/// <summary>Decodes an encoded value from an <paramref name="input"/>
/// stream.</summary>
/// <param name="input">An input stream to decode.</param>
/// <returns>A decoded value.</returns>
/// <exception cref="ArgumentException">Thrown when a given
/// <paramref name="input"/> stream is not readable.</exception>
/// <exception cref="DecodingException">Thrown when a binary
/// representation of an <paramref name="input"/> stream is not a valid
/// Bencodex encoding.</exception>
public IValue Decode(Stream input)
{
if (!input.CanRead)
{
throw new ArgumentException(
"stream cannot be read",
nameof(input)
);
}
var buffer = new ByteChunkQueue();
IValue value = Decode(buffer, input);
if (buffer.Empty)
{
buffer.ReadFrom(input, 1);
}
if (!buffer.Empty)
{
long offset = input.Position;
throw new DecodingException(
$"an unexpected byte at {offset - buffer.ByteLength}: " +
$"0x{buffer.FirstByte:x}"
);
}
return(value);
}
private byte[] DecodeBinary(ByteChunkQueue buffer, Stream input)
{
const byte colon = 0x3a; // ':'
long length = DecodeDigits(colon, buffer, input, long.Parse);
if (length < 1)
{
return(new byte[0]);
}
byte[] popped = buffer.Pop(length);
if (popped.LongLength < length)
{
byte[] result = new byte[length];
popped.CopyTo(result, 0);
// FIXME: These Int64 to Int32 casts should be corrected.
input.Read(
result,
(int)popped.LongLength,
(int)(length - popped.LongLength)
);
return(result);
}
return(popped);
}
private string DecodeText(ByteChunkQueue buffer, Stream input)
{
byte[] singleByteBuffer = buffer.Pop(1);
if (singleByteBuffer.Length < 1)
{
throw new DecodingException(
$"expected 'u' (0x75) at {input.Position - 1}, " +
"but the stream terminates"
);
}
if (singleByteBuffer[0] != 0x75)
{
throw new DecodingException(
$"expected 'u' (0x75) at {input.Position - 1}, " +
$"but 0x{singleByteBuffer[0]:x} is given"
);
}
long pos = input.Position;
byte[] utf8 = DecodeBinary(buffer, input);
try
{
return(Encoding.UTF8.GetString(utf8));
}
catch (ArgumentException e)
{
throw new DecodingException(
$"expected a UTF-8 sequence at {pos}",
e
);
}
}
public void EdgeCase1()
{
var q = new ByteChunkQueue();
q.Append(new byte[] { 1, 2, 3, 4 });
byte[] popped = q.Pop(4);
Assert.Equal(new byte[] { 1, 2, 3, 4 }, popped);
Assert.EndsWith("[]", q.ToString());
}
private T DecodeDigits <T>(
byte terminator,
ByteChunkQueue buffer,
Stream input,
Func <string, T> converter
)
{
if (buffer.Empty)
{
int read = buffer.ReadFrom(input, 1);
if (read < 1)
{
throw new DecodingException(
$"expected one or more digits at {input.Position}, " +
"but the byte stream terminates"
);
}
}
long pos;
while ((pos = buffer.IndexOf(terminator)) < 0)
{
int read = buffer.ReadFrom(input, 8);
if (read < 0)
{
