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refactor: replace lowlevel Server decorators with on_* constructor kwargs (#1985)

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Max Isbey 2026-02-12 15:55:54 +00:00 • committed by GitHub
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1 changed files with 3563 additions and 5481 deletions
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159
src/mcp/server/mcpserver/server.py
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@ -2,7 +2,9 @@
from __future__ import annotations
import base64
import inspect
import json
import re
from collections.abc import AsyncIterator, Awaitable, Callable, Iterable, Sequence
from contextlib import AbstractAsyncContextManager, asynccontextmanager
@ -29,7 +31,7 @@ from mcp.server.context import LifespanContextT, RequestT, ServerRequestContext
from mcp.server.elicitation import ElicitationResult, ElicitSchemaModelT, UrlElicitationResult, elicit_with_validation
from mcp.server.elicitation import elicit_url as _elicit_url
from mcp.server.lowlevel.helper_types import ReadResourceContents
from mcp.server.lowlevel.server import LifespanResultT, Server
from mcp.server.lowlevel.server import LifespanResultT, Server, request_ctx
from mcp.server.lowlevel.server import lifespan as default_lifespan
from mcp.server.mcpserver.exceptions import ResourceError
from mcp.server.mcpserver.prompts import Prompt, PromptManager
@ -42,7 +44,30 @@ from mcp.server.stdio import stdio_server
from mcp.server.streamable_http import EventStore
from mcp.server.streamable_http_manager import StreamableHTTPSessionManager
from mcp.server.transport_security import TransportSecuritySettings
from mcp.types import Annotations, ContentBlock, GetPromptResult, Icon, ToolAnnotations
from mcp.shared.exceptions import MCPError
from mcp.types import (
Annotations,
BlobResourceContents,
CallToolRequestParams,
CallToolResult,
CompleteRequestParams,
CompleteResult,
Completion,
ContentBlock,
GetPromptRequestParams,
GetPromptResult,
Icon,
ListPromptsResult,
ListResourcesResult,
ListResourceTemplatesResult,
ListToolsResult,
PaginatedRequestParams,
ReadResourceRequestParams,
ReadResourceResult,
TextContent,
TextResourceContents,
ToolAnnotations,
)
from mcp.types import Prompt as MCPPrompt
from mcp.types import PromptArgument as MCPPromptArgument
from mcp.types import Resource as MCPResource
@ -91,9 +116,9 @@ class Settings(BaseSettings, Generic[LifespanResultT]):
def lifespan_wrapper(
app: MCPServer[LifespanResultT],
lifespan: Callable[[MCPServer[LifespanResultT]], AbstractAsyncContextManager[LifespanResultT]],
) -> Callable[[Server[LifespanResultT, Request]], AbstractAsyncContextManager[LifespanResultT]]:
) -> Callable[[Server[LifespanResultT]], AbstractAsyncContextManager[LifespanResultT]]:
@asynccontextmanager
async def wrap(_: Server[LifespanResultT, Request]) -> AsyncIterator[LifespanResultT]:
async def wrap(_: Server[LifespanResultT]) -> AsyncIterator[LifespanResultT]:
async with lifespan(app) as context:
yield context
@ -132,6 +157,9 @@ class MCPServer(Generic[LifespanResultT]):
auth=auth,
)
self._tool_manager = ToolManager(tools=tools, warn_on_duplicate_tools=self.settings.warn_on_duplicate_tools)
self._resource_manager = ResourceManager(warn_on_duplicate_resources=self.settings.warn_on_duplicate_resources)
self._prompt_manager = PromptManager(warn_on_duplicate_prompts=self.settings.warn_on_duplicate_prompts)
self._lowlevel_server = Server(
name=name or "mcp-server",
title=title,
@ -140,13 +168,17 @@ class MCPServer(Generic[LifespanResultT]):
website_url=website_url,
icons=icons,
version=version,
on_list_tools=self._handle_list_tools,
on_call_tool=self._handle_call_tool,
on_list_resources=self._handle_list_resources,
on_read_resource=self._handle_read_resource,
on_list_resource_templates=self._handle_list_resource_templates,
on_list_prompts=self._handle_list_prompts,
on_get_prompt=self._handle_get_prompt,
# TODO(Marcelo): It seems there's a type mismatch between the lifespan type from an MCPServer and Server.
# We need to create a Lifespan type that is a generic on the server type, like Starlette does.
lifespan=(lifespan_wrapper(self, self.settings.lifespan) if self.settings.lifespan else default_lifespan), # type: ignore
)
self._tool_manager = ToolManager(tools=tools, warn_on_duplicate_tools=self.settings.warn_on_duplicate_tools)
self._resource_manager = ResourceManager(warn_on_duplicate_resources=self.settings.warn_on_duplicate_resources)
self._prompt_manager = PromptManager(warn_on_duplicate_prompts=self.settings.warn_on_duplicate_prompts)
# Validate auth configuration
if self.settings.auth is not None:
if auth_server_provider and token_verifier: # pragma: no cover
@ -164,9 +196,6 @@ class MCPServer(Generic[LifespanResultT]):
self._token_verifier = ProviderTokenVerifier(auth_server_provider)
self._custom_starlette_routes: list[Route] = []
# Set up MCP protocol handlers
self._setup_handlers()
# Configure logging
configure_logging(self.settings.log_level)
@ -263,18 +292,83 @@ class MCPServer(Generic[LifespanResultT]):
case "streamable-http": # pragma: no cover
anyio.run(lambda: self.run_streamable_http_async(**kwargs))
def _setup_handlers(self) -> None:
"""Set up core MCP protocol handlers."""
