bindcar 0.8.1

// Copyright (c) 2025 Erick Bourgeois, firestoned
// SPDX-License-Identifier: MIT

//! BIND9 RNDC API Server
//!
//! Supports two operating modes selected via subcommand:
//!
//! - `bindcar run` (default) — sidecar mode alongside a local BIND9 instance
//! - `bindcar drone` — standalone mode managing a remote BIND9 instance

use anyhow::Context;
use axum::{
    extract::State,
    http::StatusCode,
    middleware as axum_middleware,
    response::{IntoResponse, Response},
    routing::{get, post},
    Json, Router,
};
use clap::Parser;
use serde::Serialize;
use std::net::SocketAddr;
#[cfg(feature = "tls")]
use std::sync::Arc as StdArc;
use std::sync::Arc;
use tower_http::trace::TraceLayer;
use tracing::{debug, error, info, warn};
use utoipa::OpenApi;
use utoipa_swagger_ui::SwaggerUi;

// Import from the library
#[cfg(feature = "tls")]
use axum::extract::ConnectInfo;
#[cfg(feature = "tls")]
use bindcar::tls::TlsReloader;
use bindcar::tls::{scheme_for, TlsSettings, DEFAULT_RELOAD_INTERVAL_SECS};
use bindcar::{
    auth::authenticate,
    cli::{Cli, Commands},
    metrics, middleware,
    rate_limit::RateLimitConfig,
    rndc::RndcExecutor,
    types::{AppState, ErrorResponse},
    zones,
};
#[cfg(feature = "tls")]
use tower::Service as _;
use tower_governor::{
    governor::GovernorConfigBuilder, key_extractor::PeerIpKeyExtractor, GovernorLayer,
};

/// Crate version used by both the OpenAPI info block and health endpoint.
const VERSION: &str = env!("CARGO_PKG_VERSION");

/// Whether this binary was compiled with the `tls` feature.
const TLS_SUPPORTED: bool = cfg!(feature = "tls");

/// Refuse to start when TLS was configured but is not compiled in.
///
/// The same fail-closed reasoning as the runtime TLS config, extended to
/// compile-time capability: quietly ignoring `--tls-cert` would serve plaintext
/// on a deployment whose operator believes TLS is on. The flags are always
/// accepted by the parser so this produces an actionable error rather than an
/// "unknown argument".
///
/// # Arguments
/// * `tls_requested` - whether any TLS option was supplied
/// * `tls_supported` - whether this build has the `tls` feature
///
/// # Errors
/// Returns an error naming the missing feature when TLS was requested but the
/// binary cannot provide it.
fn check_tls_support(tls_requested: bool, tls_supported: bool) -> anyhow::Result<()> {
    if tls_requested && !tls_supported {
        anyhow::bail!(
            "TLS options were supplied but this bindcar binary was built without the \
`tls` feature, so it can only serve plaintext. Rebuild with `--features tls` \
(it is enabled by default), or remove the TLS options to serve plaintext deliberately."
        );
    }
    Ok(())
}

/// OpenAPI documentation structure
#[derive(OpenApi)]
#[openapi(
    paths(
        zones::create_zone,
        zones::delete_zone,
        zones::modify_zone,
        zones::reload_zone,
        zones::zone_status,
        zones::get_zone_ds,
        zones::checkds_zone,
        zones::freeze_zone,
        zones::thaw_zone,
        zones::notify_zone,
        zones::retransfer_zone,
        zones::server_status,
        zones::list_zones,
        zones::get_zone,
        bindcar::records::add_record,
        bindcar::records::remove_record,
        bindcar::records::update_record,
    ),
    components(
        schemas(
            zones::CreateZoneRequest,
            zones::ModifyZoneRequest,
            zones::ZoneResponse,
            zones::ZoneStatusResponse,
            zones::DsSetResponse,
            zones::DsRecordView,
            zones::CheckdsRequest,
            bindcar::dnssec::DnssecStatus,
            bindcar::dnssec::DnssecKeyStatus,
            bindcar::dnssec::CheckdsState,
            zones::ServerStatusResponse,
            zones::ZoneInfo,
            zones::ZoneListResponse,
            zones::ZoneConfig,
            zones::SoaRecord,
            zones::DnsRecord,
            bindcar::records::AddRecordRequest,
            bindcar::records::RemoveRecordRequest,
            bindcar::records::UpdateRecordRequest,
            bindcar::records::RecordResponse,
        )
    ),
    tags(
        (name = "zones", description = "Zone management endpoints"),
        (name = "records", description = "DNS record management endpoints"),
        (name = "server", description = "Server status endpoints")
    ),
    info(
        title = "Bindcar API",
        version = VERSION,
        description = "HTTP REST API for managing BIND9 zones and DNS records via RNDC and nsupdate",
        license(name = "MIT")
    )
)]
struct ApiDoc;

