queueflow

Python client for QueueFlow, a PostgreSQL-native distributed job queue and workflow engine.

• Typed end-to-end: request/response models (pydantic v2) mirror the server's OpenAPI 3.1 spec.
• Ergonomic: qf.create_job(...), wait_for_* pollers, and a workflow builder DSL.
• Worker runtime: qf.run_worker(...) runs Python task handlers against a remote server.
• Thin facade over a generated core: the facade (queueflow.facade) adds what codegen cannot; the generated queueflow.api.* clients and queueflow.models.* stay available for everything else.

Python 3.9 or newer.

Install

pip install queueflow

Quick start

from queueflow.facade import QueueFlow, wf

qf = QueueFlow("http://localhost:8000", "dev")

# Enqueue a job and wait for the result.
job = qf.create_job("echo", payload={"hello": "world"}, max_retries=3, timeout=30)
done = qf.wait_for_job(job.id)
print(done.status, done.result)   # completed {'hello': 'world', 'echoed': True}

# Declare and run a DAG workflow.
dag = (
    wf("etl")
    .step("extract", "echo")
    .step("transform", "echo", after=["extract"])
    .step("load", "echo", after=["transform"], on_failure="halt")
)
workflow = qf.create_workflow(dag)
finished = qf.wait_for_workflow(workflow.id)
print(finished.status, finished.context)

echo is a handler built into the server; it returns the payload plus "echoed": true.

API

Client

qf = QueueFlow(
    base_url,             # required, e.g. "http://localhost:8000"
    token,                # required: tenant bearer token (any non-empty token on the dev server)
    worker_token=None,    # credential for qf.worker and run_worker (defaults to token; dev mode only)
    timeout=30.0,         # default per-request timeout in seconds; a (connect, read) pair or None also work
)

Any generated api method accepts _request_timeout= to override the default for one call.

The generated per-tag clients hang off the facade for anything the helpers do not cover: qf.jobs, qf.workflows, qf.worker, qf.cron, qf.dlq, qf.system, qf.health_api.

Jobs

idempotency_key is sent as the Idempotency-Key header: re-submitting the same key returns the original job instead of creating a duplicate. run_at (a datetime) delays the first run.

List responses carry next_cursor when there are more pages; pass it back as cursor for keyset pagination (cheaper than deep offset).

Workflows

Workflow builder

from queueflow.facade import wf

dag = (
    wf("order_123")
    .step("validate", "validate_order")
    .step("pay", "process_payment", after=["validate"])
    .step("ship", "create_shipment", after=["pay"], on_failure="continue")
    .context(source="web")
)
# .build() runs locally first: duplicate names, dangling deps, and cycles raise
# WorkflowValidationError before any network round-trip.

step() also accepts payload=, on_success=, and config= (a models.JobConfig override).

Worker

Run task handlers in this process against a remote QueueFlow server:

import threading
from queueflow.facade import QueueFlow, NonRetryableError

qf = QueueFlow("http://localhost:8000", "tenant-key", worker_token="worker-secret")

def send_email(job):
    if not job.payload.get("to"):
        raise NonRetryableError("no recipient")   # straight to the dead-letter queue
    ...                                           # raising anything else retries per policy
    return {"sent": True}

def transcode(job, ctx):
    for chunk in chunks(job.payload):
        if ctx.cancelled:                         # lease lost / cancelled mid-run: stop,
            return {}                             # the server owns the outcome now
        process(chunk)
    return {"ok": True}

stop = threading.Event()                          # set it (e.g. from a signal handler) to drain
result = qf.run_worker(
    "orders",
    {"send_email": send_email, "transcode": transcode},
    stop=stop,
    concurrency=4,
)
for job in result.unfinished:                     # handlers still running when the drain gave up
    print("abandoned", job.id)

run_worker(
    queue, handlers,
    lease_secs=30,        # lease per job; each in-flight job is heartbeated at half this
    wait_secs=20,         # long-poll wait when the queue is empty
    stop=None,            # threading.Event: set it to stop
    on_error=None,        # called on transient lease errors (default: throttled log)
    concurrency=1,        # handlers running at once, on a ThreadPoolExecutor
    poll_wait_secs=5,     # cap on wait_secs while `stop` is provided (bounds stop latency)
    drain_timeout=30.0,   # seconds to wait for in-flight handlers after stop
) -> WorkerRunResult      # .unfinished: jobs still running when the drain gave up

run_worker heartbeats each in-flight job at half the lease interval, stops reporting when the lease is lost, and applies the server's retry policy on errors. Handlers take (job) or (job, ctx) and return the result dict (or None for {}). Delivery is at-least-once, so make handlers idempotent. The low-level calls (qf.worker.lease_jobs, heartbeat_job, complete_job, fail_job) are also exposed.

Concurrency: up to concurrency handlers run at once. Each lease asks for as many jobs as there are free slots, and no lease is issued while every slot is busy.

