diff --git a/msrplib/protocol.py b/msrplib/protocol.py
index 39377cd..5129df6 100644
--- a/msrplib/protocol.py
+++ b/msrplib/protocol.py
@@ -1,660 +1,666 @@
 # Copyright (C) 2008-2012 AG Projects. See LICENSE for details
 
 import random
 import re
 
 from collections import deque
 from application.system import host as host_module
 from twisted.internet.protocol import connectionDone
 from twisted.protocols.basic import LineReceiver
 
 from msrplib import MSRPError
 
 
 class ParsingError(MSRPError):
     pass
 
 class HeaderParsingError(ParsingError):
 
     def __init__(self, header):
         self.header = header
         ParsingError.__init__(self, "Error parsing %s header" % header)
 
 class MSRPHeaderMeta(type):
     header_classes = {}
 
     def __init__(cls, name, bases, dict):
         type.__init__(cls, name, bases, dict)
         try:
             cls.header_classes[dict['name']] = cls
         except KeyError:
             pass
 
 class MSRPHeader(object):
     __metaclass__ = MSRPHeaderMeta
 
     def __new__(cls, name, value):
         if isinstance(value, str) and name in MSRPHeaderMeta.header_classes:
             cls = MSRPHeaderMeta.header_classes[name]
         return object.__new__(cls)
 
     def __init__(self, name, value):
         self.name = name
         if isinstance(value, str):
             self.encoded = value
         else:
             self.decoded = value
 
     def _raise_error(self):
         raise HeaderParsingError(self.name)
 
     def _get_encoded(self):
         if self._encoded is None:
             self._encoded = self._encode(self._decoded)
         return self._encoded
 
     def _set_encoded(self, encoded):
         self._encoded = encoded
         self._decoded = None
 
     encoded = property(_get_encoded, _set_encoded)
 
     def _get_decoded(self):
         if self._decoded is None:
             self._decoded = self._decode(self._encoded)
         return self._decoded
 
     def _set_decoded(self, decoded):
         self._decoded = decoded
         self._encoded = None
 
     decoded = property(_get_decoded, _set_decoded)
 
     def _decode(self, encoded):
         return encoded
 
     def _encode(self, decoded):
         return decoded
 
 class MSRPNamedHeader(MSRPHeader):
 
     def __new__(cls, *args):
         if len(args) == 1:
             value = args[0]
         else:
             value = args[1]
         return MSRPHeader.__new__(cls, cls.name, value)
 
     def __init__(self, *args):
         if len(args) == 1:
             value = args[0]
         else:
             value = args[1]
         MSRPHeader.__init__(self, self.name, value)
 
 class URIHeader(MSRPNamedHeader):
 
     def _decode(self, encoded):
         try:
             return deque(parse_uri(uri) for uri in encoded.split(" "))
         except ParsingError:
             self._raise_error()
 
     def _encode(self, decoded):
         return " ".join([str(uri) for uri in decoded])
 
 class IntegerHeader(MSRPNamedHeader):
 
     def _decode(self, encoded):
         try:
             return int(encoded)
         except ValueError:
             self._raise_error()
 
     def _encode(self, decoded):
         return str(decoded)
 
 class DigestHeader(MSRPNamedHeader):
 
     def _decode(self, encoded):
         try:
             algo, params = encoded.split(" ", 1)
         except ValueError:
             self._raise_error()
         if algo != "Digest":
             self._raise_error()
         try:
             param_dict = dict((x.strip('"') for x in param.split("=", 1)) for param in params.split(", "))
         except:
             self._raise_error()
         return param_dict
 
     def _encode(self, decoded):
         return "Digest " + ", ".join(['%s="%s"' % tup for tup in decoded.iteritems()])
 
 class ToPathHeader(URIHeader):
     name = "To-Path"
 
 class FromPathHeader(URIHeader):
     name = "From-Path"
 
 class MessageIDHeader(MSRPNamedHeader):
     name = "Message-ID"
 
 class SuccessReportHeader(MSRPNamedHeader):
     name = "Success-Report"
 
     def _decode(self, encoded):
         if encoded not in ["yes", "no"]:
             self._raise_error()
         return encoded
 
