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#![recursion_limit = "256"]
//! Provides procedural derive macros for the `Encode` and `Decode` traits of the `eth2_ssz` crate.
//!
//! ## Attributes
//!
//! The following struct/enum attributes are available:
//!
//! - `#[ssz(enum_behaviour = "tag")]`: encodes and decodes an `enum` with 0 fields per variant
//! - `#[ssz(enum_behaviour = "union")]`: encodes and decodes an `enum` with a one-byte variant selector.
//! - `#[ssz(enum_behaviour = "transparent")]`: allows encoding an `enum` by serializing only the
//! value whilst ignoring outermost the `enum`. decodes by attempting to decode each variant
//! in order and the first one that is successful is returned.
//! - `#[ssz(struct_behaviour = "container")]`: encodes and decodes the `struct` as an SSZ
//! "container".
//! - `#[ssz(struct_behaviour = "transparent")]`: encodes and decodes a `struct` with exactly one
//! non-skipped field as if the outermost `struct` does not exist.
//!
//! The following field attributes are available:
//!
//! - `#[ssz(with = "module")]`: uses the methods in `module` to implement `ssz::Encode` and
//! `ssz::Decode`. This is useful when it's not possible to create an `impl` for that type
//! (e.g. the type is defined in another crate).
//! - `#[ssz(skip_serializing)]`: this field will not be included in the serialized SSZ vector.
//! - `#[ssz(skip_deserializing)]`: this field will not be expected in the serialized
//! SSZ vector and it will be initialized from a `Default` implementation.
//!
//! ## Examples
//!
//! ### Structs
//!
//! ```rust
//! use ssz::{Encode, Decode};
//! use ssz_derive::{Encode, Decode};
//!
//! /// Represented as an SSZ "list" wrapped in an SSZ "container".
//! #[derive(Debug, PartialEq, Encode, Decode)]
//! #[ssz(struct_behaviour = "container")] // "container" is the default behaviour
//! struct TypicalStruct {
//! foo: Vec<u8>
//! }
//!
//! assert_eq!(
//! TypicalStruct { foo: vec![42] }.as_ssz_bytes(),
//! vec![4, 0, 0, 0, 42]
//! );
//!
//! assert_eq!(
//! TypicalStruct::from_ssz_bytes(&[4, 0, 0, 0, 42]).unwrap(),
//! TypicalStruct { foo: vec![42] },
//! );
//!
//! /// Represented as an SSZ "list" *without* an SSZ "container".
//! #[derive(Encode, Decode)]
//! #[ssz(struct_behaviour = "transparent")]
//! struct WrapperStruct {
//! foo: Vec<u8>
//! }
//!
//! assert_eq!(
//! WrapperStruct { foo: vec![42] }.as_ssz_bytes(),
//! vec![42]
//! );
//!
//! /// Represented as an SSZ "list" *without* an SSZ "container". The `bar` byte is ignored.
//! #[derive(Debug, PartialEq, Encode, Decode)]
//! #[ssz(struct_behaviour = "transparent")]
//! struct WrapperStructSkippedField {
//! foo: Vec<u8>,
//! #[ssz(skip_serializing, skip_deserializing)]
//! bar: u8,
//! }
//!
//! assert_eq!(
//! WrapperStructSkippedField { foo: vec![42], bar: 99 }.as_ssz_bytes(),
//! vec![42]
//! );
//! assert_eq!(
//! WrapperStructSkippedField::from_ssz_bytes(&[42]).unwrap(),
//! WrapperStructSkippedField { foo: vec![42], bar: 0 }
//! );
//!
//! /// Represented as an SSZ "list" *without* an SSZ "container".
//! #[derive(Encode, Decode)]
//! #[ssz(struct_behaviour = "transparent")]
//! struct NewType(Vec<u8>);
//!
//! assert_eq!(
//! NewType(vec![42]).as_ssz_bytes(),
//! vec![42]
//! );
//!
//! /// Represented as an SSZ "list" *without* an SSZ "container". The `bar` byte is ignored.
//! #[derive(Debug, PartialEq, Encode, Decode)]
//! #[ssz(struct_behaviour = "transparent")]
//! struct NewTypeSkippedField(Vec<u8>, #[ssz(skip_serializing, skip_deserializing)] u8);
//!
