Add retry attempts to Hackney

[novabyte]

I can't find support for retry attempts in Hackney. If it's not supported I'd like to propose it as a feature enhancement.

[benoitc]

Retrying should be an application logic (since it depends when you want to do it) which is why it is not supported right now in hackney but an explicit mechanism can be added.

I think a retry mechanisms should handled the following cases:

• retry on connection error?
• retry on POST/PUT error (obviously not when streaming) or only on GET (retry function rule?)

Also if the retry is requested the request should check if it's possible before starting anything (eg. when requested for a stream request).

Did I missed anything?

[novabyte]

Hi @benoitc I was thinking of a simple retry strategy like what's in Fusco: https://github.com/esl/fusco/blob/master/src/fusco.erl#L176

[benoitc]

i wll add these feature in the next release.

[novabyte]

@benoitc Thank you sir :smiley:

[novabyte]

Hi @benoitc have you had time to consider this further? Is it still on the roadmap? Let me know if I can help in some way.

[benoitc]

@novabyte yes it's definitely on the roadmap. I expect to release the 2.0.0 on 06/19 with it.

[edgurgel]

I think had an issue related to this. Making requests with a difference of 5 seconds I would get {error, closed}, but if I waited 6-7 seconds a new connection would be used and less than 5 seconds the same connection is reused. It would be useful to reconnect/retry in this case.

[benoitc]

I am lagging behind my schedule....

@edgurgel mmm not sure to follow. Do you mean that if you're connecting < 5 sec you actually get an {error, closed} error? What is the keepalive of the server?

Anyway the coming new connection pool should address this issue. I expect now to make a release before the end of the month with it now.

[edgurgel]

@benoitc , yeah I forgot to add that the server will keep-alive for exactly 5 seconds. I get a {error, closed} when the time between two requests is too close to 5. If it's 4 or 6 it's fine to reestablish the connection or reuse the previous.

[flupke]

I implemented retries in my download code, it's fairly complete (backoff factor + number of retries, or user-defined function), feel free to use it if you want: https://github.com/flupke/hackney_message_bug/blob/master/lib/hackney_message_bug.ex

[edevil]

@benoitc Did this feature ever get implemented? It seems it wasn't since the issue is open, but @edgurgel is referring to a bug introduced by it?

In another note, are there plans to include a feature like this?

[benoitc]

it's not implemented yet :) but any patch doing that is welcome :)