reddb_server/wire/postgres/

server.rs

//! PostgreSQL wire-protocol listener (Phase 3.1 PG parity).
//!
//! Accepts TCP connections from PG-compatible clients, drives the startup
//! handshake, and routes simple/extended-query frames into the existing
//! `RedDBRuntime::execute_query` path. Results are adapted back into PG
//! `RowDescription` + `DataRow` frames via `types::value_to_pg_wire_bytes`.

use std::collections::HashMap;
use std::sync::Arc;

use tokio::io::{AsyncRead, AsyncWrite};
use tokio::net::TcpListener;

use super::catalog_views::translate_pg_catalog_query;
use super::protocol::{
    read_frame, read_startup, write_frame, write_raw_byte, BackendMessage, ColumnDescriptor,
    DescribeTarget, FrontendMessage, PgWireError, TransactionStatus,
};
use super::types::{pg_param_to_param_value, value_to_pg_wire_bytes, PgOid};
use crate::auth::Role;
use crate::runtime::query_request::{
    ParamValue, PreparedId, PreparedRegistry, QueryRequest, QueryRequestExecutor,
};
use crate::runtime::RedDBRuntime;
use crate::storage::query::unified::{UnifiedRecord, UnifiedResult};
use reddb_rql::ast::QueryExpr;
use reddb_types::Value;

/// Startup-tuned configuration for the PG wire listener.
#[derive(Debug, Clone)]
pub struct PgWireConfig {
    /// TCP bind address ("host:port"). The caller is responsible for
    /// keeping this disjoint from the native wire / gRPC / HTTP listeners.
    pub bind_addr: String,
    /// PG version string sent back in `ParameterStatus`. Many drivers
    /// sniff this to enable/disable features. RedDB advertises a
    /// recent-enough version to get the broadest client support.
    pub server_version: String,
    /// Optional TLS material. When set, an `SSLRequest` is answered with
    /// `'S'` and the connection is upgraded via a rustls handshake before
    /// the startup flow continues over the encrypted stream. The cert/key
    /// surface is the *same* [`WireTlsConfig`] the native RedWire listener
    /// uses — the two transports share one cert config rather than
    /// inventing a parallel one. `None` leaves the historical behaviour:
    /// `SSLRequest` is declined with `'N'` and clients continue in
    /// plaintext.
    pub tls: Option<crate::wire::tls::WireTlsConfig>,
}

/// The authenticated identity resolved during the PG-Wire startup
/// handshake. Installed as the thread-local execution identity for the
/// duration of each statement so every query dispatched over this
/// connection flows through the same IAM/policy gates as native
/// transports. `None` connections (loopback trust) run under the ambient
/// embedded identity, preserving the pre-auth behaviour.
#[derive(Debug, Clone)]
struct PgAuthContext {
    username: String,
    role: Role,
    tenant: Option<String>,
}

#[derive(Debug, Clone)]
struct PgPreparedStatement {
    sql: String,
    prepared_id: PreparedId,
    param_type_oids: Vec<u32>,
}

#[derive(Debug, Clone)]
struct PgPortal {
    sql: String,
    prepared_id: PreparedId,
    params: Vec<ParamValue>,
    #[allow(dead_code)]
    result_format_codes: Vec<i16>,
    row_description_sent: bool,
    result: Option<crate::runtime::OwnedQueryResult>,
    row_offset: usize,
}

impl Default for PgWireConfig {
    fn default() -> Self {
        Self {
            bind_addr: "127.0.0.1:5432".to_string(),
            server_version: "15.0 (RedDB 3.1)".to_string(),
            tls: None,
        }
    }
}

/// Run a synchronous, possibly long-parking runtime call without
/// monopolising the async worker thread.
///
/// `QUEUE READ … WAIT <budget>` parks the calling thread on a condvar
/// for up to the wait budget. Doing that directly on a tokio worker
/// holds the worker for the whole budget, which serialises every other
/// connection's query behind the parked waiter — a producer's
/// `QUEUE PUSH` could not run to notify the waiter, so an enqueue during
/// a WAIT would never be delivered — and it stalls the runtime's timer
/// driver. `block_in_place` hands the remaining tasks on this worker to
/// a sibling worker for the duration while keeping the current OS thread
/// — and therefore the per-connection thread-locals `execute_query`
/// relies on (current tenant, connection id, transaction context) —
/// intact, which `spawn_blocking` would not.
///
/// `block_in_place` panics on a current-thread runtime, so we fall back
/// to a direct call there: a single-threaded runtime has no sibling
/// worker to hand work to and nothing else to starve (e.g. the
/// `#[tokio::test]` harnesses that drive one connection at a time).
fn run_runtime_blocking<T>(f: impl FnOnce() -> T) -> T {
    use tokio::runtime::{Handle, RuntimeFlavor};
    match Handle::try_current().map(|h| h.runtime_flavor()) {
        Ok(RuntimeFlavor::MultiThread) => tokio::task::block_in_place(f),
        _ => f(),
    }
}

fn pg_frame_requires_execution(frame: &FrontendMessage) -> bool {
    matches!(
        frame,
        FrontendMessage::Query(_)
            | FrontendMessage::Parse(_)
            | FrontendMessage::Describe(_)
            | FrontendMessage::Execute(_)
    )
}

async fn acquire_pg_execution(
    runtime: &RedDBRuntime,
) -> Result<crate::transport::execution_admission::ExecutionPermit, &'static str> {
    use crate::transport::execution_admission::ExecutionAdmissionError;

    let admission = runtime.execution_admission();
    match tokio::time::timeout(runtime.execution_queue_timeout(), admission.acquire()).await {
        Ok(Ok(permit)) => Ok(permit),
        Ok(Err(ExecutionAdmissionError::QueueFull)) => {
            Err("execution_queue_full: engine execution queue is full; retryable=true")
        }
        Ok(Err(ExecutionAdmissionError::Closed)) => {
            Err("execution_admission_closed: engine execution admission is unavailable")
        }
        Err(_) => Err(
            "execution_queue_timeout: deadline expired while waiting to execute; retryable=true",
        ),
    }
}

/// Holds the execution slot only until the response starts. PG handlers do
/// all synchronous engine work before their first write; releasing at that
/// boundary prevents a slow client from occupying engine capacity while rows
/// drain through the socket.
struct ExecutionResponseWriter<'a, S> {
    inner: &'a mut S,
    permit: Option<crate::transport::execution_admission::ExecutionPermit>,
}

impl<'a, S> ExecutionResponseWriter<'a, S> {
    fn new(
        inner: &'a mut S,
        permit: Option<crate::transport::execution_admission::ExecutionPermit>,
    ) -> Self {
        Self { inner, permit }
    }
}

impl<S: AsyncWrite + Unpin> AsyncWrite for ExecutionResponseWriter<'_, S> {
    fn poll_write(
        mut self: std::pin::Pin<&mut Self>,
        cx: &mut std::task::Context<'_>,
        buf: &[u8],
    ) -> std::task::Poll<Result<usize, std::io::Error>> {
        drop(self.permit.take());
        std::pin::Pin::new(&mut *self.inner).poll_write(cx, buf)
    }

    fn poll_flush(
        mut self: std::pin::Pin<&mut Self>,
        cx: &mut std::task::Context<'_>,
    ) -> std::task::Poll<Result<(), std::io::Error>> {
        drop(self.permit.take());
        std::pin::Pin::new(&mut *self.inner).poll_flush(cx)
    }

    fn poll_shutdown(
        mut self: std::pin::Pin<&mut Self>,
        cx: &mut std::task::Context<'_>,
    ) -> std::task::Poll<Result<(), std::io::Error>> {
        drop(self.permit.take());
        std::pin::Pin::new(&mut *self.inner).poll_shutdown(cx)
    }
}

/// Run `f` with the authenticated PG-Wire identity installed as the
/// thread-local execution identity, restoring the prior state afterwards.
///
/// The runtime's query dispatch resolves `CURRENT_USER/ROLE/TENANT` and
/// folds RLS/IAM policies from these thread-locals, so installing them
/// here is what makes PG-Wire statements transport-invariant with the
/// native wire. A `None` context leaves the ambient identity untouched.
fn execute_with_pg_auth_context<T>(
    auth_context: Option<&PgAuthContext>,
    f: impl FnOnce() -> T,
) -> T {
    let Some(auth_context) = auth_context else {
        return f();
    };
    let _guard = PgAuthContextGuard::install(auth_context);
    f()
}

/// RAII guard that installs the PG-Wire auth identity + tenant on the
/// current thread and restores the previous state on drop, so pooled
/// runtime threads never leak an identity across statements.
struct PgAuthContextGuard {
    previous_tenant: Option<String>,
}

impl PgAuthContextGuard {
    fn install(auth_context: &PgAuthContext) -> Self {
        let previous_tenant = crate::runtime::execution_context::current_tenant();
        match &auth_context.tenant {
            Some(tenant) => crate::runtime::execution_context::set_current_tenant(tenant.clone()),
            None => crate::runtime::execution_context::clear_current_tenant(),
        }
        crate::runtime::execution_context::set_current_auth_identity(
            auth_context.username.clone(),
            auth_context.role,
        );
        Self { previous_tenant }
    }
}

impl Drop for PgAuthContextGuard {
    fn drop(&mut self) {
        crate::runtime::execution_context::clear_current_auth_identity();
        match self.previous_tenant.take() {
            Some(tenant) => crate::runtime::execution_context::set_current_tenant(tenant),
            None => crate::runtime::execution_context::clear_current_tenant(),
        }
    }
}

/// Whether `bind_addr` ("host:port") resolves to a loopback host. Trust
/// authentication survives only for loopback binds with no credentials
/// configured; every other bind requires a verified password.
fn is_loopback_bind(bind_addr: &str) -> bool {
    crate::transport::is_loopback_bind(bind_addr)
}

/// Extract the cleartext password from a `PasswordMessage` payload (a
/// single NUL-terminated C-string), returning `None` on malformed input.
fn password_from_message(payload: &[u8]) -> Option<String> {
    let nul = payload.iter().position(|&b| b == 0)?;
    std::str::from_utf8(&payload[..nul])
        .ok()
        .map(|password| password.to_string())
}

