rust-web-server 18.4.0

//! Typed server configuration.
//!
//! [`ServerConfig`] holds all per-instance configuration fields as typed Rust
//! values. It replaces point-of-use `env::var("RWS_CONFIG_*")` calls with a
//! struct that can be:
//!
//! - Built from environment variables once at startup: [`ServerConfig::from_env()`]
//! - Constructed directly in tests without touching the environment:
//!   [`ServerConfig::default()`] / struct update syntax
//! - Passed to [`App::with_config`] to create a fully isolated application
//!   instance — essential for parallel tests and embedded multi-tenant use
//!
//! # Test isolation example
//!
//! ```rust,ignore
//! use rust_web_server::app::App;
//! use rust_web_server::server_config::ServerConfig;
//! use rust_web_server::test_client::TestClient;
//!
//! // No env writes, no lock needed.
//! let app = App::with_config(ServerConfig {
//!     cors_allow_all: false,
//!     cors_allow_origins: "https://example.com".to_string(),
//!     ..ServerConfig::default()
//! });
//! let client = TestClient::new(app);
//! let res = client.get("/").send();
//! ```

#[cfg(test)]
mod tests;

use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::{Arc, RwLock};

use crate::entry_point::Config;

/// Bumped whenever `RWS_CONFIG_*` variables change (see [`invalidate`]).
static GENERATION: AtomicU64 = AtomicU64::new(1);

/// The snapshot [`ServerConfig::current`] hands out, with the generation it
/// was built at.
static CURRENT: RwLock<Option<(u64, Arc<ServerConfig>)>> = RwLock::new(None);

/// Mark the cached [`ServerConfig::current`] snapshot stale: the next call
/// re-reads the environment. Called by everything in the crate that writes
/// `RWS_CONFIG_*` variables (config file, command line, defaults,
/// `config_reload::reload`); call it yourself after `std::env::set_var` of
/// a setting that should take effect immediately.
pub fn invalidate() {
    GENERATION.fetch_add(1, Ordering::SeqCst);
}

/// Default `Content-Security-Policy` header value. Mirrors
/// `Header::_CONTENT_SECURITY_POLICY_VALUE_DEFAULT` without creating a
/// circular import (`server_config` ← `header` ← `cors` ← `server_config`).
const CSP_DEFAULT: &str = "default-src 'self'";
/// Default `Cache-Control` for static files: cache, but revalidate.
pub(crate) const STATIC_CACHE_CONTROL_DEFAULT: &str = "no-cache";

/// All runtime-configurable settings for one server instance.
///
/// Fields map 1-to-1 to `RWS_CONFIG_*` environment variable names documented
/// in [`Config`]. Default values match the environment-variable defaults.
///
/// Construct via [`ServerConfig::from_env()`] at startup or
/// [`ServerConfig::default()`] in tests.
#[derive(Clone, Debug, PartialEq)]
pub struct ServerConfig {
    // ── CORS ─────────────────────────────────────────────────────────────────
    /// `RWS_CONFIG_CORS_ALLOW_ALL` — when `true`, all cross-origin requests are
    /// reflected back as allowed (echo the `Origin` header). Overrides all
    /// other CORS fields. Default: `true`.
    pub cors_allow_all: bool,
    /// `RWS_CONFIG_CORS_ALLOW_ORIGINS` — comma-separated list of allowed
    /// origins when `cors_allow_all` is `false`. Default: `""` (none).
    pub cors_allow_origins: String,
    /// `RWS_CONFIG_CORS_ALLOW_CREDENTIALS` — value for the
    /// `Access-Control-Allow-Credentials` response header. Default: `""`.
    pub cors_allow_credentials: String,
    /// `RWS_CONFIG_CORS_ALLOW_METHODS` — value for
    /// `Access-Control-Allow-Methods`. Default: `""`.
    pub cors_allow_methods: String,
    /// `RWS_CONFIG_CORS_ALLOW_HEADERS` — value for
    /// `Access-Control-Allow-Headers`. Default: `""`.
    pub cors_allow_headers: String,
    /// `RWS_CONFIG_CORS_EXPOSE_HEADERS` — value for
    /// `Access-Control-Expose-Headers`. Default: `""`.
    pub cors_expose_headers: String,
    /// `RWS_CONFIG_CORS_MAX_AGE` — value for `Access-Control-Max-Age`.
    /// Default: `"86400"`.
    pub cors_max_age: String,

