diff --git a/nl80211.py b/nl80211.py
index 6a32d74..3487421 100755
--- a/nl80211.py
+++ b/nl80211.py
@@ -7,26 +7,37 @@ import struct
 
 
 class Iterator(object):
-  def __init__(self, data):
+  def __init__(self, data, offset=0, length=None):
     self.data = data
-    self.offset = 0
+    self.offset = offset
+    self.length = len(self.data) if length is None else length
+    assert self.length <= len(self.data)
 
   def __str__(self):
-    data = self.data[self.offset:]
+    data = self.data[self.offset:self.length]
     return '(%d bytes): %r' % (len(data), data)
 
   def Advance(self, offset_incr):
-    assert self.offset + offset_incr <= len(self.data)
+    assert offset_incr <= self.Remaining(), 'Want %d bytes, have %d' % (offset_incr, self.Remaining())
     self.offset += offset_incr
 
   def Extract(self, length):
-    assert self.offset + length <= len(self.data), 'Want %d bytes, have %d' % (length, len(self.data) - self.offset)
+    assert length <= self.Remaining(), 'Want %d bytes, have %d' % (length, self.Remaining())
     ret = self.data[self.offset:self.offset + length]
     self.Advance(length)
     return ret
 
+  def ExtractIterator(self, length):
+    assert length <= self.Remaining(), 'Want %d bytes, have %d' % (length, self.Remaining())
+    ret = Iterator(self.data, self.offset, self.offset + length)
+    self.Advance(length)
+    return ret
+
+  def Remaining(self):
+    return self.length - self.offset
+
   def AtEnd(self):
-    return self.offset == len(self.data)
+    return not self.Remaining()
 
 
 class Accumulator(object):
@@ -44,9 +55,7 @@ class Accumulator(object):
 
 
 class SingleStructParser(struct.Struct):
-  def Unpack(self, iterator, targetlen=None):
-    if targetlen is not None:
-      assert self.size == targetlen, 'Actual bytes: %d, expected bytes: %d' % (targetlen, self.size)
+  def Unpack(self, iterator):
     values = self.unpack_from(iterator.data, iterator.offset)
     iterator.Advance(self.size)
     assert len(values) == 1
@@ -61,9 +70,7 @@ class StructParser(struct.Struct):
     super(StructParser, self).__init__(format)
     self._fields = fields
 
-  def Unpack(self, iterator, targetlen=None):
-    if targetlen is not None:
-      assert self.size == targetlen, 'Actual bytes: %d, expected bytes: %d' % (targetlen, self.size)
+  def Unpack(self, iterator):
     values = self.unpack_from(iterator.data, iterator.offset)
     iterator.Advance(self.size)
     return dict(zip(self._fields, values))
@@ -76,16 +83,15 @@ class StructParser(struct.Struct):
 
 
 class StringParser(object):
-  def Unpack(self, iterator, targetlen):
-    return iterator.Extract(targetlen)
+  def Unpack(self, iterator):
+    return iterator.Extract(iterator.Remaining())
 
   def Pack(self, accumulator, value):
     accumulator.Append(value)
 
 
 class EmptyParser(object):
-  def Unpack(self, iterator, targetlen=None):
-    assert not targetlen
+  def Unpack(self, iterator):
     return True
 
   def Pack(self, accumulator, value=None):
@@ -103,17 +109,17 @@ class Attribute(object):
    super(Attribute, self).__init__()
    self._attributes = attributes
 
-  def Unpack(self, iterator, targetlen=None):
+  def Unpack(self, iterator):
     nlattr = self._nlattr.Unpack(iterator)
-    if targetlen is not None:
-      assert nlattr['len'] == targetlen
     value = iterator.data[iterator.offset:iterator.offset + nlattr['len'] - self._nlattr.size]
     name, sub_parser = self._attributes.get(nlattr['type'], (None, None))
     assert sub_parser, 'Unknown attribute type %d, len %d' % (nlattr['type'], nlattr['len'])
     sub_len = nlattr['len'] - self._nlattr.size
+    sub_iterator = iterator.ExtractIterator(sub_len)
     ret = {
-      name: sub_parser.Unpack(iterator, sub_len)
+      name: sub_parser.Unpack(sub_iterator)
     }
+    assert sub_iterator.AtEnd(), '%d bytes remaining' % sub_iterator.Remaining()
 
     padding = ((nlattr['len'] + 4 - 1) & ~3) - nlattr['len']
     iterator.Advance(padding)
@@ -134,9 +140,7 @@ class Attributes(object):
     self._attribute_idx = dict((v[0], k) for k, v in attributes.iteritems())
     self._attribute = Attribute(attributes)
 
