Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 822 insertions, 0 deletions

diff --git a/image/test/gtest/TestSourceBuffer.cpp b/image/test/gtest/TestSourceBuffer.cpp
new file mode 100644
index 0000000000..478ab56610
--- /dev/null
+++ b/image/test/gtest/TestSourceBuffer.cpp
@@ -0,0 +1,822 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <algorithm>
+#include <cstdint>
+#include <utility>
+
+#include "Common.h"
+#include "SourceBuffer.h"
+#include "SurfaceCache.h"
+#include "gtest/gtest.h"
+#include "nsIInputStream.h"
+
+using namespace mozilla;
+using namespace mozilla::image;
+
+using std::min;
+
+void ExpectChunkAndByteCount(const SourceBufferIterator& aIterator,
+                             uint32_t aChunks, size_t aBytes) {
+  EXPECT_EQ(aChunks, aIterator.ChunkCount());
+  EXPECT_EQ(aBytes, aIterator.ByteCount());
+}
+
+void ExpectRemainingBytes(const SourceBufferIterator& aIterator,
+                          size_t aBytes) {
+  EXPECT_TRUE(aIterator.RemainingBytesIsNoMoreThan(aBytes));
+  EXPECT_TRUE(aIterator.RemainingBytesIsNoMoreThan(aBytes + 1));
+
+  if (aBytes > 0) {
+    EXPECT_FALSE(aIterator.RemainingBytesIsNoMoreThan(0));
+    EXPECT_FALSE(aIterator.RemainingBytesIsNoMoreThan(aBytes - 1));
+  }
+}
+
+char GenerateByte(size_t aIndex) {
+  uint8_t byte = aIndex % 256;
+  return *reinterpret_cast<char*>(&byte);
+}
+
+void GenerateData(char* aOutput, size_t aOffset, size_t aLength) {
+  for (size_t i = 0; i < aLength; ++i) {
+    aOutput[i] = GenerateByte(aOffset + i);
+  }
+}
+
+void GenerateData(char* aOutput, size_t aLength) {
+  GenerateData(aOutput, 0, aLength);
+}
+
+void CheckData(const char* aData, size_t aOffset, size_t aLength) {
+  for (size_t i = 0; i < aLength; ++i) {
+    ASSERT_EQ(GenerateByte(aOffset + i), aData[i]);
+  }
+}
+
+enum class AdvanceMode { eAdvanceAsMuchAsPossible, eAdvanceByLengthExactly };
+
+class ImageSourceBuffer : public ::testing::Test {
+ public:
+  ImageSourceBuffer()
+      : mSourceBuffer(new SourceBuffer),
+        mExpectNoResume(new ExpectNoResume),
+        mCountResumes(new CountResumes) {
+    GenerateData(mData, sizeof(mData));
+    EXPECT_FALSE(mSourceBuffer->IsComplete());
+  }
+
+ protected:
+  void CheckedAppendToBuffer(const char* aData, size_t aLength) {
+    EXPECT_NS_SUCCEEDED(mSourceBuffer->Append(aData, aLength));
+  }
+
+  void CheckedAppendToBufferLastByteForLength(size_t aLength) {
+    const char lastByte = GenerateByte(aLength);
+    CheckedAppendToBuffer(&lastByte, 1);
+  }
+
+  void CheckedAppendToBufferInChunks(size_t aChunkLength, size_t aTotalLength) {
+    char* data = new char[aChunkLength];
+
+    size_t bytesWritten = 0;
+    while (bytesWritten < aTotalLength) {
+      GenerateData(data, bytesWritten, aChunkLength);
+      size_t toWrite = min(aChunkLength, aTotalLength - bytesWritten);
+      CheckedAppendToBuffer(data, toWrite);
+      bytesWritten += toWrite;
+    }
+
+    delete[] data;
+  }
+
+  void CheckedCompleteBuffer(nsresult aCompletionStatus = NS_OK) {
+    mSourceBuffer->Complete(aCompletionStatus);
+    EXPECT_TRUE(mSourceBuffer->IsComplete());
+  }
+
+  void CheckedCompleteBuffer(SourceBufferIterator& aIterator, size_t aLength,
+                             nsresult aCompletionStatus = NS_OK) {
+    CheckedCompleteBuffer(aCompletionStatus);
+    ExpectRemainingBytes(aIterator, aLength);
+  }
+
+  void CheckedAdvanceIteratorStateOnly(
+      SourceBufferIterator& aIterator, size_t aLength, uint32_t aChunks,
+      size_t aTotalLength,
+      AdvanceMode aAdvanceMode = AdvanceMode::eAdvanceAsMuchAsPossible) {
+    const size_t advanceBy =
+        aAdvanceMode == AdvanceMode::eAdvanceAsMuchAsPossible ? SIZE_MAX
+                                                              : aLength;
+
+    auto state = aIterator.AdvanceOrScheduleResume(advanceBy, mExpectNoResume);
+    ASSERT_EQ(SourceBufferIterator::READY, state);
+    EXPECT_TRUE(aIterator.Data());
+    EXPECT_EQ(aLength, aIterator.Length());
+
+    ExpectChunkAndByteCount(aIterator, aChunks, aTotalLength);
+  }
+
+  void CheckedAdvanceIteratorStateOnly(SourceBufferIterator& aIterator,
+                                       size_t aLength) {
+    CheckedAdvanceIteratorStateOnly(aIterator, aLength, 1, aLength);
+  }
+
+  void CheckedAdvanceIterator(
+      SourceBufferIterator& aIterator, size_t aLength, uint32_t aChunks,
+      size_t aTotalLength,
+      AdvanceMode aAdvanceMode = AdvanceMode::eAdvanceAsMuchAsPossible) {
+    // Check that the iterator is in the expected state.
