1// Copyright (C) 2009-2012, International Business Machines
2// Corporation and others. All Rights Reserved.
3//
4// Copyright 2007 Google Inc. All Rights Reserved.
5// Author: sanjay@google.com (Sanjay Ghemawat)
6//
7// Abstract interface that consumes a sequence of bytes (ByteSink).
8//
9// Used so that we can write a single piece of code that can operate
10// on a variety of output string types.
11//
12// Various implementations of this interface are provided:
13//   ByteSink:
14//      CheckedArrayByteSink    Write to a flat array, with bounds checking
15//      StringByteSink          Write to an STL string
16
17// This code is a contribution of Google code, and the style used here is
18// a compromise between the original Google code and the ICU coding guidelines.
19// For example, data types are ICU-ified (size_t,int->int32_t),
20// and API comments doxygen-ified, but function names and behavior are
21// as in the original, if possible.
22// Assertion-style error handling, not available in ICU, was changed to
23// parameter "pinning" similar to UnicodeString.
24//
25// In addition, this is only a partial port of the original Google code,
26// limited to what was needed so far. The (nearly) complete original code
27// is in the ICU svn repository at icuhtml/trunk/design/strings/contrib
28// (see ICU ticket 6765, r25517).
29
30#ifndef __BYTESTREAM_H__
31#define __BYTESTREAM_H__
32
33/**
34 * \file
35 * \brief C++ API: Interface for writing bytes, and implementation classes.
36 */
37
38#include "unicode/utypes.h"
39#include "unicode/uobject.h"
40#include "unicode/std_string.h"
41
42U_NAMESPACE_BEGIN
43
44/**
45 * A ByteSink can be filled with bytes.
46 * @stable ICU 4.2
47 */
48class U_COMMON_API ByteSink : public UMemory {
49public:
50  /**
51   * Default constructor.
52   * @stable ICU 4.2
53   */
54  ByteSink() { }
55  /**
56   * Virtual destructor.
57   * @stable ICU 4.2
58   */
59  virtual ~ByteSink();
60
61  /**
62   * Append "bytes[0,n-1]" to this.
63   * @param bytes the pointer to the bytes
64   * @param n the number of bytes; must be non-negative
65   * @stable ICU 4.2
66   */
67  virtual void Append(const char* bytes, int32_t n) = 0;
68
69  /**
70   * Returns a writable buffer for appending and writes the buffer's capacity to
71   * *result_capacity. Guarantees *result_capacity>=min_capacity.
72   * May return a pointer to the caller-owned scratch buffer which must have
73   * scratch_capacity>=min_capacity.
74   * The returned buffer is only valid until the next operation
75   * on this ByteSink.
76   *
77   * After writing at most *result_capacity bytes, call Append() with the
78   * pointer returned from this function and the number of bytes written.
79   * Many Append() implementations will avoid copying bytes if this function
80   * returned an internal buffer.
81   *
82   * Partial usage example:
83   *  int32_t capacity;
84   *  char* buffer = sink->GetAppendBuffer(..., &capacity);
85   *  ... Write n bytes into buffer, with n <= capacity.
86   *  sink->Append(buffer, n);
87   * In many implementations, that call to Append will avoid copying bytes.
88   *
89   * If the ByteSink allocates or reallocates an internal buffer, it should use
90   * the desired_capacity_hint if appropriate.
91   * If a caller cannot provide a reasonable guess at the desired capacity,
92   * it should pass desired_capacity_hint=0.
93   *
94   * If a non-scratch buffer is returned, the caller may only pass
95   * a prefix to it to Append().
96   * That is, it is not correct to pass an interior pointer to Append().
97   *
98   * The default implementation always returns the scratch buffer.
99   *
100   * @param min_capacity required minimum capacity of the returned buffer;
101   *                     must be non-negative
102   * @param desired_capacity_hint desired capacity of the returned buffer;
103   *                              must be non-negative
104   * @param scratch default caller-owned buffer
105   * @param scratch_capacity capacity of the scratch buffer
106   * @param result_capacity pointer to an integer which will be set to the
107   *                        capacity of the returned buffer
108   * @return a buffer with *result_capacity>=min_capacity
109   * @stable ICU 4.2
110   */
111  virtual char* GetAppendBuffer(int32_t min_capacity,
112                                int32_t desired_capacity_hint,
113                                char* scratch, int32_t scratch_capacity,
114                                int32_t* result_capacity);
115
116  /**
117   * Flush internal buffers.
118   * Some byte sinks use internal buffers or provide buffering
119   * and require calling Flush() at the end of the stream.
120   * The ByteSink should be ready for further Append() calls after Flush().
121   * The default implementation of Flush() does nothing.
122   * @stable ICU 4.2
123   */
124  virtual void Flush();
125
126private:
127  ByteSink(const ByteSink &); // copy constructor not implemented
128  ByteSink &operator=(const ByteSink &); // assignment operator not implemented
129};
130
131// -------------------------------------------------------------
132// Some standard implementations
133
134/**
135 * Implementation of ByteSink that writes to a flat byte array,
136 * with bounds-checking:
137 * This sink will not write more than capacity bytes to outbuf.