/// Server configuration
const DEFAULT_BIND_ZONE_DIR: &str = "/var/cache/bind";
const DEFAULT_API_PORT: u16 = 8080;
const DEFAULT_BIND_API_ADDRESS: &str = "0.0.0.0";

/// Health check response
#[derive(Serialize)]
struct HealthResponse {
    status: String,
    version: String,
}

/// Readiness check response
#[derive(Serialize)]
struct ReadyResponse {
    ready: bool,
    checks: Vec<String>,
}

/// Health check endpoint
async fn health_check() -> Json<HealthResponse> {
    Json(HealthResponse {
        status: "healthy".to_string(),
        version: VERSION.to_string(),
    })
}

/// Map a readiness sub-check outcome to a non-sensitive status token.
///
/// `/health`, `/ready`, and `/metrics` are intentionally unauthenticated (for
/// kubelet probes and Prometheus scraping), so their responses must never carry
/// internal detail. This emits only `"<name>: ok"` / `"<name>: error"` — the
/// underlying path or backend error text is logged server-side instead, never
/// returned to the caller.
fn ready_check_label(name: &str, ok: bool) -> String {
    format!("{}: {}", name, if ok { "ok" } else { "error" })
}

/// Metrics endpoint for Prometheus scraping
async fn metrics_handler() -> Response {
    match metrics::gather_metrics() {
        Ok(metrics_text) => (
            StatusCode::OK,
            [("Content-Type", "text/plain; version=0.0.4")],
            metrics_text,
        )
            .into_response(),
        Err(e) => {
            // Log the detail; return a generic message (this endpoint is
            // unauthenticated, so the body must not leak internals).
            error!("failed to gather metrics: {}", e);
            (
                StatusCode::INTERNAL_SERVER_ERROR,
                Json(ErrorResponse {
                    error: "Failed to gather metrics".to_string(),
                    details: None,
                }),
            )
                .into_response()
        }
    }
}

/// Probes the zone directory for the readiness endpoint.
///
/// Returns `true` only when `zone_dir` is a normalized absolute path that
/// exists and is a directory. The path and any IO error are logged
/// server-side and never returned to the caller — `/api/v1/ready` is
/// unauthenticated and must not disclose the filesystem layout.
///
/// # Arguments
/// * `zone_dir` - The configured zone directory (`BIND_ZONE_DIR`)
///
/// # Returns
/// `true` if the directory is usable, `false` otherwise. Never panics and
/// never propagates an error.
///
/// # Security
/// Defense-in-depth barrier for CodeQL `rust/path-injection`. `zone_dir` is
/// canonicalized once at startup (`zones::resolve_zone_dir`) and is operator
/// config, never HTTP input — but it reaches the handler through the axum
/// `State` extractor, which CodeQL models as untrusted. The guard therefore
/// re-asserts the startup invariant (absolute, no `..`/`.` components)
/// immediately before the `tokio::fs::metadata` sink.
///
/// The shape matters as much as the check: CodeQL's barrier guard is
/// intra-procedural and only takes effect when the guard is an early return
/// leaving the sink in straight-line code — the same shape used by
/// `zones::list_zones` before its `read_dir` sink. Expressing this as
/// `if bad { false } else { ...metadata()... }` inside `ready_check` did *not*
/// sanitize the flow (code-scanning alert #7 on PR #114). Do not inline this
/// helper back into `ready_check` or convert the guard to an if/else.
async fn probe_zone_dir(zone_dir: &str) -> bool {
    if !zones::is_normalized_zone_dir(zone_dir) || zone_dir.contains("..") {
        warn!(
            "zone directory {:?} is not a normalized absolute path; refusing to probe it",
            zone_dir
        );
        return false;
    }