+    CheckedAdvanceIteratorStateOnly(aIterator, aLength, aChunks, aTotalLength,
+                                    aAdvanceMode);
+
+    // Check that we read the expected data. To do this, we need to compute our
+    // offset in the SourceBuffer, but fortunately that's pretty easy: it's the
+    // total number of bytes the iterator has advanced through, minus the length
+    // of the current chunk.
+    const size_t offset = aIterator.ByteCount() - aIterator.Length();
+    CheckData(aIterator.Data(), offset, aIterator.Length());
+  }
+
+  void CheckedAdvanceIterator(SourceBufferIterator& aIterator, size_t aLength) {
+    CheckedAdvanceIterator(aIterator, aLength, 1, aLength);
+  }
+
+  void CheckIteratorMustWait(SourceBufferIterator& aIterator,
+                             IResumable* aOnResume) {
+    auto state = aIterator.AdvanceOrScheduleResume(1, aOnResume);
+    EXPECT_EQ(SourceBufferIterator::WAITING, state);
+  }
+
+  void CheckIteratorIsComplete(SourceBufferIterator& aIterator,
+                               uint32_t aChunks, size_t aTotalLength,
+                               nsresult aCompletionStatus = NS_OK) {
+    ASSERT_TRUE(mSourceBuffer->IsComplete());
+    auto state = aIterator.AdvanceOrScheduleResume(1, mExpectNoResume);
+    ASSERT_EQ(SourceBufferIterator::COMPLETE, state);
+    EXPECT_EQ(aCompletionStatus, aIterator.CompletionStatus());
+    ExpectRemainingBytes(aIterator, 0);
+    ExpectChunkAndByteCount(aIterator, aChunks, aTotalLength);
+  }
+
+  void CheckIteratorIsComplete(SourceBufferIterator& aIterator,
+                               size_t aTotalLength) {
+    CheckIteratorIsComplete(aIterator, 1, aTotalLength);
+  }
+
+  AutoInitializeImageLib mInit;
+  char mData[9];
+  RefPtr<SourceBuffer> mSourceBuffer;
+  RefPtr<ExpectNoResume> mExpectNoResume;
+  RefPtr<CountResumes> mCountResumes;
+};
+
+TEST_F(ImageSourceBuffer, InitialState) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // RemainingBytesIsNoMoreThan() should always return false in the initial
+  // state, since we can't know the answer until Complete() has been called.
+  EXPECT_FALSE(iterator.RemainingBytesIsNoMoreThan(0));
+  EXPECT_FALSE(iterator.RemainingBytesIsNoMoreThan(SIZE_MAX));
+
+  // We haven't advanced our iterator at all, so its counters should be zero.
+  ExpectChunkAndByteCount(iterator, 0, 0);
+
+  // Attempt to advance; we should fail, and end up in the WAITING state. We
+  // expect no resumes because we don't actually append anything to the
+  // SourceBuffer in this test.
+  CheckIteratorMustWait(iterator, mExpectNoResume);
+}
+
+TEST_F(ImageSourceBuffer, ZeroLengthBufferAlwaysFails) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Complete the buffer without writing to it, providing a successful
+  // completion status.
+  CheckedCompleteBuffer(iterator, 0);
+
+  // Completing a buffer without writing to it results in an automatic failure;
+  // make sure that the actual completion status we get from the iterator
+  // reflects this.
+  CheckIteratorIsComplete(iterator, 0, 0, NS_ERROR_FAILURE);
+}
+
+TEST_F(ImageSourceBuffer, CompleteSuccess) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Write a single byte to the buffer and complete the buffer. (We have to
+  // write at least one byte because completing a zero length buffer always
+  // fails; see the ZeroLengthBufferAlwaysFails test.)
+  CheckedAppendToBuffer(mData, 1);
+  CheckedCompleteBuffer(iterator, 1);
+
+  // We should be able to advance once (to read the single byte) and then should
+  // reach the COMPLETE state with a successful status.
