feat(mcp): expose MCP resources and prompts as read-only tools
Add MCPResourceWrapper and MCPPromptWrapper classes that expose MCP server resources and prompts as nanobot tools. Resources are read-only tools that fetch content by URI, and prompts are read-only tools that return filled prompt templates with optional arguments. - MCPResourceWrapper: reads resource content (text and binary) via URI - MCPPromptWrapper: gets prompt templates with typed arguments - Both handle timeouts, cancellation, and MCP SDK 1.x error types - Resources and prompts are registered during server connection - Gracefully handles servers that don't support resources/prompts
This commit is contained in:
Tim O'Brien
Xubin Ren
+202
-2
@@ -135,10 +135,178 @@ class MCPToolWrapper(Tool):
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return "\n".join(parts) or "(no output)"
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class MCPResourceWrapper(Tool):
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"""Wraps an MCP resource URI as a read-only nanobot Tool."""
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def __init__(
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self, session, server_name: str, resource_def, resource_timeout: int = 30
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):
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self._session = session
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self._uri = resource_def.uri
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self._name = f"mcp_{server_name}_resource_{resource_def.name}"
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desc = resource_def.description or resource_def.name
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self._description = f"[MCP Resource] {desc}\nURI: {self._uri}"
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self._parameters: dict[str, Any] = {
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"type": "object",
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"properties": {},
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"required": [],
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}
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self._resource_timeout = resource_timeout
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@property
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def name(self) -> str:
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return self._name
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@property
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def description(self) -> str:
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return self._description
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@property
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def parameters(self) -> dict[str, Any]:
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return self._parameters
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@property
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def read_only(self) -> bool:
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return True
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async def execute(self, **kwargs: Any) -> str:
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from mcp import types
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try:
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result = await asyncio.wait_for(
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self._session.read_resource(self._uri),
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timeout=self._resource_timeout,
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)
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except asyncio.TimeoutError:
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logger.warning(
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"MCP resource '{}' timed out after {}s", self._name, self._resource_timeout
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)
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return f"(MCP resource read timed out after {self._resource_timeout}s)"
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except asyncio.CancelledError:
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task = asyncio.current_task()
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if task is not None and task.cancelling() > 0:
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raise
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logger.warning("MCP resource '{}' was cancelled by server/SDK", self._name)
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return "(MCP resource read was cancelled)"
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except Exception as exc:
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logger.exception(
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"MCP resource '{}' failed: {}: {}",
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self._name,
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type(exc).__name__,
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exc,
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)
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return f"(MCP resource read failed: {type(exc).__name__})"
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parts: list[str] = []
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for block in result.contents:
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if isinstance(block, types.TextResourceContents):
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parts.append(block.text)
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elif isinstance(block, types.BlobResourceContents):
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parts.append(f"[Binary resource: {len(block.blob)} bytes]")
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else:
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parts.append(str(block))
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return "\n".join(parts) or "(no output)"
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class MCPPromptWrapper(Tool):
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"""Wraps an MCP prompt as a read-only nanobot Tool."""
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def __init__(
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self, session, server_name: str, prompt_def, prompt_timeout: int = 30
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):
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self._session = session
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self._prompt_name = prompt_def.name
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self._name = f"mcp_{server_name}_prompt_{prompt_def.name}"
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desc = prompt_def.description or prompt_def.name
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self._description = (
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f"[MCP Prompt] {desc}\n"
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"Returns a filled prompt template that can be used as a workflow guide."
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)
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self._prompt_timeout = prompt_timeout
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# Build parameters from prompt arguments
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properties: dict[str, Any] = {}
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required: list[str] = []
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for arg in prompt_def.arguments or []:
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properties[arg.name] = {"type": "string"}
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if arg.required:
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required.append(arg.name)
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self._parameters: dict[str, Any] = {
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"type": "object",
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"properties": properties,
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"required": required,
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}
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@property
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def name(self) -> str:
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return self._name
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@property
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def description(self) -> str:
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return self._description
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@property
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def parameters(self) -> dict[str, Any]:
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return self._parameters
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@property
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def read_only(self) -> bool:
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return True
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async def execute(self, **kwargs: Any) -> str:
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from mcp import types
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from mcp.shared.exceptions import McpError
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try:
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result = await asyncio.wait_for(
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self._session.get_prompt(self._prompt_name, arguments=kwargs),
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timeout=self._prompt_timeout,
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)
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except asyncio.TimeoutError:
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logger.warning(
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"MCP prompt '{}' timed out after {}s", self._name, self._prompt_timeout
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)
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return f"(MCP prompt call timed out after {self._prompt_timeout}s)"
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except asyncio.CancelledError:
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task = asyncio.current_task()
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if task is not None and task.cancelling() > 0:
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raise
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logger.warning("MCP prompt '{}' was cancelled by server/SDK", self._name)
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return "(MCP prompt call was cancelled)"
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except McpError as exc:
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logger.error(
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"MCP prompt '{}' failed: code={} message={}",
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self._name, exc.error.code, exc.error.message,
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)
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return f"(MCP prompt call failed: {exc.error.message} [code {exc.error.code}])"
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except Exception as exc:
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logger.exception(
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"MCP prompt '{}' failed: {}: {}",
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self._name, type(exc).__name__, exc,
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)
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return f"(MCP prompt call failed: {type(exc).__name__}: {exc})"
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parts: list[str] = []
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for message in result.messages:
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content = message.content
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# content is a single ContentBlock (not a list) in MCP SDK >= 1.x
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if isinstance(content, types.TextContent):
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parts.append(content.text)
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elif isinstance(content, list):
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for block in content:
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if isinstance(block, types.TextContent):
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parts.append(block.text)
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else:
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parts.append(str(block))
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else:
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parts.append(str(content))
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return "\n".join(parts) or "(no output)"
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async def connect_mcp_servers(
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mcp_servers: dict, registry: ToolRegistry, stack: AsyncExitStack
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) -> None:
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"""Connect to configured MCP servers and register their tools."""
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"""Connect to configured MCP servers and register their tools, resources, and prompts."""
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from mcp import ClientSession, StdioServerParameters
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from mcp.client.sse import sse_client
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from mcp.client.stdio import stdio_client
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@@ -247,6 +415,38 @@ async def connect_mcp_servers(
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", ".join(available_wrapped_names) or "(none)",
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)
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logger.info("MCP server '{}': connected, {} tools registered", name, registered_count)
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# --- Register resources ---
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try:
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resources_result = await session.list_resources()
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for resource in resources_result.resources:
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wrapper = MCPResourceWrapper(
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session, name, resource, resource_timeout=cfg.tool_timeout
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)
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registry.register(wrapper)
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registered_count += 1
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logger.debug(
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"MCP: registered resource '{}' from server '{}'", wrapper.name, name
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)
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except Exception as e:
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logger.debug("MCP server '{}': resources not supported or failed: {}", name, e)
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# --- Register prompts ---
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try:
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prompts_result = await session.list_prompts()
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for prompt in prompts_result.prompts:
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wrapper = MCPPromptWrapper(
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session, name, prompt, prompt_timeout=cfg.tool_timeout
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)
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registry.register(wrapper)
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registered_count += 1
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logger.debug(
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"MCP: registered prompt '{}' from server '{}'", wrapper.name, name
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)
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except Exception as e:
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logger.debug("MCP server '{}': prompts not supported or failed: {}", name, e)
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logger.info(
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"MCP server '{}': connected, {} capabilities registered", name, registered_count
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)
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except Exception as e:
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logger.error("MCP server '{}': failed to connect: {}", name, e)
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