/// Spawn the PG wire listener. Blocks until the listener errors out.
/// Each connection is handled in its own tokio task.
pub async fn start_pg_wire_listener(
    config: PgWireConfig,
    runtime: Arc<RedDBRuntime>,
) -> Result<(), Box<dyn std::error::Error>> {
    let listener = TcpListener::bind(&config.bind_addr).await?;
    start_pg_wire_listener_on(listener, config, runtime).await
}

/// Serve PostgreSQL wire traffic on a listener bound during node bootstrap.
pub async fn start_pg_wire_listener_on(
    listener: TcpListener,
    config: PgWireConfig,
    runtime: Arc<RedDBRuntime>,
) -> Result<(), Box<dyn std::error::Error>> {
    // Posture: with no auth store enabled, PG-Wire falls back to trust
    // auth for loopback binds only (see `authenticate_startup`). Surface a
    // startup warning whenever that fallback is active so an operator never
    // exposes an unauthenticated listener without noticing.
    let trust_active = runtime
        .auth_store()
        .map(|store| !store.is_enabled())
        .unwrap_or(true)
        && is_loopback_bind(&config.bind_addr);
    if trust_active {
        tracing::warn!(
            transport = "pg-wire",
            bind = %config.bind_addr,
            "PG-Wire trust authentication is active (no auth store configured); \
             loopback-only. Configure auth before exposing this listener."
        );
    }
    // Build the shared TLS acceptor once, up front, so a bad cert/key
    // fails the whole listener rather than every individual connection.
    // The acceptor is cheap to clone (an `Arc` internally) and is handed
    // to each connection so `SSLRequest` can be answered with `'S'` and
    // the rustls handshake performed before the startup flow resumes.
    let tls_acceptor = match config.tls.as_ref() {
        Some(tls_cfg) => Some(crate::wire::tls::build_tls_acceptor(tls_cfg)?),
        None => None,
    };
    tracing::info!(
        transport = "pg-wire",
        bind = %config.bind_addr,
        tls = tls_acceptor.is_some(),
        "listener online"
    );
    let cfg = Arc::new(config);
    let admission = crate::wire::admission::ConnectionAdmission::new("pg-wire");
    loop {
        let (stream, peer) = listener.accept().await?;
        // Bound concurrent sessions. Without this the accept loop spawned a
        // task per connection with no ceiling, so an unauthenticated peer
        // could exhaust descriptors before presenting a credential.
        let Some(permit) = admission.try_admit() else {
            continue;
        };
        // Small result/control frames must not wait for a client's delayed ACK
        // before the next frame (notably ReadyForQuery) can leave the server.
        if let Err(error) = stream.set_nodelay(true) {
            tracing::warn!(transport = "pg-wire", peer = %peer, err = %error,
                "failed to configure connection");
            continue;
        }
        let rt = Arc::clone(&runtime);
        let cfg = Arc::clone(&cfg);
        let acceptor = tls_acceptor.clone();
        let peer_str = peer.to_string();
        tokio::spawn(async move {
            let _permit = permit;
            if let Err(e) = handle_connection(stream, rt, cfg, acceptor).await {
                tracing::warn!(
                    transport = "pg-wire",
                    peer = %peer_str,
                    err = %e,
                    "connection failed"
                );
            }
        });
    }
}

/// Drive one connection's lifetime: SSL negotiation → startup →
/// authentication → query loop.
///
/// The first frame may be `SSLRequest` / `GSSENCRequest` (pre-auth
/// negotiation) or a plain `Startup`. When a TLS acceptor is present an
/// `SSLRequest` is answered with `'S'` and the socket is upgraded via a
/// rustls handshake; the rest of the session (a fresh `Startup`,
/// authentication, and the query loop) then runs over the encrypted
/// stream. Without an acceptor — or for `GSSENCRequest`, which we never
/// support — the request is declined with `'N'` and the client continues
/// in plaintext on the same socket.
pub(crate) async fn handle_connection<S>(
    mut stream: S,
    runtime: Arc<RedDBRuntime>,
    config: Arc<PgWireConfig>,
    tls_acceptor: Option<tokio_rustls::TlsAcceptor>,
) -> Result<(), PgWireError>
where
    S: AsyncRead + AsyncWrite + Unpin + Send,
{
    // Bound the whole pre-session negotiation. `read_startup` and the rustls
    // handshake both block on the peer, and neither had a deadline: a client
    // that connected and sent nothing (or stalled mid-handshake) pinned a
    // task and a connection slot indefinitely, before any credential was
    // presented. The loop below can iterate (SSLRequest/GSSENCRequest are
    // declined and the client retries), so each read is bounded rather than
    // the loop as a whole.
    loop {
        let startup = crate::wire::admission::with_handshake_deadline(read_startup(&mut stream))
            .await
            .map_err(PgWireError::from)??;
        match startup {
            FrontendMessage::SslRequest => {
                if let Some(acceptor) = tls_acceptor.as_ref() {
                    // 'S' = SSL supported. Perform the rustls handshake and
                    // hand the encrypted stream to the session driver.
                    write_raw_byte(&mut stream, b'S').await?;
                    let tls_stream =
                        crate::wire::admission::with_handshake_deadline(acceptor.accept(stream))
                            .await??;
                    return serve_session_after_tls(tls_stream, runtime, config).await;
                }
                // 'N' = not supported — client continues in plaintext and
                // re-sends a normal Startup on the same socket.
                write_raw_byte(&mut stream, b'N').await?;
                continue;
            }
            FrontendMessage::GssEncRequest => {
                // GSSAPI encryption is never offered; decline and let the
                // client retry with SSLRequest or plaintext Startup.
                write_raw_byte(&mut stream, b'N').await?;
                continue;
            }
            FrontendMessage::Startup(params) => {
                return run_pg_session(stream, runtime, config, false, params).await;
            }
            FrontendMessage::Unknown { .. } => {
                // CancelRequest: no response expected; drop the socket.
                return Ok(());
            }
            other => {
                return Err(PgWireError::Protocol(format!(
                    "unexpected startup frame: {other:?}"
                )));
            }
        }
    }
}

/// Continue the startup flow after a successful TLS upgrade. The client
/// now sends a fresh `Startup` over the encrypted stream; a second
/// `SSLRequest` / `GSSENCRequest` cannot be honoured (no nested
/// encryption) and is declined with `'N'`.
async fn serve_session_after_tls<S>(
    mut stream: tokio_rustls::server::TlsStream<S>,
    runtime: Arc<RedDBRuntime>,
    config: Arc<PgWireConfig>,
) -> Result<(), PgWireError>
where
    S: AsyncRead + AsyncWrite + Unpin + Send,
{
    loop {
        match read_startup(&mut stream).await? {
            FrontendMessage::SslRequest | FrontendMessage::GssEncRequest => {
                write_raw_byte(&mut stream, b'N').await?;
                continue;
            }
            FrontendMessage::Startup(params) => {
                return run_pg_session(stream, runtime, config, true, params).await;
            }
            FrontendMessage::Unknown { .. } => return Ok(()),
            other => {
                return Err(PgWireError::Protocol(format!(
                    "unexpected startup frame: {other:?}"
                )));
            }
        }
    }
}

/// Authenticate a `Startup` and drive the query loop over `stream`.
/// `over_tls` records whether the transport is encrypted, which gates the
/// cleartext-password posture in [`authenticate_startup`].
async fn run_pg_session<S>(
    mut stream: S,
    runtime: Arc<RedDBRuntime>,
    config: Arc<PgWireConfig>,
    over_tls: bool,
    params: super::protocol::StartupParams,
) -> Result<(), PgWireError>
where
    S: AsyncRead + AsyncWrite + Unpin + Send,
{
    let auth_context =
        match authenticate_startup(&mut stream, &runtime, &config, over_tls, &params).await? {
            Some(context) => context,
            // Authentication failed: the error frame was already sent and
            // the socket must close.
            None => return Ok(()),
        };

    let mut prepared: HashMap<String, PgPreparedStatement> = HashMap::new();
    let mut portals: HashMap<String, PgPortal> = HashMap::new();
    let prepared_registry = PreparedRegistry::new();

    // Main query loop.
    loop {
        let frame = match read_frame(&mut stream).await {
            Ok(f) => f,
            Err(PgWireError::Eof) => return Ok(()),
            Err(e) => return Err(e),
        };

        // PG sessions are serial, but every session competes for the same
        // runtime-wide engine budget as HTTP, gRPC and RedWire. Admission is
        // taken before any parser/planner/storage work. The response writer
        // releases it before the first socket write, so a slow client cannot
        // occupy engine capacity while rows drain.
        let mut execution_permit = if pg_frame_requires_execution(&frame) {
            match acquire_pg_execution(&runtime).await {
                Ok(permit) => Some(permit),
                Err(message) => {
                    // SQLSTATE 53000 = insufficient_resources. Keep the stable
                    // RedDB reason code in the message for clients that expose
                    // only the PostgreSQL ErrorResponse text.
                    send_error(&mut stream, "53000", message).await?;
                    write_frame(
                        &mut stream,
                        &BackendMessage::ReadyForQuery(TransactionStatus::Idle),
                    )
                    .await?;
                    continue;
                }
            }
        } else {
            None
        };

