codify "platform" into resolution logic, server-fn/fullstack overhaul (#4596)

overhaul dioxus fullstack using a new implementation of server_fn

This PR is a complete rewrite of dioxus fullstack designed to improve compatibility with axum and to fix a number of compilation errors based on feature flag unification plumbing through macros.

packages/fullstack/src/payloads/header.rs

@@ -0,0 +1,66 @@
+use super::*;
+
+pub use headers::Cookie;
+pub use headers::SetCookie;
+
+#[derive(Clone, Debug)]
+pub struct SetHeader<Data> {
+    data: Option<Data>,
+}
+
+impl<T: Header> SetHeader<T> {
+    pub fn new(
+        value: impl TryInto<HeaderValue, Error = InvalidHeaderValue>,
+    ) -> Result<Self, headers::Error> {
+        let values = value.try_into().map_err(|_| headers::Error::invalid())?;
+
+        let res = T::decode(&mut std::iter::once(&values))?;
+
+        Ok(Self { data: Some(res) })
+    }
+}
+
+impl<T: Header> IntoResponseParts for SetHeader<T> {
+    type Error = ();
+
+    fn into_response_parts(self, res: ResponseParts) -> Result<ResponseParts, Self::Error> {
+        let data = self.data.expect("SetHeader must have data to set");
+
+        let mut headers = vec![];
+        data.encode(&mut headers);
+
+        Ok(axum::response::AppendHeaders(
+            headers.into_iter().map(|value| (T::name().clone(), value)),
+        )
+        .into_response_parts(res)
+        .unwrap())
+    }
+}
+
+impl<T: Header> FromResponseParts for SetHeader<T> {
+    fn from_response_parts(parts: &mut axum::http::response::Parts) -> Result<Self, ServerFnError> {
+        let Some(header) = parts.headers.remove(T::name()) else {
+            return Ok(SetHeader { data: None });
+        };
+
+        let data = T::decode(&mut std::iter::once(&header))
+            .map_err(|_| ServerFnError::Deserialization("Failed to decode header".into()))?;
+
+        Ok(SetHeader { data: Some(data) })
+    }
+}
+
+impl<T: Header> IntoResponse for SetHeader<T> {
+    fn into_response(self) -> axum::response::Response {
+        let mut values = vec![];
+        self.data.unwrap().encode(&mut values);
+
+        let mut response = axum::response::Response::builder();
+
+        for value in values {
+            response = response.header(T::name(), value);
+        }
+
+        response.body(axum_core::body::Body::empty()).unwrap()
+    }
+}