Base64Encoder.cs

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namespace System.Net.Mime;
 
internal sealed class Base64Encoder : ByteEncoder
{
    private readonly int _lineLength;
 
    private readonly Base64WriteStateInfo _writeState;
 
    private static ReadOnlySpan<byte> Base64EncodeMap => "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="u8;
 
    internal override WriteStateInfoBase WriteState => _writeState;
 
    protected override bool HasSpecialEncodingForCRLF => false;
 
    internal Base64Encoder(Base64WriteStateInfo writeStateInfo, int lineLength)
    {
        _writeState = writeStateInfo;
        _lineLength = lineLength;
    }
 
    protected override void AppendEncodedCRLF()
    {
        throw new InvalidOperationException();
    }
 
    protected override bool LineBreakNeeded(byte b)
    {
        return LineBreakNeeded(1);
    }
 
    protected override bool LineBreakNeeded(byte[] bytes, int count)
    {
        return LineBreakNeeded(count);
    }
 
    private bool LineBreakNeeded(int numberOfBytesToAppend)
    {
        if (_lineLength == -1)
        {
            return false;
        }
        int num;
        int num2;
        switch (_writeState.Padding)
        {
        case 2:
            num = 2;
            num2 = 3;
            break;
        case 1:
            num = 1;
            num2 = 2;
            break;
        case 0:
            num = 0;
            num2 = 0;
            break;
        default:
            num = 0;
            num2 = 0;
            break;
        }
        int num3 = numberOfBytesToAppend - num;
        if (num3 <= 0)
        {
            return false;
        }
        int num4 = num3 / 3 + ((num3 % 3 != 0) ? 1 : 0);
        int num5 = num2 + num4 * 4;
        return WriteState.CurrentLineLength + num5 + _writeState.FooterLength > _lineLength;
    }
 
    protected override int GetCodepointSize(string value, int i)
    {
        if (!IsSurrogatePair(value, i))
        {
            return 1;
        }
        return 2;
    }
 
    public override void AppendPadding()
    {
        switch (_writeState.Padding)
        {
        case 2:
            _writeState.Append(Base64EncodeMap[_writeState.LastBits]);
            _writeState.Append(Base64EncodeMap[64]);
            _writeState.Append(Base64EncodeMap[64]);
            _writeState.Padding = 0;
            break;
        case 1:
            _writeState.Append(Base64EncodeMap[_writeState.LastBits]);
            _writeState.Append(Base64EncodeMap[64]);
            _writeState.Padding = 0;
            break;
        case 0:
            break;
        }
    }
 
    protected override void ApppendEncodedByte(byte b)
    {
        switch (_writeState.Padding)
        {
        case 0:
            _writeState.Append(Base64EncodeMap[(b & 0xFC) >> 2]);
            _writeState.LastBits = (byte)((b & 3) << 4);
            _writeState.Padding = 2;
            break;
        case 2:
            _writeState.Append(Base64EncodeMap[_writeState.LastBits | ((b & 0xF0) >> 4)]);
            _writeState.LastBits = (byte)((b & 0xF) << 2);
            _writeState.Padding = 1;
            break;
        case 1:
            _writeState.Append(Base64EncodeMap[_writeState.LastBits | ((b & 0xC0) >> 6)]);
            _writeState.Append(Base64EncodeMap[b & 0x3F]);
            _writeState.Padding = 0;
            break;
        }
    }
}