trick/docs/documentation/web/Extending_the_WS-API.html
2019-11-21 13:30:09 -06:00

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<h1 id="toc_0">Extending the WebSocket-API</h1>
<h2 id="toc_1">When You Create a WebSocket Connection</h2>
<p>Consider the following Javascript, that creates a web socket connection:</p>
<p><code>var ws = new WebSocket(&#39;ws://localhost:8888/api/ws/VariableServer&#39;);</code></p>
<p>In the URL: <code>ws://localhost:8888/api/ws/VariableServer</code></p>
<ul>
<li><code>ws://</code> specifies the <strong>protocol</strong> (web-socket in this case.)</li>
<li><code>localhost</code> specifies the <strong>domain</strong>,</li>
<li><code>:8888</code> specifies the <strong>port</strong>, and</li>
<li><code>/api/ws/VariableServer</code> specifies the <strong>path</strong>.</li>
</ul>
<p>In the Trick web server, the path associated with a websocket must begin with
<code>/api/ws/</code>. The remaining part of the path, i.e., <code>VariableServer</code> is the <strong>key</strong> that specifies the <strong>sub-protocol</strong>, prescribing what messages will be passed between client and server, and what those messages mean.</p>
<p>When a web-socket connection is established, the <strong>key</strong> will determine what type (sub-class) of <code>WebSocketSession</code> object to create, to manage the connection.</p>
<h2 id="toc_2">WebSocketSession</h2>
<p>A <code>WebSocketSession</code> is a pure virtual base class meant to represent the state of one of potentially many websocket connections. It provides methods to:</p>
<ol>
<li>Synchronously marshall Trick simulation data for out-going messages</li>
<li>Send messages to the websocket client, and</li>
<li>Receive and process messages from the websocket client.</li>
</ol>
<p>To implement a new websocket sub-protocol, one needs to derive a new class from this base class, and implement the required methods. <code>WebSocketSession.hh</code> can be found in <code>${TRICK_HOME}/include/trick/</code>.</p>
<h3 id="toc_3">WebSocketSession.hh</h3>
<div><pre><code class="language-c">/*************************************************************************
PURPOSE: (Represent Websocket connection.)
**************************************************************************/
#ifndef WEB_SOCKET_SESSION_HH
#define WEB_SOCKET_SESSION_HH
#include &lt;string&gt;
#ifndef SWIG
#include &quot;mongoose/mongoose.h&quot;
#endif
class WebSocketSession {
public:
WebSocketSession(struct mg_connection *nc):connection(nc){};
virtual ~WebSocketSession() {};
virtual void marshallData()=0;
virtual void sendMessage()=0;
virtual int handleMessage(std::string)=0;
struct mg_connection* connection;
};
#endif</code></pre></div>
<h3 id="toc_4">Adding Your New WebSocketSession Type to the WebServer</h3>
<p>To install your new websocket protocol, you&#39;ll need to create a function that
creates an instance of your new WebSocketSession type. Then you&#39;ll need to call
<code>HTTP_Server::installWebSocketSessionMaker</code> to install the function, with a
label.</p>
<p>The function you&#39;ll create will take <code>struct mg_connection *</code> as an argument
and return <code>WebSocketSession*</code>.</p>
<h2 id="toc_5">Example</h2>
<p>Let&#39;s create a new web socket protocol that sends the time in GMT or local time.</p>
<p>First we&#39;ll derive a new type called <code>TimeSession</code> from <code>WebSocketSession</code>.</p>
<h3 id="toc_6">TimeSession.hh</h3>
<div><pre><code class="language-c">/*************************************************************************
PURPOSE: (Represent the state of a variable server websocket connection.)
**************************************************************************/
#ifndef TIMESESSION_HH
#define TIMESESSION_HH
#include &lt;vector&gt;
#include &lt;string&gt;
#include &quot;time.h&quot;
#include &quot;trick/WebSocketSession.hh&quot;
class TimeSession : public WebSocketSession {
public:
enum Zone { GMT, LOCAL};
TimeSession(struct mg_connection *nc);
~TimeSession();
void marshallData();
void sendMessage();
int handleMessage(std::string);
private:
time_t now;
Zone zone;
};
WebSocketSession* makeTimeSession( struct mg_connection *nc );
#endif</code></pre></div>
<p>Below is our implementation. Notice the function <code>makeTimeSession</code> at the bottom.</p>
<h3 id="toc_7">TimeSession.cpp</h3>
<div><pre><code class="language-c">#include &lt;stdio.h&gt;
#include &lt;time.h&gt;
#include &lt;iostream&gt;
#include &quot;TimeSession.hh&quot;
// CONSTRUCTOR
TimeSession::TimeSession( struct mg_connection *nc ) : WebSocketSession(nc) {
time(&amp;now);
}
// DESTRUCTOR
TimeSession::~TimeSession() {}
void TimeSession::marshallData() {
time(&amp;now);
}
void TimeSession::sendMessage() {
char message[1024];
struct tm *theTime;
if (zone == TimeSession::LOCAL) {
theTime = localtime(&amp;now);
} else {
theTime = gmtime(&amp;now);
}
int hours = theTime-&gt;tm_hour;
int minutes = theTime-&gt;tm_min;
int seconds = theTime-&gt;tm_sec;
int day = theTime-&gt;tm_mday;
int month = theTime-&gt;tm_mon + 1;
int year = theTime-&gt;tm_year + 1900;
sprintf(message, &quot;Time: %02d:%02d:%02d Date: %02d/%02d/%d\n&quot;, hours, minutes, seconds, month, day, year);
mg_send_websocket_frame(connection, WEBSOCKET_OP_TEXT, message, strlen(message));
}
int TimeSession::handleMessage(std::string client_msg) {
if (client_msg.compare(&quot;GMT&quot;) == 0) {
zone = TimeSession::GMT;
} else if (client_msg.compare(&quot;LOCAL&quot;) == 0) {
zone = TimeSession::LOCAL;
} else {
std::cerr &lt;&lt; &quot;ERROR: Unknown command \&quot;&quot; &lt;&lt; client_msg &lt;&lt; &quot;\&quot;.&quot; &lt;&lt; std::endl;
}
return 0;
}
// WebSocketSessionMaker function for a TimeSession.
