Refresh relay connection token before it expires

The relay connection token expires every 24 hours for MI tokens and has
a predefined expiry for SAS tokens.

By monitoring the time the connection has been open in an outer loop we
can force the refresh of the token before it expires.

Author: steventux

src/relay_listener.py

@@ -38,6 +38,7 @@
 DB_PATH = os.getenv("MWL_DB_PATH", "/var/lib/pacs/worklist.db")
 AZURE_RELAY_SCOPE = "https://relay.azure.net/.default"
 SAS_TOKEN_EXPIRY_SECONDS = 3600
+RELAY_REFRESH_MARGIN_SECONDS = 300
 
 
 class CredentialNotAvailableError(RuntimeError):
@@ -48,15 +49,21 @@ class RelayListener:
     """
     Socket Listener for Azure Relay.
 
-    Listens for incoming messages from Azure Relay and processes worklist actions.
+    Listens for incoming messages from Azure Relay and processes worklist
+    actions.
+
     Environment variables:
-    AZURE_RELAY_NAMESPACE: Azure Relay namespace (default: relay-test.servicebus.windows.net)
-    AZURE_RELAY_HYBRID_CONNECTION: Azure Relay hybrid connection name (default: relay-test-hc)
-    MWL_DB_PATH: Path to the MWL SQLite database file (default: /var/lib/pacs/worklist.db)
+        AZURE_RELAY_NAMESPACE: Azure Relay namespace
+            (default: relay-test.servicebus.windows.net)
+        AZURE_RELAY_HYBRID_CONNECTION: Azure Relay hybrid connection name
+            (default: relay-test-hc)
+        MWL_DB_PATH: Path to the MWL SQLite database file
+            (default: /var/lib/pacs/worklist.db)
 
     Non-production only (SAS token fallback):
-    AZURE_RELAY_KEY_NAME: Shared access policy name (default: RootManageSharedAccessKey)
-    AZURE_RELAY_SHARED_ACCESS_KEY: Shared access key value
+        AZURE_RELAY_KEY_NAME: Shared access policy name
+            (default: RootManageSharedAccessKey)
+        AZURE_RELAY_SHARED_ACCESS_KEY: Shared access key value
     """
 
     def __init__(self, storage: MWLStorage):
@@ -66,64 +73,90 @@ def __init__(self, storage: MWLStorage):
     async def listen(self):
         """Listen for messages from Azure Relay."""
 
-        logger.info(f"Connecting to Azure Relay: {self.relay_uri.hybrid_connection_name}...")
+        logger.info(
+            "Connecting to Azure Relay: %s...",
+            self.relay_uri.hybrid_connection_name,
+        )
 
-        async with self._connect() as websocket:
-            logger.info("Connected - waiting for worklist actions...")
+        while True:
+            connection_url, refresh_at = self.relay_uri.connection_details()
 
-            async for message in websocket:
-                try:
-                    data = json.loads(message)
+            try:
+                async with self._connect(connection_url) as websocket:
+                    logger.info("Connected - waiting for worklist actions...")
+                    await self._listen_on_connection(websocket, refresh_at)
+            except asyncio.TimeoutError:
+                logger.info("Refreshing Azure Relay connection before expiry.")
+                continue
+
+    async def _listen_on_connection(self, websocket, refresh_at: int):
+        while True:
+            timeout = refresh_at - time.time()
+            if timeout <= 0:
+                raise asyncio.TimeoutError
 
-                    if "accept" in data:
-                        accept_url = data["accept"]["address"]
-                        logger.info("Incoming connection...")
+            try:
+                message = await asyncio.wait_for(websocket.recv(), timeout=timeout)
+            except asyncio.TimeoutError:
+                raise
 
-                        async with connect(accept_url, compression=None) as client_ws:
-                            client_message = await asyncio.wait_for(client_ws.recv(), timeout=30)
+            try:
+                data = json.loads(message)
+
+                if "accept" in data:
+                    accept_url = data["accept"]["address"]
+                    logger.info("Incoming connection...")
+
+                    async with connect(accept_url, compression=None) as client_ws:
+                        try:
+                            client_message = await asyncio.wait_for(
+                                client_ws.recv(),
+                                timeout=30,
+                            )
                             payload = json.loads(client_message)
                             response = self.process_action(payload)
 
