switch to std::variant for win32 ev_io

- sockets are a distinct (non-negative) file descriptor
- plain old file descriptors are opaque handles

this makes the specialisations of llarp::ev_io on win32 type-safe as
- TAP-Windows v9 adapter is a plain old device file (same as on UNIX and Linux)
- UDP listeners are sockets, so the type must change (from signed to unsigned int) to accomodate Winsock2

llarp/dnsd.cpp

@@ -82,7 +82,7 @@ writecname_dnss_response(std::string cname, const struct sockaddr *from,
                          dnsd_question_request *request)
 {
   const size_t BUFFER_SIZE = 1024 + (request->question.name.size() * 2);
-  char buf[BUFFER_SIZE];
+  char buf[BUFFER_SIZE]; // heh, another UNIX compiler extension: VLAs in C++
   memset(buf, 0, BUFFER_SIZE);
   char *write_buffer = buf;
   char *bufferBegin  = buf;

llarp/ev.hpp

@@ -5,14 +5,16 @@
 #ifndef _WIN32
 #include <sys/uio.h>
 #endif
-
-#ifndef _MSC_VER
 #include <unistd.h>
-#endif
 #include <llarp/buffer.h>
 #include <list>
 #include <llarp/codel.hpp>
 #include <vector>
+
+#ifdef _WIN32
+#include <variant>
+#endif
+
 #ifndef MAX_WRITE_QUEUE_SIZE
 #define MAX_WRITE_QUEUE_SIZE 1024
 #endif
@@ -29,13 +31,18 @@ namespace llarp
     int fd;
     ev_io(int f) : fd(f), m_writeq("writequeue"){};
 #else
-    SOCKET fd;
+    // on windows, udp event loops are socket fds
+    // and TUN device is a plain old fd
+    std::variant< SOCKET, HANDLE > fd;
     // the unique completion key that helps us to
     // identify the object instance for which we receive data
-    // Here, we'll use the address of the udp_listener instance, converted to
+    // Here, we'll use the address of the udp_listener instance, converted
-    // its literal int/int64 representation.
+    // to its literal int/int64 representation.
     ULONG_PTR listener_id = 0;
     ev_io(SOCKET f) : fd(f), m_writeq("writequeue"){};
+    ev_io(HANDLE t)
+        : fd(t), m_writeq("writequeue"){};  // overload for TUN device, which
+                                            // _is_ a regular file descriptor
 #endif
     virtual int
     read(void* buf, size_t sz) = 0;
@@ -50,7 +57,7 @@ namespace llarp
 #ifndef _WIN32
       return write(fd, data, sz) != -1;
 #else
-      return WriteFile((void*)fd, data, sz, nullptr, nullptr);
+      return WriteFile(std::get< HANDLE >(fd), data, sz, nullptr, nullptr);
 #endif
     }
 
@@ -129,7 +136,7 @@ namespace llarp
 #ifndef _WIN32
       ::close(fd);
 #else
-      closesocket(fd);
+      closesocket(std::get< SOCKET >(fd));
 #endif
     };
   };
@@ -156,7 +163,11 @@ struct llarp_ev_loop
     auto ev = create_udp(l, src);
     if(ev)
     {
+#ifdef _WIN32
+      l->fd = std::get< SOCKET >(ev->fd);
+#else
       l->fd = ev->fd;
+#endif
     }
     return ev && add_ev(ev, false);
   }

llarp/ev_win32.hpp

@@ -43,8 +43,8 @@ namespace llarp
       unsigned long flags = 0;
       WSABUF wbuf         = {sz, static_cast< char* >(buf)};
       // WSARecvFrom
-      int ret = ::WSARecvFrom(fd, &wbuf, 1, nullptr, &flags, addr, &slen,
+      int ret = ::WSARecvFrom(std::get< SOCKET >(fd), &wbuf, 1, nullptr, &flags,
-                              &portfds[0], nullptr);
+                              addr, &slen, &portfds[0], nullptr);
       // 997 is the error code for queued ops
       int s_errno = ::WSAGetLastError();
       if(ret && s_errno != 997)
@@ -74,9 +74,9 @@ namespace llarp
           return -1;
       }
       // WSASendTo
-      ssize_t sent =
+      ssize_t sent = ::WSASendTo(std::get< SOCKET >(fd), &wbuf, 1, nullptr, 0,
-          ::WSASendTo(fd, &wbuf, 1, nullptr, 0, to, slen, &portfds[1], nullptr);
+                                 to, slen, &portfds[1], nullptr);
-      int s_errno = ::WSAGetLastError();
+      int s_errno  = ::WSAGetLastError();
       if(sent && s_errno != 997)
       {
         llarp::LogWarn("send socket error ", s_errno);
@@ -91,7 +91,7 @@ namespace llarp
     llarp_tun_io* t;
     device* tunif;
     tun(llarp_tun_io* tio)
-        : ev_io(INVALID_SOCKET)
+        : ev_io(INVALID_HANDLE_VALUE)
         , t(tio)
         , tunif(tuntap_init())
 
