image/SourceBuffer.cpp

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #include "SourceBuffer.h"
   7
   8 #include <algorithm>
   9 #include <cmath>
  10 #include <cstring>
  11 #include "mozilla/Likely.h"
  12 #include "nsIInputStream.h"
  13 #include "MainThreadUtils.h"
  14 #include "SurfaceCache.h"
  15
  16 using std::max;
  17 using std::min;
  18
  19 namespace mozilla {
  20 namespace image {
  21
  22 //////////////////////////////////////////////////////////////////////////////
  23 // SourceBufferIterator implementation.
  24 //////////////////////////////////////////////////////////////////////////////
  25
  26 SourceBufferIterator::~SourceBufferIterator() {
  27   if (mOwner) {
  28     mOwner->OnIteratorRelease();
  29   }
  30 }
  31
  32 SourceBufferIterator& SourceBufferIterator::operator=(
  33     SourceBufferIterator&& aOther) {
  34   if (mOwner) {
  35     mOwner->OnIteratorRelease();
  36   }
  37
  38   mOwner = std::move(aOther.mOwner);
  39   mState = aOther.mState;
  40   mData = aOther.mData;
  41   mChunkCount = aOther.mChunkCount;
  42   mByteCount = aOther.mByteCount;
  43   mRemainderToRead = aOther.mRemainderToRead;
  44
  45   return *this;
  46 }
  47
  48 SourceBufferIterator::State SourceBufferIterator::AdvanceOrScheduleResume(
  49     size_t aRequestedBytes, IResumable* aConsumer) {
  50   MOZ_ASSERT(mOwner);
  51
  52   if (MOZ_UNLIKELY(!HasMore())) {
  53     MOZ_ASSERT_UNREACHABLE("Should not advance a completed iterator");
  54     return COMPLETE;
  55   }
  56
  57   // The range of data [mOffset, mOffset + mNextReadLength) has just been read
  58   // by the caller (or at least they don't have any interest in it), so consume
  59   // that data.
  60   MOZ_ASSERT(mData.mIterating.mNextReadLength <=
  61              mData.mIterating.mAvailableLength);
  62   mData.mIterating.mOffset += mData.mIterating.mNextReadLength;
  63   mData.mIterating.mAvailableLength -= mData.mIterating.mNextReadLength;
  64
  65   // An iterator can have a limit imposed on it to read only a subset of a
  66   // source buffer. If it is present, we need to mimic the same behaviour as
  67   // the owning SourceBuffer.
  68   if (MOZ_UNLIKELY(mRemainderToRead != SIZE_MAX)) {
  69     MOZ_ASSERT(mData.mIterating.mNextReadLength <= mRemainderToRead);
  70     mRemainderToRead -= mData.mIterating.mNextReadLength;
  71
  72     if (MOZ_UNLIKELY(mRemainderToRead == 0)) {
  73       mData.mIterating.mNextReadLength = 0;
  74       SetComplete(NS_OK);
  75       return COMPLETE;
  76     }
  77
  78     if (MOZ_UNLIKELY(aRequestedBytes > mRemainderToRead)) {
  79       aRequestedBytes = mRemainderToRead;
  80     }
  81   }
  82
  83   mData.mIterating.mNextReadLength = 0;
  84
  85   if (MOZ_LIKELY(mState == READY)) {
  86     // If the caller wants zero bytes of data, that's easy enough; we just
  87     // configured ourselves for a zero-byte read above!  In theory we could do
  88     // this even in the START state, but it's not important for performance and
  89     // breaking the ability of callers to assert that the pointer returned by
  90     // Data() is non-null doesn't seem worth it.
  91     if (aRequestedBytes == 0) {
  92       MOZ_ASSERT(mData.mIterating.mNextReadLength == 0);
  93       return READY;
  94     }
  95
  96     // Try to satisfy the request out of our local buffer. This is potentially
  97     // much faster than requesting data from our owning SourceBuffer because we
  98     // don't have to take the lock. Note that if we have anything at all in our
  99     // local buffer, we use it to satisfy the request; @aRequestedBytes is just
 100     // the *maximum* number of bytes we can return.
 101     if (mData.mIterating.mAvailableLength > 0) {
 102       return AdvanceFromLocalBuffer(aRequestedBytes);
 103     }
 104   }
 105
 106   // Our local buffer is empty, so we'll have to request data from our owning
 107   // SourceBuffer.