 class FailureReportHeader(MSRPNamedHeader):
     name = "Failure-Report"
 
     def _decode(self, encoded):
         if encoded not in ["yes", "no", "partial"]:
             self._raise_error()
         return encoded
 
 class ByteRangeHeader(MSRPNamedHeader):
     name = "Byte-Range"
 
     def _decode(self, encoded):
         try:
             rest, total = encoded.split("/")
             fro, to = rest.split("-")
             fro = int(fro)
         except ValueError:
             self._raise_error()
         try:
             to = int(to)
         except ValueError:
             if to != "*":
                 self._raise_error()
             to = None
         try:
             total = int(total)
         except ValueError:
             if total != "*":
                 self._raise_error()
             total = None
         return (fro, to, total)
 
     def _encode(self, decoded):
         fro, to, total = decoded
         if to is None:
             to = "*"
         if total is None:
             total = "*"
         return "%s-%s/%s" % (fro, to, total)
 
     @property
     def fro(self):
         return self.decoded[0]
 
     @property
     def to(self):
         return self.decoded[1]
 
     @property
     def total(self):
         return self.decoded[2]
 
 class StatusHeader(MSRPNamedHeader):
     name = "Status"
 
     def _decode(self, encoded):
         try:
             namespace, rest = encoded.split(" ", 1)
         except ValueError:
             self._raise_error()
         if namespace != "000":
             self._raise_error()
         rest_sp = rest.split(" ", 1)
         try:
             if len(rest_sp[0]) != 3:
                 raise ValueError
             code = int(rest_sp[0])
         except ValueError:
             self._raise_error()
         try:
             comment = rest_sp[1]
         except IndexError:
             comment = None
         return (code, comment)
 
     def _encode(self, decoded):
         code, comment = decoded
         encoded = "000 %03d" % code
         if comment is not None:
             encoded += " %s" % comment
         return encoded
 
     @property
     def code(self):
         return self.decoded[0]
 
     @property
     def comment(self):
         return self.decoded[1]
 
 class ExpiresHeader(IntegerHeader):
     name = "Expires"
 
 class MinExpiresHeader(IntegerHeader):
     name = "Min-Expires"
 
 class MaxExpiresHeader(IntegerHeader):
     name = "Max-Expires"
 
 class UsePathHeader(URIHeader):
     name = "Use-Path"
 
 class WWWAuthenticateHeader(DigestHeader):
     name = "WWW-Authenticate"
 
 class AuthorizationHeader(DigestHeader):
     name = "Authorization"
 
 class AuthenticationInfoHeader(MSRPNamedHeader):
     name = "Authentication-Info"
 
     def _decode(self, encoded):
         try:
             param_dict = dict((x.strip('"') for x in param.split("=", 1)) for param in encoded.split(", "))
         except:
             self._raise_error()
         return param_dict
 
     def _encode(self, decoded):
         return ", ".join(['%s="%s"' % tup for tup in decoded.iteritems()])
 
 class ContentTypeHeader(MSRPNamedHeader):
     name = "Content-Type"
 
 class ContentIDHeader(MSRPNamedHeader):
     name = "Content-ID"
 
 class ContentDescriptionHeader(MSRPNamedHeader):
     name = "Content-Description"
 
 class ContentDispositionHeader(MSRPNamedHeader):
     name = "Content-Disposition"
 
     def _decode(self, encoded):
         try:
             sp = encoded.split(";")
             disposition = sp[0]
             parameters = dict(param.split("=", 1) for param in sp[1:])
         except:
             self._raise_error()
         return [disposition, parameters]
 
     def _encode(self, decoded):
         disposition, parameters = decoded
         return ";".join([disposition] + ["%s=%s" % pair for pair in parameters.iteritems()])
 
 class UseNicknameHeader(MSRPNamedHeader):
     name = "Use-Nickname"
 
     def _decode(self, encoded):
         return encoded.decode('utf-8')
 
     def _encode(self, decoded):
         return decoded.encode('utf-8')
 