        match frame {
            FrontendMessage::Query(sql) => {
                let mut response =
                    ExecutionResponseWriter::new(&mut stream, execution_permit.take());
                handle_simple_query(&mut response, &runtime, auth_context.as_ref(), &sql).await?;
            }
            FrontendMessage::Parse(msg) => {
                let mut response =
                    ExecutionResponseWriter::new(&mut stream, execution_permit.take());
                handle_parse(
                    &mut response,
                    &runtime,
                    &prepared_registry,
                    &mut prepared,
                    &portals,
                    msg,
                )
                .await?;
            }
            FrontendMessage::Bind(msg) => {
                handle_bind(
                    &mut stream,
                    &prepared_registry,
                    &prepared,
                    &mut portals,
                    msg,
                )
                .await?;
            }
            FrontendMessage::Describe(msg) => {
                let mut response =
                    ExecutionResponseWriter::new(&mut stream, execution_permit.take());
                handle_describe(
                    &mut response,
                    &runtime,
                    auth_context.as_ref(),
                    &prepared_registry,
                    &prepared,
                    &mut portals,
                    msg,
                )
                .await?;
            }
            FrontendMessage::Execute(msg) => {
                let mut response =
                    ExecutionResponseWriter::new(&mut stream, execution_permit.take());
                handle_execute(
                    &mut response,
                    &runtime,
                    auth_context.as_ref(),
                    &prepared_registry,
                    &mut portals,
                    msg,
                )
                .await?;
            }
            FrontendMessage::Close(msg) => {
                handle_close(
                    &mut stream,
                    &prepared_registry,
                    &mut prepared,
                    &mut portals,
                    msg,
                )
                .await?;
            }
            FrontendMessage::Terminate => return Ok(()),
            FrontendMessage::Flush => {
                // Frames are written immediately; no additional marker is
                // needed. ReadyForQuery belongs to Sync, not Flush.
                continue;
            }
            FrontendMessage::Sync => {
                write_frame(
                    &mut stream,
                    &BackendMessage::ReadyForQuery(TransactionStatus::Idle),
                )
                .await?;
            }
            FrontendMessage::PasswordMessage(_) => {
                // Should only arrive during auth. Ignore post-auth.
                continue;
            }
            FrontendMessage::Unknown { tag, .. } => {
                send_error(
                    &mut stream,
                    "0A000",
                    &format!("unsupported frame tag 0x{tag:02x}"),
                )
                .await?;
                write_frame(
                    &mut stream,
                    &BackendMessage::ReadyForQuery(TransactionStatus::Idle),
                )
                .await?;
            }
            other => {
                send_error(
                    &mut stream,
                    "0A000",
                    &format!("unsupported frame {other:?}"),
                )
                .await?;
                write_frame(
                    &mut stream,
                    &BackendMessage::ReadyForQuery(TransactionStatus::Idle),
                )
                .await?;
            }
        }
    }
}

async fn handle_parse<S>(
    stream: &mut S,
    runtime: &RedDBRuntime,
    prepared_registry: &PreparedRegistry,
    prepared: &mut HashMap<String, PgPreparedStatement>,
    portals: &HashMap<String, PgPortal>,
    msg: super::protocol::ParseMessage,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    let inferred_param_type_oids = infer_pg_cast_param_type_oids(&msg.query);
    let sql = rewrite_pg_parameter_casts(&msg.query);
    let prepared_query = match prepared_registry.prepare(runtime, &sql) {
        Ok(prepared_query) => prepared_query,
        Err(err) => {
            send_error(stream, "42601", &err.to_string()).await?;
            return Ok(());
        }
    };
    let mut param_type_oids = msg.param_type_oids;
    if param_type_oids.is_empty() {
        param_type_oids.resize(prepared_query.parameter_count, PgOid::Unknown.as_u32());
    }
    for (idx, oid) in inferred_param_type_oids {
        if idx >= param_type_oids.len() {
            param_type_oids.resize(idx + 1, PgOid::Unknown.as_u32());
        }
        if param_type_oids[idx] == PgOid::Unknown.as_u32() {
            param_type_oids[idx] = oid;
        }
    }
    let replaced = prepared.insert(
        msg.statement,
        PgPreparedStatement {
            sql,
            prepared_id: prepared_query.id,
            param_type_oids,
        },
    );
    if let Some(replaced) = replaced {
        release_prepared_if_unreferenced(
            prepared_registry,
            replaced.prepared_id,
            prepared,
            portals,
        );
    }
    write_frame(stream, &BackendMessage::ParseComplete).await
}

async fn handle_bind<S>(
    stream: &mut S,
    prepared_registry: &PreparedRegistry,
    prepared: &HashMap<String, PgPreparedStatement>,
    portals: &mut HashMap<String, PgPortal>,
    msg: super::protocol::BindMessage,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    let Some(stmt) = prepared.get(&msg.statement) else {
        send_error(
            stream,
            "26000",
            &format!("prepared statement {:?} does not exist", msg.statement),
        )
        .await?;
        return Ok(());
    };
    let params = match bind_pg_params(stmt, &msg) {
        Ok(params) => params,
        Err(err) => {
            send_error(stream, "22023", &err).await?;
            return Ok(());
        }
    };
    let replaced = portals.insert(
        msg.portal,
        PgPortal {
            sql: stmt.sql.clone(),
            prepared_id: stmt.prepared_id,
            params,
            result_format_codes: msg.result_format_codes,
            row_description_sent: false,
            result: None,
            row_offset: 0,
        },
    );
    if let Some(replaced) = replaced {
        release_prepared_if_unreferenced(
            prepared_registry,
            replaced.prepared_id,
            prepared,
            portals,
        );
    }
    write_frame(stream, &BackendMessage::BindComplete).await
}

async fn handle_describe<S>(
    stream: &mut S,
    runtime: &RedDBRuntime,
    auth_context: Option<&PgAuthContext>,
    prepared_registry: &PreparedRegistry,
    prepared: &HashMap<String, PgPreparedStatement>,
    portals: &mut HashMap<String, PgPortal>,
    msg: super::protocol::DescribeMessage,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    match msg.target {
        DescribeTarget::Statement => {
            let Some(stmt) = prepared.get(&msg.name) else {
                send_error(
                    stream,
                    "26000",
                    &format!("prepared statement {:?} does not exist", msg.name),
                )
                .await?;
                return Ok(());
            };
            write_frame(
                stream,
                &BackendMessage::ParameterDescription(stmt.param_type_oids.clone()),
            )
            .await?;
            if is_ask_query(&stmt.sql) {
                emit_ask_row_description(stream).await
            } else {
                write_frame(stream, &BackendMessage::NoData).await
            }
        }
        DescribeTarget::Portal => {
            let Some(portal) = portals.get_mut(&msg.name) else {
                send_error(
                    stream,
                    "34000",
                    &format!("portal {:?} does not exist", msg.name),
                )
                .await?;
                return Ok(());
            };
            if is_ask_query(&portal.sql) {
                emit_ask_row_description(stream).await?;
                portal.row_description_sent = true;
                Ok(())
            } else if is_row_returning_query(&portal.sql) {
                let result = match execute_pg_query_result(
                    runtime,
                    auth_context,
                    prepared_registry,
                    portal.prepared_id,
                    &portal.sql,
                    &portal.params,
                ) {
                    Ok(result) => result,
                    Err(err) => {
                        let code = classify_sqlstate(&err);
                        send_error(stream, code, &err).await?;
                        return Ok(());
                    }
                };
                emit_row_description_for_result(stream, &result).await?;
                portal.row_description_sent = true;
                portal.result = Some(result);
                portal.row_offset = 0;
                Ok(())
            } else {
                write_frame(stream, &BackendMessage::NoData).await
            }
        }
    }
}

async fn handle_execute<S>(
    stream: &mut S,
    runtime: &RedDBRuntime,
    auth_context: Option<&PgAuthContext>,
    prepared_registry: &PreparedRegistry,
    portals: &mut HashMap<String, PgPortal>,
    msg: super::protocol::ExecuteMessage,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    let Some(portal) = portals.get_mut(&msg.portal) else {
        send_error(
            stream,
            "34000",
            &format!("portal {:?} does not exist", msg.portal),
        )
        .await?;
        return Ok(());
    };
    match prepared_registry.ddl_epoch(portal.prepared_id) {
        Some(epoch) if epoch != runtime.ddl_epoch() => {
            send_error(stream, "XX000", "prepared_needs_replan").await?;
            return Ok(());
        }
        Some(_) => {}
        None => {
            send_error(stream, "26000", "prepared statement does not exist").await?;
            return Ok(());
        }
    }
    if portal.result.is_none() {
        match execute_pg_query_result(
            runtime,
            auth_context,
            prepared_registry,
            portal.prepared_id,
            &portal.sql,
            &portal.params,
        ) {
            Ok(result) => {
                portal.result = Some(result);
                portal.row_offset = 0;
            }
            Err(err) => {
                let code = classify_sqlstate(&err);
                send_error(stream, code, &err).await?;
                return Ok(());
            }
        }
    }

    let result = portal.result.as_ref().expect("portal result populated");
    match emit_portal_execution(
        stream,
        result,
        portal.row_description_sent,
        portal.row_offset,
        msg.max_rows,
    )
    .await
    {
        Ok(PortalExecution::Complete) => {
            portal.result = None;
            portal.row_offset = 0;
            portal.row_description_sent = false;
            Ok(())
        }
        Ok(PortalExecution::Suspended { next_row_offset }) => {
            portal.row_offset = next_row_offset;
            portal.row_description_sent = true;
            Ok(())
        }
        Err(err) => {
            let code = classify_sqlstate(&err);
            send_error(stream, code, &err).await
        }
    }
}

async fn handle_close<S>(
    stream: &mut S,
    prepared_registry: &PreparedRegistry,
    prepared: &mut HashMap<String, PgPreparedStatement>,
    portals: &mut HashMap<String, PgPortal>,
    msg: super::protocol::CloseMessage,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    let prepared_id = match msg.target {
        DescribeTarget::Statement => prepared.remove(&msg.name).map(|stmt| stmt.prepared_id),
        DescribeTarget::Portal => portals.remove(&msg.name).map(|portal| portal.prepared_id),
    };
    if let Some(prepared_id) = prepared_id {
        release_prepared_if_unreferenced(prepared_registry, prepared_id, prepared, portals);
    }
    write_frame(stream, &BackendMessage::CloseComplete).await
}

fn release_prepared_if_unreferenced(
    prepared_registry: &PreparedRegistry,
    prepared_id: PreparedId,
    prepared: &HashMap<String, PgPreparedStatement>,
    portals: &HashMap<String, PgPortal>,
) {
    let statement_references_id = prepared
        .values()
        .any(|statement| statement.prepared_id == prepared_id);
    let portal_references_id = portals
        .values()
        .any(|portal| portal.prepared_id == prepared_id);
    if !statement_references_id && !portal_references_id {
        prepared_registry.release(prepared_id);
    }
}

