cantcoap
FreeSmall and lightweight coap encoder and decoder. Protocol level stuff is left to the user.
FreeFree tier
About cantcoap
cantcoap is a lightweight, minimal CoAP (Constrained Application Protocol) library focused on simplicity. It provides only PDU (Protocol Data Unit) construction and de-construction, leaving retransmissions, timeouts, and message ID matching to the user. This design is intentional for constrained devices such as simple microcontroller sensors that send infrequent packets, where a full CoAP framework would be overkill. The library also supports sending over non-UDP transports like SMS or radio bearers. It is written in C with CUnit as a testing dependency and includes example client and server implementations.
Key Features
PDU construction and de-construction only
Minimal set of functions with straightforward interface
User-managed retransmissions, timeouts, and message ID matching
Designed for constrained devices (e.g., simple microcontrollers)
Supports non-UDP transport bearers (e.g., SMS, simple radio)
Includes example client and server
Written in C with CUnit testing framework
Pros & Cons
Pros
- Extremely lightweight and simple to integrate
- Gives full control over retransmission and timing logic
- No bloated dependencies beyond CUnit for testing
- Suitable for resource-constrained microcontrollers
- Open source with permissive license
Cons
- Not a complete CoAP framework; user must implement retransmissions and message matching
- Limited documentation and examples beyond basic PDU operations
- Lacks built-in support for UDP/IP-specific handling
- Less suitable for complex CoAP interactions requiring advanced features
Best For
Constrained IoT devices sending infrequent sensor readingsEmbedded systems where a full CoAP framework is too heavyTransmitting CoAP packets over alternative bearers like SMS or radioEducational examples for understanding CoAP protocol at PDU level
FAQ
What is cantcoap?
cantcoap is a lightweight CoAP library that focuses on simplicity by providing only PDU construction and de-construction. It does not handle retransmissions, timeouts, or message ID matching, leaving those to the user for maximum flexibility on constrained devices.
What are the dependencies?
The only dependency is CUnit (CUnit testing framework). On Debian-based systems, install libcunit1 and libcunit1-dev. On openSUSE, install libcunit-dev and cunit-devel. On FreeBSD, CUnit is in the ports collection.
How do I build cantcoap?
Run 'make' (use GNU make on BSD) to build the library and test framework. Then run './test' to execute tests. Example client and server are also included.
Does cantcoap support retransmissions?
No, cantcoap intentionally does not handle retransmissions. The user is expected to implement retransmission and timeout logic themselves, which is often simpler on constrained devices with one transaction at a time.