public static object Decode(Stream stream, bool nullForCollectionEnd = false)
{
var firstOrNothing = stream.ReadByte();
if (firstOrNothing == -1)
{
throw new DecodingException("Unexpected end of stream while expecting next value.");
}
var first = (byte)firstOrNothing;
switch (first)
{
case (byte)'i':
var valueDigits = new List <byte> {
};
while (true)
{
var nextOrNothing = stream.ReadByte();
if (nextOrNothing == -1)
{
throw new DecodingException(
"Unexpected end of stream while parsing integer.");
}
var next = (byte)nextOrNothing;
if (valueDigits.Count == 0 && next == '0')
{
// Leading zeros are not allowed, so this must be i0e.
var endOrNothing = stream.ReadByte();
if (endOrNothing == -1)
{
throw new DecodingException("Unexpected end of stream while parsing zero integer.");
}
var end = (byte)endOrNothing;
if (end != 'e')
{
throw new DecodingException($"Expected 'e' after 'i0', got: {end} '{char.ConvertFromUtf32(end)}'.");
}
return((Int64)0);
}
if (valueDigits.Count == 1 && next == '0' && valueDigits[0] == '-')
{
// Negative zero and leading zeros are not allowed.
throw new DecodingException("Unexpected '-0' parsing integer.");
}
if (next == 'e')
{
if (valueDigits.Count == 0)
{
throw new DecodingException(
"Unexpected 'e' before any digits while parsing integer.");
}
else
{
break; // valid end of integer
}
}
if (next == '-')
{
if (valueDigits.Count > 0)
{
throw new DecodingException(
"Unexpected hyphen-minus after first character of integer value.");
}
}
else if (!('0' <= next && next <= '9'))
{
throw new DecodingException(
$"Expected ASCII digit while parsing integer, got: {next} '{char.ConvertFromUtf32(next)}'.");
}
valueDigits.Add(next);
}
var valueDigitsString = valueDigits.ToArray().FromASCII();
try {
return(Int64.Parse(valueDigitsString));
} catch (System.OverflowException exception) {
throw new DecodingException(
$"Integer out of supported 64-bit bounds: {valueDigitsString}", exception);
}
case (byte)'0':
// Must be the empty string.
var secondOrNothing = stream.ReadByte();
if (secondOrNothing == -1)
{
throw new DecodingException("Unexpected end of stream while parsing empty string.");
}
var second = (byte)secondOrNothing;
if (second != ':')
{
throw new DecodingException($"Expected ':' after leading '0', got: {second} '{char.ConvertFromUtf32(second)}'.");
}
return(new byte[] {});
case (byte)'1':
case (byte)'2':
case (byte)'3':
case (byte)'4':
case (byte)'5':
case (byte)'6':
case (byte)'7':
case (byte)'8':
case (byte)'9':
var lengthDigits = new List <byte> {
first
};
while (true)
{
var nextOrNothing = stream.ReadByte();
if (nextOrNothing == -1)
{
throw new DecodingException(
"Unexpected end of stream while parsing length.");
}
var next = (byte)nextOrNothing;
if (next == ':')
{
break; // valid end of length
}
if (next == '-')
{
if (lengthDigits.Count > 0)
{
throw new DecodingException(
"Unexpected hyphen-minus after first character of integer length.");
}
}
else if (!('0' <= next && next <= '9'))
{
throw new DecodingException(
$"Expected ASCII digit while parsing length, got: {next}");
}
lengthDigits.Add(next);
}
var lengthDigitsString = lengthDigits.ToArray().FromASCII();
Int32 length;
try {
length = Int32.Parse(lengthDigitsString);
} catch (System.OverflowException exception) {
throw new DecodingException(
$"Length out of supported 32-bit bounds: {lengthDigitsString}", exception);
}
var buffer = new byte[length];
var read = stream.Read(buffer, 0, (int)length);
if (read < length)
{
throw new DecodingException(
"Unexpected end of stream while reading string content.");
}
return(buffer);
case (byte)'l':
var list = new List <object> {
};
while (true)
{
var next = Decode(stream, nullForCollectionEnd: true);
if (next == null)
{
break; // valid end of list
}
list.Add(next);
}
return(list);
case (byte)'d':
var dictionary =
new Dictionary <byte[], object>(ByteArrayComparer.Instance);
byte[] previousKey = null;
while (true)
{
var key = Decode(stream, nullForCollectionEnd: true);
if (key == null)
{
break; // valid end of dictionary
}
else if (!(key is byte[]))
{
throw new DecodingException(
$"Expected byte string for dictionary key, got: {key.GetType()}");
}
var typedKey = (byte[])key;
if (previousKey != null)
{
if (!ByteArrayComparer.Ascending(previousKey, typedKey))
{
throw new DecodingException(
"Dictionary key was in the wrong order or duplicated.");
}
}
previousKey = typedKey;
var value = Decode(stream);
dictionary.Add(typedKey, value);
}
return(dictionary);
case (byte)'e':
if (nullForCollectionEnd)
{
return(null); // valid expected end of collection
}
else
{
throw new DecodingException(
$"Found end-of-collection indicator 'e' while expecting value.");
}
default:
throw new DecodingException(
$"Unexpected initial byte in value: {first} '{char.ConvertFromUtf32(first)}'.");
}
}
static ByteArrayComparer()
{
Instance = new ByteArrayComparer();
}
