winhttp: Only read as much data as advertized when draining content.

dlls/winhttp/request.c

@@ -1302,13 +1302,20 @@ done:
 /* read any content returned by the server so that the connection can be reused */
 static void drain_content( request_t *request )
 {
-    DWORD bytes_read;
+    DWORD size, bytes_read, bytes_total = 0, bytes_left = request->content_length - request->content_read;
     char buffer[2048];
 
     refill_buffer( request, FALSE );
     for (;;)
     {
-        if (!read_data( request, buffer, sizeof(buffer), &bytes_read, FALSE ) || !bytes_read) return;
+        if (request->read_chunked) size = sizeof(buffer);
+        else
+        {
+            if (bytes_total >= bytes_left) return;
+            size = min( sizeof(buffer), bytes_left - bytes_total );
+        }
+        if (!read_data( request, buffer, size, &bytes_read, FALSE ) || !bytes_read) return;
+        bytes_total += bytes_read;
     }
 }