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#include "unicode/uobject.h"
42#include "unicode/std_string.h"
43
44U_NAMESPACE_BEGIN
45
46/**
47 * A ByteSink can be filled with bytes.
48 * @stable ICU 4.2
49 */
50class U_COMMON_API ByteSink : public UMemory {
51public:
52 /**
53 * Default constructor.
54 * @stable ICU 4.2
55 */
56 ByteSink() { }
57 /**
58 * Virtual destructor.
59 * @stable ICU 4.2
60 */
61 virtual ~ByteSink();
62
63 /**
64 * Append "bytes[0,n-1]" to this.
65 * @param bytes the pointer to the bytes
66 * @param n the number of bytes; must be non-negative
67 * @stable ICU 4.2
68 */
69 virtual void Append(const char* bytes, int32_t n) = 0;
70
71 /**
72 * Returns a writable buffer for appending and writes the buffer's capacity to
73 * *result_capacity. Guarantees *result_capacity>=min_capacity.
74 * May return a pointer to the caller-owned scratch buffer which must have
75 * scratch_capacity>=min_capacity.
76 * The returned buffer is only valid until the next operation
77 * on this ByteSink.
78 *
79 * After writing at most *result_capacity bytes, call Append() with the
80 * pointer returned from this function and the number of bytes written.
81 * Many Append() implementations will avoid copying bytes if this function
82 * returned an internal buffer.
83 *
84 * Partial usage example:
85 * int32_t capacity;
86 * char* buffer = sink->GetAppendBuffer(..., &capacity);
87 * ... Write n bytes into buffer, with n <= capacity.
88 * sink->Append(buffer, n);
89 * In many implementations, that call to Append will avoid copying bytes.
90 *
91 * If the ByteSink allocates or reallocates an internal buffer, it should use
92 * the desired_capacity_hint if appropriate.
93 * If a caller cannot provide a reasonable guess at the desired capacity,
94 * it should pass desired_capacity_hint=0.
95 *
96 * If a non-scratch buffer is returned, the caller may only pass
97 * a prefix to it to Append().
98 * That is, it is not correct to pass an interior pointer to Append().
99 *
100 * The default implementation always returns the scratch buffer.
101 *
102 * @param min_capacity required minimum capacity of the returned buffer;
103 * must be non-negative
104 * @param desired_capacity_hint desired capacity of the returned buffer;
105 * must be non-negative
106 * @param scratch default caller-owned buffer
107 * @param scratch_capacity capacity of the scratch buffer
108 * @param result_capacity pointer to an integer which will be set to the
109 * capacity of the returned buffer
110 * @return a buffer with *result_capacity>=min_capacity
111 * @stable ICU 4.2
112 */
113 virtual char* GetAppendBuffer(int32_t min_capacity,
114 int32_t desired_capacity_hint,
115 char* scratch, int32_t scratch_capacity,
116 int32_t* result_capacity);
117
118 /**
119 * Flush internal buffers.
120 * Some byte sinks use internal buffers or provide buffering
121 * and require calling Flush() at the end of the stream.
122 * The ByteSink should be ready for further Append() calls after Flush().
123 * The default implementation of Flush() does nothing.
124 * @stable ICU 4.2
125 */
126 virtual void Flush();
127
128private:
129 ByteSink(const ByteSink &) = delete;
130 ByteSink &operator=(const ByteSink &) = delete;
131};
132
133// -------------------------------------------------------------
134// Some standard implementations
135
136/**
137 * Implementation of ByteSink that writes to a flat byte array,
138 * with bounds-checking:
139 * This sink will not write more than capacity bytes to outbuf.
140 * If more than capacity bytes are Append()ed, then excess bytes are ignored,
141 * and Overflowed() will return true.
142 * Overflow does not cause a runtime error.
143 * @stable ICU 4.2
144 */
145class U_COMMON_API CheckedArrayByteSink : public ByteSink {
146public:
147 /**
148 * Constructs a ByteSink that will write to outbuf[0..capacity-1].
149 * @param outbuf buffer to write to
150 * @param capacity size of the buffer
151 * @stable ICU 4.2
152 */
153 CheckedArrayByteSink(char* outbuf, int32_t capacity);
154 /**
155 * Destructor.
156 * @stable ICU 4.2
157 */
158 virtual ~CheckedArrayByteSink();
159 /**
160 * Returns the sink to its original state, without modifying the buffer.
