icuSources/common/unicode/bytestream.h

   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
  42 U_NAMESPACE_BEGIN
  43
  44 /**
  45  * A ByteSink can be filled with bytes.
  46  * @stable ICU 4.2
  47  */
  48 class U_COMMON_API ByteSink : public UMemory {
  49 public:
  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
 126 private:
 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  */
 143 class U_COMMON_API CheckedArrayByteSink : public ByteSink {
 144 public:
 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_; }
 212 private:
 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  */
 230 template<typename StringClass>
 231 class 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
 255 U_NAMESPACE_END
 256
 257 #endif  // __BYTESTREAM_H__