Reduce DNSIncoming parsing overhead (#975)

bdraco · web-flow · commit 78f9cd5123d0 · 2021-09-14T10:11:49.000-10:00
- Parsing incoming packets is the most expensive operation
  zeroconf performs on networks with high mDNS volume
diff --git a/zeroconf/__init__.py b/zeroconf/__init__.py
@@ -75,7 +75,6 @@
     IPVersion,
     get_all_addresses,
 )
-from ._utils.struct import int2byte  # noqa # import needed for backwards compat
 from ._utils.time import current_time_millis, millis_to_seconds  # noqa # import needed for backwards compat
 
 __author__ = 'Paul Scott-Murphy, William McBrine'
diff --git a/zeroconf/_protocol.py b/zeroconf/_protocol.py
@@ -28,7 +28,6 @@
 from ._dns import DNSAddress, DNSHinfo, DNSNsec, DNSPointer, DNSQuestion, DNSRecord, DNSService, DNSText
 from ._exceptions import IncomingDecodeError, NamePartTooLongException
 from ._logger import QuietLogger, log
-from ._utils.struct import int2byte
 from ._utils.time import current_time_millis
 from .const import (
     _CLASS_UNIQUE,
@@ -64,6 +63,8 @@
 class DNSMessage:
     """A base class for DNS messages."""
 
+    __slots__ = ('flags',)
+
     def __init__(self, flags: int) -> None:
         """Construct a DNS message."""
         self.flags = flags
@@ -128,11 +129,9 @@ def __repr__(self) -> str:
             ]
         )
 
-    def unpack(self, format_: bytes) -> tuple:
-        length = struct.calcsize(format_)
-        info = struct.unpack(format_, self.data[self.offset : self.offset + length])
+    def unpack(self, format_: bytes, length: int) -> tuple:
         self.offset += length
-        return info
+        return struct.unpack(format_, self.data[self.offset - length : self.offset])
 
     def read_header(self) -> None:
         """Reads header portion of packet"""
@@ -143,16 +142,14 @@ def read_header(self) -> None:
             self.num_answers,
             self.num_authorities,
             self.num_additionals,
-        ) = self.unpack(b'!6H')
+        ) = self.unpack(b'!6H', 12)
 
     def read_questions(self) -> None:
         """Reads questions section of packet"""
         for _ in range(self.num_questions):
             name = self.read_name()
-            type_, class_ = self.unpack(b'!HH')
-
-            question = DNSQuestion(name, type_, class_)
-            self.questions.append(question)
+            type_, class_ = self.unpack(b'!HH', 4)
+            self.questions.append(DNSQuestion(name, type_, class_))
 
     def read_character_string(self) -> bytes:
         """Reads a character string from the packet"""
@@ -168,15 +165,15 @@ def read_string(self, length: int) -> bytes:
 
     def read_unsigned_short(self) -> int:
         """Reads an unsigned short from the packet"""
-        return cast(int, self.unpack(b'!H')[0])
+        return cast(int, self.unpack(b'!H', 2)[0])
 
     def read_others(self) -> None:
         """Reads the answers, authorities and additionals section of the
         packet"""
         n = self.num_answers + self.num_authorities + self.num_additionals
         for _ in range(n):
             domain = self.read_name()
-            type_, class_, ttl, length = self.unpack(b'!HHiH')
+            type_, class_, ttl, length = self.unpack(b'!HHiH', 10)
             end = self.offset + length
             rec = None
             try:
@@ -266,8 +263,7 @@ def read_name(self) -> str:
         labels: List[str] = []
         self.seen_pointers.clear()
         self.offset = self._decode_labels_at_offset(self.offset, labels)
-        labels.append("")
-        name = ".".join(labels)
+        name = ".".join(labels) + "."
         if len(name) > MAX_NAME_LENGTH:
             raise IncomingDecodeError(f"DNS name {name} exceeds maximum length of {MAX_NAME_LENGTH}")
         return name
@@ -440,7 +436,7 @@ def _pack(self, format_: Union[bytes, str], value: Any) -> None:
 
     def _write_byte(self, value: int) -> None:
         """Writes a single byte to the packet"""
-        self._pack(b'!c', int2byte(value))
+        self._pack(b'!c', bytes((value,)))
 
     def _insert_short_at_start(self, value: int) -> None:
         """Inserts an unsigned short at the start of the packet"""
diff --git a/zeroconf/_services/browser.py b/zeroconf/_services/browser.py
@@ -352,21 +352,19 @@ def _async_process_record_update(
         self, now: float, record: DNSRecord, old_record: Optional[DNSRecord]
     ) -> None:
         """Process a single record update from a batch of updates."""
-        expired = record.is_expired(now)
-
         if isinstance(record, DNSPointer):
             if record.name not in self.types:
                 return
             if old_record is None:
                 self._enqueue_callback(ServiceStateChange.Added, record.name, record.alias)
-            elif expired:
+            elif record.is_expired(now):
                 self._enqueue_callback(ServiceStateChange.Removed, record.name, record.alias)
             else:
                 self.reschedule_type(record.name, record.get_expiration_time(_EXPIRE_REFRESH_TIME_PERCENT))
             return
 
         # If its expired or already exists in the cache it cannot be updated.
-        if expired or old_record:
+        if old_record or record.is_expired(now):
             return
 
         if isinstance(record, DNSAddress):
diff --git a/zeroconf/_services/info.py b/zeroconf/_services/info.py
@@ -36,7 +36,6 @@
     _encode_address,
     _is_v6_address,
 )
-from .._utils.struct import int2byte
 from .._utils.time import current_time_millis
 from ..const import (
     _CLASS_IN,
@@ -239,7 +238,7 @@ def _set_properties(self, properties: Dict) -> None:
                 record += b'=' + value
             list_.append(record)
         for item in list_:
-            result = b''.join((result, int2byte(len(item)), item))
+            result = b''.join((result, bytes((len(item),)), item))
         self.text = result
 
     def _set_text(self, text: bytes) -> None:
diff --git a/zeroconf/_utils/struct.py b/zeroconf/_utils/struct.py

Original file line number	Diff line number	Diff line change
`@@ -75,7 +75,6 @@`
`75`	`75`	`IPVersion,`
`76`	`76`	`get_all_addresses,`
`77`	`77`	`)`
`78`		`-from ._utils.struct import int2byte # noqa # import needed for backwards compat`
`79`	`78`	`from ._utils.time import current_time_millis, millis_to_seconds # noqa # import needed for backwards compat`
`80`	`79`
`81`	`80`	`__author__ = 'Paul Scott-Murphy, William McBrine'`