lib.rs

// Copyright 2025 Cloudflare, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! # pingora-proxy
//!
//! Programmable HTTP proxy built on top of [pingora_core].
//!
//! # Features
//! - HTTP/1.x and HTTP/2 for both downstream and upstream
//! - Connection pooling
//! - TLSv1.3, mutual TLS, customizable CA
//! - Request/Response scanning, modification or rejection
//! - Dynamic upstream selection
//! - Configurable retry and failover
//! - Fully programmable and customizable at any stage of a HTTP request
//!
//! # How to use
//!
//! Users of this crate defines their proxy by implementing [ProxyHttp] trait, which contains the
//! callbacks to be invoked at each stage of a HTTP request.
//!
//! Then the service can be passed into [`http_proxy_service()`] for a [pingora_core::server::Server] to
//! run it.
//!
//! See `examples/load_balancer.rs` for a detailed example.

use async_trait::async_trait;
use bytes::Bytes;
use futures::future::BoxFuture;
use futures::future::FutureExt;
use http::{header, version::Version};
use log::{debug, error, trace, warn};
use once_cell::sync::Lazy;
use pingora_http::{RequestHeader, ResponseHeader};
use std::fmt::Debug;
use std::str;
use std::sync::Arc;
use std::time::Duration;
use tokio::sync::{mpsc, Notify};
use tokio::time;

use pingora_cache::NoCacheReason;
use pingora_core::apps::{
    HttpPersistentSettings, HttpServerApp, HttpServerOptions, ReusedHttpStream,
};
use pingora_core::connectors::http::custom;
use pingora_core::connectors::{http::Connector, ConnectorOptions};
use pingora_core::modules::http::compression::ResponseCompressionBuilder;
use pingora_core::modules::http::{HttpModuleCtx, HttpModules};
use pingora_core::protocols::http::client::HttpSession as ClientSession;
use pingora_core::protocols::http::custom::CustomMessageWrite;
use pingora_core::protocols::http::v1::client::HttpSession as HttpSessionV1;
use pingora_core::protocols::http::v2::server::H2Options;
use pingora_core::protocols::http::HttpTask;
use pingora_core::protocols::http::ServerSession as HttpSession;
use pingora_core::protocols::http::SERVER_NAME;
use pingora_core::protocols::Stream;
use pingora_core::protocols::{Digest, UniqueID};
use pingora_core::server::configuration::ServerConf;
use pingora_core::server::ShutdownWatch;
use pingora_core::upstreams::peer::{HttpPeer, Peer};
use pingora_error::{Error, ErrorSource, ErrorType::*, OrErr, Result};

const TASK_BUFFER_SIZE: usize = 4;

mod proxy_cache;
mod proxy_common;
mod proxy_custom;
mod proxy_h1;
mod proxy_h2;
mod proxy_purge;
mod proxy_trait;
pub mod subrequest;

use subrequest::{BodyMode, Ctx as SubrequestCtx};

pub use proxy_cache::range_filter::{range_header_filter, RangeType};
pub use proxy_purge::PurgeStatus;
pub use proxy_trait::{FailToProxy, ProxyHttp};

pub mod prelude {
    pub use crate::{http_proxy_service, ProxyHttp, Session};
}

pub type ProcessCustomSession<SV, C> = Arc<
    dyn Fn(Arc<HttpProxy<SV, C>>, Stream, &ShutdownWatch) -> BoxFuture<'static, Option<Stream>>
        + Send
        + Sync
        + Unpin
        + 'static,
>;

