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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/
4 //
5 // Redistribution and use in source and binary forms, with or without
6 // modification, are permitted provided that the following conditions are
7 // met:
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
21 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
22 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
23 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
24 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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: kenton@google.com (Kenton Varda)
32 //  Based on original Protocol Buffers design by
33 //  Sanjay Ghemawat, Jeff Dean, and others.
34 //
35 // This file contains common implementations of the interfaces defined in
36 // zero_copy_stream.h which are included in the "lite" protobuf library.
37 // These implementations cover I/O on raw arrays and strings, as well as
38 // adaptors which make it easy to implement streams based on traditional
39 // streams.  Of course, many users will probably want to write their own
40 // implementations of these interfaces specific to the particular I/O
41 // abstractions they prefer to use, but these should cover the most common
42 // cases.
43 
44 #ifndef GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_IMPL_LITE_H__
45 #define GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_IMPL_LITE_H__
46 
47 
48 #include <iosfwd>
49 #include <memory>
50 #include <string>
51 
52 #include <google/protobuf/stubs/callback.h>
53 #include <google/protobuf/stubs/common.h>
54 #include <google/protobuf/io/zero_copy_stream.h>
55 #include <google/protobuf/stubs/stl_util.h>
56 
57 
58 #include <google/protobuf/port_def.inc>
59 
60 namespace google {
61 namespace protobuf {
62 namespace io {
63 
64 // ===================================================================
65 
66 // A ZeroCopyInputStream backed by an in-memory array of bytes.
67 class PROTOBUF_EXPORT ArrayInputStream : public ZeroCopyInputStream {
68  public:
69   // Create an InputStream that returns the bytes pointed to by "data".
70   // "data" remains the property of the caller but must remain valid until
71   // the stream is destroyed.  If a block_size is given, calls to Next()
72   // will return data blocks no larger than the given size.  Otherwise, the
73   // first call to Next() returns the entire array.  block_size is mainly
74   // useful for testing; in production you would probably never want to set
75   // it.
76   ArrayInputStream(const void* data, int size, int block_size = -1);
77   ~ArrayInputStream() override = default;
78 
79   // implements ZeroCopyInputStream ----------------------------------
80   bool Next(const void** data, int* size) override;
81   void BackUp(int count) override;
82   bool Skip(int count) override;
83   int64_t ByteCount() const override;
84 
85 
86  private:
87   const uint8* const data_;  // The byte array.
88   const int size_;           // Total size of the array.
89   const int block_size_;     // How many bytes to return at a time.
90 
91   int position_;
92   int last_returned_size_;  // How many bytes we returned last time Next()
93                             // was called (used for error checking only).
94 
95   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ArrayInputStream);
96 };
97 
98 // ===================================================================
99 
100 // A ZeroCopyOutputStream backed by an in-memory array of bytes.
101 class PROTOBUF_EXPORT ArrayOutputStream : public ZeroCopyOutputStream {
102  public:
103   // Create an OutputStream that writes to the bytes pointed to by "data".
104   // "data" remains the property of the caller but must remain valid until
105   // the stream is destroyed.  If a block_size is given, calls to Next()
106   // will return data blocks no larger than the given size.  Otherwise, the
107   // first call to Next() returns the entire array.  block_size is mainly
108   // useful for testing; in production you would probably never want to set
109   // it.
110   ArrayOutputStream(void* data, int size, int block_size = -1);
111   ~ArrayOutputStream() override = default;
112 
113   // implements ZeroCopyOutputStream ---------------------------------
114   bool Next(void** data, int* size) override;
115   void BackUp(int count) override;
116   int64_t ByteCount() const override;
117 
118  private:
119   uint8* const data_;     // The byte array.
120   const int size_;        // Total size of the array.
121   const int block_size_;  // How many bytes to return at a time.
122 
123   int position_;
124   int last_returned_size_;  // How many bytes we returned last time Next()
125                             // was called (used for error checking only).