 
 class MSRPData(object):
     def __init__(self, transaction_id, method=None, code=None, comment=None, headers=None, data='', contflag='$'):
+        if method is None and code is None:
+            raise ValueError('either method or code must be specified')
+        elif method is not None and code is not None:
+            raise ValueError('method and code cannot be both specified')
+        elif code is None and comment is not None:
+            raise ValueError('comment should only be specified when code is specified')
         self.transaction_id = transaction_id
         self.method = method
         self.code = code
         self.comment = comment
         self.headers = headers or {}
         self.data = data
         self.contflag = contflag
 
     def copy(self):
         chunk = self.__class__(self.transaction_id)
         chunk.__dict__.update(self.__dict__)
         chunk.headers = dict(self.headers.items())
         return chunk
 
     def __str__(self):
         if self.method is None:
             description = "MSRP %s %s" % (self.transaction_id, self.code)
             if self.comment is not None:
                 description += " %s" % self.comment
         else:
             description = "MSRP %s %s" % (self.transaction_id, self.method)
         return description
 
     def __repr__(self):
         klass = type(self).__name__
         if self.method is None:
             description = "%s %s" % (self.transaction_id, self.code)
             if self.comment is not None:
                 description += " %s" % self.comment
         else:
             description = "%s %s" % (self.transaction_id, self.method)
         if self.message_id is not None:
             description += ' Message-ID=%s' % self.message_id
         for key, value in self.headers.items():
             description += ' %s=%r' % (key, value.encoded)
         description += ' len=%s' % self.size
         return '<%s at %s %s %s>' % (klass, hex(id(self)), description, self.contflag)
 
     def __eq__(self, other):
         if not isinstance(other, MSRPData):
             return False
         return self.encode()==other.encode()
 
     def add_header(self, header):
         self.headers[header.name] = header
 
     def verify_headers(self):
         try: # Decode To-/From-path headers first to be able to send responses
             self.headers["To-Path"].decoded
             self.headers["From-Path"].decoded
         except KeyError, e:
             raise HeaderParsingError(e.args[0])
         for header in self.headers.itervalues():
             header.decoded
 
     @property
     def content_type(self):
         x = self.headers.get('Content-Type')
         if x is None:
             return x
         return x.decoded
 
     @property
     def message_id(self):
         x = self.headers.get('Message-ID')
         if x is None:
             return x
         return x.decoded
 
     @property
     def byte_range(self):
         x = self.headers.get('Byte-Range')
         if x is None:
             return x
         return x.decoded
 
     @property
     def status(self):
         return self.headers.get('Status')
 
     @property
     def failure_report(self):
         if "Failure-Report" in self.headers:
             return self.headers["Failure-Report"].decoded
         else:
             return "yes"
 
     @property
     def success_report(self):
         if "Success-Report" in self.headers:
             return self.headers["Success-Report"].decoded
         else:
             return "no"
 
     @property
     def size(self):
         return len(self.data)
 
     def encode_start(self):
         data = []
         if self.method is not None:
             data.append("MSRP %(transaction_id)s %(method)s" % self.__dict__)
         else:
             data.append("MSRP %(transaction_id)s %(code)03d" % self.__dict__ + (self.comment is not None and " %s" % self.comment or ""))
         headers = self.headers.copy()
         data.append("To-Path: %s" % headers.pop("To-Path").encoded)
         data.append("From-Path: %s" % headers.pop("From-Path").encoded)
         for hnameval in [(hname, headers.pop(hname).encoded) for hname in headers.keys() if not hname.startswith("Content-")]:
             data.append("%s: %s" % hnameval)
         for hnameval in [(hname, headers.pop(hname).encoded) for hname in headers.keys() if hname != "Content-Type"]:
             data.append("%s: %s" % hnameval)
         if len(headers) > 0:
             data.append("Content-Type: %s" % headers["Content-Type"].encoded)
             data.append("")
             data.append("")
         return "\r\n".join(data)
 
     def encode_end(self, continuation):
         return "\r\n-------%s%s\r\n" % (self.transaction_id, continuation)
 
     def encode(self):
         return self.encode_start() + self.data + self.encode_end(self.contflag)
 
 
 class MSRPProtocol(LineReceiver):
     MAX_LENGTH = 16384
     MAX_LINES = 64
 
     def __init__(self, msrp_transport):
         self.msrp_transport = msrp_transport
         self.term_buf = ''
         self.term_re = None
         self.term_substrings = []
         self._reset()
 
