Implement TCP and Unix sockets without using PHP resources

[fredemmott]

Regressions to be fixed in later diffs:

• SO_REUSEADDR is not supported yet as there's no new builtins for setsockopt/getsockopt. Needs HHVM change.
• getpeername() returns bad results on unix sockets at present. Test skipped until HHVM fixed.

Other changes:

• add dependencies to OS\
• set code on ErrnoException but mark it as deprecated. Explanation inline.
• return null path for Unix\ if there is no path, instead of empty string.

Design decisions:

• sticking with C naming for OS\ structs, e.g. sockaddr_un, not UnixSocketAddress, or SockAddrUn
  • UnixSocketAddress would make the most sense for Hack best practices, but would be poor for discoverability
  • Using OS\ already feels like writing C, but with Hack syntax. Every place where this differs feels jarring already.

Future work (in follow-up diffs):

• Fix regressions and other FIXMEs. This is all "add new native functions":
  • setsockopt, getsockopt
  • getaddrinfo
  • inet_pton, inet_ntop etc
• "Every place where this differs feels jarring already." - the big one is enums - e.g. OS\socket(OS\SocketDomain::PF_UNIX, OS\SocketType::SOCK_STREAM, 0); this also feels bad for discoverability. I plan on keeping the enums, but also adding const MyEnum PF_UNIX = SocketDomain::PF_UNIX to allow OS\socket(OS\PF_UNIX, OS\SOCK_STREAM, 0) without losing the type safety

[fredemmott]

Can't land without getsockopt; unable to detect socket errors after await. This is showing up on linux test runs as the following code (attempting to connect to port 0):

• fails immediately with EADDRNOTAVAIL on MacOS
• fails with EINPROGRESS on Linux; we then poll, but don't detect the error.

#include <fcntl.h>
#include <unistd.h>
#include <stddef.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/errno.h>

int main() {
  int sock = socket(AF_INET, SOCK_STREAM, 0);
  struct sockaddr_in addr;
  memset(&addr, 0, sizeof(addr));
  addr.sin_family = AF_INET;
  addr.sin_port = 0;
  addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
  int opts = fcntl(sock, F_GETFL);
  fcntl(sock, F_SETFL, opts | O_NONBLOCK);
  if (connect(sock, (struct sockaddr*) &addr, sizeof(addr)) == -1) {
    perror(NULL);
  }
  return 0;
}

[fredemmott]

#include <fcntl.h>
#include <unistd.h>
#include <stddef.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/errno.h>
#include <poll.h>

int main() {
  int sock = socket(AF_INET, SOCK_STREAM, 0);
  struct sockaddr_in addr;
  memset(&addr, 0, sizeof(addr));
  addr.sin_family = AF_INET;
  addr.sin_port = 0;
  addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
  int opts = fcntl(sock, F_GETFL);
  fcntl(sock, F_SETFL, opts | O_NONBLOCK);
  if (connect(sock, (struct sockaddr*) &addr, sizeof(addr)) == -1) {
    perror("connect() failed");
  }

  // O_NONBLOCK are ready for write when connect succeeds
  struct pollfd pollfd;
  pollfd.fd = sock;
  pollfd.events = POLLOUT;
  poll(&pollfd, 1, 1000);

  int sock_error;
  socklen_t sock_error_size = sizeof(sock_error);
  if (getsockopt(sock, SOL_SOCKET, SO_ERROR, &sock_error, &sock_error_size) == -1) {
    perror("getsockopt() failed");
  }
  errno = sock_error;
  perror("socket error after poll");
  return 0;
}

Linux:

connect() failed: Operation now in progress
socket error after poll: Connection refused

MacOS:

connect() failed: Can't assign requested address
socket error after poll: Undefined error: 0