126 
127   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ArrayOutputStream);
128 };
129 
130 // ===================================================================
131 
132 // A ZeroCopyOutputStream which appends bytes to a string.
133 class PROTOBUF_EXPORT StringOutputStream : public ZeroCopyOutputStream {
134  public:
135   // Create a StringOutputStream which appends bytes to the given string.
136   // The string remains property of the caller, but it is mutated in arbitrary
137   // ways and MUST NOT be accessed in any way until you're done with the
138   // stream. Either be sure there's no further usage, or (safest) destroy the
139   // stream before using the contents.
140   //
141   // Hint:  If you call target->reserve(n) before creating the stream,
142   //   the first call to Next() will return at least n bytes of buffer
143   //   space.
144   explicit StringOutputStream(std::string* target);
145   ~StringOutputStream() override = default;
146 
147   // implements ZeroCopyOutputStream ---------------------------------
148   bool Next(void** data, int* size) override;
149   void BackUp(int count) override;
150   int64_t ByteCount() const override;
151 
152  private:
153   static const int kMinimumSize = 16;
154 
155   std::string* target_;
156 
157   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StringOutputStream);
158 };
159 
160 // Note:  There is no StringInputStream.  Instead, just create an
161 // ArrayInputStream as follows:
162 //   ArrayInputStream input(str.data(), str.size());
163 
164 // ===================================================================
165 
166 // A generic traditional input stream interface.
167 //
168 // Lots of traditional input streams (e.g. file descriptors, C stdio
169 // streams, and C++ iostreams) expose an interface where every read
170 // involves copying bytes into a buffer.  If you want to take such an
171 // interface and make a ZeroCopyInputStream based on it, simply implement
172 // CopyingInputStream and then use CopyingInputStreamAdaptor.
173 //
174 // CopyingInputStream implementations should avoid buffering if possible.
175 // CopyingInputStreamAdaptor does its own buffering and will read data
176 // in large blocks.
177 class PROTOBUF_EXPORT CopyingInputStream {
178  public:
~CopyingInputStream()179   virtual ~CopyingInputStream() {}
180 
181   // Reads up to "size" bytes into the given buffer.  Returns the number of
182   // bytes read.  Read() waits until at least one byte is available, or
183   // returns zero if no bytes will ever become available (EOF), or -1 if a
184   // permanent read error occurred.
185   virtual int Read(void* buffer, int size) = 0;
186 
187   // Skips the next "count" bytes of input.  Returns the number of bytes
188   // actually skipped.  This will always be exactly equal to "count" unless
189   // EOF was reached or a permanent read error occurred.
190   //
191   // The default implementation just repeatedly calls Read() into a scratch
192   // buffer.
193   virtual int Skip(int count);
194 };
195 
196 // A ZeroCopyInputStream which reads from a CopyingInputStream.  This is
197 // useful for implementing ZeroCopyInputStreams that read from traditional
198 // streams.  Note that this class is not really zero-copy.
199 //
200 // If you want to read from file descriptors or C++ istreams, this is
201 // already implemented for you:  use FileInputStream or IstreamInputStream
202 // respectively.
203 class PROTOBUF_EXPORT CopyingInputStreamAdaptor : public ZeroCopyInputStream {
204  public:
205   // Creates a stream that reads from the given CopyingInputStream.
206   // If a block_size is given, it specifies the number of bytes that
207   // should be read and returned with each call to Next().  Otherwise,
208   // a reasonable default is used.  The caller retains ownership of
209   // copying_stream unless SetOwnsCopyingStream(true) is called.
210   explicit CopyingInputStreamAdaptor(CopyingInputStream* copying_stream,
211                                      int block_size = -1);
212   ~CopyingInputStreamAdaptor() override;
213 
214   // Call SetOwnsCopyingStream(true) to tell the CopyingInputStreamAdaptor to
215   // delete the underlying CopyingInputStream when it is destroyed.
