#coap #iot #networking #no-std #wasm

no-std toad-msg

Low-level CoAP message parsing & serialization

16 releases (5 breaking)

new 0.12.3 Feb 5, 2023
0.12.0 Jan 31, 2023
0.8.3 Oct 27, 2022

#1178 in Network programming

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351 downloads per month
Used in toad


2.5K SLoC

crates.io docs.rs Maintenance


Low-level representation of CoAP messages.

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


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 `toad_msg` for convenience.

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

//                        Message Payload byte buffer
//                        |
//                        |        Array of options in the message
//                        vvvvvvv  vvvvvvvvvvvvvvvvv
type VecMessage = Message<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<[Opt<ArrayVec<[u8; OPT_SIZE]>>; NUM_OPTS]>,

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


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

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


Serializing to bytes

Click to expand chart


Deserializing from bytes

Click to expand chart



Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.


~70K SLoC