fn bind_pg_params(
    stmt: &PgPreparedStatement,
    msg: &super::protocol::BindMessage,
) -> Result<Vec<ParamValue>, String> {
    if !matches!(msg.param_format_codes.len(), 0 | 1)
        && msg.param_format_codes.len() != msg.params.len()
    {
        return Err("Bind format count must be 0, 1, or match parameter count".to_string());
    }
    msg.params
        .iter()
        .enumerate()
        .map(|(idx, param)| {
            let oid = stmt
                .param_type_oids
                .get(idx)
                .copied()
                .unwrap_or(PgOid::Unknown.as_u32());
            let format_code = match msg.param_format_codes.as_slice() {
                [] => 0,
                [format] => *format,
                formats => formats[idx],
            };
            pg_param_to_param_value(oid, format_code, param.as_deref())
        })
        .collect()
}

fn execute_pg_query_result(
    runtime: &RedDBRuntime,
    auth_context: Option<&PgAuthContext>,
    prepared_registry: &PreparedRegistry,
    prepared_id: PreparedId,
    sql: &str,
    params: &[ParamValue],
) -> Result<crate::runtime::OwnedQueryResult, String> {
    let executor = QueryRequestExecutor::new(runtime, prepared_registry);
    let bound = executor
        .bind(QueryRequest::prepared(prepared_id, params.to_vec()))
        .map_err(|err| err.to_string())?;
    if pg_scalar_select_param_index(sql).is_some() {
        let values = params.iter().cloned().map(Value::from).collect::<Vec<_>>();
        if let Some(result) = try_execute_pg_scalar_select(sql, &values) {
            return runtime
                .own_query_result(result)
                .map_err(|error| error.to_string());
        }
    }
    if params.is_empty() {
        return match translate_pg_catalog_query(runtime, sql) {
            Ok(Some(result)) => runtime
                .own_query_result(crate::runtime::RuntimeQueryResult {
                    query: sql.to_string(),
                    mode: reddb_rql::modes::QueryMode::Sql,
                    statement: "select",
                    engine: "pg-catalog",
                    result,
                    affected_rows: 0,
                    statement_type: "select",
                    bookmark: None,
                    notice: None,
                })
                .map_err(|error| error.to_string()),
            Ok(None) => run_runtime_blocking(|| {
                execute_with_pg_auth_context(auth_context, || {
                    // Utility statements use the full dispatcher after registry validation.
                    // Their zero-parameter SQL can be reparsed without losing bindings;
                    // data queries retain the cached prepared shape on repeated Execute.
                    if matches!(
                        bound.prepared_expr(),
                        Some(
                            QueryExpr::Function(_)
                                | QueryExpr::Table(_)
                                | QueryExpr::Graph(_)
                                | QueryExpr::Path(_)
                                | QueryExpr::Join(_)
                                | QueryExpr::Vector(_)
                                | QueryExpr::Hybrid(_)
                                | QueryExpr::Insert(_)
                                | QueryExpr::Update(_)
                                | QueryExpr::Delete(_)
                                | QueryExpr::QueueCommand(_)
                                | QueryExpr::KvCommand(_)
                                | QueryExpr::SearchCommand(_)
                                | QueryExpr::Ask(_)
                        )
                    ) {
                        executor.execute_bound(bound)
                    } else {
                        runtime
                            .execute_query(sql)
                            .and_then(|result| runtime.own_query_result(result))
                    }
                })
            })
            .map_err(|err| err.to_string()),
            Err(err) => Err(err.to_string()),
        };
    }

    run_runtime_blocking(|| {
        execute_with_pg_auth_context(auth_context, || executor.execute_bound(bound))
    })
    .map_err(|err| err.to_string())
}

fn try_execute_pg_scalar_select(
    sql: &str,
    params: &[Value],
) -> Option<crate::runtime::RuntimeQueryResult> {
    let index = pg_scalar_select_param_index(sql)?;
    let value = params.get(index)?.clone();
    let mut result = UnifiedResult::with_columns(vec!["?column?".to_string()]);
    let mut record = UnifiedRecord::new();
    record.set("?column?", value);
    result.push(record);
    Some(crate::runtime::RuntimeQueryResult {
        query: sql.to_string(),
        mode: reddb_rql::modes::QueryMode::Sql,
        statement: "select",
        engine: "pg-wire",
        result,
        affected_rows: 0,
        statement_type: "select",
        bookmark: None,
        notice: None,
    })
}

fn pg_scalar_select_param_index(sql: &str) -> Option<usize> {
    let trimmed = sql.trim().trim_end_matches(';').trim();
    let lower = trimmed.to_ascii_lowercase();
    let body = lower.strip_prefix("select ")?;
    let param = if let Some(inner) = body.strip_prefix("cast(") {
        let end = inner.find(" as ")?;
        &inner[..end]
    } else {
        body.split_whitespace().next()?
    };
    let digits = param.strip_prefix('$')?;
    let n = digits.parse::<usize>().ok()?;
    n.checked_sub(1)
}

fn rewrite_pg_parameter_casts(sql: &str) -> String {
    let mut out = String::with_capacity(sql.len());
    let bytes = sql.as_bytes();
    let mut cursor = 0;
    let mut pos = 0;
    while pos < bytes.len() {
        if bytes[pos] != b'$' {
            pos += 1;
            continue;
        }
        let param_start = pos;
        pos += 1;
        let digits_start = pos;
        while pos < bytes.len() && bytes[pos].is_ascii_digit() {
            pos += 1;
        }
        if digits_start == pos {
            continue;
        }
        if pos + 2 <= bytes.len() && &bytes[pos..pos + 2] == b"::" {
            let param_end = pos;
            pos += 2;
            let type_start = pos;
            while pos < bytes.len()
                && (bytes[pos].is_ascii_alphanumeric() || matches!(bytes[pos], b'_' | b'.'))
            {
                pos += 1;
            }
            if type_start != pos {
                out.push_str(&sql[cursor..param_start]);
                out.push_str(&sql[param_start..param_end]);
                cursor = pos;
                continue;
            }
        }
    }
    out.push_str(&sql[cursor..]);
    out
}

fn infer_pg_cast_param_type_oids(sql: &str) -> Vec<(usize, u32)> {
    let mut out = Vec::new();
    let bytes = sql.as_bytes();
    let mut pos = 0;
    while pos < bytes.len() {
        if bytes[pos] != b'$' {
            pos += 1;
            continue;
        }
        pos += 1;
        let digits_start = pos;
        while pos < bytes.len() && bytes[pos].is_ascii_digit() {
            pos += 1;
        }
        if digits_start == pos {
            continue;
        }
        let Some(param_index) = sql[digits_start..pos]
            .parse::<usize>()
            .ok()
            .and_then(|idx| idx.checked_sub(1))
        else {
            continue;
        };
        if pos + 2 > bytes.len() || &bytes[pos..pos + 2] != b"::" {
            continue;
        }
        pos += 2;
        let type_start = pos;
        while pos < bytes.len()
            && (bytes[pos].is_ascii_alphanumeric() || matches!(bytes[pos], b'_' | b'.'))
        {
            pos += 1;
        }
        if type_start == pos {
            continue;
        }
        if let Some(oid) = pg_cast_type_oid(&sql[type_start..pos]) {
            out.push((param_index, oid));
        }
    }
    out
}

fn pg_cast_type_oid(ty: &str) -> Option<u32> {
    let lower = ty.to_ascii_lowercase();
    let short = lower.rsplit('.').next().unwrap_or(lower.as_str());
    let oid = match short {
        "bool" | "boolean" => PgOid::Bool,
        "int2" | "smallint" => PgOid::Int2,
        "int" | "int4" | "integer" => PgOid::Int4,
        "int8" | "bigint" => PgOid::Int8,
        "float4" | "real" => PgOid::Float4,
        "float8" | "double" | "doubleprecision" => PgOid::Float8,
        "numeric" | "decimal" => PgOid::Numeric,
        "bytea" => PgOid::Bytea,
        "json" => PgOid::Json,
        "jsonb" => PgOid::Jsonb,
        "text" => PgOid::Text,
        "varchar" | "character varying" => PgOid::Varchar,
        "uuid" => PgOid::Uuid,
        "timestamp" => PgOid::Timestamp,
        "timestamptz" | "timestampz" => PgOid::TimestampTz,
        "vector" => PgOid::Vector,
        _ => return None,
    };
    Some(oid.as_u32())
}

fn is_row_returning_query(sql: &str) -> bool {
    let trimmed = sql.trim_start().to_ascii_lowercase();
    trimmed.starts_with("select")
        || trimmed.starts_with("with")
        || trimmed.starts_with("ask")
        || trimmed.starts_with("search")
        || trimmed.starts_with("vector")
        || trimmed.starts_with("hybrid")
}

fn is_ask_query(sql: &str) -> bool {
    sql.trim_start().to_ascii_lowercase().starts_with("ask")
}

/// Drive the PG-Wire authentication handshake after a `StartupMessage`.
///
/// Posture:
///   * Auth store enabled → request `AuthenticationCleartextPassword`,
///     read the client's `PasswordMessage`, and verify it against the same
///     auth store the native transports use. Success installs the resolved
///     identity; failure emits `28P01` and closes the socket.
///   * No auth store enabled + loopback bind → legacy trust: send
///     `AuthenticationOk` with no credentials required (`None` context).
///   * No auth store enabled + non-loopback bind → refuse with `28P01`;
///     an unconfigured listener must never grant unauthenticated access
///     off loopback.
///
/// TLS posture: a cleartext password may only cross an *unencrypted* link
/// on a loopback bind. On a non-loopback bind we refuse to even challenge
/// for a password unless the connection is already over TLS (`over_tls`),
/// so a client using `sslmode=disable` against a remote listener never
/// leaks its password in the clear. Loopback and TLS connections are
/// challenged as before.
///
/// Returns `Ok(Some(context))` once the connection is ready for queries
/// (`context` is `None` for trust connections), or `Ok(None)` when
/// authentication failed and the error frame has already been sent.
///
/// Failures give the same `28P01` "password authentication failed" for a
/// wrong password and a missing user, so there is no user-existence oracle.
async fn authenticate_startup<S>(
    stream: &mut S,
    runtime: &RedDBRuntime,
    config: &PgWireConfig,
    over_tls: bool,
    params: &super::protocol::StartupParams,
) -> Result<Option<Option<PgAuthContext>>, PgWireError>
where
    S: AsyncRead + AsyncWrite + Unpin,
{
    let auth_store = runtime.auth_store().filter(|store| store.is_enabled());
    let Some(auth_store) = auth_store else {
        // No credentials configured: trust survives for loopback only.
        if is_loopback_bind(&config.bind_addr) {
            send_startup_ready(stream, config, params).await?;
            return Ok(Some(None));
        }
        send_error(stream, "28P01", "password authentication failed").await?;
        return Ok(None);
    };