+  CheckedAdvanceIterator(iterator, 1);
+  CheckIteratorIsComplete(iterator, 1);
+}
+
+TEST_F(ImageSourceBuffer, CompleteFailure) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Write a single byte to the buffer and complete the buffer. (We have to
+  // write at least one byte because completing a zero length buffer always
+  // fails; see the ZeroLengthBufferAlwaysFails test.)
+  CheckedAppendToBuffer(mData, 1);
+  CheckedCompleteBuffer(iterator, 1, NS_ERROR_FAILURE);
+
+  // Advance the iterator. Because a failing status is propagated to the
+  // iterator as soon as it advances, we won't be able to read the single byte
+  // that we wrote above; we go directly into the COMPLETE state.
+  CheckIteratorIsComplete(iterator, 0, 0, NS_ERROR_FAILURE);
+}
+
+TEST_F(ImageSourceBuffer, Append) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Write test data to the buffer.
+  EXPECT_NS_SUCCEEDED(mSourceBuffer->ExpectLength(sizeof(mData)));
+  CheckedAppendToBuffer(mData, sizeof(mData));
+  CheckedCompleteBuffer(iterator, sizeof(mData));
+
+  // Verify that we can read it back via the iterator, and that the final state
+  // is what we expect.
+  CheckedAdvanceIterator(iterator, sizeof(mData));
+  CheckIteratorIsComplete(iterator, sizeof(mData));
+}
+
+TEST_F(ImageSourceBuffer, HugeAppendFails) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // We should fail to append anything bigger than what the SurfaceCache can
+  // hold, so use the SurfaceCache's maximum capacity to calculate what a
+  // "massive amount of data" (see below) consists of on this platform.
+  ASSERT_LT(SurfaceCache::MaximumCapacity(), SIZE_MAX);
+  const size_t hugeSize = SurfaceCache::MaximumCapacity() + 1;
+
+  // Attempt to write a massive amount of data and verify that it fails. (We'd
+  // get a buffer overrun during the test if it succeeds, but if it succeeds
+  // that's the least of our problems.)
+  EXPECT_NS_FAILED(mSourceBuffer->Append(mData, hugeSize));
+  EXPECT_TRUE(mSourceBuffer->IsComplete());
+  CheckIteratorIsComplete(iterator, 0, 0, NS_ERROR_OUT_OF_MEMORY);
+}
+
+TEST_F(ImageSourceBuffer, AppendFromInputStream) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Construct an input stream with some arbitrary data. (We use test data from
+  // one of the decoder tests.)
+  nsCOMPtr<nsIInputStream> inputStream = LoadFile(GreenPNGTestCase().mPath);
+  ASSERT_TRUE(inputStream != nullptr);
+
+  // Figure out how much data we have.
+  uint64_t length;
+  ASSERT_NS_SUCCEEDED(inputStream->Available(&length));
+
+  // Write test data to the buffer.
+  EXPECT_TRUE(
+      NS_SUCCEEDED(mSourceBuffer->AppendFromInputStream(inputStream, length)));
+  CheckedCompleteBuffer(iterator, length);
+
+  // Verify that the iterator sees the appropriate amount of data.
+  CheckedAdvanceIteratorStateOnly(iterator, length);
+  CheckIteratorIsComplete(iterator, length);
+}
+
+TEST_F(ImageSourceBuffer, AppendAfterComplete) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Write test data to the buffer.
+  EXPECT_NS_SUCCEEDED(mSourceBuffer->ExpectLength(sizeof(mData)));
+  CheckedAppendToBuffer(mData, sizeof(mData));
+  CheckedCompleteBuffer(iterator, sizeof(mData));
+
+  // Verify that we can read it back via the iterator, and that the final state
+  // is what we expect.
+  CheckedAdvanceIterator(iterator, sizeof(mData));
+  CheckIteratorIsComplete(iterator, sizeof(mData));
+
+  // Write more data to the completed buffer.
+  EXPECT_NS_FAILED(mSourceBuffer->Append(mData, sizeof(mData)));
+
+  // Try to read with a new iterator and verify that the new data got ignored.
+  SourceBufferIterator iterator2 = mSourceBuffer->Iterator();
+  CheckedAdvanceIterator(iterator2, sizeof(mData));
+  CheckIteratorIsComplete(iterator2, sizeof(mData));
+}
+
+TEST_F(ImageSourceBuffer, MinChunkCapacity) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Write test data to the buffer using many small appends. Since
+  // ExpectLength() isn't being called, we should be able to write up to
+  // SourceBuffer::MIN_CHUNK_CAPACITY bytes without a second chunk being
+  // allocated.
+  CheckedAppendToBufferInChunks(10, SourceBuffer::MIN_CHUNK_CAPACITY);
+
+  // Verify that the iterator sees the appropriate amount of data.
