flask-idempotent2

Redis based automatic idempotent and concurrency lock support for sqlalchemy based flask applications.

Idempotent

It caches responses in redis by request_id, requests in a short time with the same request_id would get the same response. But a cached response will be expired if any its affected db resources are last changed by other requests.

from flask_idempotent2 import Idempotent

idempotent = Idempotent(app, redis_client, DBSession) # DBSession: SQLAlchemy Session

@app.route('/api', methods=['PUT'])
@idempotent.cache(15)  # Cache result for 15s
def api():
    pass

Requests Lock

@app.route('/api', methods=['PUT'])
@idempotent.lock(3)   # Lock concurrency requests for 3s
def api():
    pass

Installation

pip install flask_idempotent2

Cache Details

Here's how it works, in brief:

1. Responses are cached into redis (with expiration).
2. Return the response in redis if it exists.
3. Clear the cache if any related db changes are made.

And here's the detailed version:

1. Get request_id by preconfigured key_func.

2. Get cached response from redis by request_id.

3. Return the cached response if it exists and its related db resources are still not changed.

4. Otherwise call view_function and cache its response into redis with request_id as key and preconfigured timeout as an expiration. Then return this response.

5. All db changes during the view_function call will be recorded in redis, in format of resource-instance to request-id.A cached response is valid only if its affected resource instances are all last affected by the same request-id. If any other requests affects these db resources, the request-id will be reset, thus the cached response expires.

   Key	Value
   app-name:api-name:request-id	serialized-response, affected-resource-instances
   affected-resource:id e.g. "User:1"	request-id
   affected-resource:id...	...

How requests are distinguished?

Requests are distinguished by preconfigured keyfunc, which is a function with no arguments and should return the request_id.

from flask_idempotent2 import Idempotent, gen_keyfunc

keyfunc = gen_keyfunc(path=True, methods=True, query_string=True, data=True)
idempotent = Idempotent(app, redis_client, DBSession, keyfunc)

Unittests problem with flask.g

flask.g can't be accessed outside flask request context, so I suggest you to use a threading local object instead:

import threading
# If your service is gevent based (one request one gevent thread).
# 1. Use gevent threading local instead.
# 2. Or just make sure builtin threading is patched by gevent.
g_ = threading.local()
idempotent = Idempotent(app, redis_client, DBSession, g_=threading.local())

License

BSD.