public static bool VerifyHash(byte[] array, ref int offset)
{
ulong expected = SipHash.ComputeHash(array, 0, offset);
ulong actual = UInt64LE.Read(array, ref offset);
return(expected == actual);
}
public void WriteTo(byte[] array)
{
Debug.Assert(array.Length >= Size);
Debug.Assert(Format.IsValidPosition(ChunkBeginPosition));
int offset = 0;
UInt64LE.Write(array, ref offset, (ulong)ChunkBeginPosition);
UInt64LE.Write(array, ref offset, SipHash.ComputeHash(array, 0, offset));
}
public void WriteTo(byte[] array)
{
Debug.Assert(array.Length >= Size);
Debug.Assert(Format.IsValidContentLength(ContentLength));
int offset = 0;
UserData.WriteTo(array, ref offset);
UInt64LE.Write(array, ref offset, (ulong)ContentLength);
UInt64LE.Write(array, ref offset, ContentHash);
UInt64LE.Write(array, ref offset, SipHash.ComputeHash(array, 0, offset));
}
public async Task WriteAsync(UserData userData, byte[] array, int offset, int count)
{
if (array == null)
{
throw new ArgumentNullException(nameof(array));
}
if (offset < 0 || count < 0 || array.Length - offset < count)
{
throw new Exception($"Invalid range for array of length {array.Length}: [{offset}, {offset} + {count})");
}
if (count > MaxContentLength)
{
throw new Exception($"Chunk too big: {count}");
}
if (_torn)
{
await WritePadding();
_torn = false;
}
var meter = new Meter()
{
ChunkBeginPosition = _writer.Position
};
var header = new ChunkHeader()
{
UserData = userData,
ContentLength = count,
ContentHash = SipHash.ComputeHash(array, offset, count),
};
if (!header.EndPosition(meter.ChunkBeginPosition).HasValue)
{
throw new Exception($"File too big: {meter.ChunkBeginPosition}");
}
meter.WriteTo(_meter);
header.WriteTo(_header);
try {
await WriteMetered(_header, 0, _header.Length);
await WriteMetered(array, offset, count);
}
catch {
_torn = true;
throw;
}
}
// Returns true if it's safe to read the chunk after the specified chunk. There are
// two cases where blindly reading the next chunk can backfire:
//
// 1. By reading the next chunk you'll actually skip valid chunks. So the chunk you'll read
// won't really be the next.
// 2. Even if the next chunk decodes correctly (both its header and content hashes match),
// it may be not a real chunk but a part of some larger chunk's content.
//
// To see these horrors in action, replace the implementation of this method with `return true`
// and run tests. TrickyTruncateTest() and TrickyEmbedTest() should fail. They correspond to the
// two cases described above. Note that there is no malicious action in these tests. The chunkio
// files are produced by ChunkWriter. There are also file truncations, but they can naturally
// happen when a processing with ChunkWriter crashes.
async Task <bool> IsSkippable(long begin, ChunkHeader header)
{
long end = header.EndPosition(begin).Value;
if (begin / MeterInterval == (end - 1) / MeterInterval)
{
return(true);
}
Meter?meter = await ReadMeter(MeterBefore(end - 1));
if (meter.HasValue)
{
return(meter.Value.ChunkBeginPosition == begin);
}
var content = new byte[header.ContentLength];
long pos = MeteredPosition(begin, ChunkHeader.Size).Value;
return(await ReadMetered(pos, content, 0, content.Length) && SipHash.ComputeHash(content) == header.ContentHash);
}
public async Task <bool> ReadContentAsync(byte[] array, int offset)
{
if (array == null)
{
throw new ArgumentNullException(nameof(array));
}
if (offset < 0)
{
throw new ArgumentException($"Negative offset: {offset}");
}
if (array.Length - offset < ContentLength)
{
throw new ArgumentException($"Array too short: {array.Length}");
}
long pos = MeteredPosition(BeginPosition, ChunkHeader.Size).Value;
_skippable = await _reader.ReadMetered(pos, array, offset, ContentLength) &&
SipHash.ComputeHash(array, offset, ContentLength) == _header.ContentHash;
return(_skippable.Value);
}