 108   return mOwner->AdvanceIteratorOrScheduleResume(*this, aRequestedBytes,
 109                                                  aConsumer);
 110 }
 111
 112 bool SourceBufferIterator::RemainingBytesIsNoMoreThan(size_t aBytes) const {
 113   MOZ_ASSERT(mOwner);
 114   return mOwner->RemainingBytesIsNoMoreThan(*this, aBytes);
 115 }
 116
 117 //////////////////////////////////////////////////////////////////////////////
 118 // SourceBuffer implementation.
 119 //////////////////////////////////////////////////////////////////////////////
 120
 121 const size_t SourceBuffer::MIN_CHUNK_CAPACITY;
 122 const size_t SourceBuffer::MAX_CHUNK_CAPACITY;
 123
 124 SourceBuffer::SourceBuffer()
 125     : mMutex("image::SourceBuffer"), mConsumerCount(0), mCompacted(false) {}
 126
 127 SourceBuffer::~SourceBuffer() {
 128   MOZ_ASSERT(mConsumerCount == 0,
 129              "SourceBuffer destroyed with active consumers");
 130 }
 131
 132 nsresult SourceBuffer::AppendChunk(Maybe<Chunk>&& aChunk) {
 133   mMutex.AssertCurrentThreadOwns();
 134
 135   if (MOZ_UNLIKELY(!aChunk)) {
 136     return NS_ERROR_OUT_OF_MEMORY;
 137   }
 138
 139   if (MOZ_UNLIKELY(aChunk->AllocationFailed())) {
 140     return NS_ERROR_OUT_OF_MEMORY;
 141   }
 142
 143   if (MOZ_UNLIKELY(!mChunks.AppendElement(std::move(*aChunk), fallible))) {
 144     return NS_ERROR_OUT_OF_MEMORY;
 145   }
 146
 147   return NS_OK;
 148 }
 149
 150 Maybe<SourceBuffer::Chunk> SourceBuffer::CreateChunk(
 151     size_t aCapacity, size_t aExistingCapacity /* = 0 */,
 152     bool aRoundUp /* = true */) {
 153   if (MOZ_UNLIKELY(aCapacity == 0)) {
 154     MOZ_ASSERT_UNREACHABLE("Appending a chunk of zero size?");
 155     return Nothing();
 156   }
 157
 158   // Round up if requested.
 159   size_t finalCapacity = aRoundUp ? RoundedUpCapacity(aCapacity) : aCapacity;
 160
 161   // Use the size of the SurfaceCache as an additional heuristic to avoid
 162   // allocating huge buffers. Generally images do not get smaller when decoded,
 163   // so if we could store the source data in the SurfaceCache, we assume that
 164   // there's no way we'll be able to store the decoded version.
 165   if (MOZ_UNLIKELY(!SurfaceCache::CanHold(finalCapacity + aExistingCapacity))) {
 166     NS_WARNING(
 167         "SourceBuffer refused to create chunk too large for SurfaceCache");
 168     return Nothing();
 169   }
 170
 171   return Some(Chunk(finalCapacity));
 172 }
 173
 174 nsresult SourceBuffer::Compact() {
 175   mMutex.AssertCurrentThreadOwns();
 176
 177   MOZ_ASSERT(mConsumerCount == 0, "Should have no consumers here");
 178   MOZ_ASSERT(mWaitingConsumers.Length() == 0, "Shouldn't have waiters");
 179   MOZ_ASSERT(mStatus, "Should be complete here");
 180
 181   // If we've tried to compact once, don't attempt again.
 182   if (mCompacted) {
 183     return NS_OK;
 184   }
 185
 186   mCompacted = true;
 187
 188   // Compact our waiting consumers list, since we're complete and no future
 189   // consumer will ever have to wait.
 190   mWaitingConsumers.Compact();
 191
 192   // If we have no chunks, then there's nothing to compact.
 193   if (mChunks.Length() < 1) {
 194     return NS_OK;
 195   }
 196
 197   // If we have one chunk, then we can compact if it has excess capacity.
 198   if (mChunks.Length() == 1 && mChunks[0].Length() == mChunks[0].Capacity()) {
 199     return NS_OK;
 200   }
 201
 202   // If the last chunk has the maximum capacity, then we know the total size
 203   // will be quite large and not worth consolidating. We can likely/cheapily
 204   // trim the last chunk if it is too big however.
