feat(client): Add helper function for constructing a bit string

Author: adam-nielsen

lib/client.js

@@ -1189,5 +1189,43 @@ class Client extends EventEmitter {
   close() {
     this._transport.close();
   }
+
+  /**
+   * Helper function to take an array of enums and produce a bitstring suitable
+   * for inclusion as a property.
+   *
+   * @example
+   * [bacnet.enum.PropertyIdentifier.PROTOCOL_OBJECT_TYPES_SUPPORTED]: [
+   *   {value: bacnet.createBitstring([
+   *     bacnet.enum.ObjectTypesSupported.ANALOG_INPUT,
+   *     bacnet.enum.ObjectTypesSupported.ANALOG_OUTPUT,
+   *   ]),
+   *   type: bacnet.enum.ApplicationTags.BIT_STRING},
+   * ],
+   */
+  static createBitstring(items) {
+    let offset = 0;
+    let bytes = [];
+    let bitsUsed = 0;
+    while (items.length) {
+      // Find any values between offset and offset+8, for the next byte
+      let value = 0;
+      items = items.filter(i => {
+        if (i >= offset + 8) return true; // leave for future iteration
+        value |= 1 << (i - offset);
+        bitsUsed = Math.max(bitsUsed, i);
+        return false; // remove from list
+      });
+      bytes.push(value);
+      offset += 8;
+    }
+    bitsUsed++;
+
+    return {
+      value: bytes,
+      bitsUsed: bitsUsed,
+    };
+  }
+
 }
 module.exports = Client;

test/unit/client.spec.js

@@ -0,0 +1,38 @@
+'use strict';
+
+const expect      = require('chai').expect;
+const utils       = require('./utils');
+const baEnum      = require('../../lib/enum');
+const client      = require('../../lib/client');
+
+describe('bacstack - client', () => {
+  it('should successfuly encode a bitstring > 32 bits', () => {
+    const result = client.createBitstring([
+      baEnum.ServicesSupported.CONFIRMED_COV_NOTIFICATION,
+      baEnum.ServicesSupported.READ_PROPERTY,
+      baEnum.ServicesSupported.WHO_IS,
+    ]);
+    expect(result).to.deep.equal({
+      value: [2, 16, 0, 0, 4],
+      bitsUsed: 35,
+    });
+  });
+  it('should successfuly encode a bitstring < 8 bits', () => {
+    const result = client.createBitstring([
+      baEnum.ServicesSupported.GET_ALARM_SUMMARY,
+    ]);
+    expect(result).to.deep.equal({
+      value: [8],
+      bitsUsed: 4,
+    });
+  });
+  it('should successfuly encode a bitstring of only one bit', () => {
+    const result = client.createBitstring([
+      baEnum.ServicesSupported.ACKNOWLEDGE_ALARM,
+    ]);
+    expect(result).to.deep.equal({
+      value: [1],
+      bitsUsed: 1,
+    });
+  });
+});