WEB: Resolve opt-in decoy hostnames during config preparation #929

Co-Authored-By: brekotis <93345790+brekotis@users.noreply.github.com>

src/config/load/decode.rs

@@ -1,5 +1,6 @@
 use super::*;
 
+/// Typed source together with its exact include graph and rendered input.
 pub(super) type DecodedSourceGraph = (
     ProxyConfig,
     BTreeSet<PathBuf>,
@@ -7,6 +8,7 @@ pub(super) type DecodedSourceGraph = (
     String,
 );
 
+/// Decodes source while retaining the metadata needed for atomic mutations.
 pub(super) fn decode_source_graph(graph: ConfigSourceGraph) -> Result<DecodedSourceGraph> {
     let ConfigSourceGraph {
         source_contents,
@@ -17,6 +19,7 @@ pub(super) fn decode_source_graph(graph: ConfigSourceGraph) -> Result<DecodedSou
     let parsed_toml: toml::Value =
         toml::from_str(&processed).map_err(|e| ProxyError::Config(e.to_string()))?;
     handle_unknown_config_keys(&parsed_toml)?;
+    ProxyConfig::validate_decoy_source_keys(&parsed_toml)?;
     let general_table = parsed_toml
         .get("general")
         .and_then(|value| value.as_table());

src/config/load/decoy_dns.rs

@@ -0,0 +1,204 @@
+use std::future::Future;
+use std::time::Duration;
+
+use super::*;
+
+/// Rejects mode-specific keys even when unknown-key handling is permissive.
+pub(super) fn validate_mode_keys(document: &toml::Value) -> Result<()> {
+    if let Some(vhosts) = document
+        .get("web")
+        .and_then(|web| web.get("vhosts"))
+        .and_then(toml::Value::as_array)
+    {
+        for (idx, vhost) in vhosts.iter().enumerate() {
+            if let Some(decoy) = vhost.get("decoy")
+                && decoy.get("resolve").is_some()
+                && decoy.get("mode").and_then(toml::Value::as_str) != Some("http_upstream")
+            {
+                return Err(ProxyError::Config(format!(
+                    "web.vhosts[{idx}].decoy.resolve is only valid for mode=http_upstream"
+                )));
+            }
+        }
+    }
+    Ok(())
+}
+
+/// Parses one origin and preserves the existing literal-address containment policy.
+pub(super) fn parse_origin(
+    idx: usize,
+    upstream: &str,
+    resolve: WebDecoyResolve,
+) -> Result<url::Url> {
+    let parsed = url::Url::parse(upstream).map_err(|error| {
+        ProxyError::Config(format!(
+            "web.vhosts[{idx}].decoy.upstream is invalid: {error}"
+        ))
+    })?;
+    if parsed.scheme() != "http"
+        || parsed.host_str().is_none()
+        || !parsed.username().is_empty()
+        || parsed.password().is_some()
+        || parsed.query().is_some()
+        || parsed.fragment().is_some()
+        || parsed.path() != "/"
+        || parsed.port() == Some(0)
+    {
+        return Err(ProxyError::Config(format!(
+            "web.vhosts[{idx}].decoy.upstream must be an http origin without credentials, path, query, or fragment"
+        )));
+    }
+    match parsed.host() {
+        Some(url::Host::Ipv4(ip)) => validate_address(idx, IpAddr::V4(ip))?,
+        Some(url::Host::Ipv6(ip)) => validate_address(idx, IpAddr::V6(ip))?,
+        Some(url::Host::Domain(_)) if resolve == WebDecoyResolve::Startup => {}
+        _ => {
+            return Err(ProxyError::Config(format!(
+                "web.vhosts[{idx}].decoy.upstream host must be a loopback or private IP literal unless resolve = \"startup\""
+            )));
+        }
+    }
+    Ok(parsed)
+}
+
+fn validate_address(idx: usize, ip: IpAddr) -> Result<()> {
+    let private = match ip {
+        IpAddr::V4(ip) => ip.is_loopback() || ip.is_private() || ip.is_link_local(),
+        IpAddr::V6(ip) => ip.is_loopback() || ip.is_unique_local() || ip.is_unicast_link_local(),
+    };
+    if !private {
+        return Err(ProxyError::Config(format!(
+            "web.vhosts[{idx}].decoy.upstream must remain inside loopback or a private network"
+        )));
+    }
+    Ok(())
+}
+
+/// Returns all captured answers so non-selected addresses cannot hide a listener loop.
+pub(super) fn addresses(
+    config: &ProxyConfig,
+    idx: usize,
+    parsed: &url::Url,
+    require_resolved: bool,
+) -> Result<Vec<SocketAddr>> {
+    let port = parsed
+        .port_or_known_default()
+        .ok_or_else(|| ProxyError::Config("WEB decoy port cannot be resolved".to_string()))?;
+    let answers = match parsed.host() {
+        Some(url::Host::Ipv4(ip)) => vec![SocketAddr::new(IpAddr::V4(ip), port)],
+        Some(url::Host::Ipv6(ip)) => vec![SocketAddr::new(IpAddr::V6(ip), port)],
+        Some(url::Host::Domain(host)) => {
