此时 readStreamData 包含完整数据包，开始解析handleOneCompletePacketData;清空这次缓存数据，开始解析下一个包：readStreamData = nilcurrentHeader = nil读取数据流(读取特定长度)kHeartBeatLength 字节return;
YES
当前无包头，newData为包头一部分。readStreamData = appendData:(newData)此时 readStreamData 包含完整包头，解析包头
newData == kHeartBeatLength
reciveData:newData
NO
readStreamData = appendData:(newData)
newData == kHeaderLength - kHeartBeatLength
读取数据流(读取特定长度)kHeaderLength - kHeartBeatLengthreturn;
currentHeaderData == nil
读取数据流(读取特定长度)currentHeader.messageLength - kHeaderLengthreturn;
已存在包头，新数据属于包体readStreamData = appendData:(newData)
解析包头：currentHeader = [ECHeader alloc] initWithData:readStreamData
处理心跳包读取数据流(读取特定长度)kHeartBeatLength 字节
开始readStreamData = currentHeader = nil
isBeatPacket
当前无包头，newData为包头一部分readStreamData = appendData:(newData)