+  CheckedAdvanceIterator(iterator, SourceBuffer::MIN_CHUNK_CAPACITY);
+
+  // Write one more byte; we expect to see that it triggers an allocation.
+  CheckedAppendToBufferLastByteForLength(SourceBuffer::MIN_CHUNK_CAPACITY);
+  CheckedCompleteBuffer(iterator, 1);
+
+  // Verify that the iterator sees the new byte and a new chunk has been
+  // allocated.
+  CheckedAdvanceIterator(iterator, 1, 2, SourceBuffer::MIN_CHUNK_CAPACITY + 1);
+  CheckIteratorIsComplete(iterator, 2, SourceBuffer::MIN_CHUNK_CAPACITY + 1);
+}
+
+TEST_F(ImageSourceBuffer, ExpectLengthAllocatesRequestedCapacity) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Write SourceBuffer::MIN_CHUNK_CAPACITY bytes of test data to the buffer,
+  // but call ExpectLength() first to make SourceBuffer expect only a single
+  // byte. We expect this to still result in two chunks, because we trust the
+  // initial guess of ExpectLength() but after that it will only allocate chunks
+  // of at least MIN_CHUNK_CAPACITY bytes.
+  EXPECT_NS_SUCCEEDED(mSourceBuffer->ExpectLength(1));
+  CheckedAppendToBufferInChunks(10, SourceBuffer::MIN_CHUNK_CAPACITY);
+  CheckedCompleteBuffer(iterator, SourceBuffer::MIN_CHUNK_CAPACITY);
+
+  // Verify that the iterator sees a first chunk with 1 byte, and a second chunk
+  // with the remaining data.
+  CheckedAdvanceIterator(iterator, 1, 1, 1);
+  CheckedAdvanceIterator(iterator, SourceBuffer::MIN_CHUNK_CAPACITY - 1, 2,
+                         SourceBuffer::MIN_CHUNK_CAPACITY);
+  CheckIteratorIsComplete(iterator, 2, SourceBuffer::MIN_CHUNK_CAPACITY);
+}
+
+TEST_F(ImageSourceBuffer, ExpectLengthGrowsAboveMinCapacity) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Write two times SourceBuffer::MIN_CHUNK_CAPACITY bytes of test data to the
+  // buffer, calling ExpectLength() with the correct length first. We expect
+  // this to result in only one chunk, because ExpectLength() allows us to
+  // allocate a larger first chunk than MIN_CHUNK_CAPACITY bytes.
+  const size_t length = 2 * SourceBuffer::MIN_CHUNK_CAPACITY;
+  EXPECT_NS_SUCCEEDED(mSourceBuffer->ExpectLength(length));
+  CheckedAppendToBufferInChunks(10, length);
+
+  // Verify that the iterator sees a single chunk.
+  CheckedAdvanceIterator(iterator, length);
+
+  // Write one more byte; we expect to see that it triggers an allocation.
+  CheckedAppendToBufferLastByteForLength(length);
+  CheckedCompleteBuffer(iterator, 1);
+
+  // Verify that the iterator sees the new byte and a new chunk has been
+  // allocated.
+  CheckedAdvanceIterator(iterator, 1, 2, length + 1);
+  CheckIteratorIsComplete(iterator, 2, length + 1);
+}
+
+TEST_F(ImageSourceBuffer, HugeExpectLengthFails) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // ExpectLength() should fail if the length is bigger than what the
+  // SurfaceCache can hold, so use the SurfaceCache's maximum capacity to
+  // calculate what a "massive amount of data" (see below) consists of on this
+  // platform.
+  ASSERT_LT(SurfaceCache::MaximumCapacity(), SIZE_MAX);
+  const size_t hugeSize = SurfaceCache::MaximumCapacity() + 1;
+
+  // Attempt to write a massive amount of data and verify that it fails. (We'd
+  // get a buffer overrun during the test if it succeeds, but if it succeeds
+  // that's the least of our problems.)
+  EXPECT_NS_FAILED(mSourceBuffer->ExpectLength(hugeSize));
+  EXPECT_TRUE(mSourceBuffer->IsComplete());
+  CheckIteratorIsComplete(iterator, 0, 0, NS_ERROR_INVALID_ARG);
+}
+
+TEST_F(ImageSourceBuffer, LargeAppendsAllocateOnlyOneChunk) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Write two times SourceBuffer::MIN_CHUNK_CAPACITY bytes of test data to the
+  // buffer in a single Append() call. We expect this to result in only one
+  // chunk even though ExpectLength() wasn't called, because we should always
+  // allocate a new chunk large enough to store the data we have at hand.
+  constexpr size_t length = 2 * SourceBuffer::MIN_CHUNK_CAPACITY;
+  char data[length];
+  GenerateData(data, sizeof(data));
+  CheckedAppendToBuffer(data, length);
+
+  // Verify that the iterator sees a single chunk.
+  CheckedAdvanceIterator(iterator, length);
+
+  // Write one more byte; we expect to see that it triggers an allocation.
