Add a feature flags message to reduce bandwidth

We now only send 1 preview message of the latest type the client can
support.

We'll add a console warning when the client fails to send a feature
flags message at some point in the future.

comfy_api/feature_flags.py

@@ -0,0 +1,69 @@
+"""
+Feature flags module for ComfyUI WebSocket protocol negotiation.
+
+This module handles capability negotiation between frontend and backend,
+allowing graceful protocol evolution while maintaining backward compatibility.
+"""
+
+from typing import Any, Dict
+
+from comfy.cli_args import args
+
+# Default server capabilities
+SERVER_FEATURE_FLAGS: Dict[str, Any] = {
+    "supports_preview_metadata": True,
+    "max_upload_size": args.max_upload_size * 1024 * 1024, # Convert MB to bytes
+}
+
+
+def get_connection_feature(
+    sockets_metadata: Dict[str, Dict[str, Any]],
+    sid: str,
+    feature_name: str,
+    default: Any = False
+) -> Any:
+    """
+    Get a feature flag value for a specific connection.
+
+    Args:
+        sockets_metadata: Dictionary of socket metadata
+        sid: Session ID of the connection
+        feature_name: Name of the feature to check
+        default: Default value if feature not found
+
+    Returns:
+        Feature value or default if not found
+    """
+    if sid not in sockets_metadata:
+        return default
+
+    return sockets_metadata[sid].get("feature_flags", {}).get(feature_name, default)
+
+
+def supports_feature(
+    sockets_metadata: Dict[str, Dict[str, Any]],
+    sid: str,
+    feature_name: str
+) -> bool:
+    """
+    Check if a connection supports a specific feature.
+
+    Args:
+        sockets_metadata: Dictionary of socket metadata
+        sid: Session ID of the connection
+        feature_name: Name of the feature to check
+
+    Returns:
+        Boolean indicating if feature is supported
+    """
+    return get_connection_feature(sockets_metadata, sid, feature_name, False) is True
+
+
+def get_server_features() -> Dict[str, Any]:
+    """
+    Get the server's feature flags.
+
+    Returns:
+        Dictionary of server feature flags
+    """
+    return SERVER_FEATURE_FLAGS.copy()

comfy_execution/progress.py

@@ -6,6 +6,8 @@ from abc import ABC
 from tqdm import tqdm
 from comfy_execution.graph import DynamicPrompt
 from protocol import BinaryEventTypes
+from comfy_api import feature_flags
+
 
 class NodeState(Enum):
     Pending = "pending"
@@ -13,19 +15,23 @@ class NodeState(Enum):
     Finished = "finished"
     Error = "error"
 
+
 class NodeProgressState(TypedDict):
     """
     A class to represent the state of a node's progress.
     """
+
     state: NodeState
     value: float
     max: float
 
+
 class ProgressHandler(ABC):
     """
     Abstract base class for progress handlers.
     Progress handlers receive progress updates and display them in various ways.
     """
+
     def __init__(self, name: str):
         self.name = name
         self.enabled = True
@@ -37,8 +43,15 @@ class ProgressHandler(ABC):
         """Called when a node starts processing"""
         pass
 
-    def update_handler(self, node_id: str, value: float, max_value: float,
-                      state: NodeProgressState, prompt_id: str, image: Optional[Image.Image] = None):
+    def update_handler(
+        self,
+        node_id: str,
+        value: float,
+        max_value: float,
+        state: NodeProgressState,
+        prompt_id: str,
+        image: Optional[Image.Image] = None,
+    ):
         """Called when a node's progress is updated"""
         pass
 
@@ -58,10 +71,12 @@ class ProgressHandler(ABC):
         """Disable this handler"""
         self.enabled = False
 
+
 class CLIProgressHandler(ProgressHandler):
     """
     Handler that displays progress using tqdm progress bars in the CLI.
     """
+
     def __init__(self):
         super().__init__("cli")
         self.progress_bars: Dict[str, tqdm] = {}
@@ -75,12 +90,19 @@ class CLIProgressHandler(ProgressHandler):
                 desc=f"Node {node_id}",
                 unit="steps",
                 leave=True,
-                position=len(self.progress_bars)
+                position=len(self.progress_bars),
             )
 