throw new DecodingException(
$"expected a byte 0x{terminator:x} at " +
$"{input.Position}, but the byte stream terminates"
);
}
}
byte[] digitBytes = buffer.Pop(pos);
if (!digitBytes.All(b => b >= 0x30 && b < 0x40))
{
long digitsOffset =
input.Position - buffer.ByteLength - digitBytes.LongLength;
throw new DecodingException(
$"expected 10-base digits at {digitsOffset}: " +
BitConverter.ToString(digitBytes)
);
}
buffer.Pop(1); // pop terminator
string digits = Encoding.ASCII.GetString(digitBytes);
return(converter(digits));
}
public void EdgeCase2()
{
var q = new ByteChunkQueue();
q.Append(new byte[] { 1, 2, 3, 4, 5, 6, 7, 8 });
byte[] popped = q.Pop(7);
Assert.Equal(new byte[] { 1, 2, 3, 4, 5, 6, 7 }, popped);
Assert.EndsWith("[01-02-03-04-05-06-07|08]", q.ToString());
q.Append(new byte[] { 9, 0xa, 0xb, 0xc, 0xd, 0xe, 0xf, 0x10 });
Assert.EndsWith("[01-02-03-04-05-06-07|08 09-0A-0B-0C-0D-0E-0F-10]", q.ToString());
popped = q.Pop(1);
Assert.Equal(new byte[] { 8 }, popped);
Assert.EndsWith("[09-0A-0B-0C-0D-0E-0F-10]", q.ToString());
popped = q.Pop(1);
Assert.Equal(new byte[] { 9 }, popped);
Assert.EndsWith("[09|0A-0B-0C-0D-0E-0F-10]", q.ToString());
}
private IValue Decode(ByteChunkQueue buffer, Stream input)
{
if (buffer.Empty)
{
buffer.ReadFrom(input, 1);
}
long pos = input.Position - buffer.ByteLength;
switch (buffer.FirstByte)
{
case null:
throw new DecodingException(
$"stream terminates unexpectedly at {pos}"
);
case 0x6e: // 'n'
buffer.Pop(1);
return(default(Null));
case 0x74: // 't'
buffer.Pop(1);
return(new Bencodex.Types.Boolean(true));
case 0x66: // 'f'
buffer.Pop(1);
return(new Bencodex.Types.Boolean(false));
case 0x69: // 'i'
buffer.Pop(1);
if (buffer.Empty)
{
buffer.ReadFrom(input, 1);
}
bool negative = false;
if (buffer.FirstByte == 0x2d) // '-'
{
buffer.Pop(1);
negative = true;
}
const byte e = 0x65; // 'e'
BigInteger integer =
DecodeDigits(e, buffer, input, BigInteger.Parse);
return(new Integer(negative ? -integer : integer));
case 0x75: // 'u'
string text = DecodeText(buffer, input);
return(new Text(text));
case 0x6c: // 'l'
buffer.Pop(1);
var elements = new List <IValue>();
while (true)
{
if (buffer.Empty)
{
buffer.ReadFrom(input, 1);
}
if (buffer.FirstByte == 0x65) // 'e'
{
buffer.Pop(1);
break;
}
IValue element = Decode(buffer, input);
elements.Add(element);
}
return(new List(elements));
case 0x64: // 'd'
buffer.Pop(1);
var pairs = new List <KeyValuePair <IKey, IValue> >();
while (true)
{
if (buffer.Empty)
{
buffer.ReadFrom(input, 1);
}
byte?firstByte = buffer.FirstByte;
if (firstByte == null)
{
throw new DecodingException(
$"expected 'e' (0x65) at {pos}, but " +
"the stream terminates unexpectedly"
);
}
if (firstByte == 0x65) // 'e'
{
buffer.Pop(1);
