parser/htmlparser/nsScannerString.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim:set ts=2 sw=2 sts=2 et cindent: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef nsScannerString_h___
   8 #define nsScannerString_h___
   9
  10 #include "nsString.h"
  11 #include "nsUnicharUtils.h"  // for nsCaseInsensitiveStringComparator
  12 #include "mozilla/LinkedList.h"
  13 #include <algorithm>
  14
  15 /**
  16  * NOTE: nsScannerString (and the other classes defined in this file) are
  17  * not related to nsAString or any of the other xpcom/string classes.
  18  *
  19  * nsScannerString is based on the nsSlidingString implementation that used
  20  * to live in xpcom/string.  Now that nsAString is limited to representing
  21  * only single fragment strings, nsSlidingString can no longer be used.
  22  *
  23  * An advantage to this design is that it does not employ any virtual
  24  * functions.
  25  *
  26  * This file uses SCC-style indenting in deference to the nsSlidingString
  27  * code from which this code is derived ;-)
  28  */
  29
  30 class nsScannerIterator;
  31 class nsScannerSubstring;
  32 class nsScannerString;
  33
  34 /**
  35  * nsScannerBufferList
  36  *
  37  * This class maintains a list of heap-allocated Buffer objects.  The buffers
  38  * are maintained in a circular linked list.  Each buffer has a usage count
  39  * that is decremented by the owning nsScannerSubstring.
  40  *
  41  * The buffer list itself is reference counted.  This allows the buffer list
  42  * to be shared by multiple nsScannerSubstring objects.  The reference
  43  * counting is not threadsafe, which is not at all a requirement.
  44  *
  45  * When a nsScannerSubstring releases its reference to a buffer list, it
  46  * decrements the usage count of the first buffer in the buffer list that it
  47  * was referencing.  It informs the buffer list that it can discard buffers
  48  * starting at that prefix.  The buffer list will do so if the usage count of
  49  * that buffer is 0 and if it is the first buffer in the list.  It will
  50  * continue to prune buffers starting from the front of the buffer list until
  51  * it finds a buffer that has a usage count that is non-zero.
  52  */
  53 class nsScannerBufferList {
  54  public:
  55   /**
  56    * Buffer objects are directly followed by a data segment.  The start
  57    * of the data segment is determined by increment the |this| pointer
  58    * by 1 unit.
  59    */
  60   class Buffer : public mozilla::LinkedListElement<Buffer> {
  61    public:
  62     void IncrementUsageCount() { ++mUsageCount; }
  63     void DecrementUsageCount() { --mUsageCount; }
  64
  65     bool IsInUse() const { return mUsageCount != 0; }
  66
  67     const char16_t* DataStart() const { return (const char16_t*)(this + 1); }
  68     char16_t* DataStart() { return (char16_t*)(this + 1); }
  69
  70     const char16_t* DataEnd() const { return mDataEnd; }
  71     char16_t* DataEnd() { return mDataEnd; }
  72
  73     const Buffer* Next() const { return getNext(); }
  74     Buffer* Next() { return getNext(); }
  75
  76     const Buffer* Prev() const { return getPrevious(); }
  77     Buffer* Prev() { return getPrevious(); }
  78
  79     uint32_t DataLength() const { return mDataEnd - DataStart(); }
  80     void SetDataLength(uint32_t len) { mDataEnd = DataStart() + len; }
  81
  82    private:
  83     friend class nsScannerBufferList;
  84
  85     int32_t mUsageCount;
  86     char16_t* mDataEnd;
  87   };
  88
  89   /**
  90    * Position objects serve as lightweight pointers into a buffer list.
  91    * The mPosition member must be contained with mBuffer->DataStart()
  92    * and mBuffer->DataEnd().