+  CheckedAppendToBufferLastByteForLength(length);
+  CheckedCompleteBuffer(iterator, 1);
+
+  // Verify that the iterator sees the new byte and a new chunk has been
+  // allocated.
+  CheckedAdvanceIterator(iterator, 1, 2, length + 1);
+  CheckIteratorIsComplete(iterator, 2, length + 1);
+}
+
+TEST_F(ImageSourceBuffer, LargeAppendsAllocateAtMostOneChunk) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Allocate some data we'll use below.
+  constexpr size_t firstWriteLength = SourceBuffer::MIN_CHUNK_CAPACITY / 2;
+  constexpr size_t secondWriteLength = 3 * SourceBuffer::MIN_CHUNK_CAPACITY;
+  constexpr size_t totalLength = firstWriteLength + secondWriteLength;
+  char data[totalLength];
+  GenerateData(data, sizeof(data));
+
+  // Write half of SourceBuffer::MIN_CHUNK_CAPACITY bytes of test data to the
+  // buffer in a single Append() call. This should fill half of the first chunk.
+  CheckedAppendToBuffer(data, firstWriteLength);
+
+  // Write three times SourceBuffer::MIN_CHUNK_CAPACITY bytes of test data to
+  // the buffer in a single Append() call. We expect this to result in the first
+  // of the first chunk being filled and a new chunk being allocated for the
+  // remainder.
+  CheckedAppendToBuffer(data + firstWriteLength, secondWriteLength);
+
+  // Verify that the iterator sees a MIN_CHUNK_CAPACITY-length chunk.
+  CheckedAdvanceIterator(iterator, SourceBuffer::MIN_CHUNK_CAPACITY);
+
+  // Verify that the iterator sees a second chunk of the length we expect.
+  const size_t expectedSecondChunkLength =
+      totalLength - SourceBuffer::MIN_CHUNK_CAPACITY;
+  CheckedAdvanceIterator(iterator, expectedSecondChunkLength, 2, totalLength);
+
+  // Write one more byte; we expect to see that it triggers an allocation.
+  CheckedAppendToBufferLastByteForLength(totalLength);
+  CheckedCompleteBuffer(iterator, 1);
+
+  // Verify that the iterator sees the new byte and a new chunk has been
+  // allocated.
+  CheckedAdvanceIterator(iterator, 1, 3, totalLength + 1);
+  CheckIteratorIsComplete(iterator, 3, totalLength + 1);
+}
+
+TEST_F(ImageSourceBuffer, OversizedAppendsAllocateAtMostOneChunk) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Allocate some data we'll use below.
+  constexpr size_t writeLength = SourceBuffer::MAX_CHUNK_CAPACITY + 1;
+
+  // Write SourceBuffer::MAX_CHUNK_CAPACITY + 1 bytes of test data to the
+  // buffer in a single Append() call. This should cause one chunk to be
+  // allocated because we wrote it as a single block.
+  CheckedAppendToBufferInChunks(writeLength, writeLength);
+
+  // Verify that the iterator sees a MAX_CHUNK_CAPACITY+1-length chunk.
+  CheckedAdvanceIterator(iterator, writeLength);
+
+  CheckedCompleteBuffer(NS_OK);
+  CheckIteratorIsComplete(iterator, 1, writeLength);
+}
+
+TEST_F(ImageSourceBuffer, CompactionHappensWhenBufferIsComplete) {
+  constexpr size_t chunkLength = SourceBuffer::MIN_CHUNK_CAPACITY;
+  constexpr size_t totalLength = 2 * chunkLength;
+
+  // Write enough data to create two chunks.
+  CheckedAppendToBufferInChunks(chunkLength, totalLength);
+
+  {
+    SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+    // Verify that the iterator sees two chunks.
+    CheckedAdvanceIterator(iterator, chunkLength);
+    CheckedAdvanceIterator(iterator, chunkLength, 2, totalLength);
+  }
+
+  // Complete the buffer, which should trigger compaction implicitly.
+  CheckedCompleteBuffer();
+
+  {
+    SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+    // Verify that compaction happened and there's now only one chunk.
+    CheckedAdvanceIterator(iterator, totalLength);
+    CheckIteratorIsComplete(iterator, 1, totalLength);
+  }
+}
+
+TEST_F(ImageSourceBuffer, CompactionIsDelayedWhileIteratorsExist) {
+  constexpr size_t chunkLength = SourceBuffer::MIN_CHUNK_CAPACITY;
+  constexpr size_t totalLength = 2 * chunkLength;
+
+  {
+    SourceBufferIterator outerIterator = mSourceBuffer->Iterator();
+
+    {
+      SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+      // Write enough data to create two chunks.