/// The concrete type that holds the user defined HTTP proxy.
///
/// Users don't need to interact with this object directly.
pub struct HttpProxy<SV, C = ()>
where
    C: custom::Connector, // Upstream custom connector
{
    inner: SV, // TODO: name it better than inner
    client_upstream: Connector<C>,
    shutdown: Notify,
    pub server_options: Option<HttpServerOptions>,
    pub h2_options: Option<H2Options>,
    pub downstream_modules: HttpModules,
    max_retries: usize,
    process_custom_session: Option<ProcessCustomSession<SV, C>>,
}

impl<SV> HttpProxy<SV, ()> {
    fn new(inner: SV, conf: Arc<ServerConf>) -> Self {
        HttpProxy {
            inner,
            client_upstream: Connector::new(Some(ConnectorOptions::from_server_conf(&conf))),
            shutdown: Notify::new(),
            server_options: None,
            h2_options: None,
            downstream_modules: HttpModules::new(),
            max_retries: conf.max_retries,
            process_custom_session: None,
        }
    }
}

impl<SV, C> HttpProxy<SV, C>
where
    C: custom::Connector,
{
    fn new_custom(
        inner: SV,
        conf: Arc<ServerConf>,
        connector: C,
        on_custom: ProcessCustomSession<SV, C>,
    ) -> Self
    where
        SV: ProxyHttp + Send + Sync + 'static,
        SV::CTX: Send + Sync,
    {
        let client_upstream =
            Connector::new_custom(Some(ConnectorOptions::from_server_conf(&conf)), connector);

        HttpProxy {
            inner,
            client_upstream,
            shutdown: Notify::new(),
            server_options: None,
            downstream_modules: HttpModules::new(),
            max_retries: conf.max_retries,
            process_custom_session: Some(on_custom),
            h2_options: None,
        }
    }

    fn handle_init_modules(&mut self)
    where
        SV: ProxyHttp,
    {
        self.inner
            .init_downstream_modules(&mut self.downstream_modules);
    }

    async fn handle_new_request(
        &self,
        mut downstream_session: Box<HttpSession>,
    ) -> Option<Box<HttpSession>>
    where
        SV: ProxyHttp + Send + Sync,
        SV::CTX: Send + Sync,
    {
        // phase 1 read request header

        let res = tokio::select! {
            biased; // biased select is cheaper, and we don't want to drop already buffered requests
            res = downstream_session.read_request() => { res }
            _ = self.shutdown.notified() => {
                // service shutting down, dropping the connection to stop more req from coming in
                return None;
            }
        };
        match res {
            Ok(true) => {
                // TODO: check n==0
                debug!("Successfully get a new request");
            }
            Ok(false) => {
                return None; // TODO: close connection?
            }
            Err(mut e) => {
                e.as_down();
                error!("Fail to proxy: {e}");
                if matches!(e.etype, InvalidHTTPHeader) {
                    downstream_session
                        .respond_error(400)
                        .await
                        .unwrap_or_else(|e| {
                            error!("failed to send error response to downstream: {e}");
                        });
                } // otherwise the connection must be broken, no need to send anything
                downstream_session.shutdown().await;
                return None;
            }
        }
        trace!(
            "Request header: {:?}",
            downstream_session.req_header().as_ref()
        );
        Some(downstream_session)
    }

    // return bool: server_session can be reused, and error if any
    async fn proxy_to_upstream(
        &self,
        session: &mut Session,
        ctx: &mut SV::CTX,
    ) -> (bool, Option<Box<Error>>)
    where
        SV: ProxyHttp + Send + Sync,
        SV::CTX: Send + Sync,
    {
        let peer = match self.inner.upstream_peer(session, ctx).await {
            Ok(p) => p,
            Err(e) => return (false, Some(e)),
        };

        let client_session = self.client_upstream.get_http_session(&*peer).await;
        match client_session {
            Ok((client_session, client_reused)) => {
                let (server_reused, error) = match client_session {
                    ClientSession::H1(mut h1) => {
                        let (server_reused, client_reuse, error) = self
                            .proxy_to_h1_upstream(session, &mut h1, client_reused, &peer, ctx)
                            .await;
                        if client_reuse {
                            let session = ClientSession::H1(h1);
                            self.client_upstream
                                .release_http_session(session, &*peer, peer.idle_timeout())
                                .await;
                        }
                        (server_reused, error)
                    }
                    ClientSession::H2(mut h2) => {
                        let (server_reused, mut error) = self
                            .proxy_to_h2_upstream(session, &mut h2, client_reused, &peer, ctx)
                            .await;
                        let session = ClientSession::H2(h2);
                        self.client_upstream
                            .release_http_session(session, &*peer, peer.idle_timeout())
                            .await;

