/// <summary>
/// Generates a delta file from input, and writes it to output
/// </summary>
/// <param name="sourceData">The stream to generate the delta from</param>
/// <param name="deltaData">The stream to write the delta to</param>
public static void GenerateDeltaFile(Stream sourceData, Stream deltaData, ChecksumFileReader checksumFile)
{
#region variables
// The matched data block
DeltaBlock <long> matchedBufferIndex;
// The unmatched data block
DeltaBlock <int> unmatchedBufferIndex;
// The buffer block
DeltaBlock <int> bufferIndex;
// The moving frame that looks for the blocks
BlockLookup lookup;
byte[] workingData;
byte[] tempWork;
uint weakChecksum;
int lastPossibleBlock;
int remainingBytes;
bool loadBuffer = false;
bool recalculateWeakChecksum = false;
bool streamExhausted = false;
bool doesWeakChecksumExist;
bool finishedDeltaRun;
int tempRead;
#endregion
#region Initialize the iteration
matchedBufferIndex = new DeltaBlock <long>(0, 0);
unmatchedBufferIndex = new DeltaBlock <int>(0, 0);
bufferIndex = new DeltaBlock <int>(0, 0);
lookup = new BlockLookup(checksumFile.BlockLength);
//We use statically allocated buffers, and we need two buffers
// to prevent Array.Copy from allocating a temp buffer
workingData = new byte[BUFFER_SIZE];
tempWork = new byte[BUFFER_SIZE];
loadBuffer = false;
recalculateWeakChecksum = false;
streamExhausted = false;
finishedDeltaRun = false;
#endregion
//Read the initial buffer block
bufferIndex.Size = Utility.ForceStreamRead(sourceData, workingData);
lookup.BlockLength = Math.Min(lookup.BlockLength, bufferIndex.Size);
//Setup the initial checksum
//Calculate the Adler checksum of the buffer
weakChecksum = Adler32Checksum.Calculate(workingData, 0, lookup.BlockLength);
lookup.ResetMatchIndex();
while (lookup.BlockLength > 0)
{
//Check if the block matches somewhere, if we have force-reloaded the buffer,
//the check has already been made
if (loadBuffer)
{
loadBuffer = false;
}
else
{
lookup.MatchedIndex = checksumFile.LookupChunck(
weakChecksum,
workingData,
bufferIndex.Offset,
lookup.BlockLength,
lookup.NextMatchKey);
}
if (lookup.IsMatch)
{
// We have a match, flush the unmatched chunk into the result
// But the match is offset.
CommitUnmatchedData(workingData, unmatchedBufferIndex, deltaData);
// Matched a stream chunk in the weak checksum. We don't yet know where the actual chunk is.
// Find the chunk
LookupMatch(matchedBufferIndex, bufferIndex, lookup, deltaData);
if (bufferIndex.Size - bufferIndex.Offset < lookup.BlockLength)
{
//If this is the last chunck, compare to the last hash
if (finishedDeltaRun)
{
lookup.BlockLength = Math.Min(lookup.BlockLength, bufferIndex.Size - bufferIndex.Offset);
}
else //We are out of buffer, reload
{
recalculateWeakChecksum = true;
}
}
//Reset the checksum to fit the new block, but skip it if we are out of data
if (!recalculateWeakChecksum)
{
weakChecksum = Adler32Checksum.Calculate(workingData, bufferIndex.Offset, lookup.BlockLength);
}
}
else
{
//At this point we have not advanced the buffer_index, so the weak_checksum matches the data,
// even if we arrive here after reloading the buffer
//No match, flush accumulated matches, if any
if (matchedBufferIndex.Size > 0)
{
//Send the matching bytes as a copy
WriteCopy(matchedBufferIndex, deltaData);
matchedBufferIndex.Reset(0, 0);
//We do not immediately start tapping the unmatched bytes,
// because the buffer may be nearly empty, and we
// want to gather as many unmatched bytes as possible
// to avoid the instruction overhead in the file
if (bufferIndex.Offset != 0)
{
loadBuffer = true;
}
}
else
{
// No match
lastPossibleBlock = bufferIndex.Size - lookup.BlockLength;
if (unmatchedBufferIndex.Size == 0)
{
unmatchedBufferIndex.Offset = bufferIndex.Offset;
}
doesWeakChecksumExist = false;
//Local speedup for long non-matching regions
while (bufferIndex.Offset < lastPossibleBlock && !doesWeakChecksumExist)
{
