Revert "Fix passing Unicode strings via wxIPC when using DDE"

This reverts commit c657fd3d61 because
changing the format of DDE advise requests/replies is not a good idea:
other applications (those using previous versions of wxWidgets or even
not using wxWidgets at all) may rely on getting data in real CF_TEXT
format rather than in one of text formats preceded by the extra byte
containing the actual format and the previous commit would have silently
broken this.

Another fix for #17900 will be implemented instead.

docs/changes.txt

@@ -124,10 +124,6 @@ All (GUI):
 - Allow changing tooltip text for button allowing to enter a new string
   in wxPGArrayEditorDialog.
 
-wxMSW:
-
-- Fix passing Unicode strings via wxIPC when using DDE.
-
 
 3.1.2: (released 2018-12-10)
 ----------------------------

include/wx/msw/dde.h

@@ -70,6 +70,7 @@ public:
   WXHCONV       m_hConv;
   const void*   m_sendingData;
   int           m_dataSize;
+  wxIPCFormat   m_dataType;
 
   wxDECLARE_NO_COPY_CLASS(wxDDEConnection);
   wxDECLARE_DYNAMIC_CLASS(wxDDEConnection);

samples/ipc/server.cpp

@@ -268,11 +268,7 @@ void MyServer::Advise()
     {
         const wxDateTime now = wxDateTime::Now();
 
-        m_connection->Advise
+        m_connection->Advise(m_connection->m_advise, now.Format());
-        (
-            m_connection->m_advise,
-            wxString::FromUTF8("\xd0\x9f\xd1\x80\xd0\xb8\xd0\xb2\xd0\xb5\xd1\x82")
-        );
 
         const wxString s = now.FormatTime() + " " + now.FormatDate();
         m_connection->Advise(m_connection->m_advise, s.mb_str(), wxNO_LEN);

src/msw/dde.cpp

@@ -748,20 +748,12 @@ bool wxDDEConnection::DoAdvise(const wxString& item,
                                size_t size,
                                wxIPCFormat format)
 {
-    // Unfortunately we currently always use the same CF_TEXT in StartAdvise()
-    // but allow calling Advise() with different formats. This doesn't map well
-    // to the DDE API, so the price to pay for it is that we need to send the
-    // actual format used as part of the data, even if this means making
-    // another copy of it.
-    wxCharBuffer buf;
-    buf.extend(size + 1);
-    *buf.data() = format;
-    memcpy(buf.data() + 1, data, size);
-
     HSZ item_atom = DDEGetAtom(item);
     HSZ topic_atom = DDEGetAtom(m_topicName);
-    m_sendingData = buf.data();
+    m_sendingData = data;  // mrf: potential for scope problems here?
-    m_dataSize = size + 1;
+    m_dataSize = size;
+    // wxIPC_PRIVATE does not succeed, so use text instead
+    m_dataType = format == wxIPC_PRIVATE ? wxIPC_TEXT : format;
 
     bool ok = DdePostAdvise(DDEIdInst, topic_atom, item_atom) != 0;
     if ( !ok )
@@ -994,12 +986,11 @@ _DDECallback(UINT wType,
                                         connection->m_dataSize,
                                         0,
                                         hsz2,
-                                        wFmt,
+                                        connection->m_dataType,
                                         0
                                     );
 
                     connection->m_sendingData = NULL;
-                    connection->m_dataSize = 0;
 
                     return (DDERETURN)data;
                 }
@@ -1017,21 +1008,18 @@ _DDECallback(UINT wType,
 
                     DWORD len = DdeGetData(hData, NULL, 0, 0);
 
-                    BYTE* const data = static_cast<BYTE*>(connection->GetBufferAtLeast(len));
+                    void *data = connection->GetBufferAtLeast(len);
                     wxASSERT_MSG(data != NULL,
                                  wxT("Buffer too small in _DDECallback (XTYP_ADVDATA)") );
 
-                    DdeGetData(hData, data, len, 0);
+                    DdeGetData(hData, (LPBYTE)data, len, 0);
 
                     DdeFreeDataHandle(hData);
-
-                    // Our code in DoAdvise() prepends the actual format of the
-                    // data as the first byte, extract it back now.
                     if ( connection->OnAdvise(connection->m_topicName,
                                               item_name,
-                                              data + 1,
+                                              data,
-                                              (int)len - 1,
+                                              (int)len,
-                                              (wxIPCFormat)*data) )
+                                              (wxIPCFormat) wFmt) )
                     {
                         return (DDERETURN)(DWORD)DDE_FACK;
                     }