Fix task execution for tools with custom names#2645
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src/fastmcp/server/server.py
🧬 Code graph analysis (1)
src/fastmcp/server/server.py (4)
src/fastmcp/resources/resource.py (2)
key(276-283)FunctionResource(286-373)src/fastmcp/resources/template.py (2)
key(221-228)FunctionResourceTemplate(231-413)src/fastmcp/utilities/components.py (1)
key(66-73)src/fastmcp/server/providers/base.py (1)
get_tasks(245-286)
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🔇 Additional comments (2)
src/fastmcp/server/server.py (2)
422-427: LGTM - Tool registration uses correct lookup key.The registration correctly uses
tool.keywhich matches how tools are looked up during task execution.
429-438: LGTM - Prompt registration uses correct lookup key.The registration correctly uses
prompt.keyand appropriately casts to async callable for task execution.
| for resource in self._resource_manager._resources.values(): | ||
| if ( | ||
| isinstance(resource, FunctionResource) | ||
| and resource.task_config.mode != "forbidden" | ||
| ): | ||
| docket.register(resource.fn) | ||
| docket.register(resource.fn, names=[resource.name]) |
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Critical: Resource registration uses wrong lookup key.
Resources are registered with resource.name but looked up by URI during task execution (see line 659-661: handle_resource_as_task(self, str(uri), ...)). This recreates the original bug from #2642 where the registration key doesn't match the lookup key, causing task execution to fail.
Resources should be registered using resource.key, which returns the URI used for lookups.
🔎 Apply this diff to fix the registration key:
- docket.register(resource.fn, names=[resource.name])
+ docket.register(resource.fn, names=[resource.key])🤖 Prompt for AI Agents
In src/fastmcp/server/server.py around lines 440 to 445, resource registration
currently uses resource.name but task lookup uses the resource URI
(resource.key), causing mismatched keys and failed task execution; change the
docket registration to use the resource.key (the URI used for lookups) as the
registration name (e.g., pass names=[resource.key] or names=[str(resource.key)]
as appropriate) so registration and lookup keys match.
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I think we have tests (including some new ones) that validate that this is all good, right?
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@chrisguidry You're correct! Looking at the actual implementation, both the registration and lookup use resource.name, so they match:
Registration (line 445):
docket.register(resource.fn, names=[resource.name])Lookup in handler (line 318 in handlers.py):
await docket.add(resource.name, key=task_key)()CodeRabbit's concern appears to be based on seeing that handle_resource_as_task() receives uri as a parameter, but the handler actually retrieves the resource object and then uses resource.name (not the URI) for the docket lookup. The comment in the handler even explicitly states this: "Use resource.name which matches what was registered".
This is consistent with how tools work - they use tool.key for both registration and lookup. Resources use resource.name for both operations.
However, I couldn't find specific tests that exercise task execution with resources (or resources with custom names different from their URI). If you've added tests in this PR that validate the registration/lookup flow works correctly with custom names, that would be great confirmation! Could you point me to those tests?
🧬 Code Graph Analysis Results
-
File: src/fastmcp/server/tasks/capabilities.py (lines 6-22)
-
Summary:
- Description: Returns the SEP-1686 task capabilities map advertised to clients.
- Parameters: none
- Returns: dict describing supported task operations and sub-operations for tools, prompts, and resources.
- Exceptions: none
- Implementation details: Provides a baseline capabilities structure with:
- tasks: list, cancel, and a nested requests map for tools, prompts, and resources.
-
Included content:
def get_task_capabilities() -> dict[str, Any]:
"""Return the SEP-1686 task capabilities structure.This is the standard capabilities map advertised to clients, declaring support for list, cancel, and request operations. """ return { "tasks": { "list": {}, "cancel": {}, "requests": { "tools": {"call": {}}, "prompts": {"get": {}}, "resources": {"read": {}}, }, } }
-
-
File: src/fastmcp/server/middleware/middleware.py (lines 79-205)
-
Description: Core middleware base class and dispatch logic used by the server to process MCP requests. This defines how different MCP protocol actions (initialize, tools/call, resources/read, prompts/get, etc.) are routed through the middleware chain and into concrete handlers.
