EncodedStreamFactory.cs

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using System.Text;
 
namespace System.Net.Mime;
 
internal sealed class EncodedStreamFactory
{
    private static readonly byte[] s_footer = new byte[2] { 63, 61 };
 
    internal IEncodableStream GetEncoderForHeader(Encoding encoding, bool useBase64Encoding, int headerTextLength)
    {
        byte[] header = CreateHeader(encoding, useBase64Encoding);
        byte[] footer = s_footer;
        WriteStateInfoBase writeStateInfoBase;
        if (useBase64Encoding)
        {
            writeStateInfoBase = new Base64WriteStateInfo(1024, header, footer, 70, headerTextLength);
            return new Base64Stream((Base64WriteStateInfo)writeStateInfoBase);
        }
        writeStateInfoBase = new WriteStateInfoBase(1024, header, footer, 70, headerTextLength);
        return new QEncodedStream(writeStateInfoBase);
    }
 
    private byte[] CreateHeader(Encoding encoding, bool useBase64Encoding)
    {
        return Encoding.ASCII.GetBytes("=?" + encoding.HeaderName + "?" + (useBase64Encoding ? "B?" : "Q?"));
    }
}