Fully deserializing shreds in window-service before sending them to
retransmit stage adds latency to shreds propagation.
This commit instead channels through the payload and relies on only
partial deserialization of a few required fields: slot, shred-index,
shred-type.
Packets are at the boundary of the system where, vast majority of the
time, they are received from an untrusted source. Raw indexing into the
data buffer can open attack vectors if the offsets are invalid.
Validating offsets beforehand is verbose and error prone.
The commit updates Packet::data() api to take a SliceIndex and always to
return an Option. The call-sites are so forced to explicitly handle the
case where the offsets are invalid.
Bytes past Packet.meta.size are not valid to read from.
The commit makes the buffer field private and instead provides two
methods:
* Packet::data() which returns an immutable reference to the underlying
buffer up to Packet.meta.size. The rest of the buffer is not valid to
read from.
* Packet::buffer_mut() which returns a mutable reference to the entirety
of the underlying buffer to write into. The caller is responsible to
update Packet.meta.size after writing to the buffer.
behzad nouri
sakridge