value decoding (and encoding) needs additional access

[isoos]

My hesitance to go ahead with #342 and also with #343 has the same root: in their current form, they seem to be adding non-trivial complexity that could become barriers for the future improvements, while in the ideal world such features should be added with much less friction and much less interconnectedness.

After a some thinking and high-level fiddling, I think I have found a way forward though: we will need to refactor the value encoding/decoding to have access to:

• connection settings (like client-provided timezone)
• runtime parameter values (like server-provided timezone)
• the TypeRegistry itself (there should be no need to use any other reference than the one provided in the connection settings)
• the connection or ways to open a new connection + an OID cache that can use it to query yet-unknown identifiers (this becomes tricky in certain clusters so it shouldn't be 100% automatic caching)
• user-provided transformation functions for specific types - e.g. to pull in larger timezone databases like pg_timezone, which may not be needed for all users

I'm not entirely sure how such code would look like, but I think the above feature would now only allow the two pending features to go ahead, but also allow better overall extensibility.

/cc @insinfo @wolframm

[isoos]

I think the OID cache part has a clean separation from the rest. The other big change would be the decoding becoming async/FutureOr because of the potential need for OID type description query. It seems to be not breaking though.

[isoos]

I think this is now implemented, alongside with custom codec registration.

/cc @insinfo @wolframm: I've released a 3.4.0-dev.1 prerelease version with it, I think the API is good enough now, and you can go ahead with the PRs. Please let me know if there is something missing or in conflict with the goals.

[isoos]

Note: I've released 3.4.0-dev.2 with now with likely future-proofed async-enabled codec API (+ related message processing). Please, if possible, test and give me feedback before committing to a final version on it.

[insinfo]

Hi, I had an accident and will be away from programming for a while. It would be great if you could implement timezone support based on my implementation with the modifications you introduced. Congratulations on your work.

[isoos]

@insinfo: I'm planning to help you out with the implementation, however I won't have the bandwidth for that in the next week or so. Because of that I've published 3.4.0 as-is, and we shall figure out the details for your use-case later, I'm rather optimistic that everything need is in it.