format, add comments

README.md

@@ -3,4 +3,8 @@ mDNS server
 
 Minimalist mDNS server implementation with only core service annoucement and no conflict resolution.
 
+Listen for `http` service questiond and answer with `toto` service.
+
 To test our implementation we’re using zeroconf as a trusted client.
+
+See the [blog post](https://alexrio.fr/blog/mdns-server) for references and details.

main.py

@@ -1,3 +1,9 @@
+"""
+Simple and navie mDNS implementation.
+
+Low level socket management to listen to mDNS queries and respond to _http._tcp.local service queries with constant name.
+"""
+
 import socket
 from dnslib import DNSRecord, DNSHeader, QTYPE, A, SRV, TXT, RR, PTR
 import dns.message
@@ -6,6 +12,9 @@ multicast_group = "224.0.0.251"
 multicast_port = 5353
 interface_ip = "0.0.0.0"
 
+SERVICE_TO_ANNOUNCE = "toto"
+
+
 def main():
     sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
     sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 32)
@@ -15,12 +24,18 @@ def main():
 
     sock.bind(("", multicast_port))
     #   sock.setsockopt(socket.SOL_IP, socket.IP_ADD_MEMBERSHIP, socket.inet_aton(multicast_group) + socket.inet_aton(interface_ip))
-    sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_IF, socket.inet_aton(interface_ip))
-    sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, socket.inet_aton(multicast_group) + socket.inet_aton(interface_ip))
+    sock.setsockopt(
+        socket.IPPROTO_IP, socket.IP_MULTICAST_IF, socket.inet_aton(interface_ip)
+    )
+    sock.setsockopt(
+        socket.IPPROTO_IP,
+        socket.IP_ADD_MEMBERSHIP,
+        socket.inet_aton(multicast_group) + socket.inet_aton(interface_ip),
+    )
 
     while True:
         received, sender = sock.recvfrom(1500)
-        print(f'Received packet of {len(received)} bytes from {sender}')
+        print(f"Received packet of {len(received)} bytes from {sender}")
         try:
             msg = dns.message.from_wire(received)
         except dns.exception.FormError:
@@ -29,18 +44,36 @@ def main():
 
         if msg.opcode() == dns.opcode.QUERY:
             for question in msg.question:
-                if str(question.name) == '_http._tcp.local.':
+                if str(question.name) == "_http._tcp.local.":
                     print(f"question name {type(msg)}")
                     unicast_response = question.rdclass == 0x8001
                     response = DNSRecord(DNSHeader(id=0, bitmap=0x8400))
-                    ptr = PTR("toto._http._tcp.local")
+                    ptr = PTR(SERVICE_TO_ANNOUNCE + "._http._tcp.local")
                     srv = SRV(target="toto.local", priority=10, port=80, weight=100)
                     txt = TXT("path=/")
                     a = A("192.168.1.21")
-                    response.add_answer(RR('_http._tcp.local', QTYPE.PTR, rdata = ptr, ttl=120))
-                    response.add_ar(RR('toto._http._tcp.local', QTYPE.SRV, rdata = srv, ttl=120))
-                    response.add_ar(RR('toto._http._tcp.local', QTYPE.TXT, rdata = txt, ttl=120))
-                    response.add_ar(RR('toto.local', QTYPE.A, rdata = a, ttl=120))
+                    response.add_answer(
+                        RR("_http._tcp.local", QTYPE.PTR, rdata=ptr, ttl=120)
+                    )
+                    response.add_ar(
+                        RR(
+                            SERVICE_TO_ANNOUNCE + "._http._tcp.local",
+                            QTYPE.SRV,
+                            rdata=srv,
+                            ttl=120,
+                        )
+                    )
+                    response.add_ar(
+                        RR(
+                            SERVICE_TO_ANNOUNCE + "._http._tcp.local",
+                            QTYPE.TXT,
+                            rdata=txt,
+                            ttl=120,
+                        )
+                    )
+                    response.add_ar(
+                        RR(SERVICE_TO_ANNOUNCE + ".local", QTYPE.A, rdata=a, ttl=120)
+                    )
                     print(str(response))
                     if unicast_response:
                         print("Unicast response")
@@ -48,7 +81,8 @@ def main():
                     else:
                         print("Multicast response")
                         sock.sendto(response.pack(), (multicast_group, multicast_port))
-                    print(f'Send response to {sender}')
+                    print(f"Send response to {sender}")
+
 
 if __name__ == "__main__":
     main()

pyproject.toml

@@ -1,7 +1,7 @@
 [project]
 name = "mdns"
 version = "0.1.0"
-description = "Minimalist mdns server"
+description = "Very minimalist mdns server"
 readme = "README.md"
 requires-python = ">=3.11"
 dependencies = [