Support data streaming on server side.

webcc/view.h

@@ -13,6 +13,13 @@ public:
   virtual ~View() = default;
 
   virtual ResponsePtr Handle(RequestPtr request) = 0;
+
+  // Return true if you want the request data of the given method to be streamed
+  // to a temp file. Data streaming is useful for receiving large data, e.g.,
+  // a JPEG image, posted from the client.
+  virtual bool Stream(const std::string& /*method*/) {
+    return false;  // No streaming by default
+  }
 };
 
 using ViewPtr = std::shared_ptr<View>;