// 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;
using System.Buffers;
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.
/// </summary>
internal sealed class QEncodedStream : DelegatedStream, IEncodableStream
{
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 readonly WriteStateInfoBase _writeState;
private readonly QEncoder _encoder;
internal QEncodedStream(WriteStateInfoBase wsi) : base(new MemoryStream())
{
_writeState = wsi;
_encoder = new QEncoder(_writeState);
}
private ReadStateInfo ReadState => field ??= new ReadStateInfo();
internal WriteStateInfoBase WriteState => _writeState;
public override bool CanRead => BaseStream.CanRead;
public override bool CanWrite => BaseStream.CanWrite;
public override void Close()
{
FlushInternal();
base.Close();
}
public int DecodeBytes(Span<byte> buffer)
{
if (buffer.IsEmpty)
{
return 0;
}
int source = 0;
int destination = 0;
// 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 = buffer[source];
return 0;
}
// '=\r\n' means a soft (aka. invisible) CRLF sequence...
if (buffer[source] != '\r' || buffer[source + 1] != '\n')
{
byte b1 = HexDecodeMap[buffer[source]];
byte b2 = HexDecodeMap[buffer[source + 1]];
if (b1 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, (char)buffer[source]));
if (b2 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, (char)buffer[source + 1]));
buffer[destination++] = (byte)((b1 << 4) + b2);
}
source += 2;
}
else
{
// '=\r\n' means a soft (aka. invisible) CRLF sequence...
if (ReadState.Byte != '\r' || buffer[source] != '\n')
{
byte b1 = HexDecodeMap[ReadState.Byte];
byte b2 = HexDecodeMap[buffer[source]];
if (b1 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, (char)ReadState.Byte));
if (b2 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, (char)buffer[source]));
buffer[destination++] = (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 < buffer.Length)
{
// if the source is not an escape character, then
// just copy as-is.
if (buffer[source] != '=')
{
if (buffer[source] == '_')
{
buffer[destination++] = (byte)' ';
source++;
}
else
{
buffer[destination++] = buffer[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 (buffer.Length - source)
{
case 2:
ReadState.Byte = buffer[source + 1];
goto case 1;
case 1:
ReadState.IsEscaped = true;
goto EndWhile;
default:
if (buffer[source + 1] != '\r' || buffer[source + 2] != '\n')
{
byte b1 = HexDecodeMap[buffer[source + 1]];
byte b2 = HexDecodeMap[buffer[source + 2]];
if (b1 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, (char)buffer[source + 1]));
if (b2 == 255)
throw new FormatException(SR.Format(SR.InvalidHexDigit, (char)buffer[source + 2]));
buffer[destination++] = (byte)((b1 << 4) + b2);
}
source += 3;
break;
}
}
}
EndWhile:
return destination;
}
public int EncodeBytes(ReadOnlySpan<byte> buffer) => _encoder.EncodeBytes(buffer, true, true);
public int EncodeString(string value, Encoding encoding) => _encoder.EncodeString(value, encoding);
public string GetEncodedString() => _encoder.GetEncodedString();
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 void FlushInternal()
{
if (_writeState != null && _writeState.Length > 0)
{
BaseStream.Write(WriteState.Buffer.AsSpan(0, WriteState.Length));
WriteState.Reset();
}
}
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.Reset();
}
}
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;
}
}
}