flatten proxy flow (#6447)

## Problem

Taking my ideas from https://github.com/neondatabase/neon/pull/6283 and
doing a bit less radical changes. smaller commits.

Proxy flow was quite deeply nested, which makes adding more interesting
error handling quite tricky.

## Summary of changes

I recommend reviewing commit by commit.

1. move handshake logic into a separate file
2. move passthrough logic into a separate file
3. no longer accept a closure in CancelMap session logic
4. Remove connect_to_db, copy logic into handle_client
5. flatten auth_and_wake_compute in authenticate
6. record info for link auth

proxy/src/proxy.rs

@@ -2,37 +2,34 @@
 mod tests;
 
 pub mod connect_compute;
+pub mod handshake;
+pub mod passthrough;
 pub mod retry;
 
 use crate::{
     auth,
     cancellation::{self, CancelMap},
     compute,
-    config::{AuthenticationConfig, ProxyConfig, TlsConfig},
-    console::messages::MetricsAuxInfo,
+    config::{ProxyConfig, TlsConfig},
     context::RequestMonitoring,
-    metrics::{
-        NUM_BYTES_PROXIED_COUNTER, NUM_BYTES_PROXIED_PER_CLIENT_COUNTER,
-        NUM_CLIENT_CONNECTION_GAUGE, NUM_CONNECTION_REQUESTS_GAUGE,
-    },
+    metrics::{NUM_CLIENT_CONNECTION_GAUGE, NUM_CONNECTION_REQUESTS_GAUGE},
     protocol2::WithClientIp,
+    proxy::{handshake::handshake, passthrough::proxy_pass},
     rate_limiter::EndpointRateLimiter,
     stream::{PqStream, Stream},
-    usage_metrics::{Ids, USAGE_METRICS},
     EndpointCacheKey,
 };
 use anyhow::{bail, Context};
 use futures::TryFutureExt;
 use itertools::Itertools;
 use once_cell::sync::OnceCell;
-use pq_proto::{BeMessage as Be, FeStartupPacket, StartupMessageParams};
+use pq_proto::{BeMessage as Be, StartupMessageParams};
 use regex::Regex;
 use smol_str::{format_smolstr, SmolStr};
 use std::sync::Arc;
 use tokio::io::{AsyncRead, AsyncWrite, AsyncWriteExt};
 use tokio_util::sync::CancellationToken;
 use tracing::{error, info, info_span, Instrument};
-use utils::measured_stream::MeasuredStream;
 
 use self::connect_compute::{connect_to_compute, TcpMechanism};
 
@@ -80,6 +77,13 @@ pub async fn task_main(
         let cancel_map = Arc::clone(&cancel_map);
         let endpoint_rate_limiter = endpoint_rate_limiter.clone();
 
+        let session_span = info_span!(
+            "handle_client",
+            ?session_id,
+            peer_addr = tracing::field::Empty,
+            ep = tracing::field::Empty,
+        );
+
         connections.spawn(
             async move {
                 info!("accepted postgres client connection");
@@ -103,22 +107,18 @@ pub async fn task_main(
                 handle_client(
                     config,
                     &mut ctx,
-                    &cancel_map,
+                    cancel_map,
                     socket,
                     ClientMode::Tcp,
                     endpoint_rate_limiter,
                 )
                 .await
             }
-            .instrument(info_span!(
-                "handle_client",
-                ?session_id,
-                peer_addr = tracing::field::Empty
-            ))
             .unwrap_or_else(move |e| {
                 // Acknowledge that the task has finished with an error.
-                error!(?session_id, "per-client task finished with an error: {e:#}");
-            }),
+                error!("per-client task finished with an error: {e:#}");
+            })
+            .instrument(session_span),
         );
     }
 
@@ -171,7 +171,7 @@ impl ClientMode {
 pub async fn handle_client<S: AsyncRead + AsyncWrite + Unpin>(
     config: &'static ProxyConfig,
     ctx: &mut RequestMonitoring,
-    cancel_map: &CancelMap,
+    cancel_map: Arc<CancelMap>,
     stream: S,
     mode: ClientMode,
     endpoint_rate_limiter: Arc<EndpointRateLimiter>,
@@ -192,138 +192,88 @@ pub async fn handle_client<S: AsyncRead + AsyncWrite + Unpin>(
     let tls = config.tls_config.as_ref();
 
     let pause = ctx.latency_timer.pause();
-    let do_handshake = handshake(stream, mode.handshake_tls(tls), cancel_map);
+    let do_handshake = handshake(stream, mode.handshake_tls(tls), &cancel_map);
     let (mut stream, params) = match do_handshake.await? {
         Some(x) => x,
         None => return Ok(()), // it's a cancellation request
     };
     drop(pause);
 
