TrinityCore
zero_copy_stream.h
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1 // Protocol Buffers - Google's data interchange format
2 // Copyright 2008 Google Inc. All rights reserved.
3 // https://developers.google.com/protocol-buffers/
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6 // modification, are permitted provided that the following conditions are
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8 //
9 // * Redistributions of source code must retain the above copyright
10 // notice, this list of conditions and the following disclaimer.
11 // * Redistributions in binary form must reproduce the above
12 // copyright notice, this list of conditions and the following disclaimer
13 // in the documentation and/or other materials provided with the
14 // distribution.
15 // * Neither the name of Google Inc. nor the names of its
16 // contributors may be used to endorse or promote products derived from
17 // this software without specific prior written permission.
18 //
19 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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22 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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25 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
26 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
27 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
28 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
29 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30 
31 // Author: [email protected] (Kenton Varda)
32 // Based on original Protocol Buffers design by
33 // Sanjay Ghemawat, Jeff Dean, and others.
34 //
35 // This file contains the ZeroCopyInputStream and ZeroCopyOutputStream
36 // interfaces, which represent abstract I/O streams to and from which
37 // protocol buffers can be read and written. For a few simple
38 // implementations of these interfaces, see zero_copy_stream_impl.h.
39 //
40 // These interfaces are different from classic I/O streams in that they
41 // try to minimize the amount of data copying that needs to be done.
42 // To accomplish this, responsibility for allocating buffers is moved to
43 // the stream object, rather than being the responsibility of the caller.
44 // So, the stream can return a buffer which actually points directly into
45 // the final data structure where the bytes are to be stored, and the caller
46 // can interact directly with that buffer, eliminating an intermediate copy
47 // operation.
48 //
49 // As an example, consider the common case in which you are reading bytes
50 // from an array that is already in memory (or perhaps an mmap()ed file).
51 // With classic I/O streams, you would do something like:
52 // char buffer[BUFFER_SIZE];
53 // input->Read(buffer, BUFFER_SIZE);
54 // DoSomething(buffer, BUFFER_SIZE);
55 // Then, the stream basically just calls memcpy() to copy the data from
56 // the array into your buffer. With a ZeroCopyInputStream, you would do
57 // this instead:
58 // const void* buffer;
59 // int size;
60 // input->Next(&buffer, &size);
61 // DoSomething(buffer, size);
62 // Here, no copy is performed. The input stream returns a pointer directly
63 // into the backing array, and the caller ends up reading directly from it.
64 //
65 // If you want to be able to read the old-fashion way, you can create
66 // a CodedInputStream or CodedOutputStream wrapping these objects and use
67 // their ReadRaw()/WriteRaw() methods. These will, of course, add a copy
68 // step, but Coded*Stream will handle buffering so at least it will be
69 // reasonably efficient.
70 //
71 // ZeroCopyInputStream example:
72 // // Read in a file and print its contents to stdout.
73 // int fd = open("myfile", O_RDONLY);
74 // ZeroCopyInputStream* input = new FileInputStream(fd);
75 //
76 // const void* buffer;
77 // int size;
78 // while (input->Next(&buffer, &size)) {
79 // cout.write(buffer, size);
80 // }
81 //
82 // delete input;
83 // close(fd);
84 //
85 // ZeroCopyOutputStream example:
86 // // Copy the contents of "infile" to "outfile", using plain read() for
87 // // "infile" but a ZeroCopyOutputStream for "outfile".
88 // int infd = open("infile", O_RDONLY);
89 // int outfd = open("outfile", O_WRONLY);
90 // ZeroCopyOutputStream* output = new FileOutputStream(outfd);
91 //
92 // void* buffer;
93 // int size;
94 // while (output->Next(&buffer, &size)) {
95 // int bytes = read(infd, buffer, size);
96 // if (bytes < size) {
97 // // Reached EOF.
98 // output->BackUp(size - bytes);
99 // break;
100 // }
101 // }
102 //
103 // delete output;
104 // close(infd);
105 // close(outfd);
106 
107 #ifndef GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_H__
108 #define GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_H__
109 
110 #include <string>
112 
113 namespace google {
114 
115 namespace protobuf {
116 namespace io {
117 
118 // Defined in this file.
119 class ZeroCopyInputStream;
120 class ZeroCopyOutputStream;
121 
122 // Abstract interface similar to an input stream but designed to minimize
123 // copying.
125  public:
127  virtual ~ZeroCopyInputStream();
128 
129  // Obtains a chunk of data from the stream.
130  //
131  // Preconditions:
132  // * "size" and "data" are not NULL.
133  //
134  // Postconditions:
135  // * If the returned value is false, there is no more data to return or
136  // an error occurred. All errors are permanent.
137  // * Otherwise, "size" points to the actual number of bytes read and "data"
138  // points to a pointer to a buffer containing these bytes.
