Pre allocation in BufferReader

BufferReader is helper of where memcached response buffer are stored. Each BufferReader contains a list of DataBlocks. The length of the list is 0 after initialization of a BufferReader.

During each request(mc.get / mc.set/ ...), the DataBlock list will stretch if essential. The mininum capacity of each DataBlock is 8192. In most conditions, 8192 bytes is large enough to storage and buffer from memcached server, so that no memory allocation or memory copying will happen. When free space of a DataBlock is too small to storage the response buffer, the free space will be used first, and a new DataBlock will be created and appended to the DataBlock list. The capacity of the DataBlock depends on whether the required buffer space is known. e.g.: When processing the response of a GET command, we can get the rest buffer size after read first few bytes. If the rest space is not large enough to storage the rest buffer, we'll create a DataBlock whose capacity = rest buffer size - rest space.

After each request, the DataBlock list will be resized to 1, which contains only 1 DataBlock of capacity 8192.