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https://github.com/gotthardp/gen_coap

Generic Erlang CoAP Client/Server
https://github.com/gotthardp/gen_coap

coap coap-client coap-resources coap-server erlang

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Generic Erlang CoAP Client/Server

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# Generic Erlang CoAP Client/Server



Pure Erlang implementation of the Constrained Application Protocol (CoAP),

which aims to be conformant with:

 - CoAP core protocol [RFC 7252](https://tools.ietf.org/rfc/rfc7252.txt),

   including (since Erlang/OTP 19.2) the DTLS-Secured CoAP

 - CoAP Observe option [RFC 7641](https://tools.ietf.org/rfc/rfc7641.txt)

 - Block-wise transfers in CoAP [draft-ietf-core-block-18](https://tools.ietf.org/id/draft-ietf-core-block-18.txt)

 - CoRE link format [RFC 6690](https://tools.ietf.org/rfc/rfc6690.txt)



The following features are not (yet) implemented:

 - Proxying and virtual servers (Uri-Host, Uri-Port, Proxy-Uri and Proxy-Scheme options)



It was tested with the following CoAP implementations:

 - C [libcoap](https://www.libcoap.net/) (develop branch)

 - [coap.me](http://coap.me/)



Used in the following applications:

 - [CoAP Publish-Subscribe interface to RabbitMQ](https://github.com/gotthardp/rabbitmq-coap-pubsub)



Let me know if you (intend to) use *gen_coap*. The API may change and some

functions may not be implemented. Please

[add an Issue](https://github.com/gotthardp/gen_coap/issues/new)

if you find a bug or miss a feature.



## Usage

*gen_coap* enables you to integrate a CoAP server and/or CoAP client with

your application. For demonstration purposes it also includes a simple CoAP

client and server.



[![Build Status](https://travis-ci.org/gotthardp/gen_coap.svg?branch=master)](https://travis-ci.org/gotthardp/gen_coap)



### Client

Have a look at [sample_client.erl](examples/src/sample_client.erl). It implements a simple

command line utility for manipulation and observation of CoAP resources. It

shall demonstrate the use of the `coap_client` and `coap_observer` modules.

The tool accepts the following arguments:



 Argument      | Description

---------------|---------------

 -m *Method*   | request method (get, put, post or delete), default is 'get'

 -e *Text*     | include text as payload

 -s *Duration* | subscribe for given duration [seconds]

 *Uri*         | coap:// or coaps:// URI identifying the resource



Run the example simply by:



    $ ./coap-client.sh coap://127.0.0.1/.well-known/core

    $ ./coap-client.sh coaps://127.0.0.1/.well-known/core?rt=core.ps

    $ ./coap-client.sh coaps://127.0.0.1/resource

    $ ./coap-client.sh coap://127.0.0.1/resource -s 1000

    $ ./coap-client.sh -m put coap://127.0.0.1/resource -e data

    $ ./coap-client.sh -m delete coap://127.0.0.1/resource



In an erlang program you can get a CoAP resource by:

```erlang

{ok, content, Data} = coap_client:request(get, "coap://coap.me:5683")

```

No application need to be started to use the client.



### Server

Have a look at [sample_server.erl](examples/src/sample_server.erl). It implements a simple

resource storage, which can be accessed using CoAP. It shall demonstrate the

use of the `coap_server_registry` and `coap_responder` modules. The server

requires no arguments. Run the sample server as follows and then access

it using any CoAP client (or the *gen_coap* sample client tool):



    $ ./coap-server.sh



You can manually start the server from the Erlang command line by:



    $ erl -pa _build/default/lib/gen_coap/ebin



    1> application:ensure_all_started(gen_coap).

    {ok,[crypto,asn1,public_key,ssl,gen_coap]}



    2> coap_server:start_udp(coap_udp_socket).

    {ok,<0.78.0>}



However, the server out of a box does not offer any resources. To offer CoAP access

to some server resources you need to implement the [`coap_resource` behaviour](src/coap_resource.erl),

which defines callbacks that the server invokes upon reception of a CoAP request.

 - `coap_discover` is called when a CoAP client asks for the list of

   ".well-known/core" resources.

 - `coap_get`, `coap_post`, `coap_put` or `coap_delete` is called when the server

   receives a GET, POST, PUT or DELETE request for a resource.

 - `coap_observe` or `coap_unobserve` is called upon a GET request with an

   Observe=0 or Observe=1 option.



Since Erlang 19.2 the DTLS transport is supported. To configure certificates for

the sample coap-server do:



    $ cd gen_coap

    $ sudo openssl req -new > csr.pem

    $ sudo openssl rsa -in privkey.pem -out key.pem

    $ sudo openssl x509 -in csr.pem -out cert.pem -req -signkey key.pem



### Architecture



The following picture shows the `gen_coap` modules are their relationships:

![GitHub Logo](https://rawgit.com/gotthardp/gen_coap/master/doc/architecture.svg)



## Build Instructions



### Linux



First, you need to have [rebar](https://github.com/rebar/rebar) installed. Please

install the rebar package e.g. by



    $ sudo yum install erlang-rebar



Then, you only need to run



    $ git clone https://github.com/gotthardp/gen_coap.git

    $ cd gen_coap

    $ make



### Windows



I recommend you install the [Erlang IDE](http://erlide.org) for [Eclipse](https://www.eclipse.org).

Then, import the project:

 - Run Eclipse, select File > New > Project..., select Erlang Project and click Next.

 - Enter gen_coap as a Project name and select Location of *gen_coap* on your machine. Click Next.

 - Review the following page and click Next.

 - Set Source folders to `src;examples` and click Finish.



Run the Erlang application and then you should be able to run the client and server in your Console:



    1> sample_server:start().

    ok



    2> sample_client:start(["coap://localhost/.well-known/core"]).

    get "coap://localhost/.well-known/core"

    {ok,content,{coap_content,<<"xyz">>,60,<<"application/link-format">>,<<>>}}

    ok