                        if let Some(e) = error.as_mut() {
                            // try to downgrade if A. origin says so or B. origin sends an invalid
                            // response, which usually means origin h2 is not production ready
                            if matches!(e.etype, H2Downgrade | InvalidH2) {
                                if peer
                                    .get_alpn()
                                    .map_or(true, |alpn| alpn.get_min_http_version() == 1)
                                {
                                    // Add the peer to prefer h1 so that all following requests
                                    // will use h1
                                    self.client_upstream.prefer_h1(&*peer);
                                } else {
                                    // the peer doesn't allow downgrading to h1 (e.g. gRPC)
                                    e.retry = false.into();
                                }
                            }
                        }

                        (server_reused, error)
                    }
                    ClientSession::Custom(mut c) => {
                        let (server_reused, error) = self
                            .proxy_to_custom_upstream(session, &mut c, client_reused, &peer, ctx)
                            .await;
                        let session = ClientSession::Custom(c);
                        self.client_upstream
                            .release_http_session(session, &*peer, peer.idle_timeout())
                            .await;
                        (server_reused, error)
                    }
                };
                (
                    server_reused,
                    error.map(|e| {
                        self.inner
                            .error_while_proxy(&peer, session, e, ctx, client_reused)
                    }),
                )
            }
            Err(mut e) => {
                e.as_up();
                let new_err = self.inner.fail_to_connect(session, &peer, ctx, e);
                (false, Some(new_err.into_up()))
            }
        }
    }

    async fn upstream_filter(
        &self,
        session: &mut Session,
        task: &mut HttpTask,
        ctx: &mut SV::CTX,
    ) -> Result<Option<Duration>>
    where
        SV: ProxyHttp + Send + Sync,
        SV::CTX: Send + Sync,
    {
        let duration = match task {
            HttpTask::Header(header, _eos) => {
                self.inner
                    .upstream_response_filter(session, header, ctx)
                    .await?;
                None
            }
            HttpTask::Body(data, eos) => self
                .inner
                .upstream_response_body_filter(session, data, *eos, ctx)?,
            HttpTask::Trailer(Some(trailers)) => {
                self.inner
                    .upstream_response_trailer_filter(session, trailers, ctx)?;
                None
            }
            _ => {
                // task does not support a filter
                None
            }
        };

        Ok(duration)
    }

    async fn finish(
        &self,
        mut session: Session,
        ctx: &mut SV::CTX,
        reuse: bool,
        error: Option<&Error>,
    ) -> Option<ReusedHttpStream>
    where
        SV: ProxyHttp + Send + Sync,
        SV::CTX: Send + Sync,
    {
        self.inner.logging(&mut session, error, ctx).await;

        if reuse {
            // TODO: log error
            let persistent_settings = HttpPersistentSettings::for_session(&session);
            session
                .downstream_session
                .finish()
                .await
                .ok()
                .flatten()
                .map(|s| ReusedHttpStream::new(s, Some(persistent_settings)))
        } else {
            None
        }
    }

    fn cleanup_sub_req(&self, session: &mut Session) {
        if let Some(ctx) = session.subrequest_ctx.as_mut() {
            ctx.release_write_lock();
        }
    }
}

use pingora_cache::HttpCache;
use pingora_core::protocols::http::compression::ResponseCompressionCtx;

/// The established HTTP session
///
/// This object is what users interact with in order to access the request itself or change the proxy
/// behavior.
pub struct Session {
    /// the HTTP session to downstream (the client)
    pub downstream_session: Box<HttpSession>,
    /// The interface to control HTTP caching
    pub cache: HttpCache,
    /// (de)compress responses coming into the proxy (from upstream)
    pub upstream_compression: ResponseCompressionCtx,
    /// ignore downstream range (skip downstream range filters)
    pub ignore_downstream_range: bool,
    /// Were the upstream request headers modified?
    pub upstream_headers_mutated_for_cache: bool,
    /// The context from parent request, if this is a subrequest.
    pub subrequest_ctx: Option<Box<SubrequestCtx>>,
    /// Handle to allow spawning subrequests, assigned by the `Subrequest` app logic.
    pub subrequest_spawner: Option<SubrequestSpawner>,
    // Downstream filter modules
    pub downstream_modules_ctx: HttpModuleCtx,
}

impl Session {
    fn new(
        downstream_session: impl Into<Box<HttpSession>>,
        downstream_modules: &HttpModules,
    ) -> Self {
        Session {
            downstream_session: downstream_session.into(),
            cache: HttpCache::new(),
            // disable both upstream and downstream compression
            upstream_compression: ResponseCompressionCtx::new(0, false, false),
            ignore_downstream_range: false,
            upstream_headers_mutated_for_cache: false,
            subrequest_ctx: None,
            subrequest_spawner: None, // optionally set later on
            downstream_modules_ctx: downstream_modules.build_ctx(),
        }
    }

    /// Create a new [Session] from the given [Stream]
    ///
    /// This function is mostly used for testing and mocking.
    pub fn new_h1(stream: Stream) -> Self {
        let modules = HttpModules::new();
        Self::new(Box::new(HttpSession::new_http1(stream)), &modules)
    }

    /// Create a new [Session] from the given [Stream] with modules
    ///
    /// This function is mostly used for testing and mocking.
    pub fn new_h1_with_modules(stream: Stream, downstream_modules: &HttpModules) -> Self {
        Self::new(Box::new(HttpSession::new_http1(stream)), downstream_modules)
    }

    pub fn as_downstream_mut(&mut self) -> &mut HttpSession {
        &mut self.downstream_session
    }

    pub fn as_downstream(&self) -> &HttpSession {
        &self.downstream_session
    }

    /// Write HTTP response with the given error code to the downstream.
    pub async fn respond_error(&mut self, error: u16) -> Result<()> {
        self.as_downstream_mut().respond_error(error).await
    }

    /// Write HTTP response with the given error code to the downstream with a body.
    pub async fn respond_error_with_body(&mut self, error: u16, body: Bytes) -> Result<()> {
        self.as_downstream_mut()
            .respond_error_with_body(error, body)
            .await
    }

    /// Write the given HTTP response header to the downstream
    ///
    /// Different from directly calling [HttpSession::write_response_header], this function also
    /// invokes the filter modules.
    pub async fn write_response_header(
        &mut self,
        mut resp: Box<ResponseHeader>,
        end_of_stream: bool,
    ) -> Result<()> {
        self.downstream_modules_ctx
            .response_header_filter(&mut resp, end_of_stream)
            .await?;
        self.downstream_session.write_response_header(resp).await
    }

    /// Write the given HTTP response body chunk to the downstream
    ///
    /// Different from directly calling [HttpSession::write_response_body], this function also
    /// invokes the filter modules.
    pub async fn write_response_body(
        &mut self,
        mut body: Option<Bytes>,
        end_of_stream: bool,
    ) -> Result<()> {
        self.downstream_modules_ctx
            .response_body_filter(&mut body, end_of_stream)?;

        if body.is_none() && !end_of_stream {
            return Ok(());
        }

        let data = body.unwrap_or_default();
        self.downstream_session
            .write_response_body(data, end_of_stream)
            .await
    }

    pub async fn write_response_tasks(&mut self, mut tasks: Vec<HttpTask>) -> Result<bool> {
        for task in tasks.iter_mut() {
            match task {
                HttpTask::Header(resp, end) => {
                    self.downstream_modules_ctx
                        .response_header_filter(resp, *end)
                        .await?;
                }
                HttpTask::Body(data, end) => {
                    self.downstream_modules_ctx
                        .response_body_filter(data, *end)?;
                }
                HttpTask::Trailer(trailers) => {
                    if let Some(buf) = self
                        .downstream_modules_ctx
                        .response_trailer_filter(trailers)?
                    {
                        // Write the trailers into the body if the filter
                        // returns a buffer.
                        //
                        // Note, this will not work if end of stream has already
                        // been seen or we've written content-length bytes.
                        *task = HttpTask::Body(Some(buf), true);
                    }
                }
                HttpTask::Done => {
                    // `Done` can be sent in certain response paths to mark end
                    // of response if not already done via trailers or body with
                    // end flag set.
                    // If the filter returns body bytes on Done,
                    // write them into the response.
                    //
                    // Note, this will not work if end of stream has already
                    // been seen or we've written content-length bytes.
                    if let Some(buf) = self.downstream_modules_ctx.response_done_filter()? {
                        *task = HttpTask::Body(Some(buf), true);
                    }
                }
                _ => { /* Failed */ }
            }
        }
        self.downstream_session.response_duplex_vec(tasks).await
    }

    /// Mark the upstream headers as modified by caching. This should lead to range filters being
    /// skipped when responding to the downstream.
    pub fn mark_upstream_headers_mutated_for_cache(&mut self) {
        self.upstream_headers_mutated_for_cache = true;
    }

    /// Check whether the upstream headers were marked as mutated during the request.
    pub fn upstream_headers_mutated_for_cache(&self) -> bool {
        self.upstream_headers_mutated_for_cache
    }

    pub fn downstream_custom_message(
        &mut self,
    ) -> Result<
        Option<Box<dyn futures::Stream<Item = Result<Bytes>> + Unpin + Send + Sync + 'static>>,
    > {
        if let Some(custom_session) = self.downstream_session.as_custom_mut() {
            custom_session
                .take_custom_message_reader()
                .map(Some)
                .ok_or(Error::explain(
                    ReadError,
                    "can't extract custom reader from downstream",
                ))
        } else {
            Ok(None)
        }
    }
}

impl AsRef<HttpSession> for Session {
    fn as_ref(&self) -> &HttpSession {
        &self.downstream_session
    }
}

impl AsMut<HttpSession> for Session {
    fn as_mut(&mut self) -> &mut HttpSession {
        &mut self.downstream_session
    }
}

use std::ops::{Deref, DerefMut};

impl Deref for Session {
    type Target = HttpSession;

    fn deref(&self) -> &Self::Target {
        &self.downstream_session
    }
}

impl DerefMut for Session {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.downstream_session
    }
}

impl Debug for Session {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("Session")
            .field("downstream_session", &"HttpSession")
            .field("cache", &"HttpCache")
            .field("upstream_compression", &"ResponseCompressionCtx")
            .field("ignore_downstream_range", &self.ignore_downstream_range)
            .field(
                "upstream_headers_mutated_for_cache",
                &self.upstream_headers_mutated_for_cache,
            )
            .finish_non_exhaustive()
    }
}

// generic HTTP 502 response sent when proxy_upstream_filter refuses to connect to upstream
static BAD_GATEWAY: Lazy<ResponseHeader> = Lazy::new(|| {
    let mut resp = ResponseHeader::build(http::StatusCode::BAD_GATEWAY, Some(3)).unwrap();
    resp.insert_header(header::SERVER, &SERVER_NAME[..])
        .unwrap();
    resp.insert_header(header::CONTENT_LENGTH, 0).unwrap();
    resp.insert_header(header::CACHE_CONTROL, "private, no-store")
        .unwrap();

    resp
});

impl<SV, C> HttpProxy<SV, C>
where
    C: custom::Connector,
{
    async fn process_request(
        self: &Arc<Self>,
        mut session: Session,
        mut ctx: <SV as ProxyHttp>::CTX,
    ) -> Option<ReusedHttpStream>
    where
        SV: ProxyHttp + Send + Sync + 'static,
        <SV as ProxyHttp>::CTX: Send + Sync,
    {
        if let Err(e) = self
            .inner
            .early_request_filter(&mut session, &mut ctx)
            .await
        {
            return self
                .handle_error(session, &mut ctx, e, "Fail to early filter request:")
                .await;
        }

        if self.inner.allow_spawning_subrequest(&session, &ctx) {
            session.subrequest_spawner = Some(SubrequestSpawner::new(self.clone()));
        }

        let req = session.downstream_session.req_header_mut();

