/// <summary>
/// Tries to find a chunk in the chunk list which covers the given <paramref name="start"/> position.
/// </summary>
/// <param name="start">Start position.</param>
/// <param name="addChunkIfNotExists">If set to <c>true</c>, the requested chunk will be added to the cache if it doesn't exist yet.</param>
/// <param name="result">Returns the chunk or <c>null</c>, if no chunk was found for the given <paramref name="start"/> position.
/// The returned chunk might not be filled yet.</param>
/// <returns><c>true</c> if chunk was found.</returns>
protected bool GetMatchingChunk(long start, bool addChunkIfNotExists, out HttpRangeChunk result)
{
if (start >= 0 && start < _length)
{
for (int i = _chunkCache.Count - 1; i >= 0; i--)
{
HttpRangeChunk chunk = _chunkCache[i];
if (chunk.StartIndex <= start && chunk.EndIndex > start)
{
// Reorder LRU cache
_chunkCache.RemoveAt(i);
if (chunk.IsErroneous)
{
// Retry if a chunk was erroneous
break;
}
_chunkCache.Add(chunk);
result = chunk;
return(true);
}
}
if (addChunkIfNotExists)
{
AddChunk(start, out result);
return(true);
}
}
result = null;
return(false);
}
public override int Read(byte[] buffer, int offset, int count)
{
if (buffer == null)
{
throw new ArgumentNullException();
}
if (offset + count > buffer.Length)
{
throw new ArgumentException();
}
if (offset < 0 || count < 0)
{
throw new ArgumentOutOfRangeException();
}
if (_chunkCache == null)
{
throw new ObjectDisposedException("CachedMultiSegmentHttpStream");
}
if (_position >= _length)
{
return(0);
}
HttpRangeChunk chunk = ProvideReadAhead(_position, NUM_READAHEAD_CHUNKS);
if (chunk == null)
{
throw new IOException();
}
int numRead = chunk.Read(_position, buffer, offset, count);
_position += numRead;
return(numRead);
}
/// <summary>
/// Adds a new chunk to the cache and returns it.
/// </summary>
/// <param name="start">Start position.</param>
/// <param name="chunk">Returns the cache.</param>
/// <returns><c>true</c> if successful.</returns>
private void AddChunk(long start, out HttpRangeChunk chunk)
{
if (_chunkCache.Count == MAX_NUM_CACHES)
{
// Remove chunk which hasn't been used the longest time
_chunkCache[0].Dispose();
_chunkCache.RemoveAt(0);
}
_chunkCache.Add(chunk = new HttpRangeChunk(start, start + CHUNK_SIZE, Length, _url, _localIpAddress));
}
protected HttpRangeChunk ProvideReadAhead(long position, int numReadaheadChunks)
{
HttpRangeChunk result;
if (!GetMatchingChunk(position, true, out result))
{
return(null);
}
HttpRangeChunk currentChunk = result;
for (int i = numReadaheadChunks - 1; i > 0; i--)
{
if (!GetMatchingChunk(currentChunk.EndIndex, true, out currentChunk))
{
break;
}
}
return(result);
}
/// <summary>
/// Adds a new chunk to the cache and returns it.
/// </summary>
/// <param name="start">Start position.</param>
/// <param name="chunk">Returns the cache.</param>
/// <returns><c>true</c> if successful.</returns>
private void AddChunk(long start, out HttpRangeChunk chunk)
{
if (_chunkCache.Count == MAX_NUM_CACHES)
{
// Remove chunk which hasn't been used the longest time
_chunkCache[0].Dispose();
_chunkCache.RemoveAt(0);
}
_chunkCache.Add(chunk = new HttpRangeChunk(start, start + CHUNK_SIZE, Length, _url, _localIpAddress));
}
/// <summary>
/// Tries to find a chunk in the chunk list which covers the given <paramref name="start"/> position.
/// </summary>
/// <param name="start">Start position.</param>
/// <param name="addChunkIfNotExists">If set to <c>true</c>, the requested chunk will be added to the cache if it doesn't exist yet.</param>
/// <param name="result">Returns the chunk or <c>null</c>, if no chunk was found for the given <paramref name="start"/> position.
/// The returned chunk might not be filled yet.</param>
/// <returns><c>true</c> if chunk was found.</returns>
protected bool GetMatchingChunk(long start, bool addChunkIfNotExists, out HttpRangeChunk result)
{
if (start >= 0 && start < _length)
{
for (int i = _chunkCache.Count - 1; i >= 0; i--)
{
HttpRangeChunk chunk = _chunkCache[i];
if (chunk.StartIndex <= start && chunk.EndIndex > start)
{
// Reorder LRU cache
_chunkCache.RemoveAt(i);
if (chunk.IsErroneous)
// Retry if a chunk was erroneous
break;
_chunkCache.Add(chunk);
result = chunk;
return true;
}
}
if (addChunkIfNotExists)
{
AddChunk(start, out result);
return true;
}
}
result = null;
return false;
}