SetOwnsCopyingStream(bool value)216   void SetOwnsCopyingStream(bool value) { owns_copying_stream_ = value; }
217 
218   // implements ZeroCopyInputStream ----------------------------------
219   bool Next(const void** data, int* size) override;
220   void BackUp(int count) override;
221   bool Skip(int count) override;
222   int64_t ByteCount() const override;
223 
224  private:
225   // Insures that buffer_ is not NULL.
226   void AllocateBufferIfNeeded();
227   // Frees the buffer and resets buffer_used_.
228   void FreeBuffer();
229 
230   // The underlying copying stream.
231   CopyingInputStream* copying_stream_;
232   bool owns_copying_stream_;
233 
234   // True if we have seen a permanent error from the underlying stream.
235   bool failed_;
236 
237   // The current position of copying_stream_, relative to the point where
238   // we started reading.
239   int64 position_;
240 
241   // Data is read into this buffer.  It may be NULL if no buffer is currently
242   // in use.  Otherwise, it points to an array of size buffer_size_.
243   std::unique_ptr<uint8[]> buffer_;
244   const int buffer_size_;
245 
246   // Number of valid bytes currently in the buffer (i.e. the size last
247   // returned by Next()).  0 <= buffer_used_ <= buffer_size_.
248   int buffer_used_;
249 
250   // Number of bytes in the buffer which were backed up over by a call to
251   // BackUp().  These need to be returned again.
252   // 0 <= backup_bytes_ <= buffer_used_
253   int backup_bytes_;
254 
255   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(CopyingInputStreamAdaptor);
256 };
257 
258 // ===================================================================
259 
260 // A generic traditional output stream interface.
261 //
262 // Lots of traditional output streams (e.g. file descriptors, C stdio
263 // streams, and C++ iostreams) expose an interface where every write
264 // involves copying bytes from a buffer.  If you want to take such an
265 // interface and make a ZeroCopyOutputStream based on it, simply implement
266 // CopyingOutputStream and then use CopyingOutputStreamAdaptor.
267 //
268 // CopyingOutputStream implementations should avoid buffering if possible.
269 // CopyingOutputStreamAdaptor does its own buffering and will write data
270 // in large blocks.
271 class PROTOBUF_EXPORT CopyingOutputStream {
272  public:
~CopyingOutputStream()273   virtual ~CopyingOutputStream() {}
274 
275   // Writes "size" bytes from the given buffer to the output.  Returns true
276   // if successful, false on a write error.
277   virtual bool Write(const void* buffer, int size) = 0;
278 };
279 
280 // A ZeroCopyOutputStream which writes to a CopyingOutputStream.  This is
281 // useful for implementing ZeroCopyOutputStreams that write to traditional
282 // streams.  Note that this class is not really zero-copy.
283 //
284 // If you want to write to file descriptors or C++ ostreams, this is
285 // already implemented for you:  use FileOutputStream or OstreamOutputStream
286 // respectively.
287 class PROTOBUF_EXPORT CopyingOutputStreamAdaptor : public ZeroCopyOutputStream {
288  public:
289   // Creates a stream that writes to the given Unix file descriptor.
290   // If a block_size is given, it specifies the size of the buffers
291   // that should be returned by Next().  Otherwise, a reasonable default
292   // is used.
293   explicit CopyingOutputStreamAdaptor(CopyingOutputStream* copying_stream,
294                                       int block_size = -1);
295   ~CopyingOutputStreamAdaptor() override;
296 
297   // Writes all pending data to the underlying stream.  Returns false if a
298   // write error occurred on the underlying stream.  (The underlying
299   // stream itself is not necessarily flushed.)
300   bool Flush();
301 
302   // Call SetOwnsCopyingStream(true) to tell the CopyingOutputStreamAdaptor to
303   // delete the underlying CopyingOutputStream when it is destroyed.
SetOwnsCopyingStream(bool value)304   void SetOwnsCopyingStream(bool value) { owns_copying_stream_ = value; }
305 
306   // implements ZeroCopyOutputStream ---------------------------------
307   bool Next(void** data, int* size) override;
308   void BackUp(int count) override;
309   int64_t ByteCount() const override;
310 
311  private:
312   // Write the current buffer, if it is present.
