# CoAP client example (See the README.md file in the upper level 'examples' directory for more information about examples.) This CoAP client example is very simplified adaptation of one of the [libcoap](https://github.com/obgm/libcoap) examples. CoAP client example will connect your ESP32 device to a CoAP server, send off a GET request and fetch the response data from CoAP server. The client can be extended to PUT / POST / DELETE requests, as well as supporting the Observer extensions [RFC7641](https://tools.ietf.org/html/rfc7641). If the URI is prefixed with coaps:// instead of coap://, then the CoAP client will attempt to use the DTLS protocol using the defined Pre-Shared Keys(PSK) or Public Key Infrastructure (PKI) which the CoAP server needs to know about. If the URI is prefixed with coap+tcp://, then the CoAP will try to use TCP for the communication. NOTE: coaps+tcp:// is not currently supported, even though both libcoap and MbedTLS support it. The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained networks in the Internet of Things. The protocol is designed for machine-to-machine (M2M) applications such as smart energy and building automation. Please refer to [RFC7252](https://www.rfc-editor.org/rfc/pdfrfc/rfc7252.txt.pdf) for more details. ## How to use example ### Configure the project ``` idf.py menuconfig ``` Example Connection Configuration ---> * Set WiFi SSID under Example Configuration * Set WiFi Password under Example Configuration Example CoAP Client Configuration ---> * Set CoAP Target Uri * Set encryption method definitions (None, PSK or PKI) * If PSK Set CoAP Preshared Key to use in connection to the server * If PSK Set CoAP PSK Client identity (username) Enable CoAP debugging if required Component config ---> mbedTLS ---> [*] Enable mbedtls certificate expiry check TLS Key Exchange Methods ---> [*] Enable pre-shared-key ciphersuites [*] Enable PSK based ciphersuite modes [*] Support DTLS protocol (all versions) ### Build and Flash Build the project and flash it to the board, then run monitor tool to view serial output: ``` idf.py build idf.py -p PORT flash monitor ``` (To exit the serial monitor, type ``Ctrl-]``.) See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects. ## Example Output Prerequisite: we startup a CoAP server on coap server example, or use the default of coap://californium.eclipse.org. and you could receive data from CoAP server if succeed, such as the following log: ``` ... I (332) wifi: mode : sta (30:ae:a4:04:1b:7c) I (1672) wifi: n:11 0, o:1 0, ap:255 255, sta:11 0, prof:1 I (1672) wifi: state: init -> auth (b0) I (1682) wifi: state: auth -> assoc (0) I (1692) wifi: state: assoc -> run (10) I (1692) wifi: connected with huawei_cw, channel 11 I (1692) wifi: pm start, type: 1 I (2582) event: sta ip: 192.168.3.89, mask: 255.255.255.0, gw: 192.168.3.1 I (2582) CoAP_client: Connected to AP I (2582) CoAP_client: DNS lookup succeeded. IP=104.196.15.150 Received: ************************************************************ CoAP RFC 7252 Cf 2.0.0-SNAPSHOT ************************************************************ This server is using the Eclipse Californium (Cf) CoAP framework published under EPL+EDL: http://www.eclipse.org/californium/ (c) 2014, 2015, 2016 Institute for Pervasive Computing, ETH Zurich and others ************************************************************ ... ``` ## libcoap Documentation This can be found at https://libcoap.net/doc/reference/4.2.0/ ## Troubleshooting * Please make sure Target Url includes valid `host`, optional `port`, optional `path`, and begins with `coap://`, `coaps://` or `coap+tcp://` for a coap server that supports TCP (not all do including coap+tcp://californium.eclipse.org). * CoAP logging can be enabled by running 'make menuconfig' and enable debugging * Encryption (MbedTLS) can be enabled by running 'make menuconfig' and enable debugging