feat(s2n-events): Support defining associated C types for events

goatgoose · goatgoose · commit 5e0feee778cb · 2025-09-26T11:24:28.000-04:00
diff --git a/tools/s2n-events/src/generate_config.rs b/tools/s2n-events/src/generate_config.rs
@@ -333,6 +333,37 @@ impl GenerateConfig {
             OutputMode::Mut => quote!(),
         }
     }
+
+    pub fn c_ffi(
+        &self,
+        inner: &TokenStream,
+        connection_meta_c_type: &TokenStream,
+        connection_info_c_type: &TokenStream,
+    ) -> TokenStream {
+        if !self.c_api {
+            return quote!();
+        }
+
+        assert!(
+            !connection_meta_c_type.is_empty(),
+            "An associated C type must be specified for ConnectionMeta with the #[c_type()] \
+            attribute."
+        );
+        assert!(
+            !connection_info_c_type.is_empty(),
+            "An associated C type must be specified for ConnectionInfo with the #[c_type()] \
+            attribute."
+        );
+
+        quote!(
+            pub mod c_ffi {
+                #[allow(unused_imports)]
+                use std::ffi::*;
+
+                #inner
+            }
+        )
+    }
 }
 
 impl ToTokens for OutputMode {
diff --git a/tools/s2n-events/src/output.rs b/tools/s2n-events/src/output.rs
@@ -36,6 +36,9 @@ pub struct Output {
     pub s2n_quic_core_path: TokenStream,
     pub top_level: TokenStream,
     pub feature_alloc: TokenStream,
+    pub c_ffi: TokenStream,
+    pub connection_meta_c_type: TokenStream,
+    pub connection_info_c_type: TokenStream,
     pub root: PathBuf,
 }
 
@@ -115,6 +118,9 @@ impl ToTokens for Output {
             top_level,
             feature_alloc: _,
             crate_name,
+            c_ffi,
+            connection_meta_c_type,
+            connection_info_c_type,
             root: _,
         } = self;
 
@@ -129,6 +135,9 @@ impl ToTokens for Output {
         let query_mut = self.config.query_mut();
         let query_mut_tuple = self.config.query_mut_tuple();
         let trait_constraints = self.config.trait_constraints();
+        let c_ffi = self
+            .config
+            .c_ffi(c_ffi, connection_meta_c_type, connection_info_c_type);
 
         let ref_subscriber = self.config.ref_subscriber(quote!(
             type ConnectionContext = T::ConnectionContext;
@@ -462,6 +471,8 @@ impl ToTokens for Output {
                 }
             }
 
+            #c_ffi
+
             #[cfg(any(test, feature = "testing"))]
             pub mod testing {
                 use super::*;
diff --git a/tools/s2n-events/src/parser.rs b/tools/s2n-events/src/parser.rs
@@ -97,6 +97,34 @@ impl Struct {
     }
 
     fn to_tokens(&self, output: &mut Output) {
+        match self.attrs.c_definition {
+            true => self.to_tokens_c_definition(output),
+            false => self.to_tokens_rust_definition(output),
+        }
+    }
+
+    fn to_tokens_c_definition(&self, output: &mut Output) {
+        assert!(
+            self.attrs.event_name.is_none(),
+            "C struct definitions cannot be directly used as events."
+        );
+
+        let ident = &self.ident;
+        let extra_attrs = &self.attrs.extra;
+        let c_definition_attrs = &self.attrs.c_definition_attrs;
+        let builder_fields = self.fields.iter().map(Field::builder);
+
+        output.c_ffi.extend(quote!(
+            #c_definition_attrs
+            #[derive(Clone, Debug)]
+            #extra_attrs
+            pub struct #ident {
+                #(#builder_fields)*
+            }
+        ));
+    }
+
+    fn to_tokens_rust_definition(&self, output: &mut Output) {
         let Self {
             attrs,
             ident,
@@ -173,6 +201,12 @@ impl Struct {
             }
         ));
 
+        if ident_str == "ConnectionMeta" {
+            output.connection_meta_c_type = attrs.associated_c_type.clone();
+        } else if ident_str == "ConnectionInfo" {
+            output.connection_info_c_type = attrs.associated_c_type.clone();
+        }
+
         if let Some(event_name) = attrs.event_name.as_ref() {
             output.api.extend(quote!(
                 #allow_deprecated
@@ -296,6 +330,12 @@ impl Struct {
                             self.output #lock.push(out);
                         }
                     ));
+
+                    assert!(
+                        attrs.associated_c_type.is_empty(),
+                        "C types cannot be associated with endpoint events. Publishing endpoint \
+                        events from the C API is not yet supported."
+                    );
                 }
                 Subject::Connection => {
                     output.subscriber.extend(quote!(
@@ -405,6 +445,15 @@ impl Struct {
                             }
                         }
                     ));
+
+                    if output.config.c_api {
+                        let c_type = &attrs.associated_c_type;
+                        assert!(
+                            !c_type.is_empty(),
+                            "Events must specify an associated C type with the #[c_type()] \
+                            attribute.",
+                        );
+                    }
                 }
             }
         }
@@ -432,18 +481,41 @@ impl Enum {
     }
 
     fn to_tokens(&self, output: &mut Output) {
+        assert!(
+            self.attrs.event_name.is_none(),
+            "enum events are not currently supported"
+        );
+
+        match self.attrs.c_definition {
+            true => self.to_tokens_c_definition(output),
+            false => self.to_tokens_rust_definition(output),
+        }
+    }
+
+    fn to_tokens_c_definition(&self, output: &mut Output) {
+        let ident = &self.ident;
+        let extra_attrs = &self.attrs.extra;
+        let c_definition_attrs = &self.attrs.c_definition_attrs;
+        let builder_fields = self.variants.iter().map(Variant::builder);
+
+        output.c_ffi.extend(quote!(
+            #c_definition_attrs
+            #[derive(Clone, Debug)]
+            #extra_attrs
+            pub enum #ident {
+                #(#builder_fields)*
+            }
+        ));
+    }
+
+    fn to_tokens_rust_definition(&self, output: &mut Output) {
         let Self {
             attrs,
             ident,
             generics,
             variants,
         } = self;
 
-        assert!(
-            attrs.event_name.is_none(),
-            "enum events are not currently supported"
-        );
-
         let derive_attrs = &attrs.derive_attrs;
         let builder_derive_attrs = &attrs.builder_derive_attrs;
         let extra_attrs = &attrs.extra;
@@ -543,6 +615,9 @@ pub struct ContainerAttrs {
     pub checkpoint: Vec<Checkpoint>,
     pub measure_counter: Vec<Metric>,
     pub extra: TokenStream,
+    pub associated_c_type: TokenStream,
+    pub c_definition: bool,
+    pub c_definition_attrs: TokenStream,
 }
 
 impl ContainerAttrs {
@@ -563,6 +638,9 @@ impl ContainerAttrs {
             checkpoint: vec![],
             measure_counter: vec![],
             extra: quote!(),
+            associated_c_type: quote!(),
+            c_definition: false,
+            c_definition_attrs: TokenStream::default(),
         };
 
