seer_core/

ssl.rs

//! SSL certificate chain inspection.
//!
//! Provides detailed SSL/TLS certificate information including the certificate
//! chain, Subject Alternative Names (SANs), key details, and validity status.
//!
//! Retry boundary (deliberate): single-attempt, like [`crate::status`] — a
//! certificate inspection is a point-in-time observation, and retrying would
//! hide intermittent TLS failures from the user. Transient-failure tolerance
//! belongs to callers (e.g. watch mode).

use std::time::Duration;

use chrono::{DateTime, Utc};
use serde::{Deserialize, Serialize};
use tracing::{debug, instrument};
use x509_parser::oid_registry::Oid;
use x509_parser::prelude::*;

use crate::caa::{self, CaaPolicy};
use crate::dns::DnsResolver;
use crate::error::{Result, SeerError};
use crate::net::resolve_public_host;
use crate::tls::PresentedChain;
use crate::validation::normalize_host;

/// Default timeout for SSL operations (10 seconds).
const DEFAULT_TIMEOUT: Duration = Duration::from_secs(10);

/// Minimum acceptable RSA key size in bits (NIST SP 800-57 / CA/B Forum).
const RSA_MIN_KEY_BITS: u32 = 2048;
/// Minimum acceptable elliptic-curve key size in bits.
const EC_MIN_KEY_BITS: u32 = 256;
/// Days-until-expiry threshold below which a still-valid cert is flagged.
const CERT_EXPIRING_SOON_DAYS: i64 = 30;

/// Derives security-posture [`CertWarning`]s from an already-parsed leaf
/// certificate plus the computed validity/hostname signals. Pure — no network
/// calls — so it is unit-testable in isolation.
fn derive_cert_warnings(
    leaf: &CertDetail,
    is_valid: bool,
    hostname_verified: bool,
    days_until_expiry: i64,
) -> Vec<CertWarning> {
    let mut warnings = Vec::new();
    let critical = |message: String| CertWarning {
        severity: CertWarningSeverity::Critical,
        message,
    };
    let warn = |message: String| CertWarning {
        severity: CertWarningSeverity::Warning,
        message,
    };

    // Weak public key.
    if let (Some(kt), Some(bits)) = (leaf.key_type.as_deref(), leaf.key_bits) {
        match kt {
            "RSA" if bits < RSA_MIN_KEY_BITS => warnings.push(critical(format!(
                "RSA key size {bits} is below the {RSA_MIN_KEY_BITS}-bit minimum"
            ))),
            "EC" if bits < EC_MIN_KEY_BITS => warnings.push(critical(format!(
                "EC key size {bits} is below the {EC_MIN_KEY_BITS}-bit minimum"
            ))),
            _ => {}
        }
    }

    // Deprecated signature algorithm (SHA-1 / MD5).
    if let Some(sig) = leaf.signature_algorithm.as_deref() {
        let lower = sig.to_lowercase();
        if lower.contains("sha-1") || lower.contains("sha1") || lower.contains("md5") {
            warnings.push(critical(format!(
                "Certificate uses deprecated signature algorithm: {sig}"
            )));
        }
    }

    // Self-signed (issuer equals subject).
    if leaf.subject == leaf.issuer {
        warnings.push(warn(
            "Certificate is self-signed (issuer equals subject)".to_string(),
        ));
    }

    // Leaf certificate marked as a CA (basic-constraints misuse).
    if leaf.is_ca {
        warnings.push(warn(
            "Leaf certificate is marked as a CA certificate".to_string(),
        ));
    }

    // Validity window.
    if days_until_expiry < 0 {
        warnings.push(critical(format!(
            "Certificate expired {} day(s) ago",
            -days_until_expiry
        )));
    } else if !is_valid {
        // Date-valid check failed but not past expiry → notBefore is future.
        warnings.push(critical(
            "Certificate is not yet valid (notBefore is in the future)".to_string(),
        ));
    } else if days_until_expiry <= CERT_EXPIRING_SOON_DAYS {
        warnings.push(warn(format!(
            "Certificate expires in {days_until_expiry} day(s)"
        )));
    }

