Crate kwap_msg

Crate kwap_msg 

Source
Expand description

Low-level representation of CoAP messages.

The most notable item in kwap_msg is Message; a CoAP message very close to the actual byte layout.

§Allocation

CoAP messages have some attributes whose size is dynamic:

  • The message payload (in http terms: the request/response body)
  • the number of options (in http terms: headers)
  • the value of an option (in http terms: header value)

Message does not require an allocator and has no opinions about what kind of collection it uses internally to store these values.

It solves this problem by being generic over the collections it needs and uses an Array trait to capture its idea of what makes a collection useful.

This means that you may use a provided implementation (for Vec or tinyvec::ArrayVec) or provide your own collection (see the custom collections example)

//! Note: both of these type aliases are exported by `kwap_msg` for convenience.

use tinyvec::ArrayVec;
use kwap_msg::{Message, Opt};

//                        Message Payload byte buffer
//                        |
//                        |        Option Value byte buffer
//                        |        |
//                        |        |        Array of options in the message
//                        vvvvvvv  vvvvvvv  vvvvvvvvvvvvvvvvv
type VecMessage = Message<Vec<u8>, Vec<u8>, Vec<Opt<Vec<u8>>>>;

// Used like: `ArrayVecMessage<1024, 256, 16>`; a message that can store a payload up to 1024 bytes, and up to 16 options each with up to a 256 byte value.
type ArrayVecMessage<
       const PAYLOAD_SIZE: usize,
       const OPT_SIZE: usize,
       const NUM_OPTS: usize,
     > = Message<
           ArrayVec<[u8; PAYLOAD_SIZE]>,
           ArrayVec<[u8; OPT_SIZE]>,
           ArrayVec<[Opt<ArrayVec<[u8; OPT_SIZE]>>; NUM_OPTS]>,
         >;

It may look a little ugly, but a core goal of kwap is to be platform- and alloc-agnostic.

§Performance

This crate uses criterion to measure performance of the heaped & heapless implementations in this crate as well as coap_lite::Packet.

In general, kwap_msg::VecMessage performs identically to coap_lite (+/- 5%), and both are much faster than kwap_msg::ArrayVecMessage.

Benchmarks:

§Serializing to bytes

Click to expand chart

chart

§Deserializing from bytes

Click to expand chart

chart

Structs§

Code
CoAP Code Registries
EnumerateOptNumbersIter
Iterator yielded by EnumerateOptNumbers, wrapping an Iterator over Opts.
Id
Message ID
Message
Message struct
Opt
Options
OptDelta
The “Option Delta” is the difference between this Option’s Number and the previous Option’s number.
OptNumber
Option Numbers
OptValue
Option Value Formats
Payload
Payloads and Representations
Token
Token
Version
Version of the CoAP protocol that the message adheres to.

Enums§

CodeKind
Whether a code is for a request, response, or empty message
MessageParseError
Errors encounterable while parsing a message from bytes
OptParseError
Errors encounterable while parsing an option from bytes
OptionMustBeProcessed
Critical/Elective
Type
Indicates if this message is of type Confirmable (0), Non-confirmable (1), Acknowledgement (2), or Reset (3).
WhenOptionChanges
Proxy Unsafe or Safe-to-Forward and NoCacheKey
WhenOptionUnsupportedByProxy
Proxy Unsafe or Safe-to-Forward and NoCacheKey

Traits§

EnumerateOptNumbers
Creates an iterator which gives the current opt’s number as well as the option.
TryFromBytes
Trait for converting a sequence of bytes into some data structure
TryIntoBytes
Trait allowing fallible conversion into bytes

Type Aliases§

ArrayVecMessage
Message that uses static fixed-capacity stack-allocating byte buffers
VecMessagealloc
Message that uses Vec byte buffers