Update echo-msg window from the thread that owns the window

Change the way echo-msg window is update (thread safety).
When new echo-msg content is available for display, update the window
from the thread owning it by sending a message to it.
A blocking SendMessage (with a timeout) is used, as the window
needs access to the config's echo-msg buffer which is cleared
on return from this this call.

Signed-off-by: Selva Nair <selva.nair@gmail.com>

echo.c

@@ -259,20 +259,12 @@ echo_msg_display(connection_t *c, time_t timestamp, const char *title, int type)
     }
     if (type == ECHO_MSG_WINDOW)
     {
-
-        HWND h = echo_msg_window;
-        if (h)
+        DWORD_PTR res;
+        UINT timeout = 5000; /* msec */
+        if (echo_msg_window
+            && SendMessageTimeout(echo_msg_window, WM_OVPN_ECHOMSG, 0, (LPARAM) c, SMTO_BLOCK, timeout, &res) == 0)
         {
-            wchar_t from[256];
-            _sntprintf_0(from, L"From: %s %s", c->config_name, _wctime(&timestamp));
-
-	    /* strip \n added by _wctime */
-	    if (wcslen(from) > 0)
-	        from[wcslen(from)-1] = L'\0';
-
-            AddMessageBoxText(h, c->echo_msg.text, c->echo_msg.title, from);
-            SetForegroundWindow(h);
-            ShowWindow(h, SW_SHOW);
+            WriteStatusLog(c, L"GUI> Failed to display echo message: ", c->echo_msg.title, false);
         }
     }
     else /* notify */
@@ -537,6 +529,25 @@ MessageDialogFunc(HWND hwnd, UINT msg, UNUSED WPARAM wParam, LPARAM lParam)
         }
         break;
 
+    /* Must be sent with lParam = connection pointer
+     * Adds the current echo message and shows the window.
+     */
+    case WM_OVPN_ECHOMSG:
+        {
+            connection_t *c = (connection_t *) lParam;
+            wchar_t from[256];
+            _sntprintf_0(from, L"From: %s %s", c->config_name, _wctime(&c->echo_msg.fp.timestamp));
+
+            /* strip \n added by _wctime */
+            if (wcslen(from) > 0)
+                from[wcslen(from)-1] = L'\0';
+
+            AddMessageBoxText(hwnd, c->echo_msg.text, c->echo_msg.title, from);
+            SetForegroundWindow(hwnd);
+            ShowWindow(hwnd, SW_SHOW);
+        }
+        break;
+
     case WM_NOTIFY:
         nmh = (NMHDR*) lParam;
         /* We handle only EN_LINK messages */

main.h

@@ -60,6 +60,7 @@
 #define WM_OVPN_SILENT         (WM_APP + 18)
 #define WM_OVPN_IMPORT         (WM_APP + 20)
 #define WM_OVPN_RESCAN         (WM_APP + 21)
+#define WM_OVPN_ECHOMSG        (WM_APP + 22)
 
 /* bool definitions */
 #define bool int