Remove sync postgres_backend, tidy up its split usage.

- Add support for splitting async postgres_backend into read and write halfes.
  Safekeeper needs this for bidirectional streams. To this end, encapsulate
  reading-writing postgres messages to framed.rs with split support without any
  additional changes (relying on BufRead for reading and BytesMut out buffer for
  writing).
- Use async postgres_backend throughout safekeeper (and in proxy auth link
  part).
- In both safekeeper COPY streams, do read-write from the same thread/task with
  select! for easier error handling.
- Tidy up finishing CopyBoth streams in safekeeper sending and receiving WAL
  -- join split parts back catching errors from them before returning.

Initially I hoped to do that read-write without split at all, through polling
IO:
https://github.com/neondatabase/neon/pull/3522
However that turned out to be more complicated than I initially expected
due to 1) borrow checking and 2) anon Future types. 1) required Rc<Refcell<...>>
which is Send construct just to satisfy the checker; 2) can be workaround with
transmute. But this is so messy that I decided to leave split.

control_plane/Cargo.toml

@@ -24,6 +24,7 @@ url.workspace = true
 # Note: Do not directly depend on pageserver or safekeeper; use pageserver_api or safekeeper_api
 # instead, so that recompile times are better.
 pageserver_api.workspace = true
+postgres_backend.workspace = true
 safekeeper_api.workspace = true
 postgres_connection.workspace = true
 storage_broker.workspace = true

control_plane/src/bin/neon_local.rs

@@ -17,6 +17,7 @@ use pageserver_api::{
     DEFAULT_HTTP_LISTEN_ADDR as DEFAULT_PAGESERVER_HTTP_ADDR,
     DEFAULT_PG_LISTEN_ADDR as DEFAULT_PAGESERVER_PG_ADDR,
 };
+use postgres_backend::AuthType;
 use safekeeper_api::{
     DEFAULT_HTTP_LISTEN_PORT as DEFAULT_SAFEKEEPER_HTTP_PORT,
     DEFAULT_PG_LISTEN_PORT as DEFAULT_SAFEKEEPER_PG_PORT,
@@ -30,7 +31,6 @@ use utils::{
     auth::{Claims, Scope},
     id::{NodeId, TenantId, TenantTimelineId, TimelineId},
     lsn::Lsn,
-    postgres_backend::AuthType,
     project_git_version,
 };
 

control_plane/src/compute.rs

@@ -11,10 +11,10 @@ use std::sync::Arc;
 use std::time::Duration;
 
 use anyhow::{Context, Result};
+use postgres_backend::AuthType;
 use utils::{
     id::{TenantId, TimelineId},
     lsn::Lsn,
-    postgres_backend::AuthType,
 };
 
 use crate::local_env::{LocalEnv, DEFAULT_PG_VERSION};

control_plane/src/local_env.rs

@@ -5,6 +5,7 @@
 
 use anyhow::{bail, ensure, Context};
 
+use postgres_backend::AuthType;
 use reqwest::Url;
 use serde::{Deserialize, Serialize};
 use serde_with::{serde_as, DisplayFromStr};
@@ -19,7 +20,6 @@ use std::process::{Command, Stdio};
 use utils::{
     auth::{encode_from_key_file, Claims, Scope},
     id::{NodeId, TenantId, TenantTimelineId, TimelineId},
-    postgres_backend::AuthType,
 };
 
 use crate::safekeeper::SafekeeperNode;

control_plane/src/pageserver.rs

@@ -11,6 +11,7 @@ use anyhow::{bail, Context};
 use pageserver_api::models::{
     TenantConfigRequest, TenantCreateRequest, TenantInfo, TimelineCreateRequest, TimelineInfo,
 };
+use postgres_backend::AuthType;
 use postgres_connection::{parse_host_port, PgConnectionConfig};
 use reqwest::blocking::{Client, RequestBuilder, Response};
 use reqwest::{IntoUrl, Method};
@@ -20,7 +21,6 @@ use utils::{
     http::error::HttpErrorBody,
     id::{TenantId, TimelineId},
     lsn::Lsn,
-    postgres_backend::AuthType,
 };
 
 use crate::{background_process, local_env::LocalEnv};