  93    */
  94   class Position {
  95    public:
  96     Position() : mBuffer(nullptr), mPosition(nullptr) {}
  97
  98     Position(Buffer* buffer, char16_t* position)
  99         : mBuffer(buffer), mPosition(position) {}
 100
 101     inline explicit Position(const nsScannerIterator& aIter);
 102
 103     inline Position& operator=(const nsScannerIterator& aIter);
 104
 105     static size_t Distance(const Position& p1, const Position& p2);
 106
 107     Buffer* mBuffer;
 108     char16_t* mPosition;
 109   };
 110
 111   static Buffer* AllocBufferFromString(const nsAString&);
 112   static Buffer* AllocBuffer(uint32_t capacity);  // capacity = number of chars
 113
 114   explicit nsScannerBufferList(Buffer* buf) : mRefCnt(0) {
 115     mBuffers.insertBack(buf);
 116   }
 117
 118   void AddRef() { ++mRefCnt; }
 119   void Release() {
 120     if (--mRefCnt == 0) delete this;
 121   }
 122
 123   void Append(Buffer* buf) { mBuffers.insertBack(buf); }
 124   void InsertAfter(Buffer* buf, Buffer* prev) { prev->setNext(buf); }
 125   void SplitBuffer(const Position&);
 126   void DiscardUnreferencedPrefix(Buffer*);
 127
 128   Buffer* Head() { return mBuffers.getFirst(); }
 129   const Buffer* Head() const { return mBuffers.getFirst(); }
 130
 131   Buffer* Tail() { return mBuffers.getLast(); }
 132   const Buffer* Tail() const { return mBuffers.getLast(); }
 133
 134  private:
 135   friend class nsScannerSubstring;
 136
 137   ~nsScannerBufferList() { ReleaseAll(); }
 138   void ReleaseAll();
 139
 140   int32_t mRefCnt;
 141   mozilla::LinkedList<Buffer> mBuffers;
 142 };
 143
 144 /**
 145  * nsScannerFragment represents a "slice" of a Buffer object.
 146  */
 147 struct nsScannerFragment {
 148   typedef nsScannerBufferList::Buffer Buffer;
 149
 150   const Buffer* mBuffer;
 151   const char16_t* mFragmentStart;
 152   const char16_t* mFragmentEnd;
 153 };
 154
 155 /**
 156  * nsScannerSubstring is the base class for nsScannerString.  It provides
 157  * access to iterators and methods to bind the substring to another
 158  * substring or nsAString instance.
 159  *
 160  * This class owns the buffer list.
 161  */
 162 class nsScannerSubstring {
 163  public:
 164   typedef nsScannerBufferList::Buffer Buffer;
 165   typedef nsScannerBufferList::Position Position;
 166   typedef uint32_t size_type;
 167
 168   nsScannerSubstring();
 169   explicit nsScannerSubstring(const nsAString& s);
 170
 171   ~nsScannerSubstring();
 172
 173   nsScannerIterator& BeginReading(nsScannerIterator& iter) const;
 174   nsScannerIterator& EndReading(nsScannerIterator& iter) const;
 175
 176   size_type Length() const { return mLength; }
 177
 178   void Rebind(const nsScannerSubstring&, const nsScannerIterator&,
 179               const nsScannerIterator&);
 180   void Rebind(const nsAString&);
 181
 182   bool GetNextFragment(nsScannerFragment&) const;
 183   bool GetPrevFragment(nsScannerFragment&) const;
 184
 185   static inline Buffer* AllocBufferFromString(const nsAString& aStr) {
 186     return nsScannerBufferList::AllocBufferFromString(aStr);
 187   }
 188   static inline Buffer* AllocBuffer(size_type aCapacity) {
 189     return nsScannerBufferList::AllocBuffer(aCapacity);
 190   }
 191
 192  protected:
 193   void acquire_ownership_of_buffer_list() const {
 194     mBufferList->AddRef();
 195     mStart.mBuffer->IncrementUsageCount();
 196   }
 197
 198   void release_ownership_of_buffer_list() {
 199     if (mBufferList) {
 200       mStart.mBuffer->DecrementUsageCount();
 201       mBufferList->DiscardUnreferencedPrefix(mStart.mBuffer);
 202       mBufferList->Release();
 203     }
 204   }
 205
 206   void init_range_from_buffer_list() {
 207     mStart.mBuffer = mBufferList->Head();
 208     mStart.mPosition = mStart.mBuffer->DataStart();
 209
 210     mEnd.mBuffer = mBufferList->Tail();
 211     mEnd.mPosition = mEnd.mBuffer->DataEnd();
 212
 213     mLength = Position::Distance(mStart, mEnd);
 214   }
 215
 216   Position mStart;
 217   Position mEnd;
 218   nsScannerBufferList* mBufferList;
 219   size_type mLength;
 220
 221   friend class nsScannerSharedSubstring;
 222 };
 223
 224 /**
 225  * nsScannerString provides methods to grow and modify a buffer list.
 226  */
 227 class nsScannerString : public nsScannerSubstring {
 228  public:
 229   explicit nsScannerString(Buffer*);
 230
 231   // you are giving ownership to the string, it takes and keeps your
 232   // buffer, deleting it when done.
 233   // Use AllocBuffer or AllocBufferFromString to create a Buffer object
 234   // for use with this function.
 235   void AppendBuffer(Buffer*);
 236
 237   void DiscardPrefix(const nsScannerIterator&);
 238   // any other way you want to do this?
 239
 240   void UngetReadable(const nsAString& aReadable,
 241                      const nsScannerIterator& aCurrentPosition);
 242 };
 243
 244 /**
 245  * nsScannerSharedSubstring implements copy-on-write semantics for
 246  * nsScannerSubstring.  This class also manages releasing
 247  * the reference to the scanner buffer when it is no longer needed.
 248  */
 249
 250 class nsScannerSharedSubstring {
 251  public:
 252   nsScannerSharedSubstring() : mBuffer(nullptr), mBufferList(nullptr) {}
 253
 254   ~nsScannerSharedSubstring() {
 255     if (mBufferList) ReleaseBuffer();
 256   }
 257
 258   // Acquire a copy-on-write reference to the given substring.
 259   void Rebind(const nsScannerIterator& aStart, const nsScannerIterator& aEnd);
 260
 261   // Get a const reference to this string
 262   const nsAString& str() const { return mString; }
 263
 264  private:
 265   typedef nsScannerBufferList::Buffer Buffer;
 266
 267   void ReleaseBuffer();
 268
 269   nsDependentSubstring mString;
 270   Buffer* mBuffer;
 271   nsScannerBufferList* mBufferList;
 272 };
 273
 274 /**
 275  * nsScannerIterator works just like nsReadingIterator<CharT> except that
 276  * it knows how to iterate over a list of scanner buffers.
 277  */
 278 class nsScannerIterator {
 279  public:
 280   typedef nsScannerIterator self_type;
 281   typedef ptrdiff_t difference_type;
 282   typedef char16_t value_type;
 283   typedef const char16_t* pointer;
 284   typedef const char16_t& reference;
 285   typedef nsScannerSubstring::Buffer Buffer;
 286
 287  protected:
 288   nsScannerFragment mFragment;
 289   const char16_t* mPosition;
 290   const nsScannerSubstring* mOwner;
 291
 292   friend class nsScannerSubstring;
 293   friend class nsScannerSharedSubstring;
 294
 295  public:
 296   // nsScannerIterator();                                       // auto-generate
 297   // default constructor is OK nsScannerIterator( const nsScannerIterator& ); //
 298   // auto-generated copy-constructor OK nsScannerIterator& operator=( const
 299   // nsScannerIterator& );  // auto-generated copy-assignment operator OK
 300
 301   inline void normalize_forward();
 302   inline void normalize_backward();
 303
 304   pointer get() const { return mPosition; }
 305
 306   char16_t operator*() const { return *get(); }
 307
 308   const nsScannerFragment& fragment() const { return mFragment; }
 309
 310   const Buffer* buffer() const { return mFragment.mBuffer; }
 311
 312   self_type& operator++() {
 313     ++mPosition;
 314     normalize_forward();
 315     return *this;
 316   }
 317
 318   self_type operator++(int) {
 319     self_type result(*this);
 320     ++mPosition;
 321     normalize_forward();
 322     return result;
 323   }
 324
 325   self_type& operator--() {
 326     normalize_backward();
 327     --mPosition;
 328     return *this;
 329   }
 330
 331   self_type operator--(int) {
 332     self_type result(*this);
 333     normalize_backward();
 334     --mPosition;
 335     return result;
 336   }
 337
 338   difference_type size_forward() const {
 339     return mFragment.mFragmentEnd - mPosition;
 340   }
 341
 342   difference_type size_backward() const {
 343     return mPosition - mFragment.mFragmentStart;
 344   }
 345
 346   self_type& advance(difference_type n) {
 347     while (n > 0) {
 348       difference_type one_hop = std::min(n, size_forward());
 349
 350       NS_ASSERTION(one_hop > 0,
 351                    "Infinite loop: can't advance a reading iterator beyond the "
 352                    "end of a string");
 353       // perhaps I should |break| if |!one_hop|?
