Minimal connection example fails due to error 'protocol not available (os error 92)'

[Ducolnd]

Setup

Versions

• Rust: 1.84.1
• Diesel: 2.1.0
• Diesel_async: 0.5.0
• Database: Postgres
• Operating System Windows 11, development on WSL 2

Feature Flags

• diesel: None
• diesel_async: postgres

Problem Description

When trying to connect to a database (tried localhost and managed azure flexible postgres database), an error occurs saying "error connecting to server: Protocol not available (os error 92)".

What are you trying to accomplish?

During porting of my sync diesel project to async diesel I came across this error. I'd like to use async-diesel for my database queries. Before porting to async diesel I had not problem connecting to databases.

What is the expected output?

A succesful connection

What is the actual output?

Error: CouldntSetupConfiguration(DatabaseError(UnableToSendCommand, "error connecting to server: Protocol not available (os error 92)"))

Are you seeing any additional errors?

No

Steps to reproduce

.env file:

DATABASE_USER=[user]
DATABASE_PASSWORD=[password]
DATABASE_NAME=[database_name]
DATABASE_HOST=[host]

DATABASE_URL=postgres://${DATABASE_USER}:${DATABASE_PASSWORD}@${DATABASE_HOST}/${DATABASE_NAME}

use diesel_async::AsyncConnection;
use diesel_async::AsyncPgConnection;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    dotenvy::dotenv().ok();

    let db_url = std::env::var("DATABASE_URL").expect("Env var `DATABASE_URL` not set");
    let conn = AsyncPgConnection::establish(&db_url).await?; // Fails here
    let _ = conn;

    Ok(())
}

[weiznich]

I converted this to a support question as we have several tests (also on CI) that confirm that this example works on windows. So this seems to be more an issue with your specific environment than a bug with diesel-async. As I do not have access to that environment there is not much I can help you here other than giving you some general pointers:

• Fails to Connect in WSL 1 Due to TCP User Timeout (os error 92) sfackler/rust-postgres#1214 might be relevant (same error message)
• Double check if your database expects you to provide a SSL enabled connection, because that's not provided by default by diesel-async. You then need to perform additional configuration. Checkout the examples in this repository for details.

[Ducolnd]

Thanks! I suspect indeed it has to do something with WSL. I will try to find a working case outside of WSL and return here.