From bbeac78d266ec764e66fd1b3fe77ed0ee6085e71 Mon Sep 17 00:00:00 2001
From: Ruakij <alexander.b@railduction.eu>
Date: Mon, 2 Aug 2021 11:28:21 +0200
Subject: [PATCH] Initial script

---
 daemon.py | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100755 daemon.py

diff --git a/daemon.py b/daemon.py
new file mode 100755
index 0000000..20dae36
--- /dev/null
+++ b/daemon.py
@@ -0,0 +1,102 @@
+#!/usr/bin/python3 
+
+import os, subprocess, socket, datetime, getopt, sys, re, atexit, logging as log
+
+import dns.flags
+import dns.message
+import dns.rdataclass
+import dns.rdatatype
+import dns.name
+
+from typing import cast
+
+
+def main(args):
+    setupLogging(True)
+    log.debug("Logging started")
+
+    s = setupSocket('172.17.0.1', 53)
+    
+    startListen(s)
+
+def setupSocket(address, port):
+    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    s.bind((address, port))
+    return s
+
+def startListen(s):
+    log.debug('Now listening')
+    while True:
+        (address, dmsg) = receiveFromWire(s)
+
+        if handleQuery(s, address, dmsg) != True:
+            continue
+
+def receiveFromWire(s):
+    (wire, address) = s.recvfrom(512)
+    dmsg = dns.message.from_wire(wire)
+    return (address, dmsg)
+
+def handleQuery(s, address, dmsg):
+    log.info(f'{address[0]} |\tGot query')
+
+    opcode = dmsg.opcode()
+    if opcode != dns.opcode.NOTIFY:
+        log.error(f"{address[0]} |\tExpected opcode=NOTIFY, but was {dns.opcode.to_text(opcode)}")
+        makeResponseWithRCode(s, address, dmsg, dns.rcode.REFUSED)
+        return False
+    
+    rcode = dmsg.rcode()
+    if rcode != dns.rcode.NOERROR:
+        log.error(f"{address[0]} |\tExpected rcode=NOERROR, but was {dns.rcode.to_text(rcode)}")
+        makeResponseWithRCode(s, address, dmsg, dns.rcode.FORMERR)
+        return False
+    
+    #flags = dmsg.flags
+    #if flags != dns.flags.AA:
+    #    print('Expected flags=AA, but was', dns.flags.to_text(flags))
+    #    continue
+
+    if len(dmsg.question) != 1:
+        log.error(f'{address[0]} |\tExpected question-len=1, but was {len(dmsg.question)}')
+        makeResponseWithRCode(s, address, dmsg, dns.rcode.FORMERR)
+        return False
+    
+    # Check record in question
+    record = dmsg.question[0]
+    
+    r_datatype = record.rdtype;
+    if r_datatype != dns.rdatatype.SOA:
+        log.error(f'{address[0]} |\tExpected record to be SOA, but was {r_datatype}')
+        makeResponseWithRCode(s, address, dmsg, dns.rcode.FORMERR)
+        return False
+    
+    log.info(f'{address[0]} |\tNOTIFY for {record.name}')
+
+    response = dns.message.make_response(dmsg) # type: dns.message.Message
+    response.flags |= dns.flags.AA
+    sendResponse(s, address, response)
+    log.debug(f'{address[0]} |\tSent response')
+    
+    return True
+
+def makeResponseWithRCode(socket, address, dmsg, rcode):
+    response = dns.message.make_response(dmsg) # type: dns.message.Message
+    response.set_rcode(rcode)
+    sendResponse(socket, address, response)
+
+def sendResponse(socket, address, response):
+    wire = response.to_wire(cast(dns.name.Name, response))
+    socket.sendto(wire, address)
+
+def setupLogging(verbose: bool):
+    level = log.INFO
+    format = '%(asctime)s %(levelname)s:\t%(message)s'
+    
+    if verbose:
+        level = log.DEBUG
+
+    log.basicConfig(stream=sys.stdout, format=format, level=level)
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv))