XZI3DUAWQGVBGLOSFNXGAUHUH2SROOAZKVFIFP3JBMKH6RAQFVQQC
2WEO7OZLWJJPUYK4WXLT5FD46G2MAEIHEYMDW5GASCBUNKOPXCVAC
7FRJYUI62VW257VVFQXND6OKSAILVTHGEJCXFE6CG6FIOIUTDVYAC
r.read_byte().map_err(crate::Error::from)?; // should be 0.