from exceptions import Exception
from struct import unpack
import gzip, socket

class PGException(Exception):
    pass

# Incrementally reads PeerGuardian blocklists v1 and v2.
# See http://wiki.phoenixlabs.org/wiki/P2B_Format
class PGReader:

    def __init__(self, filename):
        print "PGReader loading",filename

        # FIXME: Catch and convert exception?
        self.fd = gzip.open(filename, "rb")

        # 4 bytes, should be 0xffffffff
        buf = self.fd.read(4)
        hdr = unpack("l", buf)[0]
        if hdr != -1:
            print "LEADER IS",hdr
            raise PGException("Invalid leader %d"%hdr)

        magic = self.fd.read(3)
        if magic != "P2B":
            raise PGException("Invalid magic code")

        buf = self.fd.read(1)
        ver = ord(buf)
        if ver != 1 and ver != 2:
            raise PGException("Invalid version %d" % ver)

    def next(self):

        # Skip over the string
        buf = -1
        while buf != 0:
            buf = self.fd.read(1)
            if buf == "":  # EOF
                return False
            buf = ord(buf)

        buf = self.fd.read(4)
        start = socket.inet_ntoa(buf)

        buf = self.fd.read(4)
        end = socket.inet_ntoa(buf)

        return (start, end)

    def close(self):
        self.fd.close()