init

backend/rocket_prost_responder_derive/src/lib.rs

@@ -0,0 +1,50 @@
+use proc_macro::TokenStream;
+use quote::quote;
+use syn::{Data, DeriveInput, parse_macro_input};
+
+#[proc_macro_derive(RocketResponder)]
+pub fn derive_rocket_responder(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+    let name = input.ident;
+
+    // Inspect whether the input is an enum. prost enums implement prost::Enumeration.
+    let expanded = match input.data {
+        Data::Enum(_) => {
+            // For enums: cast to i32 using prost::Enumeration::value
+            quote! {
+                impl<'r> rocket::response::Responder<'r, 'static> for #name {
+                    fn respond_to(self, req: &'r rocket::Request<'_>)
+                        -> rocket::response::Result<'static>
+                    {
+                        // Get integer value from prost enum
+                        let value = self.as_str_name();
+
+                        rocket::Response::build_from(value.respond_to(req)?)
+                            .header(rocket::http::ContentType::new("application", "text"))
+                            .ok()
+                    }
+                }
+            }
+        }
+
+        // For structs / messages (the prost::Message case)
+        _ => {
+            quote! {
+                impl<'r> rocket::response::Responder<'r, 'static> for #name {
+                    fn respond_to(self, req: &'r rocket::Request<'_>)
+                        -> rocket::response::Result<'static>
+                    {
+                        // encode_to_vec comes from prost::Message that prost derives for
+                        // generated types
+                        let bytes = prost::Message::encode_to_vec(&self);
+                        rocket::Response::build_from(bytes.respond_to(req)?)
+                            .header(rocket::http::ContentType::new("application", "protobuf"))
+                            .ok()
+                    }
+                }
+            }
+        }
+    };
+
+    TokenStream::from(expanded)
+}