         for attr in attrs {
@@ -591,6 +669,13 @@ impl ContainerAttrs {
                 v.checkpoint.push(attr.parse_args().unwrap());
             } else if path.is_ident("measure_counter") {
                 v.measure_counter.push(attr.parse_args().unwrap());
+            } else if path.is_ident("c_type") {
+                v.associated_c_type = attr.parse_args().unwrap();
+            } else if path.is_ident("repr") {
+                // Structs/enums with the #[repr(...)] attribute are assumed to be defined for the
+                // C API.
+                v.c_definition = true;
+                attr.to_tokens(&mut v.c_definition_attrs);
             } else {
                 attr.to_tokens(&mut v.extra)
             }
diff --git a/tools/s2n-events/tests/c_ffi_events/event/generated.rs b/tools/s2n-events/tests/c_ffi_events/event/generated.rs
@@ -155,6 +155,42 @@ pub mod api {
     impl Event for CountEvent {
         const NAME: &'static str = "count_event";
     }
+    impl IntoEvent<builder::ConnectionMeta> for &c_ffi::s2n_event_connection_meta {
+        fn into_event(self) -> builder::ConnectionMeta {
+            let duration = Duration::from_nanos(self.timestamp);
+            let timestamp =
+                unsafe { s2n_quic_core::time::Timestamp::from_duration(duration).into_event() };
+            builder::ConnectionMeta { id: 0, timestamp }
+        }
+    }
+    impl IntoEvent<builder::ConnectionInfo> for &c_ffi::s2n_event_connection_info {
+        fn into_event(self) -> builder::ConnectionInfo {
+            builder::ConnectionInfo {}
+        }
+    }
+    impl<'a> IntoEvent<builder::ByteArrayEvent<'a>> for &c_ffi::s2n_byte_array_event {
+        fn into_event(self) -> builder::ByteArrayEvent<'a> {
+            let data =
+                unsafe { std::slice::from_raw_parts(self.data, self.len.try_into().unwrap()) };
+            builder::ByteArrayEvent { data }
+        }
+    }
+    impl IntoEvent<builder::TestEnum> for c_ffi::s2n_test_enum {
+        fn into_event(self) -> builder::TestEnum {
+            match self {
+                Self::S2N_TEST_VALUE_1 => builder::TestEnum::TestValue1,
+                Self::S2N_TEST_VALUE_2 => builder::TestEnum::TestValue2,
+            }
+        }
+    }
+    impl IntoEvent<builder::EnumEvent> for &c_ffi::s2n_enum_event {
+        fn into_event(self) -> builder::EnumEvent {
+            let value = self.value.clone();
+            builder::EnumEvent {
+                value: value.into_event(),
+            }
+        }
+    }
 }
 pub mod tracing {
     #![doc = r" This module contains event integration with [`tracing`](https://docs.rs/tracing)"]
@@ -293,7 +329,7 @@ pub mod builder {
             }
         }
     }
-    #[derive(Clone, Debug)]
+    #[derive(PartialEq, Clone, Debug)]
     pub enum TestEnum {
         TestValue1,
         TestValue2,
@@ -638,6 +674,40 @@ mod traits {
         }
     }
 }
+pub mod c_ffi {
+    #[allow(unused_imports)]
+    use std::ffi::*;
+    #[repr(C)]
+    #[derive(Clone, Debug)]
+    #[allow(non_camel_case_types)]
+    pub struct s2n_event_connection_meta {
+        pub timestamp: u64,
+    }
+    #[repr(C)]
+    #[derive(Clone, Debug)]
+    #[allow(non_camel_case_types)]
+    pub struct s2n_event_connection_info {}
+    #[repr(C)]
+    #[derive(Clone, Debug)]
+    #[allow(non_camel_case_types)]
+    pub struct s2n_byte_array_event {
+        pub data: *const u8,
+        pub len: u32,
+    }
+    #[repr(C)]
+    #[derive(Clone, Debug)]
+    #[allow(non_camel_case_types)]
+    pub struct s2n_enum_event {
+        pub value: s2n_test_enum,
+    }
+    #[repr(C)]
+    #[derive(Clone, Debug)]
+    #[allow(non_camel_case_types)]
+    pub enum s2n_test_enum {
+        S2N_TEST_VALUE_1,
+        S2N_TEST_VALUE_2,
+    }
+}
 #[cfg(any(test, feature = "testing"))]
 pub mod testing {
     use super::*;
diff --git a/tools/s2n-events/tests/c_ffi_events/events/common.rs b/tools/s2n-events/tests/c_ffi_events/events/common.rs
@@ -8,11 +8,42 @@ enum Subject {
     },
 }
 
+#[c_type(s2n_event_connection_meta)]
 struct ConnectionMeta {
     id: u64,
     timestamp: Timestamp,
 }
 
+#[repr(C)]
+#[allow(non_camel_case_types)]
+struct s2n_event_connection_meta {
+    timestamp: u64,
+}
+
+impl IntoEvent<builder::ConnectionMeta> for &c_ffi::s2n_event_connection_meta {
+    fn into_event(self) -> builder::ConnectionMeta {
+        let duration = Duration::from_nanos(self.timestamp);
+        let timestamp = unsafe {
+            s2n_quic_core::time::Timestamp::from_duration(duration).into_event()
+        };
+        builder::ConnectionMeta {
+            id: 0,
+            timestamp,
+        }
+    }
+}
+
 struct EndpointMeta {}
 
+#[c_type(s2n_event_connection_info)]
 struct ConnectionInfo {}
+
+#[repr(C)]
+#[allow(non_camel_case_types)]
+struct s2n_event_connection_info {}
+
+impl IntoEvent<builder::ConnectionInfo> for &c_ffi::s2n_event_connection_info {
+    fn into_event(self) -> builder::ConnectionInfo {
+        builder::ConnectionInfo {}
+    }
+}
diff --git a/tools/s2n-events/tests/c_ffi_events/events/connection.rs b/tools/s2n-events/tests/c_ffi_events/events/connection.rs
diff --git a/tools/s2n-events/tests/test_c_ffi_events.rs b/tools/s2n-events/tests/test_c_ffi_events.rs
