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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.IO;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace System.Net.Mime
{
/// <summary>
/// This stream performs in-place decoding of quoted-printable
/// encoded streams. Encoding requires copying into a separate
/// buffer as the data being encoded will most likely grow.
/// Encoding and decoding is done transparently to the caller.
///
/// This stream should only be used for the e-mail content.
/// Use QEncodedStream for encoding headers.
/// </summary>
internal sealed class QuotedPrintableStream : DelegatedStream, IEncodableStream
{
//should we encode CRLF or not?
private readonly bool _encodeCRLF;
//number of bytes needed for a soft CRLF in folding
private const int SizeOfSoftCRLF = 3;
//each encoded byte occupies three bytes when encoded
private const int SizeOfEncodedChar = 3;
//it takes six bytes to encode a CRLF character (a CRLF that does not indicate folding)
private const int SizeOfEncodedCRLF = 6;
//if we aren't encoding CRLF then it occupies two chars
private const int SizeOfNonEncodedCRLF = 2;
private static ReadOnlySpan<byte> HexDecodeMap =>
[
// 0 1 2 3 4 5 6 7 8 9 A B C D E F
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // 0
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // 1
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // 2
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 255, 255, 255, 255, 255, 255, // 3
255, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255, 255, 255, // 4
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // 5
255, 10, 11, 12, 13, 14, 15, 255, 255, 255, 255, 255, 255, 255, 255, 255, // 6
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // 7
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // 8
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // 9
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // A
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // B
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // C
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // D
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // E
255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, // F
];
private static ReadOnlySpan<byte> HexEncodeMap => "0123456789ABCDEF"u8;
private readonly int _lineLength;
private ReadStateInfo? _readState;
private WriteStateInfoBase? _writeState;
/// <summary>
/// ctor.
/// </summary>
/// <param name="stream">Underlying stream</param>
/// <param name="lineLength">Preferred maximum line-length for writes</param>
internal QuotedPrintableStream(Stream stream, int lineLength) : base(stream)
{
ArgumentOutOfRangeException.ThrowIfNegative(lineLength);
_lineLength = lineLength;
}
internal QuotedPrintableStream(Stream stream, bool encodeCRLF) : this(stream, EncodedStreamFactory.DefaultMaxLineLength)
{
_encodeCRLF = encodeCRLF;
}
public override bool CanRead => false;
public override bool CanWrite => BaseStream.CanWrite;
private ReadStateInfo ReadState => _readState ??= new ReadStateInfo();
internal WriteStateInfoBase WriteState => _writeState ??= new WriteStateInfoBase(1024, null, null, _lineLength);
public override void Close()
{
FlushInternal();
base.Close();
}
public unsafe int DecodeBytes(Span<byte> buffer)
{
fixed (byte* pBuffer = buffer)
{
byte* start = pBuffer;
byte* source = start;
byte* dest = start;
byte* end = start + buffer.Length;
// if the last read ended in a partially decoded
// sequence, pick up where we left off.
if (ReadState.IsEscaped)
{
// this will be -1 if the previous read ended
// with an escape character.
if (ReadState.Byte == -1)
{
// if we only read one byte from the underlying
// stream, we'll need to save the byte and
// ask for more.
if (buffer.Length == 1)
{
ReadState.Byte = *source;
return 0;
}
// '=\r\n' means a soft (aka. invisible) CRLF sequence...
if (source[0] != '\r' || source[1] != '\n')
{
byte b1 = HexDecodeMap[source[0]];
byte b2 = HexDecodeMap[source[1]];
if (b1 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, b1));
if (b2 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, b2));
*dest++ = (byte)((b1 << 4) + b2);
}
source += 2;
}
else
{
// '=\r\n' means a soft (aka. invisible) CRLF sequence...
if (ReadState.Byte != '\r' || *source != '\n')
{
byte b1 = HexDecodeMap[ReadState.Byte];
byte b2 = HexDecodeMap[*source];
if (b1 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, b1));
if (b2 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, b2));
*dest++ = (byte)((b1 << 4) + b2);
}
source++;
}
// reset state for next read.
ReadState.IsEscaped = false;
ReadState.Byte = -1;
}
// Here's where most of the decoding takes place.
// We'll loop around until we've inspected all the
// bytes read.
while (source < end)
{
// if the source is not an escape character, then
// just copy as-is.
if (*source != '=')
{
*dest++ = *source++;
}
else
{
// determine where we are relative to the end
// of the data. If we don't have enough data to
// decode the escape sequence, save off what we
// have and continue the decoding in the next
// read. Otherwise, decode the data and copy
// into dest.