break;
}
IKey key;
if (firstByte == 0x75) // 'u'
{
string textKey = DecodeText(buffer, input);
key = new Text(textKey);
}
else if (firstByte >= 0x30 && firstByte < 0x40)
{
byte[] binaryKey = DecodeBinary(buffer, input);
key = new Binary(binaryKey);
}
else
{
throw new DecodingException(
$"an unexpected byte 0x{firstByte:x} at {pos}"
);
}
IValue value = Decode(buffer, input);
pairs.Add(new KeyValuePair <IKey, IValue>(key, value));
}
return(new Dictionary(pairs));
case 0x30: // '0'
case 0x31: // '1'
case 0x32: // '2'
case 0x33: // '3'
case 0x34: // '4'
case 0x35: // '5'
case 0x36: // '6'
case 0x37: // '7'
case 0x38: // '8'
case 0x39: // '9'
byte[] binary = DecodeBinary(buffer, input);
return(new Binary(binary));
}
throw new DecodingException(
$"an unexpected byte 0x{buffer.FirstByte:x} at {pos}"
);
}
public void TestByteChunkQueue()
{
var q = new ByteChunkQueue();
// {}
Assert.Equal(0, q.ByteLength);
Assert.True(q.Empty);
Assert.Throws <ArgumentException>(() => q.Pop(0));
Assert.Throws <ArgumentException>(() => q.Pop(-1));
Assert.Empty(q.Pop(1));
Assert.Empty(q.Pop(2));
Assert.True(q.StartsWith(new byte[0]));
Assert.False(q.StartsWith(new byte[] { 1, 2 }));
Assert.Null(q.FirstByte);
Assert.Equal(-1, q.IndexOf(1));
Assert.EndsWith("[]", q.ToString());
q.Append(new byte[] { 1, 2, 3, 4 });
// {1 2 3 4}
Assert.Equal(4, q.ByteLength);
Assert.False(q.Empty);
Assert.True(q.StartsWith(new byte[0]));
Assert.True(q.StartsWith(new byte[] { 1, 2 }));
Assert.True(q.StartsWith(new byte[] { 1, 2, 3, 4 }));
Assert.False(q.StartsWith(new byte[] { 1, 2, 3, 4, 5 }));
Assert.False(q.StartsWith(new byte[] { 1, 3 }));
Assert.Equal((byte)1, q.FirstByte);
Assert.Equal(0, q.IndexOf(1));
Assert.Equal(2, q.IndexOf(3));
Assert.Equal(-1, q.IndexOf(5));
Assert.EndsWith("[01-02-03-04]", q.ToString());
byte[] popped = q.Pop(2);
// {1 2 > 3 4}
Assert.Equal(new byte[] { 1, 2 }, popped);
Assert.Equal(2, q.ByteLength);
Assert.False(q.Empty);
Assert.True(q.StartsWith(new byte[0]));
Assert.True(q.StartsWith(new byte[] { 3 }));
Assert.True(q.StartsWith(new byte[] { 3, 4 }));
Assert.False(q.StartsWith(new byte[] { 3, 4, 5 }));
Assert.False(q.StartsWith(new byte[] { 1, 2 }));
Assert.Equal((byte)3, q.FirstByte);
Assert.Equal(-1, q.IndexOf(1));
Assert.Equal(0, q.IndexOf(3));
Assert.Equal(1, q.IndexOf(4));
Assert.Equal(-1, q.IndexOf(5));
Assert.EndsWith("[01-02|03-04]", q.ToString());
var input = new MemoryStream(
new byte[] { 5, 6, 7, 8, 9, 10, 11, 12 }
);
q.ReadFrom(input, 4);
// {1 2 > 3 4, 5 6 7 8}
Assert.Equal(6, q.ByteLength);
Assert.False(q.Empty);
Assert.True(q.StartsWith(new byte[0]));
Assert.True(q.StartsWith(new byte[] { 3 }));
Assert.True(q.StartsWith(new byte[] { 3, 4 }));
