Panic when network connection is lost

[basbossink-ds]

While network maintenance was being performed the following error popped-up:

 thread 'main' panicked at 
'called `Option::unwrap()` on a `None` value': 
...../sqlx-core-0.5.13/src/postgres/listener.rs:165

Unfortunately I was unable to reproduce this issue in a lab environment. Looking at the code however, I would imagine the culprit is:

sqlx/sqlx-core/src/postgres/listener.rs

Line 260 in bd40cc9

self.connection = None;

[abonander]

It's likely due to any one of these methods being called immediately after a disconnect: https://github.com/launchbadge/sqlx/blob/main/sqlx-core/src/postgres/listener.rs#L95-L145

An easy fix would look like this:

• for .listen() and .listen_all(), be sure to call .reconnect_if_needed().await? first
• for .unlisten() and .unlisten_all(), use if let Some(connection) = &mut self.connection instead of self.connection()
  • They should still delete from self.channels though

[abonander]

Oh, and this should probably be fixed in the Executor methods too: https://github.com/launchbadge/sqlx/blob/main/sqlx-core/src/postgres/listener.rs#L328-L374

.fetch_many() could probably do something like

use futures_util::TryFutureExt;

Box::pin(async move {
    self.reconnect_if_needed().await?;

    Ok(self.connection().fetch_many(query))
}.try_flatten_stream())