But you never serialize a byte by byte over the network. You encode, let's say, 1000 varints and then send them out on the wire. On the other end, you may or may not know how many varints there are to unpack but since you certainly have to know the length of the packet you can start decoding on a stream of bytes. Largest 64-bit leb128 number occupies 10 bytes whereas the largest 32-bit one occupies 5 bytes so we know the upper bound.