+      CheckedAppendToBufferInChunks(chunkLength, totalLength);
+      CheckedCompleteBuffer(iterator, totalLength);
+
+      // Verify that the iterator sees two chunks. Since there are live
+      // iterators, compaction shouldn't have happened when we completed the
+      // buffer.
+      CheckedAdvanceIterator(iterator, chunkLength);
+      CheckedAdvanceIterator(iterator, chunkLength, 2, totalLength);
+      CheckIteratorIsComplete(iterator, 2, totalLength);
+    }
+
+    // Now |iterator| has been destroyed, but |outerIterator| still exists, so
+    // we expect no compaction to have occurred at this point.
+    CheckedAdvanceIterator(outerIterator, chunkLength);
+    CheckedAdvanceIterator(outerIterator, chunkLength, 2, totalLength);
+    CheckIteratorIsComplete(outerIterator, 2, totalLength);
+  }
+
+  // Now all iterators have been destroyed. Since the buffer was already
+  // complete, we expect compaction to happen implicitly here.
+
+  {
+    SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+    // Verify that compaction happened and there's now only one chunk.
+    CheckedAdvanceIterator(iterator, totalLength);
+    CheckIteratorIsComplete(iterator, 1, totalLength);
+  }
+}
+
+TEST_F(ImageSourceBuffer, SourceBufferIteratorsCanBeMoved) {
+  constexpr size_t chunkLength = SourceBuffer::MIN_CHUNK_CAPACITY;
+  constexpr size_t totalLength = 2 * chunkLength;
+
+  // Write enough data to create two chunks. We create an iterator here to make
+  // sure that compaction doesn't happen during the test.
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+  CheckedAppendToBufferInChunks(chunkLength, totalLength);
+  CheckedCompleteBuffer(iterator, totalLength);
+
+  auto GetIterator = [&] {
+    SourceBufferIterator lambdaIterator = mSourceBuffer->Iterator();
+    CheckedAdvanceIterator(lambdaIterator, chunkLength);
+    return lambdaIterator;
+  };
+
+  // Move-construct |movedIterator| from the iterator returned from
+  // GetIterator() and check that its state is as we expect.
+  SourceBufferIterator tmpIterator = GetIterator();
+  SourceBufferIterator movedIterator(std::move(tmpIterator));
+  EXPECT_TRUE(movedIterator.Data());
+  EXPECT_EQ(chunkLength, movedIterator.Length());
+  ExpectChunkAndByteCount(movedIterator, 1, chunkLength);
+
+  // Make sure that we can advance the iterator.
+  CheckedAdvanceIterator(movedIterator, chunkLength, 2, totalLength);
+
+  // Make sure that the iterator handles completion properly.
+  CheckIteratorIsComplete(movedIterator, 2, totalLength);
+
+  // Move-assign |movedIterator| from the iterator returned from
+  // GetIterator() and check that its state is as we expect.
+  tmpIterator = GetIterator();
+  movedIterator = std::move(tmpIterator);
+  EXPECT_TRUE(movedIterator.Data());
+  EXPECT_EQ(chunkLength, movedIterator.Length());
+  ExpectChunkAndByteCount(movedIterator, 1, chunkLength);
+
+  // Make sure that we can advance the iterator.
+  CheckedAdvanceIterator(movedIterator, chunkLength, 2, totalLength);
+
+  // Make sure that the iterator handles completion properly.
+  CheckIteratorIsComplete(movedIterator, 2, totalLength);
+}
+
+TEST_F(ImageSourceBuffer, SubchunkAdvance) {
+  constexpr size_t chunkLength = SourceBuffer::MIN_CHUNK_CAPACITY;
+  constexpr size_t totalLength = 2 * chunkLength;
+
+  // Write enough data to create two chunks. We create our iterator here to make
+  // sure that compaction doesn't happen during the test.
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+  CheckedAppendToBufferInChunks(chunkLength, totalLength);
+  CheckedCompleteBuffer(iterator, totalLength);
+
+  // Advance through the first chunk. The chunk count should not increase.
+  // We check that by always passing 1 for the |aChunks| parameter of
+  // CheckedAdvanceIteratorStateOnly(). We have to call CheckData() manually
+  // because the offset calculation in CheckedAdvanceIterator() assumes that
+  // we're advancing a chunk at a time.
+  size_t offset = 0;
+  while (offset < chunkLength) {
+    CheckedAdvanceIteratorStateOnly(iterator, 1, 1, chunkLength,
+                                    AdvanceMode::eAdvanceByLengthExactly);
+    CheckData(iterator.Data(), offset++, iterator.Length());
+  }
+
+  // Read the first byte of the second chunk. This is the point at which we
+  // can't advance within the same chunk, so the chunk count should increase. We
+  // check that by passing 2 for the |aChunks| parameter of
+  // CheckedAdvanceIteratorStateOnly().