Stop and drain: set stop. The generated urllib3 client cannot cancel an in-flight long poll, so while stop is provided each lease waits at most poll_wait_secs (never more than wait_secs), which bounds stop latency to about that long; without stop, the full wait_secs is used. After the loop exits, handlers already running get up to drain_timeout seconds to finish and report. Any handler still running after that is abandoned: its ctx.cancelled flips, nothing is reported (the lease expires and the server redelivers), and the job is listed in the returned WorkerRunResult.unfinished. Python cannot kill a thread, so an abandoned handler keeps its pool thread until it returns; long handlers should check ctx.cancelled.

Timeouts: every request uses the client-wide timeout (30s by default, see Client), except the lease long poll, which gets its own timeout of the effective wait plus 35 seconds.

Rules the runtime enforces, and that any hand-rolled loop over qf.worker must honour too:

1. Worker routes authenticate with the worker token, not a tenant token. Pass it as worker_token=; without it qf.worker reuses the tenant token, which only works in the server's development mode. run_worker raises on 401/403 rather than spinning.
2. Every in-flight job is heartbeated at half its lease interval. A heartbeat showing the job no longer running (or an HTTP 409) abandons reporting and flips ctx.cancelled.
3. Raise NonRetryableError (or any exception with retryable = False) for permanent failures so they dead-letter immediately. A failed outcome report is never converted into a job failure; the lease expires and the engine redelivers.

Cron

Dead letters

System

qf.system.get_stats()    # engine counters
qf.system.list_tasks()   # registered task handler names
qf.queues()              # live per-queue backlog: pending, scheduled, running, oldest pending age
qf.health_api.get_health()
qf.health_api.get_ready()

qf.queues() (GET /api/v1/queues) returns a QueueStats per queue that currently has non-terminal jobs, so you can decide whether to add workers; idle queues are omitted. qf.system.list_queues() is the raw call.

Authentication

Every request carries Authorization: Bearer <token>. Two credentials exist:

• The tenant token (token) authenticates the job, workflow, cron, DLQ and system routes. On a server started without --api-keys, any non-empty token is accepted (development mode).
• The worker token (worker_token) authenticates the worker-protocol routes (lease, heartbeat, complete, fail). Configure it on the server with --worker-token / QUEUEFLOW_WORKER_TOKEN. It is a separate secret, never a tenant token.

Error handling

Generated calls raise queueflow.exceptions.ApiException (with .status, .reason, .body) and its subclasses BadRequestException (400), UnauthorizedException (401), ForbiddenException (403), NotFoundException (404), ServiceException (5xx). The facade adds WaitTimeout (a wait_for_* deadline passed), WorkflowValidationError (a bad DAG, raised before any request), and NonRetryableError (raise from a handler to dead-letter immediately).

from queueflow.exceptions import ApiException, NotFoundException
from queueflow.facade import WaitTimeout

try:
    job = qf.wait_for_job("missing", timeout=10)
except NotFoundException:
    ...
except WaitTimeout:
    ...
except ApiException as err:
    print(err.status, err.body)

Known limitation: stream_job_events

JobsApi.stream_job_events cannot stream: it buffers the whole SSE response until the server closes it (terminal status or the 15-minute cap). Use wait_for_job (polling) instead, or the stream_job_events_without_preload_content variant with a hand-rolled SSE parser.

Conformance tests

test/test_live.py runs the facade against a real QueueFlow server (started with the default queueflow serve, i.e. --mode all, so the built-in echo handler is registered). It creates and waits on an echo job, checks idempotent re-creation, runs a two-step workflow, exercises the cron and dead-letter endpoints, reads stats, and runs run_worker against a dedicated queue. The tests are marked live and skip themselves unless QUEUEFLOW_URL is set, so plain pytest and CI stay offline.

QUEUEFLOW_URL=http://localhost:8000 \
QUEUEFLOW_TOKEN=dev \
QUEUEFLOW_WORKER_TOKEN=worker-secret \
pytest -m live

QUEUEFLOW_TOKEN is the tenant token (default dev). QUEUEFLOW_WORKER_TOKEN is the server's --worker-token; it defaults to the tenant token, which only works when the server runs without one.

Architecture

This package is a thin hand-written facade over a generated core:

queueflow-sdk-python/
├── queueflow/
│   ├── facade.py        the hand-written facade (QueueFlow, wf, run_worker, errors)
│   ├── api/             generated per-tag clients (JobsApi, WorkflowsApi, WorkerApi, ...)
│   ├── models/          generated pydantic models
│   └── api_client.py, configuration.py, rest.py, exceptions.py   generated transport
├── docs/                generated per-endpoint and per-model reference
└── test/                test_facade.py (offline), test_live.py (conformance), generated model tests

The core is generated by openapi-generator from the server's OpenAPI spec (scripts/generate-sdks.sh python in queueflow-core). The facade is injected at generation time from sdk-templates/python/facade.mustache in that repo, so edit the template, not queueflow/facade.py. Per-endpoint reference for the generated layer lives in docs/.

Development

pip install -e . -r test-requirements.txt
pytest                 # offline tests (facade + generated model tests)
mypy                   # type-check queueflow/ and test/

Links

• Documentation: docs.queueflow.dev
• Server: github.com/elision-labs/queueflow-core
• This SDK: github.com/elision-labs/queueflow-sdk-python

License

MIT