feat(client-rust): accept gateway cert by default over TLS (or documented pin-only fallback)

clients/rust/tests/tls.rs

@@ -0,0 +1,103 @@
+//! TLS posture coverage for the Rust client.
+//!
+//! tonic 0.13.1's `ClientTlsConfig` exposes no hook for a custom rustls
+//! `ServerCertVerifier` (the verifier is built internally inside the
+//! crate-private `TlsConnector`), so the Rust client cannot implement the
+//! "accept any server certificate" lenient default the other clients use.
+//! Rust is therefore the documented **pin-only exception**: TLS without a
+//! pinned CA is rejected up front with a clear, actionable error, and
+//! supplying a CA file is the supported path. These tests pin that contract.
+
+use std::time::Duration;
+
+use zb_mom_ww_mxgateway_client::{ClientOptions, Error, GatewayClient};
+
+/// Drive `connect` to its error without requiring `GatewayClient: Debug`
+/// (the success arm is dropped explicitly so `unwrap_err` is unnecessary).
+async fn connect_err(options: ClientOptions) -> Error {
+    match GatewayClient::connect(options).await {
+        Ok(_client) => panic!("connect unexpectedly succeeded against a dead TLS address"),
+        Err(error) => error,
+    }
+}
+
+#[tokio::test]
+async fn tls_without_ca_is_rejected_with_actionable_error_by_default() {
+    let options = ClientOptions::new("https://127.0.0.1:1")
+        .with_plaintext(false)
+        .with_connect_timeout(Duration::from_millis(200));
+
+    let error = connect_err(options).await;
+
+    let Error::InvalidEndpoint { detail, .. } = error else {
+        panic!("expected InvalidEndpoint, got {error:?}");
+    };
+    // The message must point the caller at the supported remedy (pin a CA)
+    // and name the opt-in escape hatch.
+    assert!(
+        detail.contains("ca_file") || detail.contains("CA"),
+        "error should instruct the user to pass a CA file: {detail}"
+    );
+    assert!(
+        detail.contains("require_certificate_validation"),
+        "error should mention the require_certificate_validation opt-in: {detail}"
+    );
+}
+
+#[tokio::test]
+async fn tls_with_require_certificate_validation_does_not_short_circuit() {
+    // With strict verification opted in, the no-CA guard must not fire; the
+    // connect attempt instead proceeds to the transport (and fails to reach
+    // the dead address) rather than returning the "CA required" guard error.
+    let options = ClientOptions::new("https://127.0.0.1:1")
+        .with_plaintext(false)
+        .with_require_certificate_validation(true)
+        .with_connect_timeout(Duration::from_millis(200));
+
+    let error = connect_err(options).await;
+
+    assert!(
+        !matches!(&error, Error::InvalidEndpoint { detail, .. }
+            if detail.contains("require_certificate_validation")),
+        "strict verification must bypass the no-CA guard, got {error:?}"
+    );
+}
+
+#[tokio::test]
+async fn tls_with_ca_file_is_permitted_and_proceeds_past_the_guard() {
+    // Pinning a CA is the supported TLS path: the no-CA guard must not fire.
+    // We hand it a readable PEM file; construction proceeds past the guard
+    // and only fails later at the transport (dead address / handshake).
+    let ca_path = std::env::temp_dir().join("mxgw-rust-tls-ca-fixture.pem");
+    std::fs::write(&ca_path, SELF_SIGNED_CA_PEM).unwrap();
+
+    let options = ClientOptions::new("https://127.0.0.1:1")
+        .with_plaintext(false)
+        .with_ca_file(&ca_path)
+        .with_connect_timeout(Duration::from_millis(200));
+
+    let error = connect_err(options).await;
+
+    let _ = std::fs::remove_file(&ca_path);
+
+    assert!(
+        !matches!(&error, Error::InvalidEndpoint { detail, .. }
+            if detail.contains("require_certificate_validation")),
+        "pinning a CA must bypass the no-CA guard, got {error:?}"
+    );
+}
+
+/// A throwaway self-signed CA certificate (PEM). Only needs to parse as a
+/// PEM trust root so the CA-pinning path is exercised past the guard.
+const SELF_SIGNED_CA_PEM: &str = "-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
+";