     @override
-    def update_handler(self, node_id: str, value: float, max_value: float,
-                      state: NodeProgressState, prompt_id: str, image: Optional[Image.Image] = None):
+    def update_handler(
+        self,
+        node_id: str,
+        value: float,
+        max_value: float,
+        state: NodeProgressState,
+        prompt_id: str,
+        image: Optional[Image.Image] = None,
+    ):
         # Handle case where start_handler wasn't called
         if node_id not in self.progress_bars:
             self.progress_bars[node_id] = tqdm(
@@ -88,7 +110,7 @@ class CLIProgressHandler(ProgressHandler):
                 desc=f"Node {node_id}",
                 unit="steps",
                 leave=True,
-                position=len(self.progress_bars)
+                position=len(self.progress_bars),
             )
             self.progress_bars[node_id].update(value)
         else:
@@ -119,10 +141,12 @@ class CLIProgressHandler(ProgressHandler):
             bar.close()
         self.progress_bars.clear()
 
+
 class WebUIProgressHandler(ProgressHandler):
     """
     Handler that sends progress updates to the WebUI via WebSockets.
     """
+
     def __init__(self, server_instance):
         super().__init__("webui")
         self.server_instance = server_instance
@@ -145,17 +169,16 @@ class WebUIProgressHandler(ProgressHandler):
                 "prompt_id": prompt_id,
                 "display_node_id": self.registry.dynprompt.get_display_node_id(node_id),
                 "parent_node_id": self.registry.dynprompt.get_parent_node_id(node_id),
-                "real_node_id": self.registry.dynprompt.get_real_node_id(node_id)
+                "real_node_id": self.registry.dynprompt.get_real_node_id(node_id),
             }
             for node_id, state in nodes.items()
             if state["state"] != NodeState.Pending
         }
 
         # Send a combined progress_state message with all node states
-        self.server_instance.send_sync("progress_state", {
-            "prompt_id": prompt_id,
-            "nodes": active_nodes
-        })
+        self.server_instance.send_sync(
+            "progress_state", {"prompt_id": prompt_id, "nodes": active_nodes}
+        )
 
     @override
     def start_handler(self, node_id: str, state: NodeProgressState, prompt_id: str):
@@ -164,21 +187,41 @@ class WebUIProgressHandler(ProgressHandler):
             self._send_progress_state(prompt_id, self.registry.nodes)
 
     @override
-    def update_handler(self, node_id: str, value: float, max_value: float,
-                      state: NodeProgressState, prompt_id: str, image: Optional[Image.Image] = None):
+    def update_handler(
+        self,
+        node_id: str,
+        value: float,
+        max_value: float,
+        state: NodeProgressState,
+        prompt_id: str,
+        image: Optional[Image.Image] = None,
+    ):
         # Send progress state of all nodes
         if self.registry:
             self._send_progress_state(prompt_id, self.registry.nodes)
         if image:
-            metadata = {
-                "node_id": node_id,
-                "prompt_id": prompt_id,
-                "display_node_id": self.registry.dynprompt.get_display_node_id(node_id),
-                "parent_node_id": self.registry.dynprompt.get_parent_node_id(node_id),
-                "real_node_id": self.registry.dynprompt.get_real_node_id(node_id)
-            }
-            self.server_instance.send_sync(BinaryEventTypes.PREVIEW_IMAGE_WITH_METADATA, (image, metadata), self.server_instance.client_id)
-
+            # Only send new format if client supports it
+            if feature_flags.supports_feature(
+                self.server_instance.sockets_metadata,
+                self.server_instance.client_id,
+                "supports_preview_metadata",
+            ):
+                metadata = {
+                    "node_id": node_id,
+                    "prompt_id": prompt_id,
+                    "display_node_id": self.registry.dynprompt.get_display_node_id(
+                        node_id
+                    ),
+                    "parent_node_id": self.registry.dynprompt.get_parent_node_id(
+                        node_id
+                    ),
+                    "real_node_id": self.registry.dynprompt.get_real_node_id(node_id),
+                }
+                self.server_instance.send_sync(
+                    BinaryEventTypes.PREVIEW_IMAGE_WITH_METADATA,
+                    (image, metadata),
+                    self.server_instance.client_id,
+                )
 