 205   size_t capacity = mChunks.LastElement().Capacity();
 206   if (capacity == MAX_CHUNK_CAPACITY) {
 207     size_t lastLength = mChunks.LastElement().Length();
 208     if (lastLength != capacity) {
 209       mChunks.LastElement().SetCapacity(lastLength);
 210     }
 211     return NS_OK;
 212   }
 213
 214   // We can compact our buffer. Determine the total length.
 215   size_t length = 0;
 216   for (uint32_t i = 0; i < mChunks.Length(); ++i) {
 217     length += mChunks[i].Length();
 218   }
 219
 220   // If our total length is zero (which means ExpectLength() got called, but no
 221   // data ever actually got written) then just empty our chunk list.
 222   if (MOZ_UNLIKELY(length == 0)) {
 223     mChunks.Clear();
 224     return NS_OK;
 225   }
 226
 227   Chunk& mergeChunk = mChunks[0];
 228   if (MOZ_UNLIKELY(!mergeChunk.SetCapacity(length))) {
 229     NS_WARNING("Failed to reallocate chunk for SourceBuffer compacting - OOM?");
 230     return NS_OK;
 231   }
 232
 233   // Copy our old chunks into the newly reallocated first chunk.
 234   for (uint32_t i = 1; i < mChunks.Length(); ++i) {
 235     size_t offset = mergeChunk.Length();
 236     MOZ_ASSERT(offset < mergeChunk.Capacity());
 237     MOZ_ASSERT(offset + mChunks[i].Length() <= mergeChunk.Capacity());
 238
 239     memcpy(mergeChunk.Data() + offset, mChunks[i].Data(), mChunks[i].Length());
 240     mergeChunk.AddLength(mChunks[i].Length());
 241   }
 242
 243   MOZ_ASSERT(mergeChunk.Length() == mergeChunk.Capacity(),
 244              "Compacted chunk has slack space");
 245
 246   // Remove the redundant chunks.
 247   mChunks.RemoveLastElements(mChunks.Length() - 1);
 248   mChunks.Compact();
 249
 250   return NS_OK;
 251 }
 252
 253 /* static */
 254 size_t SourceBuffer::RoundedUpCapacity(size_t aCapacity) {
 255   // Protect against overflow.
 256   if (MOZ_UNLIKELY(SIZE_MAX - aCapacity < MIN_CHUNK_CAPACITY)) {
 257     return aCapacity;
 258   }
 259
 260   // Round up to the next multiple of MIN_CHUNK_CAPACITY (which should be the
 261   // size of a page).
 262   size_t roundedCapacity =
 263       (aCapacity + MIN_CHUNK_CAPACITY - 1) & ~(MIN_CHUNK_CAPACITY - 1);
 264   MOZ_ASSERT(roundedCapacity >= aCapacity, "Bad math?");
 265   MOZ_ASSERT(roundedCapacity - aCapacity < MIN_CHUNK_CAPACITY, "Bad math?");
 266
 267   return roundedCapacity;
 268 }
 269
 270 size_t SourceBuffer::FibonacciCapacityWithMinimum(size_t aMinCapacity) {
 271   mMutex.AssertCurrentThreadOwns();
 272
 273   // We grow the source buffer using a Fibonacci growth rate. It will be capped
 274   // at MAX_CHUNK_CAPACITY, unless the available data exceeds that.
