clean up header map (#1964)

actix-http/src/header/as_name.rs

@@ -0,0 +1,46 @@
+//! Helper trait for types that can be effectively borrowed as a [HeaderValue].
+
+use std::{borrow::Cow, str::FromStr};
+
+use http::header::{HeaderName, InvalidHeaderName};
+
+pub trait AsHeaderName: Sealed {}
+
+pub trait Sealed {
+    fn try_as_name(&self) -> Result<Cow<'_, HeaderName>, InvalidHeaderName>;
+}
+
+impl Sealed for HeaderName {
+    fn try_as_name(&self) -> Result<Cow<'_, HeaderName>, InvalidHeaderName> {
+        Ok(Cow::Borrowed(self))
+    }
+}
+impl AsHeaderName for HeaderName {}
+
+impl Sealed for &HeaderName {
+    fn try_as_name(&self) -> Result<Cow<'_, HeaderName>, InvalidHeaderName> {
+        Ok(Cow::Borrowed(*self))
+    }
+}
+impl AsHeaderName for &HeaderName {}
+
+impl Sealed for &str {
+    fn try_as_name(&self) -> Result<Cow<'_, HeaderName>, InvalidHeaderName> {
+        HeaderName::from_str(self).map(Cow::Owned)
+    }
+}
+impl AsHeaderName for &str {}
+
+impl Sealed for String {
+    fn try_as_name(&self) -> Result<Cow<'_, HeaderName>, InvalidHeaderName> {
+        HeaderName::from_str(self).map(Cow::Owned)
+    }
+}
+impl AsHeaderName for String {}
+
+impl Sealed for &String {
+    fn try_as_name(&self) -> Result<Cow<'_, HeaderName>, InvalidHeaderName> {
+        HeaderName::from_str(self).map(Cow::Owned)
+    }
+}
+impl AsHeaderName for &String {}