    // Hostname mismatch.
    if !hostname_verified {
        warnings.push(critical(
            "Certificate does not match the requested hostname".to_string(),
        ));
    }

    warnings
}

/// Full SSL certificate report for a domain.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SslReport {
    /// The domain that was inspected
    pub domain: String,
    /// Certificate chain as the server presented it, leaf first (servers
    /// usually omit the root)
    pub chain: Vec<CertDetail>,
    /// Negotiated TLS protocol version (`"TLSv1.3"` or `"TLSv1.2"`)
    pub protocol_version: Option<String>,
    /// Subject Alternative Names from the leaf certificate
    pub san_names: Vec<String>,
    /// Whether the leaf certificate is within its validity period.
    ///
    /// This reflects ONLY the date-range check (`notBefore <= now <=
    /// notAfter`) of the leaf certificate. It does NOT verify the certificate
    /// chain's trust (the inspection handshake accepts any presented chain so
    /// broken/self-signed certs can be inspected) nor that the certificate
    /// matches the requested hostname — see [`SslReport::hostname_verified`]. A
    /// date-valid cert may still be self-signed, issued by an untrusted CA, or
    /// presented for the wrong host.
    pub is_valid: bool,
    /// Whether the leaf certificate's SAN dNSNames (or CN as a legacy
    /// fallback) match the requested domain, per RFC 6125 (exact and
    /// single-label wildcard matches).
    ///
    /// This is an additive signal independent of `is_valid`. Chain trust is
    /// NOT verified here: a `true` value means the cert was presented for the
    /// right host, not that it was issued by a trusted CA.
    #[serde(default)]
    pub hostname_verified: bool,
    /// Days until the leaf certificate expires
    pub days_until_expiry: i64,
    /// CAA (Certification Authority Authorization) policy for the domain
    /// plus a comparison against the presented certificate's issuer.
    ///
    /// CAA is consulted by CAs at *issuance time*, not by clients at
    /// *validation time*, so a mismatch here is informational — see the
    /// `note` field on [`CaaPolicy`].
    #[serde(skip_serializing_if = "Option::is_none")]
    pub caa: Option<CaaPolicy>,
    /// Security-posture warnings derived from the leaf certificate: weak keys,
    /// deprecated signatures, self-signed / CA-marked leaves, expiry, and
    /// hostname mismatch. Empty when the leaf presents no notable issues.
    ///
    /// These are pure post-processing of already-parsed fields (no extra
    /// network calls) — a summary so consumers don't have to eyeball key sizes
    /// and algorithms.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub warnings: Vec<CertWarning>,
}

/// Severity of a [`CertWarning`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "kebab-case")]
pub enum CertWarningSeverity {
    /// A trust-affecting problem (weak key, deprecated signature, expired,
    /// hostname mismatch).
    Critical,
    /// A notable-but-not-fatal signal (self-signed, CA-marked leaf, expiring
    /// soon).
    Warning,
}

/// A single security-posture warning about a certificate.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct CertWarning {
    /// How serious the finding is.
    pub severity: CertWarningSeverity,
    /// Human-readable description of the finding.
    pub message: String,
}

/// Detailed information about a single certificate in the chain.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct CertDetail {
    /// Certificate subject (e.g., "CN=example.com")
    pub subject: String,
    /// Certificate issuer (e.g., "CN=R3, O=Let's Encrypt")
    pub issuer: String,
    /// Certificate validity start date
    pub valid_from: DateTime<Utc>,
    /// Certificate expiration date
    pub valid_until: DateTime<Utc>,
    /// Serial number in hexadecimal
    pub serial_number: String,
    /// Signature algorithm (e.g., "sha256WithRSAEncryption")
    pub signature_algorithm: Option<String>,
    /// Whether this is a Certificate Authority certificate
    pub is_ca: bool,
    /// Public key type (e.g., "RSA", "EC")
    pub key_type: Option<String>,
    /// Public key size in bits
    pub key_bits: Option<u32>,
}

/// Client for performing SSL certificate chain inspection.
#[derive(Debug, Clone)]
pub struct SslChecker {
    /// Cached DNS resolver used for CAA lookups alongside the TLS probe.
    dns_resolver: DnsResolver,
    /// Timeout for the TCP connect and TLS handshake.
    timeout: Duration,
}

impl Default for SslChecker {
    fn default() -> Self {
        Self::new()
    }
}

impl SslChecker {
    /// Creates a new SslChecker instance.
    pub fn new() -> Self {
        Self {
            dns_resolver: DnsResolver::new(),
            timeout: DEFAULT_TIMEOUT,
        }
    }

