move _convert_to_content

Author: bhosmer-ant

src/mcp/server/fastmcp/server.py

@@ -9,7 +9,6 @@
     AbstractAsyncContextManager,
     asynccontextmanager,
 )
-from itertools import chain
 from typing import Any, Generic, Literal
 
 import anyio
@@ -38,7 +37,6 @@
 from mcp.server.fastmcp.resources import FunctionResource, Resource, ResourceManager
 from mcp.server.fastmcp.tools import Tool, ToolManager
 from mcp.server.fastmcp.utilities.logging import configure_logging, get_logger
-from mcp.server.fastmcp.utilities.types import Image
 from mcp.server.lowlevel.helper_types import ReadResourceContents
 from mcp.server.lowlevel.server import LifespanResultT
 from mcp.server.lowlevel.server import Server as MCPServer
@@ -54,7 +52,6 @@
     AnyFunction,
     ContentBlock,
     GetPromptResult,
-    TextContent,
     ToolAnnotations,
 )
 from mcp.types import Prompt as MCPPrompt
@@ -968,28 +965,6 @@ async def get_prompt(self, name: str, arguments: dict[str, Any] | None = None) -
             raise ValueError(str(e))
 
 
-def _convert_to_content(
-    result: Any,
-) -> Sequence[ContentBlock]:
-    """Convert a result to a sequence of content objects."""
-    if result is None:
-        return []
-
-    if isinstance(result, ContentBlock):
-        return [result]
-
-    if isinstance(result, Image):
-        return [result.to_image_content()]
-
-    if isinstance(result, list | tuple):
-        return list(chain.from_iterable(_convert_to_content(item) for item in result))  # type: ignore[reportUnknownVariableType]
-
-    if not isinstance(result, str):
-        result = pydantic_core.to_json(result, fallback=str, indent=2).decode()
-
-    return [TextContent(type="text", text=result)]
-
-
 class Context(BaseModel, Generic[ServerSessionT, LifespanContextT, RequestT]):
     """Context object providing access to MCP capabilities.
 

src/mcp/server/fastmcp/utilities/func_metadata.py

@@ -2,9 +2,11 @@
 import json
 from collections.abc import Awaitable, Callable, Iterable, Sequence
 from dataclasses import asdict, is_dataclass
+from itertools import chain
 from types import GenericAlias
 from typing import Annotated, Any, ForwardRef, Literal, get_args, get_origin, get_type_hints
 
+import pydantic_core
 from pydantic import (
     BaseModel,
     ConfigDict,
@@ -19,7 +21,8 @@
 
 from mcp.server.fastmcp.exceptions import InvalidSignature
 from mcp.server.fastmcp.utilities.logging import get_logger
-from mcp.types import ContentBlock
+from mcp.server.fastmcp.utilities.types import Image
+from mcp.types import ContentBlock, TextContent
 
 logger = get_logger(__name__)
 
@@ -85,13 +88,11 @@ def convert_result(self, result: Any) -> Any:
         tool call handler provides generic backwards compatibility serialization of
         structured content**. This is for FastMCP backwards compatibility: we need to
         retain FastMCP's ad hoc conversion logic for constructing unstructured output
-        from function return values (see _convert_to_content in mcp.server.fastmcp.server),
-        whereas the lowlevel server simply serializes the structured output.
+        from function return values, whereas the lowlevel server simply serializes
+        the structured output.
 
         This backwards compatibility provision will be removed in a future version of FastMCP.
         """
-        from mcp.server.fastmcp.server import _convert_to_content  # type: ignore
-
         unstructured_content = _convert_to_content(result)
 
         if self.output_model is None:
@@ -271,9 +272,6 @@ def func_metadata(
                     f"Function {func.__name__}: return type {annotation} is not supported for structured output. "
                 )
 
-    import sys
-
-    print(f"HEY Function {func.__name__} metadata: {output_model=} {output_conversion=}", file=sys.stderr)
 
     return FuncMetadata(arg_model=arguments_model, output_model=output_model, output_conversion=output_conversion)
 
@@ -476,3 +474,36 @@ def _get_typed_signature(call: Callable[..., Any]) -> inspect.Signature:
     typed_return = _get_typed_annotation(signature.return_annotation, globalns)
     typed_signature = inspect.Signature(typed_params, return_annotation=typed_return)
     return typed_signature
+
+
+def _convert_to_content(
+    result: Any,
+) -> Sequence[ContentBlock]:
+    """
+    Convert a result to a sequence of content objects.
+
+    Note: This conversion logic comes from previous versions of FastMCP and is being
+    retained for purposes of backwards compatibility. It produces different unstructured
+    output than the lowlevel server tool call handler, which serializes structured content.
+    """
+    if result is None:
+        return []
+
+    if isinstance(result, ContentBlock):
+        return [result]
+
+    if isinstance(result, Image):
+        return [result.to_image_content()]
+
+    if isinstance(result, list | tuple):
+        return list(
+            chain.from_iterable(
+                _convert_to_content(item)
+                for item in result  # type: ignore
+            )
+        )
+
+    if not isinstance(result, str):
+        result = pydantic_core.to_json(result, fallback=str, indent=2).decode()
+
+    return [TextContent(type="text", text=result)]