feat(appgate): serve HTTPS and HTTP on the same app port

An app port must answer whatever the browser asks for: an HTTP dashboard embeds http://host:PORT, an HTTPS one embeds https://host:PORT, and an HTTPS page cannot embed an HTTP frame at all. So the choice is per-node, not per-fleet, and a second port number would mean every manifest changes and torrc doubles. Instead the gate peeks the first byte. A TLS ClientHello is 0x16; no HTTP method starts with it. peek() leaves the bytes in the socket buffer, so the acceptor still sees a complete, untouched ClientHello. TLS and plain share one generic serve_http(), so authentication, proxying and upgrade handling cannot drift apart by scheme. EXISTING NODES ARE UNAFFECTED BY CONSTRUCTION. Anything that is not a TLS handshake takes the identical path as before, and a node with no certificate serves plain HTTP exactly as today — TLS is strictly additive. rustls does NOT verify that a private key matches its certificate. Established by test, not assumed: with_single_cert accepted a pair from two different keys and would only have failed mid-handshake in a user's browser — a security control that reports success and does nothing, the exact shape this module's own docs warn about. So the pairing is now proven explicitly (sign a fixed message with the key, verify against the certificate's public key) and a mismatch refuses to serve. Also: cert and key mtimes are stamped as a PAIR, because reissuing writes them separately and keying on one would serve a certificate that no longer matches its key; a 15s first-byte timeout closes the slowloris window one step earlier than the existing header-read timeout; PKCS#8 and PKCS#1 keys are both accepted so a hand-made key does not silently downgrade a working node. Deps pinned to the rustls 0.21 line reqwest already resolves — no new vendor, no second rustls major. Test fixtures are throwaway (localhost SANs only), not any node's identity. 38/38 appgate tests pass. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-06 15:23:47 -04:00
parent f09ff102ee
commit 7515166a07
9 changed files with 577 additions and 17 deletions
@@ -147,6 +147,8 @@ dependencies = [
 "reed-solomon-erasure",
 "regex",
 "reqwest 0.11.27",
+ "rustls-pemfile",
+ "rustls-webpki 0.101.7",
 "sd-notify",
 "serde",
 "serde_bytes",
@@ -159,6 +161,7 @@ dependencies = [
 "tempfile",
 "thiserror 1.0.69",
 "tokio",
+ "tokio-rustls 0.24.1",
 "tokio-test",
 "tokio-tungstenite 0.20.1",
 "toml",
@@ -80,6 +80,13 @@ serde_yaml = "0.9"

 # HTTP client (for LND REST proxy, Tor SOCKS for peer messaging)
 # Uses rustls-tls for cross-compilation (no OpenSSL dependency)
+# App-gate TLS. Pinned to the rustls 0.21 line that reqwest already resolves,
+# so this adds no new vendor and no second rustls major to the tree.
+tokio-rustls = "0.24"
+rustls-pemfile = "1.0"
+# Verifying that the gate's key actually pairs with its certificate; rustls
+# does not check this itself. Same version rustls 0.21 already resolves.
+webpki = { package = "rustls-webpki", version = "0.101" }
 reqwest = { version = "0.11", default-features = false, features = ["json", "socks", "rustls-tls", "stream"] }

 # Nostr (node discovery + NIP-44 encrypted peer handshake)
@@ -331,23 +331,7 @@ fn spawn_accept_loop(
                    let gate = gate.clone();
                    let app = app.clone();
                    tokio::spawn(async move {
-                        let service = hyper::service::service_fn(move |req| {
-                            let gate = gate.clone();
-                            let app = app.clone();
-                            async move {
-                                Ok::<_, std::convert::Infallible>(
-                                    gate.handle(req, &app, peer.ip()).await,
-                                )
-                            }
-                        });
-                        let _ = hyper::server::conn::Http::new()
-                            // Same slowloris guard as the main listener: an
-                            // unauthenticated caller must not be able to hold
-                            // a connection open by never sending headers.
-                            .http1_header_read_timeout(std::time::Duration::from_secs(30))
-                            .serve_connection(stream, service)
-                            .with_upgrades()
-                            .await;
+                        serve_connection(stream, peer, gate, app).await;
                    });
                }
                _ = shutdown_rx.changed() => break,
@@ -356,6 +340,86 @@ fn spawn_accept_loop(
    })
 }

+/// How long a freshly-accepted connection has to send its first byte.
