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WS-API: VariableServer
ws://localhost:8888/api/ws/VariableServer
Purpose
JSON Variable Server
Client to Server Command Messages
Add a Trick Variable to the current session.
{ "cmd" : "var_add",
"var_name" : string
}
Stop sending periodic var_list messages (see below) from the server.
{ "cmd" : "var_pause" }
Resume sending periodic var_list response messages from the server.
{ "cmd" : "var_unpause" }
Send one var_list message from the server.
{ "cmd" : "var_send" }
Clear all variables from the current session, that is: undo all of the var_add commands.
{ "cmd" : "var_clear" }
Disconnect from the variable server.
{ "cmd" : "var_exit" }
Set the period (in milliseconds) at which var_list messages are sent form the server.
{ "cmd" : "var_cycle",
"period" : integer
}
Execute the given Python code in the host sim.
{ "cmd" : "python",
"pycode" : string
}
Send the sie structure from the server. Response will be the sie response message (below).
{ "cmd" : "sie" }
Send the units for the given variable. Response will be the units response message (below).
{ "cmd" : "units",
"var_name" : string
}
Server to Client Response Messages
Error Response
{ "msg_type" : "error",
"error_text" : string
}
Periodic response containing the values of variables requested by var_add.
{ "msg_type" : "var_list"
"time" : double
"values" : []
}
Response to the sie command (above).
{ "msg_type" : "sie",
"data" : string
}
Response to the units command (above).
{ "msg_type" : "units",
"var_name" : string,
"data" : string
}
Example Variable Server Client
<!DOCTYPE html>
<html>
<head>
<title>WS Experiments</title>
</head>
<body>
<style>
table { border-collapse: collapse; width: 100%; }
th, td { text-align: left; padding: 8px; }
tr:nth-child(even){background-color: #f2f2f2}
th { background-color: #562399; color: white; }
</style>
<header>
</header>
<div class="variableDisplay"></div>
<table class="variables">
<tr>
<th>Variable</th>
<th>Value</th>
</tr>
</table>
<div id="output"></div>
<script type="text/javascript">
function log(s) {
var p = document.createElement("p");
p.style.wordWrap = "break-word";
p.textContent = s;
output.appendChild(p);
}
function sendMessage(msg) {
ws.send(msg);
}
// Interface to Trick WebSocket Variable Server
function setPeriod(period) {
sendMessage(`{"cmd":"var_cycle","period":${period}}`);
}
function addVarTableRow(name, value) {
// create a row in the table that contains two <td>s, one for the var_name and one for its value.
let tr = document.createElement('tr');
let td1 = document.createElement('td');
td1.textContent = `${name}`;
let td2 = document.createElement('td');
td2.textContent = `${value}`;
td2.className = "values";
tr.appendChild(td1);
tr.appendChild(td2);
varTable.appendChild(tr);
}
function addVariable(name, value) {
sendMessage(`{"cmd":"var_add","var_name": "${name}"}`);
addVarTableRow(name, value);
}
var varTable = document.querySelector('table.variables');
var ws = new WebSocket('ws://localhost:8888/api/ws/VariableServer');
ws.onopen = function(e) {
setPeriod(100);
addVarTableRow("Time", 0.0);
addVariable("dyn.cannon.pos[0]", 0.0);
addVariable("dyn.cannon.pos[1]", 0.0);
addVariable("dyn.cannon.vel[0]", 0.0);
addVariable("dyn.cannon.vel[1]", 0.0);
addVariable("dyn.cannon.time", 0.0);
addVariable("dyn.cannon.timeRate", 0.0);
addVariable("dyn.cannon.impact", 0.0);
addVariable("I.dont.exist", 0.0);
sendMessage("{\"cmd\":\"var_unpause\"}");
};
ws.onmessage = function(e) {
let msg = JSON.parse(e.data);
if (msg.msg_type == "values") {
let valueNodes = varTable.getElementsByClassName("values");
valueNodes[0].textContent = msg.time;
for (let i = 0; i < msg.values.length; i++ ) {
valueNodes[i+1].textContent = msg.values[i];
}
}
};
ws.onerror = function(e) {
console.log("WebSocket Error: " , e);
handleErrors(e);
};
ws.onclose = function(e) {
console.log("Connection closed", e);
};
</script>
</body>
</html>
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