+            let key = (host.to_string(), port);
+            match config.web.decoy_dns.origins.get(&key) {
+                Some(answers) if !answers.is_empty() => answers.clone(),
+                _ if !require_resolved => return Ok(Vec::new()),
+                _ => {
+                    return Err(ProxyError::Config(format!(
+                        "web.vhosts[{idx}].decoy.upstream requires async preparation for resolve = \"startup\""
+                    )));
+                }
+            }
+        }
+        _ => return Err(ProxyError::Config("WEB decoy host is missing".to_string())),
+    };
+    for addr in &answers {
+        validate_address(idx, addr.ip())?;
+        if addr.port() != port {
+            return Err(ProxyError::Config(
+                "WEB decoy DNS snapshot port mismatch".to_string(),
+            ));
+        }
+    }
+    Ok(answers)
+}
+
+/// Captures fresh resolver evidence without publishing any partially prepared configuration.
+pub(super) async fn prepare<F, Fut>(config: &mut ProxyConfig, mut lookup: F) -> Result<()>
+where
+    F: FnMut(String, u16) -> Fut,
+    Fut: Future<Output = std::io::Result<Vec<SocketAddr>>>,
+{
+    let mut snapshot = WebDecoyDnsSnapshot::default();
+    for (idx, vhost) in config.web.vhosts.iter().enumerate() {
+        let WebDecoyConfig::HttpUpstream { upstream, resolve } = &vhost.decoy else {
+            continue;
+        };
+        let parsed = parse_origin(idx, upstream, *resolve)?;
+        let Some(url::Host::Domain(host)) = parsed.host() else {
+            continue;
+        };
+        let port = parsed
+            .port_or_known_default()
+            .ok_or_else(|| ProxyError::Config("WEB decoy port cannot be resolved".to_string()))?;
+        let key = (host.to_string(), port);
+        if snapshot.origins.contains_key(&key) {
+            continue;
+        }
+        // Dropping this wait does not forcibly cancel a running OS resolver call.
+        let answers = tokio::time::timeout(
+            Duration::from_secs(config.web.timeouts.decoy_resolve_secs),
+            lookup(key.0.clone(), port),
+        )
+        .await
+        .map_err(|_| {
+            ProxyError::Config(format!(
+                "web.vhosts[{idx}].decoy.upstream DNS resolution timed out after {} seconds",
+                config.web.timeouts.decoy_resolve_secs
+            ))
+        })?
+        .map_err(|error| {
+            ProxyError::Config(format!(
+                "web.vhosts[{idx}].decoy.upstream DNS resolution failed: {error}"
+            ))
+        })?;
+        if answers.is_empty() {
+            return Err(ProxyError::Config(format!(
+                "web.vhosts[{idx}].decoy.upstream DNS resolution returned no addresses"
+            )));
+        }
+        for addr in &answers {
+            validate_address(idx, addr.ip())?;
+        }
+        snapshot.origins.insert(key, answers);
+    }
+    config.web.decoy_dns = Arc::new(snapshot);
+    validate_web::validate_decoy_listener_separation(config)
+}
+
+/// Builds the unchanged request-time tuple from immutable configuration evidence.
+pub(super) fn build_upstream(
+    config: &ProxyConfig,
+    idx: usize,
+    upstream: &str,
+    resolve: WebDecoyResolve,
+) -> Result<WebRuntimeDecoy> {
+    let parsed = parse_origin(idx, upstream, resolve)?;
+    let addr = addresses(config, idx, &parsed, true)?
+        .first()
+        .copied()
+        .ok_or_else(|| ProxyError::Config("WEB decoy DNS snapshot is empty".to_string()))?;
+    // URL authority keeps the configured hostname and brackets IPv6 literals.
+    let authority = parsed[url::Position::BeforeHost..url::Position::AfterPort].to_string();
+    Ok(WebRuntimeDecoy::HttpUpstream { addr, authority })
+}
+
+impl ProxyConfig {
+    /// Compares selected endpoints separately from source-only configuration equality.
+    pub(crate) fn web_decoy_endpoints_equal(&self, other: &Self) -> bool {
+        fn selected(config: &ProxyConfig) -> impl Iterator<Item = (&String, SocketAddr)> {
+            config
+                .web
+                .runtime
+                .iter()
+                .flat_map(|runtime| runtime.vhosts.iter())
+                .filter_map(|(host, vhost)| match vhost.decoy {
+                    WebRuntimeDecoy::HttpUpstream { addr, .. } => Some((host, addr)),
+                    WebRuntimeDecoy::StaticDirectory(_) => None,
+                })
+        }
+        selected(self).eq(selected(other))
+    }
+}
+
+#[cfg(test)]
+mod tests;

src/config/load/decoy_dns/tests.rs

@@ -0,0 +1,330 @@
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+use super::*;
+
+const SOURCE: &str = r#"
+[access.users]
+alice = "000102030405060708090a0b0c0d0e0f"
+[[server.listeners]]
+ip = "127.0.0.1"
+port = 18080
+transport = "web"
+web_trusted_proxy_cidrs = ["127.0.0.1/32"]
+[web]
+enabled = true
+[[web.vhosts]]
+host = "proxy.example.com"
+public_addr = "203.0.113.10:443"
+[web.vhosts.decoy]
+mode = "http_upstream"
+upstream = "http://Example.COM:18081"
+resolve = "startup"
+[[web.vhosts.profiles]]
+user = "alice"
+secret_mode = "dd"
+"#;
+
+fn source(text: &str) -> ParsedConfigSource {
+    pipeline::parse_source_graph(ConfigSourceGraph {
+        rendered: text.to_string(),
+        source_contents: BTreeMap::new(),
+    })
+    .unwrap()
+}
+
+async fn prepared(answers: &[&str]) -> LoadedConfig {
+    let mut parsed = source(SOURCE);
+    let answers: Vec<SocketAddr> = answers.iter().map(|addr| addr.parse().unwrap()).collect();
+    prepare(&mut parsed.config, |_, _| {
+        std::future::ready(Ok(answers.clone()))
+    })
+    .await
+    .unwrap();
+    pipeline::finish(parsed).unwrap()
+}
+
+fn endpoint(config: &ProxyConfig) -> (SocketAddr, &str) {
+    let runtime = config.web.runtime.as_ref().unwrap();
+    match &runtime.vhosts["proxy.example.com"].decoy {
+        WebRuntimeDecoy::HttpUpstream { addr, authority } => (*addr, authority),
+        _ => panic!("expected HTTP decoy"),
+    }
+}
+
+#[tokio::test]
+async fn decoy_dns_snapshot_deduplicates_normalized_origins_and_preserves_order() {
+    let mut parsed = source(SOURCE);
+    let mut second = parsed.config.web.vhosts[0].clone();
+    second.host = "bsi.bund.de".to_string();
+    second.decoy = WebDecoyConfig::HttpUpstream {
+        upstream: "http://example.com:18081/".to_string(),
+        resolve: WebDecoyResolve::Startup,
+    };
+    parsed.config.web.vhosts.push(second);
+    let calls = AtomicUsize::new(0);
+    prepare(&mut parsed.config, |host, port| {
+        assert_eq!((host.as_str(), port), ("example.com", 18081));
+        calls.fetch_add(1, Ordering::SeqCst);
+        std::future::ready(Ok(vec![
+            "[fd00::2]:18081".parse().unwrap(),
+            "10.0.0.2:18081".parse().unwrap(),
+        ]))
+    })
+    .await
+    .unwrap();
+    let mut loaded = pipeline::finish(parsed).unwrap();
+    for _ in 0..3 {
+        loaded.config.validate_effective_web().unwrap();
+        loaded.config.rebuild_runtime_web().unwrap();
+    }
+    assert_eq!(calls.load(Ordering::SeqCst), 1);
+    assert_eq!(
+        endpoint(&loaded.config),
+        ("[fd00::2]:18081".parse().unwrap(), "example.com:18081")
+    );
+    assert_eq!(
+        loaded
+            .config
+            .web
+            .decoy_dns
+            .origins
+            .values()
+            .next()
+            .unwrap()
+            .len(),
+        2
+    );
+    assert!(
+        !serde_json::to_string(&loaded.config)
+            .unwrap()
+            .contains("fd00::2")
+    );
+}
+
+#[tokio::test]
+async fn decoy_dns_rejects_every_public_answer_including_non_selected() {
+    for disallowed in [
+        "8.8.8.8:18081",
+        "[2001:4860:4860::8888]:18081",
+        "[::ffff:127.0.0.1]:18081",
+    ] {
+        let mut parsed = source(SOURCE);
+        let error = prepare(&mut parsed.config, |_, _| {
+            std::future::ready(Ok(vec![
+                "127.0.0.2:18081".parse().unwrap(),
+                disallowed.parse().unwrap(),
+            ]))
+        })
+        .await
+        .unwrap_err();
+        assert!(error.to_string().contains("must remain inside"));
