Reduce string copies in GURL creation

third_party/WebKit/Source/platform/exported/WebStringUTF8Adaptor.cpp

 /*
- * Copyright (C) 2013 Google Inc. All rights reserved.
+ * Copyright (C) 2016 Google Inc. All rights reserved.

[haraken, 2016/01/12 23:44:37]

You can use the 3-line copyright.

// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

  *
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  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
  * copyright notice, this list of conditions and the following disclaimer
  * in the documentation and/or other materials provided with the
  * distribution.
  *     * Neither the name of Google Inc. nor the names of its
  * contributors may be used to endorse or promote products derived from
  * this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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-#ifndef WebMIDIAccessor_h
-#define WebMIDIAccessor_h
+#include "public/platform/WebStringUTF8Adaptor.h"
 
-#include "WebString.h"
+#include "public/platform/WebString.h"
+#include "wtf/text/CString.h"
+#include "wtf/text/WTFString.h"
 
 namespace blink {
 
-class WebMIDIAccessor {
-public:
-    virtual ~WebMIDIAccessor() { }
+WebStringUTF8Adaptor::WebStringUTF8Adaptor(const WebString& string)
+{
+    if (string.isEmpty())
+        return;
+    // 8-bit WTF::Strings are encoded in Latin-1. If |relative| is entirely
+    // ASCII, we luck out and can avoid mallocing a new buffer to hold the
+    // UTF-8 data because UTF-8 and Latin-1 use the same code units for ASCII
+    // code points.
+    const WTF::String& wtfString = string;
+    if (wtfString.is8Bit() && wtfString.containsOnlyASCII()) {

[haraken, 2016/01/12 23:44:37]

Instead of implementing the conversion logic here, can we reuse
StringUTF8Adaptor
(https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

It would be better to make WebStringUTF8Adaptor a think wrapper of
StringUTF8Adaptor.

[brettw, 2016/01/13 05:40:43]

The reason I didn't do this was that I can't include StringUTF8Adaptor.h in the
header so can't have it as a member. And I definitely didn't want to
heap-allocate an adapter which would eliminate the point of this change
(avoiding heap allocations in common conversion cases).

I could make UTF8StringAdaptor expose its internal buffer via a getter, use it
in the .cpp file on the stack, and take a reference to that buffer as
m_utf8Buffer on this class.

But it seemed like exposing the internal buffer on the existing adapter violates
the entire abstraction that the adapter provides, and the code is only 4 lines
of basic string manipulation. I thought it was not worth the benefit to do this.
If you prefer the alternative, I'm fine doing that, and I'm happy to hear any
other suggestions you might have.

[haraken, 2016/01/13 05:55:38]

Just help me understand: Why can't we include wtf/StringUTF8Adaptor.h in
public/platform/? public/platform/ already includes String, Vector and a bunch
of fundamental classes in wtf/. I think StringUTF8Adaptor could be a part of
it...

+        m_stringPiece = base::StringPiece(
+            reinterpret_cast<const char*>(wtfString.characters8()),
+            wtfString.length());
+    } else {
+        m_utf8Buffer = wtfString.utf8().buffer();
+        m_stringPiece = base::StringPiece(m_utf8Buffer->data(), m_utf8Buffer->length());
+    }
+}
 
-    virtual void startSession() { }
-    virtual void open(unsigned portIndex) { }
-    // |timeStamp| is measured in milliseconds as Web MIDI spec defines.
-    virtual void sendMIDIData(unsigned portIndex, const unsigned char* data, size_t length, double timeStamp) { }
-    virtual void clear(unsigned portIndex) { }
-    virtual void close(unsigned portIndex) { }
-};
+WebStringUTF8Adaptor::~WebStringUTF8Adaptor()
+{
+    m_utf8Buffer.reset();
+}
 
 } // namespace blink
-
-#endif // WebMIDIAccessor_h