Add ducktyping Filter.isFilter method

This should make some headway in avoiding instanceof pitfalls when
dealing with Filter objects.

Fix mcavage/node-ldapjs#123

lib/client/client.js

@@ -40,7 +40,6 @@ var SearchReference = messages.SearchReference;
 var SearchResponse = messages.SearchResponse;
 var Parser = messages.Parser;
 
-var Filter = filters.Filter;
 var PresenceFilter = filters.PresenceFilter;
 
 var ConnectionError = errors.ConnectionError;
@@ -640,7 +639,7 @@ Client.prototype.search = function search(base, options, controls, callback) {
     options.filter = filters.parseString(options.filter);
   } else if (!options.filter) {
     options.filter = new PresenceFilter({attribute: 'objectclass'});
-  } else if (!(options.filter instanceof Filter)) {
+  } else if (!filters.isFilter(options.filter)) {
     throw new TypeError('options.filter (Filter) required');
   }
 

lib/filters/filter.js

@@ -44,6 +44,21 @@ function Filter(options) {
     }
   });
 }
+
+Filter.isFilter = function isFilter(filter) {
+  if (!filter || typeof (filter) !== 'object') {
+    return false;
+  }
+  // Do our best to duck-type it
+  if ((filter instanceof Filter) || (
+      typeof (filter.toBer) === 'functin' &&
+      typeof (filter.matches) === 'function' &&
+      typeof (filter._type) === 'number')) {
+    return true;
+  }
+  return false;
+};
+
 module.exports = Filter;
 
 

lib/filters/index.js

@@ -547,6 +547,8 @@ module.exports = {
     return _parseString(filter);
   },
 
+  isFilter: Filter.isFilter,
+
   AndFilter: AndFilter,
   ApproximateFilter: ApproximateFilter,
   EqualityFilter: EqualityFilter,

lib/filters/not_filter.js

@@ -13,7 +13,7 @@ var Protocol = require('../protocol');
 
 function NotFilter(options) {
   if (typeof (options) === 'object') {
-    if (!options.filter || !(options.filter instanceof Filter))
+    if (!options.filter || !Filter.isFilter(options.filter))
       throw new TypeError('options.filter (Filter) required');
 
   } else {
@@ -37,7 +37,7 @@ module.exports = NotFilter;
 
 
 NotFilter.prototype.addFilter = function (f) {
-  if (!(f instanceof Filter))
+  if (!Filter.isFilter(f))
     throw new TypeError('filter (Filter) required');
   this.filter = f;
 };