public bool ReadHeader(InputBuffer input)
{
while (true)
{
int bits;
switch (gzipHeaderSubstate)
{
case GzipHeaderState.ReadingID1:
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
if (bits != GZipConstants.ID1)
{
throw new InvalidDataException("CorruptedGZipHeader");
}
gzipHeaderSubstate = GzipHeaderState.ReadingID2;
goto case GzipHeaderState.ReadingID2;
case GzipHeaderState.ReadingID2:
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
if (bits != GZipConstants.ID2)
{
throw new InvalidDataException("CorruptedGZipHeader");
}
gzipHeaderSubstate = GzipHeaderState.ReadingCM;
goto case GzipHeaderState.ReadingCM;
case GzipHeaderState.ReadingCM:
bits = input.GetBits(8);
if (bits < 0)
{
return(false);
}
if (bits != GZipConstants.Deflate)
{ // compression mode must be 8 (deflate)
throw new InvalidDataException("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 & (int)GZipOptionalHeaderFlags.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 & (int)GZipOptionalHeaderFlags.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 & (int)GZipOptionalHeaderFlags.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 & (int)GZipOptionalHeaderFlags.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("UnknownState");
}
}
}