     def _reset(self):
         self._chunk_header = ''
         self.data = None
         self.line_count = 0
 
     def connectionMade(self):
         self.msrp_transport._got_transport(self.transport)
 
     def lineReceived(self, line):
         if self.data:
             if len(line) == 0:
                 terminator = '\r\n-------' + self.data.transaction_id
                 continue_flags = [c+'\r\n' for c in '$#+']
                 self.term_buf = ''
                 self.term_re = re.compile("^(.*)%s([$#+])\r\n(.*)$" % re.escape(terminator), re.DOTALL)
                 self.term_substrings = [terminator[:i] for i in xrange(1, len(terminator)+1)] + [terminator+cont[:i] for cont in continue_flags for i in xrange(1, len(cont))]
                 self.term_substrings.reverse()
 
                 self.msrp_transport.logger.received_new_chunk(self._chunk_header+self.delimiter, self.msrp_transport, chunk=self.data)
                 self.msrp_transport._data_start(self.data)
                 self.setRawMode()
             else:
                 match = self.term_re.match(line)
                 if match:
                     continuation = match.group(1)
                     self.msrp_transport.logger.received_new_chunk(self._chunk_header, self.msrp_transport, chunk=self.data)
                     self.msrp_transport.logger.received_chunk_end(line+self.delimiter, self.msrp_transport, transaction_id=self.data.transaction_id)
                     self.msrp_transport._data_start(self.data)
                     self.msrp_transport._data_end(continuation)
                     self._reset()
                     # This line is only here because it allows the subclass MSRPPRotocol_withLogging
                     # to know that the packet ended. In need of redesign. -Luci
                     self.setLineMode('')
                 else:
                     self._chunk_header += line+self.delimiter
                     self.line_count += 1
                     if self.line_count > self.MAX_LINES:
                         self.msrp_transport.logger.received_illegal_data(self._chunk_header, self.msrp_transport)
                         self._reset()
                         return
                     try:
                         name, value = line.split(': ', 1)
                     except ValueError:
                         return # let this pass silently, we'll just not read this line
                     else:
                         self.data.add_header(MSRPHeader(name, value))
         else: # we received a new message
             try:
                 msrp, transaction_id, rest = line.split(" ", 2)
             except ValueError:
                 self.msrp_transport.logger.received_illegal_data(line+self.delimiter, self.msrp_transport)
                 return # drop connection?
             if msrp != "MSRP":
                 self.msrp_transport.logger.received_illegal_data(line+self.delimiter, self.msrp_transport)
                 return # drop connection?
             method, code, comment = None, None, None
             rest_sp = rest.split(" ", 1)
             try:
                 if len(rest_sp[0]) != 3:
                     raise ValueError
                 code = int(rest_sp[0])
             except ValueError: # we have a request
                 method = rest_sp[0]
             else: # we have a response
                 if len(rest_sp) > 1:
                     comment = rest_sp[1]
             self.data = MSRPData(transaction_id, method, code, comment)
             self.term_re = re.compile("^-------%s([$#+])$" % re.escape(transaction_id))
             self._chunk_header = line+self.delimiter
 
     def lineLengthExceeded(self, line):
         self._reset()
 
     def rawDataReceived(self, data):
         data = self.term_buf + data
         match = self.term_re.match(data)
         if match: # we got the last data for this message
             contents, continuation, extra = match.groups()
             if contents:
                 self.msrp_transport.logger.received_chunk_data(contents, self.msrp_transport, transaction_id=self.data.transaction_id)
                 self.msrp_transport._data_write(contents, final=True)
             self.msrp_transport.logger.received_chunk_end('\r\n-------%s%s\r\n' % (self.data.transaction_id, continuation), self.msrp_transport, transaction_id=self.data.transaction_id)
             self.msrp_transport._data_end(continuation)
             self._reset()
             self.setLineMode(extra)
         else:
             for term in self.term_substrings:
                 if data.endswith(term):
                     self.term_buf = data[-len(term):]
                     data = data[:-len(term)]
                     break
             else:
                 self.term_buf = ''
             self.msrp_transport.logger.received_chunk_data(data, self.msrp_transport, transaction_id=self.data.transaction_id)
             self.msrp_transport._data_write(data, final=False)
 
     def connectionLost(self, reason=connectionDone):
         self.msrp_transport._connectionLost(reason)
 
