api-macros: Make Response header fields override any defaults

ruma-api-macros/src/api.rs

@@ -289,10 +289,13 @@ impl ToTokens for Api {
                     let mut resp_builder = #ruma_api_import::exports::http::Response::builder()
                         .header(#ruma_api_import::exports::http::header::CONTENT_TYPE, "application/json");
 
+                    let mut headers =
+                        resp_builder.headers_mut().expect("`http::ResponseBuilder` is in unusable state");
                     #serialize_response_headers
 
-                    // Since we require header names to come from the `http::header` module,
+                    // This cannot fail because we parse each header value
-                    // this cannot fail.
+                    // checking for errors as each value is inserted and
+                    // we only allow keys from the `http::header` module.
                     let response = resp_builder.body(#body).unwrap();
                     Ok(response)
                 }

ruma-api-macros/src/api/response.rs

@@ -123,17 +123,19 @@ impl Response {
                     {
                         quote! {
                             if let Some(header) = response.#field_name {
-                                resp_builder = resp_builder.header(
+                                headers
+                                    .insert(
                                         #import_path::exports::http::header::#header_name,
-                                    header,
+                                        header.parse()?,
                                     );
                             }
                         }
                     }
                     _ => quote! {
-                        resp_builder = resp_builder.header(
+                        headers
+                            .insert(
                                 #import_path::exports::http::header::#header_name,
-                            response.#field_name,
+                                response.#field_name.parse()?,
                             );
                     },
                 };

ruma-api/tests/header_override.rs

@@ -0,0 +1,42 @@
+use std::convert::TryFrom;
+
+use http::header::{Entry, CONTENT_TYPE};
+use ruma_api::ruma_api;
+
+ruma_api! {
+    metadata: {
+        description: "Does something.",
+        method: GET,
+        name: "no_fields",
+        path: "/_matrix/my/endpoint",
+        rate_limited: false,
+        authentication: None,
+    }
+
+    request: {
+        #[ruma_api(header = LOCATION)]
+        pub location: Option<String>,
+    }
+
+    response: {
+        #[ruma_api(header = CONTENT_TYPE)]
+        pub stuff: String,
+    }
+}
+
+#[test]
+fn content_type_override() {
+    let res = Response { stuff: "magic".into() };
+    let mut http_res = http::Response::<Vec<u8>>::try_from(res).unwrap();
+
+    // Test that we correctly replaced the default content type,
+    // not adding another content-type header.
+    assert_eq!(
+        match http_res.headers_mut().entry(CONTENT_TYPE) {
+            Entry::Occupied(occ) => occ.iter().count(),
+            _ => 0,
+        },
+        1
+    );
+    assert_eq!(http_res.headers().get("content-type").unwrap(), "magic");
+}

ruma-api/tests/optional_headers.rs

@@ -14,6 +14,7 @@ ruma_api! {
         #[ruma_api(header = LOCATION)]
         pub location: Option<String>,
     }
+
     response: {
         #[ruma_api(header = LOCATION)]
         pub stuff: Option<String>,