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libcoap

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libcoap implements a lightweight application-protocol for devices that are constrained their resources such as computing power, RF range, memory, bandwith, or network packet sizes

FreeFree tier
Type
Open Source
Visit Website GitHub (38 stars)

About libcoap

libcoap is a C implementation of the Constrained Application Protocol (CoAP) as defined in RFC 7252. Designed for resource-constrained devices with limited computing power, memory, bandwidth, or network packet sizes, it enables lightweight communication for IoT and embedded systems. The library supports multi-platform deployment across POSIX systems and embedded environments, allowing developers to test applications on a laptop before moving to target hardware. libcoap includes a rich set of CoAP extensions such as resource observation, block-wise transfer, FETCH/PATCH, TCP transport, OSCORE security, hop-limit, group communication, and robust block-wise transfer options. It provides ready-to-use command-line tools (coap-client, coap-server, coap-rd) for testing and resource directory services. Security is supported through TLS frameworks including GnuTLS, OpenSSL, Mbed TLS, tinydtls, and wolfSSL. The library has been validated in ETSI IoT CoAP plugtests and is actively used in both academic and industrial IoT projects.

Key Features

Lightweight C implementation of Constrained Application Protocol (CoAP) per RFC 7252
Multi-platform support: runs on embedded devices and POSIX systems
CoAP extensions: resource observation, block-wise transfer, FETCH/PATCH, No-Response, TCP, OSCORE, Hop-Limit, group communication, Too Many Requests Response, Echo- and Request-Tags, Block-Wise Transfer Options for robust transmission
Includes command-line tools: coap-client (wget-like), coap-server (example server), coap-rd (resource directory)
Transport Layer Security (TLS) support via GnuTLS, OpenSSL, Mbed TLS, tinydtls, or wolfSSL
Successfully tested in ETSI IoT CoAP plugtests for interoperability
Open-source with permissive license (free)

Pros & Cons

Pros
  • Lightweight and optimized for constrained devices
  • Free and open-source with active maintenance
  • Supports a wide range of CoAP extensions beyond the core RFC
  • Multi-platform: same code can run on POSIX and embedded targets
  • Robust TLS integration with multiple crypto backends
Cons
  • Requires programming knowledge to integrate into applications (library-based, not a standalone product)
  • Limited to the CoAP protocol; not suitable for other application layer protocols
  • Documentation could be more extensive for advanced features

Best For

Developing resource-efficient CoAP servers and clients for IoT devicesPrototyping and testing CoAP applications on a laptop before deploying to embedded hardwareBuilding CoAP-based communication in industrial and academic IoT projectsInteroperability testing with other CoAP implementations via coap.space tools