On 2019-07-30 15:30, Lavrentiev, Anton (NIH/NLM/NCBI) [C] via cygwin wrote: > 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
For POSIX only non-Nagle TCP_NODELAY is required: http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/netinet_tcp.h.html and even then says: "The implementation need not allow the value of the option to be set via setsockopt() or retrieved via getsockopt()." TCP_CORK is Linux only; TCP_NOPUSH is BSD only; Windows does its own thing: https://baus.net/on-tcp_cork/ https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-tcp-socket-options Regular SO options on Windows: https://docs.microsoft.com/en-us/windows/win32/winsock/sol-socket-socket-options You can abuse Nagle to get similar behaviour cross-platform: https://stackoverflow.com/a/22118709 > 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 This is error ENOPROTOOPT, where the message is misleading, but as suggested by the name, means that the socket option is not supported for that protocol; getsockopt(3p/3posix) says: "The option is not supported by the protocol." getsockopt(2) for Linux and FreeBSD say: "The option is unknown at the level indicated." and given the POSIX statement above, that error should be treated as a warning to do something different. > 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>? If a socket option is defined, perhaps for compatibility, it should either be used or ignored, rather than giving an error. If you are not going to support a socket option, and generate an error, it would be better to not define the option and generate the error at compile time, instead of failing at run time. -- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada This email may be disturbing to some readers as it contains too much technical detail. Reader discretion is advised. -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
