Improve protocol overhead handling for MTU tlm

vkottler · Aug 12, 2024 · 7746da0 · 7746da0
1 parent ca7c600
commit 7746da0
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Showing 4 changed files with 17 additions and 12 deletions.
diff --git a/runtimepy/net/arbiter/struct/__init__.py b/runtimepy/net/arbiter/struct/__init__.py
@@ -12,7 +12,7 @@
 
 # internal
 from runtimepy.net.arbiter.info import AppInfo, RuntimeStruct
-from runtimepy.net.mtu import UDP_DEFAULT_MTU
+from runtimepy.net.mtu import UDP_DEFAULT_MTU, UDP_HEADER_SIZE
 from runtimepy.net.udp.connection import UdpConnection
 from runtimepy.primitives import Uint16, Uint64
 from runtimepy.primitives.serializable.framer import SerializableFramer
@@ -128,7 +128,9 @@ def get_payload(probe_size: int) -> bytes:
 
         # This actually sends data over this connection.
         self.framer_tx.set_mtu(
-            self.mtu(probe_create=get_payload), logger=self.logger
+            self.mtu(probe_create=get_payload),
+            logger=self.logger,
+            protocol_overhead=UDP_HEADER_SIZE,
         )
 
     def assign_app_tx(self, pattern: str, app: AppInfo) -> Optional[T]:

diff --git a/runtimepy/net/mixin.py b/runtimepy/net/mixin.py
@@ -15,7 +15,7 @@
 from runtimepy.net import IpHost as _IpHost
 from runtimepy.net import normalize_host as _normalize_host
 from runtimepy.net.connection import BinaryMessage as _BinaryMessage
-from runtimepy.net.mtu import UDP_DEFAULT_MTU, host_discover_mtu
+from runtimepy.net.mtu import ETHERNET_MTU, UDP_DEFAULT_MTU, host_discover_mtu
 
 
 class BinaryMessageQueueMixin:
@@ -54,7 +54,7 @@ def __init__(self, transport: _asyncio.BaseTransport) -> None:
     def mtu(
         self,
         probe_size: int = UDP_DEFAULT_MTU,
-        fallback: int = UDP_DEFAULT_MTU,
+        fallback: int = ETHERNET_MTU,
         probe_create: Callable[[int], bytes] = bytes,
     ) -> int:
         """

diff --git a/runtimepy/net/mtu.py b/runtimepy/net/mtu.py
@@ -30,10 +30,10 @@ class SocketConstants(IntEnum):
     IP_PMTUDISC_DO = 2
 
 
-IP_HEADER_SIZE = 60
-UDP_HEADER_SIZE = 8
 ETHERNET_MTU = 1500
-UDP_DEFAULT_MTU = ETHERNET_MTU - (IP_HEADER_SIZE + UDP_HEADER_SIZE)
+IP_HEADER_SIZE = 60
+UDP_HEADER_SIZE = IP_HEADER_SIZE + 8
+UDP_DEFAULT_MTU = ETHERNET_MTU - UDP_HEADER_SIZE
 
 
 def socket_discover_mtu(
@@ -115,7 +115,7 @@ def discover_mtu(
     *destination: IpHostlike,
     local: IpHost = None,
     probe_size: int = UDP_DEFAULT_MTU,
-    fallback: int = UDP_DEFAULT_MTU,
+    fallback: int = ETHERNET_MTU,
     kind: int = socket.SOCK_DGRAM,
     probe_create: Callable[[int], bytes] = bytes,
 ) -> int:

diff --git a/runtimepy/primitives/serializable/framer.py b/runtimepy/primitives/serializable/framer.py
@@ -24,23 +24,26 @@ def __init__(self, instance: Serializable, mtu: int) -> None:
         self.instance = instance
         self.set_mtu(mtu)
 
-    def set_mtu(self, mtu: int, logger: LoggerType = None) -> int:
+    def set_mtu(
+        self, mtu: int, logger: LoggerType = None, protocol_overhead: int = 0
+    ) -> int:
         """Set a new maximum transmission unit for this framer."""
 
         raw_length = self.instance.length()
         assert raw_length > 0
 
-        self.length = mtu // raw_length
+        self.length = (mtu - protocol_overhead) // raw_length
         assert self.length > 0
 
         self.reset()
 
         if logger is not None:
             logger.info(
-                "Set MTU to %d (%d %d-byte elements).",
-                mtu,
+                "Set MTU to %d (%d %d-byte elements, %d bytes overhead).",
+                mtu - protocol_overhead,
                 self.length,
                 raw_length,
+                protocol_overhead,
             )
 
         return self.length