Developer Documentation

snappy-sinksource.h
1 // Copyright 2011 Google Inc. All Rights Reserved.
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28
29 #ifndef THIRD_PARTY_SNAPPY_SNAPPY_SINKSOURCE_H_
30 #define THIRD_PARTY_SNAPPY_SNAPPY_SINKSOURCE_H_
31
32 #include <stddef.h>
33
34 namespace snappy {
35
36 // A Sink is an interface that consumes a sequence of bytes.
37 class Sink {
38 public:
39 Sink() { }
40 virtual ~Sink();
41
42 // Append "bytes[0,n-1]" to this.
43 virtual void Append(const char* bytes, size_t n) = 0;
44
45 // Returns a writable buffer of the specified length for appending.
46 // May return a pointer to the caller-owned scratch buffer which
47 // must have at least the indicated length. The returned buffer is
48 // only valid until the next operation on this Sink.
49 //
50 // After writing at most "length" bytes, call Append() with the
51 // pointer returned from this function and the number of bytes
52 // written. Many Append() implementations will avoid copying
53 // bytes if this function returned an internal buffer.
54 //
55 // If a non-scratch buffer is returned, the caller may only pass a
56 // prefix of it to Append(). That is, it is not correct to pass an
57 // interior pointer of the returned array to Append().
58 //
59 // The default implementation always returns the scratch buffer.
60 virtual char* GetAppendBuffer(size_t length, char* scratch);
61
62 // For higher performance, Sink implementations can provide custom
63 // AppendAndTakeOwnership() and GetAppendBufferVariable() methods.
64 // These methods can reduce the number of copies done during
65 // compression/decompression.
66
67 // Append "bytes[0,n-1] to the sink. Takes ownership of "bytes"
68 // and calls the deleter function as (*deleter)(deleter_arg, bytes, n)
69 // to free the buffer. deleter function must be non NULL.
70 //
71 // The default implementation just calls Append and frees "bytes".
72 // Other implementations may avoid a copy while appending the buffer.
73 virtual void AppendAndTakeOwnership(
74 char* bytes, size_t n, void (*deleter)(void*, const char*, size_t),
75 void *deleter_arg);
76
77 // Returns a writable buffer for appending and writes the buffer's capacity to
78 // *allocated_size. Guarantees *allocated_size >= min_size.
79 // May return a pointer to the caller-owned scratch buffer which must have
80 // scratch_size >= min_size.
81 //
82 // The returned buffer is only valid until the next operation
83 // on this ByteSink.
84 //
85 // After writing at most *allocated_size bytes, call Append() with the
86 // pointer returned from this function and the number of bytes written.
87 // Many Append() implementations will avoid copying bytes if this function
88 // returned an internal buffer.
89 //
90 // If the sink implementation allocates or reallocates an internal buffer,
91 // it should use the desired_size_hint if appropriate. If a caller cannot
92 // provide a reasonable guess at the desired capacity, it should set
93 // desired_size_hint = 0.
94 //
95 // If a non-scratch buffer is returned, the caller may only pass
96 // a prefix to it to Append(). That is, it is not correct to pass an
97 // interior pointer to Append().
98 //
99 // The default implementation always returns the scratch buffer.
100 virtual char* GetAppendBufferVariable(
101 size_t min_size, size_t desired_size_hint, char* scratch,
102 size_t scratch_size, size_t* allocated_size);
103
104 private:
105 // No copying
106 Sink(const Sink&);
107 void operator=(const Sink&);
108 };
109
110 // A Source is an interface that yields a sequence of bytes
111 class Source {
112 public:
113 Source() { }
114 virtual ~Source();
115
116 // Return the number of bytes left to read from the source
117 virtual size_t Available() const = 0;
118
119 // Peek at the next flat region of the source. Does not reposition
120 // the source. The returned region is empty iff Available()==0.
121 //
122 // Returns a pointer to the beginning of the region and store its
123 // length in *len.
124 //
125 // The returned region is valid until the next call to Skip() or
126 // until this object is destroyed, whichever occurs first.
127 //
128 // The returned region may be larger than Available() (for example
129 // if this ByteSource is a view on a substring of a larger source).
130 // The caller is responsible for ensuring that it only reads the
131 // Available() bytes.
132 virtual const char* Peek(size_t* len) = 0;
133
134 // Skip the next n bytes. Invalidates any buffer returned by
135 // a previous call to Peek().
136 // REQUIRES: Available() >= n
137 virtual void Skip(size_t n) = 0;
138
139 private:
140 // No copying
141 Source(const Source&);
142 void operator=(const Source&);
143 };
144
145 // A Source implementation that yields the contents of a flat array
146 class ByteArraySource : public Source {
147 public:
148 ByteArraySource(const char* p, size_t n) : ptr_(p), left_(n) { }
149 virtual ~ByteArraySource();
150 virtual size_t Available() const;
151 virtual const char* Peek(size_t* len);
152 virtual void Skip(size_t n);
153 private:
154 const char* ptr_;
155 size_t left_;
156 };
157
158 // A Sink implementation that writes to a flat array without any bound checks.
159 class UncheckedByteArraySink : public Sink {
160 public:
161 explicit UncheckedByteArraySink(char* dest) : dest_(dest) { }
162 virtual ~UncheckedByteArraySink();
163 virtual void Append(const char* data, size_t n);
164 virtual char* GetAppendBuffer(size_t len, char* scratch);
165 virtual char* GetAppendBufferVariable(
166 size_t min_size, size_t desired_size_hint, char* scratch,
167 size_t scratch_size, size_t* allocated_size);
168 virtual void AppendAndTakeOwnership(
169 char* bytes, size_t n, void (*deleter)(void*, const char*, size_t),
170 void *deleter_arg);
171
172 // Return the current output pointer so that a caller can see how
173 // many bytes were produced.
174 // Note: this is not a Sink method.
175 char* CurrentDestination() const { return dest_; }
176 private:
177 char* dest_;
178 };
179
180 } // namespace snappy
181
182 #endif // THIRD_PARTY_SNAPPY_SNAPPY_SINKSOURCE_H_
snappy
Definition: snappy-internal.h:36
snappy::ByteArraySource
Definition: snappy-sinksource.h:146
snappy::UncheckedByteArraySink
Definition: snappy-sinksource.h:159
snappy::Sink
Definition: snappy-sinksource.h:37
snappy::Source
Definition: snappy-sinksource.h:111