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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/RefCounted.h>
     35 #include <wtf/Vector.h>
     36 
     37 namespace WebCore {
     38 
     39 // Metadata retrieved from the embedding application's cache.
     40 //
     41 // Serialized data is NOT portable across architectures. However, reading the
     42 // data type ID will reject data generated with a different byte-order.
     43 class CachedMetadata : public RefCounted<CachedMetadata> {
     44 public:
     45     static PassRefPtr<CachedMetadata> create(unsigned dataTypeID, const char* data, size_t size)
     46     {
     47         return adoptRef(new CachedMetadata(dataTypeID, data, size));
     48     }
     49 
     50     static PassRefPtr<CachedMetadata> deserialize(const char* data, size_t size)
     51     {
     52         return adoptRef(new CachedMetadata(data, size));
     53     }
     54 
     55     const Vector<char>& serialize() const
     56     {
     57         return m_serializedData;
     58     }
     59 
     60     ~CachedMetadata() { }
     61 
     62     unsigned dataTypeID() const
     63     {
     64         return readUnsigned(dataTypeIDStart);
     65     }
     66 
     67     const char* data() const
     68     {
     69         if (m_serializedData.size() < dataStart)
     70             return 0;
     71         return m_serializedData.data() + dataStart;
     72     }
     73 
     74     size_t size() const
     75     {
     76         if (m_serializedData.size() < dataStart)
     77             return 0;
     78         return m_serializedData.size() - dataStart;
     79     }
     80 
     81 private:
     82     // Reads an unsigned value at position. Returns 0 on error.
     83     unsigned readUnsigned(size_t position) const
     84     {
     85         if (m_serializedData.size() < position + sizeof(unsigned))
     86             return 0;
     87         return *reinterpret_cast_ptr<unsigned*>(const_cast<char*>(m_serializedData.data() + position));
     88     }
     89 
     90     // Appends an unsigned value to the end of the serialized data.
     91     void appendUnsigned(unsigned value)
     92     {
     93         m_serializedData.append(reinterpret_cast<const char*>(&value), sizeof(unsigned));
     94     }
     95 
     96     CachedMetadata(const char* data, size_t size)
     97     {
     98         // Serialized metadata should have non-empty data.
     99         ASSERT(size > dataStart);
    100 
    101         m_serializedData.append(data, size);
    102     }
    103 
    104     CachedMetadata(unsigned dataTypeID, const char* data, size_t size)
    105     {
    106         // Don't allow an ID of 0, it is used internally to indicate errors.
    107         ASSERT(dataTypeID);
    108         ASSERT(data);
    109 
    110         appendUnsigned(dataTypeID);
    111         m_serializedData.append(data, size);
    112     }
    113 
    114     // Serialization offsets. Format: [DATA_TYPE_ID][DATA].
    115     static const size_t dataTypeIDStart = 0;
    116     static const size_t dataStart = sizeof(unsigned);
    117 
    118     // Since the serialization format supports random access, storing it in
    119     // serialized form avoids need for a copy during serialization.
    120     Vector<char> m_serializedData;
    121 };
    122 
    123 }
    124 
    125 #endif
    126