    let metadata = match tokio::fs::metadata(zone_dir).await {
        Ok(metadata) => metadata,
        Err(e) => {
            warn!("zone directory {:?} not accessible: {}", zone_dir, e);
            return false;
        }
    };

    if !metadata.is_dir() {
        warn!("zone directory {:?} is not a directory", zone_dir);
        return false;
    }

    true
}

/// Readiness check endpoint
async fn ready_check(State(state): State<AppState>) -> Json<ReadyResponse> {
    let mut checks = Vec::new();
    let mut ready = true;

    // Check the zone directory. The response carries only ok/error; the path and
    // any IO error are logged server-side, never returned (the endpoint is
    // unauthenticated and must not disclose the filesystem layout).
    let zone_dir_ok = probe_zone_dir(&state.zone_dir).await;
    ready &= zone_dir_ok;
    checks.push(ready_check_label("zone_dir", zone_dir_ok));

    // Check if rndc is available. The backend error is logged, not returned.
    let rndc_ok = match state.rndc.status().await {
        Ok(_) => true,
        Err(e) => {
            warn!("RNDC not ready: {}", e);
            false
        }
    };
    ready &= rndc_ok;
    checks.push(ready_check_label("rndc", rndc_ok));

    Json(ReadyResponse { ready, checks })
}

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let cli = Cli::parse();
    init_tracing(cli.debug);

    // The insecure-auth override may come from the CLI flag or an env var (the
    // latter is convenient for container deployments without changing args).
    let insecure_override = cli.i_know_this_is_insecure
        || std::env::var("BINDCAR_ALLOW_INSECURE_AUTH")
            .ok()
            .and_then(|v| v.parse::<bool>().ok())
            .unwrap_or(false);

    // Refuse loudly if TLS was asked for but this build cannot provide it,
    // before anything binds.
    let tls_requested =
        cli.tls_cert.is_some() || cli.tls_key.is_some() || cli.tls_client_ca.is_some();
    check_tls_support(tls_requested, TLS_SUPPORTED)?;

    // Resolve the TLS transport config before anything binds. A half-configured
    // listener is fatal here rather than a silent downgrade to plaintext.
    let tls_settings = bindcar::tls::resolve_tls_settings(
        cli.tls_cert.clone(),
        cli.tls_key.clone(),
        cli.tls_client_ca.clone(),
    )
    .context("invalid TLS configuration")?;

    let reload_interval = cli
        .tls_reload_interval
        .unwrap_or(DEFAULT_RELOAD_INTERVAL_SECS);

    start_server(
        cli.resolved_command(),
        insecure_override,
        tls_settings,
        reload_interval,
    )
    .await
}

fn init_tracing(debug: bool) {
    let filter = if debug {
        tracing_subscriber::EnvFilter::new("debug")
    } else {
        tracing_subscriber::EnvFilter::try_from_default_env()
            .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("info"))
    };

    tracing_subscriber::fmt()
        .with_env_filter(filter)
        .json()
        .init();
}

async fn start_server(
    command: &Commands,
    insecure_override: bool,
    tls_settings: Option<TlsSettings>,
    tls_reload_interval: u64,
) -> anyhow::Result<()> {
    match command {
        Commands::Run => info!("starting bindcar v{} [sidecar mode]", VERSION),
        Commands::Drone => info!(
            "starting bindcar v{} [drone mode] - standalone, managing remote BIND9",
            VERSION
        ),
    }

    // initialize metrics
    metrics::init_metrics();