    /// Builds a checker honoring `~/.seer/config.toml` settings.
    ///
    /// Reads `timeouts.http_secs` (clamped to 1–120s by
    /// [`crate::config::SeerConfig::load`]) for the TCP connect + TLS
    /// handshake, and `timeouts.dns_secs` (1–60s) for the internal resolver
    /// used by the parallel CAA lookup. Unlike the coarse
    /// [`SslChecker::with_timeout`] (which reuses the TLS timeout for DNS),
    /// this applies each protocol's own configured timeout — matching the
    /// [`crate::availability::AvailabilityChecker::from_config`] precedent.
    pub fn from_config(config: &crate::config::SeerConfig) -> Self {
        Self {
            dns_resolver: DnsResolver::from_config(config),
            timeout: config.http_timeout(),
        }
    }

    /// Sets the timeout for the TCP connect and TLS handshake, and for the
    /// CAA lookup's DNS queries on the resolver already configured.
    pub fn with_timeout(mut self, timeout: Duration) -> Self {
        self.timeout = timeout;
        self.dns_resolver = self.dns_resolver.with_timeout(timeout);
        self
    }

    /// Inspects the SSL certificate chain for the given domain.
    ///
    /// Connects to port 443, performs a TLS handshake, and extracts detailed
    /// certificate information including the full chain, SANs, and key details.
    ///
    /// # Arguments
    /// * `domain` - The domain name to inspect (e.g., "example.com")
    ///
    /// # Returns
    /// * `Ok(SslReport)` - Detailed SSL certificate information
    /// * `Err(SeerError)` - If connection or certificate parsing fails
    #[instrument(skip(self), fields(domain = %domain))]
    pub async fn check(&self, domain: &str) -> Result<SslReport> {
        // The exact host: `www.example.com` can serve a different
        // certificate than the apex, so `www.` must not be stripped here.
        let domain = normalize_host(domain)?;

        debug!(domain = %domain, "Checking SSL certificate chain");

        // CAA query runs concurrently with the TLS probe — it is advisory
        // and never fails the report (a resolver error yields an empty
        // policy).
        let caa_future = caa::lookup_caa(&self.dns_resolver, &domain, None);

        // Resolve + SSRF check. `resolve_public_host` already falls back to
        // hickory (Google DNS) when the OS resolver fails — important for
        // hosts where Tailscale Split-DNS or a corp resolver pins the
        // domain to a nameserver that can't answer for it.
        let resolve_future = resolve_public_host(&domain, 443);

        let (caa_policy, socket_addrs) = tokio::join!(caa_future, resolve_future);
        // `domain` is already normalized, so only a resolver miss is left,
        // and that is an empty policy anyway.
        let caa_policy = caa_policy.unwrap_or_else(|_| CaaPolicy::empty());
        let socket_addrs = socket_addrs.map_err(|e| {
            SeerError::SslError(format!(
                "could not resolve {} for SSL inspection: {}",
                domain, e
            ))
        })?;

        // Handshake against the pre-resolved (SSRF-vetted) addresses so DNS
        // cannot rebind between validation and connect. Any presented chain
        // is accepted so broken certificates can still be inspected.
        let presented =
            crate::tls::inspect(&domain, &socket_addrs, self.timeout, SeerError::SslError).await?;

        build_report(domain, presented, caa_policy)
    }
}

/// Builds the report from what the server presented. Pure (no network), so
/// the projection is unit-testable against a loopback handshake.
fn build_report(
    domain: String,
    presented: PresentedChain,
    mut caa_policy: CaaPolicy,
) -> Result<SslReport> {
    // Parse leaf certificate with x509-parser
    let (_, x509) = X509Certificate::from_der(&presented.leaf)
        .map_err(|e| SeerError::SslError(format!("Failed to parse certificate: {}", e)))?;

    // Extract SANs from the leaf certificate
    let san_names = extract_sans(&x509);
    let leaf_detail = parse_cert_detail(&x509)?;

    let now = Utc::now();
    let days_until_expiry = crate::dates::days_until(leaf_detail.valid_until, now);
    let is_valid = now >= leaf_detail.valid_from && now <= leaf_detail.valid_until;