WebSocketSession* makeTimeSession( struct mg_connection *nc ) {
std::cerr &lt;&lt; &quot;DEBUG: Creating new TimeSession.&quot; &lt;&lt; std::endl;
return new TimeSession(nc);
}</code></pre></div>
<p>We put <code>TimeSession.cpp</code> and <code>TimeSession.cpp</code> into a models directory called <code>httpMethods/</code>.</p>
<h3 id="toc_8">S_define Modifications</h3>
<ol>
<li>Specify the dependency on the <code>httpMethods/TimeSession.cpp</code> compilation unit.</li>
<li>We should already be including the WebServer sim object, otherwise we don&#39;t even have a webserver.</li>
<li>We need to include our new header file: <code>##include &quot;httpMethods/TimeSession.hh&quot;</code></li>
<li>Finally, install our WebSocketSession type: <code>web.server.installWebSocketSessionMaker(&quot;Time&quot;, &amp;makeTimeSession);</code>
The label we use for our protocol here is &quot;Time&quot;, but it can be whatever name you choose.</li>
</ol>
<div><pre><code class="language-cpp">/***********************TRICK HEADER*************************
PURPOSE:
(Cannon Numeric)
LIBRARY DEPENDENCIES:
(
(cannon/gravity/src/cannon_init.c)
(cannon/gravity/src/cannon_numeric.c)
(httpMethods/TimeSession.cpp) // &lt;--(1)
)
*************************************************************/
#include &quot;sim_objects/default_trick_sys.sm&quot;
#include &quot;sim_objects/WebServer.sm&quot; // &lt;--(2)
##include &quot;cannon/gravity/include/cannon_numeric.h&quot;
##include &quot;httpMethods/TimeSession.hh&quot; // &lt;--(3)
class CannonSimObject : public Trick::SimObject {
public:
CANNON cannon ;
int foo;
CannonSimObject() {
(&quot;default_data&quot;) cannon_default_data( &amp;cannon ) ;
(&quot;initialization&quot;) cannon_init( &amp;cannon ) ;
(&quot;derivative&quot;) cannon_deriv( &amp;cannon ) ;
(&quot;integration&quot;) trick_ret = cannon_integ( &amp;cannon ) ;
(&quot;dynamic_event&quot;) cannon_impact( &amp;cannon) ;
}
} ;
CannonSimObject dyn ;
IntegLoop dyn_integloop (0.10) dyn;
void create_connections() {
dyn_integloop.getIntegrator(Runge_Kutta_4, 5);
web.server.installWebSocketSessionMaker(&quot;Time&quot;, &amp;makeTimeSession); // &lt;--(4)
}</code></pre></div>
<h2 id="toc_9">Testing The New WebSocket Interface</h2>
<p>To test your new web socket interface, put the following <code>time.html</code> file in <code>$YOUR_SIM_DIRECTORY/www/apps</code>. Then request <code>http://localhost:8888/apps/time.html</code> from your browser. You should see the time messages from your sim.</p>
<h3 id="toc_10">time.html</h3>
<div><pre><code class="language-markup">&lt;!DOCTYPE html&gt;
&lt;html&gt;
&lt;head&gt;
&lt;title&gt;WS Example&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;div id=&quot;output&quot;&gt;&lt;/div&gt;
&lt;script type=&quot;text/javascript&quot;&gt;
function log(s) {
var p = document.createElement(&quot;p&quot;);
p.style.wordWrap = &quot;break-word&quot;;
p.textContent = s;
output.appendChild(p);
}
var ws = new WebSocket(&#39;ws://localhost:8888/api/ws/Time&#39;);
// WebSocket Event Handlers
ws.onopen = function(e) {
ws.send(&quot;GMT&quot;);
};
ws.onmessage = function(e) {
log(e.data);
};
ws.onerror = function(e) {
console.log(&quot;WebSocket Error: &quot; , e);
handleErrors(e);
};
ws.onclose = function(e) {
console.log(&quot;Connection closed&quot;, e);
};
&lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;</code></pre></div>
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