 275
 276   size_t length = mChunks.Length();
 277
 278   if (length == 0 || aMinCapacity > MAX_CHUNK_CAPACITY) {
 279     return aMinCapacity;
 280   }
 281
 282   if (length == 1) {
 283     return min(max(2 * mChunks[0].Capacity(), aMinCapacity),
 284                MAX_CHUNK_CAPACITY);
 285   }
 286
 287   return min(
 288       max(mChunks[length - 1].Capacity() + mChunks[length - 2].Capacity(),
 289           aMinCapacity),
 290       MAX_CHUNK_CAPACITY);
 291 }
 292
 293 void SourceBuffer::AddWaitingConsumer(IResumable* aConsumer) {
 294   mMutex.AssertCurrentThreadOwns();
 295
 296   MOZ_ASSERT(!mStatus, "Waiting when we're complete?");
 297
 298   if (aConsumer) {
 299     mWaitingConsumers.AppendElement(aConsumer);
 300   }
 301 }
 302
 303 void SourceBuffer::ResumeWaitingConsumers() {
 304   mMutex.AssertCurrentThreadOwns();
 305
 306   if (mWaitingConsumers.Length() == 0) {
 307     return;
 308   }
 309
 310   for (uint32_t i = 0; i < mWaitingConsumers.Length(); ++i) {
 311     mWaitingConsumers[i]->Resume();
 312   }
 313
 314   mWaitingConsumers.Clear();
 315 }
 316
 317 nsresult SourceBuffer::ExpectLength(size_t aExpectedLength) {
 318   MOZ_ASSERT(aExpectedLength > 0, "Zero expected size?");
 319
 320   MutexAutoLock lock(mMutex);
 321
 322   if (MOZ_UNLIKELY(mStatus)) {
 323     MOZ_ASSERT_UNREACHABLE("ExpectLength after SourceBuffer is complete");
 324     return NS_OK;
 325   }
 326
 327   if (MOZ_UNLIKELY(mChunks.Length() > 0)) {
 328     MOZ_ASSERT_UNREACHABLE("Duplicate or post-Append call to ExpectLength");
 329     return NS_OK;
 330   }
 331
 332   if (MOZ_UNLIKELY(!SurfaceCache::CanHold(aExpectedLength))) {
 333     NS_WARNING("SourceBuffer refused to store too large buffer");
 334     return HandleError(NS_ERROR_INVALID_ARG);
 335   }
 336
 337   size_t length = min(aExpectedLength, MAX_CHUNK_CAPACITY);
 338   if (MOZ_UNLIKELY(NS_FAILED(AppendChunk(CreateChunk(length,
 339                                                      /* aExistingCapacity */ 0,
 340                                                      /* aRoundUp */ false))))) {
 341     return HandleError(NS_ERROR_OUT_OF_MEMORY);
 342   }
 343
 344   return NS_OK;
 345 }
 346
 347 nsresult SourceBuffer::Append(const char* aData, size_t aLength) {
 348   MOZ_ASSERT(aData, "Should have a buffer");
 349   MOZ_ASSERT(aLength > 0, "Writing a zero-sized chunk");
 350
 351   size_t currentChunkCapacity = 0;
 352   size_t currentChunkLength = 0;
 353   char* currentChunkData = nullptr;
 354   size_t currentChunkRemaining = 0;
 355   size_t forCurrentChunk = 0;
 356   size_t forNextChunk = 0;
 357   size_t nextChunkCapacity = 0;
 358   size_t totalCapacity = 0;
 359
 360   {
 361     MutexAutoLock lock(mMutex);
 362
 363     if (MOZ_UNLIKELY(mStatus)) {
 364       // This SourceBuffer is already complete; ignore further data.
 365       return NS_ERROR_FAILURE;
 366     }
 367
 368     if (MOZ_UNLIKELY(mChunks.Length() == 0)) {
 369       if (MOZ_UNLIKELY(NS_FAILED(AppendChunk(CreateChunk(aLength))))) {
 370         return HandleError(NS_ERROR_OUT_OF_MEMORY);
 371       }
 372     }
 373
 374     // Copy out the current chunk's information so we can release the lock.
 375     // Note that this wouldn't be safe if multiple producers were allowed!
 376     Chunk& currentChunk = mChunks.LastElement();
 377     currentChunkCapacity = currentChunk.Capacity();
 378     currentChunkLength = currentChunk.Length();
 379     currentChunkData = currentChunk.Data();
 380
 381     // Partition this data between the current chunk and the next chunk.
 382     // (Because we always allocate a chunk big enough to fit everything passed
 383     // to Append, we'll never need more than those two chunks to store
 384     // everything.)
 385     currentChunkRemaining = currentChunkCapacity - currentChunkLength;
 386     forCurrentChunk = min(aLength, currentChunkRemaining);
 387     forNextChunk = aLength - forCurrentChunk;
 388
 389     // If we'll need another chunk, determine what its capacity should be while
 390     // we still hold the lock.
 391     nextChunkCapacity =
 392         forNextChunk > 0 ? FibonacciCapacityWithMinimum(forNextChunk) : 0;
 393
 394     for (uint32_t i = 0; i < mChunks.Length(); ++i) {
 395       totalCapacity += mChunks[i].Capacity();
 396     }
 397   }
 398
 399   // Write everything we can fit into the current chunk.
