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CoAP client example

(See the README.md file in the upper level 'examples' directory for more information about examples.) this CoAP client example is adaptation of one of the libcoap example.

CoAP client example would connect your ESP32 device to any CoAP server, fetch data from CoAP server and upstream data to CoAP server.

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 for more details.

How to use example

Configure the project

make menuconfig

Set serial port under Serial Flasher config
Set Target Uri under Example Configuration
Set WiFi SSID under Example Configuration
Set WiFi Password under Example Configuration

Build and Flash

Build the project and flash it to the board, then run monitor tool to view serial output:

make -j4 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:// or coap+tcp:// for a coap server that supports TCP (not all do including coap+tcp://californium.eclipse.org).
libcoap logging can be increased by changing #define COAP_LOGGING_LEVEL 0 to #define COAP_LOGGING_LEVEL 9

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