Ejemplo n.º 1
0
        bool ReadHeader()
        {
            // Initialize CRC for this block
            crc = new Crc32();

            // Make sure there is data in file. We can't rely on ReadLeByte() to fill the buffer, as this could be EOF,
            // which is fine, but ReadLeByte() throws an exception if it doesn't find data, so we do this part ourselves.
            if (inputBuffer.Available <= 0)
            {
                inputBuffer.Fill();
                if (inputBuffer.Available <= 0)
                {
                    // No header, EOF.
                    return false;
                }
            }

            // 1. Check the two magic bytes
            Crc32 headCRC = new Crc32();
            int magic = inputBuffer.ReadLeByte();

            if (magic < 0)
            {
                throw new EndOfStreamException("EOS reading GZIP header");
            }

            headCRC.Update(magic);
            if (magic != (GZipConstants.GZIP_MAGIC >> 8))
            {
                throw new GZipException("Error GZIP header, first magic byte doesn't match");
            }

            //magic = baseInputStream.ReadByte();
            magic = inputBuffer.ReadLeByte();

            if (magic < 0)
            {
                throw new EndOfStreamException("EOS reading GZIP header");
            }

            if (magic != (GZipConstants.GZIP_MAGIC & 0xFF))
            {
                throw new GZipException("Error GZIP header,  second magic byte doesn't match");
            }

            headCRC.Update(magic);

            // 2. Check the compression type (must be 8)
            int compressionType = inputBuffer.ReadLeByte();

            if (compressionType < 0)
            {
                throw new EndOfStreamException("EOS reading GZIP header");
            }

            if (compressionType != 8)
            {
                throw new GZipException("Error GZIP header, data not in deflate format");
            }
            headCRC.Update(compressionType);

            // 3. Check the flags
            int flags = inputBuffer.ReadLeByte();
            if (flags < 0)
            {
                throw new EndOfStreamException("EOS reading GZIP header");
            }
            headCRC.Update(flags);

            /*    This flag byte is divided into individual bits as follows:

            bit 0   FTEXT
            bit 1   FHCRC
            bit 2   FEXTRA
            bit 3   FNAME
            bit 4   FCOMMENT
            bit 5   reserved
            bit 6   reserved
            bit 7   reserved
            */

            // 3.1 Check the reserved bits are zero

            if ((flags & 0xE0) != 0)
            {
                throw new GZipException("Reserved flag bits in GZIP header != 0");
            }

            // 4.-6. Skip the modification time, extra flags, and OS type
            for (int i = 0; i < 6; i++)
            {
                int readByte = inputBuffer.ReadLeByte();
                if (readByte < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }
                headCRC.Update(readByte);
            }

            // 7. Read extra field
            if ((flags & GZipConstants.FEXTRA) != 0)
            {
                // Skip subfield id
                for (int i = 0; i < 2; i++)
                {
                    int readByte = inputBuffer.ReadLeByte();
                    if (readByte < 0)
                    {
                        throw new EndOfStreamException("EOS reading GZIP header");
                    }
                    headCRC.Update(readByte);
                }

                if (inputBuffer.ReadLeByte() < 0 || inputBuffer.ReadLeByte() < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }

                int len1, len2;
                len1 = inputBuffer.ReadLeByte();
                len2 = inputBuffer.ReadLeByte();
                if ((len1 < 0) || (len2 < 0))
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }
                headCRC.Update(len1);
                headCRC.Update(len2);

                int extraLen = (len1 << 8) | len2;
                for (int i = 0; i < extraLen; i++)
                {
                    int readByte = inputBuffer.ReadLeByte();
                    if (readByte < 0)
                    {
                        throw new EndOfStreamException("EOS reading GZIP header");
                    }
                    headCRC.Update(readByte);
                }
            }

            // 8. Read file name
            if ((flags & GZipConstants.FNAME) != 0)
            {
                int readByte;
                while ((readByte = inputBuffer.ReadLeByte()) > 0)
                {
                    headCRC.Update(readByte);
                }

                if (readByte < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }
                headCRC.Update(readByte);
            }

            // 9. Read comment
            if ((flags & GZipConstants.FCOMMENT) != 0)
            {
                int readByte;
                while ((readByte = inputBuffer.ReadLeByte()) > 0)
                {
                    headCRC.Update(readByte);
                }

                if (readByte < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }

                headCRC.Update(readByte);
            }

            // 10. Read header CRC
            if ((flags & GZipConstants.FHCRC) != 0)
            {
                int tempByte;
                int crcval = inputBuffer.ReadLeByte();
                if (crcval < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }

                tempByte = inputBuffer.ReadLeByte();
                if (tempByte < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }

                crcval = (crcval << 8) | tempByte;
                if (crcval != ((int)headCRC.Value & 0xffff))
                {
                    throw new GZipException("Header CRC value mismatch");
                }
            }

            readGZIPHeader = true;
            return true;
        }
Ejemplo n.º 2
0
        bool ReadHeader()
        {
            // Initialize CRC for this block
            crc = new Crc32();

