// Copy the compressed bytes to output buffer as a block. maxBytesToCopy limits the number of
// bytes we can copy from input. Set to any value < 1 if no limit
internal void GetBlock(DeflateInput input, OutputBuffer output, int maxBytesToCopy) {
Debug.Assert(InputAvailable(input), "call SetInput before trying to compress!");
WriteDeflatePreamble(output);
GetCompressedOutput(input, output, maxBytesToCopy);
WriteEndOfBlock(output);
}
// maxBytesToCopy limits the number of bytes we can copy from input. Set to any value < 1 if no limit
private void GetCompressedOutput(DeflateInput input, OutputBuffer output, int maxBytesToCopy) {
// snapshot for compression ratio stats
int bytesWrittenPre = output.BytesWritten;
int bytesConsumedFromInput = 0;
int inputBytesPre = BytesInHistory + input.Count;
do {
// read more input data into the window if there is space available
int bytesToCopy = (input.Count < inputWindow.FreeWindowSpace) ?
input.Count : inputWindow.FreeWindowSpace;
if (maxBytesToCopy >= 1) {
bytesToCopy = Math.Min(bytesToCopy, maxBytesToCopy - bytesConsumedFromInput);
}
if (bytesToCopy > 0) {
// copy data into history window
inputWindow.CopyBytes(input.Buffer, input.StartIndex, bytesToCopy);
input.ConsumeBytes(bytesToCopy);
bytesConsumedFromInput += bytesToCopy;
}
GetCompressedOutput(output);
} while (SafeToWriteTo(output) && InputAvailable(input) && (maxBytesToCopy < 1 || bytesConsumedFromInput < maxBytesToCopy));
// determine compression ratio, save
int bytesWrittenPost = output.BytesWritten;
int bytesWritten = bytesWrittenPost - bytesWrittenPre;
int inputBytesPost = BytesInHistory + input.Count;
int totalBytesConsumed = inputBytesPre - inputBytesPost;
if (bytesWritten != 0) {
lastCompressionRatio = (double)bytesWritten / (double)totalBytesConsumed;
}
}
internal DeflaterManaged() {
deflateEncoder = new FastEncoder();
copyEncoder = new CopyEncoder();
input = new DeflateInput();
output = new OutputBuffer();
processingState = DeflaterState.NotStarted;
}
// null input means write an empty payload with formatting info. This is needed for the final block.
public void GetBlock(DeflateInput input, OutputBuffer output, bool isFinal) {
Debug.Assert(output != null);
Debug.Assert(output.FreeBytes >= PaddingSize);
// determine number of bytes to write
int count = 0;
if (input != null) {
// allow space for padding and bits not yet flushed to buffer
count = Math.Min(input.Count, output.FreeBytes - PaddingSize - output.BitsInBuffer);
// we don't expect the output buffer to ever be this big (currently 4K), but we'll check this
// just in case that changes.
if (count > MaxUncompressedBlockSize - PaddingSize) {
count = MaxUncompressedBlockSize - PaddingSize;
}
}
// write header and flush bits
if (isFinal) {
output.WriteBits(FastEncoderStatics.BFinalNoCompressionHeaderBitCount,
FastEncoderStatics.BFinalNoCompressionHeader);
}
else {
output.WriteBits(FastEncoderStatics.NoCompressionHeaderBitCount,
FastEncoderStatics.NoCompressionHeader);
}
// now we're aligned
output.FlushBits();
// write len, nlen
WriteLenNLen((ushort)count, output);
// write uncompressed bytes
if (input != null && count > 0) {
output.WriteBytes(input.Buffer, input.StartIndex, count);
input.ConsumeBytes(count);
}
}
// Compress data but don't format as block (doesn't have header and footer)
internal void GetCompressedData(DeflateInput input, OutputBuffer output) {
GetCompressedOutput(input, output, -1);
}
private bool InputAvailable(DeflateInput input) {
return input.Count > 0 || BytesInHistory > 0;
}
int IDeflater.GetDeflateOutput(byte[] outputBuffer) {
Debug.Assert(outputBuffer != null, "Can't pass in a null output buffer!");
Debug.Assert(!NeedsInput(), "GetDeflateOutput should only be called after providing input");
output.UpdateBuffer(outputBuffer);
switch(processingState) {
case DeflaterState.NotStarted: {
// first call. Try to compress but if we get bad compression ratio, switch to uncompressed blocks.
