1 files changed, 131 insertions, 0 deletions
diff --git a/dom/media/MediaSpan.h b/dom/media/MediaSpan.h
new file mode 100644
index 0000000000..4bb512a7dc
--- /dev/null
+++ b/dom/media/MediaSpan.h
@@ -0,0 +1,131 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+#if !defined(MediaSpan_h)
+#  define MediaSpan_h
+
+#  include "MediaData.h"
+#  include "mozilla/RefPtr.h"
+#  include "mozilla/Span.h"
+
+namespace mozilla {
+
+// A MediaSpan wraps a MediaByteBuffer and exposes a slice/span, or subregion,
+// of the buffer. This allows you to slice off a logical subregion without
+// needing to reallocate a new buffer to hold it. You can also append to a
+// MediaSpan without affecting other MediaSpans referencing the same buffer
+// (the MediaSpan receiving the append will allocate a new buffer to store its
+// result if necessary, to ensure other MediaSpans referencing its original
+// buffer are unaffected). Note there are no protections here that something
+// other than MediaSpans doesn't modify the underlying MediaByteBuffer while
+// a MediaSpan is alive.
+class MediaSpan {
+ public:
+  ~MediaSpan() = default;
+
+  explicit MediaSpan(const MediaSpan& aOther) = default;
+
+  MediaSpan(MediaSpan&& aOther) = default;
+
+  explicit MediaSpan(const RefPtr<MediaByteBuffer>& aBuffer)
+      : mBuffer(aBuffer), mStart(0), mLength(aBuffer ? aBuffer->Length() : 0) {
+    MOZ_DIAGNOSTIC_ASSERT(mBuffer);
+  }
+
+  explicit MediaSpan(MediaByteBuffer* aBuffer)
+      : mBuffer(aBuffer), mStart(0), mLength(aBuffer ? aBuffer->Length() : 0) {
+    MOZ_DIAGNOSTIC_ASSERT(mBuffer);
+  }
+
+  MediaSpan& operator=(const MediaSpan& aOther) = default;
+
+  static MediaSpan WithCopyOf(const RefPtr<MediaByteBuffer>& aBuffer) {
+    RefPtr<MediaByteBuffer> buffer = new MediaByteBuffer(aBuffer->Length());
+    buffer->AppendElements(*aBuffer);
+    return MediaSpan(buffer);
+  }
+
+  bool IsEmpty() const { return Length() == 0; }
+
+  // Note: It's unsafe to store the pointer returned by this function, as an
+  // append operation could cause the wrapped MediaByteBuffer to be
+  // reallocated, invalidating pointers previously returned by this function.
+  const uint8_t* Elements() const {
+    MOZ_DIAGNOSTIC_ASSERT(mStart < mBuffer->Length());
+    return mBuffer->Elements() + mStart;
+  }
+
+  size_t Length() const { return mLength; }
+
+  uint8_t operator[](size_t aIndex) const {
+    MOZ_DIAGNOSTIC_ASSERT(aIndex < Length());
+    return (*mBuffer)[mStart + aIndex];
+  }
+
+  bool Append(const MediaSpan& aBuffer) { return Append(aBuffer.Buffer()); }
+
+  bool Append(MediaByteBuffer* aBuffer) {
+    if (!aBuffer) {
+      return true;
+    }
+    if (mStart + mLength < mBuffer->Length()) {
+      // This MediaSpan finishes before the end of its buffer. The buffer
+      // could be shared with another MediaSpan. So we can't just append to
+      // the underlying buffer without risking damaging other MediaSpans' data.
+      // So we must reallocate a new buffer, copy our old data into it, and
+      // append the new data into it.
+      RefPtr<MediaByteBuffer> buffer =
+          new MediaByteBuffer(mLength + aBuffer->Length());
+      if (!buffer->AppendElements(Elements(), Length(), fallible) ||
+          !buffer->AppendElements(*aBuffer, fallible)) {
+        return false;
+      }
+      mBuffer = buffer;
+      mLength += aBuffer->Length();
+      return true;
+    }
+    if (!mBuffer->AppendElements(*aBuffer, fallible)) {
+      return false;
+    }
+    mLength += aBuffer->Length();
+    return true;
+  }
+
+  // Returns a new MediaSpan, spanning from the start of this span,
+  // up until aEnd.
+  MediaSpan To(size_t aEnd) const {
+    MOZ_DIAGNOSTIC_ASSERT(aEnd <= Length());
+    return MediaSpan(mBuffer, mStart, aEnd);
+  }
+
+  // Returns a new MediaSpan, spanning from aStart bytes offset from
+  // the start of this span, until the end of this span.
+  MediaSpan From(size_t aStart) const {
+    MOZ_DIAGNOSTIC_ASSERT(aStart <= Length());
+    return MediaSpan(mBuffer, mStart + aStart, Length() - aStart);
+  }
+
+  void RemoveFront(size_t aNumBytes) {
+    MOZ_DIAGNOSTIC_ASSERT(aNumBytes <= Length());
+    mStart += aNumBytes;
+    mLength -= aNumBytes;
+  }
+
+  MediaByteBuffer* Buffer() const { return mBuffer; }
+
+ private:
+  MediaSpan(MediaByteBuffer* aBuffer, size_t aStart, size_t aLength)
+      : mBuffer(aBuffer), mStart(aStart), mLength(aLength) {
+    MOZ_DIAGNOSTIC_ASSERT(mStart + mLength <= mBuffer->Length());
+  }
+
+  RefPtr<MediaByteBuffer> mBuffer;
+  size_t mStart = 0;
+  size_t mLength = 0;
+};
+
+}  // namespace mozilla
+
+#endif  // MediaSpan_h