@@ -147,12 +147,12 @@ namespace llarp
         return false;
       }
 
-      fd = (SOCKET)tunif->tun_fd;
+      fd = tunif->tun_fd;
-      if(fd == -1)
+      if(std::get< HANDLE >(fd) == INVALID_HANDLE_VALUE)
         return false;
 
       // we're already non-blocking
-	  return true;
+      return true;
     }
 
     ~tun()
@@ -208,7 +208,7 @@ struct llarp_win32_loop : public llarp_ev_loop
       {
         llarp::udp_listener* ev =
             reinterpret_cast< llarp::udp_listener* >(ev_id);
-        if(ev && ev->fd)
+        if(ev && !ev->fd.valueless_by_exception())
         {
           ev->getData(readbuf, sizeof(readbuf), iolen);
         }
@@ -216,18 +216,13 @@ struct llarp_win32_loop : public llarp_ev_loop
       ++idx;
     } while(::GetQueuedCompletionStatus(iocpfd, &iolen, &ev_id, &qdata, ms));
 
-    // tick_listeners inlined since win32 does not
-    // implement ev_tun
-    for(auto& l : udp_listeners)
-    {
-      if(l->tick)
-        l->tick(l);
-    }
-
     if(!idx)
       return -1;
     else
+    {
+      tick_listeners();
       result = idx;
+    }
 
     return result;
   }
@@ -255,7 +250,7 @@ struct llarp_win32_loop : public llarp_ev_loop
       {
         llarp::udp_listener* ev =
             reinterpret_cast< llarp::udp_listener* >(ev_id);
-        if(ev && ev->fd)
+        if(ev && !ev->fd.valueless_by_exception())
         {
           ev->getData(readbuf, sizeof(readbuf), iolen);
         }
@@ -263,16 +258,13 @@ struct llarp_win32_loop : public llarp_ev_loop
       ++idx;
     } while(::GetQueuedCompletionStatus(iocpfd, &iolen, &ev_id, &qdata, 10));
 
-    for(auto& l : udp_listeners)
-    {
-      if(l->tick)
-        l->tick(l);
-    }
-
     if(!idx)
       return -1;
     else
+    {
+      tick_listeners();
       result = idx;
+    }
 
     return result;
   }
@@ -331,8 +323,9 @@ struct llarp_win32_loop : public llarp_ev_loop
   {
     // On Windows, just close the socket to decrease the iocp refcount
     // and stop any pending I/O
-    BOOL stopped = ::CancelIo(reinterpret_cast< HANDLE >(ev->fd));
+    BOOL stopped =
-    return closesocket(ev->fd) == 0 && stopped == TRUE;
+        ::CancelIo(reinterpret_cast< HANDLE >(std::get< SOCKET >(ev->fd)));
+    return closesocket(std::get< SOCKET >(ev->fd)) == 0 && stopped == TRUE;
   }
 
   llarp::ev_io*
@@ -362,11 +355,26 @@ struct llarp_win32_loop : public llarp_ev_loop
   add_ev(llarp::ev_io* ev, bool write)
   {
     ev->listener_id = reinterpret_cast< ULONG_PTR >(ev);
-    if(!::CreateIoCompletionPort(reinterpret_cast< HANDLE >(ev->fd), iocpfd,
+    switch(ev->fd.index())
-                                 ev->listener_id, 0))
     {
-      delete ev;
+      case 0:
-      return false;
+        if(!::CreateIoCompletionPort((HANDLE)std::get< 0 >(ev->fd), iocpfd,
+                                     ev->listener_id, 0))
+        {
+          delete ev;
+          return false;
+        }
+        break;
+      case 1:
+        if(!::CreateIoCompletionPort(std::get< 1 >(ev->fd), iocpfd,
+                                     ev->listener_id, 0))
+        {
+          delete ev;
+          return false;
+        }
+        break;
+      default:
+        return false;
     }
     return true;
   }