Debug.Assert(deflateEncoder.BytesInHistory == 0, "have leftover bytes in window");
// save these in case we need to switch to uncompressed format
DeflateInput.InputState initialInputState = input.DumpState();
OutputBuffer.BufferState initialOutputState = output.DumpState();
deflateEncoder.GetBlockHeader(output);
deflateEncoder.GetCompressedData(input, output);
if (!UseCompressed(deflateEncoder.LastCompressionRatio)) {
// we're expanding; restore state and switch to uncompressed
input.RestoreState(initialInputState);
output.RestoreState(initialOutputState);
copyEncoder.GetBlock(input, output, false);
FlushInputWindows();
processingState = DeflaterState.CheckingForIncompressible;
}
else {
processingState = DeflaterState.CompressThenCheck;
}
break;
}
case DeflaterState.CompressThenCheck: {
// continue assuming data is compressible. If we reach data that indicates otherwise
// finish off remaining data in history and decide whether to compress on a
// block-by-block basis
deflateEncoder.GetCompressedData(input, output);
if (!UseCompressed(deflateEncoder.LastCompressionRatio)) {
processingState = DeflaterState.SlowDownForIncompressible1;
inputFromHistory = deflateEncoder.UnprocessedInput;
}
break;
}
case DeflaterState.SlowDownForIncompressible1: {
// finish off previous compressed block
deflateEncoder.GetBlockFooter(output);
processingState = DeflaterState.SlowDownForIncompressible2;
goto case DeflaterState.SlowDownForIncompressible2; // yeah I know, but there's no fallthrough
}
case DeflaterState.SlowDownForIncompressible2: {
// clear out data from history, but add them as uncompressed blocks
if (inputFromHistory.Count > 0) {
copyEncoder.GetBlock(inputFromHistory, output, false);
}
if (inputFromHistory.Count == 0) {
// now we're clean
deflateEncoder.FlushInput();
processingState = DeflaterState.CheckingForIncompressible;
}
break;
}
case DeflaterState.CheckingForIncompressible: {
// decide whether to compress on a block-by-block basis
Debug.Assert(deflateEncoder.BytesInHistory == 0, "have leftover bytes in window");
// save these in case we need to store as uncompressed
DeflateInput.InputState initialInputState = input.DumpState();
OutputBuffer.BufferState initialOutputState = output.DumpState();
// enforce max so we can ensure state between calls
deflateEncoder.GetBlock(input, output, CleanCopySize);
if (!UseCompressed(deflateEncoder.LastCompressionRatio)) {
// we're expanding; restore state and switch to uncompressed
input.RestoreState(initialInputState);
output.RestoreState(initialOutputState);
copyEncoder.GetBlock(input, output, false);
FlushInputWindows();
}
break;
}
case DeflaterState.StartingSmallData: {
// add compressed header and data, but not footer. Subsequent calls will keep
// adding compressed data (no header and no footer). We're doing this to
// avoid overhead of header and footer size relative to compressed payload.
deflateEncoder.GetBlockHeader(output);
processingState = DeflaterState.HandlingSmallData;
goto case DeflaterState.HandlingSmallData; // yeah I know, but there's no fallthrough
}
case DeflaterState.HandlingSmallData: {
// continue adding compressed data
deflateEncoder.GetCompressedData(input, output);
break;
}
}
return output.BytesWritten;
}