Assert.True(q.StartsWith(new byte[] { 3, 4, 5 }));
Assert.True(q.StartsWith(new byte[] { 3, 4, 5, 6, 7, 8 }));
Assert.False(q.StartsWith(new byte[] { 3, 4, 5, 6, 7, 8, 9 }));
Assert.False(q.StartsWith(new byte[] { 1, 2 }));
Assert.Equal((byte)3, q.FirstByte);
Assert.Equal(-1, q.IndexOf(1));
Assert.Equal(0, q.IndexOf(3));
Assert.Equal(4, q.IndexOf(7));
Assert.Equal(-1, q.IndexOf(9));
Assert.EndsWith("[01-02|03-04 05-06-07-08]", q.ToString());
popped = q.Pop(4);
// {5 6 > 7 8}
Assert.Equal(new byte[] { 3, 4, 5, 6 }, popped);
Assert.Equal(2, q.ByteLength);
Assert.False(q.Empty);
Assert.True(q.StartsWith(new byte[0]));
Assert.True(q.StartsWith(new byte[] { 7 }));
Assert.True(q.StartsWith(new byte[] { 7, 8 }));
Assert.False(q.StartsWith(new byte[] { 7, 8, 9 }));
Assert.False(q.StartsWith(new byte[] { 1, 2 }));
Assert.False(q.StartsWith(new byte[] { 3 }));
Assert.Equal((byte)7, q.FirstByte);
Assert.Equal(-1, q.IndexOf(3));
Assert.Equal(0, q.IndexOf(7));
Assert.Equal(1, q.IndexOf(8));
Assert.Equal(-1, q.IndexOf(9));
Assert.EndsWith("[05-06|07-08]", q.ToString());
q.ReadFrom(input, 3);
// {5 6 > 7 8, 9 10 11}
Assert.Equal(5, q.ByteLength);
Assert.False(q.Empty);
Assert.True(q.StartsWith(new byte[0]));
Assert.True(q.StartsWith(new byte[] { 7 }));
Assert.True(q.StartsWith(new byte[] { 7, 8 }));
Assert.True(q.StartsWith(new byte[] { 7, 8, 9 }));
Assert.True(q.StartsWith(new byte[] { 7, 8, 9, 10, 11 }));
Assert.False(q.StartsWith(new byte[] { 7, 8, 9, 10, 11, 12 }));
Assert.False(q.StartsWith(new byte[] { 1, 2 }));
Assert.False(q.StartsWith(new byte[] { 3 }));
Assert.Equal((byte)7, q.FirstByte);
Assert.Equal(-1, q.IndexOf(3));
Assert.Equal(-1, q.IndexOf(6));
Assert.Equal(0, q.IndexOf(7));
Assert.Equal(2, q.IndexOf(9));
Assert.Equal(4, q.IndexOf(11));
Assert.Equal(-1, q.IndexOf(12));
Assert.EndsWith("[05-06|07-08 09-0A-0B]", q.ToString());
q.ReadFrom(input, 10);
// {5 6 > 7 8, 9 10 11, 12}
Assert.Equal(6, q.ByteLength);
Assert.False(q.Empty);
Assert.True(q.StartsWith(new byte[0]));
Assert.True(q.StartsWith(new byte[] { 7 }));
Assert.True(q.StartsWith(new byte[] { 7, 8, 9 }));
Assert.True(q.StartsWith(new byte[] { 7, 8, 9, 10, 11 }));
Assert.True(q.StartsWith(new byte[] { 7, 8, 9, 10, 11, 12 }));
Assert.False(q.StartsWith(new byte[] { 7, 8, 9, 10, 11, 12, 13 }));
Assert.False(q.StartsWith(new byte[] { 1, 2 }));
Assert.False(q.StartsWith(new byte[] { 3 }));
Assert.Equal((byte)7, q.FirstByte);
Assert.Equal(-1, q.IndexOf(6));
Assert.Equal(0, q.IndexOf(7));
Assert.Equal(5, q.IndexOf(12));
Assert.Equal(-1, q.IndexOf(13));
Assert.EndsWith("[05-06|07-08 09-0A-0B 0C]", q.ToString());
q.Append(new byte[] { 13, 14 });
// {5 6 > 7 8, 9 10 11, 12, 13 14}
Assert.Equal(8, q.ByteLength);