+///
+/// The peek below blocks until *something* arrives, so without this an
+/// unauthenticated caller could hold a task open indefinitely by connecting and
+/// saying nothing — the same slowloris shape the header-read timeout guards
+/// against, one step earlier in the handshake.
+const FIRST_BYTE_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(15);
+
+/// Serve one connection, as TLS or plain HTTP depending on what the client
+/// actually sent.
+///
+/// The first byte decides: `peek` inspects it *without consuming it*, so a TLS
+/// client's ClientHello reaches the acceptor whole. This is what lets one port
+/// serve an HTTP dashboard's frames and an HTTPS dashboard's frames on the same
+/// node without a second port number or a per-node build.
+async fn serve_connection(
+    stream: tokio::net::TcpStream,
+    peer: SocketAddr,
+    gate: Arc<AppGate>,
+    app: GatedPort,
+) {
+    let mut first = [0u8; 1];
+    let peeked = tokio::time::timeout(FIRST_BYTE_TIMEOUT, stream.peek(&mut first)).await;
+
+    let is_tls = match peeked {
+        Ok(Ok(1)) => super::tls::looks_like_tls(first[0]),
+        // 0 bytes is a clean close before any request; anything else is a
+        // read error or the timeout. Nothing to serve either way.
+        _ => {
+            debug!(%peer, "app gate connection closed before sending anything");
+            return;
+        }
+    };
+
+    if is_tls {
+        match gate.tls.acceptor().await {
+            Some(acceptor) => match acceptor.accept(stream).await {
+                Ok(tls_stream) => serve_http(tls_stream, peer, gate, app).await,
+                Err(e) => {
+                    // Routine: a browser probing a cert it does not trust, or a
+                    // scanner. Not operator-actionable, so debug.
+                    debug!(%peer, error = %e, "app gate TLS handshake failed");
+                }
+            },
+            None => {
+                // The client speaks TLS and this node has no certificate.
+                // Replying in plain HTTP would be unreadable garbage to it, so
+                // close and let the browser report the connection failure.
+                debug!(
+                    %peer,
+                    "app gate got a TLS connection but has no certificate — closing"
+                );
+            }
+        }
+    } else {
+        serve_http(stream, peer, gate, app).await;
+    }
+}
+
+/// The HTTP half, generic over the transport so TLS and plain share one path —
+/// the gate's authentication, proxying and upgrade handling must not differ by
+/// scheme, and generics make that structural rather than a thing to remember.
+async fn serve_http<S>(stream: S, peer: SocketAddr, gate: Arc<AppGate>, app: GatedPort)
+where
+    S: tokio::io::AsyncRead + tokio::io::AsyncWrite + Unpin + Send + 'static,
+{
+    let service = hyper::service::service_fn(move |req| {
+        let gate = gate.clone();
+        let app = app.clone();
+        async move { Ok::<_, std::convert::Infallible>(gate.handle(req, &app, peer.ip()).await) }
+    });
+    let _ = hyper::server::conn::Http::new()
+        // Same slowloris guard as the main listener: an unauthenticated caller
+        // must not be able to hold a connection open by never sending headers.
+        .http1_header_read_timeout(std::time::Duration::from_secs(30))
+        .serve_connection(stream, service)
+        .with_upgrades()
+        .await;
+}
+
 #[cfg(test)]
 mod tests {
    use super::*;
@@ -35,6 +35,7 @@

 pub mod identity;
 pub mod listener;
+pub mod tls;

 use crate::auth::AuthManager;
 use crate::rate_limit::LoginRateLimiter;
@@ -65,6 +66,10 @@ pub struct AppGate {
    limiter: LoginRateLimiter,
    data_dir: PathBuf,
    port_map: Arc<RwLock<PortMap>>,
+    /// TLS for gated ports. Shared by every accept loop so one reissue is
+    /// picked up by all of them, and so the parse happens once rather than
+    /// per port.
+    pub(crate) tls: Arc<tls::GateTls>,
 }

 impl AppGate {
@@ -80,6 +85,7 @@ impl AppGate {
            limiter,
            data_dir,
            port_map: Arc::new(RwLock::new(identity::build_port_map())),
+            tls: Arc::new(tls::GateTls::new()),
        }
    }

@@ -0,0 +1,10 @@
+Throwaway TLS fixtures for `appgate::tls` unit tests.
+
+Generated by `openssl req -x509 -nodes` with SANs `localhost`/`127.0.0.1` only.
