gistfile1.diff

diff --git a/lib/stream.js b/lib/stream.js
index 189708a..37687b0 100644
--- a/lib/stream.js
+++ b/lib/stream.js
@@ -53,3 +53,22 @@ Stream.prototype.pipe = function (dest, options) {
     if (source.readable) source.resume();
   });
 };
+
+exports.createFilter = function (listener) {
+  var filter = new Stream();
+  filter.readable = true;
+  filter.writeable = true;
+  
+  var w = function (chunk) {
+    filter.emit("data");
+  };
+  
+  filter.write = function (chunk) {
+    listener(chunk, w);
+  };
+  filter.on("end", function () {
+    listener(null, w);
+  });
+  
+  return filter;
+}