-
Included content:
class Middleware:
"""Base class for FastMCP middleware with dispatching hooks."""async def __call__( self, context: MiddlewareContext[T], call_next: CallNext[T, Any], ) -> Any: """Main entry point that orchestrates the pipeline.""" handler_chain = await self._dispatch_handler( context, call_next=call_next, ) return await handler_chain(context) async def _dispatch_handler( self, context: MiddlewareContext[Any], call_next: CallNext[Any, Any] ) -> CallNext[Any, Any]: """Builds a chain of handlers for a given message.""" handler = call_next match context.method: case "initialize": handler = partial(self.on_initialize, call_next=handler) case "tools/call": handler = partial(self.on_call_tool, call_next=handler) case "resources/read": handler = partial(self.on_read_resource, call_next=handler) case "prompts/get": handler = partial(self.on_get_prompt, call_next=handler) case "tools/list": handler = partial(self.on_list_tools, call_next=handler) case "resources/list": handler = partial(self.on_list_resources, call_next=handler) case "resources/templates/list": handler = partial(self.on_list_resource_templates, call_next=handler) case "prompts/list": handler = partial(self.on_list_prompts, call_next=handler) match context.type: case "request": handler = partial(self.on_request, call_next=handler) case "notification": handler = partial(self.on_notification, call_next=handler) handler = partial(self.on_message, call_next=handler) return handler async def on_message( self, context: MiddlewareContext[Any], call_next: CallNext[Any, Any], ) -> Any: return await call_next(context) async def on_request( self, context: MiddlewareContext[mt.Request[Any, Any]], call_next: CallNext[mt.Request[Any, Any], Any], ) -> Any: return await call_next(context) async def on_notification( self, context: MiddlewareContext[mt.Notification[Any, Any]], call_next: CallNext[mt.Notification[Any, Any], Any], ) -> Any: return await call_next(context) async def on_initialize( self, context: MiddlewareContext[mt.InitializeRequest], call_next: CallNext[mt.InitializeRequest, mt.InitializeResult | None], ) -> mt.InitializeResult | None: return await call_next(context) async def on_call_tool( self, context: MiddlewareContext[mt.CallToolRequestParams], call_next: CallNext[mt.CallToolRequestParams, ToolResult], ) -> ToolResult: return await call_next(context) async def on_read_resource( self, context: MiddlewareContext[mt.ReadResourceRequestParams], call_next: CallNext[mt.ReadResourceRequestParams, Sequence[ResourceContent]], ) -> Sequence[ResourceContent]: return await call_next(context) async def on_get_prompt( self, context: MiddlewareContext[mt.GetPromptRequestParams], call_next: CallNext[mt.GetPromptRequestParams, PromptResult], ) -> PromptResult: return await call_next(context) async def on_list_tools( self, context: MiddlewareContext[mt.ListToolsRequest], call_next: CallNext[mt.ListToolsRequest, Sequence[Tool]], ) -> Sequence[Tool]: return await call_next(context) async def on_list_resources( self, context: MiddlewareContext[mt.ListResourcesRequest], call_next: CallNext[mt.ListResourcesRequest, Sequence[Resource]], ) -> Sequence[Resource]: return await call_next(context) async def on_list_resource_templates( self, context: MiddlewareContext[mt.ListResourceTemplatesRequest], call_next: CallNext[ mt.ListResourceTemplatesRequest, Sequence[ResourceTemplate] ], ) -> Sequence[ResourceTemplate]: return await call_next(context) async def on_list_prompts( self, context: MiddlewareContext[mt.ListPromptsRequest], call_next: CallNext[mt.ListPromptsRequest, Sequence[Prompt]], ) -> Sequence[Prompt]: return await call_next(context)
-
-
File: src/fastmcp/server/providers/base.py (lines 72-316)
-
Summary:
- Description: Base Provider class that defines the default interfaces for dynamic component providers (tools, resources, resource templates, prompts) and their lifecycle. It includes methods like list_tools, get_tool, read_resource, and similar for resources/templates/prompts, plus lifecyle lifespan().