-                            # Send acknowledgment
                             await client_ws.send(json.dumps(response))
-
-                except asyncio.TimeoutError:
-                    logger.error("Timeout waiting for message")
-                except Exception as e:
-                    logger.error(f"Error: {e}")
+                        except asyncio.TimeoutError:
+                            logger.error("Timeout waiting for message")
+            except Exception as e:
+                logger.error("Error: %s", e)
 
     def process_action(self, payload: dict):
         """Process incoming action payload."""
         action_name = payload.get("action_type", "no-op")
 
         if action_name == "echo":
             return {"status": "echo", "payload": payload}
-        elif action_name == "worklist.create_item":
+        if action_name == "worklist.create_item":
             return CreateWorklistItem(self.storage).call(payload)
-        elif action_name == "worklist.create_test_item":
+        if action_name == "worklist.create_test_item":
             result = CreateWorklistItem(self.storage).call(payload)
-            patient_name = payload.get("parameters", {}).get("worklist_item", {}).get("participant", {}).get("name")
+
+            worklist_item = payload.get("parameters", {}).get("worklist_item", {})
+            participant = worklist_item.get("participant", {})
+            patient_name = participant.get("name")
 
             if not patient_name:
                 logger.warning("No patient name provided for ModalityEmulator test item processing")
                 return {
                     "status": "error",
-                    "message": "No patient name provided for ModalityEmulator test item processing",
+                    "message": ("No patient name provided for ModalityEmulator test item processing"),
                 }
 
             self.process_with_modality_emulator(patient_name=patient_name)
 
             return result
-        elif action_name == "worklist.update_status":
+        if action_name == "worklist.update_status":
             return UpdateWorklistItemStatus(self.storage).call(payload)
-        else:
-            logger.error("Unsupported action: %s", action_name)
-            return {"status": "error", "message": f"Unsupported action: {action_name}"}
 
-    def _connect(self):
+        logger.error("Unsupported action: %s", action_name)
+        return {"status": "error", "message": f"Unsupported action: {action_name}"}
+
+    def _connect(self, connection_url: str):
         """Connect to Azure Relay."""
         return connect(
-            self.relay_uri.connection_url(),
+            connection_url,
             compression=None,
         )
 
@@ -135,7 +168,10 @@ def process_with_modality_emulator(self, patient_name: str | None = None):
 
         def _run_emulator():
             try:
-                ModalityEmulator(self.storage).process_worklist_items(ae, patient_name=patient_name)
+                ModalityEmulator(self.storage).process_worklist_items(
+                    ae,
+                    patient_name=patient_name,
+                )
             except Exception:
                 logger.exception("Modality emulator processing failed")
 
@@ -150,12 +186,25 @@ def _run_emulator():
 
 class RelayURI:
     def __init__(self):
-        self.relay_namespace = os.getenv("AZURE_RELAY_NAMESPACE", "relay-test.servicebus.windows.net")
-        self.hybrid_connection_name = os.getenv("AZURE_RELAY_HYBRID_CONNECTION", "relay-test-hc")
-        self.key_name = os.getenv("AZURE_RELAY_KEY_NAME", "RootManageSharedAccessKey")
+        self.relay_namespace = os.getenv(
+            "AZURE_RELAY_NAMESPACE",
+            "relay-test.servicebus.windows.net",
+        )
+        self.hybrid_connection_name = os.getenv(
+            "AZURE_RELAY_HYBRID_CONNECTION",
+            "relay-test-hc",
+        )
+        self.key_name = os.getenv(
+            "AZURE_RELAY_KEY_NAME",
+            "RootManageSharedAccessKey",
+        )
         self.shared_access_key = os.getenv("AZURE_RELAY_SHARED_ACCESS_KEY", "")
         self._env = Environment()
-        self._credential = None if self._use_sas() else self._build_credential()
+
+        if self._use_sas():
+            self._credential = None
+        else:
+            self._credential = self._build_credential()
 
     def _use_sas(self) -> bool:
         return not self._env.production and bool(self.shared_access_key)
@@ -165,41 +214,61 @@ def _build_credential(self):
             return ManagedIdentityCredential()
         return DefaultAzureCredential()
 
