public void BuildDelta(Stream newFileStream, IOctodiffSignatureReader signatureReader, IOctodiffDeltaWriter deltaWriter)
{
var signature = signatureReader.ReadSignature();
var chunks = signature.Chunks;
var newFileHash = signature.HashAlgorithm.ComputeHash(newFileStream);
newFileStream.Seek(0, SeekOrigin.Begin);
deltaWriter.WriteMetadata(signature.HashAlgorithm, newFileHash);
chunks = OrderChunksByChecksum(chunks);
var chunkMap = CreateChunkMap(chunks, out int maxChunkSize, out int minChunkSize);
var buffer = new byte[readBufferSize];
long lastMatchPosition = 0;
while (true)
{
var startPosition = newFileStream.Position;
var read = newFileStream.Read(buffer, 0, buffer.Length);
if (read < 0)
{
break;
}
var checksumAlgorithm = signature.RollingChecksumAlgorithm;
uint checksum = 0;
var remainingPossibleChunkSize = maxChunkSize;
for (var i = 0; i < read - minChunkSize + 1; i++)
{
var readSoFar = startPosition + i;
var remainingBytes = read - i;
if (remainingBytes < maxChunkSize)
{
remainingPossibleChunkSize = minChunkSize;
}
if (i == 0 || remainingBytes < maxChunkSize)
{
checksum = checksumAlgorithm.Calculate(buffer, i, remainingPossibleChunkSize);
}
else
{
var remove = buffer[i - 1];
var add = buffer[i + remainingPossibleChunkSize - 1];
checksum = checksumAlgorithm.Rotate(checksum, remove, add, remainingPossibleChunkSize);
}
if (readSoFar - (lastMatchPosition - remainingPossibleChunkSize) < remainingPossibleChunkSize)
{
continue;
}
if (!chunkMap.ContainsKey(checksum))
{
continue;
}
var startIndex = chunkMap[checksum];
for (var j = startIndex; j < chunks.Count && chunks[j].RollingChecksum == checksum; j++)
{
var chunk = chunks[j];
var hash = signature.HashAlgorithm.ComputeHash(buffer, i, remainingPossibleChunkSize);
if (StructuralComparisons.StructuralEqualityComparer.Equals(hash, chunks[j].Hash))
{
readSoFar = readSoFar + remainingPossibleChunkSize;
var missing = readSoFar - lastMatchPosition;
if (missing > remainingPossibleChunkSize)
{
deltaWriter.WriteDataCommand(newFileStream, lastMatchPosition, missing - remainingPossibleChunkSize);
}
deltaWriter.WriteCopyCommand(new DataRange(chunk.StartOffset, chunk.Length));
lastMatchPosition = readSoFar;
break;
}
}
}
if (read < buffer.Length)
{
break;
}
newFileStream.Position = newFileStream.Position - maxChunkSize + 1;
}
if (newFileStream.Length != lastMatchPosition)
{
deltaWriter.WriteDataCommand(newFileStream, lastMatchPosition, newFileStream.Length - lastMatchPosition);
}
deltaWriter.Finish();
}
public void WriteMetadata(IHashAlgorithm hashAlgorithm, byte[] expectedNewFileHash)
{
decorated.WriteMetadata(hashAlgorithm, expectedNewFileHash);
}