endpoints.tex

\section{Endpoints}
N2O Erlang Processes are instantiated and run by Web Server.
Depending on Web Server endpoint bindings you can specify
module for HTTP requests handling.

\paragraph{}
N2O comes with three endpoint handlers for each Web Server supported.
However you are not required to use any of these.
You can implement your own endpoint handlers, e.g. for using with
Meteor.js or Angular.js and providing Erlang back-end event streaming
from server-side. Here is an example of using HTTP, WebSocket and
REST endpoint handlers with Cowboy Web Server.

\vspace{1\baselineskip}
\begin{lstlisting}
    {"/rest/:resource",     rest_cowboy, []},
    {"/rest/:resource/:id", rest_cowboy, []},
    {"/ws/[...]",           n2o_stream,  []},
    {'_',                   n2o_cowboy,  []}
\end{lstlisting}

\subsection{HTML Pages over HTTP}
This handler is used for serving initial dynamic HTML page.
In case you are serving static HTML content this handler is
not included into the running stack. {\bf {n2o}\_{cowboy}} is
a default HTML page handler.

\paragraph{}
On initial page load {\bf {n2o}\_{document}:run} of page document endpoint is started.
During its execution {\bf {wf}\_{render}:render} proceeds
by calling {\bf Module:main} selected by the routing handler.

\newpage
\subsection{JavaScript Events over WebSocket}
JavaScript handler shares the same router information as the
HTML handler because during its initial phase the same chain
of N2O handlers is called.

\paragraph{}
This handler knows how to deal with XHR and WebSocket requests.
{\bf {n2o}\_{stream}} is a default JavaScript event handler
based on Bullet library created by Loïc Hoguin, optimized and refined.

\paragraph{}
You can send several types of events directly from JavaScript
using various protocols. E.g. you may need to use client protocol:

\vspace{1\baselineskip}
\begin{lstlisting}
  JavaScript> ws.send(enc(tuple(atom('client'),
                   tuple(atom('phone_auth'),bin("+380..")))));
\end{lstlisting}
\vspace{1\baselineskip}

And catch this event at Erlang side:

\vspace{1\baselineskip}
\begin{lstlisting}
  event({client,{phone_auth,Phone}}) ->
      io:format("Phone: ~p~n",[Phone]).
\end{lstlisting}
\vspace{1\baselineskip}

You can also send direct messages to event/1, but use it carefully
because it may violate security rules.

\vspace{1\baselineskip}
\begin{lstlisting}
    > ws.send(enc(tuple(atom('direct'),atom('init'))));
\end{lstlisting}
\vspace{1\baselineskip}

With catching at Erlang side:

\vspace{1\baselineskip}
\begin{lstlisting}
    event(init) -> io:format("Init called~n").
\end{lstlisting}
\vspace{1\baselineskip}

\newpage
\subsection{HTTP API over REST}
REST handler's request context initialization differs for the one
used by HTML and JavaScript handlers. N2O handler chains are not
applied to REST requests. {\bf rest\_cowboy} is a default REST
handler.

\vspace{1\baselineskip}
\begin{lstlisting}
    {"/rest/:resource", rest_cowboy, []},
    {"/rest/:resource/:id", rest_cowboy, []},
\end{lstlisting}

\lstset{captionpos=b}
\vspace{1\baselineskip}
\begin{lstlisting}[caption=users.erl]
    -module(users).
    -behaviour(rest).
    -compile({parse_transform, rest}).
    -include("users.hrl").
    -export(?REST_API).
    -rest_record(user).

    init() -> ets:new(users,
                    [public, named_table, {keypos, #user.id}]).

    populate(Users) -> ets:insert(users, Users).
    exists(Id) -> ets:member(users, wf:to_list(Id)).
    get() -> ets:tab2list(users).
    get(Id) -> [User] = ets:lookup(users, wf:to_list(Id)), User.
    delete(Id) -> ets:delete(users, wf:to_list(Id)).
    post(#user{} = User) -> ets:insert(users, User);
    post(Data) -> post(from_json(Data, #user{})).
\end{lstlisting}
\vspace{1\baselineskip}

To add users to in-memory storage perform POST requests:

\vspace{1\baselineskip}
\begin{lstlisting}
    curl -i -X POST -d "id=vlad" localhost:8000/rest/users
    curl -i -X POST -d "id=doxtop" localhost:8000/rest/users
    curl -i -X GET localhost:8000/rest/users
    curl -i -X PUT -d "id=5HT" localhost:8000/rest/users/vlad
    curl -i -X GET localhost:8000/rest/users/5HT
    curl -i -X DELETE localhost:8000/rest/users/5HT
\end{lstlisting}
\vspace{1\baselineskip}