Allow alternative agentx socket configuration (sonic-net#92)

src/ax_interface/constants.py

@@ -1,6 +1,7 @@
 from enum import Enum, unique
 
 AGENTX_SOCKET_PATH = '/var/agentx/master'
+SNMPD_CONFIG_FILE = '/etc/snmp/snmpd.conf'
 
 # https://tools.ietf.org/html/rfc2741#section-6.1 -- PDU Header definition
 # Headers are fixed at 20 bytes.

src/ax_interface/socket_io.py

@@ -6,6 +6,7 @@
 """
 import asyncio
 import logging
+import re
 
 from . import logger, constants
 from .protocol import AgentX
@@ -25,6 +26,91 @@ def __init__(self, mib_table, run_event, loop):
 
         self.transport = self.ax_socket = None
 
+        self.ax_socket_path = constants.AGENTX_SOCKET_PATH
+
+        # The following code reads the snmp config file to see if the Agentx Socket path has been redefined
+        # from the default RFC value '/var/agentx/master'. We do not implement reading the SNMP daemon's
+        # command line to check if it has been redefined there, this should be an effort for the future
+        # perhaps via a psutil().cmdline() call
+
+        # open the snmpd config file and search for a agentx socket redefinition. Exceptions will be raised
+        # if the constants.SNMPD_CONFIG_FILE or the file in itself do not exist
+        pattern = re.compile("^agentxsocket\s+(.*)$", re.IGNORECASE)
+        try :
+            with open(constants.SNMPD_CONFIG_FILE,'rt') as config_file:
+                for line in config_file:
+                    match = pattern.search(line)
+                    if match:
+                        self.ax_socket_path = match.group(1)
+        except:
+            logger.warning("SNMPD config file not found, using default agentx file socket")
+
+        self.parse_socket()
+        logger.info("Using agentx socket type " + self.ax_socket_type + " with path " + self.ax_socket_path)
+
+    def parse_socket(self):
+        # Determine wether the socket method is supported
+        # extract the type and connection data
+
+        # lets get the unsuported methods out of the way first
+        unsuported_list = ['ssh', 'dtlsudp', 'ipx', 'aal5pvc', 'udp']
+        for method in unsuported_list:
+            if self.ax_socket_path.startswith(method):
+                # This is not a supported method
+                self.unsuported_method()
+                return
+        # Now the stuff that we are interested in
+        # First case: we have a simple number then its a local UDP port
+        # udp has been added to the unsuported_list because asyncio throws a not implemented error with udp
+        # we leave the code here for when it will be implemented
+        if self.ax_socket_path.isdigit():
+            self.unsuported_method()
+            return
+        # if we have an explicit udp socket 
+        if self.ax_socket_path.startswith('udp'):
+            self.unsuported_method()
+            return
+        # if we have an explicit tcp socket
+        if self.ax_socket_path.startswith('tcp'):
+            self.ax_socket_type = 'tcp'
+            self.host, self.port = self.get_ip_port(self.ax_socket_path.split(':',1)[1])
+            return
+        # if we have an explicit unix domain socket
+        if self.ax_socket_path.startswith('unix'):
+            self.ax_socket_type = 'unix'
+            self.ax_socket_path = self.ax_socket_path.split(':',1)[1]
+            return
+        # unix is not compulsory so you can also have a plain path
+        if '/' in self.ax_socket_path:
+            self.ax_socket_type = 'unix'
+            return
+        # if at this point we haven't matched anything yet its that we are most likely left with a host:port pair so UDP
+        if ':' in self.ax_socket_path:
+            self.unsuported_method()
+            return
+        # we should never get here but if we do it's that there is garbage so lets revert to the default of snmp
+        logger.warning("There's something weird with " + self.ax_socket_path + " , using default agentx file socket")
+        self.ax_socket_path = constants.AGENTX_SOCKET_PATH
+        self.ax_socket_type = 'unix'
+        return
+
+    def get_ip_port(self,address):
+        # determine if we only have a port or a ip:port tuple, must work with IPv6
+        address_list = address.split(':')
+        if len(address_list) == 1:
+            # we only have a port
+            return 'localhost', address_list[0]
+        else:
+            # if we get here then either: we've got garbage, an ip:port or ipv6:port or hostname:port
+            # an IP or IPv6 only is illegal
+            address_list = address.rsplit(':',1)
+            return address_list[0], address_list[1]
+
+    def unsuported_method(self):
+        logger.warning("Socket type " + self.ax_socket_path + " not supported, using default agentx file socket")
+        self.ax_socket_path = constants.AGENTX_SOCKET_PATH
+        self.ax_socket_type = 'unix'
+
     async def connection_loop(self):
         """
         Try/Retry connection coroutine to attach the socket.
@@ -37,10 +123,27 @@ async def connection_loop(self):
             try:
                 logger.info("Attempting AgentX socket bind...".format())
 
-                connection_routine = self.loop.create_unix_connection(
-                    protocol_factory=lambda: AgentX(self.mib_table, self.loop),
-                    path=constants.AGENTX_SOCKET_PATH,
-                    sock=self.ax_socket)
+                # Open the connection to the Agentx socket, we check the socket string to 
+                # lets open our socket according to its detected type
+                if self.ax_socket_type == 'unix':
+                    connection_routine = self.loop.create_unix_connection(
+                        protocol_factory=lambda: AgentX(self.mib_table, self.loop),
+                        path=self.ax_socket_path,
+                        sock=self.ax_socket)
+                elif self.ax_socket_type == 'udp':
+                    # we should not land here as the udp method is in the unsuported list
+                    # testing shows that async_io throws a NotImplementedError when udp is used
+                    # the code remains for when asyncio will implement it
+                    connection_routine = self.loop.create_datagram_endpoint(
+                        protocol_factory=lambda: AgentX(self.mib_table, self.loop),
+                        remote_addr=(self.host,self.port),
+                        sock=self.ax_socket)
+                elif self.ax_socket_type == 'tcp':
+                    connection_routine = self.loop.create_connection(
+                        protocol_factory=lambda: AgentX(self.mib_table, self.loop),
+                        host=self.host,
+                        port=self.port,
+                        sock=self.ax_socket)
 
                 # Initiate the socket connection
                 self.transport, protocol = await connection_routine