def fetch_routing_table(self, address):
""" Fetch a routing table from a given router address.
:param address: router address
:return: a new RoutingTable instance or None if the given router is
currently unable to provide routing information
:raise ServiceUnavailable: if no writers are available
:raise ProtocolError: if the routing information received is unusable
"""
new_routing_info = self.fetch_routing_info(address)
if new_routing_info is None:
return None
# Parse routing info and count the number of each type of server
new_routing_table = RoutingTable.parse_routing_info(new_routing_info)
num_routers = len(new_routing_table.routers)
num_readers = len(new_routing_table.readers)
num_writers = len(new_routing_table.writers)
# No writers are available. This likely indicates a temporary state,
# such as leader switching, so we should not signal an error.
# When no writers available, then we flag we are reading in absence of writer
self.missing_writer = (num_writers == 0)
# No routers
if num_routers == 0:
raise ProtocolError("No routing servers returned from server %r" % (address,))
# No readers
if num_readers == 0:
raise ProtocolError("No read servers returned from server %r" % (address,))
# At least one of each is fine, so return this table
return new_routing_table
def parse_routing_info(cls, records):
""" Parse the records returned from a getServers call and
return a new RoutingTable instance.
"""
if len(records) != 1:
raise ProtocolError("Expected exactly one record")
record = records[0]
routers = []
readers = []
writers = []
try:
servers = record["servers"]
for server in servers:
role = server["role"]
addresses = []
for address in server["addresses"]:
addresses.extend(resolve(SocketAddress.parse(address, DEFAULT_PORT)))
if role == "ROUTE":
routers.extend(addresses)
elif role == "READ":
readers.extend(addresses)
elif role == "WRITE":
writers.extend(addresses)
ttl = record["ttl"]
except (KeyError, TypeError):
raise ProtocolError("Cannot parse routing info")
else:
return cls(routers, readers, writers, ttl)
def driver(cls, uri, **config):
""" Acquire a :class:`.Driver` instance for the given URI and
configuration. The URI scheme determines the Driver implementation
that will be returned. Options are:
``bolt``
Returns a :class:`.DirectDriver`.
``bolt+routing``
Returns a :class:`.RoutingDriver`.
:param uri: URI for a graph database service
:param config: configuration and authentication details (valid keys are listed below)
`auth`
An authentication token for the server, for example
``("neo4j", "password")``.
`der_encoded_server_certificate`
The server certificate in DER format, if required.
`encrypted`
A boolean flag to determine whether encryption should be used.
Defaults to :const:`True`.
`trust`
Trust level: one of :attr:`.TRUST_ALL_CERTIFICATES` (default) or
:attr:`.TRUST_SYSTEM_CA_SIGNED_CERTIFICATES`.
`user_agent`
A custom user agent string, if required.
"""
parsed = urlparse(uri)
try:
driver_class = cls.uri_schemes[parsed.scheme]
except KeyError:
raise ProtocolError("URI scheme %r not supported" % parsed.scheme)
else:
return driver_class(uri, **config)
