From 9ed5fd517c899ab4b4ed58b8655a751f7d7be5fe Mon Sep 17 00:00:00 2001
From: Youngjoon Lee <5462944+youngjoon-lee@users.noreply.github.com>
Date: Thu, 11 Jul 2024 17:32:48 +0900
Subject: [PATCH] define FlaggedPacket

---
 mixnet/nomssip.py | 56 +++++++++++++++++++++++++----------------------
 1 file changed, 30 insertions(+), 26 deletions(-)

diff --git a/mixnet/nomssip.py b/mixnet/nomssip.py
index 5e76523..f0fc4e6 100644
--- a/mixnet/nomssip.py
+++ b/mixnet/nomssip.py
@@ -1,8 +1,10 @@
+from __future__ import annotations
+
 import asyncio
 import hashlib
 from dataclasses import dataclass
 from enum import Enum
-from typing import Awaitable, Callable
+from typing import Awaitable, Callable, Self
 
 from mixnet.connection import DuplexConnection, MixSimplexConnection, SimplexConnection
 
@@ -38,9 +40,9 @@ class Nomssip:
             # For simplicity of the spec, reject the connection if the peering degree is reached.
             raise ValueError("The peering degree is reached.")
 
-        noise_packet = self.__build_packet(
-            self.PacketType.NOISE, bytes(self.config.msg_size)
-        )
+        noise_packet = FlaggedPacket(
+            FlaggedPacket.Flag.NOISE, bytes(self.config.msg_size)
+        ).bytes()
         conn = DuplexConnection(
             inbound,
             MixSimplexConnection(
@@ -62,14 +64,14 @@ class Nomssip:
             if self.__check_update_cache(packet):
                 continue
 
-            flag, msg = self.__parse_packet(packet)
-            match flag:
-                case self.PacketType.NOISE:
+            packet = FlaggedPacket.from_bytes(packet)
+            match packet.flag:
+                case FlaggedPacket.Flag.NOISE:
                     # Drop noise packet
                     continue
-                case self.PacketType.REAL:
-                    await self.__gossip(packet)
-                    await self.handler(msg)
+                case FlaggedPacket.Flag.REAL:
+                    await self.__gossip_flagged_packet(packet)
+                    await self.handler(packet.message)
 
     async def gossip(self, msg: bytes):
         """
@@ -78,15 +80,15 @@ class Nomssip:
         # The message size must be fixed.
         assert len(msg) == self.config.msg_size
 
-        packet = self.__build_packet(self.PacketType.REAL, msg)
-        await self.__gossip(packet)
+        packet = FlaggedPacket(FlaggedPacket.Flag.REAL, msg)
+        await self.__gossip_flagged_packet(packet)
 
-    async def __gossip(self, packet: bytes):
+    async def __gossip_flagged_packet(self, packet: FlaggedPacket):
         """
         An internal method to send a flagged packet to all connected peers
         """
         for conn in self.conns:
-            await conn.send(packet)
+            await conn.send(packet.bytes())
 
     def __check_update_cache(self, packet: bytes) -> bool:
         """
@@ -98,22 +100,24 @@ class Nomssip:
         self.packet_cache.add(hash)
         return False
 
-    class PacketType(Enum):
+
+class FlaggedPacket:
+    class Flag(Enum):
         REAL = b"\x00"
         NOISE = b"\x01"
 
-    @staticmethod
-    def __build_packet(flag: PacketType, data: bytes) -> bytes:
-        """
-        Prepend a flag to the message, right before sending it via network channel.
-        """
-        return flag.value + data
+    def __init__(self, flag: Flag, message: bytes):
+        self.flag = flag
+        self.message = message
 
-    @staticmethod
-    def __parse_packet(data: bytes) -> tuple[PacketType, bytes]:
+    def bytes(self) -> bytes:
+        return self.flag.value + self.message
+
+    @classmethod
+    def from_bytes(cls, packet: bytes) -> Self:
         """
-        Parse the message and extract the flag.
+        Parse a flagged packet from bytes
         """
-        if len(data) < 1:
+        if len(packet) < 1:
             raise ValueError("Invalid message format")
-        return (Nomssip.PacketType(data[:1]), data[1:])
+        return cls(cls.Flag(packet[:1]), packet[1:])