    // Refuse to challenge for a cleartext password over an unencrypted
    // non-loopback link: it would traverse the network in the clear.
    // Clients must connect with `sslmode=require` (TLS) to authenticate
    // against a remote bind.
    if !over_tls && !is_loopback_bind(&config.bind_addr) {
        send_error(
            stream,
            "28000",
            "cleartext password authentication requires TLS on non-loopback binds",
        )
        .await?;
        return Ok(None);
    }

    write_frame(stream, &BackendMessage::AuthenticationCleartextPassword).await?;
    let password = match read_frame(stream).await? {
        FrontendMessage::PasswordMessage(payload) => password_from_message(&payload),
        // Anything other than a PasswordMessage is a protocol violation
        // here; treat it as an auth failure rather than leaking detail.
        _ => None,
    };
    let username = params.get("user").unwrap_or("");
    let tenant = params.get("tenant");
    let Some(password) = password else {
        send_error(stream, "28P01", "password authentication failed").await?;
        return Ok(None);
    };
    // A missing user and a wrong password both surface as the same error
    // class below — no user-existence oracle leaks over the wire.
    let session = match auth_store.authenticate_in_tenant(tenant, username, &password) {
        Ok(session) => session,
        Err(_) => {
            send_error(stream, "28P01", "password authentication failed").await?;
            return Ok(None);
        }
    };

    send_startup_ready(stream, config, params).await?;
    Ok(Some(Some(PgAuthContext {
        username: session.username,
        role: session.role,
        tenant: session.tenant_id,
    })))
}

async fn send_startup_ready<S>(
    stream: &mut S,
    config: &PgWireConfig,
    params: &super::protocol::StartupParams,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    // Authentication has succeeded (or trust applies): signal AuthenticationOk.
    write_frame(stream, &BackendMessage::AuthenticationOk).await?;

    // Standard ParameterStatus frames. Drivers gate capabilities on these.
    for (name, value) in [
        ("server_version", config.server_version.as_str()),
        ("server_encoding", "UTF8"),
        ("client_encoding", "UTF8"),
        ("DateStyle", "ISO, MDY"),
        ("TimeZone", "UTC"),
        ("integer_datetimes", "on"),
        ("standard_conforming_strings", "on"),
        (
            "application_name",
            params.get("application_name").unwrap_or(""),
        ),
    ] {
        write_frame(
            stream,
            &BackendMessage::ParameterStatus {
                name: name.to_string(),
                value: value.to_string(),
            },
        )
        .await?;
    }

    // BackendKeyData: (pid, secret_key). CancelRequest is not honoured
    // yet, but the key is what a future cancel path authenticates on, so
    // it is random per connection rather than a constant a client could
    // learn once and reuse against every session.
    write_frame(
        stream,
        &BackendMessage::BackendKeyData {
            pid: std::process::id(),
            key: random_cancel_key(),
        },
    )
    .await?;

    write_frame(
        stream,
        &BackendMessage::ReadyForQuery(TransactionStatus::Idle),
    )
    .await?;
    Ok(())
}

async fn handle_simple_query<S>(
    stream: &mut S,
    runtime: &RedDBRuntime,
    auth_context: Option<&PgAuthContext>,
    sql: &str,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    // Empty query convention: PG emits EmptyQueryResponse instead of a
    // CommandComplete. Some clients (psql `\;`) rely on this.
    if sql.trim().is_empty() {
        write_frame(stream, &BackendMessage::EmptyQueryResponse).await?;
        write_frame(
            stream,
            &BackendMessage::ReadyForQuery(TransactionStatus::Idle),
        )
        .await?;
        return Ok(());
    }

    if let Some(tag) = pg_session_compat_command_tag(sql) {
        write_frame(stream, &BackendMessage::CommandComplete(tag.to_string())).await?;
        write_frame(
            stream,
            &BackendMessage::ReadyForQuery(TransactionStatus::Idle),
        )
        .await?;
        return Ok(());
    }

    let query_result = match translate_pg_catalog_query(runtime, sql) {
        Ok(Some(result)) => runtime.own_query_result(crate::runtime::RuntimeQueryResult {
            query: sql.to_string(),
            mode: reddb_rql::modes::QueryMode::Sql,
            statement: "select",
            engine: "pg-catalog",
            result,
            affected_rows: 0,
            statement_type: "select",
            bookmark: None,
            notice: None,
        }),
        Ok(None) => run_runtime_blocking(|| {
            execute_with_pg_auth_context(auth_context, || {
                runtime
                    .execute_query(sql)
                    .and_then(|result| runtime.own_query_result(result))
            })
        }),
        Err(err) => Err(err),
    };

    match query_result {
        Ok(result) => {
            emit_success_result(stream, &result).await?;
        }
        Err(err) => {
            // PG SQLSTATE class 42 covers syntax / binding errors; we use
            // 42P01 (undefined_table) and 42601 (syntax_error) when we can
            // detect; otherwise fall back to XX000 (internal error).
            let code = classify_sqlstate(&err.to_string());
            send_error(stream, code, &crate::api::client_facing_message(&err)).await?;
        }
    }

    write_frame(
        stream,
        &BackendMessage::ReadyForQuery(TransactionStatus::Idle),
    )
    .await?;
    Ok(())
}

fn pg_session_compat_command_tag(sql: &str) -> Option<&'static str> {
    let lower = sql.trim().trim_end_matches(';').to_ascii_lowercase();
    if lower.starts_with("set ") {
        return Some("SET");
    }
    None
}

async fn emit_success_result<S>(
    stream: &mut S,
    result: &crate::runtime::RuntimeQueryResult,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    if result.statement == "ask" {
        emit_ask_result_row(stream, result).await?;
        write_frame(
            stream,
            &BackendMessage::CommandComplete("SELECT 1".to_string()),
        )
        .await?;
    } else if result_returns_rows(result) {
        emit_result_rows(stream, &result.result).await?;
        write_frame(
            stream,
            &BackendMessage::CommandComplete(format!("SELECT {}", result.result.records.len())),
        )
        .await?;
    } else {
        // DDL / DML / config statements: echo the runtime's
        // high-level statement tag back. PG format is
        // "<CMD> [<OID>] <COUNT>"; we keep the count where
        // applicable and fall back to the runtime's message.
        let tag = match result.statement_type {
            "insert" => format!("INSERT 0 {}", result.affected_rows),
            "update" => format!("UPDATE {}", result.affected_rows),
            "delete" => format!("DELETE {}", result.affected_rows),
            other => other.to_uppercase(),
        };
        write_frame(stream, &BackendMessage::CommandComplete(tag)).await?;
    }
    Ok(())
}

async fn emit_success_result_without_row_description<S>(
    stream: &mut S,
    result: &crate::runtime::RuntimeQueryResult,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    if result.statement == "ask" {
        let row = ask_query_result_to_pg_wire_row(result)
            .ok_or_else(|| PgWireError::Protocol("ASK result missing row body".to_string()))?;
        write_frame(stream, &BackendMessage::DataRow(row.cells)).await?;
        write_frame(
            stream,
            &BackendMessage::CommandComplete("SELECT 1".to_string()),
        )
        .await?;
    } else if result_returns_rows(result) {
        emit_result_data_rows(stream, &result.result).await?;
        write_frame(
            stream,
            &BackendMessage::CommandComplete(format!("SELECT {}", result.result.records.len())),
        )
        .await?;
    } else {
        let tag = match result.statement_type {
            "insert" => format!("INSERT 0 {}", result.affected_rows),
            "update" => format!("UPDATE {}", result.affected_rows),
            "delete" => format!("DELETE {}", result.affected_rows),
            other => other.to_uppercase(),
        };
        write_frame(stream, &BackendMessage::CommandComplete(tag)).await?;
    }
    Ok(())
}

enum PortalExecution {
    Complete,
    Suspended { next_row_offset: usize },
}

async fn emit_portal_execution<S>(
    stream: &mut S,
    result: &crate::runtime::RuntimeQueryResult,
    row_description_sent: bool,
    row_offset: usize,
    max_rows: u32,
) -> Result<PortalExecution, String>
where
    S: AsyncWrite + Unpin,
{
    if result.statement == "ask" && row_description_sent {
        emit_success_result_without_row_description(stream, result)
            .await
            .map_err(|err| err.to_string())?;
        Ok(PortalExecution::Complete)
    } else if result.statement == "ask" {
        emit_success_result(stream, result)
            .await
            .map_err(|err| err.to_string())?;
        Ok(PortalExecution::Complete)
    } else if result_returns_rows(result) {
        emit_row_returning_portal_execution(
            stream,
            result,
            row_description_sent,
            row_offset,
            max_rows,
        )
        .await
    } else if row_description_sent {
        emit_success_result_without_row_description(stream, result)
            .await
            .map_err(|err| err.to_string())?;
        Ok(PortalExecution::Complete)
    } else {
        emit_success_result(stream, result)
            .await
            .map_err(|err| err.to_string())?;
        Ok(PortalExecution::Complete)
    }
}

async fn emit_row_returning_portal_execution<S>(
    stream: &mut S,
    result: &crate::runtime::RuntimeQueryResult,
    row_description_sent: bool,
    row_offset: usize,
    max_rows: u32,
) -> Result<PortalExecution, String>
where
    S: AsyncWrite + Unpin,
{
    if !row_description_sent {
        emit_result_row_description(stream, &result.result)
            .await
            .map_err(|err| err.to_string())?;
    }

    let total_rows = result.result.records.len();
    let remaining_rows = total_rows.saturating_sub(row_offset);
    let rows_to_emit = if max_rows == 0 {
        remaining_rows
    } else {
        remaining_rows.min(max_rows as usize)
    };
    emit_result_data_rows_range(stream, &result.result, row_offset, rows_to_emit)
        .await
        .map_err(|err| err.to_string())?;