 354
 355       mPosition += one_hop;
 356       normalize_forward();
 357       n -= one_hop;
 358     }
 359
 360     while (n < 0) {
 361       normalize_backward();
 362       difference_type one_hop = std::max(n, -size_backward());
 363
 364       NS_ASSERTION(one_hop < 0,
 365                    "Infinite loop: can't advance (backward) a reading iterator "
 366                    "beyond the end of a string");
 367       // perhaps I should |break| if |!one_hop|?
 368
 369       mPosition += one_hop;
 370       n -= one_hop;
 371     }
 372
 373     return *this;
 374   }
 375 };
 376
 377 inline bool SameFragment(const nsScannerIterator& a,
 378                          const nsScannerIterator& b) {
 379   return a.fragment().mFragmentStart == b.fragment().mFragmentStart;
 380 }
 381
 382 /**
 383  * this class is needed in order to make use of the methods in nsAlgorithm.h
 384  */
 385 template <>
 386 struct nsCharSourceTraits<nsScannerIterator> {
 387   typedef nsScannerIterator::difference_type difference_type;
 388
 389   static uint32_t readable_distance(const nsScannerIterator& first,
 390                                     const nsScannerIterator& last) {
 391     return uint32_t(SameFragment(first, last) ? last.get() - first.get()
 392                                               : first.size_forward());
 393   }
 394
 395   static const nsScannerIterator::value_type* read(
 396       const nsScannerIterator& iter) {
 397     return iter.get();
 398   }
 399
 400   static void advance(nsScannerIterator& s, difference_type n) { s.advance(n); }
 401 };
 402
 403 /**
 404  * inline methods follow
 405  */
 406
 407 inline void nsScannerIterator::normalize_forward() {
 408   while (mPosition == mFragment.mFragmentEnd &&
 409          mOwner->GetNextFragment(mFragment))
 410     mPosition = mFragment.mFragmentStart;
 411 }
 412
 413 inline void nsScannerIterator::normalize_backward() {
 414   while (mPosition == mFragment.mFragmentStart &&
 415          mOwner->GetPrevFragment(mFragment))
 416     mPosition = mFragment.mFragmentEnd;
 417 }
 418
 419 inline bool operator==(const nsScannerIterator& lhs,
 420                        const nsScannerIterator& rhs) {
 421   return lhs.get() == rhs.get();
 422 }
 423
 424 inline bool operator!=(const nsScannerIterator& lhs,
 425                        const nsScannerIterator& rhs) {
 426   return lhs.get() != rhs.get();
 427 }
 428
 429 inline nsScannerBufferList::Position::Position(const nsScannerIterator& aIter)
 430     : mBuffer(const_cast<Buffer*>(aIter.buffer())),
 431       mPosition(const_cast<char16_t*>(aIter.get())) {}
 432
 433 inline nsScannerBufferList::Position& nsScannerBufferList::Position::operator=(
 434     const nsScannerIterator& aIter) {
 435   mBuffer = const_cast<Buffer*>(aIter.buffer());
 436   mPosition = const_cast<char16_t*>(aIter.get());
 437   return *this;
 438 }
 439
 440 /**
 441  * scanner string utils
 442  *
 443  * These methods mimic the API provided by nsReadableUtils in xpcom/string.
 444  * Here we provide only the methods that the htmlparser module needs.
 445  */
 446
 447 inline size_t Distance(const nsScannerIterator& aStart,
 448                        const nsScannerIterator& aEnd) {
 449   typedef nsScannerBufferList::Position Position;
 450   return Position::Distance(Position(aStart), Position(aEnd));
 451 }
 452
 453 bool CopyUnicodeTo(const nsScannerIterator& aSrcStart,
 454                    const nsScannerIterator& aSrcEnd, nsAString& aDest);
 455
 456 bool AppendUnicodeTo(const nsScannerIterator& aSrcStart,
 457                      const nsScannerIterator& aSrcEnd, nsAString& aDest);
 458
 459 #endif  // !defined(nsScannerString_h___)