        // Built-in downstream request filters go first
        if let Err(e) = session
            .downstream_modules_ctx
            .request_header_filter(req)
            .await
        {
            return self
                .handle_error(
                    session,
                    &mut ctx,
                    e,
                    "Failed in downstream modules request filter:",
                )
                .await;
        }

        match self.inner.request_filter(&mut session, &mut ctx).await {
            Ok(response_sent) => {
                if response_sent {
                    // TODO: log error
                    self.inner.logging(&mut session, None, &mut ctx).await;
                    self.cleanup_sub_req(&mut session);
                    let persistent_settings = HttpPersistentSettings::for_session(&session);
                    return session
                        .downstream_session
                        .finish()
                        .await
                        .ok()
                        .flatten()
                        .map(|s| ReusedHttpStream::new(s, Some(persistent_settings)));
                }
                /* else continue */
            }
            Err(e) => {
                return self
                    .handle_error(session, &mut ctx, e, "Fail to filter request:")
                    .await;
            }
        }

        if let Some((reuse, err)) = self.proxy_cache(&mut session, &mut ctx).await {
            // cache hit
            return self.finish(session, &mut ctx, reuse, err.as_deref()).await;
        }
        // either uncacheable, or cache miss

        // there should not be a write lock in the sub req ctx after this point
        self.cleanup_sub_req(&mut session);

        // decide if the request is allowed to go to upstream
        match self
            .inner
            .proxy_upstream_filter(&mut session, &mut ctx)
            .await
        {
            Ok(proxy_to_upstream) => {
                if !proxy_to_upstream {
                    // The hook can choose to write its own response, but if it doesn't, we respond
                    // with a generic 502
                    if session.cache.enabled() {
                        // drop the cache lock that this request may be holding onto
                        session.cache.disable(NoCacheReason::DeclinedToUpstream);
                    }
                    if session.response_written().is_none() {
                        match session.write_response_header_ref(&BAD_GATEWAY).await {
                            Ok(()) => {}
                            Err(e) => {
                                return self
                                    .handle_error(
                                        session,
                                        &mut ctx,
                                        e,
                                        "Error responding with Bad Gateway:",
                                    )
                                    .await;
                            }
                        }
                    }

                    return self.finish(session, &mut ctx, true, None).await;
                }
                /* else continue */
            }
            Err(e) => {
                if session.cache.enabled() {
                    session.cache.disable(NoCacheReason::InternalError);
                }

                return self
                    .handle_error(
                        session,
                        &mut ctx,
                        e,
                        "Error deciding if we should proxy to upstream:",
                    )
                    .await;
            }
        }

        let mut retries: usize = 0;

        let mut server_reuse = false;
        let mut proxy_error: Option<Box<Error>> = None;

        while retries < self.max_retries {
            retries += 1;

            let (reuse, e) = self.proxy_to_upstream(&mut session, &mut ctx).await;
            server_reuse = reuse;

            match e {
                Some(error) => {
                    let retry = error.retry();
                    proxy_error = Some(error);
                    if !retry {
                        break;
                    }
                    // only log error that will be retried here, the final error will be logged below
                    warn!(
                        "Fail to proxy: {}, tries: {}, retry: {}, {}",
                        proxy_error.as_ref().unwrap(),
                        retries,
                        retry,
                        self.inner.request_summary(&session, &ctx)
                    );
                }
                None => {
                    proxy_error = None;
                    break;
                }
            };
        }

        // serve stale if error
        // Check both error and cache before calling the function because await is not cheap
        // allow unwrap until if let chains
        #[allow(clippy::unnecessary_unwrap)]
        let serve_stale_result = if proxy_error.is_some() && session.cache.can_serve_stale_error() {
            self.handle_stale_if_error(&mut session, &mut ctx, proxy_error.as_ref().unwrap())
                .await
        } else {
            None
        };

        let final_error = if let Some((reuse, stale_cache_error)) = serve_stale_result {
            // don't reuse server conn if serve stale polluted it
            server_reuse = server_reuse && reuse;
            stale_cache_error
        } else {
            proxy_error
        };

        if let Some(e) = final_error.as_ref() {
            // If we have errored and are still holding a cache lock, release it.
            if session.cache.enabled() {
                let reason = if *e.esource() == ErrorSource::Upstream {
                    NoCacheReason::UpstreamError
                } else {
                    NoCacheReason::InternalError
                };
                session.cache.disable(reason);
            }
            let res = self.inner.fail_to_proxy(&mut session, e, &mut ctx).await;