    // Hostname verification (RFC 6125, shared with `status`): independent of
    // `is_valid` and of chain trust (not verified here — see the field docs),
    // so consumers can tell a date-valid-but-wrong-host cert from a match.
    let hostname_verified = crate::tls::cert_matches_host(&x509, &domain);

    // Annotate the CAA policy with the issuer comparison before
    // attaching it to the report.
    // RFC 8659 §4.3: `issuewild` governs a wildcard certificate.
    let wildcard = crate::tls::cert_names_wildcard(&x509);
    caa_policy.issuer_match = Some(caa::classify_issuer(
        &leaf_detail.issuer,
        &caa_policy,
        wildcard,
    ));

    // Derive posture warnings from the parsed leaf (pure post-processing).
    let warnings =
        derive_cert_warnings(&leaf_detail, is_valid, hostname_verified, days_until_expiry);

    // The chain as the server sent it, leaf first. Every verdict above comes
    // from the leaf, so an extra certificate that fails to parse is skipped
    // rather than failing the whole report.
    let mut chain = vec![leaf_detail];
    chain.extend(presented.intermediates.iter().filter_map(|der| {
        let detail = X509Certificate::from_der(der)
            .ok()
            .and_then(|(_, cert)| parse_cert_detail(&cert).ok());
        if detail.is_none() {
            debug!("skipping unparseable certificate in the presented chain");
        }
        detail
    }));

    Ok(SslReport {
        domain,
        chain,
        protocol_version: presented.protocol,
        san_names,
        is_valid,
        hostname_verified,
        days_until_expiry,
        caa: Some(caa_policy),
        warnings,
    })
}

/// Extracts Subject Alternative Names from a certificate.
fn extract_sans(cert: &X509Certificate) -> Vec<String> {
    let mut sans = Vec::new();
    if let Ok(Some(ext)) = cert.subject_alternative_name() {
        for name in &ext.value.general_names {
            match name {
                GeneralName::DNSName(dns) => {
                    sans.push(dns.to_string());
                }
                GeneralName::IPAddress(ip_bytes) => {
                    sans.push(format_ip_san(ip_bytes));
                }
                _ => {}
            }
        }
    }
    sans
}

/// Renders an IPAddress SAN from its raw bytes into canonical text form:
/// dotted-quad IPv4, or zero-compressed IPv6 (e.g. `::1`, not
/// `0000:0000:...:0001`). Any other length is unexpected for an IPAddress
/// general name, so it falls back to a debug rendering of the bytes rather
/// than guessing.
fn format_ip_san(ip_bytes: &[u8]) -> String {
    crate::tls::san_ip(ip_bytes).map_or_else(|| format!("{:?}", ip_bytes), |ip| ip.to_string())
}

/// Parses detailed information from an X.509 certificate.
fn parse_cert_detail(cert: &X509Certificate) -> Result<CertDetail> {
    let subject = cert.subject().to_string();
    let issuer = cert.issuer().to_string();

    let (valid_from, valid_until) = crate::tls::validity_window(cert)
        .ok_or_else(|| SeerError::SslError("invalid certificate timestamp".to_string()))?;

    let serial_number = cert.serial.to_str_radix(16);

    let signature_algorithm = Some(oid_to_name(&cert.signature_algorithm.algorithm));

    let is_ca = cert.is_ca();

    // Extract public key info
    let spki = cert.public_key();
    let (key_type, key_bits) = extract_key_info(spki);

    Ok(CertDetail {
        subject,
        issuer,
        valid_from,
        valid_until,
        serial_number,
        signature_algorithm,
        is_ca,
        key_type,
        key_bits,
    })
}

/// Extracts key type and size from a SubjectPublicKeyInfo.
fn extract_key_info(spki: &SubjectPublicKeyInfo) -> (Option<String>, Option<u32>) {
    use x509_parser::public_key::PublicKey;
    let oid = &spki.algorithm.algorithm;
    let key_type = Some(oid_to_key_type(oid));
    let key_bits = match spki.parsed() {
        Ok(PublicKey::RSA(rsa)) => Some(rsa.key_size() as u32),
        Ok(PublicKey::EC(ec)) => Some(ec.key_size() as u32),
        _ => None,
    };
    (key_type, key_bits)
}