 400   MOZ_ASSERT(currentChunkLength + forCurrentChunk <= currentChunkCapacity);
 401   memcpy(currentChunkData + currentChunkLength, aData, forCurrentChunk);
 402
 403   // If there's something left, create a new chunk and write it there.
 404   Maybe<Chunk> nextChunk;
 405   if (forNextChunk > 0) {
 406     MOZ_ASSERT(nextChunkCapacity >= forNextChunk, "Next chunk too small?");
 407     nextChunk = CreateChunk(nextChunkCapacity, totalCapacity);
 408     if (MOZ_LIKELY(nextChunk && !nextChunk->AllocationFailed())) {
 409       memcpy(nextChunk->Data(), aData + forCurrentChunk, forNextChunk);
 410       nextChunk->AddLength(forNextChunk);
 411     }
 412   }
 413
 414   // Update shared data structures.
 415   {
 416     MutexAutoLock lock(mMutex);
 417
 418     // Update the length of the current chunk.
 419     Chunk& currentChunk = mChunks.LastElement();
 420     MOZ_ASSERT(currentChunk.Data() == currentChunkData, "Multiple producers?");
 421     MOZ_ASSERT(currentChunk.Length() == currentChunkLength,
 422                "Multiple producers?");
 423
 424     currentChunk.AddLength(forCurrentChunk);
 425
 426     // If we created a new chunk, add it to the series.
 427     if (forNextChunk > 0) {
 428       if (MOZ_UNLIKELY(!nextChunk)) {
 429         return HandleError(NS_ERROR_OUT_OF_MEMORY);
 430       }
 431
 432       if (MOZ_UNLIKELY(NS_FAILED(AppendChunk(std::move(nextChunk))))) {
 433         return HandleError(NS_ERROR_OUT_OF_MEMORY);
 434       }
 435     }
 436
 437     // Resume any waiting readers now that there's new data.
 438     ResumeWaitingConsumers();
 439   }
 440
 441   return NS_OK;
 442 }
 443
 444 static nsresult AppendToSourceBuffer(nsIInputStream*, void* aClosure,
 445                                      const char* aFromRawSegment, uint32_t,
 446                                      uint32_t aCount, uint32_t* aWriteCount) {
 447   SourceBuffer* sourceBuffer = static_cast<SourceBuffer*>(aClosure);
 448
 449   // Copy the source data. Unless we hit OOM, we squelch the return value here,
 450   // because returning an error means that ReadSegments stops reading data, and
 451   // we want to ensure that we read everything we get. If we hit OOM then we
 452   // return a failed status to the caller.
 453   nsresult rv = sourceBuffer->Append(aFromRawSegment, aCount);
 454   if (rv == NS_ERROR_OUT_OF_MEMORY) {
 455     return rv;
 456   }
 457
 458   // Report that we wrote everything we got.
 459   *aWriteCount = aCount;
 460
 461   return NS_OK;
 462 }
 463
 464 nsresult SourceBuffer::AppendFromInputStream(nsIInputStream* aInputStream,
 465                                              uint32_t aCount) {
 466   uint32_t bytesRead;
 467   nsresult rv = aInputStream->ReadSegments(AppendToSourceBuffer, this, aCount,
 468                                            &bytesRead);
 469   if (NS_WARN_IF(NS_FAILED(rv))) {
 470     return rv;
 471   }
 472
 473   if (bytesRead == 0) {
 474     // The loading of the image has been canceled.
 475     return NS_ERROR_FAILURE;
 476   }
 477
 478   if (bytesRead != aCount) {
 479     // Only some of the given data was read. We may have failed in
 480     // SourceBuffer::Append but ReadSegments swallowed the error. Otherwise the
 481     // stream itself failed to yield the data.
 482     MutexAutoLock lock(mMutex);
 483     if (mStatus) {
 484       MOZ_ASSERT(NS_FAILED(*mStatus));
 485       return *mStatus;
 486     }
 487
 488     MOZ_ASSERT_UNREACHABLE("AppendToSourceBuffer should consume everything");
 489   }
 490
 491   return rv;
 492 }
 493
 494 void SourceBuffer::Complete(nsresult aStatus) {
 495   MutexAutoLock lock(mMutex);
 496
 497   // When an error occurs internally (e.g. due to an OOM), we save the status.
