fix: correct name length package generation

Fixed an issue with name length generation for domain names
which resulted into micropython-mdns creating wrongly
formatted dns packages which couldn't be parsed by
certain implementations of mdns like avahi.

Fixes #6

src/mdns_client/responder.py

@@ -186,7 +186,7 @@ def _get_service_of(self, query: str) -> "Optional[str]":
     def _ptr_record_for(self, query: str) -> DNSRecord:
         ptr_target = ".".join((self.host, query))
         # For some reason the PTR is shortened and the last two bytes are removed
-        ptr_target_bytes = name_to_bytes(ptr_target)[:-2] 
+        ptr_target_bytes = name_to_bytes(ptr_target)
         return DNSRecord(query, TYPE_PTR, CLASS_IN, DEFAULT_TTL, ptr_target_bytes)
 
     def _srv_record_for(self, query: str) -> "Optional[DNSRecord]":

src/mdns_client/structs.py

@@ -57,11 +57,11 @@ def checked_name(self) -> "List[bytes]":
 
     def to_bytes(self) -> bytes:
         checked_name = self.checked_name
+        # Require a null bit in the end of the string
         query_len = string_packed_len(checked_name)
-        header_length = query_len + 8
+        header_length = query_len + 10
         rdata_length = len(self.rdata)
-        payload_length = 2 + rdata_length
-        buffer = bytearray(header_length + payload_length)
+        buffer = bytearray(header_length + rdata_length)
         pack_name(buffer, checked_name)
         index = query_len
         pack_into("!HHLH", buffer, index, self.record_type, self.query_class, self.time_to_live, rdata_length)

src/mdns_client/util.py

@@ -33,17 +33,17 @@ def check_name(n: str) -> "List[bytes]":
         n = n.split(".")
         if n[-1] == "":
             n = n[:-1]
-    n = [i.encode("UTF8") if isinstance(i, str) else i for i in n]
+    n = [i.encode("UTF-8") if isinstance(i, str) else i for i in n]
     return n
 
 
-def string_packed_len(string: "List[bytes]") -> int:
-    return sum(len(i) + 1 for i in string) + 1
+def string_packed_len(byte_list: "List[bytes]") -> int:
+    return sum(len(i) + 1 for i in byte_list) + 1
 
 
 def name_to_bytes(name: str) -> bytes:
     name_bytes = check_name(name)
-    buffer = bytearray(len(name_bytes) + len(name))
+    buffer = bytearray(string_packed_len(name_bytes))
     pack_name(buffer, name_bytes)
     return buffer
 
@@ -60,7 +60,7 @@ def pack_name(buffer: bytes, string: "List[bytes]") -> None:
         after_size_next_index = output_index + 1
         end_of_pack_name_index = after_size_next_index + part_length
         buffer[after_size_next_index:end_of_pack_name_index] = part
-        output_index += part_length + 1
+        output_index = end_of_pack_name_index
     buffer[output_index] = 0
 
 

test/run-test.py

@@ -0,0 +1,23 @@
+from zeroconf import ServiceBrowser, ServiceListener, Zeroconf
+
+
+class MyListener(ServiceListener):
+
+    def update_service(self, zc: Zeroconf, type_: str, name: str) -> None:
+        print(f"Service {name} updated")
+
+    def remove_service(self, zc: Zeroconf, type_: str, name: str) -> None:
+        print(f"Service {name} removed")
+
+    def add_service(self, zc: Zeroconf, type_: str, name: str) -> None:
+        info = zc.get_service_info(type_, name)
+        print(f"Service {name} added, service info: {info}")
+
+
+zeroconf = Zeroconf()
+listener = MyListener()
+browser = ServiceBrowser(zeroconf, "_myawesomeservice._tcp.local.", listener)
+try:
+    input("Press enter to exit...\n\n")
+finally:
+    zeroconf.close()

test/service_announcement.py

@@ -0,0 +1,40 @@
+import uasyncio as asyncio
+
+from mdns_client import Client
+from mdns_client.responder import Responder, generate_random_postfix
+
+print("Connected to WIFI!")
+
+
+async def serve_client(reader, writer):
+    writer.write("HTTP/1.0 200 OK\r\nContent-type: text/html\r\n\r\n")
+    writer.write("<h1>test response</h1>")
+    await writer.drain()
+    await writer.wait_closed()
+    print("disconnected")
+
+
+async def setup_mdns():
+    local_ip = "0.0.0.0"
+    print(f"Setting up MDNS on local ip: {local_ip}")
+    client = Client(local_ip)
+    host = "pico-{}".format(generate_random_postfix())
+    responder = Responder(
+        client,
+        own_ip=lambda: local_ip,
+        host=lambda: host,
+    )
+    responder.debug = True
+    responder.advertise("_myawesomeservice", "_tcp", port=1234)
+
+
+
+async def run():
+    await setup_mdns()
+    await asyncio.create_task(asyncio.start_server(serve_client, "0.0.0.0", 1234)) # open port 1234 
+
+    while True:
+        await asyncio.sleep(3)
+
+
+asyncio.run(run())