//! assert_eq!(
//! NewTypeSkippedField(vec![42], 99).as_ssz_bytes(),
//! vec![42]
//! );
//! assert_eq!(
//! NewTypeSkippedField::from_ssz_bytes(&[42]).unwrap(),
//! NewTypeSkippedField(vec![42], 0)
//! );
//! ```
//!
//! ### Enums
//!
//! ```rust
//! use ssz::{Encode, Decode};
//! use ssz_derive::{Encode, Decode};
//!
//! /// Represented as an SSZ "union".
//! #[derive(Debug, PartialEq, Encode, Decode)]
//! #[ssz(enum_behaviour = "union")]
//! enum UnionEnum {
//! Foo(u8),
//! Bar(Vec<u8>),
//! }
//!
//! assert_eq!(
//! UnionEnum::Foo(42).as_ssz_bytes(),
//! vec![0, 42]
//! );
//! assert_eq!(
//! UnionEnum::from_ssz_bytes(&[1, 42, 42]).unwrap(),
//! UnionEnum::Bar(vec![42, 42]),
//! );
//!
//! /// Represented as only the value in the enum variant.
//! #[derive(Debug, PartialEq, Encode, Decode)]
//! #[ssz(enum_behaviour = "transparent")]
//! enum TransparentEnum {
//! Foo(u8),
//! Bar(Vec<u8>),
//! }
//!
//! assert_eq!(
//! TransparentEnum::Foo(42).as_ssz_bytes(),
//! vec![42]
//! );
//! assert_eq!(
//! TransparentEnum::Bar(vec![42, 42]).as_ssz_bytes(),
//! vec![42, 42]
//! );
//! assert_eq!(
//! TransparentEnum::from_ssz_bytes(&[42, 42]).unwrap(),
//! TransparentEnum::Bar(vec![42, 42]),
//! );
//!
//! /// Representated as an SSZ "uint8"
//! #[derive(Debug, PartialEq, Encode, Decode)]
//! #[ssz(enum_behaviour = "tag")]
//! enum TagEnum {
//! Foo,
//! Bar,
//! }
//! assert_eq!(
//! TagEnum::Foo.as_ssz_bytes(),
//! vec![0]
//! );
//! assert_eq!(
//! TagEnum::from_ssz_bytes(&[1]).unwrap(),
//! TagEnum::Bar,
//! );
//! ```
use darling::{FromDeriveInput, FromMeta};
use proc_macro::TokenStream;
use quote::quote;
use std::convert::TryInto;
use syn::{parse_macro_input, DataEnum, DataStruct, DeriveInput, Ident, Index};
/// The highest possible union selector value (higher values are reserved for backwards compatible
/// extensions).
const MAX_UNION_SELECTOR: u8 = 127;
const NO_ENUM_BEHAVIOUR_ERROR: &str = "enums require an \"enum_behaviour\" attribute with \
a \"transparent\", \"union\", or \"tag\" value, e.g., #[ssz(enum_behaviour = \"transparent\")]";
#[derive(Debug, FromDeriveInput)]
#[darling(attributes(ssz))]
struct StructOpts {
#[darling(default)]
enum_behaviour: Option<String>,
#[darling(default)]
struct_behaviour: Option<String>,
}
/// Field-level configuration.
#[derive(Debug, Default, FromMeta)]
struct FieldOpts {
#[darling(default)]
with: Option<Ident>,
#[darling(default)]
skip_serializing: bool,
#[darling(default)]
skip_deserializing: bool,
}
enum Procedure<'a> {
Struct {
data: &'a syn::DataStruct,
behaviour: StructBehaviour,
},
Enum {
data: &'a syn::DataEnum,
behaviour: EnumBehaviour,
},
}
enum StructBehaviour {
Container,
Transparent,
}
enum EnumBehaviour {
Union,
Transparent,
Tag,
}
impl<'a> Procedure<'a> {
fn read(item: &'a DeriveInput) -> Self {
let opts = StructOpts::from_derive_input(item).unwrap();
match &item.data {
syn::Data::Struct(data) => {
if opts.enum_behaviour.is_some() {
panic!("cannot use \"enum_behaviour\" for a struct");
}
match opts.struct_behaviour.as_deref() {
Some("container") | None => Procedure::Struct {
data,
behaviour: StructBehaviour::Container,
},
Some("transparent") => Procedure::Struct {
data,
behaviour: StructBehaviour::Transparent,
},
Some(other) => panic!(
"{} is not a valid struct behaviour, use \"container\" or \"transparent\"",
other
),
}
}
syn::Data::Enum(data) => {
if opts.struct_behaviour.is_some() {
panic!("cannot use \"struct_behaviour\" for an enum");
}
match opts.enum_behaviour.as_deref() {
Some("union") => Procedure::Enum {
data,
behaviour: EnumBehaviour::Union,
},
Some("transparent") => Procedure::Enum {
data,
behaviour: EnumBehaviour::Transparent,
},
Some("tag") => Procedure::Enum {
data,
behaviour: EnumBehaviour::Tag,
},
Some(other) => panic!(
"{} is not a valid enum behaviour, use \"container\" or \"transparent\"",
other
),
None => panic!("{}", NO_ENUM_BEHAVIOUR_ERROR),
}
}
_ => panic!("ssz_derive only supports structs and enums"),
}
}
}
fn parse_ssz_fields(
struct_data: &syn::DataStruct,
) -> Vec<(&syn::Type, Option<&syn::Ident>, FieldOpts)> {
struct_data
.fields
.iter()
.map(|field| {
let ty = &field.ty;
let ident = field.ident.as_ref();
let field_opts_candidates = field
.attrs
.iter()
.filter(|attr| attr.path.get_ident().map_or(false, |ident| *ident == "ssz"))
.collect::<Vec<_>>();
if field_opts_candidates.len() > 1 {
panic!("more than one field-level \"ssz\" attribute provided")
}
let field_opts = field_opts_candidates
.first()
.map(|attr| {
let meta = attr.parse_meta().unwrap();
FieldOpts::from_meta(&meta).unwrap()
})
.unwrap_or_default();
(ty, ident, field_opts)
})
.collect()
}
/// Implements `ssz::Encode` for some `struct` or `enum`.
#[proc_macro_derive(Encode, attributes(ssz))]
pub fn ssz_encode_derive(input: TokenStream) -> TokenStream {
let item = parse_macro_input!(input as DeriveInput);
let procedure = Procedure::read(&item);
match procedure {
Procedure::Struct { data, behaviour } => match behaviour {
StructBehaviour::Transparent => ssz_encode_derive_struct_transparent(&item, data),
StructBehaviour::Container => ssz_encode_derive_struct(&item, data),
},
Procedure::Enum { data, behaviour } => match behaviour {
EnumBehaviour::Transparent => ssz_encode_derive_enum_transparent(&item, data),
EnumBehaviour::Union => ssz_encode_derive_enum_union(&item, data),
EnumBehaviour::Tag => ssz_encode_derive_enum_tag(&item, data),
},
}
}
/// Derive `ssz::Encode` for a struct.
///
/// Fields are encoded in the order they are defined.
///
/// ## Field attributes
///
/// - `#[ssz(skip_serializing)]`: the field will not be serialized.
fn ssz_encode_derive_struct(derive_input: &DeriveInput, struct_data: &DataStruct) -> TokenStream {
let name = &derive_input.ident;
let (impl_generics, ty_generics, where_clause) = &derive_input.generics.split_for_impl();
let field_is_ssz_fixed_len = &mut vec![];
let field_fixed_len = &mut vec![];
let field_ssz_bytes_len = &mut vec![];
let field_encoder_append = &mut vec![];
for (ty, ident, field_opts) in parse_ssz_fields(struct_data) {
if field_opts.skip_serializing {
continue;
}
let ident = match ident {
Some(ref ident) => ident,
_ => panic!(
"#[ssz(struct_behaviour = \"container\")] only supports named struct fields."
),
};
if let Some(module) = field_opts.with {
let module = quote! { #module::encode };
field_is_ssz_fixed_len.push(quote! { #module::is_ssz_fixed_len() });
field_fixed_len.push(quote! { #module::ssz_fixed_len() });
field_ssz_bytes_len.push(quote! { #module::ssz_bytes_len(&self.#ident) });
field_encoder_append.push(quote! {
encoder.append_parameterized(
#module::is_ssz_fixed_len(),
|buf| #module::ssz_append(&self.#ident, buf)
)
});
} else {
field_is_ssz_fixed_len.push(quote! { <#ty as ssz::Encode>::is_ssz_fixed_len() });
field_fixed_len.push(quote! { <#ty as ssz::Encode>::ssz_fixed_len() });
field_ssz_bytes_len.push(quote! { self.#ident.ssz_bytes_len() });
field_encoder_append.push(quote! { encoder.append(&self.#ident) });
}
}
let output = quote! {
impl #impl_generics ssz::Encode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
#(
#field_is_ssz_fixed_len &&
)*
true
}
fn ssz_fixed_len() -> usize {
if <Self as ssz::Encode>::is_ssz_fixed_len() {
let mut len: usize = 0;
#(
len = len
.checked_add(#field_fixed_len)
.expect("encode ssz_fixed_len length overflow");
)*
len
} else {
ssz::BYTES_PER_LENGTH_OFFSET
}
}
fn ssz_bytes_len(&self) -> usize {
if <Self as ssz::Encode>::is_ssz_fixed_len() {
<Self as ssz::Encode>::ssz_fixed_len()
} else {
let mut len: usize = 0;
#(
if #field_is_ssz_fixed_len {
len = len
.checked_add(#field_fixed_len)
.expect("encode ssz_bytes_len length overflow");
} else {
len = len
.checked_add(ssz::BYTES_PER_LENGTH_OFFSET)
.expect("encode ssz_bytes_len length overflow for offset");
len = len
.checked_add(#field_ssz_bytes_len)
.expect("encode ssz_bytes_len length overflow for bytes");
}
)*
len
}
}
fn ssz_append(&self, buf: &mut Vec<u8>) {
let mut offset: usize = 0;
#(
offset = offset
.checked_add(#field_fixed_len)
.expect("encode ssz_append offset overflow");
)*
let mut encoder = ssz::SszEncoder::container(buf, offset);
#(
#field_encoder_append;
)*
encoder.finalize();
}
}
};
output.into()
}
/// Derive `ssz::Encode` "transparently" for a struct which has exactly one non-skipped field.
///
/// The single field is encoded directly, making the outermost `struct` transparent.
///
/// ## Field attributes
///
/// - `#[ssz(skip_serializing)]`: the field will not be serialized.
fn ssz_encode_derive_struct_transparent(
derive_input: &DeriveInput,
struct_data: &DataStruct,
) -> TokenStream {
let name = &derive_input.ident;
let (impl_generics, ty_generics, where_clause) = &derive_input.generics.split_for_impl();
let ssz_fields = parse_ssz_fields(struct_data);
let num_fields = ssz_fields
.iter()
.filter(|(_, _, field_opts)| !field_opts.skip_deserializing)
.count();
if num_fields != 1 {
panic!(
"A \"transparent\" struct must have exactly one non-skipped field ({} fields found)",
num_fields
);
}
let (index, (ty, ident, _field_opts)) = ssz_fields
.iter()
.enumerate()
.find(|(_, (_, _, field_opts))| !field_opts.skip_deserializing)
.expect("\"transparent\" struct must have at least one non-skipped field");
// Remove the `_usize` suffix from the value to avoid a compiler warning.
let index = Index::from(index);
let output = if let Some(field_name) = ident {
quote! {
impl #impl_generics ssz::Encode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
<#ty as ssz::Encode>::is_ssz_fixed_len()
}
fn ssz_fixed_len() -> usize {
<#ty as ssz::Encode>::ssz_fixed_len()
}
fn ssz_bytes_len(&self) -> usize {
self.#field_name.ssz_bytes_len()
}
fn ssz_append(&self, buf: &mut Vec<u8>) {
self.#field_name.ssz_append(buf)
}
}
}
} else {
quote! {
impl #impl_generics ssz::Encode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
<#ty as ssz::Encode>::is_ssz_fixed_len()
}
fn ssz_fixed_len() -> usize {
<#ty as ssz::Encode>::ssz_fixed_len()
}
fn ssz_bytes_len(&self) -> usize {
self.#index.ssz_bytes_len()
}
fn ssz_append(&self, buf: &mut Vec<u8>) {
self.#index.ssz_append(buf)
}
}
}
};
output.into()
}
/// Derive `ssz::Encode` for an enum in the "transparent" method.
///
/// The "transparent" method is distinct from the "union" method specified in the SSZ specification.
/// When using "transparent", the enum will be ignored and the contained field will be serialized as
/// if the enum does not exist.
///
/// ## Limitations
///
/// Only supports:
/// - Enums with a single field per variant, where
/// - All fields are variably sized from an SSZ-perspective (not fixed size).
///
/// ## Panics
///
/// Will panic at compile-time if the single field requirement isn't met, but will panic *at run
/// time* if the variable-size requirement isn't met.
fn ssz_encode_derive_enum_transparent(
derive_input: &DeriveInput,
enum_data: &DataEnum,
) -> TokenStream {
let name = &derive_input.ident;
let (impl_generics, ty_generics, where_clause) = &derive_input.generics.split_for_impl();
let (patterns, assert_exprs): (Vec<_>, Vec<_>) = enum_data
.variants
.iter()
.map(|variant| {
let variant_name = &variant.ident;
if variant.fields.len() != 1 {
panic!("ssz::Encode can only be derived for enums with 1 field per variant");
}
let pattern = quote! {
#name::#variant_name(ref inner)
};
let ty = &(&variant.fields).into_iter().next().unwrap().ty;
let type_assert = quote! {
!<#ty as ssz::Encode>::is_ssz_fixed_len()
};
(pattern, type_assert)
})
.unzip();
let output = quote! {
impl #impl_generics ssz::Encode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
assert!(
#(
#assert_exprs &&
)* true,
"not all enum variants are variably-sized"
);
false
}
fn ssz_bytes_len(&self) -> usize {
match self {
#(
#patterns => inner.ssz_bytes_len(),
)*
}
}
fn ssz_append(&self, buf: &mut Vec<u8>) {
match self {
#(
#patterns => inner.ssz_append(buf),
)*
}
}
}
};
output.into()
}
/// Derive `ssz::Encode` for an `enum` following the "tag" method.
///
/// The union selector will be determined based upon the order in which the enum variants are
/// defined. E.g., the top-most variant in the enum will have a selector of `0`, the variant
/// beneath it will have a selector of `1` and so on.
///
/// # Limitations
///
/// Only supports enums where each variant has no fields
fn ssz_encode_derive_enum_tag(derive_input: &DeriveInput, enum_data: &DataEnum) -> TokenStream {
let name = &derive_input.ident;
let (impl_generics, ty_generics, where_clause) = &derive_input.generics.split_for_impl();
let patterns: Vec<_> = enum_data
.variants
.iter()
.map(|variant| {
let variant_name = &variant.ident;
if !variant.fields.is_empty() {
panic!("ssz::Encode tag behaviour can only be derived for enums with no fields");
}
quote! {
#name::#variant_name
}
})
.collect();
let union_selectors = compute_union_selectors(patterns.len());
let output = quote! {
impl #impl_generics ssz::Encode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
true
}
fn ssz_fixed_len() -> usize {
1
}
fn ssz_bytes_len(&self) -> usize {
1
}
fn ssz_append(&self, buf: &mut Vec<u8>) {
match self {
#(
#patterns => {
let union_selector: u8 = #union_selectors;
debug_assert!(union_selector <= ssz::MAX_UNION_SELECTOR);
buf.push(union_selector);
},
)*
}
}
}
};
output.into()
}
/// Derive `ssz::Encode` for an `enum` following the "union" SSZ spec.
///
/// The union selector will be determined based upon the order in which the enum variants are
/// defined. E.g., the top-most variant in the enum will have a selector of `0`, the variant
/// beneath it will have a selector of `1` and so on.
///
/// # Limitations
///
/// Only supports enums where each variant has a single field.
fn ssz_encode_derive_enum_union(derive_input: &DeriveInput, enum_data: &DataEnum) -> TokenStream {
let name = &derive_input.ident;
let (impl_generics, ty_generics, where_clause) = &derive_input.generics.split_for_impl();
let patterns: Vec<_> = enum_data
.variants
.iter()
.map(|variant| {
let variant_name = &variant.ident;
if variant.fields.len() != 1 {
panic!("ssz::Encode can only be derived for enums with 1 field per variant");
}
let pattern = quote! {
#name::#variant_name(ref inner)
};
pattern
})
.collect();
let union_selectors = compute_union_selectors(patterns.len());
let output = quote! {
impl #impl_generics ssz::Encode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
false
}
fn ssz_bytes_len(&self) -> usize {
match self {
#(
#patterns => inner
.ssz_bytes_len()
.checked_add(1)
.expect("encoded length must be less than usize::max_value"),
)*
}
}
fn ssz_append(&self, buf: &mut Vec<u8>) {
match self {
#(
#patterns => {
let union_selector: u8 = #union_selectors;
debug_assert!(union_selector <= ssz::MAX_UNION_SELECTOR);
buf.push(union_selector);
inner.ssz_append(buf)
},
)*
}
}
}
};
output.into()
}
/// Derive `ssz::Decode` for a struct or enum.
#[proc_macro_derive(Decode, attributes(ssz))]
pub fn ssz_decode_derive(input: TokenStream) -> TokenStream {
let item = parse_macro_input!(input as DeriveInput);
let procedure = Procedure::read(&item);
match procedure {
Procedure::Struct { data, behaviour } => match behaviour {
StructBehaviour::Transparent => ssz_decode_derive_struct_transparent(&item, data),
StructBehaviour::Container => ssz_decode_derive_struct(&item, data),
},
Procedure::Enum { data, behaviour } => match behaviour {
EnumBehaviour::Union => ssz_decode_derive_enum_union(&item, data),
EnumBehaviour::Tag => ssz_decode_derive_enum_tag(&item, data),
EnumBehaviour::Transparent => ssz_decode_derive_enum_transparent(&item, data),
},
}
}
/// Implements `ssz::Decode` for some `struct`.
///
/// Fields are decoded in the order they are defined.
///
/// ## Field attributes
///
/// - `#[ssz(skip_deserializing)]`: during de-serialization the field will be instantiated from a
/// `Default` implementation. The decoder will assume that the field was not serialized at all
/// (e.g., if it has been serialized, an error will be raised instead of `Default` overriding it).
fn ssz_decode_derive_struct(item: &DeriveInput, struct_data: &DataStruct) -> TokenStream {
let name = &item.ident;
let (impl_generics, ty_generics, where_clause) = &item.generics.split_for_impl();
let mut register_types = vec![];
let mut field_names = vec![];
let mut fixed_decodes = vec![];
let mut decodes = vec![];
let mut is_fixed_lens = vec![];
let mut fixed_lens = vec![];
for (ty, ident, field_opts) in parse_ssz_fields(struct_data) {
let ident = match ident {
Some(ref ident) => ident,
_ => panic!(
"#[ssz(struct_behaviour = \"container\")] only supports named struct fields."
),
};
field_names.push(quote! {
#ident
});
// Field should not be deserialized; use a `Default` impl to instantiate.
if field_opts.skip_deserializing {
decodes.push(quote! {
let #ident = <_>::default();
});
fixed_decodes.push(quote! {
let #ident = <_>::default();
});
continue;
}
let is_ssz_fixed_len;
let ssz_fixed_len;
let from_ssz_bytes;
if let Some(module) = field_opts.with {
let module = quote! { #module::decode };
is_ssz_fixed_len = quote! { #module::is_ssz_fixed_len() };
ssz_fixed_len = quote! { #module::ssz_fixed_len() };
from_ssz_bytes = quote! { #module::from_ssz_bytes(slice) };
register_types.push(quote! {
builder.register_type_parameterized(#is_ssz_fixed_len, #ssz_fixed_len)?;
});
decodes.push(quote! {
let #ident = decoder.decode_next_with(|slice| #module::from_ssz_bytes(slice))?;
});
} else {
is_ssz_fixed_len = quote! { <#ty as ssz::Decode>::is_ssz_fixed_len() };
ssz_fixed_len = quote! { <#ty as ssz::Decode>::ssz_fixed_len() };
from_ssz_bytes = quote! { <#ty as ssz::Decode>::from_ssz_bytes(slice) };
register_types.push(quote! {
builder.register_type::<#ty>()?;
});
decodes.push(quote! {
let #ident = decoder.decode_next()?;
});
}
fixed_decodes.push(quote! {
let #ident = {
start = end;
end = end
.checked_add(#ssz_fixed_len)
.ok_or_else(|| ssz::DecodeError::OutOfBoundsByte {
i: usize::max_value()
})?;
let slice = bytes.get(start..end)
.ok_or_else(|| ssz::DecodeError::InvalidByteLength {
len: bytes.len(),
expected: end
})?;
#from_ssz_bytes?
};
});
is_fixed_lens.push(is_ssz_fixed_len);
fixed_lens.push(ssz_fixed_len);
}
let output = quote! {
impl #impl_generics ssz::Decode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
#(
#is_fixed_lens &&
)*
true
}
fn ssz_fixed_len() -> usize {
if <Self as ssz::Decode>::is_ssz_fixed_len() {
let mut len: usize = 0;
#(
len = len
.checked_add(#fixed_lens)
.expect("decode ssz_fixed_len overflow");
)*
len
} else {
ssz::BYTES_PER_LENGTH_OFFSET
}
}
fn from_ssz_bytes(bytes: &[u8]) -> std::result::Result<Self, ssz::DecodeError> {
if <Self as ssz::Decode>::is_ssz_fixed_len() {
if bytes.len() != <Self as ssz::Decode>::ssz_fixed_len() {
return Err(ssz::DecodeError::InvalidByteLength {
len: bytes.len(),
expected: <Self as ssz::Decode>::ssz_fixed_len(),
});
}
let mut start: usize = 0;
let mut end = start;
#(
#fixed_decodes
)*
Ok(Self {
#(
#field_names,
)*
})
} else {
let mut builder = ssz::SszDecoderBuilder::new(bytes);
#(
#register_types
)*
let mut decoder = builder.build()?;
#(
#decodes
)*
Ok(Self {
#(
#field_names,
)*
})
}
}
}
};
output.into()
}
/// Implements `ssz::Decode` "transparently" for a `struct` with exactly one non-skipped field.
///
/// The bytes will be decoded as if they are the inner field, without the outermost struct. The
/// outermost struct will then be applied artificially.
///
/// ## Field attributes
///
/// - `#[ssz(skip_deserializing)]`: during de-serialization the field will be instantiated from a
/// `Default` implementation. The decoder will assume that the field was not serialized at all
/// (e.g., if it has been serialized, an error will be raised instead of `Default` overriding it).
fn ssz_decode_derive_struct_transparent(
item: &DeriveInput,
struct_data: &DataStruct,
) -> TokenStream {
let name = &item.ident;
let (impl_generics, ty_generics, where_clause) = &item.generics.split_for_impl();
let ssz_fields = parse_ssz_fields(struct_data);
let num_fields = ssz_fields
.iter()
.filter(|(_, _, field_opts)| !field_opts.skip_deserializing)
.count();
if num_fields != 1 {
panic!(
"A \"transparent\" struct must have exactly one non-skipped field ({} fields found)",
num_fields
);
}
let mut fields = vec![];
let mut wrapped_type = None;
for (i, (ty, ident, field_opts)) in ssz_fields.into_iter().enumerate() {
if let Some(name) = ident {
if field_opts.skip_deserializing {
fields.push(quote! {
#name: <_>::default(),
});
} else {
fields.push(quote! {
#name: <_>::from_ssz_bytes(bytes)?,
});
wrapped_type = Some(ty);
}
} else {
let index = syn::Index::from(i);
if field_opts.skip_deserializing {
fields.push(quote! {
#index:<_>::default(),
});
} else {
fields.push(quote! {
#index:<_>::from_ssz_bytes(bytes)?,
});
wrapped_type = Some(ty);
}
}
}
let ty = wrapped_type.unwrap();
let output = quote! {
impl #impl_generics ssz::Decode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
<#ty as ssz::Decode>::is_ssz_fixed_len()
}
fn ssz_fixed_len() -> usize {
<#ty as ssz::Decode>::ssz_fixed_len()
}
fn from_ssz_bytes(bytes: &[u8]) -> std::result::Result<Self, ssz::DecodeError> {
Ok(Self {
#(
#fields
)*
})
}
}
};
output.into()
}
/// Derive `ssz::Decode` for an `enum` following the "tag" SSZ spec.
fn ssz_decode_derive_enum_tag(derive_input: &DeriveInput, enum_data: &DataEnum) -> TokenStream {
let name = &derive_input.ident;
let (impl_generics, ty_generics, where_clause) = &derive_input.generics.split_for_impl();
let patterns: Vec<_> = enum_data
.variants
.iter()
.map(|variant| {
let variant_name = &variant.ident;
if !variant.fields.is_empty() {
panic!("ssz::Decode tag behaviour can only be derived for enums with no fields");
}
quote! {
#name::#variant_name
}
})
.collect();
let union_selectors = compute_union_selectors(patterns.len());
let output = quote! {
impl #impl_generics ssz::Decode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
true
}
fn ssz_fixed_len() -> usize {
1
}
fn from_ssz_bytes(bytes: &[u8]) -> std::result::Result<Self, ssz::DecodeError> {
let byte = bytes
.first()
.copied()
.ok_or(ssz::DecodeError::OutOfBoundsByte { i: 0 })?;
match byte {
#(
#union_selectors => {
Ok(#patterns)
},
)*
other => Err(ssz::DecodeError::UnionSelectorInvalid(other)),
}
}
}
};
output.into()
}
/// Derive `ssz::Decode` for an `enum` following the "union" SSZ spec.
fn ssz_decode_derive_enum_union(derive_input: &DeriveInput, enum_data: &DataEnum) -> TokenStream {
let name = &derive_input.ident;
let (impl_generics, ty_generics, where_clause) = &derive_input.generics.split_for_impl();
let (constructors, var_types): (Vec<_>, Vec<_>) = enum_data
.variants
.iter()
.map(|variant| {
let variant_name = &variant.ident;
if variant.fields.len() != 1 {
panic!("ssz::Decode can only be derived for enums with 1 field per variant");
}
let constructor = quote! {
#name::#variant_name
};
let ty = &(&variant.fields).into_iter().next().unwrap().ty;
(constructor, ty)
})
.unzip();
let union_selectors = compute_union_selectors(constructors.len());
let output = quote! {
impl #impl_generics ssz::Decode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
false
}
fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, ssz::DecodeError> {
// Sanity check to ensure the definition here does not drift from the one defined in
// `ssz`.
debug_assert_eq!(#MAX_UNION_SELECTOR, ssz::MAX_UNION_SELECTOR);
let (selector, body) = ssz::split_union_bytes(bytes)?;
match selector.into() {
#(
#union_selectors => {
<#var_types as ssz::Decode>::from_ssz_bytes(body).map(#constructors)
},
)*
other => Err(ssz::DecodeError::UnionSelectorInvalid(other))
}
}
}
};
output.into()
}
/// Derive `ssz::Decode` for an enum in the "transparent" method.
///
/// The "transparent" method attempts to decode into an enum by trying to decode each variant in
/// order until one is successful. If no variant decodes successfully,
/// `ssz::DecodeError::NoMatchingVariant` is returned.
///
/// ## Limitations
///
/// Only supports enums with a single field per variant.
///
/// ## Considerations
///
/// The ordering of the enum variants matters. For example, a variant containing a single
/// "variable-size" type may always result in a successful decoding (e.g. MyEnum::Foo(Vec<u8>)).
fn ssz_decode_derive_enum_transparent(
derive_input: &DeriveInput,
enum_data: &DataEnum,
) -> TokenStream {
let name = &derive_input.ident;
let (impl_generics, ty_generics, where_clause) = &derive_input.generics.split_for_impl();
let (constructors, var_types): (Vec<_>, Vec<_>) = enum_data
.variants
.iter()
.map(|variant| {
let variant_name = &variant.ident;
if variant.fields.len() != 1 {
panic!("ssz::Decode can only be derived for enums with 1 field per variant");
}
let constructor = quote! {
#name::#variant_name
};
let ty = &(&variant.fields).into_iter().next().unwrap().ty;
(constructor, ty)
})
.unzip();
let output = quote! {
impl #impl_generics ssz::Decode for #name #ty_generics #where_clause {
fn is_ssz_fixed_len() -> bool {
false
}
fn from_ssz_bytes(bytes: &[u8]) -> Result<Self, ssz::DecodeError> {
#(
if let Ok(var) = <#var_types as ssz::Decode>::from_ssz_bytes(bytes) {
return Ok(#constructors(var));
}
)*
Err(ssz::DecodeError::NoMatchingVariant)
}
}
};
output.into()
}
fn compute_union_selectors(num_variants: usize) -> Vec<u8> {
let union_selectors = (0..num_variants)
.map(|i| {
i.try_into()
.expect("union selector exceeds u8::max_value, union has too many variants")
})
.collect::<Vec<u8>>();
let highest_selector = union_selectors
.last()
.copied()
.expect("0-variant union is not permitted");
assert!(
highest_selector <= MAX_UNION_SELECTOR,
"union selector {} exceeds limit of {}, enum has too many variants",
highest_selector,
MAX_UNION_SELECTOR
);
union_selectors
}