    // get configuration from environment
    let zone_dir =
        std::env::var("BIND_ZONE_DIR").unwrap_or_else(|_| DEFAULT_BIND_ZONE_DIR.to_string());
    let api_port = std::env::var("API_PORT")
        .ok()
        .and_then(|p| p.parse().ok())
        .unwrap_or(DEFAULT_API_PORT);
    let bind_host =
        std::env::var("BIND_API_ADDRESS").unwrap_or_else(|_| DEFAULT_BIND_API_ADDRESS.to_string());
    let disable_auth = std::env::var("DISABLE_AUTH")
        .ok()
        .and_then(|v| v.parse::<bool>().ok())
        .unwrap_or(false);

    info!("zone directory: {}", zone_dir);
    info!("api address: {}:{}", bind_host, api_port);
    // Startup guard (B-4): never silently expose an unauthenticated or
    // presence-only API on a non-loopback interface. Requires real auth
    // (TokenReview feature or BIND_API_TOKEN), a loopback bind, or an explicit
    // operator override.
    if let Err(e) = bindcar::auth::check_startup_auth_posture(
        !disable_auth,
        bindcar::auth::has_real_auth(),
        &bind_host,
        insecure_override,
    ) {
        error!("{}", e);
        return Err(anyhow::anyhow!(e));
    }

    if disable_auth {
        warn!("⚠️  authentication is disabled - api endpoints are unprotected!");
        warn!("⚠️  this should only be used in trusted environments (e.g., linkerd service mesh)");
    } else {
        info!("authentication is enabled");
        if std::env::var(bindcar::auth::BIND_API_TOKEN_ENV)
            .map(|v| !v.is_empty())
            .unwrap_or(false)
        {
            info!("shared-secret API token authentication is active (BIND_API_TOKEN)");
        }

        #[cfg(feature = "k8s-token-review")]
        {
            use bindcar::auth::{
                check_authorization_posture, detect_kube_auth_mode, shared_secret_configured,
                KubeAuthMode, TokenReviewConfig, ALLOW_ANY_SERVICE_ACCOUNT_ENV,
            };

            // TokenReview and shared-secret auth are mutually exclusive: a
            // configured shared secret (BIND_API_TOKEN) selects shared-secret
            // mode, in which TokenReview is never consulted at request time
            // (see auth::authenticate). Only enforce the fail-closed TokenReview
            // authorization posture (A2) when TokenReview is the active mode.
            if shared_secret_configured() {
                info!("auth mode: shared-secret (BIND_API_TOKEN) — Kubernetes TokenReview is not active");
            } else {
                // Fail-closed authorization posture (A2): with TokenReview active
                // but no namespace/service-account allowlist, any authenticated
                // ServiceAccount in the cluster would be authorized. Refuse to
                // start unless the operator configured an allowlist or opted in.
                let tr_config = TokenReviewConfig::from_env();
                let allow_any = std::env::var(ALLOW_ANY_SERVICE_ACCOUNT_ENV)
                    .ok()
                    .and_then(|v| v.parse::<bool>().ok())
                    .unwrap_or(false);
                if let Err(e) =
                    check_authorization_posture(tr_config.is_authorization_restricted(), allow_any)
                {
                    error!("{}", e);
                    return Err(anyhow::anyhow!(e));
                }
                if allow_any && !tr_config.is_authorization_restricted() {
                    warn!("⚠️  BIND_ALLOW_ANY_SERVICEACCOUNT is set: every authenticated ServiceAccount in the cluster is authorized");
                }

                match detect_kube_auth_mode() {
                    KubeAuthMode::Explicit { ref server, .. } => {
                        info!(
                            "kubernetes auth mode: explicit (KUBE_API_SERVER={})",
                            server
                        );
                    }
                    KubeAuthMode::Default => {
                        info!("kubernetes auth mode: try_default (KUBECONFIG / ~/.kube/config / in-cluster)");
                    }
                }
            }
        }
    }

    // load rate limiting configuration
    let rate_limit_config = RateLimitConfig::from_env();
    if let Err(e) = rate_limit_config.validate() {
        error!("invalid rate limit configuration: {}", e);
        return Err(anyhow::anyhow!("invalid rate limit configuration: {}", e));
    }

    if rate_limit_config.enabled {
        info!(
            "rate limiting enabled: {} requests per {} seconds (burst: {})",
            rate_limit_config.requests_per_period,
            rate_limit_config.period_secs,
            rate_limit_config.burst_size
        );
    } else {
        warn!("⚠️  rate limiting is disabled");
    }

