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A CoAP (RFC 7252) implementation in C

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libcoap: A C implementation of the Constrained Application Protocol (RFC 7252)

Build Status: main Build Status: develop Static Analysis Fuzzing Status

Copyright (C) 2010—2021 by Olaf Bergmann [email protected] and others


libcoap is a C implementation of a lightweight application-protocol for devices that are constrained their resources such as computing power, RF range, memory, bandwidth, or network packet sizes. This protocol, CoAP, is standardized by the IETF as RFC 7252. For further information related to CoAP, see

You might want to check out libcoap-minimal for usage examples.


Documentation and further information can be found at


This package contains a protocol parser and basic networking functions for platforms with support for malloc() and BSD-style sockets. In addition, there is support for Contiki, LwIP and Espressif/ESP-IDF hosted environments.

The following RFCs are supported

  • RFC7252: The Constrained Application Protocol (CoAP)

  • RFC7641: Observing Resources in the Constrained Application Protocol (CoAP)

  • RFC7959: Block-Wise Transfers in the Constrained Application Protocol (CoAP)

  • RFC7967: Constrained Application Protocol (CoAP) Option for No Server Response

  • RFC8132: PATCH and FETCH Methods for the Constrained Application Protocol (CoAP)

  • RFC8323: CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets [No WebSockets support]

  • RFC8768: Constrained Application Protocol (CoAP) Hop-Limit Option

There is (D)TLS support for the following libraries

  • OpenSSL (Minimum version 1.1.0) [PKI, PSK and PKCS11]

  • GnuTLS (Minimum version 3.3.0) [PKI, PSK, RPK(3.6.6+) and PKCS11]

  • Mbed TLS (Minimum version 2.7.10) [PKI and PSK]

  • TinyDTLS [PSK and RPK] [DTLS Only]

The examples directory contain a CoAP client, CoAP Resource Directory server and a CoAP server to demonstrate the use of this library.


Further information can be found at and BUILDING.


This library is published as open-source software without any warranty of any kind. Use is permitted under the terms of the simplified BSD license. It includes public domain software. libcoap binaries may also include open-source software with their respective licensing terms. Please refer to LICENSE for further details.

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