not available

The same code works under Linux just fine.  I straced both.

gcc cork.c
./a.out 8.8.8.8 443

Any ideas?  Is TCP_NOPUSH (which is a BSDism, BTW) not actually usable on Cygwin?  If not, why is it in the header file <netinet/tcp.h>?

TIA!


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