namespace System.IO.Compression { using System.Diagnostics; internal class CopyEncoder { // padding for copy encoder formatting // - 1 byte for header // - 4 bytes for len, nlen private const int PaddingSize = 5; // max uncompressed deflate block size is 64K. private const int MaxUncompressedBlockSize = 65536; // null input means write an empty payload with formatting info. This is needed for the final block. public void GetBlock(DeflateInput input, OutputBuffer output, bool isFinal) { Debug.Assert(output != null); Debug.Assert(output.FreeBytes >= PaddingSize); // determine number of bytes to write int count = 0; if (input != null) { // allow space for padding and bits not yet flushed to buffer count = Math.Min(input.Count, output.FreeBytes - PaddingSize - output.BitsInBuffer); // we don't expect the output buffer to ever be this big (currently 4K), but we'll check this // just in case that changes. if (count > MaxUncompressedBlockSize - PaddingSize) { count = MaxUncompressedBlockSize - PaddingSize; } } // write header and flush bits if (isFinal) { output.WriteBits(FastEncoderStatics.BFinalNoCompressionHeaderBitCount, FastEncoderStatics.BFinalNoCompressionHeader); } else { output.WriteBits(FastEncoderStatics.NoCompressionHeaderBitCount, FastEncoderStatics.NoCompressionHeader); } // now we're aligned output.FlushBits(); // write len, nlen WriteLenNLen((ushort)count, output); // write uncompressed bytes if (input != null && count > 0) { output.WriteBytes(input.Buffer, input.StartIndex, count); input.ConsumeBytes(count); } } private void WriteLenNLen(ushort len, OutputBuffer output) { // len output.WriteUInt16(len); // nlen ushort onesComp = (ushort)(~(ushort)len); output.WriteUInt16(onesComp); } } }