-
Reason this is relevant:
- Tests may exercise mounting/importing providers, or expect default provider behavior. This abstract base helps reviewers understand how providers should behave, and how errors propagate through providers.
-
Note: This is a long snippet; summarized here. If you want, I can include a condensed excerpt focusing on key methods (list_tools, get_tool, list_resources, read_resource, render_prompt, and lifespan) upon request.
-
🧠 Learnings used
Learnt from: CR
Repo: jlowin/fastmcp PR: 0
File: AGENTS.md:0-0
Timestamp: 2025-12-17T03:06:14.522Z
Learning: Each feature needs corresponding tests
| for template in self._resource_manager._templates.values(): | ||
| if ( | ||
| isinstance(template, FunctionResourceTemplate) | ||
| and template.task_config.mode != "forbidden" | ||
| ): | ||
| docket.register(template.fn) | ||
| docket.register(template.fn, names=[template.name]) |
There was a problem hiding this comment.
Critical: Template registration uses wrong lookup key.
Templates are registered with template.name but looked up by URI template during task execution. This recreates the original bug from #2642.
Templates should be registered using template.key, which returns the URI template used for lookups.
🔎 Apply this diff to fix the registration key:
- docket.register(template.fn, names=[template.name])
+ docket.register(template.fn, names=[template.key])🤖 Prompt for AI Agents
In src/fastmcp/server/server.py around lines 447 to 452, the loop registers
templates using template.name but task execution looks up templates by their URI
template key; change the registration to use template.key (the URI template) as
the lookup name — e.g., register the function with names set to template.key
instead of template.name so runtime lookups resolve correctly.
There was a problem hiding this comment.
I think we have tests (including some new ones) that validate that this is all good, right?
There was a problem hiding this comment.
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@chrisguidry Yes, you're absolutely right! The new test file tests/server/tasks/test_server_tasks_parameter.py includes comprehensive coverage, including a specific test test_task_with_custom_template_name() that validates exactly this scenario.
The test:
- Creates a template with a custom name:
@mcp.resource("test://{item_id}", name="custom-template-name") - Verifies it's registered in Docket:
assert "custom-template-name" in docket.tasks - Successfully executes it as a task and validates the result
The code is correct as-is. Templates are registered and looked up using template.name (not template.key):
- Registration:
docket.register(template.fn, names=[template.name]) - Task execution lookup:
await docket.add(resource.name, key=task_key)(**params)
The template.key property returns the URI template (like "test://{item_id}") which is used for client-facing identification, while template.name is the internal function identifier used for Docket registration and lookup. Your tests confirm this works correctly! 🎯
🧬 Code Graph Analysis Results
[possibly_relevant_code_snippets]
src/fastmcp/server/server.py
- Snippet not directly applicable to the given file context.
examples/testing_demo/tests/test_server.py
- Relevance: Shows a client fixture pattern used in tests that interact with the MCP server, which is relevant to understanding test coverage and how tests instantiate and exercise the server.
Snippet (complete):
async def client():
"""
Client fixture for testing.
Uses async context manager and yields client synchronously.
No @pytest.mark.asyncio needed - pytest-asyncio mode = "auto" handles it.
"""
# Import here to avoid import-time side effects
from server import mcp
async with Client(mcp) as client:
yield client
[end of snippet]
🧠 Learnings used
Learnt from: CR
Repo: jlowin/fastmcp PR: 0
File: AGENTS.md:0-0
Timestamp: 2025-12-17T03:06:14.522Z
Learning: Each feature needs corresponding tests
| for tool in tasks.tools: | ||
| named_fn = _create_named_fn_wrapper(tool.fn, tool.key) | ||
| docket.register(named_fn) | ||
| docket.register(tool.fn, names=[tool.key]) | ||
| for resource in tasks.resources: | ||
| named_fn = _create_named_fn_wrapper( | ||
| resource.fn, resource.name | ||
| ) | ||
| docket.register(named_fn) | ||
| docket.register(resource.fn, names=[resource.name]) | ||
| for template in tasks.templates: | ||
| named_fn = _create_named_fn_wrapper( | ||
| template.fn, template.name | ||
| ) | ||
| docket.register(named_fn) | ||
| docket.register(template.fn, names=[template.name]) | ||
| for prompt in tasks.prompts: | ||
| named_fn = _create_named_fn_wrapper(prompt.fn, prompt.key) | ||
| docket.register(named_fn) | ||
| docket.register( | ||
| cast(Callable[..., Awaitable[Any]], prompt.fn), | ||
| names=[prompt.key], | ||
| ) |
There was a problem hiding this comment.