 498   // This will indirectly trigger a failure higher up and that will call
 499   // SourceBuffer::Complete. Since it doesn't necessarily know we are already
 500   // complete, it is safe to ignore.
 501   if (mStatus && (MOZ_UNLIKELY(NS_SUCCEEDED(*mStatus) ||
 502                                aStatus != NS_IMAGELIB_ERROR_FAILURE))) {
 503     MOZ_ASSERT_UNREACHABLE("Called Complete more than once");
 504     return;
 505   }
 506
 507   if (MOZ_UNLIKELY(NS_SUCCEEDED(aStatus) && IsEmpty())) {
 508     // It's illegal to succeed without writing anything.
 509     aStatus = NS_ERROR_FAILURE;
 510   }
 511
 512   mStatus = Some(aStatus);
 513
 514   // Resume any waiting consumers now that we're complete.
 515   ResumeWaitingConsumers();
 516
 517   // If we still have active consumers, just return.
 518   if (mConsumerCount > 0) {
 519     return;
 520   }
 521
 522   // Attempt to compact our buffer down to a single chunk.
 523   Compact();
 524 }
 525
 526 bool SourceBuffer::IsComplete() {
 527   MutexAutoLock lock(mMutex);
 528   return bool(mStatus);
 529 }
 530
 531 size_t SourceBuffer::SizeOfIncludingThisWithComputedFallback(
 532     MallocSizeOf aMallocSizeOf) const {
 533   MutexAutoLock lock(mMutex);
 534
 535   size_t n = aMallocSizeOf(this);
 536   n += mChunks.ShallowSizeOfExcludingThis(aMallocSizeOf);
 537
 538   for (uint32_t i = 0; i < mChunks.Length(); ++i) {
 539     size_t chunkSize = aMallocSizeOf(mChunks[i].Data());
 540
 541     if (chunkSize == 0) {
 542       // We're on a platform where moz_malloc_size_of always returns 0.
 543       chunkSize = mChunks[i].Capacity();
 544     }
 545
 546     n += chunkSize;
 547   }
 548
 549   return n;
 550 }
 551
 552 SourceBufferIterator SourceBuffer::Iterator(size_t aReadLength) {
 553   {
 554     MutexAutoLock lock(mMutex);
 555     mConsumerCount++;
 556   }
 557
 558   return SourceBufferIterator(this, aReadLength);
 559 }
 560
 561 void SourceBuffer::OnIteratorRelease() {
 562   MutexAutoLock lock(mMutex);
 563
 564   MOZ_ASSERT(mConsumerCount > 0, "Consumer count doesn't add up");
 565   mConsumerCount--;
 566
 567   // If we still have active consumers, or we're not complete yet, then return.
 568   if (mConsumerCount > 0 || !mStatus) {
 569     return;
 570   }
 571
 572   // Attempt to compact our buffer down to a single chunk.
 573   Compact();
 574 }
 575
 576 bool SourceBuffer::RemainingBytesIsNoMoreThan(
 577     const SourceBufferIterator& aIterator, size_t aBytes) const {
 578   MutexAutoLock lock(mMutex);
 579
 580   // If we're not complete, we always say no.
 581   if (!mStatus) {
 582     return false;
 583   }
 584
 585   // If the iterator's at the end, the answer is trivial.
 586   if (!aIterator.HasMore()) {
 587     return true;
 588   }
 589
 590   uint32_t iteratorChunk = aIterator.mData.mIterating.mChunk;
 591   size_t iteratorOffset = aIterator.mData.mIterating.mOffset;
 592   size_t iteratorLength = aIterator.mData.mIterating.mAvailableLength;
 593
 594   // Include the bytes the iterator is currently pointing to in the limit, so
 595   // that the current chunk doesn't have to be a special case.
 596   size_t bytes = aBytes + iteratorOffset + iteratorLength;
 597
 598   // Count the length over all of our chunks, starting with the one that the
 599   // iterator is currently pointing to. (This is O(N), but N is expected to be
 600   // ~1, so it doesn't seem worth caching the length separately.)
