icuSources/common/unicode/bytestream.h

   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
  47 U_NAMESPACE_BEGIN
  48
  49 /**
  50  * A ByteSink can be filled with bytes.
  51  * @stable ICU 4.2
  52  */
  53 class U_COMMON_API ByteSink : public UMemory {
  54 public:
  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
 131 private:
 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  */
 148 class U_COMMON_API CheckedArrayByteSink : public ByteSink {
 149 public:
 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_; }
 217 private:
 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  */
 234 template<typename StringClass>
 235 class 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
 271 U_NAMESPACE_END
 272
 273 #endif /* U_SHOW_CPLUSPLUS_API */
 274
 275 #endif  // __BYTESTREAM_H__