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Yet another CCSDS space packet protocol implementation with built in encoding and decoding.

### Why another packet crate?
This crate's interface provides a wrapper for a CCSDS packet payload (including secondary headers), opposed to just parsing header bytes.
The full packet is parsed into a SpacePacket struct, all overhead for the payload encoding length (including with CRC validation) is handled for the end user.

This crate was created after viewing other rust-based CCSDS crates and wanting a more friendly user interface for packet interaction.

Currently this crate assumes Big Endian for all byte streams. Though this may change to be generic over endianness in the future.


## Optional Features
#### CRC Support
This crate provides data validation via CRC-16 calculation through the [crc crate](https://github.com/mrhooray/crc-rs).
#### Sink/Stream Support
Another optional feature this crate provides is support for for sapcepacket I/O via sinks and stream through the async-codec and tokio-codec features.
This allows users to easily create asynchronous listeners for spacepackets with optional sync markers and CRC support.
#### TC/TM Support and CLTU Generation
TeleComamand (TC) and Telemetry (TM) Frames are supported when the `tctm` feature is enabled.

Communications Link Transmission Unit (CLTU) packets can also be constructed
when this feature is enabled. Currently only BCH and Randomized BCH
encoding is supported however LDPC encoding is planned as a future enhancement.


# Examples
```rust
use spacepacket::{GroupingFlag, PacketType, SpacePacket};

let payload = b"secret payload".to_vec();
let packet = SpacePacket::new(
    0,
    PacketType::Command,
    0x012,
    GroupingFlag::Unsegm,
    3,
    true,
    payload,
);

let bytestream = packet.encode();
let recovered_packet = SpacePacket::decode(&mut bytestream.as_slice()).unwrap();
assert_eq!(packet, recovered_packet)
```