Add wxInputStream::ReadAll() and wxOutputStream::WriteAll().

Unlike Read() and Write(), these functions always transfer exactly the
specified number of bytes or fail.

See #12056.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74034 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/stream.h

@@ -537,6 +537,20 @@ public:
     */
     wxOutputStream& Write(wxInputStream& stream_in);
 
+    /**
+        Writes exactly the specified number of bytes from the buffer.
+
+        Returns @true if exactly @a size bytes were written. Otherwise, returns
+        @false and LastWrite() should be used to retrieve the exact amount of
+        the data written if necessary.
+
+        This method uses repeated calls to Write() (which may return writing
+        only part of the data) if necessary.
+
+        @since 2.9.5
+    */
+    bool WriteAll(const void* buffer, size_t size);
+
 protected:
     /**
         Internal function. It is called when the stream wants to write data of the
@@ -629,6 +643,23 @@ public:
     */
     wxInputStream& Read(wxOutputStream& stream_out);
 
+    /**
+        Reads exactly the specified number of bytes into the buffer.
+
+        Returns @true only if the entire amount of data was read, otherwise
+        @false is returned and the number of bytes really read can be retrieved
+        using LastRead(), as with Read().
+
+        This method uses repeated calls to Read() (which may return after
+        reading less than the requested number of bytes) if necessary.
+
+        @warning
+        The buffer absolutely needs to have at least the specified size.
+
+        @since 2.9.5
+    */
+    bool ReadAll(void* buffer, size_t size);
+
     /**
         Changes the stream current position.