+        assert!(parsed.config.web.runtime.is_none());
+    }
+}
+
+#[tokio::test]
+async fn decoy_dns_rejects_non_selected_direct_and_wildcard_listener_loops() {
+    for listener in ["127.0.0.1", "0.0.0.0"] {
+        let mut parsed = source(&SOURCE.replace("Example.COM:18081", "example.com:18080"));
+        parsed.config.server.listeners[0].ip = listener.parse().unwrap();
+        let error = prepare(&mut parsed.config, |_, _| {
+            std::future::ready(Ok(vec![
+                "[fd00::2]:18080".parse().unwrap(),
+                "127.0.0.1:18080".parse().unwrap(),
+            ]))
+        })
+        .await
+        .unwrap_err();
+        assert!(error.to_string().contains("overlaps WEB listener"));
+    }
+}
+
+#[tokio::test]
+async fn decoy_dns_empty_answers_and_resolver_errors_fail_closed() {
+    let mut parsed = source(SOURCE);
+    let error = prepare(&mut parsed.config, |_, _| {
+        std::future::ready(Ok(Vec::new()))
+    })
+    .await
+    .unwrap_err();
+    assert!(error.to_string().contains("returned no addresses"));
+    let error = prepare(&mut parsed.config, |_, _| {
+        std::future::ready(Err(std::io::Error::new(
+            std::io::ErrorKind::NotFound,
+            "test resolver failure",
+        )))
+    })
+    .await
+    .unwrap_err();
+    assert!(error.to_string().contains("DNS resolution failed"));
+}
+
+#[tokio::test]
+async fn decoy_dns_timeout_is_bounded() {
+    let mut parsed = source(SOURCE);
+    parsed.config.web.timeouts.decoy_resolve_secs = 1;
+    let error = tokio::time::timeout(
+        Duration::from_secs(3),
+        prepare(&mut parsed.config, |_, _| {
+            std::future::pending::<std::io::Result<Vec<SocketAddr>>>()
+        }),
+    )
+    .await
+    .unwrap()
+    .unwrap_err();
+    assert!(error.to_string().contains("timed out after 1 seconds"));
+}
+
+#[tokio::test]
+async fn decoy_dns_literal_startup_never_looks_up_and_keeps_ipv6_authority() {
+    let mut parsed = source(&SOURCE.replace("Example.COM:18081", "[::1]:18081"));
+    prepare(&mut parsed.config, |_, _| {
+        std::future::ready(Err(std::io::Error::other("IP literals must not reach DNS")))
+    })
+    .await
+    .unwrap();
+    let loaded = pipeline::finish(parsed).unwrap();
+    assert_eq!(
+        endpoint(&loaded.config),
+        ("[::1]:18081".parse().unwrap(), "[::1]:18081")
+    );
+}
+
+#[test]
+fn decoy_dns_source_parse_is_not_a_prepared_runtime() {
+    let parsed = source(SOURCE);
+    assert!(parsed.config.web.runtime.is_none());
+    assert!(parsed.config.web.decoy_dns.origins.is_empty());
+    assert!(
+        pipeline::finish(parsed)
+            .unwrap_err()
+            .to_string()
+            .contains("requires async preparation")
+    );
+}
+
+#[tokio::test]
+async fn decoy_dns_evidence_is_bound_to_origin_and_port() {
+    let loaded = prepared(&["10.0.0.2:18081"]).await;
+    for changed in ["http://telekom.com:18081", "http://example.com:18082"] {
+        let mut config = loaded.config.clone();
+        config.web.vhosts[0].decoy = WebDecoyConfig::HttpUpstream {
+            upstream: changed.to_string(),
+            resolve: WebDecoyResolve::Startup,
+        };
+        assert!(
+            config
+                .validate_effective_web()
+                .unwrap_err()
+                .to_string()
+                .contains("requires async preparation")
+        );
+        assert!(config.rebuild_runtime_web().is_err());
+    }
+}
+
+#[tokio::test]
+async fn decoy_dns_reload_pins_old_generation_and_detects_dns_only_changes() {
+    let old = prepared(&["10.0.0.2:18081"]).await;
+    let new = prepared(&["10.0.0.3:18081"]).await;
+    assert_eq!(old.rendered_hash, new.rendered_hash);
+    assert_eq!(
+        serde_json::to_value(&old.config).unwrap(),
+        serde_json::to_value(&new.config).unwrap()
+    );
+    let resolved =
+        crate::maestro::runtime_build::resolve_reload_config(&old.config, &new.config).unwrap();
+    assert!(resolved.runtime_changed);
+    assert!(!old.config.web_decoy_endpoints_equal(&new.config));
+    assert_eq!(endpoint(&old.config).0, "10.0.0.2:18081".parse().unwrap());
+    let same = prepared(&["10.0.0.3:18081", "10.0.0.4:18081"]).await;
+    assert!(same.config.web_decoy_endpoints_equal(&new.config));
+}
+
+#[tokio::test]
+async fn decoy_dns_effective_listener_overlay_rechecks_every_answer() {
+    let old = prepared(&["10.0.0.2:18081"]).await;
+    let mut parsed = source(SOURCE);
+    parsed.config.server.listeners[0].port = Some(18082);
+    parsed.config.web.vhosts[0].decoy = WebDecoyConfig::HttpUpstream {
+        upstream: "http://example.com:18080".to_string(),
+        resolve: WebDecoyResolve::Startup,
+    };
+    prepare(&mut parsed.config, |_, _| {
+        std::future::ready(Ok(vec![
+            "10.0.0.2:18080".parse().unwrap(),
+            "127.0.0.1:18080".parse().unwrap(),
+        ]))
+    })
+    .await
+    .unwrap();
+    let desired = pipeline::finish(parsed).unwrap();
+    assert!(
+        crate::maestro::runtime_build::resolve_reload_config(&old.config, &desired.config)
+            .err()
+            .unwrap()
+            .contains("overlaps WEB listener")
+    );
+}
+
+#[tokio::test]
+async fn decoy_dns_rejects_ipv6_direct_and_wildcard_listener_loops() {
+    for listener in ["::1", "::"] {
+        let mut parsed = source(&SOURCE.replace("Example.COM:18081", "example.com:18080"));
+        parsed.config.network.ipv6 = Some(true);
+        parsed.config.server.listeners[0].ip = listener.parse().unwrap();
+        let error = prepare(&mut parsed.config, |_, _| {
+            std::future::ready(Ok(vec![
+                "10.0.0.2:18080".parse().unwrap(),
+                "[::1]:18080".parse().unwrap(),
+            ]))
+        })
+        .await
+        .unwrap_err();
+        assert!(error.to_string().contains("overlaps WEB listener"));
+    }
+}
+
+#[test]
+fn decoy_dns_startup_does_not_relax_origin_url_rules() {
+    for url in [
+        "https://example.com",
+        "http://user@example.com",
+        "http://user:pass@example.com",
+        "http://example.com/path",
+        "http://example.com/?q=1",
+        "http://example.com/#fragment",
+        "http://example.com:0",
+    ] {
+        assert!(
+            parse_origin(0, url, WebDecoyResolve::Startup).is_err(),
+            "accepted {url}"
+        );
+    }
+}
+
+#[tokio::test]
+async fn decoy_dns_default_port_authority_and_evidence_port_fence() {
+    let mut parsed = source(&SOURCE.replace("Example.COM:18081", "example.com"));
+    prepare(&mut parsed.config, |_, port| {
+        assert_eq!(port, 80);
+        std::future::ready(Ok(vec!["127.0.0.2:80".parse().unwrap()]))
+    })
+    .await
+    .unwrap();
+    let loaded = pipeline::finish(parsed).unwrap();
+    assert_eq!(endpoint(&loaded.config).1, "example.com");
+    let mut config = loaded.config.clone();
+    Arc::make_mut(&mut config.web.decoy_dns).origins.insert(
+        ("example.com".to_string(), 80),
+        vec!["127.0.0.2:81".parse().unwrap()],
+    );
+    assert!(
+        config
+            .validate_effective_web()
+            .unwrap_err()
+            .to_string()
+            .contains("port mismatch")
+    );
+    assert!(config.rebuild_runtime_web().is_err());
+}