    let next_row_offset = row_offset + rows_to_emit;
    if next_row_offset < total_rows {
        write_frame(stream, &BackendMessage::PortalSuspended)
            .await
            .map_err(|err| err.to_string())?;
        Ok(PortalExecution::Suspended { next_row_offset })
    } else {
        write_frame(
            stream,
            &BackendMessage::CommandComplete(format!("SELECT {}", total_rows)),
        )
        .await
        .map_err(|err| err.to_string())?;
        Ok(PortalExecution::Complete)
    }
}

async fn emit_row_description_for_result<S>(
    stream: &mut S,
    result: &crate::runtime::RuntimeQueryResult,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    if result.statement == "ask" {
        emit_ask_row_description(stream).await
    } else if result_returns_rows(result) {
        emit_result_row_description(stream, &result.result).await
    } else {
        write_frame(stream, &BackendMessage::NoData).await
    }
}

fn result_returns_rows(result: &crate::runtime::RuntimeQueryResult) -> bool {
    result.statement_type == "select"
}

async fn emit_result_rows<S>(
    stream: &mut S,
    result: &crate::storage::query::unified::UnifiedResult,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    emit_result_row_description(stream, result).await?;
    emit_result_data_rows(stream, result).await
}

async fn emit_result_row_description<S>(
    stream: &mut S,
    result: &crate::storage::query::unified::UnifiedResult,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    // RowDescription: derived from the first record's column ordering.
    // When `result.columns` is non-empty we honour that order; otherwise
    // we synthesise one from the record's field order.
    let columns: Vec<String> = if !result.columns.is_empty() {
        result.columns.clone()
    } else if let Some(first) = result.records.first() {
        record_field_names(first)
    } else {
        Vec::new()
    };

    // Peek at the first record for per-column type OIDs. When there's no
    // data row we fall back to TEXT for every column — clients render
    // empty result sets happily.
    let type_oids: Vec<PgOid> = columns
        .iter()
        .map(|col| {
            result
                .records
                .first()
                .and_then(|r| record_get(r, col))
                .map(PgOid::from_value)
                .unwrap_or(PgOid::Text)
        })
        .collect();

    let descriptors: Vec<ColumnDescriptor> = columns
        .iter()
        .zip(type_oids.iter())
        .map(|(name, oid)| ColumnDescriptor {
            name: name.clone(),
            table_oid: 0,
            column_attr: 0,
            type_oid: oid.as_u32(),
            type_size: -1,
            type_mod: -1,
            format: 0,
        })
        .collect();

    write_frame(stream, &BackendMessage::RowDescription(descriptors)).await
}

async fn emit_result_data_rows<S>(
    stream: &mut S,
    result: &crate::storage::query::unified::UnifiedResult,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    emit_result_data_rows_range(stream, result, 0, result.records.len()).await
}

async fn emit_result_data_rows_range<S>(
    stream: &mut S,
    result: &crate::storage::query::unified::UnifiedResult,
    row_offset: usize,
    row_count: usize,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    let columns: Vec<String> = if !result.columns.is_empty() {
        result.columns.clone()
    } else if let Some(first) = result.records.first() {
        record_field_names(first)
    } else {
        Vec::new()
    };
    for record in result.records.iter().skip(row_offset).take(row_count) {
        let fields: Vec<Option<Vec<u8>>> = columns
            .iter()
            .map(|col| record_get(record, col).and_then(value_to_pg_wire_bytes))
            .collect();
        write_frame(stream, &BackendMessage::DataRow(fields)).await?;
    }

    Ok(())
}

async fn emit_ask_result_row<S>(
    stream: &mut S,
    result: &crate::runtime::RuntimeQueryResult,
) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    let row = ask_query_result_to_pg_wire_row(result)
        .ok_or_else(|| PgWireError::Protocol("ASK result missing row body".to_string()))?;

    emit_ask_row_description(stream).await?;
    write_frame(stream, &BackendMessage::DataRow(row.cells)).await?;
    Ok(())
}

async fn emit_ask_row_description<S>(stream: &mut S) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    let descriptors: Vec<ColumnDescriptor> = crate::runtime::ai::pg_wire_ask_row_encoder::columns()
        .iter()
        .map(|col| ColumnDescriptor {
            name: col.name.to_string(),
            table_oid: 0,
            column_attr: 0,
            type_oid: col.oid.as_u32(),
            type_size: -1,
            type_mod: -1,
            format: 0,
        })
        .collect();
    write_frame(stream, &BackendMessage::RowDescription(descriptors)).await
}

fn ask_query_result_to_pg_wire_row(
    result: &crate::runtime::RuntimeQueryResult,
) -> Option<crate::runtime::ai::pg_wire_ask_row_encoder::AskRow> {
    if result.statement != "ask" {
        return None;
    }
    let ask = crate::presentation::query_result::ask_result_from_unified_result(&result.result)?;

    Some(crate::runtime::ai::pg_wire_ask_row_encoder::encode(&ask))
}

/// Best-effort field lookup on a `UnifiedRecord`. The record API lives in
/// `storage::query::unified` and today uses `HashMap<String, Value>` under
/// the hood — we use `get` if it exists, else fall back to serialised map.
fn record_get<'a>(record: &'a UnifiedRecord, key: &str) -> Option<&'a Value> {
    record.get(key)
}

/// Extract column names in iteration order from a single record. When
/// the caller didn't supply an explicit `columns` projection we use the
/// first record's field ordering as the canonical tuple shape.
///
/// HashMap iteration order is non-deterministic — for Phase 3.1 we
/// accept the shuffle since PG clients receive the ordered header via
/// RowDescription and match cells positionally. A stable ordering
/// would require keeping an insertion-order index alongside `values`.
fn record_field_names(record: &UnifiedRecord) -> Vec<String> {
    // `column_names()` merges the columnar scan side-channel with
    // the HashMap so scan rows (which populate only columnar) still
    // surface their field names in PG wire output.
    record
        .column_names()
        .into_iter()
        .map(|k| k.to_string())
        .collect()
}

async fn send_error<S>(stream: &mut S, code: &str, message: &str) -> Result<(), PgWireError>
where
    S: AsyncWrite + Unpin,
{
    write_frame(
        stream,
        &BackendMessage::ErrorResponse {
            severity: "ERROR".to_string(),
            code: code.to_string(),
            message: message.to_string(),
        },
    )
    .await
}

/// Heuristically map a runtime error message onto a PG SQLSTATE. Full
/// coverage would map every `RedDBError` variant; this is enough for the
/// common psql / JDBC paths.
fn classify_sqlstate(msg: &str) -> &'static str {
    let lower = msg.to_ascii_lowercase();
    if lower.contains("not found") || lower.contains("does not exist") {
        // 42P01 undefined_table; close enough for collection-not-found.
        "42P01"
    } else if lower.contains("parse") || lower.contains("expected") || lower.contains("syntax") {
        "42601"
    } else if lower.contains("already exists") {
        "42P07"
    } else if lower.contains("permission") || lower.contains("auth") {
        "28000"
    } else {
        "XX000"
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::api::RedDBOptions;
    use crate::auth::{AuthConfig, AuthStore};
    use crate::runtime::RuntimeQueryResult;
    use crate::storage::query::unified::UnifiedResult;
    use reddb_rql::modes::QueryMode;
    use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};

    #[tokio::test]
    async fn response_writer_releases_execution_slot_before_socket_write() {
        let runtime = RedDBRuntime::with_options(RedDBOptions::in_memory()).unwrap();
        runtime.configure_execution_admission(1, 0, 100);
        let admission = runtime.execution_admission();
        let permit = admission.acquire().await.expect("execution permit");
        assert_eq!(admission.active(), 1);

        let (mut server_io, mut client_io) = tokio::io::duplex(64);
        let mut writer = ExecutionResponseWriter::new(&mut server_io, Some(permit));
        writer.write_all(b"ok").await.unwrap();
        assert_eq!(admission.active(), 0);

        let mut received = [0_u8; 2];
        client_io.read_exact(&mut received).await.unwrap();
        assert_eq!(&received, b"ok");
    }

    #[tokio::test]
    async fn enabled_auth_store_rejects_bad_pgwire_password_with_28p01() {
        let runtime = Arc::new(RedDBRuntime::with_options(RedDBOptions::in_memory()).unwrap());
        let auth = Arc::new(AuthStore::new(AuthConfig {
            enabled: true,
            require_auth: true,
            ..AuthConfig::default()
        }));
        auth.create_user("alice", "secret", Role::Write).unwrap();
        runtime.set_auth_store(auth);

        let config = Arc::new(PgWireConfig::default());
        let (server_io, mut client_io) = tokio::io::duplex(64 * 1024);
        let server = tokio::spawn(async move {
            handle_connection(server_io, runtime, config, None)
                .await
                .unwrap();
        });

        write_startup_params(&mut client_io, &[("user", "alice")]).await;
        // Server must challenge for a cleartext password first.
        let (tag, body) = read_backend_frame(&mut client_io).await;
        assert_eq!(tag, b'R');
        assert_eq!(i32::from_be_bytes(body[..4].try_into().unwrap()), 3);

        write_frontend_frame(&mut client_io, b'p', cstring_body("wrong")).await;
        let (tag, body) = read_backend_frame(&mut client_io).await;
        assert_eq!(tag, b'E');
        assert_eq!(error_response_field(&body, b'C'), Some("28P01"));

        // The connection is closed after an auth failure.
        let mut eof = [0u8; 1];
        assert_eq!(client_io.read(&mut eof).await.unwrap(), 0);
        server.await.unwrap();
    }

