Remove sync postgres_backend_async, tidy up its split usage.

- Use postgres_backend_async throughout safekeeper.
- Use framed.rs in postgres_backend_async, similar to tokio_util::codec::Framed
  but with slightly more efficient split. Now IO functions are also cancellation
  safe. Also, there is no allocation in each message read anymore, and data in
  read messages still directly point to input buffer without copies.
- 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.

proxy stream.rs is adapted with minimal changes. It also benefits from framed.rs
improvements described above.

libs/postgres_backend/tests/cert.pem

@@ -0,0 +1,21 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

libs/postgres_backend/tests/key.pem

@@ -0,0 +1,27 @@
+-----BEGIN RSA PRIVATE KEY-----
+MIIEpAIBAAKCAQEA4j1L6eHwAEynmOlvtZZ8Biu0YngLuCL0g9NUhHFJKu3kqCUT
+Kys6IqWFqfVS3Z7wIK53O11e0K9Pz+CglaWbGkUhCQSuUKw50Yd4QnQRnGhTV8yQ
+EBBV/pFvUkT2Vp0bb4PV7vK/GYyp89W5TyWP6Q2cRI/4jcRI0K26qC19wSvG7dO6
+FLNXayVKLmWthALARGAJ6+XotQ13aYRph1LiaYnhFmpzYLjLsk7nBIOOBrwYgEcl
+WjvQdFWy9ft4Tyvq0w/YfIbKicGK0EoBzZARAi9wsK4w5O1MGVhwy9OYkQ4cUrAg
+lebReZB8BZ4oV/Irvj3d8Hga77wNzXEL4gdpMQIDAQABAoIBAQClKycO+zpinZQG
+GPbLVa/6OVIaSZYUusBUtaaQgrxuMPusnlSeQZLR1JH/APGchvq8gWLe3k3ogPT9
+yPq0BhF0Xl+928L/dp1HkWWE7oQk8i1Wfiv27lY54iepoltN5KkxAsjfCC3oEz/I
+mpINbFjiRmN90rYdmd2nLA6H1Z5ntZQm5AcTo3OJZlTVN9eH9TV8f0AQRQgUJsL9
+75agSmj7euqZOqvvwfpsYzaZEhzMSG2QIcS3WglInbHy8c6ikZSm36J36wgsatMz
+CBZ6pMNtonRSKvAECQhBGEA73evtnGbLH0EY9KouN4KSHEHob89dGVeeXozksf9x
+QUE1/yOhAoGBAP818f7vIH6Z3QwWgTMwQsPBW+wNOIbTZrbZaihnz2K9XMu39TV6
+DWQHMsOlvg2QURZGwqB3jFn4wqZHmt7XYwk553E60kIw4hDvgpkkqmXVwK3kZASQ
+RRUax3hZ1gCWxpXlRZ1SvHNXjN9KEFwqQbR33XcxzC3TpSp0KYghT9jFAoGBAOLw
+agejqSF+f/5W1QhEKlM+tSlluo2sn5kKVkM4nNezFukb3pu5oScFjoQQGsoaz5aU
+kLlxW5h/aSxquhgcuo6I4Ux5dcgNm4QeonCCp+Qycn7tzyoJFL4odT9vYPQa5O9E
+hD9aSqhBBD1IIOS2T3vcW6VxibKZx1CRMDdRz119AoGALflr1L8DHYteNLVBJRWG
+kXkdtBJVooQmtr3Hz+uTgngWZWSIOc/45ZIeZPxQlmTvFpI8sWeX0wVrG0U+8vHe
+F2Vk+hLcmavwrZhX8HqYb6vn/+tq0R+kMj8Wu+mDEawXrh0VQ1gKNsUIzZisBc5e
+88G8FaLU41SDJniymqFVnvkCgYEA1ou/UfWRwg6b5tIkmKoI8aZJExgPpDzcrYyu
+POLatLmlIUCt1b9K8V85evTWvtdWBd/yar8WfzeFMO69fGo8nOAfT3NMvJLQwblM
+jN2Y6A4hXIpq3iyzpYsOPaiImn6KjQHTnSk5h5Pf9CeqoU8SGeEb629JZMYpPqvk
+T4hSaOkCgYBPaf51oSAstqdj0vxrsFS3EN3D8Fk0xQWt9Ss3ZGFAlTaEq5xoIk4k
+YfKVDv1S6/vlzbheIIzQ2lzVvG4AW+drQLsmEx5iMKvbNtFAur9kwUFU202Q2dki
+ZQJ/JvjnPYFKxy+SVlLJ1h9RD9E3dgL/Ai7OUfbmX771vN0IQF7Z6Q==
+-----END RSA PRIVATE KEY-----