src/config/load/effective.rs

@@ -1,5 +1,6 @@
 use super::*;
 
+/// Normalizes source policy and authentication data before external decoy preparation.
 pub(super) fn apply(config: &mut ProxyConfig) -> Result<()> {
     // Normalize optional TLS fetch scope: whitespace-only values disable scoped routing.
     config.censorship.tls_fetch_scope = config.censorship.tls_fetch_scope.trim().to_string();
@@ -217,6 +218,5 @@ pub(super) fn apply(config: &mut ProxyConfig) -> Result<()> {
     validate_logging_config(&config.logging)?;
     validate_upstreams(config)?;
     config.rebuild_runtime_user_auth()?;
-    config.rebuild_runtime_web()?;
     Ok(())
 }

src/config/load/pipeline.rs

@@ -1,18 +1,51 @@
 use super::*;
 
+/// Completes legacy synchronous loads without performing hostname resolution.
 pub(super) fn load_source_graph(graph: ConfigSourceGraph) -> Result<LoadedConfig> {
+    finish(parse_source_graph(graph)?)
+}
+
+/// Normalizes source while leaving DNS and immutable site acquisition to preparation.
+pub(super) fn parse_source_graph(graph: ConfigSourceGraph) -> Result<ParsedConfigSource> {
     let (mut config, source_files, source_contents, processed) =
         decode::decode_source_graph(graph)?;
     validate_core::validate(&mut config)?;
     validate_runtime::validate(&mut config)?;
     validate_me::validate(&mut config)?;
     validate_server::validate(&mut config)?;
-    validate_web::validate(&mut config)?;
+    validate_web::validate_source(&mut config)?;
     effective::apply(&mut config)?;
-    Ok(LoadedConfig {
+    Ok(ParsedConfigSource {
         config,
         source_files: source_files.into_iter().collect(),
         source_contents,
         rendered_hash: hash_rendered_snapshot(&processed),
     })
 }
+
+/// Completes synchronous validation and static acquisition after DNS is captured.
+pub(super) fn finish(mut parsed: ParsedConfigSource) -> Result<LoadedConfig> {
+    parsed.config.validate_effective_web()?;
+    parsed.config.rebuild_runtime_web()?;
+    Ok(LoadedConfig {
+        config: parsed.config,
+        source_files: parsed.source_files,
+        source_contents: parsed.source_contents,
+        rendered_hash: parsed.rendered_hash,
+    })
+}
+
+impl ParsedConfigSource {
+    /// Resolves each unique decoy origin once, then builds a fully validated candidate.
+    pub(crate) async fn prepare(mut self) -> Result<LoadedConfig> {
+        decoy_dns::prepare(&mut self.config, |host, port| async move {
+            tokio::net::lookup_host((host.as_str(), port))
+                .await
+                .map(|answers| answers.collect())
+        })
+        .await?;
+        tokio::task::spawn_blocking(move || finish(self))
+            .await
+            .map_err(|error| ProxyError::Config(format!("config preparation failed: {error}")))?
+    }
+}

src/config/load/runtime_web.rs

@@ -47,8 +47,10 @@ pub(super) fn rebuild(config: &mut ProxyConfig) -> Result<()> {
     let mut static_bytes = 0usize;
 
     let carrier_candidates: Arc<[WebCarrier]> = config.web.carrier_candidates().into();
-    for vhost in &config.web.vhosts {
+    for (vhost_idx, vhost) in config.web.vhosts.iter().enumerate() {
         let decoy = build_decoy(
+            config,
+            vhost_idx,
             vhost,
             &config.web.limits,
             &mut static_files,
@@ -182,42 +184,16 @@ fn client_secret(secret: [u8; 16], mode: WebSecretMode) -> ([u8; 17], usize) {
 }
 
 fn build_decoy(
+    config: &ProxyConfig,
+    vhost_idx: usize,
     vhost: &WebVhostConfig,
     limits: &WebLimitsConfig,
     static_files: &mut usize,
     static_bytes: &mut usize,
 ) -> Result<WebRuntimeDecoy> {
     match &vhost.decoy {
-        WebDecoyConfig::HttpUpstream { upstream } => {
-            let parsed = url::Url::parse(upstream).map_err(|error| {
-                ProxyError::Config(format!(
-                    "WEB decoy upstream for `{}` is invalid: {error}",
-                    vhost.host
-                ))
-            })?;
-            let ip = match parsed.host() {
-                Some(url::Host::Ipv4(ip)) => std::net::IpAddr::V4(ip),
-                Some(url::Host::Ipv6(ip)) => std::net::IpAddr::V6(ip),
-                _ => {
-                    return Err(ProxyError::Config(
-                        "WEB decoy host must be an IP literal".to_string(),
-                    ));
-                }
-            };
-            let host = ip.to_string();
-            let port = parsed.port_or_known_default().ok_or_else(|| {
-                ProxyError::Config("WEB decoy port cannot be resolved".to_string())
-            })?;
-            let authority = match (ip, parsed.port()) {
-                (std::net::IpAddr::V6(_), Some(_)) => format!("[{host}]:{port}"),
-                (std::net::IpAddr::V6(_), None) => format!("[{host}]"),
-                (std::net::IpAddr::V4(_), Some(_)) => format!("{host}:{port}"),
-                (std::net::IpAddr::V4(_), None) => host.clone(),
-            };
-            Ok(WebRuntimeDecoy::HttpUpstream {
-                addr: SocketAddr::new(ip, port),
-                authority,
-            })
+        WebDecoyConfig::HttpUpstream { upstream, resolve } => {
+            decoy_dns::build_upstream(config, vhost_idx, upstream, *resolve)
         }
         WebDecoyConfig::StaticDirectory { directory, index } => {
             let site = load_static_site(directory, index, limits, static_files, static_bytes)?;

src/config/load/strict_keys.rs

@@ -365,10 +365,11 @@ const WEB_TIMEOUTS_CONFIG_KEYS: &[&str] = &[
     "http_overload_timeout_ms",
     "shutdown_secs",
     "decoy_header_secs",
+    "decoy_resolve_secs",
 ];
 
 const WEB_VHOST_CONFIG_KEYS: &[&str] = &["host", "base_path", "public_addr", "decoy", "profiles"];
-const WEB_DECOY_CONFIG_KEYS: &[&str] = &["mode", "upstream", "directory", "index"];
+const WEB_DECOY_CONFIG_KEYS: &[&str] = &["mode", "upstream", "directory", "index", "resolve"];
 const WEB_PROFILE_CONFIG_KEYS: &[&str] = &[
     "user",
     "secret_mode",

src/config/load/validate_web.rs

@@ -27,6 +27,12 @@ const MAX_WEB_MEMORY_ENVELOPE_BYTES: usize = 4 * 1024 * 1024 * 1024;
 
 /// Validates WEB policy and resource bounds before building runtime state.
 pub(super) fn validate(config: &mut ProxyConfig) -> Result<()> {
+    validate_source(config)?;
+    validate_decoy_listener_separation(config)
+}
+
+/// Validates source policy without requiring DNS evidence for opted-in origins.
+pub(super) fn validate_source(config: &mut ProxyConfig) -> Result<()> {
     let web_listener_count = config
         .server
         .listeners
@@ -83,12 +89,19 @@ pub(super) fn validate(config: &mut ProxyConfig) -> Result<()> {
     timeouts::validate(&config.web.timeouts)?;
     websocket::validate(&carriers, &config.web.limits, &config.web.timeouts)?;
     validate_vhosts(config)?;
-    validate_decoy_listener_separation(config)?;
+    validate_decoy_listener_separation_inner(config, false)?;
     Ok(())
 }
 
