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      1 /*
      2  * Copyright (C) 2010 Google Inc. All rights reserved.
      3  *
      4  * Redistribution and use in source and binary forms, with or without
      5  * modification, are permitted provided that the following conditions are
      6  * met:
      7  *
      8  *     * Redistributions of source code must retain the above copyright
      9  * notice, this list of conditions and the following disclaimer.
     10  *     * Redistributions in binary form must reproduce the above
     11  * copyright notice, this list of conditions and the following disclaimer
     12  * in the documentation and/or other materials provided with the
     13  * distribution.
     14  *     * Neither the name of Google Inc. nor the names of its
     15  * contributors may be used to endorse or promote products derived from
     16  * this software without specific prior written permission.
     17  *
     18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
     19  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
     20  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
     21  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
     22  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
     23  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
     24  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     26  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     27  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
     28  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     29  */
     30 
     31 #ifndef CachedMetadata_h
     32 #define CachedMetadata_h
     33 
     34 #include "wtf/Forward.h"
     35 #include "wtf/RefCounted.h"
     36 #include "wtf/Vector.h"
     37 
     38 namespace blink {
     39 
     40 // Metadata retrieved from the embedding application's cache.
     41 //
     42 // Serialized data is NOT portable across architectures. However, reading the
     43 // data type ID will reject data generated with a different byte-order.
     44 class CachedMetadata : public RefCounted<CachedMetadata> {
     45 public:
     46     static PassRefPtr<CachedMetadata> create(unsigned dataTypeID, const char* data, size_t size)
     47     {
     48         return adoptRef(new CachedMetadata(dataTypeID, data, size));
     49     }
     50 
     51     static PassRefPtr<CachedMetadata> deserialize(const char* data, size_t size)
     52     {
     53         return adoptRef(new CachedMetadata(data, size));
     54     }
     55 
     56     const Vector<char>& serialize() const
     57     {
     58         return m_serializedData;
     59     }
     60 
     61     ~CachedMetadata() { }
     62 
     63     unsigned dataTypeID() const
     64     {
     65         return readUnsigned(dataTypeIDStart);
     66     }
     67 
     68     const char* data() const
     69     {
     70         if (m_serializedData.size() < dataStart)
     71             return 0;
     72         return m_serializedData.data() + dataStart;
     73     }
     74 
     75     size_t size() const
     76     {
     77         if (m_serializedData.size() < dataStart)
     78             return 0;
     79         return m_serializedData.size() - dataStart;
     80     }
     81 
     82 private:
     83     // Reads an unsigned value at position. Returns 0 on error.
     84     unsigned readUnsigned(size_t position) const
     85     {
     86         if (m_serializedData.size() < position + sizeof(unsigned))
     87             return 0;
     88         return *reinterpret_cast_ptr<unsigned*>(const_cast<char*>(m_serializedData.data() + position));
     89     }
     90 
     91     // Appends an unsigned value to the end of the serialized data.
     92     void appendUnsigned(unsigned value)
     93     {
     94         m_serializedData.append(reinterpret_cast<const char*>(&value), sizeof(unsigned));
     95     }
     96 
     97     CachedMetadata(const char* data, size_t size)
     98     {
     99         // Serialized metadata should have non-empty data.
    100         ASSERT(size > dataStart);
    101 
    102         m_serializedData.append(data, size);
    103     }
    104 
    105     CachedMetadata(unsigned dataTypeID, const char* data, size_t size)
    106     {
    107         // Don't allow an ID of 0, it is used internally to indicate errors.
    108         ASSERT(dataTypeID);
    109         ASSERT(data);
    110 
    111         appendUnsigned(dataTypeID);
    112         m_serializedData.append(data, size);
    113     }
    114 
    115     // Serialization offsets. Format: [DATA_TYPE_ID][DATA].
    116     static const size_t dataTypeIDStart = 0;
    117     static const size_t dataStart = sizeof(unsigned);
    118 
    119     // Since the serialization format supports random access, storing it in
    120     // serialized form avoids need for a copy during serialization.
    121     Vector<char> m_serializedData;
    122 };
    123 
    124 }
    125 
    126 #endif
    127