    // get rndc configuration from environment or fallback to rndc.conf
    // Each parameter is checked independently - env var takes priority, then rndc.conf

    // Try to parse rndc.conf file first to have fallback values
    let config_paths = vec!["/etc/bind/rndc.conf", "/etc/rndc.conf"];
    let mut parsed_config = None;

    for path in &config_paths {
        match bindcar::rndc::parse_rndc_conf(path) {
            Ok(cfg) => {
                info!("successfully parsed rndc configuration from {}", path);
                parsed_config = Some(cfg);
                break;
            }
            Err(e) => {
                debug!("failed to parse {}: {}", path, e);
            }
        }
    }

    // Check each parameter independently: env var first, then rndc.conf, then hardcoded default
    let rndc_server = if let Ok(server) = std::env::var("RNDC_SERVER") {
        info!("using RNDC_SERVER from environment: {}", server);
        server
    } else if let Some(ref cfg) = parsed_config {
        info!("using server from rndc.conf: {}", cfg.server);
        cfg.server.clone()
    } else {
        let default = "127.0.0.1:953".to_string();
        warn!("using default RNDC_SERVER: {}", default);
        default
    };

    let rndc_algorithm = if let Ok(algorithm) = std::env::var("RNDC_ALGORITHM") {
        info!("using RNDC_ALGORITHM from environment: {}", algorithm);
        algorithm
    } else if let Some(ref cfg) = parsed_config {
        info!("using algorithm from rndc.conf: {}", cfg.algorithm);
        cfg.algorithm.clone()
    } else {
        let default = "sha256".to_string();
        warn!("using default RNDC_ALGORITHM: {}", default);
        default
    };

    let rndc_secret = if let Ok(secret) = std::env::var("RNDC_SECRET") {
        info!("using RNDC_SECRET from environment");
        secret
    } else if let Some(ref cfg) = parsed_config {
        info!("using secret from rndc.conf");
        cfg.secret.clone()
    } else {
        error!("rndc configuration not found!");
        error!("either set RNDC_SECRET environment variable or ensure /etc/bind/rndc.conf exists");
        return Err(anyhow::anyhow!(
            "rndc configuration required: set RNDC_SECRET env var or create /etc/bind/rndc.conf"
        ));
    };

    // Resolve and validate the zone directory once at startup. Canonicalizing the
    // operator-provided BIND_ZONE_DIR resolves symlinks and `..`, rejects a missing
    // or non-directory path up front, and breaks the env->filesystem taint flow
    // before the value is reused by the read_dir/metadata handlers (B-1).
    let zone_dir = zones::resolve_zone_dir(&zone_dir)
        .map_err(|e| anyhow::anyhow!("zone directory not usable: {}", e))?;
    info!("resolved zone directory: {}", zone_dir);

    // Optional DNSSEC key directory (ADR-0001): required only by the DS
    // endpoint. Same canonicalize-at-startup treatment as the zone
    // directory; a configured-but-unusable path is a hard startup error
    // rather than a silent downgrade.
    let key_dir = match std::env::var("BIND_KEY_DIR") {
        Ok(raw) => {
            let resolved = zones::resolve_zone_dir(&raw)
                .map_err(|e| anyhow::anyhow!("key directory not usable: {}", e))?;
            info!("resolved DNSSEC key directory: {}", resolved);
            Some(resolved)
        }
        Err(_) => {
            info!("BIND_KEY_DIR not set; the DS endpoint will return 501");
            None
        }
    };

    // create rndc executor
    let rndc = Arc::new(
        RndcExecutor::new(
            rndc_server.clone(),
            rndc_algorithm.clone(),
            rndc_secret.clone(),
        )
        .context("failed to create rndc client")?,
    );

