+ /**
+ * When data becomes available, isBufferMovable() will be invoked to figure
+ * out which API will be used, readBufferAvailable() or
+ * readDataAvailable(). If isBufferMovable() returns true, that means
+ * ReadCallback supports the IOBuf ownership transfer and
+ * readBufferAvailable() will be used. Otherwise, not.
+
+ * By default, isBufferMovable() always return false. If
+ * readBufferAvailable() is implemented and to be invoked, You should
+ * overwrite isBufferMovable() and return true in the inherited class.
+ *
+ * This method allows the AsyncSocket/AsyncSSLSocket do buffer allocation by
+ * itself until data becomes available. Compared with the pre/post buffer
+ * allocation in getReadBuffer()/readDataAvailabe(), readBufferAvailable()
+ * has two advantages. First, this can avoid memcpy. E.g., in
+ * AsyncSSLSocket, the decrypted data was copied from the openssl internal
+ * buffer to the readbuf buffer. With the buffer ownership transfer, the
+ * internal buffer can be directly "moved" to ReadCallback. Second, the
+ * memory allocation can be more precise. The reason is
+ * AsyncSocket/AsyncSSLSocket can allocate the memory of precise size
+ * because they have more context about the available data than
+ * ReadCallback. Think about the getReadBuffer() pre-allocate 4072 bytes
+ * buffer, but the available data is always 16KB (max OpenSSL record size).
+ */
+
+ virtual bool isBufferMovable() noexcept {
+ return false;
+ }
+
+ /**
+ * readBufferAvailable() will be invoked when data has been successfully
+ * read.
+ *
+ * Note that only either readBufferAvailable() or readDataAvailable() will
+ * be invoked according to the return value of isBufferMovable(). The timing
+ * and aftereffect of readBufferAvailable() are the same as
+ * readDataAvailable()
+ *
+ * @param readBuf The unique pointer of read buffer.
+ */
+
+ virtual void readBufferAvailable(std::unique_ptr<IOBuf> readBuf)
+ noexcept {};
+