add loading fallback certificates

src/certificates.rs

@@ -4,7 +4,14 @@ use {
         sign::{CertifiedKey, RSASigningKey},
         ResolvesServerCert,
     },
-    std::{fs::File, io::BufReader, path::PathBuf, sync::Arc},
+    std::{
+        ffi::OsStr,
+        fmt::{Display, Formatter},
+        fs::File,
+        io::BufReader,
+        path::Path,
+        sync::Arc,
+    },
     webpki::DNSNameRef,
 };
 
@@ -18,68 +25,151 @@ pub(crate) struct CertStore {
 static CERT_FILE_NAME: &str = "cert.pem";
 static KEY_FILE_NAME: &str = "key.rsa";
 
+#[derive(Debug)]
+pub enum CertLoadError {
+    /// could not access the certificate root directory
+    NoReadCertDir,
+    /// the specified domain name cannot be processed correctly
+    BadDomain(String),
+    /// the key file for the specified domain is bad (e.g. does not contain a
+    /// key or is invalid)
+    BadKey(String),
+    /// the certificate file for the specified domain is bad (e.g. invalid)
+    BadCert(String),
+    /// the key file for the specified domain is missing (but a certificate
+    /// file was present)
+    MissingKey(String),
+    /// the certificate file for the specified domain is missing (but a key
+    /// file was present)
+    MissingCert(String),
+    /// neither a key file nor a certificate file were present for the given
+    /// domain (but a folder was present)
+    EmptyDomain(String),
+}
+
+impl Display for CertLoadError {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::NoReadCertDir => write!(f, "Could not read from certificate directory."),
+            Self::BadDomain(domain) if !domain.is_ascii() => write!(
+                f,
+                "The domain name {} cannot be processed, it must be punycoded.",
+                domain
+            ),
+            Self::BadDomain(domain) => write!(f, "The domain name {} cannot be processed.", domain),
+            Self::BadKey(domain) => write!(f, "The key file for {} is malformed.", domain),
+            Self::BadCert(domain) => write!(f, "The certificate file for {} is malformed.", domain),
+            Self::MissingKey(domain) => write!(f, "The key file for {} is missing.", domain),
+            Self::MissingCert(domain) => {
+                write!(f, "The certificate file for {} is missing.", domain)
+            }
+            Self::EmptyDomain(domain) => write!(
+                f,
+                "A folder for {} exists, but there is no certificate or key file.",
+                domain
+            ),
+        }
+    }
+}
+
+impl std::error::Error for CertLoadError {}
+
+fn load_domain(certs_dir: &Path, domain: String) -> Result<CertifiedKey, CertLoadError> {
+    let mut path = certs_dir.to_path_buf();
+    path.push(&domain);
+    // load certificate from file
+    path.push(CERT_FILE_NAME);
+    if !path.is_file() {
+        return Err(if !path.with_file_name(KEY_FILE_NAME).is_file() {
+            CertLoadError::EmptyDomain(domain)
+        } else {
+            CertLoadError::MissingCert(domain)
+        });
+    }
+
+    let cert_chain = match certs(&mut BufReader::new(File::open(&path).unwrap())) {
+        Ok(cert) => cert,
+        Err(_) => return Err(CertLoadError::BadCert(domain)),
+    };
+
+    // load key from file
+    path.set_file_name(KEY_FILE_NAME);
+    if !path.is_file() {
+        return Err(CertLoadError::MissingKey(domain));
+    }
+    let key = match pkcs8_private_keys(&mut BufReader::new(File::open(&path).unwrap())) {
+        Ok(mut keys) if !keys.is_empty() => keys.remove(0),
+        _ => return Err(CertLoadError::BadKey(domain)),
+    };
+
+    // transform key to correct format
+    let key = match RSASigningKey::new(&key) {
+        Ok(key) => key,
+        Err(_) => return Err(CertLoadError::BadKey(domain)),
+    };
+    Ok(CertifiedKey::new(cert_chain, Arc::new(Box::new(key))))
+}
+
 impl CertStore {
     /// Load certificates from a certificate directory.
     /// Certificates should be stored in a folder for each hostname, for example
     /// the certificate and key for `example.com` should be in the files
     /// `certs_dir/example.com/{cert.pem,key.rsa}` respectively.
-    pub fn load_from(certs_dir: PathBuf) -> Result<Self, String> {
+    ///
+    /// If there are `cert.pem` and `key.rsa` directly in certs_dir, these will be
+    /// loaded as default certificates.
+    pub fn load_from(certs_dir: &Path) -> Result<Self, CertLoadError> {
         // load all certificates from directories
-        let mut certs = certs_dir
+        let mut certs = vec![];
+
+        // try to load fallback certificate and key
+        match load_domain(certs_dir, ".".to_string()) {
+            Err(CertLoadError::EmptyDomain(_)) => { /* there are no fallback keys */ }
+            Err(CertLoadError::NoReadCertDir) => unreachable!(),
+            Err(CertLoadError::BadDomain(_)) => unreachable!(),
+            Err(CertLoadError::BadKey(_)) => {
+                return Err(CertLoadError::BadKey("fallback".to_string()))
+            }
+            Err(CertLoadError::BadCert(_)) => {
+                return Err(CertLoadError::BadCert("fallback".to_string()))
+            }
+            Err(CertLoadError::MissingKey(_)) => {
+                return Err(CertLoadError::MissingKey("fallback".to_string()))
+            }
+            Err(CertLoadError::MissingCert(_)) => {
+                return Err(CertLoadError::MissingCert("fallback".to_string()))
+            }
+            // if there are files, just push them because there is no domain
+            // name to check against
+            Ok(key) => certs.push((String::new(), key)),
+        }
+
+        for file in certs_dir
             .read_dir()
-            .expect("could not read from certificate directory")
+            .or(Err(CertLoadError::NoReadCertDir))?
             .filter_map(Result::ok)
-            .filter_map(|entry| {
-                if !entry.metadata().map_or(false, |data| data.is_dir()) {
-                    None
-                } else if !entry.file_name().to_str().map_or(false, |s| s.is_ascii()) {
-                    Some(Err(
-                        "domain for certificate is not US-ASCII, must be punycoded".to_string(),
-                    ))
-                } else {
-                    let filename = entry.file_name();
-                    let dns_name = match DNSNameRef::try_from_ascii_str(filename.to_str().unwrap())
-                    {
-                        Ok(name) => name,
-                        Err(e) => return Some(Err(e.to_string())),
-                    };
+            .filter(|x| x.path().is_dir())
+        {
+            let path = file.path();
+            let filename = path
+                .file_name()
+                .and_then(OsStr::to_str)
+                .unwrap()
+                .to_string();
 