/// Maps common OIDs to human-readable algorithm names; any other OID is
/// shown in dotted form.
fn oid_to_name(oid: &Oid) -> String {
    let name = match oid.to_id_string().as_str() {
        "1.2.840.113549.1.1.11" => "SHA-256 with RSA",
        "1.2.840.113549.1.1.12" => "SHA-384 with RSA",
        "1.2.840.113549.1.1.13" => "SHA-512 with RSA",
        "1.2.840.113549.1.1.5" => "SHA-1 with RSA",
        // Deprecated algorithms are named (rather than left as raw OIDs) so
        // the "sha1"/"md5" signature warning can recognize them.
        "1.2.840.113549.1.1.4" => "MD5 with RSA",
        "1.2.840.10045.4.1" => "ECDSA with SHA-1",
        "1.2.840.10040.4.3" => "DSA with SHA-1",
        "1.2.840.113549.1.1.14" => "SHA-224 with RSA",
        "1.2.840.10045.4.3.2" => "ECDSA with SHA-256",
        "1.2.840.10045.4.3.3" => "ECDSA with SHA-384",
        "1.2.840.10045.4.3.4" => "ECDSA with SHA-512",
        "1.3.101.112" => "Ed25519",
        "1.3.101.113" => "Ed448",
        other => return other.to_string(),
    };
    name.to_string()
}

/// Maps public key algorithm OIDs to human-readable key type names; any
/// other OID is shown in dotted form.
fn oid_to_key_type(oid: &Oid) -> String {
    let name = match oid.to_id_string().as_str() {
        "1.2.840.113549.1.1.1" => "RSA",
        "1.2.840.10045.2.1" => "EC",
        "1.3.101.112" => "Ed25519",
        "1.3.101.113" => "Ed448",
        other => return other.to_string(),
    };
    name.to_string()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_ssl_checker_creation() {
        let _checker = SslChecker::new();
        let _default_checker = SslChecker::default();
    }

    /// Regression: `with_timeout` swapped the configured resolver for a
    /// fresh default one, dropping whatever it had been set up with.
    #[tokio::test]
    async fn with_timeout_keeps_the_configured_resolver() {
        use crate::dns::test_support::{mock_dns_resolver_default, spawn_mock_dns, MockMode};

        // Only the loopback zone has a CAA policy at `seer.test`.
        let port = spawn_mock_dns(MockMode::Zone).await;
        let checker = SslChecker {
            dns_resolver: mock_dns_resolver_default(port),
            ..SslChecker::new()
        }
        .with_timeout(Duration::from_secs(3));
        assert_eq!(checker.dns_resolver.timeout(), Duration::from_secs(3));
        let policy = caa::lookup_caa(&checker.dns_resolver, "seer.test", None)
            .await
            .unwrap();
        assert!(policy.has_policy, "the configured resolver must be kept");
    }

    #[test]
    fn from_config_applies_http_timeout() {
        let mut config = crate::config::SeerConfig::default();
        config.timeouts.http_secs = 77;
        let checker = SslChecker::from_config(&config);
        assert_eq!(checker.timeout, Duration::from_secs(77));
    }

    #[test]
    fn test_oid_to_name() {
        let oid = Oid::from(&[1, 2, 840, 113549, 1, 1, 11][..]).unwrap();
        assert_eq!(oid_to_name(&oid), "SHA-256 with RSA");
    }

    #[test]
    fn test_oid_to_key_type() {
        let oid = Oid::from(&[1, 2, 840, 113549, 1, 1, 1][..]).unwrap();
        assert_eq!(oid_to_key_type(&oid), "RSA");
    }

    /// Live-network sanity check: a real public site with valid TLS
    /// completes a full chain inspection. Exercises the
    /// [`resolve_public_host`] code path in `net.rs` (hickory fallback
    /// engages if the test environment has a broken OS resolver) and the
    /// rest of the TLS handshake + cert-parse pipeline.
    #[tokio::test]
    #[ignore = "requires network — performs a real TLS handshake"]
    async fn check_live_example_com_succeeds() {
        let report = SslChecker::new().check("example.com").await.unwrap();
        assert_eq!(report.domain, "example.com");
        assert!(!report.chain.is_empty(), "expected at least a leaf cert");
        assert!(
            report.is_valid,
            "example.com's leaf cert should be currently valid"
        );
    }

