mirror of https://github.com/SixLabors/ImageSharp
Drawaes
9 years ago
5 changed files with 154 additions and 271 deletions
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// <copyright file="ZlibInflateStream.cs" company="James Jackson-South">
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// Copyright (c) James Jackson-South and contributors.
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// Licensed under the Apache License, Version 2.0.
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// </copyright>
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namespace ImageSharp.Formats |
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{ |
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using System; |
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using System.IO; |
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using System.IO.Compression; |
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/// <summary>
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/// Provides methods and properties for decompressing streams by using the Zlib Deflate algorithm.
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/// </summary>
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internal sealed class ZlibInflateStream : Stream |
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{ |
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/// <summary>
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/// The raw stream containing the uncompressed image data.
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/// </summary>
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private readonly Stream rawStream; |
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/// <summary>
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/// A value indicating whether this instance of the given entity has been disposed.
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/// </summary>
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/// <value><see langword="true"/> if this instance has been disposed; otherwise, <see langword="false"/>.</value>
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/// <remarks>
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/// If the entity is disposed, it must not be disposed a second
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/// time. The isDisposed field is set the first time the entity
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/// is disposed. If the isDisposed field is true, then the Dispose()
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/// method will not dispose again. This help not to prolong the entity's
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/// life in the Garbage Collector.
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/// </remarks>
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private bool isDisposed; |
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/// <summary>
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/// The read crc data.
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/// </summary>
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private byte[] crcread; |
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/// <summary>
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/// The stream responsible for decompressing the input stream.
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/// </summary>
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private DeflateStream deflateStream; |
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/// <summary>
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/// Initializes a new instance of the <see cref="ZlibInflateStream"/> class.
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/// </summary>
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/// <param name="stream">The stream.</param>
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/// <exception cref="Exception">
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/// Thrown if the compression method is incorrect.
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/// </exception>
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public ZlibInflateStream(Stream stream) |
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{ |
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// The DICT dictionary identifier identifying the used dictionary.
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// The preset dictionary.
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bool fdict; |
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this.rawStream = stream; |
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// Read the zlib header : http://tools.ietf.org/html/rfc1950
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// CMF(Compression Method and flags)
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// This byte is divided into a 4 - bit compression method and a
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// 4-bit information field depending on the compression method.
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// bits 0 to 3 CM Compression method
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// bits 4 to 7 CINFO Compression info
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//
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// 0 1
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// +---+---+
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// |CMF|FLG|
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// +---+---+
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int cmf = this.rawStream.ReadByte(); |
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int flag = this.rawStream.ReadByte(); |
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if (cmf == -1 || flag == -1) |
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{ |
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return; |
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} |
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if ((cmf & 0x0f) != 8) |
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{ |
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throw new Exception($"Bad compression method for ZLIB header: cmf={cmf}"); |
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} |
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// CINFO is the base-2 logarithm of the LZ77 window size, minus eight.
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// int cinfo = ((cmf & (0xf0)) >> 8);
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fdict = (flag & 32) != 0; |
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if (fdict) |
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{ |
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// The DICT dictionary identifier identifying the used dictionary.
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byte[] dictId = new byte[4]; |
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for (int i = 0; i < 4; i++) |
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{ |
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// We consume but don't use this.
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dictId[i] = (byte)this.rawStream.ReadByte(); |
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} |
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} |
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// Initialize the deflate Stream.
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this.deflateStream = new DeflateStream(this.rawStream, CompressionMode.Decompress, true); |
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} |
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/// <inheritdoc/>
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public override bool CanRead => true; |
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/// <inheritdoc/>
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public override bool CanSeek => false; |
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/// <inheritdoc/>
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public override bool CanWrite => false; |
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/// <inheritdoc/>
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public override long Length |
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{ |
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get |
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{ |
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throw new NotSupportedException(); |
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} |
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} |
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/// <inheritdoc/>
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public override long Position |
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{ |
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get |
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{ |
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throw new NotSupportedException(); |
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} |
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set |
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{ |
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throw new NotSupportedException(); |
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} |
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} |
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/// <inheritdoc/>
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public override void Flush() |
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{ |
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this.deflateStream?.Flush(); |
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} |
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/// <inheritdoc/>
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public override int Read(byte[] buffer, int offset, int count) |
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{ |
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// We dont't check CRC on reading
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int read = this.deflateStream.Read(buffer, offset, count); |
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if (read < 1 && this.crcread == null) |
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{ |
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// The deflater has ended. We try to read the next 4 bytes from raw stream (crc)
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this.crcread = new byte[4]; |
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for (int i = 0; i < 4; i++) |
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{ |
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// we dont really check/use this
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this.crcread[i] = (byte)this.rawStream.ReadByte(); |
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} |
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} |
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return read; |
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} |
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/// <inheritdoc/>
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public override long Seek(long offset, SeekOrigin origin) |
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{ |
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throw new NotSupportedException(); |
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} |
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/// <inheritdoc/>
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public override void SetLength(long value) |
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{ |
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throw new NotSupportedException(); |
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} |
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/// <inheritdoc/>
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public override void Write(byte[] buffer, int offset, int count) |
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{ |
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throw new NotSupportedException(); |
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} |
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/// <inheritdoc/>
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protected override void Dispose(bool disposing) |
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{ |
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if (this.isDisposed) |
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{ |
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return; |
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} |
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if (disposing) |
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{ |
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// dispose managed resources
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if (this.deflateStream != null) |
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{ |
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this.deflateStream.Dispose(); |
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this.deflateStream = null; |
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if (this.crcread == null) |
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{ |
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// Consume the trailing 4 bytes
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this.crcread = new byte[4]; |
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for (int i = 0; i < 4; i++) |
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{ |
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this.crcread[i] = (byte)this.rawStream.ReadByte(); |
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} |
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} |
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} |
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} |
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base.Dispose(disposing); |
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// Call the appropriate methods to clean up
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// unmanaged resources here.
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// Note disposing is done.
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this.isDisposed = true; |
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} |
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} |
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} |
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