    // Configure nsupdate executor (hybrid approach: env vars → rndc credentials)
    let nsupdate_key_name = std::env::var("NSUPDATE_KEY_NAME")
        .ok()
        .or_else(|| std::env::var("RNDC_KEY_NAME").ok())
        .or(Some("rndc-key".to_string()));

    let nsupdate_algorithm = std::env::var("NSUPDATE_ALGORITHM")
        .ok()
        .or(Some(rndc_algorithm.clone()));

    let nsupdate_secret = std::env::var("NSUPDATE_SECRET")
        .ok()
        .or(Some(rndc_secret.clone()));

    let nsupdate_server = std::env::var("NSUPDATE_SERVER")
        .ok()
        .unwrap_or_else(|| "127.0.0.1".to_string());

    let nsupdate_port = std::env::var("NSUPDATE_PORT")
        .ok()
        .and_then(|p| p.parse().ok())
        .unwrap_or(53);

    info!("nsupdate executor configuration:");
    info!("  server: {}:{}", nsupdate_server, nsupdate_port);
    info!("  TSIG key: {:?}", nsupdate_key_name);

    // create nsupdate executor
    let nsupdate = Arc::new(
        bindcar::nsupdate::NsupdateExecutor::new(
            nsupdate_server,
            nsupdate_port,
            nsupdate_key_name,
            nsupdate_algorithm,
            nsupdate_secret,
        )
        .context("failed to create nsupdate executor")?,
    );

    // create application state
    let state = AppState {
        rndc,
        nsupdate,
        zone_dir: zone_dir.clone(),
        key_dir,
    };

    // build api routes
    let api_routes = Router::new()
        .route("/zones", post(zones::create_zone).get(zones::list_zones))
        .route(
            "/zones/{name}",
            get(zones::get_zone)
                .delete(zones::delete_zone)
                .patch(zones::modify_zone),
        )
        .route("/zones/{name}/reload", post(zones::reload_zone))
        .route("/zones/{name}/status", get(zones::zone_status))
        .route("/zones/{name}/ds", get(zones::get_zone_ds))
        .route("/zones/{name}/dnssec/checkds", post(zones::checkds_zone))
        .route("/zones/{name}/freeze", post(zones::freeze_zone))
        .route("/zones/{name}/thaw", post(zones::thaw_zone))
        .route("/zones/{name}/notify", post(zones::notify_zone))
        .route("/zones/{name}/retransfer", post(zones::retransfer_zone))
        .route(
            "/zones/{name}/records",
            post(bindcar::records::add_record)
                .delete(bindcar::records::remove_record)
                .put(bindcar::records::update_record),
        )
        .route("/server/status", get(zones::server_status))
        .with_state(state.clone());

    // conditionally apply authentication middleware
    let api_routes = if !disable_auth {
        api_routes.layer(axum_middleware::from_fn(authenticate))
    } else {
        api_routes
    };

    // conditionally apply rate limiting layer
    let api_routes = if rate_limit_config.enabled {
        // Governor is configured by the interval between replenished cells, not
        // by requests-per-period. Deriving it here with integer division silently
        // floored the budget: the 100-per-60s default became 1 request per
        // second, and the operator's zone replay — a burst of create/freeze/
        // update/thaw/notify calls issued whenever a BIND9 Pod comes back empty —
        // ran straight into HTTP 429. The operator answers 429 with exponential
        // backoff, so a ~30s recovery stretched to ~130s.
        let replenish_period = rate_limit_config.replenish_period();

        // Build governor configuration
        // A-1: key on the real TCP peer IP, NOT the spoofable X-Forwarded-For /
        // X-Real-IP / Forwarded headers (SmartIpKeyExtractor). bindcar is reached
        // directly by the operator's pods (no trusted L7 proxy in front), so
        // trusting client-supplied forwarding headers would let any caller evade
        // the limit (rotate the header) or exhaust another client's bucket
        // (spoof the victim's IP).
        let governor_conf = Arc::new(
            GovernorConfigBuilder::default()
                .key_extractor(PeerIpKeyExtractor)
                .period(replenish_period)
                .burst_size(rate_limit_config.burst_size)
                .finish()
                .expect("Failed to create governor config"),
        );

        api_routes.layer(GovernorLayer::new(governor_conf))
    } else {
        api_routes
    };