 /// Rejects a direct decoy recursion into an effective WEB listener.
 pub(super) fn validate_decoy_listener_separation(config: &ProxyConfig) -> Result<()> {
+    validate_decoy_listener_separation_inner(config, true)
+}
+
+fn validate_decoy_listener_separation_inner(
+    config: &ProxyConfig,
+    require_resolved: bool,
+) -> Result<()> {
     let web_listeners = config
         .server
         .listeners
@@ -101,30 +114,19 @@ pub(super) fn validate_decoy_listener_separation(config: &ProxyConfig) -> Result
         .map(|listener| SocketAddr::new(listener.ip, listener.port.unwrap_or(config.server.port)))
         .collect::<Vec<_>>();
     for (vhost_idx, vhost) in config.web.vhosts.iter().enumerate() {
-        let WebDecoyConfig::HttpUpstream { upstream } = &vhost.decoy else {
+        let WebDecoyConfig::HttpUpstream { upstream, resolve } = &vhost.decoy else {
             continue;
         };
-        let parsed = url::Url::parse(upstream).map_err(|error| {
-            ProxyError::Config(format!(
-                "web.vhosts[{vhost_idx}].decoy.upstream is invalid: {error}"
-            ))
-        })?;
-        let Some(port) = parsed.port_or_known_default() else {
-            continue;
-        };
-        let upstream_ip = match parsed.host() {
-            Some(url::Host::Ipv4(ip)) => IpAddr::V4(ip),
-            Some(url::Host::Ipv6(ip)) => IpAddr::V6(ip),
-            _ => continue,
-        };
-        let upstream_addr = SocketAddr::new(upstream_ip, port);
-        if web_listeners
-            .iter()
-            .any(|listener| listener_covers(*listener, upstream_addr))
-        {
-            return config_error(&format!(
-                "web.vhosts[{vhost_idx}].decoy upstream overlaps WEB listener {upstream_addr}"
-            ));
+        let parsed = decoy_dns::parse_origin(vhost_idx, upstream, *resolve)?;
+        for upstream_addr in decoy_dns::addresses(config, vhost_idx, &parsed, require_resolved)? {
+            if web_listeners
+                .iter()
+                .any(|listener| listener_covers(*listener, upstream_addr))
+            {
+                return config_error(&format!(
+                    "web.vhosts[{vhost_idx}].decoy upstream overlaps WEB listener {upstream_addr}"
+                ));
+            }
         }
     }
     Ok(())

src/config/load/validate_web/timeouts.rs

@@ -26,6 +26,7 @@ pub(super) fn validate(timeouts: &WebTimeoutsConfig) -> Result<()> {
         ("http_idle_secs", timeouts.http_idle_secs),
         ("shutdown_secs", timeouts.shutdown_secs),
         ("decoy_header_secs", timeouts.decoy_header_secs),
+        ("decoy_resolve_secs", timeouts.decoy_resolve_secs),
     ];
     if let Some((field, _)) = values
         .into_iter()

src/config/load/validate_web/vhosts.rs

@@ -150,45 +150,8 @@ pub(super) fn web_host_last_label_is_numeric(host: &str) -> bool {
 
 pub(super) fn validate_decoy(vhost_idx: usize, decoy: &WebDecoyConfig) -> Result<()> {
     match decoy {
-        WebDecoyConfig::HttpUpstream { upstream } => {
-            let parsed = url::Url::parse(upstream).map_err(|error| {
-                ProxyError::Config(format!(
-                    "web.vhosts[{vhost_idx}].decoy.upstream is invalid: {error}"
-                ))
-            })?;
-            if parsed.scheme() != "http"
-                || parsed.host_str().is_none()
-                || !parsed.username().is_empty()
-                || parsed.password().is_some()
-                || parsed.query().is_some()
-                || parsed.fragment().is_some()
-                || parsed.path() != "/"
-                || parsed.port() == Some(0)
-            {
-                return config_error(&format!(
-                    "web.vhosts[{vhost_idx}].decoy.upstream must be an http origin without credentials, path, query, or fragment"
-                ));
-            }
-            let ip = match parsed.host() {
-                Some(url::Host::Ipv4(ip)) => IpAddr::V4(ip),
-                Some(url::Host::Ipv6(ip)) => IpAddr::V6(ip),
-                _ => {
-                    return config_error(&format!(
-                        "web.vhosts[{vhost_idx}].decoy.upstream host must be a loopback or private IP literal"
-                    ));
-                }
-            };
-            let private = match ip {
-                IpAddr::V4(ip) => ip.is_loopback() || ip.is_private() || ip.is_link_local(),
-                IpAddr::V6(ip) => {
-                    ip.is_loopback() || ip.is_unique_local() || ip.is_unicast_link_local()
-                }
-            };
-            if !private {
-                return config_error(&format!(
-                    "web.vhosts[{vhost_idx}].decoy.upstream must remain inside loopback or a private network"
-                ));
-            }
+        WebDecoyConfig::HttpUpstream { upstream, resolve } => {
+            decoy_dns::parse_origin(vhost_idx, upstream, *resolve)?;
         }
         WebDecoyConfig::StaticDirectory { directory, index } => {
             if !directory.is_absolute() {