public bool ReadGzipHeader()
{
while (true)
{
int bits;
switch (gzipHeaderSubstate)
{
case GZIPHeaderState.ReadingID1:
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
if (bits != 0x1F)
{
throw new InvalidDataException("SR.CorruptedGZipHeader");
}
gzipHeaderSubstate = GZIPHeaderState.ReadingID2;
goto case GZIPHeaderState.ReadingID2;
case GZIPHeaderState.ReadingID2:
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
if (bits != 0x8b)
{
throw new InvalidDataException("SR.CorruptedGZipHeader");
}
gzipHeaderSubstate = GZIPHeaderState.ReadingCM;
goto case GZIPHeaderState.ReadingCM;
case GZIPHeaderState.ReadingCM:
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
if (bits != 0x8)
{ // compression mode must be 8 (deflate)
throw new InvalidDataException("SR.UnknownCompressionMode");
}
gzipHeaderSubstate = GZIPHeaderState.ReadingFLG;;
goto case GZIPHeaderState.ReadingFLG;
case GZIPHeaderState.ReadingFLG:
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
gzip_header_flag = bits;
gzipHeaderSubstate = GZIPHeaderState.ReadingMMTime;
loopCounter = 0; // 4 MMTIME bytes
goto case GZIPHeaderState.ReadingMMTime;
case GZIPHeaderState.ReadingMMTime:
bits = 0;
while (loopCounter < 4)
{
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
loopCounter++;
}
gzipHeaderSubstate = GZIPHeaderState.ReadingXFL;
loopCounter = 0;
goto case GZIPHeaderState.ReadingXFL;
case GZIPHeaderState.ReadingXFL: // ignore XFL
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
gzipHeaderSubstate = GZIPHeaderState.ReadingOS;
goto case GZIPHeaderState.ReadingOS;
case GZIPHeaderState.ReadingOS: // ignore OS
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
gzipHeaderSubstate = GZIPHeaderState.ReadingXLen1;
goto case GZIPHeaderState.ReadingXLen1;
case GZIPHeaderState.ReadingXLen1:
if ((gzip_header_flag & ExtraFieldsFlag) == 0)
{
goto case GZIPHeaderState.ReadingFileName;
}
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
gzip_header_xlen = bits;
gzipHeaderSubstate = GZIPHeaderState.ReadingXLen2;
goto case GZIPHeaderState.ReadingXLen2;
case GZIPHeaderState.ReadingXLen2:
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
gzip_header_xlen |= (bits << 8);
gzipHeaderSubstate = GZIPHeaderState.ReadingXLenData;
loopCounter = 0; // 0 bytes of XLEN data read so far
goto case GZIPHeaderState.ReadingXLenData;
case GZIPHeaderState.ReadingXLenData:
bits = 0;
while (loopCounter < gzip_header_xlen)
{
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
loopCounter++;
}
gzipHeaderSubstate = GZIPHeaderState.ReadingFileName;
loopCounter = 0;
goto case GZIPHeaderState.ReadingFileName;
case GZIPHeaderState.ReadingFileName:
if ((gzip_header_flag & FileNameFlag) == 0)
{
gzipHeaderSubstate = GZIPHeaderState.ReadingComment;
goto case GZIPHeaderState.ReadingComment;
}
do
{
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
if (bits == 0)
{ // see '\0' in the file name string
break;
}
} while (true);
gzipHeaderSubstate = GZIPHeaderState.ReadingComment;
goto case GZIPHeaderState.ReadingComment;
case GZIPHeaderState.ReadingComment:
if ((gzip_header_flag & CommentFlag) == 0)
{
gzipHeaderSubstate = GZIPHeaderState.ReadingCRC16Part1;
goto case GZIPHeaderState.ReadingCRC16Part1;
}
do
{
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
if (bits == 0)
{ // see '\0' in the file name string
break;
}
} while (true);
gzipHeaderSubstate = GZIPHeaderState.ReadingCRC16Part1;
goto case GZIPHeaderState.ReadingCRC16Part1;
case GZIPHeaderState.ReadingCRC16Part1:
if ((gzip_header_flag & CRCFlag) == 0)
{
gzipHeaderSubstate = GZIPHeaderState.Done;
goto case GZIPHeaderState.Done;
}
bits = input.GetBits(8); // ignore crc
if (bits < 0)
{
return(false);
}
gzipHeaderSubstate = GZIPHeaderState.ReadingCRC16Part2;
goto case GZIPHeaderState.ReadingCRC16Part2;
case GZIPHeaderState.ReadingCRC16Part2:
bits = input.GetBits(8); // ignore crc
if (bits < 0)
{
return(false);
}
gzipHeaderSubstate = GZIPHeaderState.Done;
goto case GZIPHeaderState.Done;
case GZIPHeaderState.Done:
return(true);
default:
Debug.Assert(false, "We should not reach unknown state!");
throw new InvalidDataException("SR.UnknownState");
}
}
}
//Each block of compressed data begins with 3 header bits
// containing the following data:
// first bit BFINAL
// next 2 bits BTYPE
// Note that the header bits do not necessarily begin on a byte
// boundary, since a block does not necessarily occupy an integral
// number of bytes.
