# gcoap Example

This application provides command line access to gcoap, a GNRC implementation of CoAP. See the [CoAP spec][1] for background, and the Modules>Networking>GNRC>CoAP topic in the source documentation for the structure of the implementation.

We support two setup options for this example:

### Native networking
Build with the standard `Makefile`. Follow the setup [instructions][2] for the gnrc_networking example.

### SLIP-based border router

Build with `Makefile.slip`. Follow the setup instructions in README-slip.md, which are based on the [SLIP instructions][3] for the gnrc_border_router example. We also plan to provide or reference the ethos/UHCP instructions, but we don't have it working yet.

## Current Status
gcoap includes server and client capability. Available features include:

* Server and Client provide helper functions for writing the response/request. See the CoAP topic in the source documentation for details. See the gcoap example for sample implementations.
* Server allows an application to register a 'listener', which includes an array of endpoint paths and function callbacks used to write a response.
* Server listens on a port at startup; defaults to 5683.
* Client operates asynchronously; sends request and then handles response in a user provided callback. Also executes callback on timeout.
* Client generates token; length defined at compile time.
* Message Type: Supports non-confirmable (NON) messaging.
* Options: Supports Content-Format for response payload.


## Example Use
This example uses gcoap as a server on RIOT native. Then we send a request from a libcoap example client on the Linux host.

### Verify setup from RIOT terminal

    > coap info

Expected response:

    CoAP server is listening on port 5683
     CLI requests sent: 0
    CoAP open requests: 0

### Query from libcoap example client
gcoap does not provide any output to the CoAP terminal when it handles a request. We recommend use of Wireshark to see the request and response. You also can add some debug output in the endpoint function callback.

    ./coap-client -N -m get -p 5683 coap://[fe80::1843:8eff:fe40:4eaa%tap0]/.well-known/core

Example response:

    v:1 t:NON c:GET i:0daa {} [ ]
    </cli/stats>

The response shows the endpoint registered by the gcoap CLI example.

### Send query to libcoap example server
Start the libcoap example server with the command below.

    ./coap-server

Enter the query below in the RIOT CLI.

    > coap get fe80::d8b8:65ff:feee:121b 5683 /.well-known/core

CLI output:

    gcoap_cli: sending msg ID 743, 75 bytes
    > gcoap: response Success, code 2.05, 105 bytes
    </>;title="General Info";ct=0,</time>;if="clock";rt="Ticks";title="Internal Clock";ct=0;obs,</async>;ct=0


[1]: https://tools.ietf.org/html/rfc7252    "CoAP spec"
[2]: https://github.com/RIOT-OS/RIOT/tree/master/examples/gnrc_networking    "instructions"
[3]: https://github.com/RIOT-OS/RIOT/tree/master/examples/gnrc_border_router    "SLIP instructions"