feat(mcp): add streamable HTTP and stdio (#1911)

* feat(mcp): add streamable HTTP

alongside with frontend UI change, w/ support for stdio

* fix(mcp): address copilot reviews

* Update src/langbot/pkg/provider/tools/loaders/mcp.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* fix: resolve copilot reviews

* fix: Message -> MessageChunk

* feat: upgrade mcp module

* feat: add i18n

* feat(mcp): enhance MCPCardComponent with mode badge and reorder select items in MCPFormDialog

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: WangCham <651122857@qq.com>
Co-authored-by: Junyan Qin (Chin) <rockchinq@gmail.com>

src/langbot/pkg/entity/persistence/mcp.py

@@ -9,7 +9,7 @@ class MCPServer(Base):
     uuid = sqlalchemy.Column(sqlalchemy.String(255), primary_key=True, unique=True)
     name = sqlalchemy.Column(sqlalchemy.String(255), nullable=False)
     enable = sqlalchemy.Column(sqlalchemy.Boolean, nullable=False, default=False)
-    mode = sqlalchemy.Column(sqlalchemy.String(255), nullable=False)  # stdio, sse
+    mode = sqlalchemy.Column(sqlalchemy.String(255), nullable=False)  # stdio, sse, http
     extra_args = sqlalchemy.Column(sqlalchemy.JSON, nullable=False, default={})
     created_at = sqlalchemy.Column(sqlalchemy.DateTime, nullable=False, server_default=sqlalchemy.func.now())
     updated_at = sqlalchemy.Column(

src/langbot/pkg/provider/runners/localagent.py

@@ -215,16 +215,24 @@ class LocalAgentRunner(runner.RequestRunner):
                     parameters = json.loads(func.arguments)
 
                     func_ret = await self.ap.tool_mgr.execute_func_call(func.name, parameters, query=query)
+                    
+                    # Handle return value content
+                    tool_content = None
+                    if isinstance(func_ret, list) and len(func_ret) > 0 and isinstance(func_ret[0], provider_message.ContentElement):
+                        tool_content = func_ret
+                    else:
+                        tool_content = json.dumps(func_ret, ensure_ascii=False)
+
                     if is_stream:
                         msg = provider_message.MessageChunk(
                             role='tool',
-                            content=json.dumps(func_ret, ensure_ascii=False),
+                            content=tool_content,
                             tool_call_id=tool_call.id,
                         )
                     else:
                         msg = provider_message.Message(
                             role='tool',
-                            content=json.dumps(func_ret, ensure_ascii=False),
+                            content=tool_content,
                             tool_call_id=tool_call.id,
                         )
 

src/langbot/pkg/provider/tools/loaders/mcp.py

@@ -7,14 +7,18 @@ import traceback
 from langbot_plugin.api.entities.events import pipeline_query
 import sqlalchemy
 import asyncio
+import httpx
+
 import uuid as uuid_module
 from mcp import ClientSession, StdioServerParameters
 from mcp.client.stdio import stdio_client
 from mcp.client.sse import sse_client
+from mcp.client.streamable_http import streamable_http_client
 
 from .. import loader
 from ....core import app
 import langbot_plugin.api.entities.builtin.resource.tool as resource_tool
+import langbot_plugin.api.entities.builtin.provider.message as provider_message
 from ....entity.persistence import mcp as persistence_mcp
 
 
@@ -35,7 +39,7 @@ class RuntimeMCPSession:
 
     server_config: dict
 
-    session: ClientSession
+    session: ClientSession | None
 
     exit_stack: AsyncExitStack
 
@@ -52,6 +56,8 @@ class RuntimeMCPSession:
 
     _ready_event: asyncio.Event
 
+    error_message: str | None = None
+
     def __init__(self, server_name: str, server_config: dict, enable: bool, ap: app.Application):
         self.server_name = server_name
         self.server_uuid = server_config.get('uuid', '')
@@ -100,6 +106,24 @@ class RuntimeMCPSession:
 
         await self.session.initialize()
 
+    async def _init_streamable_http_server(self):
+        transport = await self.exit_stack.enter_async_context(
+            streamable_http_client(
+                self.server_config['url'],
+                http_client=httpx.AsyncClient(
+                    headers=self.server_config.get('headers', {}),
+                    timeout=self.server_config.get('timeout', 10),
+                    follow_redirects=True,
+                ),
+            )
+        )
+
+        read, write, _ = transport
+
+        self.session = await self.exit_stack.enter_async_context(ClientSession(read, write))
+
+        await self.session.initialize()
+
     async def _lifecycle_loop(self):
         """在后台任务中管理整个MCP会话的生命周期"""
         try:
@@ -107,6 +131,8 @@ class RuntimeMCPSession:
                 await self._init_stdio_python_server()
             elif self.server_config['mode'] == 'sse':
                 await self._init_sse_server()
+            elif self.server_config['mode'] == 'http':
+                await self._init_streamable_http_server()
             else:
                 raise ValueError(f'无法识别 MCP 服务器类型: {self.server_name}: {self.server_config}')
 
@@ -122,6 +148,7 @@ class RuntimeMCPSession:
 
         except Exception as e:
             self.status = MCPSessionStatus.ERROR
+            self.error_message = str(e)
             self.ap.logger.error(f'Error in MCP session lifecycle {self.server_name}: {e}\n{traceback.format_exc()}')
             # 即使出错也要设置ready事件，让start()方法知道初始化已完成
             self._ready_event.set()
@@ -154,6 +181,9 @@ class RuntimeMCPSession:
             raise Exception('Connection failed, please check URL')
 
     async def refresh(self):
+        if not self.session:
+            return
+
         self.functions.clear()
 
         tools = await self.session.list_tools()
@@ -163,18 +193,36 @@ class RuntimeMCPSession:
         for tool in tools.tools:
 
             async def func(*, _tool=tool, **kwargs):
+                if not self.session:
+                    raise Exception("MCP session is not connected")
+
                 result = await self.session.call_tool(_tool.name, kwargs)
                 if result.isError:
-                    raise Exception(result.content[0].text)
-                return result.content[0].text
+                    error_texts = []
+                    for content in result.content:
+                        if content.type == 'text':
+                            error_texts.append(content.text)
+                    raise Exception("\n".join(error_texts) if error_texts else "Unknown error from MCP tool")
+                
+                result_contents: list[provider_message.ContentElement] = []
+                for content in result.content:
+                    if content.type == 'text':
+                        result_contents.append(provider_message.ContentElement.from_text(content.text))
+                    elif content.type == 'image':
+                        result_contents.append(provider_message.ContentElement.from_image_base64(content.image_base64))
+                    elif content.type == 'resource':
+                        # TODO: Handle resource content
+                        pass
+                
+                return result_contents
 
             func.__name__ = tool.name
 
             self.functions.append(
                 resource_tool.LLMTool(
                     name=tool.name,
-                    human_desc=tool.description,
-                    description=tool.description,
+                    human_desc=tool.description or "",
+                    description=tool.description or "",
                     parameters=tool.inputSchema,
                     func=func,
                 )
@@ -186,6 +234,7 @@ class RuntimeMCPSession:
     def get_runtime_info_dict(self) -> dict:
         return {
             'status': self.status.value,
+            'error_message': self.error_message,
             'tool_count': len(self.get_tools()),
             'tools': [
                 {