self._lowlevel_server.list_tools()(self.list_tools)
# Note: we disable the lowlevel server's input validation.
# MCPServer does ad hoc conversion of incoming data before validating -
# for now we preserve this for backwards compatibility.
self._lowlevel_server.call_tool(validate_input=False)(self.call_tool)
self._lowlevel_server.list_resources()(self.list_resources)
self._lowlevel_server.read_resource()(self.read_resource)
self._lowlevel_server.list_prompts()(self.list_prompts)
self._lowlevel_server.get_prompt()(self.get_prompt)
self._lowlevel_server.list_resource_templates()(self.list_resource_templates)
async def _handle_list_tools(
self, ctx: ServerRequestContext[LifespanResultT], params: PaginatedRequestParams | None
) -> ListToolsResult:
return ListToolsResult(tools=await self.list_tools())
async def _handle_call_tool(
self, ctx: ServerRequestContext[LifespanResultT], params: CallToolRequestParams
) -> CallToolResult:
try:
result = await self.call_tool(params.name, params.arguments or {})
except MCPError:
raise
except Exception as e:
return CallToolResult(content=[TextContent(type="text", text=str(e))], is_error=True)
if isinstance(result, CallToolResult):
return result
if isinstance(result, tuple) and len(result) == 2:
unstructured_content, structured_content = result
return CallToolResult(
content=list(unstructured_content), # type: ignore[arg-type]
structured_content=structured_content, # type: ignore[arg-type]
)
if isinstance(result, dict): # pragma: no cover
# TODO: this code path is unreachable — convert_result never returns a raw dict.
# The call_tool return type (Sequence[ContentBlock] | dict[str, Any]) is wrong
# and needs to be cleaned up.
return CallToolResult(
content=[TextContent(type="text", text=json.dumps(result, indent=2))],
structured_content=result,
)
return CallToolResult(content=list(result))
async def _handle_list_resources(
self, ctx: ServerRequestContext[LifespanResultT], params: PaginatedRequestParams | None
) -> ListResourcesResult:
return ListResourcesResult(resources=await self.list_resources())
async def _handle_read_resource(
self, ctx: ServerRequestContext[LifespanResultT], params: ReadResourceRequestParams
) -> ReadResourceResult:
results = await self.read_resource(params.uri)
contents: list[TextResourceContents | BlobResourceContents] = []
for item in results:
if isinstance(item.content, bytes):
contents.append(
BlobResourceContents(
uri=params.uri,
blob=base64.b64encode(item.content).decode(),
mime_type=item.mime_type or "application/octet-stream",
_meta=item.meta,
)
)
else:
contents.append(
TextResourceContents(
uri=params.uri,
text=item.content,
mime_type=item.mime_type or "text/plain",
_meta=item.meta,
)
)
return ReadResourceResult(contents=contents)
async def _handle_list_resource_templates(
self, ctx: ServerRequestContext[LifespanResultT], params: PaginatedRequestParams | None
) -> ListResourceTemplatesResult:
return ListResourceTemplatesResult(resource_templates=await self.list_resource_templates())
async def _handle_list_prompts(
self, ctx: ServerRequestContext[LifespanResultT], params: PaginatedRequestParams | None
) -> ListPromptsResult:
return ListPromptsResult(prompts=await self.list_prompts())
async def _handle_get_prompt(
self, ctx: ServerRequestContext[LifespanResultT], params: GetPromptRequestParams
) -> GetPromptResult:
return await self.get_prompt(params.name, params.arguments)
async def list_tools(self) -> list[MCPTool]:
"""List all available tools."""
@ -298,7 +392,7 @@ class MCPServer(Generic[LifespanResultT]):
during a request; outside a request, most methods will error.
"""
try:
request_context = self._lowlevel_server.request_context
request_context = request_ctx.get()
except LookupError:
request_context = None
return Context(request_context=request_context, mcp_server=self)
@ -486,7 +580,24 @@ class MCPServer(Generic[LifespanResultT]):
return Completion(values=["option1", "option2"])
return None
"""
return self._lowlevel_server.completion()
def decorator(func: _CallableT) -> _CallableT:
async def handler(
ctx: ServerRequestContext[LifespanResultT], params: CompleteRequestParams
) -> CompleteResult:
result = await func(params.ref, params.argument, params.context)
return CompleteResult(
completion=result if result is not None else Completion(values=[], total=None, has_more=None),
)
# TODO(maxisbey): remove private access — completion needs post-construction
# handler registration, find a better pattern for this
self._lowlevel_server._add_request_handler( # pyright: ignore[reportPrivateUsage]
"completion/complete", handler
)
return func
return decorator
def add_resource(self, resource: Resource) -> None:
"""Add a resource to the server.