from cStringIO import StringIO                                                  
import struct

HEADER_FMT = '!L'
HEADER_SIZE = 4

class NSBuffer(object):
    def __init__(self):
        self.buf = StringIO()

    def write(self, s):
        self.buf.write(s)

    def extract(self):
        v = self.buf.getvalue()
        res = []
        while len(v) >= HEADER_SIZE:
            l, = struct.unpack(HEADER_FMT, v[:HEADER_SIZE])
            truncated = v[HEADER_SIZE:]
            if len(truncated) >= l:
                res.append(truncated[:l])
                v = truncated[l:]
            else:
                break
        self.buf = StringIO()
        self.buf.write(v)
        return res

def ns_encode(s):
    return struct.pack(HEADER_FMT, len(s)) + s