Fix memoization of request target parses

It wasn't working because the symbols were created anew in each call
to Request.target_form.

CHANGELOG.rst

@@ -14,6 +14,7 @@ Added
 - HTTPolice can now use much less memory when parsing long TCP streams.
 - Similarly, large HTML reports need much less memory to produce.
 - Checks for the `Forwarded`_ header (notices `1296`_, `1297`_).
+- Minor speedup in case when request URLs often repeat.
 
 .. _Forwarded: https://tools.ietf.org/html/rfc7239
 .. _chunk extensions: https://tools.ietf.org/html/rfc7230#section-4.1.1

httpolice/parse.py

@@ -134,9 +134,7 @@ def parse(data, symbol, complain=None, fail_notice_id=None,
 
 _memo = OrderedDict()
 
-# This value was obtained by running on a large tcpflow input and increasing
-# until it stopped getting faster.
-MEMO_LIMIT = 200
+MEMO_LIMIT = 500
 
 
 def _splice_annotations(data, annotations):

httpolice/request.py

@@ -25,6 +25,11 @@
 from httpolice.util.text import force_unicode
 
 
+normal_target = mark(origin_form) | mark(absolute_form)
+options_target = mark(origin_form) | mark(asterisk_form) | mark(absolute_form)
+connect_target = mark(authority_form)
+
+
 class Request(message.Message):
 
     def __init__(self, scheme, method, target, version, header_entries,
@@ -118,12 +123,11 @@ def __repr__(self):
     @derived_property
     def target_form(self):
         if self.method == m.CONNECT:
-            symbol = mark(authority_form)
+            symbol = connect_target
         elif self.method == m.OPTIONS:
-            symbol = (mark(origin_form) | mark(asterisk_form) |
-                      mark(absolute_form))
+            symbol = options_target
         else:
-            symbol = mark(origin_form) | mark(absolute_form)
+            symbol = normal_target
         r = parse(self.target, symbol, self.complain, 1045,
                   place=u'request target')
         if okay(r):