private static async Task <BValue> ReadValueAsync(PeekableReader reader)
{
var firstChar = reader.PeekByte();
if (firstChar < 0)
{
throw new Exception("Unexpected end of stream.");
}
switch (firstChar)
{
case 'd':
return(await ReadDictionaryAsync(reader));
case 'i':
return(await ReadNumberAsync(reader));
case 'l':
return(await ReadListAsync(reader));
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
case '0':
return(await ReadStringAsync(reader));
}
throw new NotImplementedException();
}
private static Task <BString> ReadStringAsync(PeekableReader reader)
{
var lengthBuilder = new StringBuilder();
while (reader.PeekByte() != ':')
{
lengthBuilder.Append((char)reader.ReadByte());
}
Expect(reader, ':');
var length = Convert.ToInt32(lengthBuilder.ToString());
var buffer = new byte[length];
for (var i = 0; i < length; i++)
{
var b = reader.ReadByte();
if (b < 0)
{
throw new Exception("Unexpected end of stream");
}
buffer[i] = (byte)b;
}
return(Task.FromResult(new BString(buffer)));
}
public Task <BValue> DecodeAsync(Stream stream)
{
if (stream is null)
{
throw new ArgumentNullException(nameof(stream));
}
var reader = new PeekableReader(stream);
return(ReadValueAsync(reader));
}
private static void Expect(PeekableReader reader, char expectedChar)
{
var foundChar = reader.ReadByte();
if (foundChar < 0)
{
throw new Exception("Unexpected end of stream");
}
if (foundChar != expectedChar)
{
throw new Exception("Unexpected character: " + foundChar);
}
}
private static async Task <BList> ReadListAsync(PeekableReader reader)
{
Expect(reader, 'l');
var list = new BList();
while (reader.PeekByte() != 'e')
{
list.Add(await ReadValueAsync(reader));
}
Expect(reader, 'e');
return(list);
}
private static Task <BNumber> ReadNumberAsync(PeekableReader reader)
{
Expect(reader, 'i');
var builder = new StringBuilder();
while (reader.PeekByte() != 'e')
{
builder.Append((char)reader.ReadByte());
}
Expect(reader, 'e');
var num = Convert.ToInt64(builder.ToString());
return(Task.FromResult(new BNumber(num)));
}
private static async Task <BDictionary> ReadDictionaryAsync(PeekableReader reader)
{
Expect(reader, 'd');
var dict = new BDictionary();
while (reader.PeekByte() != 'e')
{
var key = await ReadStringAsync(reader);
var val = await ReadValueAsync(reader);
dict.Add(key, val);
}
Expect(reader, 'e');
return(dict);
}