+  CheckedAdvanceIteratorStateOnly(iterator, 1, 2, totalLength,
+                                  AdvanceMode::eAdvanceByLengthExactly);
+  CheckData(iterator.Data(), offset++, iterator.Length());
+
+  // Read the rest of the second chunk. The chunk count should not increase.
+  while (offset < totalLength) {
+    CheckedAdvanceIteratorStateOnly(iterator, 1, 2, totalLength,
+                                    AdvanceMode::eAdvanceByLengthExactly);
+    CheckData(iterator.Data(), offset++, iterator.Length());
+  }
+
+  // Make sure we reached the end.
+  CheckIteratorIsComplete(iterator, 2, totalLength);
+}
+
+TEST_F(ImageSourceBuffer, SubchunkZeroByteAdvance) {
+  constexpr size_t chunkLength = SourceBuffer::MIN_CHUNK_CAPACITY;
+  constexpr size_t totalLength = 2 * chunkLength;
+
+  // Write enough data to create two chunks. We create our iterator here to make
+  // sure that compaction doesn't happen during the test.
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+  CheckedAppendToBufferInChunks(chunkLength, totalLength);
+  CheckedCompleteBuffer(iterator, totalLength);
+
+  // Make an initial zero-length advance. Although a zero-length advance
+  // normally won't cause us to read a chunk from the SourceBuffer, we'll do so
+  // if the iterator is in the initial state to keep the invariant that
+  // SourceBufferIterator in the READY state always returns a non-null pointer
+  // from Data().
+  CheckedAdvanceIteratorStateOnly(iterator, 0, 1, chunkLength,
+                                  AdvanceMode::eAdvanceByLengthExactly);
+
+  // Advance through the first chunk. As in the |SubchunkAdvance| test, the
+  // chunk count should not increase. We do a zero-length advance after each
+  // normal advance to ensure that zero-length advances do not change the
+  // iterator's position or cause a new chunk to be read.
+  size_t offset = 0;
+  while (offset < chunkLength) {
+    CheckedAdvanceIteratorStateOnly(iterator, 1, 1, chunkLength,
+                                    AdvanceMode::eAdvanceByLengthExactly);
+    CheckData(iterator.Data(), offset++, iterator.Length());
+    CheckedAdvanceIteratorStateOnly(iterator, 0, 1, chunkLength,
+                                    AdvanceMode::eAdvanceByLengthExactly);
+  }
+
+  // Read the first byte of the second chunk. This is the point at which we
+  // can't advance within the same chunk, so the chunk count should increase. As
+  // before, we do a zero-length advance afterward.
+  CheckedAdvanceIteratorStateOnly(iterator, 1, 2, totalLength,
+                                  AdvanceMode::eAdvanceByLengthExactly);
+  CheckData(iterator.Data(), offset++, iterator.Length());
+  CheckedAdvanceIteratorStateOnly(iterator, 0, 2, totalLength,
+                                  AdvanceMode::eAdvanceByLengthExactly);
+
+  // Read the rest of the second chunk. The chunk count should not increase. As
+  // before, we do a zero-length advance after each normal advance.
+  while (offset < totalLength) {
+    CheckedAdvanceIteratorStateOnly(iterator, 1, 2, totalLength,
+                                    AdvanceMode::eAdvanceByLengthExactly);
+    CheckData(iterator.Data(), offset++, iterator.Length());
+    CheckedAdvanceIteratorStateOnly(iterator, 0, 2, totalLength,
+                                    AdvanceMode::eAdvanceByLengthExactly);
+  }
+
+  // Make sure we reached the end.
+  CheckIteratorIsComplete(iterator, 2, totalLength);
+}
+
+TEST_F(ImageSourceBuffer, SubchunkZeroByteAdvanceWithNoData) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Check that advancing by zero bytes still makes us enter the WAITING state.
+  // This is because if we entered the READY state before reading any data at
+  // all, we'd break the invariant that SourceBufferIterator::Data() always
+  // returns a non-null pointer in the READY state.
+  auto state = iterator.AdvanceOrScheduleResume(0, mCountResumes);
+  EXPECT_EQ(SourceBufferIterator::WAITING, state);
+
+  // Call Complete(). This should trigger a resume.
+  CheckedCompleteBuffer();
+  EXPECT_EQ(1u, mCountResumes->Count());
+}
+
+TEST_F(ImageSourceBuffer, NullIResumable) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Check that we can't advance.
+  CheckIteratorMustWait(iterator, nullptr);
+
+  // Append to the buffer, which would cause a resume if we had passed a
+  // non-null IResumable.
+  CheckedAppendToBuffer(mData, sizeof(mData));
+  CheckedCompleteBuffer(iterator, sizeof(mData));
+}
+
+TEST_F(ImageSourceBuffer, AppendTriggersResume) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Check that we can't advance.
+  CheckIteratorMustWait(iterator, mCountResumes);
+
+  // Call Append(). This should trigger a resume.
