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

Author: adam-nielsen

lib/client.js

@@ -1204,5 +1204,34 @@ 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 value = 0;
+    items.forEach(i => value |= 1 << i);
+    let bytes = [], bitsUsed = 0;
+    while (value & 0xFF) {
+      bytes.push(value & 0xFF);
+      bitsUsed += 8;
+      value >>= 8;
+    }
+    return {
+      value: bytes,
+      bitsUsed: bitsUsed,
+    };
+  }
+
 }
 module.exports = Client;