//Roll the weak checksum buffer by 1 byte until you find a match or you reach the end
weakChecksum = Adler32Checksum.Roll(
workingData[bufferIndex.Offset],
workingData[bufferIndex.Offset + lookup.BlockLength],
weakChecksum,
lookup.BlockLength);
//Check if the new weak checksum roll is a match
doesWeakChecksumExist = checksumFile.DoesWeakExist(weakChecksum >> 16);
//Update offset for future reference
bufferIndex.Offset++;
}
// Calculating the unmatched chunk size
unmatchedBufferIndex.Size = bufferIndex.Offset - unmatchedBufferIndex.Offset;
//If this is the last block, claim the remaining bytes as unmatched
if (finishedDeltaRun)
{
//There may be a minor optimization possible here, as the last chunk of the original file may still fit
// and be smaller than the block length
unmatchedBufferIndex.Size += lookup.BlockLength;
lookup.BlockLength = 0;
}
}
}
//If we are out of buffer, try to load some more
if (loadBuffer || bufferIndex.Size - bufferIndex.Offset <= checksumFile.BlockLength)
{
// This section will flush the located unmatched into the delta stream(if any)
// And will refill the working buffer with the remainder of the previous buffer
// And fresh data from the source stream
//The number of unused bytes the the buffer
remainingBytes = bufferIndex.Size - bufferIndex.Offset;
//If we have read the last bytes or the buffer is already full, skip this
if (!finishedDeltaRun && tempWork.Length - remainingBytes > 0)
{
// Load the delta amount of data into temp work buffer
Buffer.BlockCopy(workingData, bufferIndex.Offset, tempWork, 0, remainingBytes);
//Prevent reading the stream after it has been exhausted because some streams break on that
if (streamExhausted)
{
tempRead = 0;
}
else
{
// Fill the remainder of tempWork from the source data
tempRead = Utility.ForceStreamRead(
sourceData,
tempWork,
remainingBytes,
tempWork.Length - remainingBytes);
}
// If anything was read
if (tempRead > 0)
{
//We are about to discard some data, if it is unmatched, write it to stream
CommitUnmatchedData(workingData, unmatchedBufferIndex, deltaData);
//Now swap the arrays
SwapBuffers(ref workingData, ref tempWork);
bufferIndex.Offset = 0;
bufferIndex.Size = remainingBytes + tempRead;
}
else
{
//Prevent reading the stream after it has been exhausted because some streams break on that
streamExhausted = true;
if (remainingBytes <= checksumFile.BlockLength)
{
//Mark as done
finishedDeltaRun = true;
//The last round has a smaller block length
lookup.BlockLength = remainingBytes;
}
}
//If we run out of buffer, we may need to recalculate the checksum
if (recalculateWeakChecksum)
{
weakChecksum = Adler32Checksum.Calculate(workingData, bufferIndex.Offset, lookup.BlockLength);
recalculateWeakChecksum = false;
}
}
}
}
//There cannot be both matched and unmatched bytes written
if (matchedBufferIndex.Size > 0 && unmatchedBufferIndex.Size > 0)
{
throw new Exception(Strings.DeltaFile.InternalBufferError);
}
//Commit all remaining matched content
if (matchedBufferIndex.Size > 0)
{
WriteCopy(matchedBufferIndex, deltaData);
}
//Commit all remaining unmatched content
CommitUnmatchedData(workingData, unmatchedBufferIndex, deltaData);
//Write end command
deltaData.WriteByte((byte)RDiffBinary.EndCommand);
deltaData.Flush();
}
private static void LookupMatch(DeltaBlock <long> matched, DeltaBlock <int> buffer, BlockLookup lookup, Stream output)
{
//First match
if (matched.Size == 0)
{
// Applying the lookup offset to the match
matched.Offset = lookup.MatchedIndex * lookup.BlockLength;
}
else if (!lookup.DoesSequenceFit)
{
//Subsequent match, but the sequence does not fit
WriteCopy(matched, output);
//Pretend this was the first block
matched.Size = 0;
matched.Offset = lookup.MatchedIndex * lookup.BlockLength;
}
//If the next block matches this signature, we can write larger
// copy instructions and thus safe space
lookup.NextMatchKey = lookup.MatchedIndex + 1;
//Adjust the counters
matched.Size += lookup.BlockLength;
buffer.Offset += lookup.BlockLength;
}
