A couple issues creating a Postgresql wrapper connection for Amazon Aurora DSQL

[txase]

Setup

Versions

• Rust: 1.83.0
• Diesel: 2.2.6
• Database: Amazon Aurora DSQL Preview
• Operating System: MacOS

Feature Flags

• diesel: postgres, i-implement-a-third-party-backend-and-opt-into-breaking-changes

Problem Description

I hit a couple annoying API issues with the diesel Connection traits while creating a wrapper for DSQL around the built-in Postgresql connection type. I'm raising these concerns together as a single issue, but I'm happy to fork them to separate issues if the maintainers find them to be valid and want to deal with them separately. None of these are show-stoppers, they just made it "annoying" to implement.

I may also be implementing this at the wrong layer of the stack. If so, please provide guidance and I'll happily close this issue!

What are you trying to accomplish?

I wanted to play with DSQL for a side project that already uses Postgresql. FWIW, after removing foreign key constraints, Diesel seemed to "just work" once I got my connection driver working. I added this code directly to my side project, but I assume a production-ready version should exist as a separate crate.

What issues were found?

• Connection::establish is synchronous, but we need to do some async stuff for DSQL to generate temporary auth tokens. I made it work by spawning and blocking on threads as needed, but it feels like this method should be async.
• ConnectionError doesn't implement the Clone Trait, which makes error handling onerous.
• It feels like a wrapper connection, like this is, shouldn't need to forward so many traits and opt into the i-implement-a-third-party-backend-and-opt-into-breaking-changes feature flag. All this does is transform one connection string into a postgresql connection string. The breaking-changes feature flag concerns me most.

Steps to reproduce

You can find my code at this gist. See line 96 for annoyance in handling ConnectionError without Clone. Search for thread to find the two places we need to perform asynchronous processing to generate a postgres connection string.

Checklist

• I have already looked over the issue tracker and the discussion forum for similar possible closed issues.