+    let hostname = mode.hostname(stream.get_ref());
+
+    let common_names = tls.map(|tls| &tls.common_names);
+
     // Extract credentials which we're going to use for auth.
-    let user_info = {
-        let hostname = mode.hostname(stream.get_ref());
+    let result = config
+        .auth_backend
+        .as_ref()
+        .map(|_| auth::ComputeUserInfoMaybeEndpoint::parse(ctx, &params, hostname, common_names))
+        .transpose();
 
-        let common_names = tls.map(|tls| &tls.common_names);
-        let result = config
-            .auth_backend
-            .as_ref()
-            .map(|_| {
-                auth::ComputeUserInfoMaybeEndpoint::parse(ctx, &params, hostname, common_names)
-            })
-            .transpose();
+    let user_info = match result {
+        Ok(user_info) => user_info,
+        Err(e) => stream.throw_error(e).await?,
+    };
 
-        match result {
-            Ok(user_info) => user_info,
-            Err(e) => stream.throw_error(e).await?,
+    // check rate limit
+    if let Some(ep) = user_info.get_endpoint() {
+        if !endpoint_rate_limiter.check(ep) {
+            return stream
+                .throw_error(auth::AuthError::too_many_connections())
+                .await;
+        }
+    }
+
+    let user = user_info.get_user().to_owned();
+    let (mut node_info, user_info) = match user_info
+        .authenticate(
+            ctx,
+            &mut stream,
+            mode.allow_cleartext(),
+            &config.authentication_config,
+        )
+        .await
+    {
+        Ok(auth_result) => auth_result,
+        Err(e) => {
+            let db = params.get("database");
+            let app = params.get("application_name");
+            let params_span = tracing::info_span!("", ?user, ?db, ?app);
+
+            return stream.throw_error(e).instrument(params_span).await;
         }
     };
 
-    ctx.set_endpoint_id(user_info.get_endpoint());
+    node_info.allow_self_signed_compute = mode.allow_self_signed_compute(config);
 
-    let client = Client::new(
-        stream,
-        user_info,
-        &params,
-        mode.allow_self_signed_compute(config),
-        endpoint_rate_limiter,
-    );
-    cancel_map
-        .with_session(|session| {
-            client.connect_to_db(ctx, session, mode, &config.authentication_config)
-        })
-        .await
-}
+    let aux = node_info.aux.clone();
+    let mut node = connect_to_compute(
+        ctx,
+        &TcpMechanism { params: &params },
+        node_info,
+        &user_info,
+    )
+    .or_else(|e| stream.throw_error(e))
+    .await?;
 
-/// Establish a (most probably, secure) connection with the client.
-/// For better testing experience, `stream` can be any object satisfying the traits.
-/// It's easier to work with owned `stream` here as we need to upgrade it to TLS;
-/// we also take an extra care of propagating only the select handshake errors to client.
-#[tracing::instrument(skip_all)]
-async fn handshake<S: AsyncRead + AsyncWrite + Unpin>(
-    stream: S,
-    mut tls: Option<&TlsConfig>,
-    cancel_map: &CancelMap,
-) -> anyhow::Result<Option<(PqStream<Stream<S>>, StartupMessageParams)>> {
-    // Client may try upgrading to each protocol only once
-    let (mut tried_ssl, mut tried_gss) = (false, false);
+    let session = cancel_map.get_session();
+    prepare_client_connection(&node, &session, &mut stream).await?;
 
-    let mut stream = PqStream::new(Stream::from_raw(stream));
-    loop {
-        let msg = stream.read_startup_packet().await?;
-        info!("received {msg:?}");
+    // Before proxy passing, forward to compute whatever data is left in the
+    // PqStream input buffer. Normally there is none, but our serverless npm
+    // driver in pipeline mode sends startup, password and first query
+    // immediately after opening the connection.
+    let (stream, read_buf) = stream.into_inner();
+    node.stream.write_all(&read_buf).await?;
 
