[core] _WIN32 alternative fdarray for Windows

_WIN32 SOCKET (long long unsigned) handles are assigned differently
from how POSIX allocates file descriptors (lowest number available).

On _WIN32, the SOCKET descriptor should not be used to index an array
of (fdnode *), so this commit provides an alternative method to store
(fdnode *) for use by select() and by WSAPoll().

select(): commonly used unix select() idioms may be incorrect on _WIN32
https://devblogs.microsoft.com/oldnewthing/20221102-00/?p=107343
https://devblogs.microsoft.com/oldnewthing/20161221-00/?p=94985

WSAPoll():
https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-wsapoll
As of Windows 10 version 2004, when a TCP socket fails to connect,
(POLLHUP | POLLERR | POLLWRNORM) is indicated.
(note: this was broken in WSAPoll() in all earlier Windows versions)

1 files changed, 22 insertions, 2 deletions

diff --git a/src/fdevent_fdnode.c b/src/fdevent_fdnode.c
index 4dbb3878..f498c57b 100644
--- a/src/fdevent_fdnode.c
+++ b/src/fdevent_fdnode.c
@@ -25,7 +25,12 @@ fdnode_free (fdnode *fdn)
 fdnode *
 fdevent_register (fdevents *ev, int fd, fdevent_handler handler, void *ctx)
 {
+  #ifdef _WIN32
+    fdnode *fdn  = fdnode_init();
+    ev->fdarray[(fdn->fda_ndx = ev->count++)] = fdn;
+  #else
     fdnode *fdn  = ev->fdarray[fd] = fdnode_init();
+  #endif
     fdn->handler = handler;
     fdn->fd      = fd;
     fdn->ctx     = ctx;
@@ -34,11 +39,26 @@ fdevent_register (fdevents *ev, int fd, fdevent_handler handler, void *ctx)
     return fdn;
 }
 
+#ifdef _WIN32
+#define fdevent_fdarray_slot(ev,fdn) &(ev)->fdarray[(fdn)->fda_ndx]
+#else
+#define fdevent_fdarray_slot(ev,fdn) &(ev)->fdarray[(fdn)->fd]
+#endif
+
 void
 fdevent_unregister (fdevents *ev, fdnode *fdn)
 {
-    fdnode **fdn_slot = &ev->fdarray[fdn->fd];
+    fdnode **fdn_slot = fdevent_fdarray_slot(ev, fdn);
     if ((uintptr_t)*fdn_slot & 0x3) return; /*(should not happen)*/
+  #ifdef _WIN32
+    if (--ev->count != fdn->fda_ndx) {
+        /* compact fdarray; move element in last slot */
+        fdnode **fdn_last = &ev->fdarray[ev->count];
+        *fdn_slot = *fdn_last;
+        ((fdnode *)((uintptr_t)*fdn_slot & ~0x3))->fda_ndx = fdn->fda_ndx;
+        fdn_slot = fdn_last;
+    }
+  #endif
     *fdn_slot = NULL;
     fdnode_free(fdn);
 }
@@ -46,7 +66,7 @@ fdevent_unregister (fdevents *ev, fdnode *fdn)
 void
 fdevent_sched_close (fdevents *ev, fdnode *fdn)
 {
-    fdnode **fdn_slot = &ev->fdarray[fdn->fd];
+    fdnode **fdn_slot = fdevent_fdarray_slot(ev, fdn);
     if ((uintptr_t)*fdn_slot & 0x3) return;
     *fdn_slot = (fdnode *)((uintptr_t)fdn | 0x3);
     fdn->handler = (fdevent_handler)NULL;