0.35.4

src/settings.rs

@@ -454,13 +454,35 @@ impl ServerHeader {
                 headers.remove(::http::header::SERVER);
             }
             ServerMode::Custom => {
-                if let Ok(value) = self.value.parse() {
+                if let Some(value) = cached_header_value(&self.value) {
                     headers.insert(::http::header::SERVER, value);
                 }
             }
         }
     }
 }
+/// Returns a reusable `HeaderValue` for a configured, already validated header
+/// string. Values are parsed once per worker thread and then cloned (a reference
+/// count bump) instead of being re-validated and re-allocated on every response.
+pub(crate) fn cached_header_value(value: &str) -> Option<HeaderValue> {
+    const CAPACITY: usize = 16;
+    thread_local! {
+        static CACHE: std::cell::RefCell<Vec<(Box<str>, HeaderValue)>> =
+            const { std::cell::RefCell::new(Vec::new()) };
+    }
+    CACHE.with(|cache| {
+        let mut cache = cache.borrow_mut();
+        if let Some((_, header)) = cache.iter().find(|(key, _)| key.as_ref() == value) {
+            return Some(header.clone());
+        }
+        let header = HeaderValue::from_maybe_shared(bytes::Bytes::copy_from_slice(value.as_bytes())).ok()?;
+        if cache.len() >= CAPACITY {
+            cache.remove(0);
+        }
+        cache.push((value.into(), header.clone()));
+        Some(header)
+    })
+}
 include!("settings/public_origin.rs");
 #[cfg(test)]
 include!("settings/tests.rs");