Add .insert() to HttpResponseBuilder

src/httpresponse.rs

@@ -426,6 +426,38 @@ impl HttpResponseBuilder {
         }
         self
     }
+    /// Set or replace a header with a single value.
+    ///
+    /// ```rust
+    /// # extern crate actix_web;
+    /// use actix_web::{http, HttpRequest, HttpResponse};
+    ///
+    /// fn index(req: HttpRequest) -> HttpResponse {
+    ///     HttpResponse::Ok()
+    ///         .insert("X-TEST", "value")
+    ///         .insert(http::header::CONTENT_TYPE, "application/json")
+    ///         .finish()
+    /// }
+    /// fn main() {}
+    /// ```
+    pub fn insert<K, V>(&mut self, key: K, value: V) -> &mut Self
+    where
+        HeaderName: HttpTryFrom<K>,
+        V: IntoHeaderValue,
+    {
+        if let Some(parts) = parts(&mut self.response, &self.err) {
+            match HeaderName::try_from(key) {
+                Ok(key) => match value.try_into() {
+                    Ok(value) => {
+                        parts.headers.insert(key, value);
+                    }
+                    Err(e) => self.err = Some(e.into()),
+                },
+                Err(e) => self.err = Some(e.into()),
+            };
+        }
+        self
+    }
 
     /// Remove all instances of a header already set on this `HttpResponseBuilder`.
     ///
@@ -1155,6 +1187,15 @@ mod tests {
         assert_eq!(resp.status(), StatusCode::OK);
     }
 
+    #[test]
+    fn test_insert() {
+        let resp = HttpResponse::Ok()
+            .insert("deleteme", "old value")
+            .insert("deleteme", "new value")
+            .finish();
+        assert_eq!("new value", resp.headers().get("deleteme").expect("new value"));
+    }
+
     #[test]
     fn test_remove() {
         let resp = HttpResponse::Ok()