            // Make sure there is data in file. We can't rely on ReadLeByte() to fill the buffer, as this could be EOF,
            // which is fine, but ReadLeByte() throws an exception if it doesn't find data, so we do this part ourselves.
            if (inputBuffer.Available <= 0)
            {
                inputBuffer.Fill();
                if (inputBuffer.Available <= 0)
                {
                    // No header, EOF.
                    return(false);
                }
            }

            // 1. Check the two magic bytes
            Crc32 headCRC = new Crc32();
            int   magic   = inputBuffer.ReadLeByte();

            if (magic < 0)
            {
                throw new EndOfStreamException("EOS reading GZIP header");
            }

            headCRC.Update(magic);
            if (magic != (GZipConstants.GZIP_MAGIC >> 8))
            {
                throw new GZipException("Error GZIP header, first magic byte doesn't match");
            }

            //magic = baseInputStream.ReadByte();
            magic = inputBuffer.ReadLeByte();

            if (magic < 0)
            {
                throw new EndOfStreamException("EOS reading GZIP header");
            }

            if (magic != (GZipConstants.GZIP_MAGIC & 0xFF))
            {
                throw new GZipException("Error GZIP header,  second magic byte doesn't match");
            }

            headCRC.Update(magic);

            // 2. Check the compression type (must be 8)
            int compressionType = inputBuffer.ReadLeByte();

            if (compressionType < 0)
            {
                throw new EndOfStreamException("EOS reading GZIP header");
            }

            if (compressionType != 8)
            {
                throw new GZipException("Error GZIP header, data not in deflate format");
            }
            headCRC.Update(compressionType);

            // 3. Check the flags
            int flags = inputBuffer.ReadLeByte();

            if (flags < 0)
            {
                throw new EndOfStreamException("EOS reading GZIP header");
            }
            headCRC.Update(flags);

            /*    This flag byte is divided into individual bits as follows:
             *
             * bit 0   FTEXT
             * bit 1   FHCRC
             * bit 2   FEXTRA
             * bit 3   FNAME
             * bit 4   FCOMMENT
             * bit 5   reserved
             * bit 6   reserved
             * bit 7   reserved
             */

            // 3.1 Check the reserved bits are zero

            if ((flags & 0xE0) != 0)
            {
                throw new GZipException("Reserved flag bits in GZIP header != 0");
            }

            // 4.-6. Skip the modification time, extra flags, and OS type
            for (int i = 0; i < 6; i++)
            {
                int readByte = inputBuffer.ReadLeByte();
                if (readByte < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }
                headCRC.Update(readByte);
            }

            // 7. Read extra field
            if ((flags & GZipConstants.FEXTRA) != 0)
            {
                // Skip subfield id
                for (int i = 0; i < 2; i++)
                {
                    int readByte = inputBuffer.ReadLeByte();
                    if (readByte < 0)
                    {
                        throw new EndOfStreamException("EOS reading GZIP header");
                    }
                    headCRC.Update(readByte);
                }

                if (inputBuffer.ReadLeByte() < 0 || inputBuffer.ReadLeByte() < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }

                int len1, len2;
                len1 = inputBuffer.ReadLeByte();
                len2 = inputBuffer.ReadLeByte();
                if ((len1 < 0) || (len2 < 0))
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }
                headCRC.Update(len1);
                headCRC.Update(len2);

                int extraLen = (len1 << 8) | len2;
                for (int i = 0; i < extraLen; i++)
                {
                    int readByte = inputBuffer.ReadLeByte();
                    if (readByte < 0)
                    {
                        throw new EndOfStreamException("EOS reading GZIP header");
                    }
                    headCRC.Update(readByte);
                }
            }

            // 8. Read file name
            if ((flags & GZipConstants.FNAME) != 0)
            {
                int readByte;
                while ((readByte = inputBuffer.ReadLeByte()) > 0)
                {
                    headCRC.Update(readByte);
                }

                if (readByte < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }
                headCRC.Update(readByte);
            }

            // 9. Read comment
            if ((flags & GZipConstants.FCOMMENT) != 0)
            {
                int readByte;
                while ((readByte = inputBuffer.ReadLeByte()) > 0)
                {
                    headCRC.Update(readByte);
                }

                if (readByte < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }

                headCRC.Update(readByte);
            }

            // 10. Read header CRC
            if ((flags & GZipConstants.FHCRC) != 0)
            {
                int tempByte;
                int crcval = inputBuffer.ReadLeByte();
                if (crcval < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }

                tempByte = inputBuffer.ReadLeByte();
                if (tempByte < 0)
                {
                    throw new EndOfStreamException("EOS reading GZIP header");
                }

                crcval = (crcval << 8) | tempByte;
                if (crcval != ((int)headCRC.Value & 0xffff))
                {
                    throw new GZipException("Header CRC value mismatch");
                }
            }

            readGZIPHeader = true;
            return(true);
        }