Support latched topics in udp bridge

udp_bridge/aes_helper.py

@@ -29,18 +29,18 @@ def __init__(self, key: str | None):
         else:
             self.encryption_key = None
 
-    def encrypt(self, message: str) -> bytes:
+    def encrypt(self, message: bytes) -> bytes:
         if message == "":
             raise ValueError("Cannot encrypt empty message")
         if self.encryption_key is None:
             return bytes(message, encoding="UTF-8")
 
-        return Fernet(key=self.encryption_key).encrypt(bytes(message, encoding="UTF-8"))
+        return Fernet(key=self.encryption_key).encrypt(message)
 
-    def decrypt(self, enc: bytes) -> str:
+    def decrypt(self, enc: bytes) -> bytes:
         if len(enc) == 0:
             raise ValueError("Cannot decrypt empty data")
         if self.encryption_key is None:
             return str(enc, encoding="UTF-8")
 
-        return str(Fernet(key=self.encryption_key).decrypt(enc), encoding="UTF-8")
+        return Fernet(key=self.encryption_key).decrypt(enc)

udp_bridge/message_handler.py

@@ -1,20 +1,19 @@
 import base64
 import pickle
+import zlib
 
 from udp_bridge.aes_helper import AESCipher
 
 
 class MessageHandler:
-    PACKAGE_DELIMITER = b"\xff\xff\xff"
-
     def __init__(self, encryption_key: str | None):
         self.cipher = AESCipher(encryption_key)
 
     def encrypt_and_encode(self, data: dict) -> bytes:
-        serialized_data = base64.b64encode(pickle.dumps(data, pickle.HIGHEST_PROTOCOL)).decode("ASCII")
+        serialized_data = zlib.compress(pickle.dumps(data, pickle.HIGHEST_PROTOCOL))
         return self.cipher.encrypt(serialized_data)
 
-    def dencrypt_and_decode(self, msg: bytes):
+    def decrypt_and_decode(self, msg: bytes):
         decrypted_msg = self.cipher.decrypt(msg)
-        binary_msg = base64.b64decode(decrypted_msg)
+        binary_msg = zlib.decompress(decrypted_msg)
         return pickle.loads(binary_msg)

udp_bridge/receiver.py

@@ -32,15 +32,11 @@ def recv_message(self):
         """
         Receive a message from the network, process it and publish it into ROS
         """
-        acc = b""
         while rclpy.ok():
             try:
-                acc += self.sock.recv(10240)
-
-                if acc[-3:] == MessageHandler.PACKAGE_DELIMITER:
-                    self.handle_message(acc[:-3])
-                    acc = b""
-
+                # 65535 is the upper limit for the size because of network properties
+                msg = self.sock.recv(65535)
+                self.handle_message(msg)
             except socket.timeout:
                 pass
 
@@ -49,7 +45,7 @@ def handle_message(self, msg: bytes):
         Handle a new message which came in from the socket
         """
         try:
-            deserialized_msg = self.message_handler.dencrypt_and_decode(msg)
+            deserialized_msg = self.message_handler.decrypt_and_decode(msg)
             data = deserialized_msg.get("data")
             topic: str = deserialized_msg.get("topic")
             hostname: str = deserialized_msg.get("hostname")

udp_bridge/sender.py

@@ -2,13 +2,15 @@
 
 import socket
 from queue import Empty, Full, Queue
+import zlib
 
 import rclpy
 from bitbots_utils.utils import get_parameters_from_other_node
 from rclpy.executors import SingleThreadedExecutor
 from rclpy.node import Node
 from rclpy.subscription import Subscription
 from rclpy.timer import Timer
+from rclpy.qos import DurabilityPolicy, QoSProfile
 from ros2topic.api import get_msg_class, get_topic_names
 
 from udp_bridge.message_handler import MessageHandler
@@ -36,6 +38,7 @@ def __init__(self, topic: str, queue_size: int, message_handler: MessageHandler,
         self.timer: Timer | None = None
 
         self.__subscriber: Subscription | None = None
+        self.__latched_subscriber: Subscription | None = None
         self.__subscribe()
 
     def __subscribe(self, backoff=1.0):
@@ -55,19 +58,28 @@ def __subscribe(self, backoff=1.0):
 
         if topic is not None:
             data_class = get_msg_class(self.node, topic)
-            self.node.get_logger().info(str(data_class))
 
         if data_class is not None:
             # topic is known
-            self.node.get_logger().info(f"Want to subscribe to topic {self.topic}")
+            self.node.get_logger().debug(f"Want to subscribe to topic {self.topic}")
+            # find out if topic is latched / transient local
+            publisher_infos = self.node.get_publishers_info_by_topic(topic)
+            latched = any(info.qos_profile.durability == DurabilityPolicy.TRANSIENT_LOCAL for info in publisher_infos)
             self.__subscriber = self.node.create_subscription(data_class, self.topic, self.__message_callback, 1)
-            self.node.get_logger().info(f"Subscribed to topic {self.topic}")
+            if latched:
+                self.__latched_subscriber = self.node.create_subscription(
+                        data_class,
+                        self.topic,
+                        lambda msg: self.__message_callback(msg, latched=True),
+                        QoSProfile(depth=1, durability=DurabilityPolicy.TRANSIENT_LOCAL)
+                )
+            self.node.get_logger().debug(f"Subscribed to topic {self.topic}")
         else:
             # topic is not yet known
-            self.node.get_logger().info(f"Topic {self.topic} is not yet known. Retrying in {backoff} seconds")
+            self.node.get_logger().debug(f"Topic {self.topic} is not yet known. Retrying in {backoff} seconds")
             self.timer = self.node.create_timer(backoff, lambda: self.__subscribe(backoff * 1.2))
 
-    def __message_callback(self, data):
+    def __message_callback(self, data, latched=False):
         encrypted_msg = self.message_handler.encrypt_and_encode(
             {
                 "data": data,
@@ -81,6 +93,11 @@ def __message_callback(self, data):
         except Full:
             self.node.get_logger().warn(f"Could not enqueue new message of topic {self.topic}. Queue full.")
 
+        # for latched messages, republish them every ten seconds because we cannot latch on the other side
+        if latched:
+            if self.timer:
+                self.timer.cancel()
+            self.timer = self.node.create_timer(10.0, lambda: self.__message_callback(data, latched=True))
 
 # @TODO: replace by usage of https://github.com/PickNikRobotics/generate_parameter_library
 def validate_params(node: Node) -> bool:
@@ -157,7 +174,7 @@ def send_messages_in_queue(self):
                 data = subscriber.queue.get_nowait()
 
                 try:
-                    self.sock.sendto(data + MessageHandler.PACKAGE_DELIMITER, (self.target, self.port))
+                    self.sock.sendto(data, (self.target, self.port))
                 except Exception as e:
                     self.node.get_logger().error(
                         f"Could not send data of topic {subscriber.topic} to {self.target} with error {str(e)}"