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124 lines
2.9 KiB
C#
124 lines
2.9 KiB
C#
// ClassicalSharp copyright 2014-2016 UnknownShadow200 | Licensed under MIT
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using System;
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using System.IO;
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namespace ClassicalSharp.Network {
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internal class GZipHeaderReader {
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enum State {
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Header1, Header2, CompressionMethod, Flags,
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LastModifiedTime, CompressionFlags, OperatingSystem,
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HeaderChecksum, Filename, Comment, Done,
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}
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State state = State.Header1;
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public bool done;
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int flags;
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int partsRead;
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public bool ReadHeader( Stream s ) {
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switch( state ) {
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case State.Header1:
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if( !ReadAndCheckHeaderByte( s, 0x1F ) )
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return false;
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goto case State.Header2;
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case State.Header2:
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if( !ReadAndCheckHeaderByte( s, 0x8B ) )
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return false;
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goto case State.CompressionMethod;
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case State.CompressionMethod:
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if( !ReadAndCheckHeaderByte( s, 0x08 ) )
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return false;
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goto case State.Flags;
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case State.Flags:
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if( !ReadHeaderByte( s, out flags ) )
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return false;
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if( (flags & 0x04) != 0 )
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throw new NotSupportedException( "Unsupported gzip flags: " + flags );
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goto case State.LastModifiedTime;
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case State.LastModifiedTime:
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for( ; partsRead < 4; partsRead++ ) {
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int part = s.ReadByte();
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if( part == -1 )
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return false;
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}
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partsRead = 0;
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state = State.CompressionFlags;
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goto case State.CompressionFlags;
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case State.CompressionFlags:
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int comFlags;
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if( !ReadHeaderByte( s, out comFlags ) )
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return false;
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goto case State.OperatingSystem;
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case State.OperatingSystem:
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int os;
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if( !ReadHeaderByte( s, out os ) )
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return false;
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goto case State.Filename;
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case State.Filename:
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if( (flags & 0x08) != 0 ) {
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for( ; ; ) {
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int part = s.ReadByte();
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if( part == -1 ) return false;
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if( part == 0 ) break;
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}
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}
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state = State.Comment;
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goto case State.Comment;
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case State.Comment:
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if( (flags & 0x10) != 0 ) {
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for( ; ; ) {
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int part = s.ReadByte();
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if( part == -1 ) return false;
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if( part == 0 ) break;
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}
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}
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state = State.HeaderChecksum;
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goto case State.HeaderChecksum;
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case State.HeaderChecksum:
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if( ( flags & 0x02 ) != 0 ) {
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for( ; partsRead < 2; partsRead++ ) {
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int part = s.ReadByte();
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if( part == -1 )
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return false;
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}
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}
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partsRead = 0;
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state = State.Done;
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done = true;
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return true;
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}
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return true;
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}
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bool ReadAndCheckHeaderByte( Stream s, byte expected ) {
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int value;
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if( !ReadHeaderByte( s, out value ) )
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return false;
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if( value != expected )
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throw new InvalidDataException( "Unepxected constant in GZip header. (" + expected + "-" + value + ")" );
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return true;
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}
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bool ReadHeaderByte( Stream s, out int value ) {
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value = s.ReadByte();
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if( value == -1 )
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return false;
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state++;
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return true;
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}
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}
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} |