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Implement SSZ union type (#2579)

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## Issue Addressed

NA

## Proposed Changes

Implements the "union" type from the SSZ spec for `ssz`, `ssz_derive`, `tree_hash` and `tree_hash_derive` so it may be derived for `enums`:

https://github.com/ethereum/consensus-specs/blob/v1.1.0-beta.3/ssz/simple-serialize.md#union

The union type is required for the merge, since the `Transaction` type is defined as a single-variant union `Union[OpaqueTransaction]`.

### Crate Updates

This PR will (hopefully) cause CI to publish new versions for the following crates:

- `eth2_ssz_derive`: `0.2.1` -> `0.3.0`
- `eth2_ssz`: `0.3.0` -> `0.4.0`
- `eth2_ssz_types`: `0.2.0` -> `0.2.1`
- `tree_hash`: `0.3.0` -> `0.4.0`
- `tree_hash_derive`: `0.3.0` -> `0.4.0`

These these crates depend on each other, I've had to add a workspace-level `[patch]` for these crates. A follow-up PR will need to remove this patch, ones the new versions are published.

### Union Behaviors

We already had SSZ `Encode` and `TreeHash` derive for enums, however it just did a "transparent" pass-through of the inner value. Since the "union" decoding from the spec is in conflict with the transparent method, I've required that all `enum` have exactly one of the following enum-level attributes:

#### SSZ

-  `#[ssz(enum_behaviour = "union")]`
    - matches the spec used for the merge
-  `#[ssz(enum_behaviour = "transparent")]`
    - maintains existing functionality
    - not supported for `Decode` (never was)
    
#### TreeHash

-  `#[tree_hash(enum_behaviour = "union")]`
    - matches the spec used for the merge
-  `#[tree_hash(enum_behaviour = "transparent")]`
    - maintains existing functionality

This means that we can maintain the existing transparent behaviour, but all existing users will get a compile-time error until they explicitly opt-in to being transparent.

### Legacy Option Encoding

Before this PR, we already had a union-esque encoding for `Option<T>`. However, this was with the *old* SSZ spec where the union selector was 4 bytes. During merge specification, the spec was changed to use 1 byte for the selector.

Whilst the 4-byte `Option` encoding was never used in the spec, we used it in our database. Writing a migrate script for all occurrences of `Option` in the database would be painful, especially since it's used in the `CommitteeCache`. To avoid the migrate script, I added a serde-esque `#[ssz(with = "module")]` field-level attribute to `ssz_derive` so that we can opt into the 4-byte encoding on a field-by-field basis.

The `ssz::legacy::four_byte_impl!` macro allows a one-liner to define the module required for the `#[ssz(with = "module")]` for some `Option<T> where T: Encode + Decode`.

Notably, **I have removed `Encode` and `Decode` impls for `Option`**. I've done this to force a break on downstream users. Like I mentioned, `Option` isn't used in the spec so I don't think it'll be *that* annoying. I think it's nicer than quietly having two different union implementations or quietly breaking the existing `Option` impl.

### Crate Publish Ordering

I've modified the order in which CI publishes crates to ensure that we don't publish a crate without ensuring we already published a crate that it depends upon.

## TODO

- [ ] Queue a follow-up `[patch]`-removing PR.
This commit is contained in:
Paul Hauner
2021-09-25 05:58:36 +00:00
parent a844ce5ba9
commit fe52322088
63 changed files with 1515 additions and 571 deletions
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204
consensus/ssz/tests/tests.rs
View File

