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,
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24  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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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:
create(unsigned dataTypeID,const char * data,size_t size)45     static PassRefPtr<CachedMetadata> create(unsigned dataTypeID, const char* data, size_t size)
46     {
47         return adoptRef(new CachedMetadata(dataTypeID, data, size));
48     }
49 
deserialize(const char * data,size_t size)50     static PassRefPtr<CachedMetadata> deserialize(const char* data, size_t size)
51     {
52         return adoptRef(new CachedMetadata(data, size));
53     }
54 
serialize()55     const Vector<char>& serialize() const
56     {
57         return m_serializedData;
58     }
59 
~CachedMetadata()60     ~CachedMetadata() { }
61 
dataTypeID()62     unsigned dataTypeID() const
63     {
64         return readUnsigned(dataTypeIDStart);
65     }
66 
data()67     const char* data() const
68     {
69         if (m_serializedData.size() < dataStart)
70             return 0;
71         return m_serializedData.data() + dataStart;
72     }
73 
size()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.
readUnsigned(size_t position)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.
appendUnsigned(unsigned value)91     void appendUnsigned(unsigned value)
92     {
93         m_serializedData.append(reinterpret_cast<const char*>(&value), sizeof(unsigned));
94     }
95 
CachedMetadata(const char * data,size_t size)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 
CachedMetadata(unsigned dataTypeID,const char * data,size_t size)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