feat: add mcp support (#1964) (#1977)

* feat: add mcp support

* chore: split mcp button component

* feat: persist mcps in localstorage & reconnect

* feat: add copy button for mcp command/url

* feat: add mcp reconnect button

Author: willydouhard

.github/actions/poetry-python-install/action.yaml

@@ -5,7 +5,7 @@ inputs:
   python-version:
     description: Python version
     required: true
-    default: '3.9'
+    default: '3.10'
   poetry-version:
     description: Poetry version
     required: true

.github/workflows/pytest.yaml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['3.9', '3.10', '3.11', '3.12']
+        python-version: ['3.10', '3.11', '3.12']
         fastapi-version: ['0.115']
     env:
       BACKEND_DIR: ./backend

CHANGELOG.md

@@ -4,6 +4,12 @@ All notable changes to Chainlit will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [2.4.0rc0] - 2025-03-09
+
+### Added
+
+- MCP support through `@cl.on_mcp_connect` and `@cl.on_mcp_disconnect`
+
 ## [2.3.0] - 2025-03-09
 
 ### Added

CONTRIBUTING.md

@@ -25,7 +25,7 @@ I've copy/pasted the whole document there, and then formatted it with prettier.
 
 ### Requirements
 
-1. Python >= `3.9`
+1. Python >= `3.10`
 2. Poetry ([See how to install](https://python-poetry.org/docs/#installation))
 3. NodeJS >= `16` ([See how to install](https://nodejs.org/en/download))
 4. Pnpm ([See how to install](https://pnpm.io/installation))

backend/chainlit/__init__.py

@@ -67,6 +67,8 @@
     on_chat_resume,
     on_chat_start,
     on_logout,
+    on_mcp_connect,
+    on_mcp_disconnect,
     on_message,
     on_settings_update,
     on_stop,
@@ -78,7 +80,6 @@
 )
 
 if TYPE_CHECKING:
-    from chainlit.haystack.callbacks import HaystackAgentCallbackHandler
     from chainlit.langchain.callbacks import (
         AsyncLangchainCallbackHandler,
         LangchainCallbackHandler,
@@ -111,7 +112,6 @@ def acall(self):
         "LangchainCallbackHandler": "chainlit.langchain.callbacks",
         "AsyncLangchainCallbackHandler": "chainlit.langchain.callbacks",
         "LlamaIndexCallbackHandler": "chainlit.llama_index.callbacks",
-        "HaystackAgentCallbackHandler": "chainlit.haystack.callbacks",
         "instrument_openai": "chainlit.openai",
         "instrument_mistralai": "chainlit.mistralai",
     }
@@ -135,7 +135,6 @@ def acall(self):
     "ErrorMessage",
     "File",
     "GenerationMessage",
-    "HaystackAgentCallbackHandler",
     "Image",
     "InputAudioChunk",
     "LangchainCallbackHandler",
@@ -174,6 +173,8 @@ def acall(self):
     "on_chat_resume",
     "on_chat_start",
     "on_logout",
+    "on_mcp_connect",
+    "on_mcp_disconnect",
     "on_message",
     "on_settings_update",
     "on_stop",

backend/chainlit/auth/jwt.py

@@ -29,9 +29,12 @@ def create_jwt(data: User) -> str:
 
 
 def decode_jwt(token: str) -> User:
+    secret = get_jwt_secret()
+    assert secret
+
     dict = pyjwt.decode(
         token,
-        get_jwt_secret(),
+        secret,
         algorithms=["HS256"],
         options={"verify_signature": True},
     )

backend/chainlit/callbacks.py

@@ -2,12 +2,14 @@
 from typing import Any, Awaitable, Callable, Dict, List, Optional
 
 from fastapi import Request, Response
+from mcp import ClientSession
 from starlette.datastructures import Headers
 
 from chainlit.action import Action
 from chainlit.config import config
 from chainlit.context import context
 from chainlit.data.base import BaseDataLayer
+from chainlit.mcp import McpConnection
 from chainlit.message import Message
 from chainlit.oauth_providers import get_configured_oauth_providers
 from chainlit.step import Step, step
@@ -300,6 +302,26 @@ def author_rename(
     return func
 
 
+@trace
+def on_mcp_connect(func: Callable[[McpConnection, ClientSession], None]) -> Callable:
+    """
+    Called everytime an MCP is connected
+    """
+
+    config.code.on_mcp_connect = wrap_user_function(func)
+    return func
+
+
+@trace
+def on_mcp_disconnect(func: Callable[[str, ClientSession], None]) -> Callable:
+    """
+    Called everytime an MCP is disconnected
+    """
+
+    config.code.on_mcp_disconnect = wrap_user_function(func)
+    return func
+
+
 @trace
 def on_stop(func: Callable) -> Callable:
     """

backend/chainlit/config.py

@@ -214,6 +214,7 @@ class AudioFeature(DataClassJsonMixin):
 class FeaturesSettings(DataClassJsonMixin):
     spontaneous_file_upload: Optional[SpontaneousFileUploadFeature] = None
     audio: Optional[AudioFeature] = Field(default_factory=AudioFeature)
+    mcp: bool = False
     latex: bool = False
     unsafe_allow_html: bool = False
     auto_tag_thread: bool = True
@@ -273,6 +274,8 @@ class CodeSettings:
     on_audio_start: Optional[Callable[[], Any]] = None
     on_audio_chunk: Optional[Callable[["InputAudioChunk"], Any]] = None
     on_audio_end: Optional[Callable[[], Any]] = None
+    on_mcp_connect: Optional[Callable] = None
+    on_mcp_disconnect: Optional[Callable] = None
 
     author_rename: Optional[Callable[[str], Awaitable[str]]] = None
     on_settings_update: Optional[Callable[[Dict[str, Any]], Any]] = None
@@ -297,7 +300,7 @@ class ProjectSettings(DataClassJsonMixin):
     lc_cache_path: Optional[str] = None
     # Path to the local chat db
     # Duration (in seconds) during which the session is saved when the connection is lost
-    session_timeout: int = 3600
+    session_timeout: int = 300
     # Duration (in seconds) of the user session expiry
     user_session_timeout: int = 1296000  # 15 days
     # Enable third parties caching (e.g LangChain cache)

backend/chainlit/discord/app.py

@@ -292,7 +292,7 @@ async def process_discord_message(
         except Exception as e:
             logger.error(f"Error updating thread: {e}")
 
-    ctx.session.delete()
+    await ctx.session.delete()
 
 
 @client.event