-        use FeStartupPacket::*;
-        match msg {
-            SslRequest => match stream.get_ref() {
-                Stream::Raw { .. } if !tried_ssl => {
-                    tried_ssl = true;
-
-                    // We can't perform TLS handshake without a config
-                    let enc = tls.is_some();
-                    stream.write_message(&Be::EncryptionResponse(enc)).await?;
-                    if let Some(tls) = tls.take() {
-                        // Upgrade raw stream into a secure TLS-backed stream.
-                        // NOTE: We've consumed `tls`; this fact will be used later.
-
-                        let (raw, read_buf) = stream.into_inner();
-                        // TODO: Normally, client doesn't send any data before
-                        // server says TLS handshake is ok and read_buf is empy.
-                        // However, you could imagine pipelining of postgres
-                        // SSLRequest + TLS ClientHello in one hunk similar to
-                        // pipelining in our node js driver. We should probably
-                        // support that by chaining read_buf with the stream.
-                        if !read_buf.is_empty() {
-                            bail!("data is sent before server replied with EncryptionResponse");
-                        }
-                        let tls_stream = raw.upgrade(tls.to_server_config()).await?;
-
-                        let (_, tls_server_end_point) = tls
-                            .cert_resolver
-                            .resolve(tls_stream.get_ref().1.server_name())
-                            .context("missing certificate")?;
-
-                        stream = PqStream::new(Stream::Tls {
-                            tls: Box::new(tls_stream),
-                            tls_server_end_point,
-                        });
-                    }
-                }
-                _ => bail!(ERR_PROTO_VIOLATION),
-            },
-            GssEncRequest => match stream.get_ref() {
-                Stream::Raw { .. } if !tried_gss => {
-                    tried_gss = true;
-
-                    // Currently, we don't support GSSAPI
-                    stream.write_message(&Be::EncryptionResponse(false)).await?;
-                }
-                _ => bail!(ERR_PROTO_VIOLATION),
-            },
-            StartupMessage { params, .. } => {
-                // Check that the config has been consumed during upgrade
-                // OR we didn't provide it at all (for dev purposes).
-                if tls.is_some() {
-                    stream.throw_error_str(ERR_INSECURE_CONNECTION).await?;
-                }
-
-                info!(session_type = "normal", "successful handshake");
-                break Ok(Some((stream, params)));
-            }
-            CancelRequest(cancel_key_data) => {
-                cancel_map.cancel_session(cancel_key_data).await?;
-
-                info!(session_type = "cancellation", "successful handshake");
-                break Ok(None);
-            }
-        }
-    }
+    proxy_pass(ctx, stream, node.stream, aux).await
 }
 
 /// Finish client connection initialization: confirm auth success, send params, etc.
 #[tracing::instrument(skip_all)]
 async fn prepare_client_connection(
     node: &compute::PostgresConnection,
-    session: cancellation::Session<'_>,
+    session: &cancellation::Session,
     stream: &mut PqStream<impl AsyncRead + AsyncWrite + Unpin>,
 ) -> anyhow::Result<()> {
     // Register compute's query cancellation token and produce a new, unique one.
@@ -349,151 +299,6 @@ async fn prepare_client_connection(
     Ok(())
 }
 
