diff --git a/core/src/main/groovy/com/muwire/core/collections/FileCollection.groovy b/core/src/main/groovy/com/muwire/core/collections/FileCollection.groovy
index f821a840..71a09585 100644
--- a/core/src/main/groovy/com/muwire/core/collections/FileCollection.groovy
+++ b/core/src/main/groovy/com/muwire/core/collections/FileCollection.groovy
@@ -118,68 +118,4 @@ class FileCollection {
         }
         os.write(payload)
     }
-    
-    static class PathTree {
-        
-        private final Map<PathNode.Key, PathNode> keyToNode = new HashMap<>()
-        
-        final PathNode root
-        PathTree(String root) {
-            this.root = new PathNode(root, null)
-            keyToNode.put(this.root.key(), this.root)
-        }
-        
-        void add(List<String> paths) {
-            PathNode current = null
-            for (String path : paths) {
-                if (current == null) {
-                    if (path == root.path) {
-                        current = root
-                        continue
-                    }
-                }
-                
-                
-                PathNode child = new PathNode(path, current)
-                PathNode.Key childKey = child.key()
-                if (!keyToNode.containsKey(childKey)) {
-                    keyToNode.put(childKey, child)
-                    current.children.add(child)
-                }
-                current = keyToNode.get(childKey)
-            }
-        }
-    }
-    
-    static class PathNode {
-        final String path
-        final PathNode parent
-        final Set<PathNode> children = new LinkedHashSet<>()
-        private final int hashCode
-        
-        PathNode(String path, PathNode parent) {
-            this.parent = parent
-            this.path = path
-            this.hashCode = Objects.hash(path, parent)
-        }
-        
-
-        Key key() {
-            return new Key()
-        }
-        
-        private class Key {
-            
-            private final PathNode node = PathNode.this
-            
-            public int hashCode() {
-                hashCode
-            }
-            public boolean equals(Object o) {
-                Key other = (Key)o
-                Objects.equals(path, other.node.path) &&
-                    Objects.equals(parent, other.node.parent)
-            }
-        }         
-    }
 }
diff --git a/core/src/main/groovy/com/muwire/core/collections/PathTree.groovy b/core/src/main/groovy/com/muwire/core/collections/PathTree.groovy
new file mode 100644
index 00000000..e63a8ec1
--- /dev/null
+++ b/core/src/main/groovy/com/muwire/core/collections/PathTree.groovy
@@ -0,0 +1,86 @@
+package com.muwire.core.collections
+
+class PathTree {
+
+    private final Map<PathNode.Key, PathNode> keyToNode = new HashMap<>()
+
+    final PathNode root
+    PathTree(String root) {
+        this.root = new PathNode(root, null)
+        keyToNode.put(this.root.key(), this.root)
+    }
+
+    void add(List<String> paths) {
+        PathNode current = null
+        for (String path : paths) {
+            if (current == null) {
+                if (path == root.path) {
+                    current = root
+                    continue
+                }
+            }
+
+
+            PathNode child = new PathNode(path, current)
+            PathNode.Key childKey = child.key()
+            if (!keyToNode.containsKey(childKey)) {
+                keyToNode.put(childKey, child)
+                current.children.add(child)
+            }
+            current = keyToNode.get(childKey)
+        }
+    }
+    
+    public void traverse(Callback cb) {
+        doTraverse(root, cb)
+    }
+    
+    private void doTraverse(PathNode node, Callback cb) {
+        if (node.children.isEmpty())
+            cb.onFile(node.path)
+        else {
+            cb.onDirectoryEnter(node.path)
+            for (PathNode child : node.children)
+                doTraverse(child, cb)
+            cb.onDirectoryLeave()
+        }
+    }
+
+    static class PathNode {
+        final String path
+        final PathNode parent
+        final Set<PathNode> children = new LinkedHashSet<>()
+        private final int hashCode
+
+        PathNode(String path, PathNode parent) {
+            this.parent = parent
+            this.path = path
+            this.hashCode = Objects.hash(path, parent)
+        }
+
+
+        Key key() {
+            return new Key()
+        }
+
+        private class Key {
+
+            private final PathNode node = PathNode.this
+
+            public int hashCode() {
+                hashCode
+            }
+            public boolean equals(Object o) {
+                Key other = (Key)o
+                Objects.equals(path, other.node.path) &&
+                        Objects.equals(parent, other.node.parent)
+            }
+        }
+    }
+    
+    public static interface Callback {
+        public void onDirectoryEnter(String name)
+        public void onDirectoryLeave()
+        public void onFile(String name)
+    }
+}