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Fix bug with tools that return lists

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This commit is contained in:
Jeremiah Lowin 2025-04-11 10:51:07 -04:00
commit 5b32ffb77f
2 changed files with 44 additions and 55 deletions
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27
src/fastmcp/server/server.py
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@ -8,7 +8,6 @@ from contextlib import (
AbstractAsyncContextManager,
asynccontextmanager,
)
from itertools import chain
from typing import TYPE_CHECKING, Any, Generic, Literal
import anyio
@ -618,7 +617,8 @@ class FastMCP(Generic[LifespanResultT]):
def _convert_to_content(
result: Any,
) -> Sequence[TextContent | ImageContent | EmbeddedResource]:
_process_as_single_item: bool = False,
) -> list[TextContent | ImageContent | EmbeddedResource]:
"""Convert a result to a sequence of content objects."""
if result is None:
return []
@ -629,8 +629,27 @@ def _convert_to_content(
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 isinstance(result, list | tuple) and not _process_as_single_item:
# if the result is a list, then it could either be a list of MCP types,
# or a "regular" list that the tool is returning, or a mix of both.
#
# so we extract all the MCP types / images and convert them as individual content elements,
# and aggregate the rest as a single content element
mcp_types = []
other_content = []
for item in result:
if isinstance(item, (TextContent, ImageContent, EmbeddedResource, Image)):
mcp_types.append(_convert_to_content(item)[0])
else:
other_content.append(item)
if other_content:
other_content = _convert_to_content(
other_content, _process_as_single_item=True
)
return other_content + mcp_types
if not isinstance(result, str):
try: