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(SR.GetString(SR.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(SR.GetString(SR.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(SR.GetString(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 & (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(SR.GetString(SR.UnknownState));
}
}
}
public bool ReadFooter(InputBuffer input) {
input.SkipToByteBoundary();
if (gzipFooterSubstate == GzipHeaderState.ReadingCRC) {
while (loopCounter < 4) {
int bits = input.GetBits(8);
if (bits < 0) {
return false;
}
expectedCrc32 |= ((uint)bits << (8 * loopCounter));
loopCounter++;
}
gzipFooterSubstate = GzipHeaderState.ReadingFileSize;
loopCounter = 0;
}
if (gzipFooterSubstate == GzipHeaderState.ReadingFileSize) {
if (loopCounter == 0)
expectedOutputStreamSizeModulo = 0;
while (loopCounter < 4) {
int bits = input.GetBits(8);
if (bits < 0) {
return false;
}
expectedOutputStreamSizeModulo |= ((uint) bits << (8 * loopCounter));
loopCounter++;
}
}
return true;
}
