Add settings 'write-back' capability (Singer SDK)

[MeltyBot]

Migrated from GitLab: https://gitlab.com/meltano/sdk/-/issues/106

Originally created by @aaronsteers on 2021-04-15 21:08:05

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Related to similar issue for Meltano: https://gitlab.com/meltano/meltano/-/issues/2710

Some tap and target implementations use a writeback method (we think?) to store settings (such as auth tokens) back in the config.json file for future use.

There's currently no similar way for a tap developer using the SDK to write back settings for use in future invocations.

Wanted:

For this issue, we are currently gaging feedback and asking for developers to provide use cases if this is a blocker for them. If this affects you, please post to the comments.

Related

• https://github.com/meltano/meltano/issues/2660

[MeltyBot]

View 2 previous comments from the original issue on GitLab

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[pnadolny13]

@edgarrmondragon I implemented a version of this with the SDK in tap-gohighlevel.

• I had to override the tap init to capture the config file path and save it to the tap instance. I also chose to raise an exception if the configs are passed in outside of a config file.
• Then when my authenticator is being instantiated by pull the config path variable out and pass it in. The way I access that var is definitely not nice but it works.
• I overrode update_access_token to catch the new refresh token
• Then call a method _write_back_to_config that overwrites the file.

I honestly didnt spend a lot of time thinking through the cleanest way to pass this stuff around so let me know if theres a better approach.

[edgarrmondragon]

Thanks for sharing the implementation @pnadolny13!

• I had to override the tap init to capture the config file path and save it to the tap instance. I also chose to raise an exception if the configs are passed in outside of a config file.

Yeah, I hadn't thought about it but more multiple --config values or --config=ENV don't really work with write-back, and write-back is a hard requirement for tap so it makes sense to straight-out fail.

That's a not a problem for Meltano because it always uses a (single) config file under the hood, and I'm willing to bet close to no one uses multiple --config flags.

That implementation does not seem to handle cases where --config=ENV is used to pass the refresh token, though.

• Then when my authenticator is being instantiated by pull the config path variable out and pass it in. The way I access that var is definitely not nice but it works.

Cool! Though I don't particularly love create_for_stream cause in general it does not provide any benefits over a regular __init__ but it couples the stream and authenticator classes in a circular manner 😅.

• I overrode update_access_token to catch the new refresh token
• Then call a method _write_back_to_config that overwrites the file.

This combination makes me want to add a hook somewhere in the SDK that lets developers send a signal that the input config file should be updated.

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I think the implementation makes sense, since it works well with Meltano's standard config location (as opposed to writing back to an arbitrary file) and it gives a reference implementation to adapt upstream here.

Unfortunately https://github.com/meltano/meltano/issues/2660 is certainly harder to reason about and implement, but we can get something out for the SDK with this as a start.