In device_issue_read() there is no need to reset Offset and OffsetHigh

to 0; they are only used for seekable files (not sockets).

Reset the write event before the call to WriteFile().  This is
consistent with how the read event is reset before ReadFile().

Clear device_write_packet.len() if WriteFile() fails with an error
other than ERROR_IO_PENDING; otherwise write_packet() will call
GetOverlappedResult() the next time it is run even though there is
no write in progress.

src/mingw/device.c

@@ -48,9 +48,6 @@ static const char *device_info = "Windows tap device";
 extern char *myport;
 
 static void device_issue_read() {
-	device_read_overlapped.Offset = 0;
-	device_read_overlapped.OffsetHigh = 0;
-
 	int status;
 
 	for(;;) {
@@ -311,20 +308,28 @@ static bool write_packet(vpn_packet_t *packet) {
 		   which according to MSDN is a no-no. */
 
 		if(!GetOverlappedResult(device_handle, &device_write_overlapped, &outlen, FALSE)) {
-			int log_level = (GetLastError() == ERROR_IO_INCOMPLETE) ? DEBUG_TRAFFIC : DEBUG_ALWAYS;
-			logger(log_level, LOG_ERR, "Error while checking previous write to %s %s: %s", device_info, device, winerror(GetLastError()));
-			return false;
+			if(GetLastError() != ERROR_IO_INCOMPLETE) {
+				logger(DEBUG_ALWAYS, LOG_ERR, "Error completing previously queued write to %s %s: %s", device_info, device, winerror(GetLastError()));
+			} else {
+				logger(DEBUG_TRAFFIC, LOG_ERR, "Previous overlapped write to %s %s still in progress", device_info, device);
+				// drop this packet
+				return true;
+			}
 		}
 	}
 
 	/* Copy the packet, since the write operation might still be ongoing after we return. */
 
 	memcpy(&device_write_packet, packet, sizeof(*packet));
 
+	ResetEvent(device_write_overlapped.hEvent);
+
 	if(WriteFile(device_handle, DATA(&device_write_packet), device_write_packet.len, &outlen, &device_write_overlapped)) {
+		// Write was completed immediately.
 		device_write_packet.len = 0;
 	} else if(GetLastError() != ERROR_IO_PENDING) {
 		logger(DEBUG_ALWAYS, LOG_ERR, "Error while writing to %s %s: %s", device_info, device, winerror(GetLastError()));
+		device_write_packet.len = 0;
 		return false;
 	}