// BFINAL is set if and only if this is the last block of the data
// set.
// BTYPE specifies how the data are compressed, as follows:
// 00 - no compression
// 01 - compressed with fixed Huffman codes
// 10 - compressed with dynamic Huffman codes
// 11 - reserved (error)
// The only difference between the two compressed cases is how the
// Huffman codes for the literal/length and distance alphabets are
// defined.
//
// This function returns true for success (end of block or output window is full,)
// false if we are short of input
//
private bool Decode()
{
bool eob = false;
bool result = false;
if (Finished())
{
return true;
}
if (_usingGzip)
{
if (_state == InflaterState.ReadingGZIPHeader)
{
if (!_gZipDecoder.ReadGzipHeader())
{
return false;
}
_state = InflaterState.ReadingBFinal;
}
else if (_state == InflaterState.StartReadingGZIPFooter || _state == InflaterState.ReadingGZIPFooter)
{
if (!_gZipDecoder.ReadGzipFooter())
return false;
_state = InflaterState.VerifyingGZIPFooter;
return true;
}
}
if (_state == InflaterState.ReadingBFinal)
{
// reading bfinal bit
// Need 1 bit
if (!_input.EnsureBitsAvailable(1))
return false;
_bfinal = _input.GetBits(1);
_state = InflaterState.ReadingBType;
}
if (_state == InflaterState.ReadingBType)
{
// Need 2 bits
if (!_input.EnsureBitsAvailable(2))
{
_state = InflaterState.ReadingBType;
return false;
}
blockType = (BlockType) _input.GetBits(2);
if (blockType == BlockType.Dynamic)
{
_state = InflaterState.ReadingNumLitCodes;
}
else if (blockType == BlockType.Static)
{
_literalLengthTree = HuffmanTree.StaticLiteralLengthTree;
_distanceTree = HuffmanTree.StaticDistanceTree;
_state = InflaterState.DecodeTop;
}
else if (blockType == BlockType.Uncompressed)
{
_state = InflaterState.UncompressedAligning;
}
else
{
throw new InvalidDataException("SR.UnknownBlockType");
}
}
if (blockType == BlockType.Dynamic)
{
if (_state < InflaterState.DecodeTop)
{
// we are reading the header
result = DecodeDynamicBlockHeader();
}
else
{
result = DecodeBlock(out eob); // this can returns true when output is full
}
}
else if (blockType == BlockType.Static)
{
result = DecodeBlock(out eob);
}
else if (blockType == BlockType.Uncompressed)
{
result = DecodeUncompressedBlock(out eob);
}
else
{
throw new InvalidDataException("SR.UnknownBlockType");
}
//
// If we reached the end of the block and the block we were decoding had
// bfinal=1 (final block)
//
if (eob && (_bfinal != 0))
{
if (_usingGzip)
_state = InflaterState.StartReadingGZIPFooter;
else
_state = InflaterState.Done;
}
return result;
}