1// © 2016 and later: Unicode, Inc. and others.
2// License & terms of use: http://www.unicode.org/copyright.html
3// Copyright (C) 2009-2012, International Business Machines
4// Corporation and others. All Rights Reserved.
5//
6// Copyright 2007 Google Inc. All Rights Reserved.
7// Author: sanjay@google.com (Sanjay Ghemawat)
8//
9// Abstract interface that consumes a sequence of bytes (ByteSink).
10//
11// Used so that we can write a single piece of code that can operate
12// on a variety of output string types.
13//
14// Various implementations of this interface are provided:
15// ByteSink:
16// CheckedArrayByteSink Write to a flat array, with bounds checking
17// StringByteSink Write to an STL string
18
19// This code is a contribution of Google code, and the style used here is
20// a compromise between the original Google code and the ICU coding guidelines.
21// For example, data types are ICU-ified (size_t,int->int32_t),
22// and API comments doxygen-ified, but function names and behavior are
23// as in the original, if possible.
24// Assertion-style error handling, not available in ICU, was changed to
25// parameter "pinning" similar to UnicodeString.
26//
27// In addition, this is only a partial port of the original Google code,
28// limited to what was needed so far. The (nearly) complete original code
29// is in the ICU svn repository at icuhtml/trunk/design/strings/contrib
30// (see ICU ticket 6765, r25517).
31
32#ifndef __BYTESTREAM_H__
33#define __BYTESTREAM_H__
34
35/**
36 * \file
37 * \brief C++ API: Interface for writing bytes, and implementation classes.
38 */
39
40#include "unicode/utypes.h"
41
42#if U_SHOW_CPLUSPLUS_API
43
44#include "unicode/uobject.h"
45#include "unicode/std_string.h"
46
47U_NAMESPACE_BEGIN
48
49/**
50 * A ByteSink can be filled with bytes.
51 * @stable ICU 4.2
52 */
53class U_COMMON_API ByteSink : public UMemory {
54public:
55 /**
56 * Default constructor.
57 * @stable ICU 4.2
58 */
59 ByteSink() { }
60 /**
61 * Virtual destructor.
62 * @stable ICU 4.2
63 */
64 virtual ~ByteSink();
65
66 /**
67 * Append "bytes[0,n-1]" to this.
68 * @param bytes the pointer to the bytes
69 * @param n the number of bytes; must be non-negative
70 * @stable ICU 4.2
71 */
72 virtual void Append(const char* bytes, int32_t n) = 0;
73
74 /**
75 * Returns a writable buffer for appending and writes the buffer's capacity to
76 * *result_capacity. Guarantees *result_capacity>=min_capacity.
77 * May return a pointer to the caller-owned scratch buffer which must have
78 * scratch_capacity>=min_capacity.
79 * The returned buffer is only valid until the next operation
80 * on this ByteSink.
81 *
82 * After writing at most *result_capacity bytes, call Append() with the
83 * pointer returned from this function and the number of bytes written.
84 * Many Append() implementations will avoid copying bytes if this function
85 * returned an internal buffer.
86 *
87 * Partial usage example:
88 * int32_t capacity;
89 * char* buffer = sink->GetAppendBuffer(..., &capacity);
90 * ... Write n bytes into buffer, with n <= capacity.
91 * sink->Append(buffer, n);
92 * In many implementations, that call to Append will avoid copying bytes.
93 *
94 * If the ByteSink allocates or reallocates an internal buffer, it should use
95 * the desired_capacity_hint if appropriate.
96 * If a caller cannot provide a reasonable guess at the desired capacity,
97 * it should pass desired_capacity_hint=0.
98 *
99 * If a non-scratch buffer is returned, the caller may only pass
100 * a prefix to it to Append().
101 * That is, it is not correct to pass an interior pointer to Append().
102 *
103 * The default implementation always returns the scratch buffer.
104 *
105 * @param min_capacity required minimum capacity of the returned buffer;
106 * must be non-negative
107 * @param desired_capacity_hint desired capacity of the returned buffer;
108 * must be non-negative
109 * @param scratch default caller-owned buffer
110 * @param scratch_capacity capacity of the scratch buffer
111 * @param result_capacity pointer to an integer which will be set to the
112 * capacity of the returned buffer
113 * @return a buffer with *result_capacity>=min_capacity
114 * @stable ICU 4.2
115 */
116 virtual char* GetAppendBuffer(int32_t min_capacity,
117 int32_t desired_capacity_hint,
118 char* scratch, int32_t scratch_capacity,
119 int32_t* result_capacity);
120
121 /**
122 * Flush internal buffers.
123 * Some byte sinks use internal buffers or provide buffering
124 * and require calling Flush() at the end of the stream.
125 * The ByteSink should be ready for further Append() calls after Flush().
126 * The default implementation of Flush() does nothing.
127 * @stable ICU 4.2
128 */
129 virtual void Flush();
130
131private:
132 ByteSink(const ByteSink &) = delete;
133 ByteSink &operator=(const ByteSink &) = delete;
134};
135
136// -------------------------------------------------------------
137// Some standard implementations
138
139/**
140 * Implementation of ByteSink that writes to a flat byte array,
141 * with bounds-checking:
142 * This sink will not write more than capacity bytes to outbuf.
