FastAPI 0.69 app with SQLAlchemy hangs in pytest when HTTPError is raised

[sscherfke]

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Example Code

"""
test_fastapi.py

Requires:

- python3
- docker

Setup:

  virtualenv -p /usr/bin/python3 .venv
  source .venv/bin/activate
  pip install fastapi==0.69 sqlalchemy mysqlclient pytest requests

Usage:

  pytest test_fastapi.py -vvs
"""
import subprocess
import time

import pytest
from fastapi import Body, FastAPI, HTTPException, Path
from fastapi.testclient import TestClient
from pydantic import BaseModel
from sqlalchemy import (
    Column,
    Integer,
    MetaData,
    String,
    Table,
    create_engine,
    insert,
    select,
)


# Config for the docker container
CONTAINER = "mariadb-fastapi"
MYSQL_PORT = "33072"
MYSQL_DATABASE = "test"
MYSQL_ROOT_PASSWORD = "rootmysql"
DB_URL = f"mysql://root:{MYSQL_ROOT_PASSWORD}@127.0.0.1:{MYSQL_PORT}/{MYSQL_DATABASE}"

# SQLAlchemy
ENGINE = create_engine(DB_URL)
METADATA = MetaData()
T = Table(
    "job",
    METADATA,
    Column("id", Integer(), primary_key=True),
    Column("name", String(length=50)),
)


# FastAPI model and app
class Job(BaseModel):
    name: str


app = FastAPI()


@app.get("/jobs/{job_id}")
def get_job(job_id: int = Path(...)):
    conn = ENGINE.connect()
    stmt = select([T]).with_for_update().where(T.c.id == job_id)
    conn.execute(stmt).fetchone()  # The result does not matter
    # This exception that is raised in the first test causes the second test to
    # hang during its setup.
    # If we do "return None" instead, the second test will be run.
    # return None
    raise HTTPException(404, f'Job with ID "{job_id}" not found')


@app.post("/jobs")
def create_job(job: Job = Body(...)):
    with ENGINE.begin() as conn:
        ins = insert(T).values(**job.dict())
        conn.execute(ins)


#
# Tests
#


@pytest.fixture(autouse=True, scope="module")
def mariadb_docker():
    with subprocess.Popen(
        [
            "docker",
            "run",
            "--rm",
            "--env",
            f"MYSQL_DATABASE={MYSQL_DATABASE}",
            "--env",
            f"MYSQL_ROOT_PASSWORD={MYSQL_ROOT_PASSWORD}",
            f"--name={CONTAINER}",
            f"--publish={MYSQL_PORT}:3306",
            "mariadb",
        ]
    ):
        print("connecting ", end="")
        while True:
            try:
                ENGINE.connect()
                print("done")
                break
            except:
                print(".", end="")
                time.sleep(1)
        yield
        subprocess.run(["docker", "stop", CONTAINER], check=False)


@pytest.fixture
def session():
    print("SESSION drop all")
    METADATA.drop_all(ENGINE)
    print("SESSION create all")
    METADATA.create_all(ENGINE)
    print("SESSION make client")
    client = TestClient(app)
    print("SESSION setup done")
    return client


def test_function_raising_error(session):
    print("TEST starting")
    response = session.get(f"/jobs/2")
    assert response.status_code == 404, response.text
    print("TEST end")


def test_hangs_in_setup(session):
    print("TEST starting")
    response = session.post(f"/jobs", data={"name": "test"})
    assert response.status_code == 422
    print("TEST end")
import subprocess
import time

import pytest
from fastapi import Body, FastAPI, HTTPException, Path
from fastapi.testclient import TestClient
from pydantic import BaseModel
from sqlalchemy import (
    Column,
    Integer,
    MetaData,
    String,
    Table,
    create_engine,
    insert,
    select,
)


# Config for the docker container
CONTAINER = "mariadb-fastapi"
MYSQL_PORT = "33072"
MYSQL_DATABASE = "test"
MYSQL_ROOT_PASSWORD = "rootmysql"
DB_URL = f"mysql://root:{MYSQL_ROOT_PASSWORD}@127.0.0.1:{MYSQL_PORT}/{MYSQL_DATABASE}"

# SQLAlchemy
ENGINE = create_engine(DB_URL)
METADATA = MetaData()
T = Table(
    "job",
    METADATA,
    Column("id", Integer(), primary_key=True),
    Column("name", String(length=50)),
)


# FastAPI model and app
class Job(BaseModel):
    name: str


app = FastAPI()


@app.get("/jobs/{job_id}")
def get_job(job_id: int = Path(...)):
    conn = ENGINE.connect()
    stmt = select([T]).with_for_update().where(T.c.id == job_id)
    row = conn.execute(stmt).fetchone()
    if row is None:
        # This exception that is raised in the first test causes the second test to
        # hang during its setup.
        # If we do "return None" instead, the second test will be run.
        # return None
        raise HTTPException(404, f'Job with ID "{job_id}" not found')
    return row


