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102 lines
3.8 KiB
Markdown
102 lines
3.8 KiB
Markdown
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# CoAP client example
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(See the README.md file in the upper level 'examples' directory for more information about examples.)
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This CoAP client example is very simplified adaptation of one of the
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[libcoap](https://github.com/obgm/libcoap) examples.
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CoAP client example will connect your ESP32 device to a CoAP server, send off a GET request and
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fetch the response data from CoAP server. The client can be extended to PUT / POST / DELETE requests,
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as well as supporting the Observer extensions [RFC7641](https://tools.ietf.org/html/rfc7641).
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If the URI is prefixed with coaps:// instead of coap://, then the CoAP client will attempt to use
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the DTLS protocol using the defined Pre-Shared Keys(PSK) or Public Key Infrastructure (PKI) which the
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CoAP server needs to know about.
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If the URI is prefixed with coap+tcp://, then the CoAP will try to use TCP for the communication.
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NOTE: coaps+tcp:// is not currently supported, even though both libcoap and MbedTLS support it.
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The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with
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constrained nodes and constrained networks in the Internet of Things.
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The protocol is designed for machine-to-machine (M2M) applications such as smart energy and
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building automation.
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Please refer to [RFC7252](https://www.rfc-editor.org/rfc/pdfrfc/rfc7252.txt.pdf) for more details.
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## How to use example
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### Configure the project
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```
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idf.py menuconfig
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```
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Example Connection Configuration --->
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* Set WiFi SSID under Example Configuration
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* Set WiFi Password under Example Configuration
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Example CoAP Client Configuration --->
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* Set CoAP Target Uri
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* If PSK, Set CoAP Preshared Key to use in connection to the server
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* If PSK, Set CoAP PSK Client identity (username)
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Component config --->
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CoAP Configuration --->
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* Set encryption method definition, PSK (default) or PKI
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* Enable CoAP debugging if required
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### Build and Flash
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Build the project and flash it to the board, then run monitor tool to view serial output:
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```
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idf.py build
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idf.py -p PORT flash monitor
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```
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(To exit the serial monitor, type ``Ctrl-]``.)
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See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
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## Example Output
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Prerequisite: we startup a CoAP server on coap server example,
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or use the default of coap://californium.eclipse.org.
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and you could receive data from CoAP server if succeed,
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such as the following log:
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```
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...
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I (332) wifi: mode : sta (30:ae:a4:04:1b:7c)
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I (1672) wifi: n:11 0, o:1 0, ap:255 255, sta:11 0, prof:1
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I (1672) wifi: state: init -> auth (b0)
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I (1682) wifi: state: auth -> assoc (0)
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I (1692) wifi: state: assoc -> run (10)
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I (1692) wifi: connected with huawei_cw, channel 11
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I (1692) wifi: pm start, type: 1
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I (2582) event: sta ip: 192.168.3.89, mask: 255.255.255.0, gw: 192.168.3.1
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I (2582) CoAP_client: Connected to AP
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I (2582) CoAP_client: DNS lookup succeeded. IP=104.196.15.150
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Received:
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************************************************************
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CoAP RFC 7252 Cf 2.0.0-SNAPSHOT
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************************************************************
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This server is using the Eclipse Californium (Cf) CoAP framework
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published under EPL+EDL: http://www.eclipse.org/californium/
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(c) 2014, 2015, 2016 Institute for Pervasive Computing, ETH Zurich and others
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************************************************************
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...
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```
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## libcoap Documentation
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This can be found at https://libcoap.net/doc/reference/4.2.0/
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## Troubleshooting
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* Please make sure Target Url includes valid `host`, optional `port`,
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optional `path`, and begins with `coap://`, `coaps://` or `coap+tcp://`
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for a coap server that supports TCP
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(not all do including coap+tcp://californium.eclipse.org).
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* CoAP logging can be enabled by running 'idf.py menuconfig -> Component config -> CoAP Configuration' and setting appropriate log level
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