feat: add resource annotations support to FastMCP (modelcontextprotocol#1468)

Author: fennb

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

@@ -25,7 +25,7 @@ class TextResource(Resource):
 
     async def read(self, context: Any | None = None) -> str:
         """Read the text content."""
-        return self.text
+        return self.text  # pragma: no cover
 
 
 class BinaryResource(Resource):
@@ -35,7 +35,7 @@ class BinaryResource(Resource):
 
     async def read(self, context: Any | None = None) -> bytes:
         """Read the binary content."""
-        return self.data
+        return self.data  # pragma: no cover
 
 
 class FunctionResource(Resource):
@@ -66,6 +66,14 @@ async def read(self, context: Any | None = None) -> str | bytes:
             else:
                 result = self.fn(**args)
 
+            # Support cases where a sync function returns a coroutine
+            if inspect.iscoroutine(result):
+                result = await result
+
+            # Support returning a Resource instance (recursive read)
+            if isinstance(result, Resource):
+                return await result.read(context)
+
             if isinstance(result, str | bytes):
                 return result
             if isinstance(result, pydantic.BaseModel):
@@ -93,7 +101,7 @@ def from_function(
     ) -> "FunctionResource":
         """Create a FunctionResource from a function."""
         func_name = name or fn.__name__
-        if func_name == "<lambda>":
+        if func_name == "<lambda>":  # pragma: no cover
             raise ValueError("You must provide a name for lambda functions")
 
         context_kwarg = find_context_parameter(fn)
@@ -132,7 +140,7 @@ class FileResource(Resource):
 
     @pydantic.field_validator("path")
     @classmethod
-    def validate_absolute_path(cls, path: Path) -> Path:
+    def validate_absolute_path(cls, path: Path) -> Path:  # pragma: no cover
         """Ensure path is absolute."""
         if not path.is_absolute():
             raise ValueError("Path must be absolute")
@@ -181,13 +189,13 @@ class DirectoryResource(Resource):
 
     @pydantic.field_validator("path")
     @classmethod
-    def validate_absolute_path(cls, path: Path) -> Path:
+    def validate_absolute_path(cls, path: Path) -> Path:  # pragma: no cover
         """Ensure path is absolute."""
         if not path.is_absolute():
             raise ValueError("Path must be absolute")
         return path
 
-    def list_files(self) -> list[Path]:
+    def list_files(self) -> list[Path]:  # pragma: no cover
         """List files in the directory."""
         if not self.path.exists():
             raise FileNotFoundError(f"Directory not found: {self.path}")
@@ -201,11 +209,11 @@ def list_files(self) -> list[Path]:
         except Exception as e:
             raise ValueError(f"Error listing directory {self.path}: {e}")
 
-    async def read(self, context: Any | None = None) -> str:  # Always returns JSON string
+    async def read(self, context: Any | None = None) -> str:  # Always returns JSON string  # pragma: no cover
         """Read the directory listing."""
         try:
             files = await anyio.to_thread.run_sync(self.list_files)
             file_list = [str(f.relative_to(self.path)) for f in files if f.is_file()]
             return json.dumps({"files": file_list}, indent=2)
         except Exception as e:
-            raise ValueError(f"Error reading directory {self.path}: {e}")
+            raise ValueError(f"Error reading directory {self.path}: {e}")