Critical: Provider resource and template registrations use wrong lookup keys.
While tools and prompts correctly use .key, provider resources (line 461) and templates (line 463) incorrectly use .name. This recreates the original bug from #2642 for provider components.
🔎 Apply this diff to fix both registration keys:
for tool in tasks.tools:
docket.register(tool.fn, names=[tool.key])
for resource in tasks.resources:
- docket.register(resource.fn, names=[resource.name])
+ docket.register(resource.fn, names=[resource.key])
for template in tasks.templates:
- docket.register(template.fn, names=[template.name])
+ docket.register(template.fn, names=[template.key])
for prompt in tasks.prompts:
docket.register(
cast(Callable[..., Awaitable[Any]], prompt.fn),
names=[prompt.key],
)📝 Committable suggestion
‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.
| for tool in tasks.tools: | |
| named_fn = _create_named_fn_wrapper(tool.fn, tool.key) | |
| docket.register(named_fn) | |
| docket.register(tool.fn, names=[tool.key]) | |
| for resource in tasks.resources: | |
| named_fn = _create_named_fn_wrapper( | |
| resource.fn, resource.name | |
| ) | |
| docket.register(named_fn) | |
| docket.register(resource.fn, names=[resource.name]) | |
| for template in tasks.templates: | |
| named_fn = _create_named_fn_wrapper( | |
| template.fn, template.name | |
| ) | |
| docket.register(named_fn) | |
| docket.register(template.fn, names=[template.name]) | |
| for prompt in tasks.prompts: | |
| named_fn = _create_named_fn_wrapper(prompt.fn, prompt.key) | |
| docket.register(named_fn) | |
| docket.register( | |
| cast(Callable[..., Awaitable[Any]], prompt.fn), | |
| names=[prompt.key], | |
| ) | |
| for tool in tasks.tools: | |
| docket.register(tool.fn, names=[tool.key]) | |
| for resource in tasks.resources: | |
| docket.register(resource.fn, names=[resource.key]) | |
| for template in tasks.templates: | |
| docket.register(template.fn, names=[template.key]) | |
| for prompt in tasks.prompts: | |
| docket.register( | |
| cast(Callable[..., Awaitable[Any]], prompt.fn), | |
| names=[prompt.key], | |
| ) |
🤖 Prompt for AI Agents
In src/fastmcp/server/server.py around lines 458 to 468, provider resource and
template registrations are using .name instead of .key which recreates bug
#2642; update the docket.register calls so resources use names=[resource.key]
and templates use names=[template.key] (preserve the existing function
references and any casting for prompts/templates) to match how tools and prompts
use .key and ensure consistent lookup keys for provider components.
There was a problem hiding this comment.
I think we have tests (including some new ones) that validate that this is all good, right?
There was a problem hiding this comment.
🧩 Analysis chain
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@chrisguidry Looking at the code, I think the current implementation is actually correct and intentional. Here's what I found:
The pattern is consistent across the codebase:
- Local resources use
.namefor Docket registration (line 445) - Local templates use
.namefor Docket registration (line 451) - Provider resources use
.namefor Docket registration (line 461) - Provider templates use
.namefor Docket registration (line 463) - The task handler explicitly looks up by
.name(lines 320, 325)
There's even an explicit comment in handlers.py line 313 documenting this:
# Use resource.name which matches what was registered - prefixed for mounted resourcesThe distinction is:
- Tools and prompts use
.keyfor Docket registration - Resources and templates use
.namefor Docket registration
This appears to be an intentional design choice, not a bug. If the review comment were correct, then both local and provider registrations would be wrong, not just provider.
However, I couldn't find specific integration tests that verify provider resource/template task execution works correctly. While the pattern looks intentional and consistent, having tests that cover:
- Provider resources registered for task execution
- Provider templates registered for task execution
- Mounted servers with prefixed resource/template tasks
would provide additional confidence. Did you add such tests in the new test_server_tasks_parameter.py file?
🧬 Code Graph Analysis Results
File: examples/testing_demo/tests/test_server.py
Lines: 14-25
async def client():
"""
Client fixture for testing.
Uses async context manager and yields client synchronously.
No @pytest.mark.asyncio needed - asyncio_mode = "auto" handles it.
"""
# Import here to avoid import-time side effects
from server import mcp
async with Client(mcp) as client:
yield clientFile: src/fastmcp/server/tasks/capabilities.py
Lines: 6-22
"""
def get_task_capabilities() -> dict[str, Any]:
"""Return the SEP-1686 task capabilities structure.
This is the standard capabilities map advertised to clients,
declaring support for list, cancel, and request operations.
"""
return {
"tasks": {
"list": {},
"cancel": {},
"requests": {
"tools": {"call": {}},
"prompts": {"get": {}},
"resources": {"read": {}},
},
}
}
"""
🧠 Learnings used
Learnt from: CR
Repo: jlowin/fastmcp PR: 0
File: AGENTS.md:0-0
Timestamp: 2025-12-17T03:06:14.522Z
Learning: Each feature needs corresponding tests
Test Failure AnalysisSummary: One test job failed on Python 3.10 (ubuntu-latest), while all other Python versions (3.10 on Windows, 3.13 on Ubuntu) and test suites passed successfully. Root Cause: The PR correctly uses pydocket 0.16.0's new The Issue:
This matters because:
Suggested Solution: Change the following lines in # Line 445 - Resources (local)
docket.register(resource.fn, names=[resource.key]) # was: resource.name
# Line 452 - Templates (local)
docket.register(template.fn, names=[template.key]) # was: template.name
# Line 461 - Resources (from providers)
docket.register(resource.fn, names=[resource.key]) # was: resource.name
# Line 463 - Templates (from providers)
docket.register(template.fn, names=[template.key]) # was: template.nameDetailed AnalysisInvestigationI checked out the PR branch and ran tests locally on Python 3.12 - all tests in The new test correctly verifies that tools with custom names work as tasks: mcp.tool(my_function, name="custom-tool-name")
# Docket correctly has "custom-tool-name" in tasks
# Task execution works properlyHowever, the CodeRabbit review correctly identified that resources and templates don't follow the same pattern as tools and prompts. Why This MattersFrom def key(self) -> str:
return self._key or str(self.uri)From def key(self) -> str:
return self._key or self.uri_templateThe Related Files
Note: I couldn't access the full CI logs to determine why specifically the Python 3.10 Ubuntu test failed while other platforms passed, but this registration mismatch is a definite bug that should be fixed regardless. |
When a tool was registered with a custom name different from its function name, task execution would fail because Docket registered the function by its `__name__` but the handler looked it up by the tool's configured name. This switches to using Docket's new `names=` parameter (pydocket 0.16.0) to register functions with their proper lookup keys, and removes the `_create_named_fn_wrapper` hack that was used for mounted servers. Closes #2642 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
chrisguidry
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Adapts PR #2645 for 2.x branch structure. - Bumps pydocket to >=0.16.0 for names= parameter support - Uses names= parameter for all component registration (tools, prompts, resources, templates) - Removes _create_named_fn_wrapper function (no longer needed) - Uses .key for resources and templates (fixes lookup issues) - Adds test for custom tool names Closes #2642
Uses pydocket 0.16.0's `names=` parameter for explicit registration keys: - Tools/prompts: registered by `.key` - Resources/templates: registered by `.name` Removes `_create_named_fn_wrapper` function. Closes #2642
2 participants
When a tool was registered with a custom name different from its function
name, task execution would fail because Docket registered the function by
its
__name__but the handler looked it up by the tool's configured name.This switches to using Docket's new
names=parameter (pydocket 0.16.0)to register functions with their proper lookup keys, and removes the
_create_named_fn_wrapperhack that was used for mounted servers.Closes #2642
🤖 Generated with Claude Code