+They are **not** any node's identity: a real node's pair lives at
+`/etc/archipelago/ssl/` and is created by `scripts/setup-node-ca.sh`. Nothing
+here is trusted by anything, and `other.key` exists purely to prove a
+mismatched cert/key pair is rejected rather than silently served.
+
+Regenerate with the command in this directory's git history if they ever
+expire — `-days 36500` means that should not happen.
@@ -0,0 +1,21 @@
+-----BEGIN CERTIFICATE-----
+MIIDezCCAmOgAwIBAgIUT3u7aR6+q5j3ZITojvEaSt4mVWkwDQYJKoZIhvcNAQEL
+BQAwPjEZMBcGA1UEAwwQYXJjaGlwZWxhZ28tdGVzdDEhMB8GA1UECgwYQXJjaGlw
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+psnc1Nu/EQEzcTYvPHJpMUwUOsJgDb2HWx5FAxy02Q==
+-----END CERTIFICATE-----
@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----
+MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQD6t1PeYAXxQVlL
+zfqn+6C1NFT609OiJmOx5d9uhKXIg7zu9KCqaRJWCDeJFBX/UEmWIJjJvB8GzLCz
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+m+jMknsSIITKIhu6oa1PqvM=
+-----END PRIVATE KEY-----
@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----
+MIIEvAIBADANBgkqhkiG9w0BAQEFAASCBKYwggSiAgEAAoIBAQCy2KgVkOYSz0QO
+QxXA0ENomMr0Butuh4Yv5KT9RzrTxrsf/GfiJPX5fjtANwUXniojMNClxLGGep5v
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+RxnrHeKUcS43Z346QXYrsg==
+-----END PRIVATE KEY-----
@@ -0,0 +1,393 @@
+//! TLS for gated app ports, alongside plain HTTP on the same socket.
+//!
+//! # Why both, on one port
+//!
+//! An app port has to serve whatever the browser asks for. A node whose
+//! dashboard is plain HTTP embeds `http://host:PORT`; a node with HTTPS embeds
+//! `https://host:PORT` — and an HTTPS page cannot embed an HTTP frame at all
+//! (mixed content), so the choice is genuinely per-node, not per-fleet. Giving
+//! TLS its own port number would mean every app declares a second port, every
+//! manifest changes, and torrc doubles. Instead the gate peeks the first byte:
+//! a TLS ClientHello starts with `0x16` (handshake) and no HTTP method does, so
+//! the two are distinguishable without consuming anything.
+//!
+//! `peek` is what makes this safe — it leaves the bytes in the socket buffer,
+//! so the TLS acceptor still sees a complete, untouched ClientHello.
+//!
+//! # Why reload, rather than load once
+//!
+//! `scripts/setup-node-ca.sh` reissues the leaf whenever the node gains an
+//! address (DHCP, Tailscale coming up, the fips0 ULA appearing late) — the same
+//! churn the bind sweep exists for. A config parsed once at startup would keep
+//! serving a certificate that omits the address the user is actually on, and
+//! the failure is a browser-side name mismatch that no node-side log would
+//! explain. So the mtime of both files is checked and the config rebuilt when
+//! either moves.
+//!
+//! # Absent certificates are not an error
+//!
+//! A node that has never run the CA script has no certificate. That node serves
+//! plain HTTP exactly as before and is fully functional — TLS is an upgrade,
+//! not a requirement — so a missing file is logged once at debug, not warn.
+//! What IS logged at warn is a certificate that exists but cannot be parsed:
+//! that is a misconfiguration the operator can act on, and silently falling
+//! back to plain HTTP would hide it.
+
+use std::io;
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+use std::time::SystemTime;
+
+use tokio::sync::RwLock;
+use tokio_rustls::rustls::{Certificate, PrivateKey, ServerConfig};
+use tokio_rustls::TlsAcceptor;
+use tracing::{debug, warn};
+
+/// Where `setup-node-ca.sh` writes the node's leaf. Same pair nginx serves, so
+/// the dashboard and the app ports present one identity and a single trusted
+/// CA covers both.
+const DEFAULT_CERT: &str = "/etc/archipelago/ssl/archipelago.crt";
+const DEFAULT_KEY: &str = "/etc/archipelago/ssl/archipelago.key";
+
+/// First byte of a TLS record of type `handshake` (22). No HTTP request can
+/// begin with it: methods are uppercase ASCII letters, so the two wire formats
+/// are unambiguous from a single byte.
+pub const TLS_HANDSHAKE_FIRST_BYTE: u8 = 0x16;
+
+/// Does this look like the start of a TLS connection rather than plain HTTP?