    /// Regression: native-tls exposed only the leaf, so `chain` always held
    /// one entry and `protocol_version` was always `None`.
    #[tokio::test]
    async fn report_carries_the_presented_chain_and_protocol() {
        use crate::tls::test_support::{serve_once, CA_DER, LEAF_DER};

        let addr = serve_once(&[LEAF_DER, CA_DER], &[&rustls::version::TLS12]).await;
        let presented = crate::tls::inspect(
            "chain.test",
            &[addr],
            Duration::from_secs(5),
            SeerError::SslError,
        )
        .await
        .unwrap();
        let report = build_report("chain.test".to_string(), presented, CaaPolicy::empty()).unwrap();

        let subjects: Vec<&str> = report.chain.iter().map(|c| c.subject.as_str()).collect();
        assert_eq!(subjects, ["CN=chain.test", "CN=Seer Test CA"]);
        assert!(report.chain[1].is_ca);
        assert_eq!(report.protocol_version.as_deref(), Some("TLSv1.2"));
        assert!(report.hostname_verified);
    }

    /// Regression: an RSA-1024 leaf failed the inspection handshake, so the
    /// weak-key warning could never fire for a live certificate.
    #[tokio::test]
    async fn an_rsa_1024_leaf_is_inspected_and_flagged() {
        use crate::tls::test_support::{serve_once, RSA_1024_LEAF};

        let addr = serve_once(&[RSA_1024_LEAF], rustls::DEFAULT_VERSIONS).await;
        let presented = crate::tls::inspect(
            "weak-rsa.test",
            &[addr],
            Duration::from_secs(5),
            SeerError::SslError,
        )
        .await
        .unwrap();
        let report =
            build_report("weak-rsa.test".to_string(), presented, CaaPolicy::empty()).unwrap();

        assert_eq!(report.chain[0].key_type.as_deref(), Some("RSA"));
        assert_eq!(report.chain[0].key_bits, Some(1024));
        assert!(
            report
                .warnings
                .iter()
                .any(|w| w.severity == CertWarningSeverity::Critical
                    && w.message == "RSA key size 1024 is below the 2048-bit minimum"),
            "got {:?}",
            report.warnings
        );
    }

    #[test]
    fn test_ssl_report_serialization() {
        let report = SslReport {
            domain: "example.com".to_string(),
            chain: vec![CertDetail {
                subject: "CN=example.com".to_string(),
                issuer: "CN=R3, O=Let's Encrypt".to_string(),
                valid_from: Utc::now(),
                valid_until: Utc::now(),
                serial_number: "abc123".to_string(),
                signature_algorithm: Some("SHA-256 with RSA".to_string()),
                is_ca: false,
                key_type: Some("RSA".to_string()),
                key_bits: Some(2048),
            }],
            protocol_version: None,
            san_names: vec!["example.com".to_string(), "*.example.com".to_string()],
            is_valid: true,
            hostname_verified: true,
            days_until_expiry: 90,
            caa: None,
            warnings: vec![],
        };
        let json = serde_json::to_string(&report).unwrap();
        assert!(json.contains("example.com"));
        assert!(json.contains("SHA-256 with RSA"));
        assert!(json.contains("\"is_valid\":true"));
        assert!(json.contains("\"hostname_verified\":true"));
    }

    #[test]
    fn format_ip_san_renders_canonical_addresses() {
        // IPv4: dotted quad.
        assert_eq!(format_ip_san(&[192, 168, 0, 1]), "192.168.0.1");
        // IPv6 ::1 — must be zero-compressed, NOT 0000:0000:...:0001.
        let mut loopback = [0u8; 16];
        loopback[15] = 1;
        assert_eq!(format_ip_san(&loopback), "::1");
        // A fuller IPv6 address still round-trips through canonical form.
        // 2001:db8::1
        let mut addr = [0u8; 16];
        addr[0] = 0x20;
        addr[1] = 0x01;
        addr[2] = 0x0d;
        addr[3] = 0xb8;
        addr[15] = 1;
        assert_eq!(format_ip_san(&addr), "2001:db8::1");
    }

    fn sample_leaf() -> CertDetail {
        CertDetail {
            subject: "CN=example.com".to_string(),
            issuer: "CN=R3, O=Let's Encrypt".to_string(),
            valid_from: Utc::now(),
            valid_until: Utc::now(),
            serial_number: "abc123".to_string(),
            signature_algorithm: Some("SHA-256 with RSA".to_string()),
            is_ca: false,
            key_type: Some("RSA".to_string()),
            key_bits: Some(2048),
        }
    }

    #[test]
    fn derive_cert_warnings_clean_cert_has_none() {
        let w = derive_cert_warnings(&sample_leaf(), true, true, 90);
        assert!(w.is_empty(), "clean cert should have no warnings: {:?}", w);
    }

    #[test]
    fn derive_cert_warnings_flags_weak_rsa_key() {
        let mut leaf = sample_leaf();
        leaf.key_bits = Some(1024);
        let w = derive_cert_warnings(&leaf, true, true, 90);
        assert!(w.iter().any(|x| x.message.contains("RSA key size 1024")
            && x.severity == CertWarningSeverity::Critical));
    }

    #[test]
    fn derive_cert_warnings_flags_sha1_signature() {
        let mut leaf = sample_leaf();
        leaf.signature_algorithm = Some("SHA-1 with RSA".to_string());
        let w = derive_cert_warnings(&leaf, true, true, 90);
        assert!(w
            .iter()
            .any(|x| x.message.to_lowercase().contains("deprecated signature")));
    }

    #[test]
    fn derive_cert_warnings_flags_self_signed_expired_and_mismatch() {
        let mut leaf = sample_leaf();
        leaf.issuer = leaf.subject.clone();
        let w = derive_cert_warnings(&leaf, false, false, -3);
        assert!(w.iter().any(|x| x.message.contains("self-signed")));
        assert!(w.iter().any(|x| x.message.contains("expired 3 day(s) ago")));
        assert!(w.iter().any(|x| x.message.contains("does not match")));
    }

    #[test]
    fn derive_cert_warnings_flags_expiring_soon_as_warning() {
        let w = derive_cert_warnings(&sample_leaf(), true, true, 10);
        assert_eq!(w.len(), 1);
        assert_eq!(w[0].severity, CertWarningSeverity::Warning);
        assert!(w[0].message.contains("expires in 10 day(s)"));
    }

    #[test]
    fn a_just_expired_cert_is_reported_expired_not_not_yet_valid() {
        let now = Utc::now();
        let days = crate::dates::days_until(now - chrono::Duration::hours(5), now);
        let w = derive_cert_warnings(&sample_leaf(), false, true, days);
        assert!(
            w.iter().any(|x| x.message.contains("expired 1 day(s) ago")),
            "a just-expired cert must be reported expired: {w:?}"
        );
        assert!(!w.iter().any(|x| x.message.contains("not yet valid")));
    }

    #[test]
    fn deprecated_signature_oids_are_named_and_flagged() {
        for (arcs, name) in [
            (&[1u64, 2, 840, 113549, 1, 1, 4][..], "MD5 with RSA"),
            (&[1u64, 2, 840, 10045, 4, 1][..], "ECDSA with SHA-1"),
            (&[1u64, 2, 840, 10040, 4, 3][..], "DSA with SHA-1"),
        ] {
            let oid = Oid::from(arcs).unwrap();
            assert_eq!(oid_to_name(&oid), name);
            let mut leaf = sample_leaf();
            leaf.signature_algorithm = Some(oid_to_name(&oid));
            let w = derive_cert_warnings(&leaf, true, true, 90);
            assert!(
                w.iter().any(|x| x.message.contains("deprecated signature")),
                "{name} must be flagged: {w:?}"
            );
        }
    }

    #[test]
    fn derive_cert_warnings_flags_ca_marked_leaf() {
        let mut leaf = sample_leaf();
        leaf.is_ca = true;
        let w = derive_cert_warnings(&leaf, true, true, 90);
        assert!(w.iter().any(|x| x.message.contains("marked as a CA")));
    }

    /// Regression: `seer ssl` switched the CN fallback off for any SAN, so an
    /// IP-SAN-only cert failed here while `seer status` verified it. Both now
    /// share `tls::cert_matches_host`.
    #[test]
    fn ip_only_san_still_falls_back_to_the_cn() {
        use crate::tls::test_support::{cert, CN_VICTIM_SAN_IP};

        let presented = PresentedChain {
            leaf: cert(CN_VICTIM_SAN_IP),
            intermediates: vec![],
            protocol: None,
        };
        let report =
            build_report("victim.example".to_string(), presented, CaaPolicy::empty()).unwrap();
        assert!(report.hostname_verified);
        assert_eq!(report.san_names, ["203.0.113.7"]);
    }
}