138 * If more than capacity bytes are Append()ed, then excess bytes are ignored,
139 * and Overflowed() will return true.
140 * Overflow does not cause a runtime error.
141 * @stable ICU 4.2
142 */
143class U_COMMON_API CheckedArrayByteSink : public ByteSink {
144public:
145  /**
146   * Constructs a ByteSink that will write to outbuf[0..capacity-1].
147   * @param outbuf buffer to write to
148   * @param capacity size of the buffer
149   * @stable ICU 4.2
150   */
151  CheckedArrayByteSink(char* outbuf, int32_t capacity);
152  /**
153   * Destructor.
154   * @stable ICU 4.2
155   */
156  virtual ~CheckedArrayByteSink();
157  /**
158   * Returns the sink to its original state, without modifying the buffer.
159   * Useful for reusing both the buffer and the sink for multiple streams.
160   * Resets the state to NumberOfBytesWritten()=NumberOfBytesAppended()=0
161   * and Overflowed()=FALSE.
162   * @return *this
163   * @stable ICU 4.6
164   */
165  virtual CheckedArrayByteSink& Reset();
166  /**
167   * Append "bytes[0,n-1]" to this.
168   * @param bytes the pointer to the bytes
169   * @param n the number of bytes; must be non-negative
170   * @stable ICU 4.2
171   */
172  virtual void Append(const char* bytes, int32_t n);
173  /**
174   * Returns a writable buffer for appending and writes the buffer's capacity to
175   * *result_capacity. For details see the base class documentation.
176   * @param min_capacity required minimum capacity of the returned buffer;
177   *                     must be non-negative
178   * @param desired_capacity_hint desired capacity of the returned buffer;
179   *                              must be non-negative
180   * @param scratch default caller-owned buffer
181   * @param scratch_capacity capacity of the scratch buffer
182   * @param result_capacity pointer to an integer which will be set to the
183   *                        capacity of the returned buffer
184   * @return a buffer with *result_capacity>=min_capacity
185   * @stable ICU 4.2
186   */
187  virtual char* GetAppendBuffer(int32_t min_capacity,
188                                int32_t desired_capacity_hint,
189                                char* scratch, int32_t scratch_capacity,
190                                int32_t* result_capacity);
191  /**
192   * Returns the number of bytes actually written to the sink.
193   * @return number of bytes written to the buffer
194   * @stable ICU 4.2
195   */
196  int32_t NumberOfBytesWritten() const { return size_; }
197  /**
198   * Returns true if any bytes were discarded, i.e., if there was an
199   * attempt to write more than 'capacity' bytes.
200   * @return TRUE if more than 'capacity' bytes were Append()ed
201   * @stable ICU 4.2
202   */
203  UBool Overflowed() const { return overflowed_; }
204  /**
205   * Returns the number of bytes appended to the sink.
206   * If Overflowed() then NumberOfBytesAppended()>NumberOfBytesWritten()
207   * else they return the same number.
208   * @return number of bytes written to the buffer
209   * @stable ICU 4.6
210   */
211  int32_t NumberOfBytesAppended() const { return appended_; }
212private:
213  char* outbuf_;
214  const int32_t capacity_;
215  int32_t size_;
216  int32_t appended_;
217  UBool overflowed_;
218  CheckedArrayByteSink(); ///< default constructor not implemented
219  CheckedArrayByteSink(const CheckedArrayByteSink &); ///< copy constructor not implemented
220  CheckedArrayByteSink &operator=(const CheckedArrayByteSink &); ///< assignment operator not implemented
221};
222
223#if U_HAVE_STD_STRING
224
225/**
226 * Implementation of ByteSink that writes to a "string".
227 * The StringClass is usually instantiated with a std::string.
228 * @stable ICU 4.2
229 */
230template<typename StringClass>
231class StringByteSink : public ByteSink {
232 public:
233  /**
234   * Constructs a ByteSink that will append bytes to the dest string.
235   * @param dest pointer to string object to append to
236   * @stable ICU 4.2
237   */
238  StringByteSink(StringClass* dest) : dest_(dest) { }
239  /**
240   * Append "bytes[0,n-1]" to this.
241   * @param data the pointer to the bytes
242   * @param n the number of bytes; must be non-negative
243   * @stable ICU 4.2
244   */
245  virtual void Append(const char* data, int32_t n) { dest_->append(data, n); }
246 private:
247  StringClass* dest_;
248  StringByteSink(); ///< default constructor not implemented
249  StringByteSink(const StringByteSink &); ///< copy constructor not implemented
250  StringByteSink &operator=(const StringByteSink &); ///< assignment operator not implemented
251};
252
253#endif
254
255U_NAMESPACE_END
256
257#endif  // __BYTESTREAM_H__
258