161 * Useful for reusing both the buffer and the sink for multiple streams.
162 * Resets the state to NumberOfBytesWritten()=NumberOfBytesAppended()=0
163 * and Overflowed()=FALSE.
164 * @return *this
165 * @stable ICU 4.6
166 */
167 virtual CheckedArrayByteSink& Reset();
168 /**
169 * Append "bytes[0,n-1]" to this.
170 * @param bytes the pointer to the bytes
171 * @param n the number of bytes; must be non-negative
172 * @stable ICU 4.2
173 */
174 virtual void Append(const char* bytes, int32_t n);
175 /**
176 * Returns a writable buffer for appending and writes the buffer's capacity to
177 * *result_capacity. For details see the base class documentation.
178 * @param min_capacity required minimum capacity of the returned buffer;
179 * must be non-negative
180 * @param desired_capacity_hint desired capacity of the returned buffer;
181 * must be non-negative
182 * @param scratch default caller-owned buffer
183 * @param scratch_capacity capacity of the scratch buffer
184 * @param result_capacity pointer to an integer which will be set to the
185 * capacity of the returned buffer
186 * @return a buffer with *result_capacity>=min_capacity
187 * @stable ICU 4.2
188 */
189 virtual char* GetAppendBuffer(int32_t min_capacity,
190 int32_t desired_capacity_hint,
191 char* scratch, int32_t scratch_capacity,
192 int32_t* result_capacity);
193 /**
194 * Returns the number of bytes actually written to the sink.
195 * @return number of bytes written to the buffer
196 * @stable ICU 4.2
197 */
198 int32_t NumberOfBytesWritten() const { return size_; }
199 /**
200 * Returns true if any bytes were discarded, i.e., if there was an
201 * attempt to write more than 'capacity' bytes.
202 * @return TRUE if more than 'capacity' bytes were Append()ed
203 * @stable ICU 4.2
204 */
205 UBool Overflowed() const { return overflowed_; }
206 /**
207 * Returns the number of bytes appended to the sink.
208 * If Overflowed() then NumberOfBytesAppended()>NumberOfBytesWritten()
209 * else they return the same number.
210 * @return number of bytes written to the buffer
211 * @stable ICU 4.6
212 */
213 int32_t NumberOfBytesAppended() const { return appended_; }
214private:
215 char* outbuf_;
216 const int32_t capacity_;
217 int32_t size_;
218 int32_t appended_;
219 UBool overflowed_;
220
221 CheckedArrayByteSink() = delete;
222 CheckedArrayByteSink(const CheckedArrayByteSink &) = delete;
223 CheckedArrayByteSink &operator=(const CheckedArrayByteSink &) = delete;
224};
225
226/**
227 * Implementation of ByteSink that writes to a "string".
228 * The StringClass is usually instantiated with a std::string.
229 * @stable ICU 4.2
230 */
231template<typename StringClass>
232class StringByteSink : public ByteSink {
233 public:
234 /**
235 * Constructs a ByteSink that will append bytes to the dest string.
236 * @param dest pointer to string object to append to
237 * @stable ICU 4.2
238 */
239 StringByteSink(StringClass* dest) : dest_(dest) { }
240 /**
241 * Constructs a ByteSink that reserves append capacity and will append bytes to the dest string.
242 *
243 * @param dest pointer to string object to append to
244 * @param initialAppendCapacity capacity beyond dest->length() to be reserve()d
245 * @stable ICU 60
246 */
247 StringByteSink(StringClass* dest, int32_t initialAppendCapacity) : dest_(dest) {
248 if (initialAppendCapacity > 0 &&
249 (uint32_t)initialAppendCapacity > (dest->capacity() - dest->length())) {
250 dest->reserve(dest->length() + initialAppendCapacity);
251 }
252 }
253 /**
254 * Append "bytes[0,n-1]" to this.
255 * @param data the pointer to the bytes
256 * @param n the number of bytes; must be non-negative
257 * @stable ICU 4.2
258 */
259 virtual void Append(const char* data, int32_t n) { dest_->append(data, n); }
260 private:
261 StringClass* dest_;
262
263 StringByteSink() = delete;
264 StringByteSink(const StringByteSink &) = delete;
265 StringByteSink &operator=(const StringByteSink &) = delete;
266};
267
268U_NAMESPACE_END
269
270#endif // __BYTESTREAM_H__
271