     @override
     def finish_handler(self, node_id: str, state: NodeProgressState, prompt_id: str):
@@ -186,10 +229,12 @@ class WebUIProgressHandler(ProgressHandler):
         if self.registry:
             self._send_progress_state(prompt_id, self.registry.nodes)
 
+
 class ProgressRegistry:
     """
     Registry that maintains node progress state and notifies registered handlers.
     """
+
     def __init__(self, prompt_id: str, dynprompt: DynamicPrompt):
         self.prompt_id = prompt_id
         self.dynprompt = dynprompt
@@ -221,9 +266,7 @@ class ProgressRegistry:
         """Ensure a node entry exists"""
         if node_id not in self.nodes:
             self.nodes[node_id] = NodeProgressState(
-                state = NodeState.Pending,
-                value = 0,
-                max = 1
+                state=NodeState.Pending, value=0, max=1
             )
         return self.nodes[node_id]
 
@@ -239,7 +282,9 @@ class ProgressRegistry:
             if handler.enabled:
                 handler.start_handler(node_id, entry, self.prompt_id)
 
-    def update_progress(self, node_id: str, value: float, max_value: float, image: Optional[Image.Image]) -> None:
+    def update_progress(
+        self, node_id: str, value: float, max_value: float, image: Optional[Image.Image]
+    ) -> None:
         """Update progress for a node"""
         entry = self.ensure_entry(node_id)
         entry["state"] = NodeState.Running
@@ -249,7 +294,9 @@ class ProgressRegistry:
         # Notify all enabled handlers
         for handler in self.handlers.values():
             if handler.enabled:
-                handler.update_handler(node_id, value, max_value, entry, self.prompt_id, image)
+                handler.update_handler(
+                    node_id, value, max_value, entry, self.prompt_id, image
+                )
 
     def finish_progress(self, node_id: str) -> None:
         """Finish progress tracking for a node"""
@@ -267,8 +314,12 @@ class ProgressRegistry:
         for handler in self.handlers.values():
             handler.reset()
 
+
 # Global registry instance
-global_progress_registry: ProgressRegistry = ProgressRegistry(prompt_id="", dynprompt=DynamicPrompt({}))
+global_progress_registry: ProgressRegistry = ProgressRegistry(
+    prompt_id="", dynprompt=DynamicPrompt({})
+)
+
 
 def reset_progress_state(prompt_id: str, dynprompt: DynamicPrompt) -> None:
     global global_progress_registry
@@ -280,9 +331,11 @@ def reset_progress_state(prompt_id: str, dynprompt: DynamicPrompt) -> None:
     # Create new registry
     global_progress_registry = ProgressRegistry(prompt_id, dynprompt)
 
+
 def add_progress_handler(handler: ProgressHandler) -> None:
     handler.set_registry(global_progress_registry)
     global_progress_registry.register_handler(handler)
 
+
 def get_progress_state() -> ProgressRegistry:
     return global_progress_registry

main.py

@@ -13,6 +13,7 @@ import logging
 import sys
 from comfy_execution.progress import get_progress_state
 from comfy_execution.utils import get_executing_context
+from comfy_api import feature_flags
 
 if __name__ == "__main__":
     #NOTE: These do not do anything on core ComfyUI, they are for custom nodes.
@@ -246,9 +247,17 @@ def hijack_progress(server_instance):
 
         server_instance.send_sync("progress", progress, server_instance.client_id)
         if preview_image is not None:
-            # Also send old method for backward compatibility
-            # TODO - Remove after this repo is updated to frontend with metadata support
-            server_instance.send_sync(BinaryEventTypes.UNENCODED_PREVIEW_IMAGE, preview_image, server_instance.client_id)
+            # Only send old method if client doesn't support preview metadata
+            if not feature_flags.supports_feature(
+                server_instance.sockets_metadata,
+                server_instance.client_id,
+                "supports_preview_metadata",
+            ):
+                server_instance.send_sync(
+                    BinaryEventTypes.UNENCODED_PREVIEW_IMAGE,
+                    preview_image,
+                    server_instance.client_id,
+                )
 