    #[tokio::test]
    async fn pgwire_password_auth_installs_statement_identity() {
        let runtime = Arc::new(RedDBRuntime::with_options(RedDBOptions::in_memory()).unwrap());
        let auth = Arc::new(AuthStore::new(AuthConfig {
            enabled: true,
            require_auth: true,
            ..AuthConfig::default()
        }));
        auth.create_user_in_tenant(Some("acme"), "alice", "secret", Role::Write)
            .unwrap();
        runtime.set_auth_store(auth);

        let config = Arc::new(PgWireConfig::default());
        let (server_io, mut client_io) = tokio::io::duplex(64 * 1024);
        let server = tokio::spawn(async move {
            handle_connection(server_io, runtime, config, None)
                .await
                .unwrap();
        });

        write_startup_params(&mut client_io, &[("user", "alice"), ("tenant", "acme")]).await;
        let (tag, body) = read_backend_frame(&mut client_io).await;
        assert_eq!(tag, b'R');
        assert_eq!(i32::from_be_bytes(body[..4].try_into().unwrap()), 3);
        write_frontend_frame(&mut client_io, b'p', cstring_body("secret")).await;
        read_until_ready(&mut client_io).await;

        // The authenticated identity must drive CURRENT_USER/ROLE/TENANT so
        // the simple-query path yields real rows (T,D,C,Z), transport-
        // invariant with the native wire.
        write_frontend_frame(
            &mut client_io,
            b'Q',
            cstring_body("SELECT CURRENT_USER(), CURRENT_ROLE(), CURRENT_TENANT()"),
        )
        .await;
        let frames = read_until_ready(&mut client_io).await;
        assert_eq!(
            frames.iter().map(|(tag, _)| *tag).collect::<Vec<_>>(),
            b"TDCZ"
        );
        let cells = decode_data_row(&frames[1].1);
        assert_eq!(cells[0].as_deref(), Some(b"alice".as_slice()));
        assert_eq!(cells[1].as_deref(), Some(b"write".as_slice()));
        assert_eq!(cells[2].as_deref(), Some(b"acme".as_slice()));

        write_frontend_frame(&mut client_io, b'X', Vec::new()).await;
        server.await.unwrap();
    }

    #[tokio::test]
    async fn extended_parse_bind_execute_returns_rows() {
        let runtime = Arc::new(RedDBRuntime::with_options(RedDBOptions::in_memory()).unwrap());
        let config = Arc::new(PgWireConfig::default());
        let (server_io, mut client_io) = tokio::io::duplex(64 * 1024);
        let server = tokio::spawn(async move {
            handle_connection(server_io, runtime, config, None)
                .await
                .unwrap();
        });

        write_startup(&mut client_io).await;
        read_until_ready(&mut client_io).await;

        write_frontend_frame(
            &mut client_io,
            b'P',
            parse_body("", "SELECT $1::int", &[PgOid::Int4.as_u32()]),
        )
        .await;
        write_frontend_frame(
            &mut client_io,
            b'B',
            bind_body("", "", &[0], &[Some(b"42".as_slice())], &[]),
        )
        .await;
        write_frontend_frame(&mut client_io, b'D', describe_body(b'P', "")).await;
        write_frontend_frame(&mut client_io, b'E', execute_body("", 0)).await;
        write_frontend_frame(&mut client_io, b'S', Vec::new()).await;

        let frames = read_until_ready(&mut client_io).await;
        assert_eq!(
            frames.iter().map(|(tag, _)| *tag).collect::<Vec<_>>(),
            b"12TDCZ"
        );
        let columns = decode_row_description(&frames[2].1);
        assert_eq!(columns.len(), 1);
        let cells = decode_data_row(&frames[3].1);
        assert_eq!(cells.len(), 1);
        assert_eq!(cells[0].as_deref(), Some(b"42".as_slice()));
        assert_eq!(decode_command_complete(&frames[4].1), "SELECT 1");

        write_frontend_frame(&mut client_io, b'X', Vec::new()).await;
        server.await.unwrap();
    }

    #[test]
    fn prepared_pg_utility_statements_preserve_ddl_and_transactions() {
        let runtime = RedDBRuntime::in_memory().expect("runtime");
        let registry = PreparedRegistry::new();
        let execute = |sql: &str, params: Vec<ParamValue>| {
            let prepared = registry
                .prepare(&runtime, sql)
                .expect("prepare utility or DML");
            execute_pg_query_result(&runtime, None, &registry, prepared.id, sql, &params)
                .unwrap_or_else(|error| panic!("{sql}: {error}"))
        };
        execute("CREATE TABLE pg_utilities (id INT)", Vec::new());
        execute("BEGIN", Vec::new());
        execute(
            "INSERT INTO pg_utilities (id) VALUES ($1)",
            vec![ParamValue::Int64(1)],
        );
        execute("SAVEPOINT before_second", Vec::new());
        execute(
            "INSERT INTO pg_utilities (id) VALUES ($1)",
            vec![ParamValue::Int64(2)],
        );
        execute("ROLLBACK TO SAVEPOINT before_second", Vec::new());
        execute("COMMIT", Vec::new());
        let result = execute("SELECT id FROM pg_utilities", Vec::new());
        assert_eq!(result.result.records.len(), 1);
        assert_eq!(result.result.records[0].get("id"), Some(&Value::Integer(1)));
        execute("DROP TABLE pg_utilities", Vec::new());
        assert!(runtime
            .db()
            .store()
            .get_collection("pg_utilities")
            .is_none());
    }

    #[tokio::test]
    async fn extended_repeated_execute_parses_prepared_shape_once() {
        let runtime = RedDBRuntime::with_options(RedDBOptions::in_memory()).unwrap();
        runtime
            .execute_query("CREATE TABLE pg_parse_once (id INT)")
            .unwrap();
        runtime
            .execute_query("INSERT INTO pg_parse_once (id) VALUES (42)")
            .unwrap();
        let prepared_registry = PreparedRegistry::new();
        let mut prepared = HashMap::new();
        let mut portals = HashMap::new();
        let (mut server_io, _client_io) = tokio::io::duplex(64 * 1024);

        handle_parse(
            &mut server_io,
            &runtime,
            &prepared_registry,
            &mut prepared,
            &portals,
            super::super::protocol::ParseMessage {
                statement: "parse_once_stmt".to_string(),
                query: "SELECT id FROM pg_parse_once WHERE id = $1".to_string(),
                param_type_oids: vec![PgOid::Int4.as_u32()],
            },
        )
        .await
        .unwrap();
        assert_eq!(prepared_registry.parse_count(), 1);

        handle_bind(
            &mut server_io,
            &prepared_registry,
            &prepared,
            &mut portals,
            super::super::protocol::BindMessage {
                portal: "parse_once_portal".to_string(),
                statement: "parse_once_stmt".to_string(),
                param_format_codes: vec![0],
                params: vec![Some(b"42".to_vec())],
                result_format_codes: Vec::new(),
            },
        )
        .await
        .unwrap();

        for _ in 0..2 {
            handle_execute(
                &mut server_io,
                &runtime,
                None,
                &prepared_registry,
                &mut portals,
                super::super::protocol::ExecuteMessage {
                    portal: "parse_once_portal".to_string(),
                    max_rows: 0,
                },
            )
            .await
            .unwrap();
        }
        assert_eq!(prepared_registry.parse_count(), 1);
    }

    #[tokio::test]
    async fn non_loopback_plaintext_refuses_cleartext_password_without_tls() {
        // Posture (issue #1653): a cleartext password may not be challenged
        // over an unencrypted non-loopback link. The server must refuse
        // *before* sending AuthenticationCleartextPassword, so a driver
        // using sslmode=disable against a remote bind never leaks its
        // password in the clear. `tls_acceptor = None` + no SSLRequest is
        // exactly that plaintext, no-TLS path.
        let runtime = Arc::new(RedDBRuntime::with_options(RedDBOptions::in_memory()).unwrap());
        let auth = Arc::new(AuthStore::new(AuthConfig {
            enabled: true,
            require_auth: true,
            ..AuthConfig::default()
        }));
        auth.create_user("alice", "secret", Role::Write).unwrap();
        runtime.set_auth_store(auth);

        // Non-loopback bind: the wildcard address is not a loopback host.
        let config = Arc::new(PgWireConfig {
            bind_addr: "0.0.0.0:5432".to_string(),
            ..PgWireConfig::default()
        });
        let (server_io, mut client_io) = tokio::io::duplex(64 * 1024);
        let server = tokio::spawn(async move {
            handle_connection(server_io, runtime, config, None)
                .await
                .unwrap();
        });

        write_startup_params(&mut client_io, &[("user", "alice")]).await;
        // The refusal arrives directly — never an 'R' cleartext challenge.
        let (tag, body) = read_backend_frame(&mut client_io).await;
        assert_eq!(tag, b'E', "expected an ErrorResponse, not a challenge");
        assert_eq!(error_response_field(&body, b'C'), Some("28000"));

        // The connection is closed after the refusal.
        let mut eof = [0u8; 1];
        assert_eq!(client_io.read(&mut eof).await.unwrap(), 0);
        server.await.unwrap();
    }

    #[test]
    fn infer_pg_cast_param_type_oids_from_parameter_casts() {
        assert_eq!(
            infer_pg_cast_param_type_oids("INSERT INTO t (id, name) VALUES ($1::int, $2::text)"),
            vec![(0, PgOid::Int4.as_u32()), (1, PgOid::Text.as_u32())]
        );
        assert_eq!(
            infer_pg_cast_param_type_oids("SEARCH SIMILAR [1.0] COLLECTION v LIMIT $1::int8"),
            vec![(0, PgOid::Int8.as_u32())]
        );
    }

    #[test]
    fn pg_session_compat_accepts_driver_setup_set_commands() {
        assert_eq!(
            pg_session_compat_command_tag("SET extra_float_digits = 3"),
            Some("SET")
        );
        assert_eq!(
            pg_session_compat_command_tag("SET application_name = 'pgjdbc'"),
            Some("SET")
        );
        assert_eq!(pg_session_compat_command_tag("SELECT 1"), None);
    }

