add safety annotation to unsafe enum discriminant code

Author: jadebenn

lu_packets_derive/src/replica_serde.rs

@@ -1,6 +1,9 @@
 use proc_macro2::{Ident, Span, TokenStream};
 use quote::quote;
-use syn::{parse_macro_input, parse_quote, Attribute, Data, DataEnum, DeriveInput, Field, Fields, Generics, Lit, LitInt, Meta, NestedMeta};
+use syn::{
+	Attribute, Data, DataEnum, DeriveInput, Field, Fields, Lit, LitInt, Meta, NestedMeta,
+	parse_macro_input, parse_quote,
+};
 
 pub fn derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
 	let input = parse_macro_input!(input as DeriveInput);
@@ -10,14 +13,14 @@ pub fn derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
 	match &input.data {
 		Data::Struct(data) => {
 			deser_code = gen_deser_code_struct(&data.fields);
-			ser_code = gen_ser_code_struct(&data.fields, &name);
-		},
+			ser_code = gen_ser_code_struct(&data.fields, name);
+		}
 		Data::Enum(data) => {
 			let ty = get_enum_type(&input);
 			let pre_disc_padding = get_pre_disc_padding(&input);
 			let post_disc_padding = get_post_disc_padding(&input);
-			deser_code = gen_deser_code_enum(data, &name, &ty, &pre_disc_padding, &post_disc_padding);
-			ser_code = gen_ser_code_enum(data, &name, &ty, &pre_disc_padding, &post_disc_padding, &input.generics);
+			deser_code = gen_deser_code_enum(data, name, &ty, &pre_disc_padding, &post_disc_padding);
+			ser_code = gen_ser_code_enum(data, name, &ty, &pre_disc_padding, &post_disc_padding);
 		}
 		Data::Union(_) => unimplemented!(),
 	}
@@ -182,7 +185,7 @@ fn gen_ser_code_struct(fields: &Fields, name: &Ident) -> TokenStream {
 	}
 }
 
-fn gen_ser_code_enum(data: &DataEnum, name: &Ident, ty: &Ident, pre_disc_padding: &Option<LitInt>, post_disc_padding: &Option<LitInt>, generics: &Generics) -> TokenStream {
+fn gen_ser_code_enum(data: &DataEnum, name: &Ident, ty: &Ident, pre_disc_padding: &Option<LitInt>, post_disc_padding: &Option<LitInt>) -> TokenStream {
 	let mut arms = vec![];
 	for f in &data.variants {
 		let ident = &f.ident;
@@ -194,7 +197,7 @@ fn gen_ser_code_enum(data: &DataEnum, name: &Ident, ty: &Ident, pre_disc_padding
 	let write_post_padding = gen_write_padding(post_disc_padding);
 	quote! {
 		#write_pre_padding
-		let disc = unsafe { *(self as *const #name #generics as *const #ty) };
+		let disc = unsafe { *::std::ptr::from_ref(self).cast::<#ty>() };
 		::endio::LEWrite::write(writer, disc)?;
 		#write_post_padding
 		match self {

src/auth/client/mod.rs

@@ -1,14 +1,17 @@
 //! Client-received auth messages.
-use std::io::{Error, ErrorKind::InvalidData, Result as Res, Read};
+use std::{
+	io::{Error, ErrorKind::InvalidData, Read, Result as Res},
+	ptr,
+};
 
-use endio::{LEWrite, LERead, Deserialize, Serialize};
-use endio::LittleEndian as LE;
-use lu_packets_derive::MessageFromVariants;
-use lu_packets_derive::VariantTests;
+use endio::{Deserialize, LERead, LEWrite, LittleEndian as LE, Serialize};
+use lu_packets_derive::{MessageFromVariants, VariantTests};
 
-use crate::common::{LuString3, LuString33, LuString37, LuVarWString, LuWString33, ServiceId};
-use crate::general::client::{DisconnectNotify, Handshake, GeneralMessage};
-use crate::world::server::Language;
+use crate::{
+	common::{LuString3, LuString33, LuString37, LuVarWString, LuWString33, ServiceId},
+	general::client::{DisconnectNotify, GeneralMessage, Handshake},
+	world::server::Language,
+};
 
 /// All messages that can be received by a client from an auth server.
 pub type Message = crate::raknet::client::Message<LuMessage>;
@@ -128,7 +131,10 @@ where
 	&'a LuVarWString<u16>: Serialize<LE, W>,
 {
 	fn serialize(self, writer: &mut W) -> Res<()> {
-		let disc = unsafe { *(self as *const LoginResponse as *const u8) };
+		// SAFETY: Because `LoginResponse` is marked `repr(u8)`, its layout is a `repr(C)` `union`
+		// between `repr(C)` structs, each of which has the `u8` discriminant as its first
+		// field, so we can read the discriminant without offsetting the pointer.
+		let disc = unsafe { *ptr::from_ref(self).cast::<u8>() };
 		writer.write(disc)?;
 		match self {
 			LoginResponse::Ok { events, version, session_key, redirect_address, chat_server_address, cdn_key, cdn_ticket, language, country_code, just_upgraded_from_ftp, is_ftp, time_remaining_in_ftp, stamps } => {

src/world/client/mod.rs

@@ -1,17 +1,18 @@
 //! Client-received world messages.
-use std::io::{Error, ErrorKind::InvalidData, Read, Write};
-use std::io::Result as Res;
+use std::{
+	io::{Error, ErrorKind::InvalidData, Read, Result as Res, Write},
+	ptr,
+};
 
-use endio::{Deserialize, LERead, LEWrite, Serialize};
-use endio::LittleEndian as LE;
+use endio::{Deserialize, LERead, LEWrite, LittleEndian as LE, Serialize};
 use lu_packets_derive::{MessageFromVariants, VariantTests};
 
-use crate::chat::ChatChannel;
-use crate::chat::client::ChatMessage;
-use crate::common::{ObjId, LuString33, LuWString33, LuWString42, LVec, ServiceId};
-use crate::general::client::{DisconnectNotify, Handshake, GeneralMessage};
-use super::{Lot, lnv::LuNameValue, Vector3, ZoneId};
-use super::gm::client::SubjectGameMessage;
+use super::{Lot, Vector3, ZoneId, gm::client::SubjectGameMessage, lnv::LuNameValue};
+use crate::{
+	chat::{ChatChannel, client::ChatMessage},
+	common::{LVec, LuString33, LuWString33, LuWString42, ObjId, ServiceId},
+	general::client::{DisconnectNotify, GeneralMessage, Handshake},
+};
 
 /// All messages that can be received by a client from a world server.
 pub type Message = crate::raknet::client::Message<LuMessage>;
@@ -378,9 +379,12 @@ impl<R: Read> Deserialize<LE, R> for AddFriendResponse {
 	}
 }
 
-impl<'a, W: Write> Serialize<LE, W> for &'a AddFriendResponse {
+impl<W: Write> Serialize<LE, W> for &AddFriendResponse {
 	fn serialize(self, writer: &mut W) -> Res<()> {
-		let disc = unsafe { *(&self.response_type as *const AddFriendResponseType as *const u8) };
+		// SAFETY: Because `AddFriendResponseType` is marked `repr(u8)`, its layout is a `repr(C)` `union`
+		// between `repr(C)` structs, each of which has the `u8` discriminant as its first
+		// field, so we can read the discriminant without offsetting the pointer.
+		let disc = unsafe { *ptr::from_ref(self).cast::<u8>() };
 		LEWrite::write(writer, disc)?;
 		let mut is_online_x = &false;
 		let mut sender_id_x = &0;