rlp.py

def binary_length(n):
    if n == 0: return 0
    else: return 1 + binary_length(n / 256)

def to_binary_array(n,L=None):
    if L is None: L = binary_length(n)
    if n == 0: return []
    else:
        x = to_binary_array(n / 256)
        x.append(n % 256)
        return x

def to_binary(n,L=None): return ''.join([chr(x) for x in to_binary_array(n,L)])

def from_binary(b):
    if len(b) == 0: return 0
    else: return from_binary(b[:-1]) * 256 + ord(b[-1])

def __decode(s,pos=0):
    if not s:
        return (None, 0)
    else:
        fchar = ord(s[pos])
    if fchar < 24:
        return (ord(s[pos]), pos+1)
    elif fchar < 56:
        b = ord(s[pos]) - 23
        return (from_binary(s[pos+1:pos+1+b]), pos+1+b)
    elif fchar < 64:
        b = ord(s[pos]) - 55
        b2 = from_binary(s[pos+1:pos+1+b])
        return (from_binary(s[pos+1+b:pos+1+b+b2]), pos+1+b+b2)
    elif fchar < 120:
        b = ord(s[pos]) - 64
        return (s[pos+1:pos+1+b], pos+1+b)
    elif fchar < 128:
        b = ord(s[pos]) - 119
        b2 = from_binary(s[pos+1:pos+1+b])
        return (s[pos+1+b:pos+1+b+b2], pos+1+b+b2)
    elif fchar < 184:
        b = ord(s[pos]) - 128
        o, pos = [], pos+1
        for i in range(b):
            obj, pos = __decode(s,pos)
            o.append(obj)
        return (o,pos)
    elif fchar < 192:
        b = ord(s[pos]) - 183
        b2 = from_binary(s[pos+1:pos+1+b])
        o, pos = [], pos+1+b
        for i in range(b):
            obj, pos = __decode(s,pos)
            o.append(obj)
        return (o,pos)
    else:
        raise Exception("byte not supported: "+fchar)

def decode(s): return __decode(s)[0]

def encode(s):
    if isinstance(s,(int,long)):
        if s < 0:
            raise Exception("can't handle negative ints")
        elif s >= 0 and s < 24:
            return chr(s)
        elif s <= 2**256:
            b = to_binary(s)
            return chr(len(b) + 23) + b
        else:
            b = to_binary(s)
            b2 = to_binary(len(b))
            return chr(len(b2) + 55) + b2 + b
    elif isinstance(s,str):
        if len(s) < 56:
            return chr(len(s) + 64) + s
        else:
            b2 = to_binary(len(s))
            return chr(len(b2) + 119) + b2 + s
    elif isinstance(s,list):
        if len(s) < 56:
            return chr(len(s) + 128) + ''.join([encode(x) for x in s])
        else:
            b2 = to_binary(len(s))
            return chr(len(b2) + 183) + b2 + ''.join([encode(x) for x in s])
    else:
        raise Exception("Encoding for "+s+" not yet implemented")