            // final error will have > 0 status unless downstream connection is dead
            if !self.inner.suppress_error_log(&session, &ctx, e) {
                error!(
                    "Fail to proxy: {}, status: {}, tries: {}, retry: {}, {}",
                    final_error.as_ref().unwrap(),
                    res.error_code,
                    retries,
                    false, // we never retry here
                    self.inner.request_summary(&session, &ctx)
                );
            }
        }

        // logging() will be called in finish()
        self.finish(session, &mut ctx, server_reuse, final_error.as_deref())
            .await
    }

    async fn handle_error(
        &self,
        mut session: Session,
        ctx: &mut <SV as ProxyHttp>::CTX,
        e: Box<Error>,
        context: &str,
    ) -> Option<ReusedHttpStream>
    where
        SV: ProxyHttp + Send + Sync + 'static,
        <SV as ProxyHttp>::CTX: Send + Sync,
    {
        let res = self.inner.fail_to_proxy(&mut session, &e, ctx).await;
        if !self.inner.suppress_error_log(&session, ctx, &e) {
            error!(
                "{context} {}, status: {}, {}",
                e,
                res.error_code,
                self.inner.request_summary(&session, ctx)
            );
        }
        self.inner.logging(&mut session, Some(&e), ctx).await;
        self.cleanup_sub_req(&mut session);

        if res.can_reuse_downstream {
            let persistent_settings = HttpPersistentSettings::for_session(&session);
            session
                .downstream_session
                .finish()
                .await
                .ok()
                .flatten()
                .map(|s| ReusedHttpStream::new(s, Some(persistent_settings)))
        } else {
            None
        }
    }
}

/* Make process_subrequest() a trait to workaround https://github.com/rust-lang/rust/issues/78649
   if process_subrequest() is implemented as a member of HttpProxy, rust complains

error[E0391]: cycle detected when computing type of `proxy_cache::<impl at pingora-proxy/src/proxy_cache.rs:7:1: 7:23>::proxy_cache::{opaque#0}`
   --> pingora-proxy/src/proxy_cache.rs:13:10
    |
13  |     ) -> Option<(bool, Option<Box<Error>>)>

*/
#[async_trait]
pub trait Subrequest {
    async fn process_subrequest(
        self: Arc<Self>,
        session: Box<HttpSession>,
        sub_req_ctx: Box<SubrequestCtx>,
    );
}

#[async_trait]
impl<SV, C> Subrequest for HttpProxy<SV, C>
where
    SV: ProxyHttp + Send + Sync + 'static,
    <SV as ProxyHttp>::CTX: Send + Sync,
    C: custom::Connector,
{
    async fn process_subrequest(
        self: Arc<Self>,
        session: Box<HttpSession>,
        sub_req_ctx: Box<SubrequestCtx>,
    ) {
        debug!("starting subrequest");

        let mut session = match self.handle_new_request(session).await {
            Some(downstream_session) => Session::new(downstream_session, &self.downstream_modules),
            None => return, // bad request
        };

        // no real downstream to keepalive, but it doesn't matter what is set here because at the end
        // of this fn the dummy connection will be dropped
        session.set_keepalive(None);

        session.subrequest_ctx.replace(sub_req_ctx);
        trace!("processing subrequest");
        let ctx = self.inner.new_ctx();
        self.process_request(session, ctx).await;
        trace!("subrequest done");
    }
}

/// A handle to the underlying HTTP proxy app that allows spawning subrequests.
pub struct SubrequestSpawner {
    app: Arc<dyn Subrequest + Send + Sync>,
}

impl SubrequestSpawner {
    /// Create a new [`SubrequestSpawner`].
    pub fn new(app: Arc<dyn Subrequest + Send + Sync>) -> SubrequestSpawner {
        SubrequestSpawner { app }
    }