 
 _re_uri = re.compile("^(?P<scheme>.*?)://(((?P<user>.*?)@)?(?P<host>.*?)(:(?P<port>[0-9]+?))?)(/(?P<session_id>.*?))?;(?P<transport>.*?)(;(?P<parameters>.*))?$")
 def parse_uri(uri_str):
     match = _re_uri.match(uri_str)
     if match is None:
         raise ParsingError("Cannot parse URI")
     uri_params = match.groupdict()
     if uri_params["port"] is not None:
         uri_params["port"] = int(uri_params["port"])
     if uri_params["parameters"] is not None:
         try:
             uri_params["parameters"] = dict(param.split("=") for param in uri_params["parameters"].split(";"))
         except ValueError:
             raise ParsingError("Cannot parse URI parameters")
     scheme = uri_params.pop("scheme")
     if scheme == "msrp":
         uri_params["use_tls"] = False
     elif scheme == "msrps":
         uri_params["use_tls"] = True
     else:
         raise ParsingError("Invalid scheme user in URI: %s" % scheme)
     if uri_params["transport"] != "tcp":
         raise ParsingError('Invalid transport in URI, only "tcp" is accepted: %s' % uri_params["transport"])
     return URI(**uri_params)
 
 class ConnectInfo(object):
     host = None
     use_tls = True
     port = 2855
 
     def __init__(self, host=None, use_tls=None, port=None, credentials=None):
         if host is not None:
             self.host = host
         if use_tls is not None:
             self.use_tls = use_tls
         if port is not None:
             self.port = port
         self.credentials = credentials
         if self.use_tls and self.credentials is None:
             from gnutls.interfaces.twisted import X509Credentials
             self.credentials = X509Credentials(None, None)
 
     @property
     def scheme(self):
         if self.use_tls:
             return 'msrps'
         else:
             return 'msrp'
 
 
 # use TLS_URI and TCP_URI ?
 class URI(ConnectInfo):
 
     def __init__(self, host=None, use_tls=None, user=None, port=None,
                  session_id=None, transport="tcp", parameters=None,
                  credentials=None):
         ConnectInfo.__init__(self, host or host_module.default_ip, use_tls=use_tls, port=port, credentials=credentials)
         self.user = user
         if session_id is None:
             session_id = '%x' % random.getrandbits(80)
         self.session_id = session_id
         self.transport = transport
         if parameters is None:
             self.parameters = {}
         else:
             self.parameters = parameters
 
     def __repr__(self):
         params = [self.host, self.use_tls, self.user, self.port, self.session_id, self.transport, self.parameters]
         defaults = [False, None, None, None, 'tcp', {}]
         while defaults and params[-1]==defaults[-1]:
             del params[-1]
             del defaults[-1]
         return '%s(%s)' % (self.__class__.__name__, ', '.join(`x` for x in params))
 
     def __str__(self):
         uri_str = []
         if self.use_tls:
             uri_str.append("msrps://")
         else:
             uri_str.append("msrp://")
         if self.user:
             uri_str.extend([self.user, "@"])
         uri_str.append(self.host)
         if self.port:
             uri_str.extend([":", str(self.port)])
         if self.session_id:
             uri_str.extend(["/", self.session_id])
         uri_str.extend([";", self.transport])
         for key, value in self.parameters.iteritems():
             uri_str.extend([";", key, "=", value])
         return "".join(uri_str)
 
     def __eq__(self, other):
         """MSRP URI comparison according to section 6.1 of RFC 4975"""
         if self is other:
             return True
         try:
             if self.use_tls != other.use_tls:
                 return False
             if self.host.lower() != other.host.lower():
                 return False
             if self.port != other.port:
                 return False
             if self.session_id != other.session_id:
                 return False
             if self.transport.lower() != other.transport.lower():
                 return False
         except AttributeError:
             return False
         return True
 
     def __ne__(self, other):
         return not self == other
 
     def __hash__(self):
         return hash((self.use_tls, self.host.lower(), self.port, self.session_id, self.transport.lower()))