    #[tokio::test]
    async fn ask_success_result_uses_canonical_pg_wire_row_shape() {
        let mut result = UnifiedResult::with_columns(vec![
            "answer".into(),
            "provider".into(),
            "model".into(),
            "prompt_tokens".into(),
            "completion_tokens".into(),
            "sources_count".into(),
            "sources_flat".into(),
            "citations".into(),
            "validation".into(),
        ]);
        let mut record = UnifiedRecord::new();
        record.set("answer", Value::text("Deploy failed [^1]."));
        record.set("provider", Value::text("openai"));
        record.set("model", Value::text("gpt-4o-mini"));
        record.set("prompt_tokens", Value::Integer(11));
        record.set("completion_tokens", Value::Integer(7));
        record.set(
            "sources_flat",
            Value::Json(
                br#"[{"urn":"urn:reddb:row:deployments:1","kind":"row","collection":"deployments","id":"1"}]"#
                    .to_vec(),
            ),
        );
        record.set(
            "citations",
            Value::Json(br#"[{"marker":1,"urn":"urn:reddb:row:deployments:1"}]"#.to_vec()),
        );
        record.set(
            "validation",
            Value::Json(br#"{"ok":true,"warnings":[],"errors":[]}"#.to_vec()),
        );
        result.push(record);

        let qr = RuntimeQueryResult {
            query: "ASK 'why did deploy fail?'".to_string(),
            mode: QueryMode::Sql,
            statement: "ask",
            engine: "runtime-ai",
            result,
            affected_rows: 0,
            statement_type: "select",
            bookmark: None,
            notice: None,
        };

        let mut out = Vec::new();
        emit_success_result(&mut out, &qr).await.unwrap();
        let frames = decode_frames(&out);

        assert_eq!(
            frames.iter().map(|(tag, _)| *tag).collect::<Vec<_>>(),
            b"TDC"
        );

        let columns = decode_row_description(frames[0].1);
        assert_eq!(
            columns,
            vec![
                ("answer".to_string(), PgOid::Text.as_u32()),
                ("cache_hit".to_string(), PgOid::Bool.as_u32()),
                ("citations".to_string(), PgOid::Jsonb.as_u32()),
                ("completion_tokens".to_string(), PgOid::Int8.as_u32()),
                ("cost_usd".to_string(), PgOid::Numeric.as_u32()),
                ("mode".to_string(), PgOid::Text.as_u32()),
                ("model".to_string(), PgOid::Text.as_u32()),
                ("prompt_tokens".to_string(), PgOid::Int8.as_u32()),
                ("provider".to_string(), PgOid::Text.as_u32()),
                ("retry_count".to_string(), PgOid::Int8.as_u32()),
                ("sources_flat".to_string(), PgOid::Jsonb.as_u32()),
                ("validation".to_string(), PgOid::Jsonb.as_u32()),
            ]
        );

        let cells = decode_data_row(frames[1].1);
        assert_eq!(cells.len(), 12);
        assert_eq!(cells[0].as_deref(), Some(b"Deploy failed [^1].".as_slice()));
        assert_eq!(cells[1].as_deref(), Some(b"f".as_slice()));
        assert_eq!(cells[4].as_deref(), Some(b"0".as_slice()));
        assert_eq!(cells[5].as_deref(), Some(b"strict".as_slice()));
        assert_eq!(cells[9].as_deref(), Some(b"0".as_slice()));
        assert!(std::str::from_utf8(cells[10].as_deref().unwrap())
            .unwrap()
            .contains(r#""payload""#));
        assert_eq!(decode_command_complete(frames[2].1), "SELECT 1");
    }

    fn decode_frames(bytes: &[u8]) -> Vec<(u8, &[u8])> {
        let mut pos = 0;
        let mut frames = Vec::new();
        while pos < bytes.len() {
            let tag = bytes[pos];
            let len = u32::from_be_bytes([
                bytes[pos + 1],
                bytes[pos + 2],
                bytes[pos + 3],
                bytes[pos + 4],
            ]) as usize;
            let body_start = pos + 5;
            let body_end = pos + 1 + len;
            frames.push((tag, &bytes[body_start..body_end]));
            pos = body_end;
        }
        frames
    }

    fn decode_row_description(body: &[u8]) -> Vec<(String, u32)> {
        let count = i16::from_be_bytes([body[0], body[1]]) as usize;
        let mut pos = 2;
        let mut columns = Vec::with_capacity(count);
        for _ in 0..count {
            let end = body[pos..].iter().position(|&b| b == 0).unwrap() + pos;
            let name = std::str::from_utf8(&body[pos..end]).unwrap().to_string();
            pos = end + 1;
            pos += 4; // table oid
            pos += 2; // column attr
            let oid = u32::from_be_bytes([body[pos], body[pos + 1], body[pos + 2], body[pos + 3]]);
            pos += 4;
            pos += 2; // type size
            pos += 4; // type mod
            pos += 2; // format
            columns.push((name, oid));
        }
        columns
    }

    fn decode_data_row(body: &[u8]) -> Vec<Option<Vec<u8>>> {
        let count = i16::from_be_bytes([body[0], body[1]]) as usize;
        let mut pos = 2;
        let mut cells = Vec::with_capacity(count);
        for _ in 0..count {
            let len = i32::from_be_bytes([body[pos], body[pos + 1], body[pos + 2], body[pos + 3]]);
            pos += 4;
            if len < 0 {
                cells.push(None);
            } else {
                let len = len as usize;
                cells.push(Some(body[pos..pos + len].to_vec()));
                pos += len;
            }
        }
        cells
    }

    fn decode_command_complete(body: &[u8]) -> &str {
        let nul = body.iter().position(|&b| b == 0).unwrap_or(body.len());
        std::str::from_utf8(&body[..nul]).unwrap()
    }

    async fn write_startup<W: AsyncWrite + Unpin>(stream: &mut W) {
        write_startup_params(stream, &[("user", "reddb")]).await;
    }

    async fn write_startup_params<W: AsyncWrite + Unpin>(stream: &mut W, params: &[(&str, &str)]) {
        let mut payload = Vec::new();
        payload.extend_from_slice(&crate::wire::postgres::protocol::PG_PROTOCOL_V3.to_be_bytes());
        for (name, value) in params {
            push_pg_cstring(&mut payload, name);
            push_pg_cstring(&mut payload, value);
        }
        payload.push(0);
        let len = (payload.len() + 4) as u32;
        stream.write_all(&len.to_be_bytes()).await.unwrap();
        stream.write_all(&payload).await.unwrap();
    }

    fn cstring_body(value: &str) -> Vec<u8> {
        let mut out = Vec::new();
        push_pg_cstring(&mut out, value);
        out
    }

    fn error_response_field(body: &[u8], field_tag: u8) -> Option<&str> {
        let mut pos = 0;
        while pos < body.len() && body[pos] != 0 {
            let tag = body[pos];
            pos += 1;
            let end = body[pos..].iter().position(|&b| b == 0)? + pos;
            if tag == field_tag {
                return std::str::from_utf8(&body[pos..end]).ok();
            }
            pos = end + 1;
        }
        None
    }

    async fn write_frontend_frame<W: AsyncWrite + Unpin>(
        stream: &mut W,
        tag: u8,
        payload: Vec<u8>,
    ) {
        stream.write_all(&[tag]).await.unwrap();
        stream
            .write_all(&((payload.len() + 4) as u32).to_be_bytes())
            .await
            .unwrap();
        stream.write_all(&payload).await.unwrap();
    }

    async fn read_backend_frame<R: AsyncRead + Unpin>(stream: &mut R) -> (u8, Vec<u8>) {
        let mut tag = [0u8; 1];
        stream.read_exact(&mut tag).await.unwrap();
        let mut len = [0u8; 4];
        stream.read_exact(&mut len).await.unwrap();
        let len = u32::from_be_bytes(len) as usize;
        let mut body = vec![0u8; len - 4];
        stream.read_exact(&mut body).await.unwrap();
        (tag[0], body)
    }

    async fn read_until_ready<R: AsyncRead + Unpin>(stream: &mut R) -> Vec<(u8, Vec<u8>)> {
        let mut frames = Vec::new();
        loop {
            let frame = read_backend_frame(stream).await;
            let done = frame.0 == b'Z';
            frames.push(frame);
            if done {
                return frames;
            }
        }
    }

    fn parse_body(statement: &str, query: &str, oids: &[u32]) -> Vec<u8> {
        let mut out = Vec::new();
        push_pg_cstring(&mut out, statement);
        push_pg_cstring(&mut out, query);
        out.extend_from_slice(&(oids.len() as i16).to_be_bytes());
        for oid in oids {
            out.extend_from_slice(&oid.to_be_bytes());
        }
        out
    }

    fn bind_body(
        portal: &str,
        statement: &str,
        formats: &[i16],
        params: &[Option<&[u8]>],
        result_formats: &[i16],
    ) -> Vec<u8> {
        let mut out = Vec::new();
        push_pg_cstring(&mut out, portal);
        push_pg_cstring(&mut out, statement);
        out.extend_from_slice(&(formats.len() as i16).to_be_bytes());
        for format in formats {
            out.extend_from_slice(&format.to_be_bytes());
        }
        out.extend_from_slice(&(params.len() as i16).to_be_bytes());
        for param in params {
            match param {
                Some(bytes) => {
                    out.extend_from_slice(&(bytes.len() as i32).to_be_bytes());
                    out.extend_from_slice(bytes);
                }
                None => out.extend_from_slice(&(-1i32).to_be_bytes()),
            }
        }
        out.extend_from_slice(&(result_formats.len() as i16).to_be_bytes());
        for format in result_formats {
            out.extend_from_slice(&format.to_be_bytes());
        }
        out
    }

    fn describe_body(target: u8, name: &str) -> Vec<u8> {
        let mut out = vec![target];
        push_pg_cstring(&mut out, name);
        out
    }

    fn execute_body(portal: &str, max_rows: u32) -> Vec<u8> {
        let mut out = Vec::new();
        push_pg_cstring(&mut out, portal);
        out.extend_from_slice(&max_rows.to_be_bytes());
        out
    }

    fn push_pg_cstring(out: &mut Vec<u8>, value: &str) {
        out.extend_from_slice(value.as_bytes());
        out.push(0);
    }
}

/// A fresh 32-bit cancel key from the OS CSPRNG. Falls back to a
/// process/time-derived value only if the CSPRNG is unavailable — the
/// key guards nothing yet, so refusing the connection would be the
/// wrong trade.
fn random_cancel_key() -> u32 {
    let mut bytes = [0u8; 4];
    if crate::crypto::os_random::fill_bytes(&mut bytes).is_ok() {
        return u32::from_le_bytes(bytes);
    }
    let nanos = std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map(|d| d.subsec_nanos())
        .unwrap_or(0);
    std::process::id() ^ nanos
}