inflaterinputstream.cs

用C#實現能產生PDF格式文件的源碼

				this.len = (int)baseInputStream.Length;
			} else {
				this.len = 0;
			}
		}
		
		/// <summary>
		/// Returns 0 once the end of the stream (EOF) has been reached.
		/// Otherwise returns 1.
		/// </summary>
		public virtual int Available {
			get {
				return inf.IsFinished ? 0 : 1;
			}
		}
		
		/// <summary>
		/// Closes the input stream.  When <see cref="IsStreamOwner"></see>
		/// is true the underlying stream is also closed.
		/// </summary>
		public override void Close()
		{
			if ( isStreamOwner ) {
				baseInputStream.Close();
			}
		}

		int readChunkSize = 0;

		/// <summary>
		/// Sets the size of chunks to read from the input stream
		/// 0 means as larger as possible.
		/// </summary>
		/// <remarks>
		/// Used to handle decryption where the length of stream is unknown.
		/// </remarks>
		protected int BufferReadSize {
			get { 
				return readChunkSize;
			}
			
			set {
				readChunkSize = value;
			}
		}

		/// <summary>
		/// Fill input buffer with a chunk of data.
		/// </summary>		
		protected void FillInputBuffer()
		{
			if (readChunkSize <= 0) {
				len = baseInputStream.Read(buf, 0, buf.Length);
			} else {
				len = baseInputStream.Read(buf, 0, readChunkSize);
			}
			
		}
		/// <summary>
		/// Fills the buffer with more data to decompress.
		/// </summary>
		/// <exception cref="SharpZipBaseException">
		/// Stream ends early
		/// </exception>
		protected void Fill()
		{
			FillInputBuffer();
			
			if (keys != null) {
				DecryptBlock(buf, 0, len);
			}
			
#if READ_SINGLE_WHEN_DECRYPTING
			// This solves some decryption problems but there are still some lurking.
			// At issue is exactly where the stream and decryption should finish.
			if (keys == null) {
				len = baseInputStream.Read(buf, 0, buf.Length);
			} else {
				len = baseInputStream.Read(buf, 0, 1);
			}
			
			if (keys != null) {
				DecryptBlock(buf, 0, len);
			}
#endif

#if STANDARD
			len = baseInputStream.Read(buf, 0, buf.Length);
			
			if (keys != null) {
				DecryptBlock(buf, 0, System.Math.Min((int)(csize - inf.TotalIn), len));
			}
#endif

			if (len <= 0) {
				throw new SharpZipBaseException("Deflated stream ends early.");
			}
			
			inf.SetInput(buf, 0, len);
		}
		
		/// <summary>
		/// Reads one byte of decompressed data.
		///
		/// The byte is baseInputStream the lower 8 bits of the int.
		/// </summary>
		/// <returns>
		/// The byte read cast to an int, or -1 on end of stream.
		/// </returns>
		public override int ReadByte()
		{
			int nread = Read(onebytebuffer, 0, 1); // read one byte
			if (nread > 0) {
				return onebytebuffer[0] & 0xff;
			}
			return -1; // ok
		}
		
		/// <summary>
		/// Decompresses data into the byte array
		/// </summary>
		/// <param name ="b">
		/// The array to read and decompress data into
		/// </param>
		/// <param name ="off">
		/// The offset indicating where the data should be placed
		/// </param>
		/// <param name ="len">
		/// The number of bytes to decompress
		/// </param>
		/// <returns>The number of bytes read.  Zero signals the end of stream</returns>
		/// <exception cref="SharpZipBaseException">
		/// Inflater needs a dictionary
		/// </exception>
		public override int Read(byte[] b, int off, int len)
		{
			for (;;) {
				int count;
				try {
					count = inf.Inflate(b, off, len);
				} catch (Exception e) {
					throw new SharpZipBaseException(e.ToString());
				}
				
				if (count > 0) {
					return count;
				}
				
				if (inf.IsNeedingDictionary) {
					throw new SharpZipBaseException("Need a dictionary");
				} else if (inf.IsFinished) {
					return 0;
				} else if (inf.IsNeedingInput) {
					Fill();
				} else {
					throw new InvalidOperationException("Don't know what to do");
				}
			}
		}
		
		/// <summary>
		/// Skip specified number of bytes of uncompressed data
		/// </summary>
		/// <param name ="n">
		/// Number of bytes to skip
		/// </param>
		/// <returns>
		/// The number of bytes skipped, zero if the end of 
		/// stream has been reached
		/// </returns>
		/// <exception cref="ArgumentOutOfRangeException">
		/// Number of bytes to skip is zero or less
		/// </exception>
		public long Skip(long n)
		{
			if (n <= 0) {
				throw new ArgumentOutOfRangeException("n");
			}
			
			// v0.80 Skip by seeking if underlying stream supports it...
			if (baseInputStream.CanSeek) {
				baseInputStream.Seek(n, SeekOrigin.Current);
				return n;
			} else {
				int len = 2048;
				if (n < len) {
					len = (int) n;
				}
				byte[] tmp = new byte[len];
				return (long)baseInputStream.Read(tmp, 0, tmp.Length);
			}
		}
		
		#region Encryption stuff
		
		// TODO  Refactor this code.  The presence of Zip specific code in this low level class is wrong
		
		/// <summary>
		/// A buffer used for decrypting data.  Used to hold Zip crypto header.
		/// </summary>
		protected byte[] cryptbuffer = null;
		
		uint[] keys = null;
		
		/// <summary>
		/// Decrypt a single byte
		/// </summary>
		/// <returns>plain text byte value</returns>
		protected byte DecryptByte()
		{
			uint temp = ((keys[2] & 0xFFFF) | 2);
			return (byte)((temp * (temp ^ 1)) >> 8);
		}
		
		/// <summary>
		/// Decrypt cipher text block, updating keys
		/// </summary>
		/// <param name="buf">Data to decrypt</param>
		/// <param name="off">Offset of first byte to process</param>
		/// <param name="len">Number of bytes to process</param>
		protected void DecryptBlock(byte[] buf, int off, int len)
		{
			for (int i = off; i < off + len; ++i) {
				buf[i] ^= DecryptByte();
				UpdateKeys(buf[i]);
			}
		}
		
		/// <summary>
		/// Initialise the decryption keys
		/// </summary>
		/// <param name="password">The password used to initialise the keys</param>
		protected void InitializePassword(string password)
		{
			keys = new uint[] {
				0x12345678,
				0x23456789,
				0x34567890
			};
			for (int i = 0; i < password.Length; ++i) {
				UpdateKeys((byte)password[i]);
			}
		}
		
		/// <summary>
		/// Update the decryption keys
		/// </summary>
		/// <param name="ch">Character to update the keys with</param>
		protected void UpdateKeys(byte ch)
		{
			keys[0] = Crc32.ComputeCrc32(keys[0], ch);
			keys[1] = keys[1] + (byte)keys[0];
			keys[1] = keys[1] * 134775813 + 1;
			keys[2] = Crc32.ComputeCrc32(keys[2], (byte)(keys[1] >> 24));
		}

		/// <summary>
		/// Clear any cryptographic state.
		/// </summary>		
		protected void StopDecrypting()
		{
			keys = null;
			cryptbuffer = null;
		}
		#endregion
	}
}