@@ -292,68 +292,6 @@ mod round_trip {
);
}
#[derive(Debug, PartialEq, Encode, Decode)]
struct TwoVariableLenOptions {
a: u16,
b: Option<u16>,
c: Option<Vec<u16>>,
d: Option<Vec<u16>>,
}
#[test]
#[allow(clippy::zero_prefixed_literal)]
fn two_variable_len_options_encoding() {
let s = TwoVariableLenOptions {
a: 42,
b: None,
c: Some(vec![0]),
d: None,
};
let bytes = vec![
// 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
// | option<u16> | offset | offset | option<u16 | 1st list
42, 00, 14, 00, 00, 00, 18, 00, 00, 00, 24, 00, 00, 00, 00, 00, 00, 00, 01, 00, 00, 00,
// 23 24 25 26 27
// | 2nd list
00, 00, 00, 00, 00, 00,
];
assert_eq!(s.as_ssz_bytes(), bytes);
}
#[test]
fn two_variable_len_options_round_trip() {
let vec: Vec<TwoVariableLenOptions> = vec![
TwoVariableLenOptions {
a: 42,
b: Some(12),
c: Some(vec![0]),
d: Some(vec![1]),
},
TwoVariableLenOptions {
a: 42,
b: Some(12),
c: Some(vec![0]),
d: None,
},
TwoVariableLenOptions {
a: 42,
b: None,
c: Some(vec![0]),
d: None,
},
TwoVariableLenOptions {
a: 42,
b: None,
c: None,
d: None,
},
];
round_trip(vec);
}
#[test]
fn tuple_u8_u16() {
let vec: Vec<(u8, u16)> = vec![
@@ -384,3 +322,145 @@ mod round_trip {
round_trip(vec);
}
}
mod derive_macro {
use ssz::{Decode, Encode};
use ssz_derive::{Decode, Encode};
use std::fmt::Debug;
fn assert_encode<T: Encode>(item: &T, bytes: &[u8]) {
assert_eq!(item.as_ssz_bytes(), bytes);
}
fn assert_encode_decode<T: Encode + Decode + PartialEq + Debug>(item: &T, bytes: &[u8]) {
assert_encode(item, bytes);
assert_eq!(T::from_ssz_bytes(bytes).unwrap(), *item);
}
#[derive(PartialEq, Debug, Encode, Decode)]
#[ssz(enum_behaviour = "union")]
enum TwoFixedUnion {
U8(u8),
U16(u16),
}
#[derive(PartialEq, Debug, Encode, Decode)]
struct TwoFixedUnionStruct {
a: TwoFixedUnion,
}
#[test]
fn two_fixed_union() {
let eight = TwoFixedUnion::U8(1);
let sixteen = TwoFixedUnion::U16(1);
assert_encode_decode(&eight, &[0, 1]);
assert_encode_decode(&sixteen, &[1, 1, 0]);
assert_encode_decode(&TwoFixedUnionStruct { a: eight }, &[4, 0, 0, 0, 0, 1]);
assert_encode_decode(&TwoFixedUnionStruct { a: sixteen }, &[4, 0, 0, 0, 1, 1, 0]);
}
#[derive(PartialEq, Debug, Encode, Decode)]
struct VariableA {
a: u8,
b: Vec<u8>,
}
#[derive(PartialEq, Debug, Encode, Decode)]
struct VariableB {
a: Vec<u8>,
b: u8,
}
#[derive(PartialEq, Debug, Encode)]
#[ssz(enum_behaviour = "transparent")]
enum TwoVariableTrans {
A(VariableA),
B(VariableB),
}
#[derive(PartialEq, Debug, Encode)]
struct TwoVariableTransStruct {
a: TwoVariableTrans,
}
#[derive(PartialEq, Debug, Encode, Decode)]
#[ssz(enum_behaviour = "union")]
enum TwoVariableUnion {
A(VariableA),
B(VariableB),
}
#[derive(PartialEq, Debug, Encode, Decode)]
struct TwoVariableUnionStruct {
a: TwoVariableUnion,
}
#[test]
fn two_variable_trans() {
let trans_a = TwoVariableTrans::A(VariableA {
a: 1,
b: vec![2, 3],
});
let trans_b = TwoVariableTrans::B(VariableB {
a: vec![1, 2],
b: 3,
});
assert_encode(&trans_a, &[1, 5, 0, 0, 0, 2, 3]);
assert_encode(&trans_b, &[5, 0, 0, 0, 3, 1, 2]);
assert_encode(
&TwoVariableTransStruct { a: trans_a },
&[4, 0, 0, 0, 1, 5, 0, 0, 0, 2, 3],
);
assert_encode(
&TwoVariableTransStruct { a: trans_b },
&[4, 0, 0, 0, 5, 0, 0, 0, 3, 1, 2],
);
}
#[test]
fn two_variable_union() {
let union_a = TwoVariableUnion::A(VariableA {
a: 1,
b: vec![2, 3],
});
let union_b = TwoVariableUnion::B(VariableB {
a: vec![1, 2],
b: 3,
});
assert_encode_decode(&union_a, &[0, 1, 5, 0, 0, 0, 2, 3]);
assert_encode_decode(&union_b, &[1, 5, 0, 0, 0, 3, 1, 2]);
assert_encode_decode(
&TwoVariableUnionStruct { a: union_a },
&[4, 0, 0, 0, 0, 1, 5, 0, 0, 0, 2, 3],
);
assert_encode_decode(
&TwoVariableUnionStruct { a: union_b },
&[4, 0, 0, 0, 1, 5, 0, 0, 0, 3, 1, 2],
);
}
#[derive(PartialEq, Debug, Encode, Decode)]
#[ssz(enum_behaviour = "union")]
enum TwoVecUnion {
A(Vec<u8>),
B(Vec<u8>),
}
#[test]
fn two_vec_union() {
assert_encode_decode(&TwoVecUnion::A(vec![]), &[0]);
assert_encode_decode(&TwoVecUnion::B(vec![]), &[1]);
assert_encode_decode(&TwoVecUnion::A(vec![0]), &[0, 0]);
assert_encode_decode(&TwoVecUnion::B(vec![0]), &[1, 0]);
assert_encode_decode(&TwoVecUnion::A(vec![0, 1]), &[0, 0, 1]);
assert_encode_decode(&TwoVecUnion::B(vec![0, 1]), &[1, 0, 1]);
}
}