1// Protocol Buffers - Google's data interchange format
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3// https://developers.google.com/protocol-buffers/
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18//
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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
60namespace google {
61namespace protobuf {
62namespace io {
63
64// ===================================================================
65
66// A ZeroCopyInputStream backed by an in-memory array of bytes.
67class 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.
101class 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.
133class 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.
177class PROTOBUF_EXPORT CopyingInputStream {
178 public:
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.
203class 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.
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.
271class PROTOBUF_EXPORT CopyingOutputStream {
272 public:
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.
287class 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.
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.
347class 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().
385inline 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.
395inline std::pair<char*, bool> as_string_data(std::string* s) {
396 char* p = mutable_string_data(s);
397 return std::make_pair(x&: p, y: 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

source code of include/google/protobuf/io/zero_copy_stream_impl_lite.h