143 * If more than capacity bytes are Append()ed, then excess bytes are ignored,
144 * and Overflowed() will return true.
145 * Overflow does not cause a runtime error.
146 * @stable ICU 4.2
147 */
148class U_COMMON_API CheckedArrayByteSink : public ByteSink {
149public:
150 /**
151 * Constructs a ByteSink that will write to outbuf[0..capacity-1].
152 * @param outbuf buffer to write to
153 * @param capacity size of the buffer
154 * @stable ICU 4.2
155 */
156 CheckedArrayByteSink(char* outbuf, int32_t capacity);
157 /**
158 * Destructor.
159 * @stable ICU 4.2
160 */
161 virtual ~CheckedArrayByteSink();
162 /**
163 * Returns the sink to its original state, without modifying the buffer.
164 * Useful for reusing both the buffer and the sink for multiple streams.
165 * Resets the state to NumberOfBytesWritten()=NumberOfBytesAppended()=0
166 * and Overflowed()=FALSE.
167 * @return *this
168 * @stable ICU 4.6
169 */
170 virtual CheckedArrayByteSink& Reset();
171 /**
172 * Append "bytes[0,n-1]" to this.
173 * @param bytes the pointer to the bytes
174 * @param n the number of bytes; must be non-negative
175 * @stable ICU 4.2
176 */
177 virtual void Append(const char* bytes, int32_t n);
178 /**
179 * Returns a writable buffer for appending and writes the buffer's capacity to
180 * *result_capacity. For details see the base class documentation.
181 * @param min_capacity required minimum capacity of the returned buffer;
182 * must be non-negative
183 * @param desired_capacity_hint desired capacity of the returned buffer;
184 * must be non-negative
185 * @param scratch default caller-owned buffer
186 * @param scratch_capacity capacity of the scratch buffer
187 * @param result_capacity pointer to an integer which will be set to the
188 * capacity of the returned buffer
189 * @return a buffer with *result_capacity>=min_capacity
190 * @stable ICU 4.2
191 */
192 virtual char* GetAppendBuffer(int32_t min_capacity,
193 int32_t desired_capacity_hint,
194 char* scratch, int32_t scratch_capacity,
195 int32_t* result_capacity);
196 /**
197 * Returns the number of bytes actually written to the sink.
198 * @return number of bytes written to the buffer
199 * @stable ICU 4.2
200 */
201 int32_t NumberOfBytesWritten() const { return size_; }
202 /**
203 * Returns true if any bytes were discarded, i.e., if there was an
204 * attempt to write more than 'capacity' bytes.
205 * @return TRUE if more than 'capacity' bytes were Append()ed
206 * @stable ICU 4.2
207 */
208 UBool Overflowed() const { return overflowed_; }
209 /**
210 * Returns the number of bytes appended to the sink.
211 * If Overflowed() then NumberOfBytesAppended()>NumberOfBytesWritten()
212 * else they return the same number.
213 * @return number of bytes written to the buffer
214 * @stable ICU 4.6
215 */
216 int32_t NumberOfBytesAppended() const { return appended_; }
217private:
218 char* outbuf_;
219 const int32_t capacity_;
220 int32_t size_;
221 int32_t appended_;
222 UBool overflowed_;
223
224 CheckedArrayByteSink() = delete;
225 CheckedArrayByteSink(const CheckedArrayByteSink &) = delete;
226 CheckedArrayByteSink &operator=(const CheckedArrayByteSink &) = delete;
227};
228
229/**
230 * Implementation of ByteSink that writes to a "string".
231 * The StringClass is usually instantiated with a std::string.
232 * @stable ICU 4.2
233 */
234template<typename StringClass>
235class StringByteSink : public ByteSink {
236 public:
237 /**
238 * Constructs a ByteSink that will append bytes to the dest string.
239 * @param dest pointer to string object to append to
240 * @stable ICU 4.2
241 */
242 StringByteSink(StringClass* dest) : dest_(dest) { }
243 /**
244 * Constructs a ByteSink that reserves append capacity and will append bytes to the dest string.
245 *
246 * @param dest pointer to string object to append to
247 * @param initialAppendCapacity capacity beyond dest->length() to be reserve()d
248 * @stable ICU 60
249 */
250 StringByteSink(StringClass* dest, int32_t initialAppendCapacity) : dest_(dest) {
251 if (initialAppendCapacity > 0 &&
252 (uint32_t)initialAppendCapacity > (dest->capacity() - dest->length())) {
253 dest->reserve(dest->length() + initialAppendCapacity);
254 }
255 }
256 /**
257 * Append "bytes[0,n-1]" to this.
258 * @param data the pointer to the bytes
259 * @param n the number of bytes; must be non-negative
260 * @stable ICU 4.2
261 */
262 virtual void Append(const char* data, int32_t n) { dest_->append(data, n); }
263 private:
264 StringClass* dest_;
265
266 StringByteSink() = delete;
267 StringByteSink(const StringByteSink &) = delete;
268 StringByteSink &operator=(const StringByteSink &) = delete;
269};
270
271U_NAMESPACE_END
272
273#endif /* U_SHOW_CPLUSPLUS_API */
274
275#endif // __BYTESTREAM_H__
276