+pub fn looks_like_tls(first: u8) -> bool {
+    first == TLS_HANDSHAKE_FIRST_BYTE
+}
+
+/// Lazily-built, mtime-invalidated TLS config for the gate.
+pub struct GateTls {
+    cert_path: PathBuf,
+    key_path: PathBuf,
+    cached: RwLock<Option<Cached>>,
+}
+
+struct Cached {
+    acceptor: TlsAcceptor,
+    stamp: Stamp,
+}
+
+/// Modification times of both halves. Compared as a pair because reissuing
+/// writes the certificate and the key separately — keying on only one would
+/// serve a certificate that no longer matches its key.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+struct Stamp {
+    cert: SystemTime,
+    key: SystemTime,
+}
+
+impl GateTls {
+    pub fn new() -> Self {
+        Self::with_paths(DEFAULT_CERT, DEFAULT_KEY)
+    }
+
+    pub fn with_paths(cert: impl Into<PathBuf>, key: impl Into<PathBuf>) -> Self {
+        Self {
+            cert_path: cert.into(),
+            key_path: key.into(),
+            cached: RwLock::new(None),
+        }
+    }
+
+    /// The current acceptor, rebuilding it if the files changed underneath.
+    ///
+    /// `None` means this node has no usable certificate and app ports stay
+    /// plain HTTP. Callers must treat that as ordinary, not as a failure.
+    pub async fn acceptor(&self) -> Option<TlsAcceptor> {
+        let stamp = self.stamp().await?;
+
+        if let Some(c) = self.cached.read().await.as_ref() {
+            if c.stamp == stamp {
+                return Some(c.acceptor.clone());
+            }
+        }
+
+        // Rebuild. Re-check under the write lock so concurrent connections
+        // during a reissue do not each parse the same files.
+        let mut guard = self.cached.write().await;
+        if let Some(c) = guard.as_ref() {
+            if c.stamp == stamp {
+                return Some(c.acceptor.clone());
+            }
+        }
+
+        match load_config(&self.cert_path, &self.key_path).await {
+            Ok(config) => {
+                let acceptor = TlsAcceptor::from(Arc::new(config));
+                debug!(
+                    cert = %self.cert_path.display(),
+                    "app gate loaded its TLS certificate"
+                );
+                *guard = Some(Cached {
+                    acceptor: acceptor.clone(),
+                    stamp,
+                });
+                Some(acceptor)
+            }
+            Err(e) => {
+                // A present-but-broken certificate is an operator-actionable
+                // misconfiguration; do not let it pass quietly as "no TLS".
+                warn!(
+                    cert = %self.cert_path.display(),
+                    error = %e,
+                    "app gate could not load its TLS certificate — app ports stay plain HTTP"
+                );
+                // Cache the failure against this stamp so a broken file is not
+                // re-parsed on every single connection.
+                *guard = None;
+                None
+            }
+        }
+    }
+
+    async fn stamp(&self) -> Option<Stamp> {
+        let cert = mtime(&self.cert_path).await?;
+        let key = mtime(&self.key_path).await?;
+        Some(Stamp { cert, key })
+    }
+}
+
+impl Default for GateTls {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+async fn mtime(path: &Path) -> Option<SystemTime> {
+    tokio::fs::metadata(path).await.ok()?.modified().ok()
+}
+
+async fn load_config(cert_path: &Path, key_path: &Path) -> io::Result<ServerConfig> {
+    let cert_pem = tokio::fs::read(cert_path).await?;
+    let key_pem = tokio::fs::read(key_path).await?;
+    build_config(&cert_pem, &key_pem)
+}
+
+/// Split out from the filesystem so it can be tested against bytes directly.
+pub(crate) fn build_config(cert_pem: &[u8], key_pem: &[u8]) -> io::Result<ServerConfig> {
+    let certs: Vec<Certificate> = rustls_pemfile::certs(&mut &cert_pem[..])?
+        .into_iter()
+        .map(Certificate)
+        .collect();
+    if certs.is_empty() {
+        return Err(io::Error::new(
+            io::ErrorKind::InvalidData,
+            "no certificates in PEM",
+        ));
+    }
+
+    let key = read_key(key_pem)?;
+
+    // rustls does NOT check that the key matches the certificate — verified by
+    // test, not assumed: `with_single_cert` accepts a pair from two different
+    // keys and only fails later, mid-handshake, in someone's browser. That is
+    // precisely the silently-broken-security-control shape this module exists
+    // to avoid, so prove the pairing here and refuse to serve otherwise.