@app.post("/jobs")
def create_job(job: Job = Body(...)):
    with ENGINE.begin() as conn:
        ins = insert(T).values(**job.dict())
        conn.execute(ins)


#
# Tests
#


@pytest.fixture(autouse=True, scope="module")
def mariadb_docker():
    with subprocess.Popen(
        [
            "docker",
            "run",
            "--rm",
            "--env",
            f"MYSQL_DATABASE={MYSQL_DATABASE}",
            "--env",
            f"MYSQL_ROOT_PASSWORD={MYSQL_ROOT_PASSWORD}",
            f"--name={CONTAINER}",
            f"--publish={MYSQL_PORT}:3306",
            "mariadb",
        ]
    ):
        print("connecting ", end="")
        while True:
            try:
                ENGINE.connect()
                print("done")
                break
            except:
                print(".", end="")
                time.sleep(1)
        yield
        subprocess.run(["docker", "stop", CONTAINER], check=False)


@pytest.fixture
def session():
    print("SESSION drop all")
    METADATA.drop_all(ENGINE)
    print("SESSION create all")
    METADATA.create_all(ENGINE)
    print("SESSION make client")
    client = TestClient(app)
    print("SESSION setup done")
    return client


def test_function_raising_error(session):
    print("TEST starting")
    response = session.get(f"/jobs/2")
    assert response.status_code == 404, response.text
    print("TEST end")


def test_hangs_in_setup(session):
    print("TEST starting")
    response = session.post(f"/jobs", data={"name": "test"})
    assert response.status_code == 422
    print("TEST end")

Description

Starting with FastAPI 0.69, pytest tests started to hang under obscure conditions. The same code worked as expected with FastAPI 0.68.2.

I had issues with hanging tests in multiple projects. One was related to working with temp file handlers and the other one is shown in the example and related to working with SQLAlchemy/MariaDB.

In the example, the first test calls an endpoint that does an SQLAlchemy query and raises an HTTPException.

Any test after that will hang during setup (when METADATA.drop_all() is called).

This is what I get when I run the example:

$ pytest test_fastapi.py -vvs
=========================================================================================== test session starts ============================================================================================
platform linux -- Python 3.9.7, pytest-6.2.5, py-1.11.0, pluggy-1.0.0 -- /tmp/.venv/bin/python
cachedir: .pytest_cache
rootdir: /tmp
plugins: anyio-3.4.0
collected 2 items

test_fastapi.py::test_function_raising_error connecting done
SESSION drop all
SESSION create all
docker: Error response from daemon: Conflict. The container name "/mariadb-fastapi" is already in use by container "70717ec0e7ee7f8b721c2866a79eca73cfcd7bb3758978a9b7fe8e9b8f008786". You have to remove (or rename) that container to be able to reuse that name.
See 'docker run --help'.
SESSION make client
SESSION setup done
TEST starting
TEST end
PASSED
test_fastapi.py::test_hangs_in_setup SESSION drop all

Operating System

Linux

Operating System Details

Fedora 34

FastAPI Version

0.69.0

Python Version

3.9.7

Additional Context

Docker 20.10.11

[sscherfke]

The issue is not appearing with sqlite, but with mysql+mysqlclient, mysql+pymysql and postgres.

[Feijo]

I'm having a similar issue in version 0.73.0

[backbord]

Changing the endpoint from def get_job(...) to async def get_job(...) seems to work with FastAPI versions 0.69.0 up to 0.73.0.
Beginning with 0.74.0 a similar behavior comes up even with async def.

Edit: this issue persists in the current version 0.77.1

[backbord]

Closing the connection seems to help in all of the mentioned FastAPI versions (at least on my machine).

Edit: This does not require the endpoints to be async def functions.

before

@app.get("/jobs/{job_id}")
def get_job(job_id: int = Path(...)):
    conn = ENGINE.connect()
    stmt = select([T]).with_for_update().where(T.c.id == job_id)
    row = conn.execute(stmt).fetchone()
    if row is None:
        # This exception that is raised in the first test causes the second test to
        # hang during its setup.
        # If we do "return None" instead, the second test will be run.
        # return None
        raise HTTPException(404, f'Job with ID "{job_id}" not found')
    return row

after

@app.get("/jobs/{job_id}")
def get_job(job_id: int = Path(...)):
    with ENGINE.connect() as conn:
        stmt = select([T]).with_for_update().where(T.c.id == job_id)
        row = conn.execute(stmt).fetchone()
        if row is None:
            # This exception that is raised in the first test causes the second test to
            # hang during its setup.
            # If we do "return None" instead, the second test will be run.
            # return None
            raise HTTPException(404, f'Job with ID "{job_id}" not found')
        return row

[sscherfke]

Yup, that solves it for me. Thx. :)