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replace inefficient use of to_jsonable_python #545

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Merged
merged 1 commit into from
Apr 26, 2025
Merged

replace inefficient use of to_jsonable_python #545

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5 changes: 3 additions & 2 deletions src/mcp/server/fastmcp/prompts/base.py
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Original file line number Diff line number Diff line change
@@ -1,7 +1,6 @@
"""Base classes for FastMCP prompts."""

import inspect
import json
from collections.abc import Awaitable, Callable, Sequence
from typing import Any, Literal

Expand Down Expand Up @@ -155,7 +154,9 @@ async def render(self, arguments: dict[str, Any] | None = None) -> list[Message]
content = TextContent(type="text", text=msg)
messages.append(UserMessage(content=content))
else:
content = json.dumps(pydantic_core.to_jsonable_python(msg))
content = pydantic_core.to_json(
msg, fallback=str, indent=2
).decode()
messages.append(Message(role="user", content=content))
except Exception:
raise ValueError(
Expand Down
13 changes: 5 additions & 8 deletions src/mcp/server/fastmcp/resources/types.py
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@
import anyio
import anyio.to_thread
import httpx
import pydantic.json
import pydantic
import pydantic_core
from pydantic import Field, ValidationInfo

Expand Down Expand Up @@ -59,15 +59,12 @@ async def read(self) -> str | bytes:
)
if isinstance(result, Resource):
return await result.read()
if isinstance(result, bytes):
elif isinstance(result, bytes):
return result
if isinstance(result, str):
elif isinstance(result, str):
return result
try:
return json.dumps(pydantic_core.to_jsonable_python(result))
except (TypeError, pydantic_core.PydanticSerializationError):
# If JSON serialization fails, try str()
return str(result)
else:
return pydantic_core.to_json(result, fallback=str, indent=2).decode()
except Exception as e:
raise ValueError(f"Error reading resource {self.uri}: {e}")

Expand Down
7 changes: 2 additions & 5 deletions src/mcp/server/fastmcp/server.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,6 @@
from __future__ import annotations as _annotations

import inspect
import json
import re
from collections.abc import AsyncIterator, Callable, Iterable, Sequence
from contextlib import (
Expand Down Expand Up @@ -466,6 +465,7 @@ async def run_stdio_async(self) -> None:
async def run_sse_async(self) -> None:
"""Run the server using SSE transport."""
import uvicorn

starlette_app = self.sse_app()

config = uvicorn.Config(
Expand Down Expand Up @@ -550,10 +550,7 @@ def _convert_to_content(
return list(chain.from_iterable(_convert_to_content(item) for item in result)) # type: ignore[reportUnknownVariableType]

if not isinstance(result, str):
try:
result = json.dumps(pydantic_core.to_jsonable_python(result))
except Exception:
result = str(result)
result = pydantic_core.to_json(result, fallback=str, indent=2).decode()

return [TextContent(type="text", text=result)]

Expand Down
2 changes: 1 addition & 1 deletion tests/server/fastmcp/resources/test_function_resources.py
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Original file line number Diff line number Diff line change
Expand Up @@ -100,7 +100,7 @@ class MyModel(BaseModel):
fn=lambda: MyModel(name="test"),
)
content = await resource.read()
assert content == '{"name": "test"}'
assert content == '{\n "name": "test"\n}'

@pytest.mark.anyio
async def test_custom_type_conversion(self):
Expand Down
2 changes: 1 addition & 1 deletion tests/server/fastmcp/resources/test_resource_template.py
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Original file line number Diff line number Diff line change
Expand Up @@ -185,4 +185,4 @@ def get_data(value: str) -> CustomData:

assert isinstance(resource, FunctionResource)
content = await resource.read()
assert content == "hello"
assert content == '"hello"'
8 changes: 2 additions & 6 deletions tests/server/fastmcp/servers/test_file_server.py
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Expand Up @@ -114,17 +114,13 @@ async def test_read_resource_file(mcp: FastMCP):

@pytest.mark.anyio
async def test_delete_file(mcp: FastMCP, test_dir: Path):
await mcp.call_tool(
"delete_file", arguments={"path": str(test_dir / "example.py")}
)
await mcp.call_tool("delete_file", arguments={"path": str(test_dir / "example.py")})
assert not (test_dir / "example.py").exists()


@pytest.mark.anyio
async def test_delete_file_and_check_resources(mcp: FastMCP, test_dir: Path):
await mcp.call_tool(
"delete_file", arguments={"path": str(test_dir / "example.py")}
)
await mcp.call_tool("delete_file", arguments={"path": str(test_dir / "example.py")})
res_iter = await mcp.read_resource("file://test_dir/example.py")
res_list = list(res_iter)
assert len(res_list) == 1
Expand Down
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