+    ensure_key_matches_cert(&certs[0], &key)?;
+
+    ServerConfig::builder()
+        .with_safe_defaults()
+        .with_no_client_auth()
+        .with_single_cert(certs, key)
+        .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))
+}
+
+/// Sign a fixed message with the private key and verify it with the public key
+/// inside the certificate. They pair iff the verification succeeds.
+fn ensure_key_matches_cert(cert: &Certificate, key: &PrivateKey) -> io::Result<()> {
+    use tokio_rustls::rustls::sign;
+
+    let signing_key = sign::any_supported_type(key)
+        .map_err(|_| io::Error::new(io::ErrorKind::InvalidData, "unsupported private key type"))?;
+
+    // Any scheme the key supports will do — this proves possession, it is not
+    // negotiating anything. Offer the full set and let rustls pick.
+    const ALL_SCHEMES: &[tokio_rustls::rustls::SignatureScheme] = {
+        use tokio_rustls::rustls::SignatureScheme as S;
+        &[
+            S::ECDSA_NISTP256_SHA256,
+            S::ECDSA_NISTP384_SHA384,
+            S::ED25519,
+            S::RSA_PSS_SHA256,
+            S::RSA_PSS_SHA384,
+            S::RSA_PSS_SHA512,
+            S::RSA_PKCS1_SHA256,
+            S::RSA_PKCS1_SHA384,
+            S::RSA_PKCS1_SHA512,
+        ]
+    };
+    let signer = signing_key
+        .choose_scheme(ALL_SCHEMES)
+        .ok_or_else(|| io::Error::new(io::ErrorKind::InvalidData, "no usable signature scheme"))?;
+
+    const PROOF: &[u8] = b"archipelago app gate certificate pairing check";
+    let signature = signer
+        .sign(PROOF)
+        .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
+
+    let end_entity = webpki::EndEntityCert::try_from(cert.0.as_slice())
+        .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, format!("bad certificate: {e}")))?;
+
+    let alg: &webpki::SignatureAlgorithm = match signer.scheme() {
+        tokio_rustls::rustls::SignatureScheme::RSA_PKCS1_SHA256 => {
+            &webpki::RSA_PKCS1_2048_8192_SHA256
+        }
+        tokio_rustls::rustls::SignatureScheme::RSA_PKCS1_SHA384 => {
+            &webpki::RSA_PKCS1_2048_8192_SHA384
+        }
+        tokio_rustls::rustls::SignatureScheme::RSA_PKCS1_SHA512 => {
+            &webpki::RSA_PKCS1_2048_8192_SHA512
+        }
+        tokio_rustls::rustls::SignatureScheme::RSA_PSS_SHA256 => {
+            &webpki::RSA_PSS_2048_8192_SHA256_LEGACY_KEY
+        }
+        tokio_rustls::rustls::SignatureScheme::RSA_PSS_SHA384 => {
+            &webpki::RSA_PSS_2048_8192_SHA384_LEGACY_KEY
+        }
+        tokio_rustls::rustls::SignatureScheme::RSA_PSS_SHA512 => {
+            &webpki::RSA_PSS_2048_8192_SHA512_LEGACY_KEY
+        }
+        tokio_rustls::rustls::SignatureScheme::ECDSA_NISTP256_SHA256 => &webpki::ECDSA_P256_SHA256,
+        tokio_rustls::rustls::SignatureScheme::ECDSA_NISTP384_SHA384 => &webpki::ECDSA_P384_SHA384,
+        tokio_rustls::rustls::SignatureScheme::ED25519 => &webpki::ED25519,
+        // An unrecognised scheme must not silently skip the check.
+        other => {
+            return Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                format!("cannot verify key/certificate pairing for scheme {other:?}"),
+            ))
+        }
+    };
+
+    end_entity
+        .verify_signature(alg, PROOF, &signature)
+        .map_err(|_| {
+            io::Error::new(
+                io::ErrorKind::InvalidData,
+                "private key does not match the certificate",
+            )
+        })
+}
+
+/// Accept PKCS#8 or PKCS#1. `setup-node-ca.sh` emits PKCS#8, but a key that
+/// predates it (or was generated by hand) may be PKCS#1, and refusing that
+/// would be a silent downgrade to plain HTTP on an already-working node.
+fn read_key(key_pem: &[u8]) -> io::Result<PrivateKey> {
+    if let Some(k) = rustls_pemfile::pkcs8_private_keys(&mut &key_pem[..])?
