fix: set Content-Type correctly on server function error responses (closes #4209 )

chore: fix outdated descriptions in FromServerFnError docs
2025-12-27 16:54:41 -05:00 · 2025-08-24 14:51:35 -04:00 · 2025-08-24 13:50:14 -04:00
7 changed files with 50 additions and 7 deletions
--- a/server_fn/src/error.rs
+++ b/server_fn/src/error.rs
@@ -568,7 +568,7 @@ pub trait FromServerFnError: std::fmt::Debug + Sized + 'static {
    /// Converts a [`ServerFnErrorErr`] into the application-specific custom error type.
    fn from_server_fn_error(value: ServerFnErrorErr) -> Self;

-    /// Converts the custom error type to a [`String`].
+    /// Serializes the custom error type to bytes, according to the encoding given by `Self::Encoding`.
    fn ser(&self) -> Bytes {
        Self::Encoder::encode(self).unwrap_or_else(|e| {
            Self::Encoder::encode(&Self::from_server_fn_error(
@@ -581,7 +581,7 @@ pub trait FromServerFnError: std::fmt::Debug + Sized + 'static {
        })
    }

-    /// Deserializes the custom error type from a [`&str`].
+    /// Deserializes the custom error type, according to the encoding given by `Self::Encoding`.
    fn de(data: Bytes) -> Self {
        Self::Encoder::decode(data).unwrap_or_else(|e| {
            ServerFnErrorErr::Deserialization(e.to_string()).into_app_error()
--- a/server_fn/src/lib.rs
+++ b/server_fn/src/lib.rs
@@ -319,6 +319,12 @@ pub trait ServerFn: Send + Sized {
                        )
                    });

+            if err.is_some() {
+                res.set_content_type(
+                    <<Self::Error as FromServerFnError>::Encoder>::CONTENT_TYPE,
+                );
+            }
+
            // if it accepts HTML, we'll redirect to the Referer
            #[cfg(feature = "form-redirects")]
            if accepts_html {
--- a/server_fn/src/middleware/mod.rs
+++ b/server_fn/src/middleware/mod.rs
@@ -72,6 +72,8 @@ mod axum {
            let inner = self.call(req);
            Box::pin(async move {
                inner.await.unwrap_or_else(|e| {
+                    // TODO: this needs to set the Content-Type correctly depending on the error type
+                    // note that this only applies to middleware errors
                    let err =
                        ser(ServerFnErrorErr::MiddlewareError(e.to_string()));
                    Response::<Body>::error_response(&path, err)
@@ -149,6 +151,8 @@ mod actix {
            let inner = self.call(req);
            Box::pin(async move {
                inner.await.unwrap_or_else(|e| {
+                    // TODO: this needs to set the Content-Type correctly depending on the error type
+                    // note that this only applies to middleware errors
                    let err =
                        ser(ServerFnErrorErr::MiddlewareError(e.to_string()));
                    ActixResponse::error_response(&path, err).take()
--- a/server_fn/src/response/actix.rs
+++ b/server_fn/src/response/actix.rs
@@ -4,8 +4,7 @@ use crate::error::{
 };
 use actix_web::{
    http::{
-        header,
-        header::{HeaderValue, LOCATION},
+        header::{self, HeaderValue, CONTENT_TYPE, LOCATION},
        StatusCode,
    },
    HttpResponse,
@@ -80,6 +79,12 @@ impl Res for ActixResponse {
        ))
    }

+    fn set_content_type(&mut self, content_type: &str) {
+        self.0
+            .headers_mut()
+            .append(CONTENT_TYPE, HeaderValue::from_str(content_type).unwrap());
+    }
+
    fn redirect(&mut self, path: &str) {
        if let Ok(path) = HeaderValue::from_str(path) {
            *self.0.status_mut() = StatusCode::FOUND;
--- a/server_fn/src/response/generic.rs
+++ b/server_fn/src/response/generic.rs
@@ -19,7 +19,10 @@ use crate::error::{
 };
 use bytes::Bytes;
 use futures::{Stream, TryStreamExt};
-use http::{header, HeaderValue, Response, StatusCode};
+use http::{
+    header::{self, CONTENT_TYPE},
+    HeaderValue, Response, StatusCode,
+};
 use std::pin::Pin;
 use throw_error::Error;

@@ -100,6 +103,11 @@ impl Res for Response<Body> {
            .unwrap()
    }

+    fn set_content_type(&mut self, content_type: &str) {
+        self.headers_mut()
+            .append(CONTENT_TYPE, HeaderValue::from_str(content_type).unwrap());
+    }
+
    fn redirect(&mut self, path: &str) {
        if let Ok(path) = HeaderValue::from_str(path) {
            self.headers_mut().insert(header::LOCATION, path);
--- a/server_fn/src/response/http.rs
+++ b/server_fn/src/response/http.rs
@@ -6,7 +6,10 @@ use crate::error::{
 use axum::body::Body;
 use bytes::Bytes;
 use futures::{Stream, TryStreamExt};
-use http::{header, HeaderValue, Response, StatusCode};
+use http::{
+    header::{self, CONTENT_TYPE},
+    HeaderValue, Response, StatusCode,
+};

 impl<E> TryRes<E> for Response<Body>
 where
@@ -60,6 +63,11 @@ impl Res for Response<Body> {
            .unwrap()
    }

+    fn set_content_type(&mut self, content_type: &str) {
+        self.headers_mut()
+            .append(CONTENT_TYPE, HeaderValue::from_str(content_type).unwrap());
+    }
+
    fn redirect(&mut self, path: &str) {
        if let Ok(path) = HeaderValue::from_str(path) {
            self.headers_mut().insert(header::LOCATION, path);
--- a/server_fn/src/response/mod.rs
+++ b/server_fn/src/response/mod.rs
@@ -37,9 +37,16 @@ where

 /// Represents the response as created by the server;
 pub trait Res {
-    /// Converts an error into a response, with a `500` status code and the error text as its body.
+    /// Converts an error into a response, with a `500` status code and the error as its body.
    fn error_response(path: &str, err: Bytes) -> Self;

+    /// Sets the `Content-Type` header on the response.
+    fn set_content_type(&mut self, content_type: &str) {
+        // TODO 0.9: remove this method and default implementation
+        // it is included here to make this change non-breaking
+        _ = content_type;
+    }
+
    /// Redirect the response by setting a 302 code and Location header.
    fn redirect(&mut self, path: &str);
 }
@@ -103,6 +110,11 @@ impl Res for BrowserMockRes {
        unreachable!()
    }

+    fn set_content_type(&mut self, content_type: &str) {
+        _ = content_type;
+        unreachable!()
+    }
+
    fn redirect(&mut self, _path: &str) {
        unreachable!()
    }
Author	SHA1	Message	Date
Greg Johnston	e8d80e0733	fix: set `Content-Type` correctly on server function error responses (closes #4209 )	2025-08-24 14:51:35 -04:00
Greg Johnston	0f2168b92c	chore: fix outdated descriptions in `FromServerFnError` docs	2025-08-24 13:50:14 -04:00