# CoAP server example

(See the README.md file in the upper level 'examples' directory for more information about examples.)  
This CoAP server example is adaptation of one of the [libcoap](https://github.com/obgm/libcoap) example.

CoAP server example would startup a daemon task, receive data from CoAP client and transmit data to CoAP client.

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
```

* Set default serial port under Serial Flasher config
* 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:

```
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
current CoAP server would startup a daemon task,   
and the log is such as the following:  

```
...
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 (2622) event: sta ip: 192.168.3.84, mask: 255.255.255.0, gw: 192.168.3.1
I (2622) CoAP_server: Connected to AP
...
```

if a CoAP client query `/Espressif` resource, CoAP server would return `"no data"`  
until a CoAP client does a PUT with some data.

## libcoap Documentation
This can be found at https://libcoap.net/doc/reference/4.2.0/

## Troubleshooting
* Please make sure CoAP client fetchs or puts data under path: `/Espressif` or
fetches `/.well-known/core`

* libcoap logging can be increased by changing `#define COAP_LOGGING_LEVEL 0`
to `#define COAP_LOGGING_LEVEL 9`