    // ── Security headers ──────────────────────────────────────────────────────
    /// `RWS_CONFIG_CSP` — `Content-Security-Policy` header value. An empty
    /// string suppresses the header. Unset: `default-src 'self'` when
    /// [`security_headers`](Self::security_headers) is on, otherwise no header
    /// (18.0.0; was always `default-src 'self'`).
    pub csp: String,
    /// `RWS_CONFIG_SECURITY_HEADERS` — send `X-Frame-Options: SAMEORIGIN`,
    /// `Referrer-Policy` and `Permissions-Policy` on every response (and the
    /// default CSP, unless `RWS_CONFIG_CSP` is set). Off by default (18.0.0;
    /// was always on): nginx sends none of them, and over HTTP/2 every header
    /// costs HPACK work. `X-Content-Type-Options: nosniff` is always sent.
    pub security_headers: bool,
    /// `RWS_CONFIG_NANOS_HEADERS` — send `Date-Unix-Epoch-Nanos` and, for
    /// static files, `Last-Modified-Unix-Epoch-Nanos`. Off by default (18.0.0;
    /// was always on): they change on every response, so HTTP/2 can't index
    /// them, and `Date`/`Last-Modified` carry the same information to the second.
    pub nanos_headers: bool,
    /// `RWS_CONFIG_CLIENT_HINTS` — send `Accept-CH`, `Critical-CH` and the
    /// client hints in `Vary` on every response. Off by default (18.0.0; was
    /// always on): ~700 bytes per response, and `Critical-CH` makes Chromium
    /// retry a request that came without the hints.
    pub client_hints: bool,
    /// `RWS_CONFIG_STATIC_CACHE_CONTROL` — `Cache-Control` for static files
    /// (other responses keep `no-store, …`). Default `"no-cache"` (18.0.0; was
    /// `no-store, …`): browsers keep the file and revalidate it with
    /// `If-None-Match` / `If-Modified-Since` (a 304). An empty value keeps
    /// the `no-store` default for static files too.
    pub static_cache_control: String,

    // ── Server internals ──────────────────────────────────────────────────────
    /// `RWS_CONFIG_LOG_FORMAT` — `"json"` or `"combined"`. Default: `"json"`.
    pub log_format: String,
    /// `RWS_CONFIG_REQUEST_ALLOCATION_SIZE_IN_BYTES` — bytes allocated for
    /// incoming request parsing. Default: `10000`.
    pub request_allocation_size: i64,
}

impl Default for ServerConfig {
    fn default() -> Self {
        Self {
            cors_allow_all: Config::RWS_CONFIG_CORS_ALLOW_ALL_DEFAULT_VALUE
                .eq_ignore_ascii_case("true"),
            cors_allow_origins: Config::RWS_CONFIG_CORS_ALLOW_ORIGINS_DEFAULT_VALUE.to_string(),
            cors_allow_credentials: Config::RWS_CONFIG_CORS_ALLOW_CREDENTIALS_DEFAULT_VALUE
                .to_string(),
            cors_allow_methods: Config::RWS_CONFIG_CORS_ALLOW_METHODS_DEFAULT_VALUE.to_string(),
            cors_allow_headers: Config::RWS_CONFIG_CORS_ALLOW_HEADERS_DEFAULT_VALUE.to_string(),
            cors_expose_headers: Config::RWS_CONFIG_CORS_EXPOSE_HEADERS_DEFAULT_VALUE.to_string(),
            cors_max_age: Config::RWS_CONFIG_CORS_MAX_AGE_DEFAULT_VALUE.to_string(),
            csp: String::new(),
            security_headers: false,
            nanos_headers: false,
            client_hints: false,
            static_cache_control: STATIC_CACHE_CONTROL_DEFAULT.to_string(),
            log_format: Config::RWS_CONFIG_LOG_FORMAT_DEFAULT_VALUE.to_string(),
            request_allocation_size: *Config::RWS_DEFAULT_REQUEST_ALLOCATION_SIZE_IN_BYTES,
        }
    }
}