libs/postgres_backend/tests/simple_select.rs

@@ -0,0 +1,139 @@
+/// Test postgres_backend_async with tokio_postgres
+use once_cell::sync::Lazy;
+use postgres_backend::{AuthType, Handler, PostgresBackend, QueryError};
+use pq_proto::{BeMessage, RowDescriptor};
+use std::io::Cursor;
+use std::{future, sync::Arc};
+use tokio::net::{TcpListener, TcpStream};
+use tokio_postgres::config::SslMode;
+use tokio_postgres::tls::MakeTlsConnect;
+use tokio_postgres::{Config, NoTls, SimpleQueryMessage};
+use tokio_postgres_rustls::MakeRustlsConnect;
+
+// generate client, server test streams
+async fn make_tcp_pair() -> (TcpStream, TcpStream) {
+    let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
+    let addr = listener.local_addr().unwrap();
+    let client_stream = TcpStream::connect(addr).await.unwrap();
+    let (server_stream, _) = listener.accept().await.unwrap();
+    (client_stream, server_stream)
+}
+
+struct TestHandler {}
+
+#[async_trait::async_trait]
+impl Handler for TestHandler {
+    // return single col 'hey' for any query
+    async fn process_query(
+        &mut self,
+        pgb: &mut PostgresBackend,
+        _query_string: &str,
+    ) -> Result<(), QueryError> {
+        pgb.write_message_noflush(&BeMessage::RowDescription(&[RowDescriptor::text_col(
+            b"hey",
+        )]))?
+        .write_message_noflush(&BeMessage::DataRow(&[Some("hey".as_bytes())]))?
+        .write_message_noflush(&BeMessage::CommandComplete(b"SELECT 1"))?;
+        Ok(())
+    }
+}
+
+// test that basic select works
+#[tokio::test]
+async fn simple_select() {
+    let (client_sock, server_sock) = make_tcp_pair().await;
+
+    // create and run pgbackend
+    let pgbackend =
+        PostgresBackend::new(server_sock, AuthType::Trust, None).expect("pgbackend creation");
+
+    tokio::spawn(async move {
+        let mut handler = TestHandler {};
+        pgbackend.run(&mut handler, future::pending::<()>).await
+    });
+
+    let conf = Config::new();
+    let (client, connection) = conf.connect_raw(client_sock, NoTls).await.expect("connect");
+    // The connection object performs the actual communication with the database,
+    // so spawn it off to run on its own.
+    tokio::spawn(async move {
+        if let Err(e) = connection.await {
+            eprintln!("connection error: {}", e);
+        }
+    });
+
+    let first_val = &(client.simple_query("SELECT 42;").await.expect("select"))[0];
+    if let SimpleQueryMessage::Row(row) = first_val {
+        let first_col = row.get(0).expect("first column");
+        assert_eq!(first_col, "hey");
+    } else {
+        panic!("expected SimpleQueryMessage::Row");
+    }
+}
+
+static KEY: Lazy<rustls::PrivateKey> = Lazy::new(|| {
+    let mut cursor = Cursor::new(include_bytes!("key.pem"));
+    rustls::PrivateKey(rustls_pemfile::rsa_private_keys(&mut cursor).unwrap()[0].clone())
+});
+
+static CERT: Lazy<rustls::Certificate> = Lazy::new(|| {
+    let mut cursor = Cursor::new(include_bytes!("cert.pem"));
+    rustls::Certificate(rustls_pemfile::certs(&mut cursor).unwrap()[0].clone())
+});
+
+// test that basic select with ssl works
+#[tokio::test]
+async fn simple_select_ssl() {
+    let (client_sock, server_sock) = make_tcp_pair().await;
+
+    let server_cfg = rustls::ServerConfig::builder()
+        .with_safe_defaults()
+        .with_no_client_auth()
+        .with_single_cert(vec![CERT.clone()], KEY.clone())
+        .unwrap();
+    let tls_config = Some(Arc::new(server_cfg));
+    let pgbackend =
+        PostgresBackend::new(server_sock, AuthType::Trust, tls_config).expect("pgbackend creation");
+
+    tokio::spawn(async move {
+        let mut handler = TestHandler {};
+        pgbackend.run(&mut handler, future::pending::<()>).await
+    });
+
+    let client_cfg = rustls::ClientConfig::builder()
+        .with_safe_defaults()
+        .with_root_certificates({
+            let mut store = rustls::RootCertStore::empty();
+            store.add(&CERT).unwrap();
+            store
+        })
+        .with_no_client_auth();
+    let mut make_tls_connect = tokio_postgres_rustls::MakeRustlsConnect::new(client_cfg);
+    let tls_connect = <MakeRustlsConnect as MakeTlsConnect<TcpStream>>::make_tls_connect(
+        &mut make_tls_connect,
+        "localhost",
+    )
+    .expect("make_tls_connect");
+
+    let mut conf = Config::new();
+    conf.ssl_mode(SslMode::Require);
+    let (client, connection) = conf
+        .connect_raw(client_sock, tls_connect)
+        .await
+        .expect("connect");
+    // The connection object performs the actual communication with the database,
+    // so spawn it off to run on its own.
+    tokio::spawn(async move {
+        if let Err(e) = connection.await {
+            eprintln!("connection error: {}", e);
+        }
+    });
+
+    let first_val = &(client.simple_query("SELECT 42;").await.expect("select"))[0];
+    if let SimpleQueryMessage::Row(row) = first_val {
+        let first_col = row.get(0).expect("first column");
+        assert_eq!(first_col, "hey");
+    } else {
+        panic!("expected SimpleQueryMessage::Row");
+    }
+}