# UDT: UDP-based Data Transfer Protocol

UDT (UDP-based Data Transfer Protocol) is a transfer protocol on top of UDP. See https://udt.sourceforge.io/ for the original spec and the reference implementation.

This code is a fork from https://github.com/odysseus654/go-udt which itself is a fork.

## Stream vs Datagram

```
// TypeSTREAM describes a reliable streaming protocol (e.g. TCP)
TypeSTREAM SocketType = 1

// TypeDGRAM describes a partially-reliable messaging protocol
TypeDGRAM SocketType = 2

UDT supports both reliable data streaming and partial reliable 
messaging. The data streaming semantics is similar to that of TCP, 
while the messaging semantics can be regarded as a subset of SCTP 
[RFC4960]. 
```

From `udtSocket.Read`:

```
// for datagram sockets, block until we have a message to return and then return it
// if the buffer isn't big enough, return a truncated message (discarding the rest) and return an error

// for streaming sockets, block until we have at least something to return, then
// fill up the passed buffer as far as we can without blocking again
```

## Deviations

MTU negotiation is disabled. Peernet uses a hardcoded max packet size (see protocol package). Packets may be routed through any network adapter, therefore pinning a MTU specific to a network adapter would not make much sense.

The "rendezvous" functionality has been removed since Peernet supports native Traverse messages for UDP hole punching.

Multiplexing multiple UDT sockets to a single UDT connection is removed. It added complexity without benefits in this case. Peernet uses a single UDP port and UDP connection between two peers. Multiplexing has no effect other than breaking the concept and the security of Peernet message sequences.