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Serve subscriptions/listen with a pluggable event bus (SEP-2575) (#3035)

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Max 2026-06-30 23:01:04 +01:00 • committed by GitHub
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1 changed files with 1722 additions and 66 deletions
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30
src/mcp/server/mcpserver/server.py
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@ -88,6 +88,7 @@ from mcp.server.sse import SseServerTransport
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.subscriptions import InMemorySubscriptionBus, ListenHandler, SubscriptionBus
from mcp.server.transport_security import TransportSecuritySettings
from mcp.shared.exceptions import MCPError
from mcp.shared.uri_template import UriTemplate
@ -182,6 +183,7 @@ class MCPServer(Generic[LifespanResultT]):
resource_security: ResourceSecurity = DEFAULT_RESOURCE_SECURITY,
request_state_security: RequestStateSecurity | None = None,
cache_hints: Mapping[CacheableMethod, CacheHint] | None = None,
subscriptions: SubscriptionBus | None = None,
):
self._resource_security = resource_security
self.settings = Settings(
@ -201,6 +203,10 @@ class MCPServer(Generic[LifespanResultT]):
resources=resources, warn_on_duplicate_resources=self.settings.warn_on_duplicate_resources
)
self._prompt_manager = PromptManager(warn_on_duplicate_prompts=self.settings.warn_on_duplicate_prompts)
# The subscriptions/listen fan-out seam (2026-07-28). The default bus is
# in-process; pass an `SubscriptionBus` implementation over an external pub/sub
# backend to fan events out across replicas.
self._subscriptions: SubscriptionBus = subscriptions if subscriptions is not None else InMemorySubscriptionBus()
self._lowlevel_server = Server(
name=name or "mcp-server",
title=title,
@ -217,6 +223,7 @@ class MCPServer(Generic[LifespanResultT]):
on_list_resource_templates=self._handle_list_resource_templates,
on_list_prompts=self._handle_list_prompts,
on_get_prompt=self._handle_get_prompt,
on_subscriptions_listen=ListenHandler(self._subscriptions),
# 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
@ -396,7 +403,7 @@ class MCPServer(Generic[LifespanResultT]):
async def _handle_call_tool(
self, ctx: ServerRequestContext[LifespanResultT], params: CallToolRequestParams
) -> CallToolResult | InputRequiredResult:
context = Context(request_context=ctx, mcp_server=self, input_params=params)
context = Context(request_context=ctx, mcp_server=self, input_params=params, subscriptions=self._subscriptions)
try:
return await self.call_tool(params.name, params.arguments or {}, context)
except MCPError:
@ -412,7 +419,7 @@ class MCPServer(Generic[LifespanResultT]):
async def _handle_read_resource(
self, ctx: ServerRequestContext[LifespanResultT], params: ReadResourceRequestParams
) -> ReadResourceResult | InputRequiredResult:
context = Context(request_context=ctx, mcp_server=self, input_params=params)
context = Context(request_context=ctx, mcp_server=self, input_params=params, subscriptions=self._subscriptions)
try:
results = await self.read_resource(params.uri, context)
except ResourceNotFoundError as err:
@ -456,7 +463,7 @@ class MCPServer(Generic[LifespanResultT]):
async def _handle_get_prompt(
self, ctx: ServerRequestContext[LifespanResultT], params: GetPromptRequestParams
) -> GetPromptResult | InputRequiredResult:
context = Context(request_context=ctx, mcp_server=self, input_params=params)
context = Context(request_context=ctx, mcp_server=self, input_params=params, subscriptions=self._subscriptions)
return await self.get_prompt(params.name, params.arguments, context)
async def list_tools(self) -> list[MCPTool]:
@ -481,7 +488,7 @@ class MCPServer(Generic[LifespanResultT]):
) -> CallToolResult | InputRequiredResult:
"""Call a tool by name with arguments."""
if context is None:
context = Context(mcp_server=self)
context = Context(mcp_server=self, subscriptions=self._subscriptions)
return await self._tool_manager.call_tool(name, arguments, context, convert_result=True)
async def list_resources(self) -> list[MCPResource]:
@ -533,7 +540,7 @@ class MCPServer(Generic[LifespanResultT]):
ResourceError: If template creation or resource reading fails.
"""
if context is None:
context = Context(mcp_server=self)
context = Context(mcp_server=self, subscriptions=self._subscriptions)
resource = await self._resource_manager.get_resource(uri, context)
if isinstance(resource, InputRequiredResult):
return resource
@ -879,6 +886,17 @@ class MCPServer(Generic[LifespanResultT]):
"""
self._prompt_manager.add_prompt(prompt)
def remove_prompt(self, name: str) -> None:
"""Remove a prompt from the server by name.
Args:
name: The name of the prompt to remove
Raises:
ValueError: If the prompt does not exist
"""
self._prompt_manager.remove_prompt(name)
def prompt(
self,
name: str | None = None,
@ -1242,7 +1260,7 @@ class MCPServer(Generic[LifespanResultT]):
carrying the echoed opaque state.
"""
if context is None:
context = Context(mcp_server=self)
context = Context(mcp_server=self, subscriptions=self._subscriptions)
try:
prompt = self._prompt_manager.get_prompt(name)
if not prompt: