The length is only a single byte in the transfer. However, the struct
had a uint32_t in that place, breaking the sizeof() calculation and
seemingly creating issues for certain lengths of user id strings (which
depend on the username).
Fix this by changing the type to uint8_t. Also add the initial 0x43
prefix byte and a byte of apparent padding that the struct contains.
Leave the two reserved bytes at the end, as they seem to actually have a
meaning (i.e. they are seemingly send in listings).
This effectively makes the struct one byte smaller, bringing it down to
127 bytes from 128 bytes.
Closes: #428, #404
17ff49f85c