-                    // load certificate from file
-                    let mut path = entry.path();
-                    path.push(CERT_FILE_NAME);
-                    if !path.is_file() {
-                        return Some(Err(format!("expected certificate {:?}", path)));
-                    }
-                    let cert_chain = match certs(&mut BufReader::new(File::open(&path).unwrap())) {
-                        Ok(cert) => cert,
-                        Err(_) => return Some(Err("bad cert file".to_string())),
-                    };
+            let dns_name = match DNSNameRef::try_from_ascii_str(&filename) {
+                Ok(name) => name,
+                Err(_) => return Err(CertLoadError::BadDomain(filename)),
+            };
 
-                    // load key from file
-                    path.set_file_name(KEY_FILE_NAME);
-                    if !path.is_file() {
-                        return Some(Err(format!("expected key {:?}", path)));
-                    }
-                    let key =
-                        match pkcs8_private_keys(&mut BufReader::new(File::open(&path).unwrap())) {
-                            Ok(mut keys) if !keys.is_empty() => keys.remove(0),
-                            Ok(_) => return Some(Err(format!("key file empty {:?}", path))),
-                            Err(_) => return Some(Err("bad key file".to_string())),
-                        };
+            let key = load_domain(certs_dir, filename.clone())?;
+            if key.cross_check_end_entity_cert(Some(dns_name)).is_err() {
+                return Err(CertLoadError::BadCert(filename));
+            }
+
+            certs.push((filename, key));
+        }
 
-                    // transform key to correct format
-                    let key = match RSASigningKey::new(&key) {
-                        Ok(key) => key,
-                        Err(_) => return Some(Err("bad key".to_string())),
-                    };
-                    let key = CertifiedKey::new(cert_chain, Arc::new(Box::new(key)));
-                    if let Err(e) = key.cross_check_end_entity_cert(Some(dns_name)) {
-                        return Some(Err(e.to_string()));
-                    }
-                    Some(Ok((entry.file_name().to_str().unwrap().to_string(), key)))
-                }
-            })
-            .collect::<Result<Vec<_>, _>>()?;
         certs.sort_unstable_by(|(a, _), (b, _)| {
             // try to match as many as possible. If one is a substring of the other,
             // the `zip` will make them look equal and make the length decide.
@@ -91,6 +181,7 @@ impl CertStore {
             // longer domains first
             a.len().cmp(&b.len()).reverse()
         });
+
         Ok(Self { certs })
     }
 }

src/main.rs

@@ -160,7 +160,7 @@ fn args() -> Result<Args> {
         ];
     }
 
-    let certs = Arc::new(certificates::CertStore::load_from(check_path(
+    let certs = Arc::new(certificates::CertStore::load_from(&check_path(
         matches.opt_get_default("certs", ".certificates".into())?,
     )?)?);
 
@@ -188,15 +188,15 @@ fn check_path(s: String) -> Result<PathBuf, String> {
 }
 
 /// TLS configuration.
-static TLS: Lazy<TlsAcceptor> = Lazy::new(|| acceptor().unwrap());
+static TLS: Lazy<TlsAcceptor> = Lazy::new(acceptor);
 
-fn acceptor() -> Result<TlsAcceptor> {
+fn acceptor() -> TlsAcceptor {
     let mut config = ServerConfig::new(NoClientAuth::new());
     if ARGS.only_tls13 {
         config.versions = vec![rustls::ProtocolVersion::TLSv1_3];
     }
     config.cert_resolver = ARGS.certs.clone();
-    Ok(TlsAcceptor::from(Arc::new(config)))
+    TlsAcceptor::from(Arc::new(config))
 }
 
 struct RequestHandle {