+  mSourceBuffer->Append(mData, sizeof(mData));
+  EXPECT_EQ(1u, mCountResumes->Count());
+}
+
+TEST_F(ImageSourceBuffer, OnlyOneResumeTriggeredPerAppend) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Check that we can't advance.
+  CheckIteratorMustWait(iterator, mCountResumes);
+
+  // Allocate some data we'll use below.
+  constexpr size_t firstWriteLength = SourceBuffer::MIN_CHUNK_CAPACITY / 2;
+  constexpr size_t secondWriteLength = 3 * SourceBuffer::MIN_CHUNK_CAPACITY;
+  constexpr size_t totalLength = firstWriteLength + secondWriteLength;
+  char data[totalLength];
+  GenerateData(data, sizeof(data));
+
+  // Write half of SourceBuffer::MIN_CHUNK_CAPACITY bytes of test data to the
+  // buffer in a single Append() call. This should fill half of the first chunk.
+  // This should trigger a resume.
+  CheckedAppendToBuffer(data, firstWriteLength);
+  EXPECT_EQ(1u, mCountResumes->Count());
+
+  // Advance past the new data and wait again.
+  CheckedAdvanceIterator(iterator, firstWriteLength);
+  CheckIteratorMustWait(iterator, mCountResumes);
+
+  // Write three times SourceBuffer::MIN_CHUNK_CAPACITY bytes of test data to
+  // the buffer in a single Append() call. We expect this to result in the first
+  // of the first chunk being filled and a new chunk being allocated for the
+  // remainder. Even though two chunks are getting written to here, only *one*
+  // resume should get triggered, for a total of two in this test.
+  CheckedAppendToBuffer(data + firstWriteLength, secondWriteLength);
+  EXPECT_EQ(2u, mCountResumes->Count());
+}
+
+TEST_F(ImageSourceBuffer, CompleteTriggersResume) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Check that we can't advance.
+  CheckIteratorMustWait(iterator, mCountResumes);
+
+  // Call Complete(). This should trigger a resume.
+  CheckedCompleteBuffer();
+  EXPECT_EQ(1u, mCountResumes->Count());
+}
+
+TEST_F(ImageSourceBuffer, ExpectLengthDoesNotTriggerResume) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator();
+
+  // Check that we can't advance.
+  CheckIteratorMustWait(iterator, mExpectNoResume);
+
+  // Call ExpectLength(). If this triggers a resume, |mExpectNoResume| will
+  // ensure that the test fails.
+  mSourceBuffer->ExpectLength(1000);
+}
+
+TEST_F(ImageSourceBuffer, CompleteSuccessWithSameReadLength) {
+  SourceBufferIterator iterator = mSourceBuffer->Iterator(1);
+
+  // Write a single byte to the buffer and complete the buffer. (We have to
+  // write at least one byte because completing a zero length buffer always
+  // fails; see the ZeroLengthBufferAlwaysFails test.)
+  CheckedAppendToBuffer(mData, 1);
+  CheckedCompleteBuffer(iterator, 1);
+
+  // We should be able to advance once (to read the single byte) and then should
+  // reach the COMPLETE state with a successful status.
+  CheckedAdvanceIterator(iterator, 1);
+  CheckIteratorIsComplete(iterator, 1);
+}
+
+TEST_F(ImageSourceBuffer, CompleteSuccessWithSmallerReadLength) {
+  // Create an iterator limited to one byte.
+  SourceBufferIterator iterator = mSourceBuffer->Iterator(1);
+
+  // Write two bytes to the buffer and complete the buffer. (We have to
+  // write at least one byte because completing a zero length buffer always
+  // fails; see the ZeroLengthBufferAlwaysFails test.)
+  CheckedAppendToBuffer(mData, 2);
+  CheckedCompleteBuffer(iterator, 2);
+
+  // We should be able to advance once (to read the single byte) and then should
+  // reach the COMPLETE state with a successful status, because our iterator is
+  // limited to a single byte, rather than the full length.
+  CheckedAdvanceIterator(iterator, 1);
+  CheckIteratorIsComplete(iterator, 1);
+}
+
+TEST_F(ImageSourceBuffer, CompleteSuccessWithGreaterReadLength) {
+  // Create an iterator limited to one byte.
+  SourceBufferIterator iterator = mSourceBuffer->Iterator(2);
+
+  // Write a single byte to the buffer and complete the buffer. (We have to
+  // write at least one byte because completing a zero length buffer always
+  // fails; see the ZeroLengthBufferAlwaysFails test.)
+  CheckedAppendToBuffer(mData, 1);
+  CheckedCompleteBuffer(iterator, 1);
+
+  // We should be able to advance once (to read the single byte) and then should
+  // reach the COMPLETE state with a successful status. Our iterator lets us
+  // read more but the underlying buffer has been completed.
+  CheckedAdvanceIterator(iterator, 1);
+  CheckIteratorIsComplete(iterator, 1);
+}