-  def Unpack(self, iterator, targetlen=None):
-    if targetlen is not None:
-      iterator = Iterator(iterator.Extract(targetlen))
+  def Unpack(self, iterator):
     ret = {}
     while not iterator.AtEnd():
       ret.update(self._attribute.Unpack(iterator))
@@ -154,13 +158,14 @@ class Array(object):
     super(Array, self).__init__()
     self._child = child
 
-  def Unpack(self, iterator, targetlen=None):
-    if targetlen is not None:
-      iterator = Iterator(iterator.Extract(targetlen))
+  def Unpack(self, iterator):
     ret = []
     while not iterator.AtEnd():
       hdr = self._arrayhdr.Unpack(iterator)
-      ret.append(self._child.Unpack(iterator, hdr['len'] - self._arrayhdr.size))
+      sub_len = hdr['len'] - self._arrayhdr.size
+      sub_iterator = iterator.ExtractIterator(sub_len)
+      ret.append(self._child.Unpack(sub_iterator))
+      assert sub_iterator.AtEnd(), '%d bytes remaining' % sub_iterator.Remaining()
     return ret
 
 
@@ -258,42 +263,52 @@ STA_FLAG_TDLS_PEER = 1 << 5
 STA_FLAG_ASSOCIATED = 1 << 6
 
 
-int_genquery = Accumulator()
-genlmsghdr.Pack(
-  int_genquery,
-  cmd=CMD_GET_STATION,
-  version=0,
-  reserved=0)
-nl80211_attr.Pack(
-  int_genquery,
-  ifindex=6)
-genquery = Accumulator()
-nlmsghdr.Pack(
-  genquery, 
-  length=nlmsghdr.size + len(int_genquery),
-  type=20, # XXX
-  flags=F_REQUEST | F_ACK | F_DUMP,
-  seq=random.randint(0, 2 ** 32 - 1),
-  pid=os.getpid())
-genquery.Append(str(int_genquery))
+class Connection(object):
+  def __init__(self):
+    self._sock = socket.socket(socket.AF_NETLINK, socket.SOCK_DGRAM, 16)
+    self._sock.bind((0, 0))
 
-sock = socket.socket(socket.AF_NETLINK, socket.SOCK_DGRAM, 16)
-sock.bind((0, 0))
+  def Send(self, msg):
+    self._sock.send(msg)
+
+  def RecvAndUnpack(self):
+    data = self._sock.recv(4096)
+    iterator = Iterator(data)
+    myhdr = nlmsghdr.Unpack(iterator)
+    print 'nlmsghdr: %s' % myhdr
+    int_iterator = iterator.ExtractIterator(myhdr['length'] - nlmsghdr.size)
+    print 'genlmsghdr: %s' % genlmsghdr.Unpack(int_iterator)
+    print 'ctrl_attr: %s' % ctrl_attr.Unpack(int_iterator)
+
+
+#int_genquery = Accumulator()
+#genlmsghdr.Pack(
+#  int_genquery,
+#  cmd=CMD_GET_STATION,
+#  version=0,
+#  reserved=0)
+#nl80211_attr.Pack(
+#  int_genquery,
+#  ifindex=6)
+#genquery = Accumulator()
+#nlmsghdr.Pack(
+#  genquery, 
+#  length=nlmsghdr.size + len(int_genquery),
+#  type=20, # XXX
+#  flags=F_REQUEST | F_ACK | F_DUMP,
+#  seq=random.randint(0, 2 ** 32 - 1),
+#  pid=os.getpid())
+#genquery.Append(str(int_genquery))
 
 #sock.send(str(genquery))
 #data = sock.recv(4096)
-#
+
 #iterator = Iterator(data)
 #print 'nlmsghdr: %s' % nlmsghdr.Unpack(iterator)
 #print 'genlmsghdr: %s' % genlmsghdr.Unpack(iterator)
 #print 'nl80211_attr: %s' % nl80211_attr.Unpack(iterator)
 
 query = '\24\0\0\0\20\0\5\3a\6\256T\v\17\0\0\3\1\0\0'
-sock.send(query)
-data = sock.recv(4096)
-iterator = Iterator(data)
-myhdr = nlmsghdr.Unpack(iterator)
-print 'nlmsghdr: %s' % myhdr
-int_iterator = Iterator(iterator.Extract(myhdr['length'] - nlmsghdr.size))
-print 'genlmsghdr: %s' % genlmsghdr.Unpack(int_iterator)
-print 'ctrl_attr: %s' % ctrl_attr.Unpack(int_iterator)
+conn = Connection()
+conn.Send(query)
+conn.RecvAndUnpack()