313   bool WriteBuffer();
314   // Insures that buffer_ is not NULL.
315   void AllocateBufferIfNeeded();
316   // Frees the buffer.
317   void FreeBuffer();
318 
319   // The underlying copying stream.
320   CopyingOutputStream* copying_stream_;
321   bool owns_copying_stream_;
322 
323   // True if we have seen a permanent error from the underlying stream.
324   bool failed_;
325 
326   // The current position of copying_stream_, relative to the point where
327   // we started writing.
328   int64 position_;
329 
330   // Data is written from this buffer.  It may be NULL if no buffer is
331   // currently in use.  Otherwise, it points to an array of size buffer_size_.
332   std::unique_ptr<uint8[]> buffer_;
333   const int buffer_size_;
334 
335   // Number of valid bytes currently in the buffer (i.e. the size last
336   // returned by Next()).  When BackUp() is called, we just reduce this.
337   // 0 <= buffer_used_ <= buffer_size_.
338   int buffer_used_;
339 
340   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(CopyingOutputStreamAdaptor);
341 };
342 
343 // ===================================================================
344 
345 // A ZeroCopyInputStream which wraps some other stream and limits it to
346 // a particular byte count.
347 class PROTOBUF_EXPORT LimitingInputStream : public ZeroCopyInputStream {
348  public:
349   LimitingInputStream(ZeroCopyInputStream* input, int64 limit);
350   ~LimitingInputStream() override;
351 
352   // implements ZeroCopyInputStream ----------------------------------
353   bool Next(const void** data, int* size) override;
354   void BackUp(int count) override;
355   bool Skip(int count) override;
356   int64_t ByteCount() const override;
357 
358 
359  private:
360   ZeroCopyInputStream* input_;
361   int64 limit_;  // Decreases as we go, becomes negative if we overshoot.
362   int64 prior_bytes_read_;  // Bytes read on underlying stream at construction
363 
364   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(LimitingInputStream);
365 };
366 
367 
368 // ===================================================================
369 
370 // mutable_string_data() and as_string_data() are workarounds to improve
371 // the performance of writing new data to an existing string.  Unfortunately
372 // the methods provided by the string class are suboptimal, and using memcpy()
373 // is mildly annoying because it requires its pointer args to be non-NULL even
374 // if we ask it to copy 0 bytes.  Furthermore, string_as_array() has the
375 // property that it always returns NULL if its arg is the empty string, exactly
376 // what we want to avoid if we're using it in conjunction with memcpy()!
377 // With C++11, the desired memcpy() boils down to memcpy(..., &(*s)[0], size),
378 // where s is a string*.  Without C++11, &(*s)[0] is not guaranteed to be safe,
379 // so we use string_as_array(), and live with the extra logic that tests whether
380 // *s is empty.
381 
382 // Return a pointer to mutable characters underlying the given string.  The
383 // return value is valid until the next time the string is resized.  We
384 // trust the caller to treat the return value as an array of length s->size().
mutable_string_data(std::string * s)385 inline char* mutable_string_data(std::string* s) {
386   // This should be simpler & faster than string_as_array() because the latter
387   // is guaranteed to return NULL when *s is empty, so it has to check for that.
388   return &(*s)[0];
389 }
390 
391 // as_string_data(s) is equivalent to
392 //  ({ char* p = mutable_string_data(s); make_pair(p, p != NULL); })
393 // Sometimes it's faster: in some scenarios p cannot be NULL, and then the
394 // code can avoid that check.
as_string_data(std::string * s)395 inline std::pair<char*, bool> as_string_data(std::string* s) {
396   char* p = mutable_string_data(s);
397   return std::make_pair(p, true);
398 }
399 
400 }  // namespace io
401 }  // namespace protobuf
402 }  // namespace google
403 
404 #include <google/protobuf/port_undef.inc>
405 
406 #endif  // GOOGLE_PROTOBUF_IO_ZERO_COPY_STREAM_IMPL_LITE_H__
407