Avoid allocating String in CertificateOrder::cache_key.

Also, prefer first available DNS name.

Author: bavshin-f5

src/conf/order.rs

@@ -43,20 +43,22 @@ where
     }
 
     /// Generates a stable unique identifier for this order.
-    pub fn cache_key(&self) -> std::string::String
+    pub fn cache_key(&self) -> PrintableOrderId<'_, S, A>
     where
         S: fmt::Display + hash::Hash,
     {
-        if self.identifiers.is_empty() {
-            return "".into();
-        }
-
-        let name = self.identifiers[0].value();
+        PrintableOrderId(self)
+    }
 
-        let mut hasher = SipHasher::default();
-        self.hash(&mut hasher);
+    /// Attempts to find the first DNS identifier, with fallback to a first identifier of any kind.
+    pub fn first_name(&self) -> Option<&S> {
+        let dns = self
+            .identifiers
+            .iter()
+            .find(|x| matches!(x, Identifier::Dns(_)));
 
-        std::format!("{name}-{hash:x}", hash = hasher.finish())
+        dns.or_else(|| self.identifiers.first())
+            .map(Identifier::value)
     }
 
     pub fn to_str_order<NewA>(&self, alloc: NewA) -> CertificateOrder<&str, NewA>
@@ -247,6 +249,30 @@ impl CertificateOrder<ngx_str_t, Pool> {
     }
 }
 
+/// Unique identifier for the CertificateOrder.
+///
+/// This identifier should be suitable for logs, file names or cache keys.
+pub struct PrintableOrderId<'a, S, A>(&'a CertificateOrder<S, A>)
+where
+    A: ngx::allocator::Allocator;
+
+impl<S, A> fmt::Display for PrintableOrderId<'_, S, A>
+where
+    A: ngx::allocator::Allocator,
+    S: fmt::Display + hash::Hash,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Some(name) = self.0.first_name() else {
+            return Ok(());
+        };
+
+        let mut hasher = SipHasher::default();
+        self.0.hash(&mut hasher);
+
+        write!(f, "{name}-{hash:x}", hash = hasher.finish())
+    }
+}
+
 fn validate_host(pool: &Pool, mut host: ngx_str_t) -> Result<ngx_str_t, Status> {
     let mut pool = pool.clone();
     let rc = Status(unsafe { nginx_sys::ngx_http_validate_host(&mut host, pool.as_mut(), 1) });