-    def connection_url(self) -> str:
+    def connection_details(self) -> tuple[str, int]:
         base = f"wss://{self.relay_namespace}/$hc/{self.hybrid_connection_name}?sb-hc-action=listen"
+
         if self._use_sas():
-            token = self._create_sas_token()
+            token, expires_on = self._create_sas_token()
         else:
-            token = self._create_bearer_token()
-        return f"{base}&sb-hc-token={urllib.parse.quote_plus(token)}"
+            token, expires_on = self._create_bearer_token()
+
+        connection_url = f"{base}&sb-hc-token={urllib.parse.quote_plus(token)}"
+        return connection_url, expires_on
 
-    def _create_bearer_token(self) -> str:
+    def connection_url(self) -> str:
+        connection_url, _ = self.connection_details()
+        return connection_url
+
+    def _create_bearer_token(self) -> tuple[str, int]:
         if self._credential is None:
             raise CredentialNotAvailableError(
                 "No credential available — _credential should never be None when not using SAS"
             )
-        return f"Bearer {self._credential.get_token(AZURE_RELAY_SCOPE).token}"
 
-    def _create_sas_token(self, expiry_seconds: int = SAS_TOKEN_EXPIRY_SECONDS) -> str:
+        access_token = self._credential.get_token(AZURE_RELAY_SCOPE)
+        return f"Bearer {access_token.token}", int(access_token.expires_on)
+
+    def _create_sas_token(
+        self,
+        expiry_seconds: int = SAS_TOKEN_EXPIRY_SECONDS,
+    ) -> tuple[str, int]:
         uri = f"http://{self.relay_namespace}/{self.hybrid_connection_name}"
         encoded_uri = urllib.parse.quote_plus(uri)
-        expiry = str(int(time.time() + expiry_seconds))
-        signature = base64.b64encode(
-            hmac.new(self.shared_access_key.encode(), f"{encoded_uri}\n{expiry}".encode(), hashlib.sha256).digest()
-        )
+        expiry = int(time.time() + expiry_seconds)
+        string_to_sign = f"{encoded_uri}\n{expiry}".encode()
+        digest = hmac.new(
+            self.shared_access_key.encode(),
+            string_to_sign,
+            hashlib.sha256,
+        ).digest()
+        signature = base64.b64encode(digest).decode("ascii")
+
         return (
             f"SharedAccessSignature sr={encoded_uri}"
             f"&sig={urllib.parse.quote_plus(signature)}"
-            f"&se={expiry}&skn={self.key_name}"
+            f"&se={expiry}&skn={self.key_name}",
+            expiry,
         )
 
 
 def verify_credentials():
     """
     Verify relay credentials are available at startup.
 
-    In production, raises ClientAuthenticationError if managed identity is not configured.
-    In non-production with a SAS key present, logs the auth method and returns immediately.
+    In production, raises ClientAuthenticationError if managed identity is
+    not configured.
+    In non-production with a SAS key present, logs the auth method and
+    returns immediately.
     """
     uri = RelayURI()
     if uri._use_sas():
@@ -211,13 +280,16 @@ def verify_credentials():
             )
         uri._credential.get_token(AZURE_RELAY_SCOPE)
         credential_type = "ManagedIdentityCredential" if uri._env.production else "DefaultAzureCredential"
-        logger.info(f"Azure Relay credentials verified ({credential_type}).")
+        logger.info("Azure Relay credentials verified (%s).", credential_type)
 
 
 async def main():
     logging.basicConfig(
         level=os.getenv("LOG_LEVEL", "INFO").upper(),
-        format=os.getenv("LOG_FORMAT", "%(asctime)s - %(name)s - %(levelname)s - %(message)s"),
+        format=os.getenv(
+            "LOG_FORMAT",
+            "%(asctime)s - %(name)s - %(levelname)s - %(message)s",
+        ),
     )
     configure_telemetry(service_name="relay-listener")
 
@@ -234,11 +306,11 @@ async def main():
         except ConnectionClosedError as e:
             code = e.rcvd.code if e.rcvd else "N/A"
             reason = e.rcvd.reason if e.rcvd else "N/A"
-            logger.warning(f"Connection closed with code {code}: {reason}")
+            logger.warning("Connection closed with code %s: %s", code, reason)
             logger.warning("Retrying in 5 seconds...")
             await asyncio.sleep(5)
         except Exception as e:
-            logger.warning(f"Connection error: {e}")
+            logger.warning("Connection error: %s", e)
             logger.warning("Retrying in 5 seconds...")
             await asyncio.sleep(5)