switch (end - source)
{
case 2:
ReadState.Byte = source[1];
goto case 1;
case 1:
ReadState.IsEscaped = true;
goto EndWhile;
default:
if (source[1] != '\r' || source[2] != '\n')
{
byte b1 = HexDecodeMap[source[1]];
byte b2 = HexDecodeMap[source[2]];
if (b1 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, b1));
if (b2 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, b2));
*dest++ = (byte)((b1 << 4) + b2);
}
source += 3;
break;
}
}
}
EndWhile:
return (int)(dest - start);
}
}
public int EncodeBytes(ReadOnlySpan<byte> buffer)
{
int processed = 0;
for (; processed < buffer.Length; processed++)
{
//only fold if we're before a whitespace or if we're at the line limit
//add two to the encoded Byte Length to be conservative so that we guarantee that the line length is acceptable
if ((_lineLength != -1 && WriteState.CurrentLineLength + SizeOfEncodedChar + 2 >= _lineLength && (buffer[processed] == ' ' ||
buffer[processed] == '\t' || buffer[processed] == '\r' || buffer[processed] == '\n')) ||
_writeState!.CurrentLineLength + SizeOfEncodedChar + 2 >= EncodedStreamFactory.DefaultMaxLineLength)
{
if (WriteState.Buffer.Length - WriteState.Length < SizeOfSoftCRLF)
{
return processed; //ok because folding happens externally
}
WriteState.Append((byte)'=');
WriteState.AppendCRLF(false);
}
// We don't need to worry about RFC 2821 4.5.2 (encoding first dot on a line),
// it is done by the underlying 7BitStream
//detect a CRLF in the input and encode it.
if (buffer[processed] == '\r' && processed + 1 < buffer.Length && buffer[processed + 1] == '\n')
{
if (WriteState.Buffer.Length - WriteState.Length < (_encodeCRLF ? SizeOfEncodedCRLF : SizeOfNonEncodedCRLF))
{
return processed;
}
processed++;
if (_encodeCRLF)
{
// The encoding for CRLF is =0D=0A
WriteState.Append("=0D=0A"u8);
}
else
{
WriteState.AppendCRLF(false);
}
}
//ascii chars less than 32 (control chars) and greater than 126 (non-ascii) are not allowed so we have to encode
else if ((buffer[processed] < 32 && buffer[processed] != '\t') ||
buffer[processed] == '=' ||
buffer[processed] > 126)
{
if (WriteState.Buffer.Length - WriteState.Length < SizeOfSoftCRLF)
{
return processed;
}
//append an = to indicate an encoded character
WriteState.Append((byte)'=');
//shift 4 to get the first four bytes only and look up the hex digit
WriteState.Append(HexEncodeMap[buffer[processed] >> 4]);
//clear the first four bytes to get the last four and look up the hex digit
WriteState.Append(HexEncodeMap[buffer[processed] & 0xF]);
}
else
{
if (WriteState.Buffer.Length - WriteState.Length < 1)
{
return processed;
}
//detect special case: is whitespace at end of line? we must encode it if it is
if ((buffer[processed] == (byte)'\t' || buffer[processed] == (byte)' ') &&
(processed + 1 >= buffer.Length))
{
if (WriteState.Buffer.Length - WriteState.Length < SizeOfEncodedChar)
{
return processed;
}
//append an = to indicate an encoded character
WriteState.Append((byte)'=');
//shift 4 to get the first four bytes only and look up the hex digit
WriteState.Append(HexEncodeMap[buffer[processed] >> 4]);
//clear the first four bytes to get the last four and look up the hex digit
WriteState.Append(HexEncodeMap[buffer[processed] & 0xF]);
}
else
{
WriteState.Append(buffer[processed]);
}
}
}
return processed;
}
public int EncodeString(string value, Encoding encoding)
{
byte[] buffer = encoding.GetBytes(value);
return EncodeBytes(buffer);
}
public string GetEncodedString() => Encoding.ASCII.GetString(WriteState.Buffer, 0, WriteState.Length);
public override void Flush()
{
FlushInternal();
base.Flush();
}
public override async Task FlushAsync(CancellationToken cancellationToken)
{
await FlushInternalAsync(cancellationToken).ConfigureAwait(false);
await base.FlushAsync(cancellationToken).ConfigureAwait(false);
}
private async ValueTask FlushInternalAsync(CancellationToken cancellationToken)
{
if (_writeState != null && _writeState.Length > 0)
{
await BaseStream.WriteAsync(WriteState.Buffer.AsMemory(0, WriteState.Length), cancellationToken).ConfigureAwait(false);
WriteState.BufferFlushed();
}
}
private void FlushInternal()
{
if (_writeState != null && _writeState.Length > 0)
{
BaseStream.Write(WriteState.Buffer, 0, WriteState.Length);
WriteState.BufferFlushed();
}
}
protected override int ReadInternal(Span<byte> buffer)
{
throw new NotImplementedException();
}
protected override ValueTask<int> ReadAsyncInternal(Memory<byte> buffer, CancellationToken cancellationToken = default)
{
throw new NotImplementedException();
}
protected override void WriteInternal(ReadOnlySpan<byte> buffer)
{
int written = 0;
while (true)
{
written += EncodeBytes(buffer.Slice(written));
if (written < buffer.Length)
{
FlushInternal();
}
else
{
break;
}
}
}
protected override async ValueTask WriteAsyncInternal(ReadOnlyMemory<byte> buffer, CancellationToken cancellationToken = default)
{
int written = 0;
while (true)
{
written += EncodeBytes(buffer.Span.Slice(written));
if (written < buffer.Length)
{
await FlushInternalAsync(cancellationToken).ConfigureAwait(false);
}
else
{
break;
}
}
}
private sealed class ReadStateInfo
{
internal bool IsEscaped { get; set; }
internal short Byte { get; set; } = -1;
}
}
}
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