139  // * Ownership of this buffer remains with the stream, and the buffer
140  // remains valid only until some other method of the stream is called
141  // or the stream is destroyed.
142  // * It is legal for the returned buffer to have zero size, as long
143  // as repeatedly calling Next() eventually yields a buffer with non-zero
144  // size.
145  virtual bool Next(const void** data, int* size) = 0;
146 
147  // Backs up a number of bytes, so that the next call to Next() returns
148  // data again that was already returned by the last call to Next(). This
149  // is useful when writing procedures that are only supposed to read up
150  // to a certain point in the input, then return. If Next() returns a
151  // buffer that goes beyond what you wanted to read, you can use BackUp()
152  // to return to the point where you intended to finish.
153  //
154  // Preconditions:
155  // * The last method called must have been Next().
156  // * count must be less than or equal to the size of the last buffer
157  // returned by Next().
158  //
159  // Postconditions:
160  // * The last "count" bytes of the last buffer returned by Next() will be
161  // pushed back into the stream. Subsequent calls to Next() will return
162  // the same data again before producing new data.
163  virtual void BackUp(int count) = 0;
164 
165  // Skips a number of bytes. Returns false if the end of the stream is
166  // reached or some input error occurred. In the end-of-stream case, the
167  // stream is advanced to the end of the stream (so ByteCount() will return
168  // the total size of the stream).
169  virtual bool Skip(int count) = 0;
170 
171  // Returns the total number of bytes read since this object was created.
172  virtual int64 ByteCount() const = 0;
173 
174 
175  private:
177 };
178 
179 // Abstract interface similar to an output stream but designed to minimize
180 // copying.
182  public:
184  virtual ~ZeroCopyOutputStream();
185 
186  // Obtains a buffer into which data can be written. Any data written
187  // into this buffer will eventually (maybe instantly, maybe later on)
188  // be written to the output.
189  //
190  // Preconditions:
191  // * "size" and "data" are not NULL.
192  //
193  // Postconditions:
194  // * If the returned value is false, an error occurred. All errors are
195  // permanent.
196  // * Otherwise, "size" points to the actual number of bytes in the buffer
197  // and "data" points to the buffer.
198  // * Ownership of this buffer remains with the stream, and the buffer
199  // remains valid only until some other method of the stream is called
200  // or the stream is destroyed.
201  // * Any data which the caller stores in this buffer will eventually be
202  // written to the output (unless BackUp() is called).
203  // * It is legal for the returned buffer to have zero size, as long
204  // as repeatedly calling Next() eventually yields a buffer with non-zero
205  // size.
206  virtual bool Next(void** data, int* size) = 0;
207 
208  // Backs up a number of bytes, so that the end of the last buffer returned
209  // by Next() is not actually written. This is needed when you finish
210  // writing all the data you want to write, but the last buffer was bigger
211  // than you needed. You don't want to write a bunch of garbage after the
212  // end of your data, so you use BackUp() to back up.
213  //
214  // Preconditions:
215  // * The last method called must have been Next().
216  // * count must be less than or equal to the size of the last buffer
217  // returned by Next().
218  // * The caller must not have written anything to the last "count" bytes
219  // of that buffer.
220  //
221  // Postconditions:
222  // * The last "count" bytes of the last buffer returned by Next() will be
223  // ignored.
224  virtual void BackUp(int count) = 0;
225 
226  // Returns the total number of bytes written since this object was created.
227  virtual int64 ByteCount() const = 0;
228 
229  // Write a given chunk of data to the output. Some output streams may
230  // implement this in a way that avoids copying. Check AllowsAliasing() before
231  // calling WriteAliasedRaw(). It will GOOGLE_CHECK fail if WriteAliasedRaw() is
232  // called on a stream that does not allow aliasing.
233  //
234  // NOTE: It is caller's responsibility to ensure that the chunk of memory
235  // remains live until all of the data has been consumed from the stream.
236  virtual bool WriteAliasedRaw(const void* data, int size);
237  virtual bool AllowsAliasing() const { return false; }
238 
239 
240  private:
242 };
243 
244 } // namespace io
245 } // namespace protobuf
246 
247 } // namespace google
248 #endif // GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_H__
Definition: zero_copy_stream.h:124
constexpr auto data(C &c)
Definition: advstd.h:96
#define GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(TypeName)
Definition: common.h:89
ZeroCopyInputStream()
Definition: zero_copy_stream.h:126
constexpr auto size(const C &c)
Definition: advstd.h:89
virtual bool AllowsAliasing() const
Definition: zero_copy_stream.h:237
Definition: zero_copy_stream.h:181
#define LIBPROTOBUF_EXPORT
Definition: common.h:105
int64_t int64
Definition: common.h:173
ZeroCopyOutputStream()
Definition: zero_copy_stream.h:183
Definition: BnetFileGenerator.h:47