MQTT support (#1224)

* Add mqtt() method and documentation
* Documentation clarifications for MIDI and OSC

packages/mqtt/mqtt.mjs

@@ -0,0 +1,87 @@
+/*
+mqtt.mjs - for patterning the internet of things from strudel
+Copyright (C) 2022 Strudel contributors - see <https://github.com/tidalcycles/strudel/blob/main/packages/serial/serial.mjs>
+This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more details. You should have received a copy of the GNU Affero General Public License along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+import { Pattern, isPattern } from '@strudel/core';
+import Paho from 'paho-mqtt';
+
+const connections = {};
+
+// Handle connection loss
+function onConnectionLost(responseObject) {
+  if (responseObject.errorCode !== 0) {
+    console.error(' mqtt connection lost: ', responseObject.errorMessage);
+  }
+}
+
+// Handle received messages
+function onMessageArrived(message) {
+  console.log('incoming mqtt message: ', message.payloadString); // prettier-ignore
+}
+
+function onFailure(err) {
+  console.error('Connection failed: ', err);
+}
+
+Pattern.prototype.mqtt = function (
+  username = undefined,
+  password = undefined,
+  topic = undefined,
+  host = 'wss://localhost:8883/',
+  client = undefined,
+  latency = 0,
+) {
+  const key = host + '-' + client;
+  let connected = false;
+  if (!client) {
+    client = 'strudel-' + String(Math.floor(Math.random() * 1000000));
+  }
+  function onConnect() {
+    console.log('Connected to mqtt broker');
+    connected = true;
+  }
+
+  let cx;
+  if (connections[key]) {
+    cx = connections[key];
+  } else {
+    cx = new Paho.Client(host, client);
+    cx.onConnectionLost = onConnectionLost;
+    cx.onMessageArrived = onMessageArrived;
+    const props = {
+      onSuccess: onConnect,
+      onFailure: onFailure,
+      useSSL: true,
+    };
+
+    if (username) {
+      props.userName = username;
+      props.password = password;
+    }
+    cx.connect(props);
+  }
+  return this.withHap((hap) => {
+    const onTrigger = (t_deprecate, hap, currentTime, cps, targetTime) => {
+      if (!connected) {
+        return;
+      }
+      let message = '';
+      if (typeof hap.value === 'object') {
+        message = JSON.stringify(hap.value);
+      } else {
+        message = hap.value;
+      }
+      message = new Paho.Message(message);
+      message.destinationName = topic;
+
+      const offset = (targetTime - currentTime + latency) * 1000;
+
+      window.setTimeout(function () {
+        cx.send(message);
+      }, offset);
+    };
+    return hap.setContext({ ...hap.context, onTrigger, dominantTrigger: true });
+  });
+};