Assert.False(q.Empty);
Assert.True(q.StartsWith(new byte[0]));
Assert.True(q.StartsWith(new byte[] { 7 }));
Assert.True(q.StartsWith(new byte[] { 7, 8, 9 }));
Assert.True(q.StartsWith(new byte[] { 7, 8, 9, 10, 11, 12 }));
Assert.True(q.StartsWith(new byte[] { 7, 8, 9, 10, 11, 12, 13 }));
Assert.False(
q.StartsWith(new byte[] { 7, 8, 9, 10, 11, 12, 13, 14, 15 })
);
Assert.False(q.StartsWith(new byte[] { 1, 2 }));
Assert.False(q.StartsWith(new byte[] { 3 }));
Assert.Equal((byte)7, q.FirstByte);
Assert.Equal(-1, q.IndexOf(6));
Assert.Equal(0, q.IndexOf(7));
Assert.Equal(7, q.IndexOf(14));
Assert.Equal(-1, q.IndexOf(15));
Assert.EndsWith("[05-06|07-08 09-0A-0B 0C 0D-0E]", q.ToString());
q.Append(new byte[] { 15 });
// {5 6 > 7 8, 9 10 11, 12, 13 14, 15}
Assert.Equal(9, q.ByteLength);
Assert.False(q.Empty);
Assert.True(q.StartsWith(new byte[0]));
Assert.True(q.StartsWith(new byte[] { 7 }));
Assert.True(q.StartsWith(new byte[] { 7, 8, 9 }));
Assert.True(
q.StartsWith(new byte[] { 7, 8, 9, 10, 11, 12, 13, 14, 15 })
);
Assert.False(
q.StartsWith(new byte[] { 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 })
);
Assert.False(q.StartsWith(new byte[] { 1, 2 }));
Assert.False(q.StartsWith(new byte[] { 3 }));
Assert.Equal((byte)7, q.FirstByte);
Assert.Equal(-1, q.IndexOf(6));
Assert.Equal(0, q.IndexOf(7));
Assert.Equal(8, q.IndexOf(15));
Assert.Equal(-1, q.IndexOf(16));
Assert.EndsWith("[05-06|07-08 09-0A-0B 0C 0D-0E 0F]", q.ToString());
popped = q.Pop(7);
// {13 > 14, 15}
Assert.Equal(new byte[] { 7, 8, 9, 10, 11, 12, 13 }, popped);
Assert.Equal(2, q.ByteLength);
Assert.False(q.Empty);
Assert.True(q.StartsWith(new byte[0]));
Assert.True(q.StartsWith(new byte[] { 14 }));
Assert.True(q.StartsWith(new byte[] { 14, 15 }));
Assert.False(q.StartsWith(new byte[] { 14, 15, 16 }));
Assert.False(q.StartsWith(new byte[] { 1, 2 }));
Assert.False(q.StartsWith(new byte[] { 7 }));
Assert.False(q.StartsWith(new byte[] { 7, 8, 9 }));
Assert.Equal((byte)14, q.FirstByte);
Assert.Equal(-1, q.IndexOf(7));
Assert.Equal(-1, q.IndexOf(13));
Assert.Equal(0, q.IndexOf(14));
Assert.Equal(1, q.IndexOf(15));
Assert.Equal(-1, q.IndexOf(16));
Assert.EndsWith("[0D|0E 0F]", q.ToString());
popped = q.Pop(10);
// {}
Assert.Equal(new byte[] { 14, 15 }, popped);
Assert.Equal(0, q.ByteLength);
Assert.True(q.Empty);
Assert.True(q.StartsWith(new byte[0]));
Assert.False(q.StartsWith(new byte[] { 1, 2 }));
Assert.False(q.StartsWith(new byte[] { 14 }));
Assert.False(q.StartsWith(new byte[] { 14, 15 }));
Assert.False(q.StartsWith(new byte[] { 14, 15, 16 }));
Assert.Null(q.FirstByte);
Assert.Equal(-1, q.IndexOf(13));
Assert.Equal(-1, q.IndexOf(15));
Assert.Equal(-1, q.IndexOf(16));
Assert.EndsWith("[]", q.ToString());
}