    // The Swagger UI and OpenAPI spec are served UNAUTHENTICATED and disclose the
    // full mutate-API surface, so they are OFF by default and only mounted when
    // BIND_ENABLE_DOCS is truthy (A13). Enable them for local development only.
    let enable_docs = std::env::var("BIND_ENABLE_DOCS")
        .ok()
        .and_then(|v| v.parse::<bool>().ok())
        .unwrap_or(false);

    // build main router
    let mut app = Router::new();
    if enable_docs {
        info!("serving unauthenticated API docs at /api/v1/docs (BIND_ENABLE_DOCS=true)");
        app = app
            .merge(SwaggerUi::new("/api/v1/docs").url("/api/v1/openapi.json", ApiDoc::openapi()));
    }
    let app = app
        .route("/api/v1/health", get(health_check))
        .route("/api/v1/ready", get(ready_check))
        .route("/metrics", get(metrics_handler))
        .nest("/api/v1", api_routes)
        .with_state(state)
        .layer(axum_middleware::from_fn(middleware::track_metrics))
        .layer(TraceLayer::new_for_http());

    // start server
    let addr = format!("{}:{}", bind_host, api_port);
    let scheme = scheme_for(tls_settings.as_ref());

    info!(
        "bind9 rndc api server listening on {} ({})",
        addr,
        if tls_settings.is_some() {
            "TLS"
        } else {
            "plaintext"
        }
    );
    if enable_docs {
        info!("swagger ui available at {}://{}/api/v1/docs", scheme, addr);
    }

    let listener = tokio::net::TcpListener::bind(&addr).await?;

    // A build without the `tls` feature can only serve plaintext. `main` has
    // already refused to start if TLS was configured, so reaching here means
    // plaintext was intended.
    #[cfg(not(feature = "tls"))]
    {
        let _ = (tls_settings, tls_reload_interval);
        warn_plaintext_transport(&bind_host);
        axum::serve(
            listener,
            app.into_make_service_with_connect_info::<SocketAddr>(),
        )
        .await
        .context("server error")
    }

    #[cfg(feature = "tls")]
    {
        let Some(tls_settings) = tls_settings else {
            // Plaintext path — unchanged from previous releases.
            warn_plaintext_transport(&bind_host);
            axum::serve(
                listener,
                app.into_make_service_with_connect_info::<SocketAddr>(),
            )
            .await
            .context("server error")?;
            return Ok(());
        };

        if tls_settings.requires_client_auth() {
            info!(
            "mutual TLS enabled; clients must present a certificate trusted by the configured CA"
        );
        }

        // A failure here is fatal: there is no known-good configuration to fall back
        // to, and serving plaintext instead would be a silent downgrade.
        let reloader =
            StdArc::new(TlsReloader::new(tls_settings).context("failed to build TLS config")?);

        if TlsReloader::reloading_enabled(tls_reload_interval) {
            info!(
            "watching TLS certificate material for renewals every {}s (BIND_TLS_RELOAD_INTERVAL=0 to disable)",
            tls_reload_interval
        );
            spawn_tls_reload_task(StdArc::clone(&reloader), tls_reload_interval);
        } else {
            info!("TLS certificate reloading is disabled; a renewal requires a restart");
        }

        serve_tls(listener, app, reloader).await
    }
}

#[cfg(feature = "tls")]
/// Poll the TLS material for renewals, and reload on `SIGHUP`.
///
/// Polling rather than watching is deliberate: Kubernetes swaps a `..data`
/// symlink instead of rewriting files in place, which defeats inode-based
/// watchers. `SIGHUP` is offered alongside it so an operator can make rotation
/// deterministic instead of waiting out the interval.
///
/// # Arguments
/// * `reloader` - the shared reloader holding the live configuration
/// * `interval_secs` - seconds between polls; the caller has already checked it is non-zero
fn spawn_tls_reload_task(reloader: StdArc<TlsReloader>, interval_secs: u64) {
    tokio::spawn(async move {
        let mut ticker = tokio::time::interval(std::time::Duration::from_secs(interval_secs));
        // The first tick fires immediately; skip it so startup does not
        // pointlessly rebuild the config it just built.
        ticker.tick().await;