    /// Spawn a background subrequest and return a join handle.
    // TODO: allow configuring the subrequest session before use
    pub fn spawn_background_subrequest(
        &self,
        session: &HttpSession,
        ctx: SubrequestCtx,
    ) -> tokio::task::JoinHandle<()> {
        let new_app = self.app.clone(); // Clone the Arc
        let (mut session, handle) = subrequest::create_session(session);
        if ctx.body_mode() == BodyMode::NoBody {
            session
                .as_subrequest_mut()
                .expect("created subrequest session")
                .clear_request_body_headers();
        }
        let sub_req_ctx = Box::new(ctx);
        handle.drain_tasks();
        tokio::spawn(async move {
            new_app
                .process_subrequest(Box::new(session), sub_req_ctx)
                .await;
        })
    }
}

#[async_trait]
impl<SV, C> HttpServerApp for HttpProxy<SV, C>
where
    SV: ProxyHttp + Send + Sync + 'static,
    <SV as ProxyHttp>::CTX: Send + Sync,
    C: custom::Connector,
{
    async fn process_new_http(
        self: &Arc<Self>,
        session: HttpSession,
        _shutdown: &ShutdownWatch,
    ) -> Option<ReusedHttpStream> {
        let session = Box::new(session);

        // TODO: keepalive pool, use stack
        let session = match self.handle_new_request(session).await {
            Some(downstream_session) => Session::new(downstream_session, &self.downstream_modules),
            None => return None, // bad request
        };

        let ctx = self.inner.new_ctx();
        self.process_request(session, ctx).await
    }

    async fn http_cleanup(&self) {
        // Notify all keepalived requests blocking on read_request() to abort
        self.shutdown.notify_waiters();

        // TODO: impl shutting down flag so that we don't need to read stack.is_shutting_down()
    }

    fn server_options(&self) -> Option<&HttpServerOptions> {
        self.server_options.as_ref()
    }

    fn h2_options(&self) -> Option<H2Options> {
        self.h2_options.clone()
    }
    async fn process_custom_session(
        self: Arc<Self>,
        stream: Stream,
        shutdown: &ShutdownWatch,
    ) -> Option<Stream> {
        let app = self.clone();

        let Some(process_custom_session) = app.process_custom_session.as_ref() else {
            warn!("custom was called on an empty on_custom");
            return None;
        };

        process_custom_session(self.clone(), stream, shutdown).await
    }

    // TODO implement h2_options
}

use pingora_core::services::listening::Service;

/// Create a [Service] from the user implemented [ProxyHttp].
///
/// The returned [Service] can be hosted by a [pingora_core::server::Server] directly.
pub fn http_proxy_service<SV>(conf: &Arc<ServerConf>, inner: SV) -> Service<HttpProxy<SV, ()>>
where
    SV: ProxyHttp,
{
    http_proxy_service_with_name(conf, inner, "Pingora HTTP Proxy Service")
}

/// Create a [Service] from the user implemented [ProxyHttp].
///
/// The returned [Service] can be hosted by a [pingora_core::server::Server] directly.
pub fn http_proxy_service_with_name<SV>(
    conf: &Arc<ServerConf>,
    inner: SV,
    name: &str,
) -> Service<HttpProxy<SV, ()>>
where
    SV: ProxyHttp,
{
    let mut proxy = HttpProxy::new(inner, conf.clone());
    proxy.handle_init_modules();
    Service::new(name.to_string(), proxy)
}

/// Create a [Service] from the user implemented [ProxyHttp].
///
/// The returned [Service] can be hosted by a [pingora_core::server::Server] directly.
pub fn http_proxy_service_with_name_custom<SV, C>(
    conf: &Arc<ServerConf>,
    inner: SV,
    name: &str,
    connector: C,
    on_custom: ProcessCustomSession<SV, C>,
) -> Service<HttpProxy<SV, C>>
where
    SV: ProxyHttp + Send + Sync + 'static,
    SV::CTX: Send + Sync + 'static,
    C: custom::Connector,
{
    let mut proxy = HttpProxy::new_custom(inner, conf.clone(), connector, on_custom);
    proxy.handle_init_modules();

    Service::new(name.to_string(), proxy)
}