feat: Allow FastMCP resources to return ResourceContents objects directly

Updated FastMCP server and resource base classes to support returning
TextResourceContents and BlobResourceContents objects directly from
resource handlers, matching the low-level server functionality.

- Updated Resource.read() abstract method to accept ResourceContents types
- Modified FunctionResource to handle ResourceContents in wrapped functions
- Updated FastMCP server read_resource to pass through ResourceContents
- Updated Context.read_resource to match new return types

This provides FastMCP users with more control over resource properties
and maintains consistency with the low-level server API.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: alexanderreiff

src/mcp/server/fastmcp/resources/base.py

@@ -13,6 +13,7 @@
     field_validator,
 )
 
+import mcp.types as types
 from mcp.types import Icon
 
 
@@ -43,6 +44,6 @@ def set_default_name(cls, name: str | None, info: ValidationInfo) -> str:
         raise ValueError("Either name or uri must be provided")
 
     @abc.abstractmethod
-    async def read(self) -> str | bytes:
+    async def read(self) -> str | bytes | types.TextResourceContents | types.BlobResourceContents:
         """Read the resource content."""
         pass

src/mcp/server/fastmcp/resources/types.py

@@ -13,6 +13,7 @@
 import pydantic_core
 from pydantic import AnyUrl, Field, ValidationInfo, validate_call
 
+import mcp.types as types
 from mcp.server.fastmcp.resources.base import Resource
 from mcp.types import Icon
 
@@ -52,7 +53,7 @@ class FunctionResource(Resource):
 
     fn: Callable[[], Any] = Field(exclude=True)
 
-    async def read(self) -> str | bytes:
+    async def read(self) -> str | bytes | types.TextResourceContents | types.BlobResourceContents:
         """Read the resource by calling the wrapped function."""
         try:
             # Call the function first to see if it returns a coroutine
@@ -63,6 +64,8 @@ async def read(self) -> str | bytes:
 
             if isinstance(result, Resource):
                 return await result.read()
+            elif isinstance(result, (types.TextResourceContents, types.BlobResourceContents)):
+                return result
             elif isinstance(result, bytes):
                 return result
             elif isinstance(result, str):

src/mcp/server/fastmcp/server.py

@@ -43,7 +43,16 @@
 from mcp.server.streamable_http_manager import StreamableHTTPSessionManager
 from mcp.server.transport_security import TransportSecuritySettings
 from mcp.shared.context import LifespanContextT, RequestContext, RequestT
-from mcp.types import AnyFunction, ContentBlock, GetPromptResult, Icon, ToolAnnotations
+from mcp.types import (
+    AnyFunction,
+    BlobResourceContents,
+    ContentBlock,
+    GetPromptResult,
+    Icon,
+    ResourceContents,
+    TextResourceContents,
+    ToolAnnotations,
+)
 from mcp.types import Prompt as MCPPrompt
 from mcp.types import PromptArgument as MCPPromptArgument
 from mcp.types import Resource as MCPResource
@@ -340,7 +349,9 @@ async def list_resource_templates(self) -> list[MCPResourceTemplate]:
             for template in templates
         ]
 
-    async def read_resource(self, uri: AnyUrl | str) -> Iterable[ReadResourceContents]:
+    async def read_resource(
+        self, uri: AnyUrl | str
+    ) -> Iterable[ReadResourceContents | TextResourceContents | BlobResourceContents]:
         """Read a resource by URI."""
 
         context = self.get_context()
@@ -350,7 +361,10 @@ async def read_resource(self, uri: AnyUrl | str) -> Iterable[ReadResourceContent
 
         try:
             content = await resource.read()
-            return [ReadResourceContents(content=content, mime_type=resource.mime_type)]
+            if isinstance(content, ResourceContents):
+                return [content]
+            else:
+                return [ReadResourceContents(content=content, mime_type=resource.mime_type)]
         except Exception as e:
             logger.exception(f"Error reading resource {uri}")
             raise ResourceError(str(e))
@@ -1124,7 +1138,9 @@ async def report_progress(self, progress: float, total: float | None = None, mes
             message=message,
         )
 
-    async def read_resource(self, uri: str | AnyUrl) -> Iterable[ReadResourceContents]:
+    async def read_resource(
+        self, uri: str | AnyUrl
+    ) -> Iterable[ReadResourceContents | TextResourceContents | BlobResourceContents]:
         """Read a resource by URI.
 
         Args: