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// Code mostly made by gemini somehow
use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, Data, DeriveInput, Fields};
#[proc_macro_derive(ByteEncode)]
pub fn derive_byte_encode(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let name = input.ident;
// We only support structs with named fields for this example
let fields = match input.data {
Data::Struct(data) => match data.fields {
Fields::Named(fields) => fields.named,
_ => panic!("Only named fields are supported"),
},
_ => panic!("Only structs are supported"),
};
// --- 1. Generate from_le_bytes parsing logic ---
let mut current_offset = quote! { 0 };
let from_le_bytes_initializers = fields.iter().map(|f| {
let field_name = &f.ident;
let field_type = &f.ty;
// Calculate start and end bounds for the current field slice
let start = quote! { #current_offset };
let end = quote! { #start + <#field_type>::SIZE };
// Update the offset tracking for the next iteration loop
current_offset = quote! { #end };
quote! {
#field_name: <#field_type as ByteEncode<{<#field_type>::SIZE}>>::from_le_bytes(
buffer[#start..#end].try_into().unwrap()
)
}
});
let mut current_offset = quote! { 0 };
let from_be_bytes_initializers = fields.iter().map(|f| {
let field_name = &f.ident;
let field_type = &f.ty;
// Calculate start and end bounds for the current field slice
let start = quote! { #current_offset };
let end = quote! { #start + <#field_type>::SIZE };
// Update the offset tracking for the next iteration loop
current_offset = quote! { #end };
quote! {
#field_name: <#field_type as ByteEncode<{<#field_type>::SIZE}>>::from_be_bytes(
&mut buffer[#start..#end].try_into().unwrap()
)
}
});
// --- 2. Generate to_le_bytes serialization logic ---
let mut current_offset = quote! { 0 };
let to_le_bytes_writers = fields.iter().map(|f| {
let field_name = &f.ident;
let field_type = &f.ty;
let start = quote! { #current_offset };
let end = quote! { #start + <#field_type>::SIZE };
current_offset = quote! { #end };
quote! {
res[#start..#end].copy_from_slice(&self.#field_name.to_le_bytes());
}
});
let mut current_offset = quote! { 0 };
let to_be_bytes_writers = fields.iter().map(|f| {
let field_name = &f.ident;
let field_type = &f.ty;
let start = quote! { #current_offset };
let end = quote! { #start + <#field_type>::SIZE };
current_offset = quote! { #end };
quote! {
res[#start..#end].copy_from_slice(&self.#field_name.to_be_bytes());
}
});
// --- 3. Construct final token stream ---
// This dynamically sums up sizes like: 0 + Field1::SIZE + Field2::SIZE ...
let total_size_expr = fields.iter().fold(quote! { 0 }, |acc, f| {
let field_type = &f.ty;
quote! { #acc + <#field_type>::SIZE }
});
let expanded = quote! {
impl ByteEncode<{ #total_size_expr }> for #name {
fn from_le_bytes(buffer: &[u8; { #total_size_expr }]) -> Self {
Self {
#( #from_le_bytes_initializers, )*
}
}
fn to_le_bytes(&self) -> [u8; { #total_size_expr }] {
let mut res = [0u8; { #total_size_expr }];
#( #to_le_bytes_writers )*
res
}
fn from_be_bytes(buffer: &mut [u8; { #total_size_expr }]) -> Self {
Self {
#( #from_be_bytes_initializers, )*
}
}
fn to_be_bytes(&self) -> [u8; { #total_size_expr }] {
let mut res = [0u8; { #total_size_expr }];
#( #to_be_bytes_writers )*
res
}
}
};
TokenStream::from(expanded)
}
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