Reads one chunk, for a read that has to be divisible across invocations.
Returns null for a file that is not stored AND for a seq past the end, because both mean "no bytes here" to a caller walking chunks until it runs out.
seq
Reads one chunk, for a read that has to be divisible across invocations.
Returns null for a file that is not stored AND for a
seqpast the end, because both mean "no bytes here" to a caller walking chunks until it runs out.