 601   size_t lengthSoFar = 0;
 602   for (uint32_t i = iteratorChunk; i < mChunks.Length(); ++i) {
 603     lengthSoFar += mChunks[i].Length();
 604     if (lengthSoFar > bytes) {
 605       return false;
 606     }
 607   }
 608
 609   return true;
 610 }
 611
 612 SourceBufferIterator::State SourceBuffer::AdvanceIteratorOrScheduleResume(
 613     SourceBufferIterator& aIterator, size_t aRequestedBytes,
 614     IResumable* aConsumer) {
 615   MutexAutoLock lock(mMutex);
 616
 617   MOZ_ASSERT(aIterator.HasMore(),
 618              "Advancing a completed iterator and "
 619              "AdvanceOrScheduleResume didn't catch it");
 620
 621   if (MOZ_UNLIKELY(mStatus && NS_FAILED(*mStatus))) {
 622     // This SourceBuffer is complete due to an error; all reads fail.
 623     return aIterator.SetComplete(*mStatus);
 624   }
 625
 626   if (MOZ_UNLIKELY(mChunks.Length() == 0)) {
 627     // We haven't gotten an initial chunk yet.
 628     AddWaitingConsumer(aConsumer);
 629     return aIterator.SetWaiting(!!aConsumer);
 630   }
 631
 632   uint32_t iteratorChunkIdx = aIterator.mData.mIterating.mChunk;
 633   MOZ_ASSERT(iteratorChunkIdx < mChunks.Length());
 634
 635   const Chunk& currentChunk = mChunks[iteratorChunkIdx];
 636   size_t iteratorEnd = aIterator.mData.mIterating.mOffset +
 637                        aIterator.mData.mIterating.mAvailableLength;
 638   MOZ_ASSERT(iteratorEnd <= currentChunk.Length());
 639   MOZ_ASSERT(iteratorEnd <= currentChunk.Capacity());
 640
 641   if (iteratorEnd < currentChunk.Length()) {
 642     // There's more data in the current chunk.
 643     return aIterator.SetReady(iteratorChunkIdx, currentChunk.Data(),
 644                               iteratorEnd, currentChunk.Length() - iteratorEnd,
 645                               aRequestedBytes);
 646   }
 647
 648   if (iteratorEnd == currentChunk.Capacity() &&
 649       !IsLastChunk(iteratorChunkIdx)) {
 650     // Advance to the next chunk.
 651     const Chunk& nextChunk = mChunks[iteratorChunkIdx + 1];
 652     return aIterator.SetReady(iteratorChunkIdx + 1, nextChunk.Data(), 0,
 653                               nextChunk.Length(), aRequestedBytes);
 654   }
 655
 656   MOZ_ASSERT(IsLastChunk(iteratorChunkIdx), "Should've advanced");
 657
 658   if (mStatus) {
 659     // There's no more data and this SourceBuffer completed successfully.
 660     MOZ_ASSERT(NS_SUCCEEDED(*mStatus), "Handled failures earlier");
 661     return aIterator.SetComplete(*mStatus);
 662   }
 663
 664   // We're not complete, but there's no more data right now. Arrange to wake up
 665   // the consumer when we get more data.
 666   AddWaitingConsumer(aConsumer);
 667   return aIterator.SetWaiting(!!aConsumer);
 668 }
 669
 670 nsresult SourceBuffer::HandleError(nsresult aError) {
 671   MOZ_ASSERT(NS_FAILED(aError), "Should have an error here");
 672   MOZ_ASSERT(aError == NS_ERROR_OUT_OF_MEMORY || aError == NS_ERROR_INVALID_ARG,
 673              "Unexpected error; may want to notify waiting readers, which "
 674              "HandleError currently doesn't do");
 675
 676   mMutex.AssertCurrentThreadOwns();
 677
 678   NS_WARNING("SourceBuffer encountered an unrecoverable error");
 679
 680   // Record the error.
 681   mStatus = Some(aError);
 682
 683   // Drop our references to waiting readers.
 684   mWaitingConsumers.Clear();
 685
 686   return *mStatus;
 687 }
 688
 689 bool SourceBuffer::IsEmpty() {
 690   mMutex.AssertCurrentThreadOwns();
 691   return mChunks.Length() == 0 || mChunks[0].Length() == 0;
 692 }
 693
 694 bool SourceBuffer::IsLastChunk(uint32_t aChunk) {
 695   mMutex.AssertCurrentThreadOwns();
 696   return aChunk + 1 == mChunks.Length();
 697 }
 698
 699 }  // namespace image
 700 }  // namespace mozilla