feat: speed up parsing NSEC records

bench/incoming.py

@@ -3,7 +3,15 @@
 import timeit
 from typing import List
 
-from zeroconf import DNSAddress, DNSIncoming, DNSOutgoing, DNSService, DNSText, const
+from zeroconf import (
+    DNSAddress,
+    DNSIncoming,
+    DNSNsec,
+    DNSOutgoing,
+    DNSService,
+    DNSText,
+    const,
+)
 
 
 def generate_packets() -> List[bytes]:
@@ -150,6 +158,16 @@ def generate_packets() -> List[bytes]:
                 record["address"],  # type: ignore
             )
         )
+        out.add_additional_answer(
+            DNSNsec(
+                record["name"],  # type: ignore
+                const._TYPE_NSEC,
+                const._CLASS_IN | const._CLASS_UNIQUE,
+                const._DNS_OTHER_TTL,
+                record["name"],  # type: ignore
+                [const._TYPE_TXT, const._TYPE_SRV],
+            )
+        )
 
     return out.packets()
 

src/zeroconf/_protocol/incoming.pxd

@@ -95,6 +95,16 @@ cdef class DNSIncoming:
     )
     cdef _read_record(self, object domain, unsigned int type_, object class_, object ttl, unsigned int length)
 
+    @cython.locals(
+        offset=cython.uint,
+        offset_plus_one=cython.uint,
+        offset_plus_two=cython.uint,
+        window=cython.uint,
+        bit=cython.uint,
+        byte=cython.uint,
+        i=cython.uint,
+        bitmap_length=cython.uint,
+    )
     cdef _read_bitmap(self, unsigned int end)
 
     cdef _read_name(self)

src/zeroconf/_protocol/incoming.py

@@ -318,9 +318,13 @@ def _read_bitmap(self, end: int) -> List[int]:
         """Reads an NSEC bitmap from the packet."""
         rdtypes = []
         while self.offset < end:
-            window = self.data[self.offset]
-            bitmap_length = self.data[self.offset + 1]
-            for i, byte in enumerate(self.data[self.offset + 2 : self.offset + 2 + bitmap_length]):
+            offset = self.offset
+            offset_plus_one = offset + 1
+            offset_plus_two = offset + 2
+            window = self.data[offset]
+            bitmap_length = self.data[offset_plus_one]
+            bitmap_end = offset_plus_two + bitmap_length
+            for i, byte in enumerate(self.data[offset_plus_two:bitmap_end]):
                 for bit in range(0, 8):
                     if byte & (0x80 >> bit):
                         rdtypes.append(bit + window * 256 + i * 8)