Adds limits subscription to the Telemetry API

e2e/baseFixtures.js

@@ -29,7 +29,7 @@
  */
 
 const base = require('@playwright/test');
-const { expect } = base;
+const { expect, request } = base;
 const fs = require('fs');
 const path = require('path');
 const { v4: uuid } = require('uuid');
@@ -179,4 +179,5 @@ exports.test = base.test.extend({
 });
 
 exports.expect = expect;
+exports.request = request;
 exports.waitForAnimations = waitForAnimations;

e2e/pluginFixtures.js

@@ -26,7 +26,7 @@
  * and appActions. These fixtures should be generalized across all plugins.
  */
 
-const { test, expect } = require('./baseFixtures');
+const { test, expect, request } = require('./baseFixtures');
 // const { createDomainObjectWithDefaults } = require('./appActions');
 const path = require('path');
 
@@ -147,6 +147,7 @@ exports.test = test.extend({
   }
 });
 exports.expect = expect;
+exports.request = request;
 
 /**
  * Takes a readable stream and returns a string.

src/api/telemetry/TelemetryAPI.js

@@ -489,6 +489,62 @@ export default class TelemetryAPI {
     }.bind(this);
   }
 
+  /**
+   * Subscribe to run-time changes in configured telemetry limits for a specific domain object.
+   * The callback will be called whenever data is received from a
+   * limit provider.
+   *
+   * @method subscribeToLimits
+   * @memberof module:openmct.TelemetryAPI~TelemetryProvider#
+   * @param {module:openmct.DomainObject} domainObject the object
+   *        which has associated limits
+   * @param {Function} callback the callback to invoke with new data, as
+   *        it becomes available
+   * @returns {Function} a function which may be called to terminate
+   *          the subscription
+   */
+  subscribeToLimits(domainObject, callback) {
+    if (domainObject.type === 'unknown') {
+      return () => {};
+    }
+
+    const provider = this.#findLimitEvaluator(domainObject);
+
+    if (!this.limitsSubscribeCache) {
+      this.limitsSubscribeCache = {};
+    }
+
+    const keyString = objectUtils.makeKeyString(domainObject.identifier);
+    let subscriber = this.limitsSubscribeCache[keyString];
+
+    if (!subscriber) {
+      subscriber = this.limitsSubscribeCache[keyString] = {
+        callbacks: [callback]
+      };
+      if (provider && provider.subscribeToLimits) {
+        subscriber.unsubscribe = provider.subscribeToLimits(domainObject, function (value) {
+          subscriber.callbacks.forEach(function (cb) {
+            cb(value);
+          });
+        });
+      } else {
+        subscriber.unsubscribe = function () {};
+      }
+    } else {
+      subscriber.callbacks.push(callback);
+    }
+
+    return function unsubscribe() {
+      subscriber.callbacks = subscriber.callbacks.filter(function (cb) {
+        return cb !== callback;
+      });
+      if (subscriber.callbacks.length === 0) {
+        subscriber.unsubscribe();
+        delete this.limitsSubscribeCache[keyString];
+      }
+    }.bind(this);
+  }
+
   /**
    * Request telemetry staleness for a domain object.
    *

src/plugins/plot/configuration/PlotSeries.js

@@ -141,6 +141,10 @@ export default class PlotSeries extends Model {
       this.unsubscribe();
     }
 
+    if (this.unsubscribeLimits) {
+      this.unsubscribeLimits();
+    }
+
     if (this.removeMutationListener) {
       this.removeMutationListener();
     }
@@ -320,10 +324,26 @@ export default class PlotSeries extends Model {
   async load(options) {
     await this.fetch(options);
     this.emit('load');
+    this.loadLimits();
+  }
+
+  async loadLimits() {
     const limitsResponse = await this.limitDefinition.limits();
-    this.limits = [];
+    this.limits = {};
+    if (!this.unsubscribeLimits) {
+      this.unsubscribeLimits = this.openmct.telemetry.subscribeToLimits(
+        this.domainObject,
+        this.limitsUpdated.bind(this)
+      );
+    }
+    this.limitsUpdated(limitsResponse);
+  }
+
+  limitsUpdated(limitsResponse) {
     if (limitsResponse) {
       this.limits = limitsResponse;
+    } else {
+      this.limits = {};
     }
 
     this.emit('limits', this);