From 2ae91ed495f3972ddac383bd5f63c47946d5cdb5 Mon Sep 17 00:00:00 2001
From: Robert Pluim <rpluim@gmail.com>
Date: Mon, 27 Sep 2021 17:25:27 +0200
Subject: [PATCH] Make UDP sockets work on Windows
To: emacs-devel@gnu.org

* admin/CPP-DEFINES: remove BROKEN_DATAGRAM_SOCKETS
* nt/inc/ms-w32.h: remove BROKEN_DATAGRAM_SOCKETS.
* src/process.c (DATAGRAM_SOCKETS): remove dependency on
!BROKEN_DATAGRAM_SOCKETS.
* src/w32.c (_sys_wait_readable): New function.  Calls
pfn_WSAEventSelect for sockets to see if data can be read, so the
1-byte readahead is no longer necessary.
(sys_read): Only do 1-byte readahead for non-sockets.
* src/w32.h: Add prototype for _sys_wait_readable.
* src/w32proc.c (reader_thread): Call _sys_wait_readable for socket
handles.
---
 admin/CPP-DEFINES |  1 -
 nt/inc/ms-w32.h   |  4 ----
 src/process.c     |  8 +++-----
 src/w32.c         | 49 +++++++++++++++++++++++++++++++++++++++++++----
 src/w32.h         |  1 +
 src/w32proc.c     |  2 ++
 6 files changed, 51 insertions(+), 14 deletions(-)

diff --git a/admin/CPP-DEFINES b/admin/CPP-DEFINES
index 06986ec8f48..2704bc57675 100644
--- a/admin/CPP-DEFINES
+++ b/admin/CPP-DEFINES
@@ -103,7 +103,6 @@ getting at the full user name.  Only MSDOS overrides the default.
 anymore, so they can be removed.
 
 AMPERSAND_FULL_NAME
-BROKEN_DATAGRAM_SOCKETS
 BROKEN_GET_CURRENT_DIR_NAME
 BROKEN_PTY_READ_AFTER_EAGAIN
 DEFAULT_SOUND_DEVICE
diff --git a/nt/inc/ms-w32.h b/nt/inc/ms-w32.h
index 58be1199345..535d24cd57b 100644
--- a/nt/inc/ms-w32.h
+++ b/nt/inc/ms-w32.h
@@ -89,10 +89,6 @@ #define _CALLBACK_ __cdecl
    Look in <sys/time.h> for a timeval structure.  */
 #define HAVE_TIMEVAL 1
 
-/* Our select emulation does 1-byte read-ahead waiting for received
-   packets, so datagrams are broken.  */
-#define BROKEN_DATAGRAM_SOCKETS 1
-
 #define MAIL_USE_SYSTEM_LOCK 1
 
 /* Define to 1 if GCC-style __attribute__ ((__aligned__ (expr))) works. */
diff --git a/src/process.c b/src/process.c
index 67d1d3e425f..8f7fccfe538 100644
--- a/src/process.c
+++ b/src/process.c
@@ -234,11 +234,9 @@ #define PIPECONN1_P(p) (EQ (p->type, Qpipe))
    "non-destructive" select.  So we require either native select,
    or emulation of select using FIONREAD.  */
 
-#ifndef BROKEN_DATAGRAM_SOCKETS
-# if defined HAVE_SELECT || defined USABLE_FIONREAD
-#  if defined HAVE_SENDTO && defined HAVE_RECVFROM && defined EMSGSIZE
-#   define DATAGRAM_SOCKETS
-#  endif
+#if defined HAVE_SELECT || defined USABLE_FIONREAD
+# if defined HAVE_SENDTO && defined HAVE_RECVFROM && defined EMSGSIZE
+#  define DATAGRAM_SOCKETS
 # endif
 #endif
 
diff --git a/src/w32.c b/src/w32.c
index 47d79abc5b0..ef7d3de861b 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -8940,6 +8940,43 @@ _sys_wait_accept (int fd)
   return cp->status;
 }
 
+int
+_sys_wait_readable (int fd)
+{
+  HANDLE hEv;
+  child_process * cp;
+  int rc;
+
+  if (fd < 0 || fd >= MAXDESC)
+    return STATUS_READ_ERROR;
+
+  cp = fd_info[fd].cp;
+
+  if (cp == NULL || cp->fd != fd || cp->status != STATUS_READ_READY)
+    return STATUS_READ_ERROR;
+
+  cp->status = STATUS_READ_FAILED;
+
+  hEv = pfn_WSACreateEvent ();
+  rc = pfn_WSAEventSelect (SOCK_HANDLE (fd), hEv, FD_READ);
+  if (rc != SOCKET_ERROR)
+    {
+      do
+        {
+          rc = WaitForSingleObject (hEv, 500);
+          Sleep (5);
+        } while (rc == WAIT_TIMEOUT
+                 && cp->status != STATUS_READ_ERROR
+                 && cp->char_avail);
+      pfn_WSAEventSelect (SOCK_HANDLE (fd), NULL, 0);
+      if (rc == WAIT_OBJECT_0)
+        cp->status = STATUS_READ_SUCCEEDED;
+    }
+  pfn_WSACloseEvent (hEv);
+
+  return cp->status;
+}
+
 int
 _sys_wait_connect (int fd)
 {
@@ -9065,10 +9102,14 @@ sys_read (int fd, char * buffer, unsigned int count)
 	      return -1;
 
 	    case STATUS_READ_SUCCEEDED:
-	      /* consume read-ahead char */
-	      *buffer++ = cp->chr;
-	      count--;
-	      nchars++;
+              /* select on sockets no longer requires a 1-byte read.  */
+              if ((fd_info[fd].flags & FILE_SOCKET) == 0)
+		{
+		  /* consume read-ahead char */
+		  *buffer++ = cp->chr;
+		  count--;
+		  nchars++;
+		}
 	      cp->status = STATUS_READ_ACKNOWLEDGED;
 	      ResetEvent (cp->char_avail);
 
diff --git a/src/w32.h b/src/w32.h
index a3d0b75359a..4eba0fabe94 100644
--- a/src/w32.h
+++ b/src/w32.h
@@ -177,6 +177,7 @@ #define FILE_DONT_CLOSE         0x1000
 
 extern int _sys_read_ahead (int fd);
 extern int _sys_wait_accept (int fd);
+extern int _sys_wait_readable (int fd);
 extern int _sys_wait_connect (int fd);
 
 extern HMODULE w32_delayed_load (Lisp_Object);
diff --git a/src/w32proc.c b/src/w32proc.c
index 77a4ac1ff7e..19d9fc7d0e7 100644
--- a/src/w32proc.c
+++ b/src/w32proc.c
@@ -1243,6 +1243,8 @@ reader_thread (void *arg)
 	rc = _sys_wait_connect (fd);
       else if (fd >= 0 && (fd_info[fd].flags & FILE_LISTEN) != 0)
 	rc = _sys_wait_accept (fd);
+      else if (fd_info[fd].flags & FILE_SOCKET)
+	rc = _sys_wait_readable (fd);
       else
 	rc = _sys_read_ahead (fd);
 
-- 
2.38.1.420.g319605f8f0