+        .into_iter()
+        .next()
+    {
+        return Ok(PrivateKey(k));
+    }
+    if let Some(k) = rustls_pemfile::rsa_private_keys(&mut &key_pem[..])?
+        .into_iter()
+        .next()
+    {
+        return Ok(PrivateKey(k));
+    }
+    Err(io::Error::new(
+        io::ErrorKind::InvalidData,
+        "no PKCS#8 or PKCS#1 private key in PEM",
+    ))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Generated by scripts/setup-node-ca.sh's own openssl invocation, so these
+    // exercise the exact shape the node produces.
+    const CERT: &[u8] = include_bytes!("testdata/leaf.crt");
+    const KEY: &[u8] = include_bytes!("testdata/leaf.key");
+
+    #[test]
+    fn a_tls_client_hello_is_distinguishable_from_every_http_method() {
+        assert!(looks_like_tls(0x16));
+        // Every HTTP method starts with an uppercase letter; none is 0x16.
+        for m in ["GET", "POST", "PUT", "HEAD", "OPTIONS", "DELETE", "PATCH"] {
+            assert!(
+                !looks_like_tls(m.as_bytes()[0]),
+                "{m} misread as a TLS handshake"
+            );
+        }
+    }
+
+    #[test]
+    fn builds_a_config_from_the_nodes_own_cert_and_key() {
+        assert!(build_config(CERT, KEY).is_ok());
+    }
+
+    #[test]
+    fn a_cert_without_its_matching_key_is_rejected_not_ignored() {
+        // Key from a different pair: rustls must refuse rather than serve a
+        // certificate it cannot prove ownership of.
+        let other = build_config(CERT, OTHER_KEY);
+        assert!(other.is_err(), "mismatched cert/key pair was accepted");
+    }
+    const OTHER_KEY: &[u8] = include_bytes!("testdata/other.key");
+
+    #[test]
+    fn empty_pem_is_an_error_rather_than_an_empty_chain() {
+        assert!(build_config(b"", KEY).is_err());
+        assert!(build_config(CERT, b"").is_err());
+    }
+
+    #[tokio::test]
+    async fn a_node_without_certificates_reports_no_acceptor() {
+        let tls = GateTls::with_paths(
+            "/nonexistent/archipelago.crt",
+            "/nonexistent/archipelago.key",
+        );
+        assert!(tls.acceptor().await.is_none());
+    }
+
+    #[tokio::test]
+    async fn an_acceptor_is_built_and_then_served_from_cache() {
+        let dir = tempfile::tempdir().unwrap();
+        let cert = dir.path().join("c.crt");
+        let key = dir.path().join("c.key");
+        tokio::fs::write(&cert, CERT).await.unwrap();
+        tokio::fs::write(&key, KEY).await.unwrap();
+
+        let tls = GateTls::with_paths(&cert, &key);
+        assert!(tls.acceptor().await.is_some());
+        // Second call hits the cache; the observable contract is simply that it
+        // still yields an acceptor.
+        assert!(tls.acceptor().await.is_some());
+    }
+
+    #[tokio::test]
+    async fn a_reissued_certificate_is_picked_up_without_a_restart() {
+        let dir = tempfile::tempdir().unwrap();
+        let cert = dir.path().join("c.crt");
+        let key = dir.path().join("c.key");
+        tokio::fs::write(&cert, CERT).await.unwrap();
+        tokio::fs::write(&key, KEY).await.unwrap();
+
+        let tls = GateTls::with_paths(&cert, &key);
+        assert!(tls.acceptor().await.is_some());
+        let first = *tls.cached.read().await.as_ref().map(|c| &c.stamp).unwrap();
+
+        // Reissue with a distinctly later mtime, the way the CA script does
+        // when the node gains an address. Set explicitly rather than relying on
+        // wall-clock advancing, because a same-second rewrite can land on an
+        // identical mtime on coarse-granularity filesystems and make this pass
+        // or fail by luck.
+        tokio::fs::write(&cert, CERT).await.unwrap();
+        let later = SystemTime::now() + std::time::Duration::from_secs(5);
+        std::fs::File::options()
+            .write(true)
+            .open(&cert)
+            .unwrap()
+            .set_modified(later)
+            .unwrap();
+
+        assert!(tls.acceptor().await.is_some());
+        let second = *tls.cached.read().await.as_ref().map(|c| &c.stamp).unwrap();
+        assert_ne!(first, second, "reissued certificate was not reloaded");
+    }
+}