impl ServerConfig {
    /// Build a `ServerConfig` by reading all `RWS_CONFIG_*` environment
    /// variables. Missing variables fall back to their default values.
    ///
    /// Each call reads every variable — the environment lock is taken once
    /// per variable — so per-request code uses [`ServerConfig::current`].
    pub fn from_env() -> Self {
        let read = |key: &str| std::env::var(key).unwrap_or_default();
        Self {
            cors_allow_all: read(Config::RWS_CONFIG_CORS_ALLOW_ALL)
                .eq_ignore_ascii_case("true"),
            cors_allow_origins: read(Config::RWS_CONFIG_CORS_ALLOW_ORIGINS),
            cors_allow_credentials: read(Config::RWS_CONFIG_CORS_ALLOW_CREDENTIALS),
            cors_allow_methods: read(Config::RWS_CONFIG_CORS_ALLOW_METHODS),
            cors_allow_headers: read(Config::RWS_CONFIG_CORS_ALLOW_HEADERS),
            cors_expose_headers: read(Config::RWS_CONFIG_CORS_EXPOSE_HEADERS),
            cors_max_age: read(Config::RWS_CONFIG_CORS_MAX_AGE),
            csp: std::env::var("RWS_CONFIG_CSP").unwrap_or_else(|_| {
                if read("RWS_CONFIG_SECURITY_HEADERS").eq_ignore_ascii_case("true") {
                    CSP_DEFAULT.to_string()
                } else {
                    String::new()
                }
            }),
            security_headers: read("RWS_CONFIG_SECURITY_HEADERS").eq_ignore_ascii_case("true"),
            nanos_headers: read("RWS_CONFIG_NANOS_HEADERS").eq_ignore_ascii_case("true"),
            client_hints: read("RWS_CONFIG_CLIENT_HINTS").eq_ignore_ascii_case("true"),
            static_cache_control: std::env::var("RWS_CONFIG_STATIC_CACHE_CONTROL")
                .unwrap_or_else(|_| STATIC_CACHE_CONTROL_DEFAULT.to_string()),
            log_format: read(Config::RWS_CONFIG_LOG_FORMAT),
            request_allocation_size: std::env::var(
                Config::RWS_CONFIG_REQUEST_ALLOCATION_SIZE_IN_BYTES,
            )
            .ok()
            .and_then(|v| v.parse().ok())
            .unwrap_or(*Config::RWS_DEFAULT_REQUEST_ALLOCATION_SIZE_IN_BYTES),
        }
    }

    /// The configuration from the environment, read once and shared: an
    /// atomic load and an `Arc` clone per call instead of ten `getenv`s.
    /// Rebuilt after [`invalidate`] — which `config_reload::reload()` (SIGHUP,
    /// `POST /admin/config/reload`) and every config writer in the crate call,
    /// so hot reload still takes effect on the next request.
    pub fn current() -> Arc<ServerConfig> {
        let generation = GENERATION.load(Ordering::SeqCst);
        if let Some((built_at, config)) = CURRENT.read().unwrap_or_else(|e| e.into_inner()).as_ref() {
            if *built_at == generation {
                return Arc::clone(config);
            }
        }
        // Built from the generation read *before* the environment: a change
        // during the rebuild leaves the cache stale, not wrong.
        let fresh = Arc::new(ServerConfig::from_env());
        *CURRENT.write().unwrap_or_else(|e| e.into_inner()) = Some((generation, Arc::clone(&fresh)));
        fresh
    }
}