Code:
/ DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / fx / src / Sys / System / IO / compression / GZipDecoder.cs / 1 / GZipDecoder.cs
namespace System.IO.Compression { using System; using System.Diagnostics; internal enum GZIPHeaderState{ // GZIP header ReadingID1, ReadingID2, ReadingCM, ReadingFLG, ReadingMMTime, // iterates 4 times ReadingXFL, ReadingOS, ReadingXLen1, ReadingXLen2, ReadingXLenData, ReadingFileName, ReadingComment, ReadingCRC16Part1, ReadingCRC16Part2, Done, // done reading GZIP header // GZIP footer ReadingCRC, // iterates 4 times ReadingFileSize // iterates 4 times } // This class decodes GZip header and footer information. // See RFC 1952 for details about the format. internal class GZipDecoder { const int FileText = 1; const int CRCFlag = 2; const int ExtraFieldsFlag = 4; const int FileNameFlag = 8; const int CommentFlag= 16; private InputBuffer input; GZIPHeaderState gzipHeaderSubstate; GZIPHeaderState gzipFooterSubstate; int gzip_header_flag; int gzip_header_xlen; uint gzipCrc32; uint gzipOutputStreamSize; int loopCounter; public GZipDecoder(InputBuffer input) { this.input = input; Reset(); } public void Reset() { gzipHeaderSubstate = GZIPHeaderState.ReadingID1; gzipFooterSubstate = GZIPHeaderState.ReadingCRC; gzipCrc32 = 0; gzipOutputStreamSize = 0; } public uint Crc32 { get { return gzipCrc32; } } public uint StreamSize { get { return gzipOutputStreamSize; } } public bool ReadGzipHeader() { while(true) { int bits; switch (gzipHeaderSubstate) { case GZIPHeaderState.ReadingID1: bits = input.GetBits(8); if( bits < 0) { return false; } if( bits != 0x1F) { throw new InvalidDataException(SR.GetString(SR.CorruptedGZipHeader)); } gzipHeaderSubstate = GZIPHeaderState.ReadingID2; goto case GZIPHeaderState.ReadingID2; case GZIPHeaderState.ReadingID2: bits = input.GetBits(8); if( bits < 0) { return false; } if( bits != 0x8b) { throw new InvalidDataException(SR.GetString(SR.CorruptedGZipHeader)); } gzipHeaderSubstate = GZIPHeaderState.ReadingCM; goto case GZIPHeaderState.ReadingCM; case GZIPHeaderState.ReadingCM: bits = input.GetBits(8); if( bits < 0) { return false; } if( bits != 0x8) { // compression mode must be 8 (deflate) throw new InvalidDataException(SR.GetString(SR.UnknownCompressionMode)); } gzipHeaderSubstate = GZIPHeaderState.ReadingFLG;; goto case GZIPHeaderState.ReadingFLG; case GZIPHeaderState.ReadingFLG: bits = input.GetBits(8); if( bits < 0) { return false; } gzip_header_flag = bits; gzipHeaderSubstate = GZIPHeaderState.ReadingMMTime; loopCounter = 0; // 4 MMTIME bytes goto case GZIPHeaderState.ReadingMMTime; case GZIPHeaderState.ReadingMMTime: bits = 0; while(loopCounter < 4) { bits = input.GetBits(8); if( bits < 0) { return false; } loopCounter++; } gzipHeaderSubstate = GZIPHeaderState.ReadingXFL; loopCounter = 0; goto case GZIPHeaderState.ReadingXFL; case GZIPHeaderState.ReadingXFL: // ignore XFL bits = input.GetBits(8); if( bits < 0) { return false; } gzipHeaderSubstate = GZIPHeaderState.ReadingOS; goto case GZIPHeaderState.ReadingOS; case GZIPHeaderState.ReadingOS: // ignore OS bits = input.GetBits(8); if( bits < 0) { return false; } gzipHeaderSubstate = GZIPHeaderState.ReadingXLen1; goto case GZIPHeaderState.ReadingXLen1; case GZIPHeaderState.ReadingXLen1: if ((gzip_header_flag & ExtraFieldsFlag) == 0) { goto case GZIPHeaderState.ReadingFileName; } bits = input.GetBits(8); if( bits < 0) { return false; } gzip_header_xlen = bits; gzipHeaderSubstate = GZIPHeaderState.ReadingXLen2; goto case GZIPHeaderState.ReadingXLen2; case GZIPHeaderState.ReadingXLen2: bits = input.GetBits(8); if( bits < 0) { return false; } gzip_header_xlen |= (bits << 8); gzipHeaderSubstate = GZIPHeaderState.ReadingXLenData; loopCounter = 0; // 0 bytes of XLEN data read so far goto case GZIPHeaderState.ReadingXLenData; case GZIPHeaderState.ReadingXLenData: bits = 0; while(loopCounter < gzip_header_xlen) { bits = input.GetBits(8); if( bits < 0) { return false; } loopCounter++; } gzipHeaderSubstate = GZIPHeaderState.ReadingFileName; loopCounter = 0; goto case GZIPHeaderState.ReadingFileName; case GZIPHeaderState.ReadingFileName: if ((gzip_header_flag & FileNameFlag) == 0) { gzipHeaderSubstate = GZIPHeaderState.ReadingComment; goto case GZIPHeaderState.ReadingComment; } do { bits = input.GetBits(8); if( bits < 0) { return false; } if( bits == 0) { // see '\0' in the file name string break; } } while (true); gzipHeaderSubstate = GZIPHeaderState.ReadingComment; goto case GZIPHeaderState.ReadingComment; case GZIPHeaderState.ReadingComment: if ((gzip_header_flag & CommentFlag) == 0) { gzipHeaderSubstate = GZIPHeaderState.ReadingCRC16Part1; goto case GZIPHeaderState.ReadingCRC16Part1; } do { bits = input.GetBits(8); if( bits < 0) { return false; } if( bits == 0) { // see '\0' in the file name string break; } } while (true); gzipHeaderSubstate = GZIPHeaderState.ReadingCRC16Part1; goto case GZIPHeaderState.ReadingCRC16Part1; case GZIPHeaderState.ReadingCRC16Part1: if ((gzip_header_flag & CRCFlag) == 0) { gzipHeaderSubstate = GZIPHeaderState.Done; goto case GZIPHeaderState.Done; } bits = input.GetBits(8); // ignore crc if( bits < 0) { return false; } gzipHeaderSubstate = GZIPHeaderState.ReadingCRC16Part2; goto case GZIPHeaderState.ReadingCRC16Part2; case GZIPHeaderState.ReadingCRC16Part2: bits = input.GetBits(8); // ignore crc if( bits < 0) { return false; } gzipHeaderSubstate = GZIPHeaderState.Done; goto case GZIPHeaderState.Done; case GZIPHeaderState.Done: return true; default: Debug.Assert(false, "We should not reach unknown state!"); throw new InvalidDataException(SR.GetString(SR.UnknownState)); } } } public bool ReadGzipFooter() { input.SkipToByteBoundary(); if( gzipFooterSubstate == GZIPHeaderState.ReadingCRC) { while (loopCounter < 4 ) { int bits = input.GetBits(8); if( bits < 0) { return false; } gzipCrc32 |= ((uint)bits << (8*loopCounter)); loopCounter++; } gzipFooterSubstate = GZIPHeaderState.ReadingFileSize; loopCounter = 0; } if (gzipFooterSubstate == GZIPHeaderState.ReadingFileSize) { if (loopCounter == 0) gzipOutputStreamSize = 0; while (loopCounter < 4) { int bits = input.GetBits(8); if( bits < 0) { return false; } gzipOutputStreamSize |= ((uint)bits << (8*loopCounter)); loopCounter++; } } return true; } } }
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