Fix incorrect lookup in non-root nodes

Given the following non-root tree:

  tree = Tree(Symbol).new
  tree.add "/prefix/", :prefix
  tree.add "/prefix/foo", :foo

Attempt to lookup for `/foo` was incorrectly identifying `:foo` entry as
the correct value.

This change ensures that child nodes of the current node are not scanned
if key and path being looked up do not match.

Fixes #27

CHANGELOG.md

@@ -8,6 +8,7 @@ so please check *Changed* and *Removed* notes before upgrading.
 
 ### Fixed
 - Correct lookup issue caused by partial shared key with glob [#23](https://github.com/luislavena/radix/issues/23)
+- Correct lookup caused by non-root key in suffix [#27](https://github.com/luislavena/radix/issues/27)
 
 ### Removed
 - Remove `Radix::Result#key` since exposes internal details about structure (breaking change)

spec/radix/tree_spec.cr

@@ -353,6 +353,15 @@ module Radix
           result.found?.should be_true
           result.payload.should eq(:tags)
         end
+
+        it "do not find when lookup for non-root key" do
+          tree = Tree(Symbol).new
+          tree.add "/prefix/", :prefix
+          tree.add "/prefix/foo", :foo
+
+          result = tree.find "/foo"
+          result.found?.should be_false
+        end
       end
 
       context "unicode nodes with shared parent" do

src/radix/tree.cr

@@ -299,6 +299,14 @@ module Radix
         end
       end
 
+      # determine if remaining part of key and path are still the same
+      if (key_reader.has_next? && path_reader.has_next?) &&
+         (key_reader.current_char != path_reader.current_char ||
+         key_reader.peek_next_char != path_reader.peek_next_char)
+        # path and key differ, skipping
+        return
+      end
+
       # still path to walk, check for possible trailing slash or children
       # nodes
       if path_reader.has_next?