From 683f80ef751f02dc8fd14313af6b4a37d9deac9d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Laura=20Kl=C3=BCnder?= <laura@codingcatgirl.de>
Date: Mon, 4 Apr 2022 14:48:43 +0200
Subject: [PATCH] set up base websocket server for mesh communication

---
 src/c3nav/mesh/consumers.py |  21 +++++---
 src/c3nav/mesh/messages.py  | 101 ++++++++++++++++++++++++++++++++++++
 src/c3nav/mesh/urls.py      |   4 +-
 3 files changed, 117 insertions(+), 9 deletions(-)
 create mode 100644 src/c3nav/mesh/messages.py

diff --git a/src/c3nav/mesh/consumers.py b/src/c3nav/mesh/consumers.py
index 9dd9b2eb..4ffe6e86 100644
--- a/src/c3nav/mesh/consumers.py
+++ b/src/c3nav/mesh/consumers.py
@@ -1,12 +1,19 @@
-from channels.generic.websocket import WebsocketConsumer
+from channels.generic.websocket import AsyncWebsocketConsumer
+
+from c3nav.mesh import messages
 
 
-class EchoConsumer(WebsocketConsumer):
-    def connect(self):
-        self.accept()
+class MeshConsumer(AsyncWebsocketConsumer):
+    async def connect(self):
+        await self.accept()
 
-    def disconnect(self, close_code):
+    async def disconnect(self, close_code):
         pass
 
-    def receive(self, text_data):
-        self.send(text_data=text_data)
+    async def receive(self, text_data=None, bytes_data=None):
+        if bytes_data is None:
+            return
+        msg = messages.Message.decode(bytes_data)
+        print('Received message:', msg)
+        if isinstance(msg, messages.MeshSigninMessage):
+            await self.send(messages.MeshLayerAnnounceMessage(messages.NO_LAYER).encode())
diff --git a/src/c3nav/mesh/messages.py b/src/c3nav/mesh/messages.py
new file mode 100644
index 00000000..7c46bbd0
--- /dev/null
+++ b/src/c3nav/mesh/messages.py
@@ -0,0 +1,101 @@
+import struct
+from dataclasses import dataclass, field, fields
+
+NO_LAYER = 0xFF
+MAC_FMT = '%02x:%02x:%02x:%02x:%02x:%02x'
+
+
+class SimpleFormat:
+    def __init__(self, fmt):
+        self.fmt = fmt
+        self.size = struct.calcsize(fmt)
+
+    def encode(self, value):
+        return struct.pack(self.fmt, value)
+
+    def decode(self, data: bytes):
+        return struct.unpack(self.fmt, data[:self.size]), data[self.size:]
+
+
+class VarStrFormat:
+    def encode(self, value: str) -> bytes:
+        return bytes((len(value)+1, )) + value.encode() + bytes((0, ))
+
+    def decode(self, data: bytes):
+        return data[1:data[0]].decode(), data[data[0]+1:]
+
+
+class MacAddressFormat:
+    def encode(self, value: str) -> bytes:
+        return bytes(int(value[i*3:i*3+2], 16) for i in range(6))
+
+    def decode(self, data: bytes):
+        return (MAC_FMT % tuple(data[:6])), data[6:]
+
+
+class MacAddressesListFormat:
+    def encode(self, value: list[str]) -> bytes:
+        return bytes((len(value), )) + sum(
+            (bytes((int(mac[i*3:i*3+2], 16) for i in range(6))) for mac in value),
+            b''
+        )
+
+    def decode(self, data: bytes):
+        return [MAC_FMT % tuple(data[1+6*i:1+6+6*i]) for i in range(data[0])], data[1+data[0]*6]
+
+
+@dataclass
+class Message:
+    msg_types = {}
+
+    # noinspection PyMethodOverriding
+    def __init_subclass__(cls, /, msg_id=None, **kwargs):
+        super().__init_subclass__(**kwargs)
+        if msg_id:
+            cls.msg_id = msg_id
+            Message.msg_types[msg_id] = cls
+
+    def encode(self):
+        data = bytes((self.msg_id, ))
+        for field_ in fields(self):
+            data += field_.metadata['format'].encode(getattr(self, field_.name))
+        return data
+
+    @classmethod
+    def decode(cls, data: bytes):
+        klass = cls.msg_types[data[0]]
+        data = data[1:]
+        values = {}
+        for field_ in fields(klass):
+            values[field_.name], data = field_.metadata['format'].decode(data)
+        return klass(**values)
+
+
+@dataclass
+class EchoMessage(Message, msg_id=0x01):
+    content: str = field(default='', metadata={'format': VarStrFormat()})
+
+
+@dataclass
+class MeshSigninMessage(Message, msg_id=0x02):
+    mac_address: str = field(metadata={'format': MacAddressFormat()})
+
+
+@dataclass
+class MeshLayerAnnounceMessage(Message, msg_id=0x03):
+    layer: int = field(metadata={'format': SimpleFormat('B')})
+
+
+@dataclass
+class BaseMeshDestinationsMessage(Message):
+    mac_addresses: list[str] = field(default_factory=list, metadata={'format': MacAddressesListFormat()})
+
+
+@dataclass
+class MeshAddDestinationsMessage(BaseMeshDestinationsMessage, msg_id=0x04):
+    pass
+
+
+@dataclass
+class MeshRemoveDestinationsMessage(BaseMeshDestinationsMessage, msg_id=0x05):
+    pass
diff --git a/src/c3nav/mesh/urls.py b/src/c3nav/mesh/urls.py
index dd2bc410..4d075a86 100644
--- a/src/c3nav/mesh/urls.py
+++ b/src/c3nav/mesh/urls.py
@@ -1,7 +1,7 @@
 from django.urls import path
 
-from c3nav.mesh.consumers import EchoConsumer
+from c3nav.mesh.consumers import MeshConsumer
 
 websocket_urlpatterns = [
-    path('ws', EchoConsumer.as_asgi()),
+    path('ws', MeshConsumer.as_asgi()),
 ]