[KURL] Avoid re-hashing input if is already canonicalized

third_party/WebKit/Source/platform/weborigin/KURL.cpp

 /*
  * Copyright (C) 2004, 2007, 2008, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Research In Motion Limited. All rights reserved.
  * Copyright (C) 2008, 2009, 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 699 matching lines @@
   if (url.is8Bit())
     return url::FindAndCompareScheme(asURLChar8Subtle(url), url.length(),
                                      protocol, 0);
   return url::FindAndCompareScheme(url.characters16(), url.length(), protocol,
                                    0);
 }
 
 void KURL::init(const KURL& base,
                 const String& relative,
                 const WTF::TextEncoding* queryEncoding) {
+  url::RawCanonOutputT<char> canonical;
   if (!relative.isNull() && relative.is8Bit()) {
     StringUTF8Adaptor relativeUTF8(relative);
-    init(base, relativeUTF8.data(), relativeUTF8.length(), queryEncoding);
-  } else
-    init(base, relative.characters16(), relative.length(), queryEncoding);
+    int relativeLength = static_cast<int>(relativeUTF8.length());

[esprehn, 2016/10/25 22:23:50]

This is scary, our strings can be unsigned in length, but net URL is using int?
I think this means you can overflow this thing. I think you'd want to clamp?

[Charlie Harrison, 2016/10/27 02:12:36]

Done.

+    init(base, relativeUTF8.data(), relativeLength, queryEncoding, &canonical);
+
+    // If the relative input is exactly equal to the canonical output, do not
+    // re-allocate the string. Note that this dangerously makes the input String
+    // an AtomicString, which is not safe for Strings that are meant to be
+    // passed between threads.
+    if (!relative.isEmpty() && relative.containsOnlyASCII() &&

[esprehn, 2016/10/25 22:23:50]

Why does containsOnlyASCII() matter here? I don't think there's any situation
where the length is the same and the latin1 representation and the utf8
representation mean different things.

[Charlie Harrison, 2016/10/27 02:12:36]

You're right. removed.

+        relativeLength == canonical.length() &&
+        !memcmp(canonical.data(), relativeUTF8.data(), canonical.length())) {
+      m_string = AtomicString(relative);
+    }
+  } else {
+    init(base, relative.characters16(), relative.length(), queryEncoding,
+         &canonical);
+  }
+
+  if (!m_string)
+    m_string = AtomicString::fromUTF8(canonical.data(), canonical.length());
+
   initProtocolIsInHTTPFamily();
   initInnerURL();
 }
 
 template <typename CHAR>
 void KURL::init(const KURL& base,
                 const CHAR* relative,
                 int relativeLength,
-                const WTF::TextEncoding* queryEncoding) {
+                const WTF::TextEncoding* queryEncoding,
+                url::RawCanonOutputT<char>* output) {
   // As a performance optimization, we do not use the charset converter
   // if encoding is UTF-8 or other Unicode encodings. Note that this is
   // per HTML5 2.5.3 (resolving URL). The URL canonicalizer will be more
   // efficient with no charset converter object because it can do UTF-8
   // internally with no extra copies.
 
   // We feel free to make the charset converter object every time since it's
   // just a wrapper around a reference.
   KURLCharsetConverter charsetConverterObject(queryEncoding);
   KURLCharsetConverter* charsetConverter =
       (!queryEncoding || isUnicodeEncoding(queryEncoding))
           ? 0
           : &charsetConverterObject;
 
   StringUTF8Adaptor baseUTF8(base.getString());
 
-  url::RawCanonOutputT<char> output;
   m_isValid = url::ResolveRelative(baseUTF8.data(), baseUTF8.length(),
                                    base.m_parsed, relative, relativeLength,
-                                   charsetConverter, &output, &m_parsed);
-
-  // See FIXME in KURLPrivate in the header. If canonicalization has not
-  // changed the string, we can avoid an extra allocation by using assignment.
-  m_string = AtomicString::fromUTF8(output.data(), output.length());
+                                   charsetConverter, output, &m_parsed);
 }
 
 void KURL::initInnerURL() {
   if (!m_isValid) {
     m_innerURL.reset();
     return;
   }
   if (url::Parsed* innerParsed = m_parsed.inner_parsed())
     m_innerURL = wrapUnique(new KURL(
         ParsedURLString,
@@ skipping 100 matching lines @@
   m_parsed = newParsed;
   m_string = AtomicString::fromUTF8(output.data(), output.length());
 }
 
 bool KURL::isSafeToSendToAnotherThread() const {
   return m_string.isSafeToSendToAnotherThread() &&
          (!m_innerURL || m_innerURL->isSafeToSendToAnotherThread());
 }
 
 }  // namespace blink