     comfy.utils.set_progress_bar_global_hook(hook)
 

server.py

@@ -26,6 +26,7 @@ import mimetypes
 from comfy.cli_args import args
 import comfy.utils
 import comfy.model_management
+from comfy_api import feature_flags
 import node_helpers
 from comfyui_version import __version__
 from app.frontend_management import FrontendManager
@@ -174,6 +175,7 @@ class PromptServer():
         max_upload_size = round(args.max_upload_size * 1024 * 1024)
         self.app = web.Application(client_max_size=max_upload_size, middlewares=middlewares)
         self.sockets = dict()
+        self.sockets_metadata = dict()
         self.web_root = (
             FrontendManager.init_frontend(args.front_end_version)
             if args.front_end_root is None
@@ -198,20 +200,53 @@ class PromptServer():
             else:
                 sid = uuid.uuid4().hex
 
+            # Store WebSocket for backward compatibility
             self.sockets[sid] = ws
+            # Store metadata separately
+            self.sockets_metadata[sid] = {"feature_flags": {}}
 
             try:
                 # Send initial state to the new client
-                await self.send("status", { "status": self.get_queue_info(), 'sid': sid }, sid)
+                await self.send("status", {"status": self.get_queue_info(), "sid": sid}, sid)
                 # On reconnect if we are the currently executing client send the current node
                 if self.client_id == sid and self.last_node_id is not None:
                     await self.send("executing", { "node": self.last_node_id }, sid)
 
+                # Flag to track if we've received the first message
+                first_message = True
+
                 async for msg in ws:
                     if msg.type == aiohttp.WSMsgType.ERROR:
                         logging.warning('ws connection closed with exception %s' % ws.exception())
+                    elif msg.type == aiohttp.WSMsgType.TEXT:
+                        try:
+                            data = json.loads(msg.data)
+                            # Check if first message is feature flags
+                            if first_message and data.get("type") == "feature_flags":
+                                # Store client feature flags
+                                client_flags = data.get("data", {})
+                                self.sockets_metadata[sid]["feature_flags"] = client_flags
+
+                                # Send server feature flags in response
+                                await self.send(
+                                    "feature_flags",
+                                    feature_flags.get_server_features(),
+                                    sid,
+                                )
+
+                                logging.info(
+                                    f"Feature flags negotiated for client {sid}: {client_flags}"
+                                )
+                            first_message = False
+                        except json.JSONDecodeError:
+                            logging.warning(
+                                f"Invalid JSON received from client {sid}: {msg.data}"
+                            )
+                        except Exception as e:
+                            logging.error(f"Error processing WebSocket message: {e}")
             finally:
                 self.sockets.pop(sid, None)
+                self.sockets_metadata.pop(sid, None)
             return ws
 
         @routes.get("/")
@@ -544,6 +579,10 @@ class PromptServer():
             }
             return web.json_response(system_stats)
 
+        @routes.get("/features")
+        async def get_features(request):
+            return web.json_response(feature_flags.get_server_features())
+
         @routes.get("/prompt")
         async def get_prompt(request):
             return web.json_response(self.get_queue_info())
@@ -882,10 +921,10 @@ class PromptServer():
         ssl_ctx = None
         scheme = "http"
         if args.tls_keyfile and args.tls_certfile:
-                ssl_ctx = ssl.SSLContext(protocol=ssl.PROTOCOL_TLS_SERVER, verify_mode=ssl.CERT_NONE)
-                ssl_ctx.load_cert_chain(certfile=args.tls_certfile,
+            ssl_ctx = ssl.SSLContext(protocol=ssl.PROTOCOL_TLS_SERVER, verify_mode=ssl.CERT_NONE)
+            ssl_ctx.load_cert_chain(certfile=args.tls_certfile,
                                 keyfile=args.tls_keyfile)
-                scheme = "https"
+            scheme = "https"
 
