Return plain text 404 for non-HTML requests

Checks the `Accept` header for 404 responses. If HTML is not
preferred, a plain text 404 is returned, avoiding the
`_default_404.sql` processing. HTML-preferring clients
continue to receive the custom SQL-based 404 page.

Author: lovasoa

CHANGELOG.md

@@ -7,6 +7,7 @@
   - fixes an issue introduced in 0.35 where custom SQLite extension loading would not work.
  - When an user requests a page that does not exist (and the site owner did not provide a custom 404.sql file), we now serve a nice visual 404 web page instead of the ugly textual message and the verbose log messages we used to have.
    - ![screenshot 404](https://github.com/user-attachments/assets/02525f9e-91ec-4657-a70f-1b7990cbe25f)
+   - still returns plain text 404 for non-HTML requests
 
 
 ## v0.35.1

src/webserver/http.rs

@@ -377,11 +377,21 @@ pub async fn main_handler(
     };
     match routing_action {
         NotFound => {
-            let mut response =
-                process_sql_request(&mut service_request, PathBuf::from("_default_404.sql"))
-                    .await?;
-            *response.status_mut() = StatusCode::NOT_FOUND;
-            Ok(response)
+            let accept_header =
+                header::Accept::parse(&service_request).unwrap_or(header::Accept::star());
+            let prefers_html = accept_header.iter().any(|h| h.item.subtype() == "html");
+
+            if prefers_html {
+                let mut response =
+                    process_sql_request(&mut service_request, PathBuf::from("_default_404.sql"))
+                        .await?;
+                *response.status_mut() = StatusCode::NOT_FOUND;
+                Ok(response)
+            } else {
+                Ok(HttpResponse::NotFound()
+                    .content_type(ContentType::plaintext())
+                    .body("404 Not Found\n"))
+            }
         }
         Execute(path) => process_sql_request(&mut service_request, path).await,
         CustomNotFound(path) => {

tests/common/mod.rs

@@ -24,6 +24,7 @@ pub async fn get_request_to_with_data(
     Ok(test::TestRequest::get()
         .uri(path)
         .insert_header(ContentType::plaintext())
+        .insert_header(header::Accept::html())
         .app_data(payload_config(&data))
         .app_data(form_config(&data))
         .app_data(data))