예제 #1
0
		void ReadHeader() 
		{
			// 1. Check the two magic bytes
			Crc32 headCRC = new Crc32();
			int magic = baseInputStream.ReadByte();

			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();

			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 = baseInputStream.ReadByte();

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

				if (baseInputStream.ReadByte() < 0 || baseInputStream.ReadByte() < 0) {
					throw new EndOfStreamException("EOS reading GZIP header");
				}
				
				int len1, len2;
				len1 = baseInputStream.ReadByte();
				len2 = baseInputStream.ReadByte();
				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 = baseInputStream.ReadByte();
					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 = baseInputStream.ReadByte()) > 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 = baseInputStream.ReadByte()) > 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 = baseInputStream.ReadByte();
				if (crcval < 0) {
					throw new EndOfStreamException("EOS reading GZIP header");
				}
				
				tempByte = baseInputStream.ReadByte();
				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;
		}
예제 #2
0
        /// <summary>Calculates the CRC32 check-sum on specified portion of a buffer.</summary>
        /// <param name="data">Data buffer to perform check-sum on.</param>
        /// <param name="startIndex">Starts index in data buffer to begin check-sum.</param>
        /// <param name="length">Total number of bytes from <paramref name="startIndex">startIndex</paramref> to
        /// perform check-sum over.</param>
        /// <returns>Computed CRC32 checksum over the specified portion of the buffer.</returns>
        public static uint Crc32Checksum(this byte[] data, int startIndex, int length)
        {
            Crc32 checksum = new Crc32();

            checksum.Update(data, startIndex, length);

            return checksum.Value;
        }
예제 #3
0
		/// <summary>
		/// Closes the zip input stream
		/// </summary>
		public override void Close()
		{
			internalReader = new ReadDataHandler(ReadingNotAvailable);
			crc = null;
			entry = null;

			base.Close();
		}