         if verbose:
             logging.info("Starting server\n")

tests-unit/feature_flags_test.py

@@ -0,0 +1,98 @@
+"""Tests for feature flags functionality."""
+
+from comfy_api.feature_flags import (
+    get_connection_feature,
+    supports_feature,
+    get_server_features,
+    SERVER_FEATURE_FLAGS,
+)
+
+
+class TestFeatureFlags:
+    """Test suite for feature flags functions."""
+
+    def test_get_server_features_returns_copy(self):
+        """Test that get_server_features returns a copy of the server flags."""
+        features = get_server_features()
+        # Verify it's a copy by modifying it
+        features["test_flag"] = True
+        # Original should be unchanged
+        assert "test_flag" not in SERVER_FEATURE_FLAGS
+
+    def test_get_server_features_contains_expected_flags(self):
+        """Test that server features contain expected flags."""
+        features = get_server_features()
+        assert "supports_preview_metadata" in features
+        assert features["supports_preview_metadata"] is True
+        assert "max_upload_size" in features
+        assert isinstance(features["max_upload_size"], (int, float))
+
+    def test_get_connection_feature_with_missing_sid(self):
+        """Test getting feature for non-existent session ID."""
+        sockets_metadata = {}
+        result = get_connection_feature(sockets_metadata, "missing_sid", "some_feature")
+        assert result is False  # Default value
+
+    def test_get_connection_feature_with_custom_default(self):
+        """Test getting feature with custom default value."""
+        sockets_metadata = {}
+        result = get_connection_feature(
+            sockets_metadata, "missing_sid", "some_feature", default="custom_default"
+        )
+        assert result == "custom_default"
+
+    def test_get_connection_feature_with_feature_flags(self):
+        """Test getting feature from connection with feature flags."""
+        sockets_metadata = {
+            "sid1": {
+                "feature_flags": {
+                    "supports_preview_metadata": True,
+                    "custom_feature": "value",
+                },
+            }
+        }
+        result = get_connection_feature(sockets_metadata, "sid1", "supports_preview_metadata")
+        assert result is True
+
+        result = get_connection_feature(sockets_metadata, "sid1", "custom_feature")
+        assert result == "value"
+
+    def test_get_connection_feature_missing_feature(self):
+        """Test getting non-existent feature from connection."""
+        sockets_metadata = {
+            "sid1": {"feature_flags": {"existing_feature": True}}
+        }
+        result = get_connection_feature(sockets_metadata, "sid1", "missing_feature")
+        assert result is False
+
+    def test_supports_feature_returns_boolean(self):
+        """Test that supports_feature always returns boolean."""
+        sockets_metadata = {
+            "sid1": {
+                "feature_flags": {
+                    "bool_feature": True,
+                    "string_feature": "value",
+                    "none_feature": None,
+                },
+            }
+        }
+
+        # True boolean feature
+        assert supports_feature(sockets_metadata, "sid1", "bool_feature") is True
+
+        # Non-boolean values should return False
+        assert supports_feature(sockets_metadata, "sid1", "string_feature") is False
+        assert supports_feature(sockets_metadata, "sid1", "none_feature") is False
+        assert supports_feature(sockets_metadata, "sid1", "missing_feature") is False
+
+    def test_supports_feature_with_missing_connection(self):
+        """Test supports_feature with missing connection."""
+        sockets_metadata = {}
+        assert supports_feature(sockets_metadata, "missing_sid", "any_feature") is False
+
+    def test_empty_feature_flags_dict(self):
+        """Test connection with empty feature flags dictionary."""
+        sockets_metadata = {"sid1": {"feature_flags": {}}}
+        result = get_connection_feature(sockets_metadata, "sid1", "any_feature")
+        assert result is False
+        assert supports_feature(sockets_metadata, "sid1", "any_feature") is False