-/// Forward bytes in both directions (client <-> compute).
-#[tracing::instrument(skip_all)]
-pub async fn proxy_pass(
-    ctx: &mut RequestMonitoring,
-    client: impl AsyncRead + AsyncWrite + Unpin,
-    compute: impl AsyncRead + AsyncWrite + Unpin,
-    aux: MetricsAuxInfo,
-) -> anyhow::Result<()> {
-    ctx.set_success();
-    ctx.log();
-
-    let usage = USAGE_METRICS.register(Ids {
-        endpoint_id: aux.endpoint_id.clone(),
-        branch_id: aux.branch_id.clone(),
-    });
-
-    let m_sent = NUM_BYTES_PROXIED_COUNTER.with_label_values(&["tx"]);
-    let m_sent2 = NUM_BYTES_PROXIED_PER_CLIENT_COUNTER.with_label_values(&aux.traffic_labels("tx"));
-    let mut client = MeasuredStream::new(
-        client,
-        |_| {},
-        |cnt| {
-            // Number of bytes we sent to the client (outbound).
-            m_sent.inc_by(cnt as u64);
-            m_sent2.inc_by(cnt as u64);
-            usage.record_egress(cnt as u64);
-        },
-    );
-
-    let m_recv = NUM_BYTES_PROXIED_COUNTER.with_label_values(&["rx"]);
-    let m_recv2 = NUM_BYTES_PROXIED_PER_CLIENT_COUNTER.with_label_values(&aux.traffic_labels("rx"));
-    let mut compute = MeasuredStream::new(
-        compute,
-        |_| {},
-        |cnt| {
-            // Number of bytes the client sent to the compute node (inbound).
-            m_recv.inc_by(cnt as u64);
-            m_recv2.inc_by(cnt as u64);
-        },
-    );
-
-    // Starting from here we only proxy the client's traffic.
-    info!("performing the proxy pass...");
-    let _ = tokio::io::copy_bidirectional(&mut client, &mut compute).await?;
-
-    Ok(())
-}
-
-/// Thin connection context.
-struct Client<'a, S> {
-    /// The underlying libpq protocol stream.
-    stream: PqStream<Stream<S>>,
-    /// Client credentials that we care about.
-    user_info: auth::BackendType<'a, auth::ComputeUserInfoMaybeEndpoint>,
-    /// KV-dictionary with PostgreSQL connection params.
-    params: &'a StartupMessageParams,
-    /// Allow self-signed certificates (for testing).
-    allow_self_signed_compute: bool,
-    /// Rate limiter for endpoints
-    endpoint_rate_limiter: Arc<EndpointRateLimiter>,
-}
-
-impl<'a, S> Client<'a, S> {
-    /// Construct a new connection context.
-    fn new(
-        stream: PqStream<Stream<S>>,
-        user_info: auth::BackendType<'a, auth::ComputeUserInfoMaybeEndpoint>,
-        params: &'a StartupMessageParams,
-        allow_self_signed_compute: bool,
-        endpoint_rate_limiter: Arc<EndpointRateLimiter>,
-    ) -> Self {
-        Self {
-            stream,
-            user_info,
-            params,
-            allow_self_signed_compute,
-            endpoint_rate_limiter,
-        }
-    }
-}
-
-impl<S: AsyncRead + AsyncWrite + Unpin> Client<'_, S> {
-    /// Let the client authenticate and connect to the designated compute node.
-    // Instrumentation logs endpoint name everywhere. Doesn't work for link
-    // auth; strictly speaking we don't know endpoint name in its case.
-    #[tracing::instrument(name = "", fields(ep = %self.user_info.get_endpoint().unwrap_or_default()), skip_all)]
-    async fn connect_to_db(
-        self,
-        ctx: &mut RequestMonitoring,
-        session: cancellation::Session<'_>,
-        mode: ClientMode,
-        config: &'static AuthenticationConfig,
-    ) -> anyhow::Result<()> {
-        let Self {
-            mut stream,
-            user_info,
-            params,
-            allow_self_signed_compute,
-            endpoint_rate_limiter,
-        } = self;
-
-        // check rate limit
-        if let Some(ep) = user_info.get_endpoint() {
-            if !endpoint_rate_limiter.check(ep) {
-                return stream
-                    .throw_error(auth::AuthError::too_many_connections())
-                    .await;
-            }
-        }
-
-        let user = user_info.get_user().to_owned();
-        let auth_result = match user_info
-            .authenticate(ctx, &mut stream, mode.allow_cleartext(), config)
-            .await
-        {
-            Ok(auth_result) => auth_result,
-            Err(e) => {
-                let db = params.get("database");
-                let app = params.get("application_name");
-                let params_span = tracing::info_span!("", ?user, ?db, ?app);
-
-                return stream.throw_error(e).instrument(params_span).await;
-            }
-        };
-
-        let (mut node_info, user_info) = auth_result;
-
-        node_info.allow_self_signed_compute = allow_self_signed_compute;
-
-        let aux = node_info.aux.clone();
-        let mut node = connect_to_compute(ctx, &TcpMechanism { params }, node_info, &user_info)
-            .or_else(|e| stream.throw_error(e))
-            .await?;
-
-        prepare_client_connection(&node, session, &mut stream).await?;
-        // Before proxy passing, forward to compute whatever data is left in the
-        // PqStream input buffer. Normally there is none, but our serverless npm
-        // driver in pipeline mode sends startup, password and first query
-        // immediately after opening the connection.
-        let (stream, read_buf) = stream.into_inner();
-        node.stream.write_all(&read_buf).await?;
-        proxy_pass(ctx, stream, node.stream, aux).await
-    }
-}
-
 #[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub struct NeonOptions(Vec<(SmolStr, SmolStr)>);