        #[cfg(unix)]
        let mut sighup = match tokio::signal::unix::signal(tokio::signal::unix::SignalKind::hangup())
        {
            Ok(s) => Some(s),
            Err(e) => {
                warn!("could not install SIGHUP handler for TLS reload: {}", e);
                None
            }
        };

        loop {
            #[cfg(unix)]
            {
                match sighup.as_mut() {
                    Some(hup) => {
                        tokio::select! {
                            _ = ticker.tick() => {}
                            _ = hup.recv() => {
                                info!("SIGHUP received; checking TLS material now");
                            }
                        }
                    }
                    None => {
                        ticker.tick().await;
                    }
                }
            }
            #[cfg(not(unix))]
            {
                ticker.tick().await;
            }

            reloader.reload_if_changed();
        }
    });
}

/// Warn when a credential-bearing API is about to be served in the clear.
///
/// bindcar's callers authenticate with a Kubernetes ServiceAccount token or the
/// shared `BIND_API_TOKEN`. Over plaintext that credential is readable by
/// anything observing the link, so the operator should see this at every start.
/// Loopback binds are exempt — the traffic never leaves the host.
fn warn_plaintext_transport(bind_host: &str) {
    if bind_host.starts_with("127.") || bind_host == "localhost" || bind_host == "::1" {
        return;
    }

    warn!(
        "serving the API over plaintext HTTP on a non-loopback address; API credentials \
cross the network in the clear. Set --tls-cert/--tls-key (BIND_TLS_CERT/BIND_TLS_KEY) to enable TLS."
    );
}

#[cfg(feature = "tls")]
/// Serve the router over TLS.
///
/// Runs a manual accept loop so each connection is wrapped by
/// [`tokio_rustls::TlsAcceptor`] before hyper sees it. Peer address is injected
/// as [`ConnectInfo`] on every request, because the rate limiter's
/// `PeerIpKeyExtractor` reads it and would otherwise reject every request once
/// the listener stopped being an `axum::serve` one.
///
/// The configuration is read from `reloader` on every accept rather than being
/// captured once, so a certificate renewal reaches new connections without a
/// restart (roadmap 06).
///
/// # Arguments
/// * `listener` - the bound TCP listener
/// * `app` - the fully-built axum router
/// * `reloader` - holds the live rustls configuration
///
/// # Errors
/// Returns an error only if the listener itself fails. Per-connection failures
/// (handshake errors, client disconnects) are logged and skipped so one bad
/// client cannot take the server down.
async fn serve_tls(
    listener: tokio::net::TcpListener,
    app: Router,
    reloader: StdArc<TlsReloader>,
) -> anyhow::Result<()> {
    loop {
        let (stream, peer) = listener.accept().await.context("accept failed")?;
        // Read the live config per connection so a reload reaches new
        // connections immediately. `TlsAcceptor::from` wraps the `Arc`, so this
        // costs one atomic increment. Established connections keep the
        // certificate they started with, which is what makes rotation
        // non-disruptive.
        let acceptor = tokio_rustls::TlsAcceptor::from(reloader.current());
        let app = app.clone();

        tokio::spawn(async move {
            let tls_stream = match acceptor.accept(stream).await {
                Ok(s) => s,
                Err(e) => {
                    // Handshake failures are routine (probes, wrong SNI, a client
                    // with no cert under mTLS) and must not be fatal.
                    debug!("TLS handshake with {} failed: {}", peer, e);
                    return;
                }
            };

            let service = hyper::service::service_fn(
                move |mut req: hyper::Request<hyper::body::Incoming>| {
                    req.extensions_mut().insert(ConnectInfo(peer));
                    app.clone().call(req)
                },
            );

            if let Err(e) =
                hyper_util::server::conn::auto::Builder::new(hyper_util::rt::TokioExecutor::new())
                    .serve_connection_with_upgrades(
                        hyper_util::rt::TokioIo::new(tls_stream),
                        service,
                    )
                    .await
            {
                debug!("connection from {} ended: {}", peer, e);
            }
        });
    }
}

#[cfg(test)]
mod main_test;