tests-unit/websocket_feature_flags_test.py

@@ -0,0 +1,128 @@
+"""Simplified tests for WebSocket feature flags functionality."""
+from unittest.mock import Mock, patch
+from comfy_api import feature_flags
+
+
+class TestWebSocketFeatureFlags:
+    """Test suite for WebSocket feature flags integration."""
+
+    @patch('main.server')
+    def test_preview_message_with_feature_support(self, mock_server):
+        """Test that UNENCODED_PREVIEW_IMAGE is not sent when client supports metadata."""
+        # Setup mock server with client that supports preview metadata
+        mock_server.client_id = "test_client"
+        mock_server.sockets_metadata = {
+            "test_client": {
+                "feature_flags": {"supports_preview_metadata": True}
+            }
+        }
+        mock_server.send_sync = Mock()
+
+        # Import the function we're testing
+        from main import hijack_progress
+
+        # Call hijack_progress
+        hijack_progress(mock_server)
+
+        # Verify feature flags can check support
+        assert feature_flags.supports_feature(
+            mock_server.sockets_metadata,
+            "test_client",
+            "supports_preview_metadata"
+        ) is True
+
+    @patch('main.server')
+    def test_preview_message_without_feature_support(self, mock_server):
+        """Test that UNENCODED_PREVIEW_IMAGE is sent when client doesn't support metadata."""
+        # Setup mock server with legacy client
+        mock_server.client_id = "legacy_client"
+        mock_server.sockets_metadata = {
+            "legacy_client": {
+                "feature_flags": {}  # No features
+            }
+        }
+        mock_server.send_sync = Mock()
+
+        # Import the function we're testing
+        from main import hijack_progress
+
+        # Call hijack_progress
+        hijack_progress(mock_server)
+
+        # Verify feature flags check returns False
+        assert feature_flags.supports_feature(
+            mock_server.sockets_metadata,
+            "legacy_client",
+            "supports_preview_metadata"
+        ) is False
+
+    def test_server_feature_flags_response(self):
+        """Test server feature flags are properly formatted."""
+        features = feature_flags.get_server_features()
+
+        # Check expected server features
+        assert "supports_preview_metadata" in features
+        assert features["supports_preview_metadata"] is True
+        assert "max_upload_size" in features
+        assert isinstance(features["max_upload_size"], (int, float))
+
+    def test_progress_py_checks_feature_flags(self):
+        """Test that progress.py checks feature flags before sending metadata."""
+        # This simulates the check in progress.py
+        client_id = "test_client"
+        sockets_metadata = {"test_client": {"feature_flags": {}}}
+
+        # The actual check would be in progress.py
+        supports_metadata = feature_flags.supports_feature(
+            sockets_metadata, client_id, "supports_preview_metadata"
+        )
+
+        assert supports_metadata is False
+
+    def test_multiple_clients_different_features(self):
+        """Test handling multiple clients with different feature support."""
+        sockets_metadata = {
+            "modern_client": {
+                "feature_flags": {"supports_preview_metadata": True}
+            },
+            "legacy_client": {
+                "feature_flags": {}
+            }
+        }
+
+        # Check modern client
+        assert feature_flags.supports_feature(
+            sockets_metadata, "modern_client", "supports_preview_metadata"
+        ) is True
+
+        # Check legacy client
+        assert feature_flags.supports_feature(
+            sockets_metadata, "legacy_client", "supports_preview_metadata"
+        ) is False
+
+    def test_feature_negotiation_message_format(self):
+        """Test the format of feature negotiation messages."""
+        # Client message format
+        client_message = {
+            "type": "feature_flags",
+            "data": {
+                "supports_preview_metadata": True,
+                "api_version": "1.0.0"
+            }
+        }
+
+        # Verify structure
+        assert client_message["type"] == "feature_flags"
+        assert "supports_preview_metadata" in client_message["data"]
+
+        # Server response format (what would be sent)
+        server_features = feature_flags.get_server_features()
+        server_message = {
+            "type": "feature_flags",
+            "data": server_features
+        }
+
+        # Verify structure
+        assert server_message["type"] == "feature_flags"
+        assert "supports_preview_metadata" in server_message["data"]
+        assert server_message["data"]["supports_preview_metadata"] is True