官方文档:
https://www.w3.org/TR/PNG-CRCAppendix.html
CRC32校验的数据,看原文
A four-byte CRC (Cyclic Redundancy Code) calculated on the preceding bytes in the chunk, including the chunk type field and chunk data fields, but not including the length field. The CRC can be used to check for corruption of the data. The CRC is always present, even for chunks containing no data. See 5.5: Cyclic Redundancy Code algorithm.
难怪把字节写回去就跪了,crc32校验码写错了
