Make more fixes and improvements

- Remove PAGESIZE constant
- Fix realloc() documentation
- Fix ttyname_r() error reporting
- Make forking more reliable on Windows
- Make execvp() a few microseconds faster
- Make system() a few microseconds faster
- Tighten up the socket-related magic numbers
- Loosen restrictions on mmap() offset alignment
- Improve GetProgramExecutableName() with getenv("_")
- Use mkstemp() as basis for mktemp(), tmpfile(), tmpfd()
- Fix flakes in pthread_cancel_test, unix_test, fork_test
- Fix recently introduced futex stack overflow regression
- Let sockets be passed as stdio to subprocesses on Windows
- Improve security of bind() on Windows w/ SO_EXCLUSIVEADDRUSE

libc/sock/socket-nt.c

@@ -16,14 +16,19 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
 #include "libc/calls/internal.h"
 #include "libc/calls/state.internal.h"
+#include "libc/errno.h"
+#include "libc/intrin/kprintf.h"
 #include "libc/mem/mem.h"
 #include "libc/nt/enum/fileflagandattributes.h"
 #include "libc/nt/iphlpapi.h"
 #include "libc/nt/winsock.h"
 #include "libc/sock/internal.h"
 #include "libc/sock/yoink.inc"
+#include "libc/str/str.h"
+#include "libc/sysv/consts/af.h"
 #include "libc/sysv/consts/ipproto.h"
 #include "libc/sysv/consts/o.h"
 #include "libc/sysv/consts/so.h"
@@ -42,13 +47,22 @@ __static_yoink("_dupsockfd");
 textwindows int sys_socket_nt(int family, int type, int protocol) {
   int64_t h;
   struct SockFd *sockfd;
-  int fd, oflags, truetype;
+  int fd, oflags, truetype, yes = 1;
   fd = __reservefd(-1);
   if (fd == -1) return -1;
   truetype = type & ~(SOCK_CLOEXEC | SOCK_NONBLOCK);
   if ((h = WSASocket(family, truetype, protocol, NULL, 0,
                      kNtWsaFlagOverlapped)) != -1) {
-    oflags = 0;
+
+    // sets SO_EXCLUSIVEADDRUSE on all sockets so they won't get pilfered
+    // you can read a blog post on this subject in the find_unused_port()
+    // pydoc of this file third_party/python/Lib/test/support/__init__.py
+    // this needs to happen right after socket is called or it won't work
+    if (family == AF_INET || family == AF_INET6) {
+      unassert(__sys_setsockopt_nt(h, SOL_SOCKET, -5, &yes, 4) != -1);
+    }
+
+    oflags = O_RDWR;
     if (type & SOCK_CLOEXEC) oflags |= O_CLOEXEC;
     if (type & SOCK_NONBLOCK) oflags |= O_NONBLOCK;
     sockfd = calloc(1, sizeof(struct SockFd));
@@ -62,6 +76,7 @@ textwindows int sys_socket_nt(int family, int type, int protocol) {
     g_fds.p[fd].handle = h;
     g_fds.p[fd].extra = (uintptr_t)sockfd;
     __fds_unlock();
+
     return fd;
   } else {
     __releasefd(fd);