# SSZ comparison

Attempting to compare the result of Ssz from py-ssz (python library) and eth2-ssz (rust crate)

The sede structure is currently being tried out by me in the hopes of implementing it as the epoch accumulator in the portal network

## Sedes Structure

`List[ Container[ block_hash : byte32, total_difficulty : int], 2048]`

## Test data

The examples are constructed using the data of Block#0 which resembles:

Block 
{
block_hash:String =  "0xd4e56740f876aef8c010b86a40d5f56745a118d0906a34e69aec8c0db1cb8fa3",
total_difficulty:u64 = 17179869184
}

## Example of code snippet

### Python (py-ssz)

from typing import NamedTuple, Optional, Tuple, List
from eth_typing import Hash32
import ssz
from ssz import sedes as ssz_sedes
from eth_utils import to_bytes


class AccumulatorLeaf(NamedTuple):
    block_hash: Hash32
    total_difficulty: int

AccumulatorLeafSedes = ssz_sedes.Container(
    field_sedes=(ssz_sedes.bytes32, ssz_sedes.uint256)
)
EpochAccumulatorSedes = ssz_sedes.List(AccumulatorLeafSedes, max_length=EPOCH_SIZE)

class Block:
    def __init__(self, block_hash: Hash32, total_difficulty: int):
        self.block_hash = block_hash
        self.total_difficulty = total_difficulty


def test() :
    ##block data here
    block = Block("0xd4e56740f876aef8c010b86a40d5f56745a118d0906a34e69aec8c0db1cb8fa3",17179869184)
    
    leaf = AccumulatorLeaf(
            block_hash=Hash32(to_bytes(hexstr=block.block_hash)),
            total_difficulty=int(block.total_difficulty),
        )
        
    epoch_accumulator = (leaf,)
    
    #getting the hash
    epoch_accumulator_root = ssz.get_hash_tree_root(
            epoch_accumulator, sedes=EpochAccumulatorSedes,
        )
        
    #encode to ssz
    epoch_encoded = ssz.encode(epoch_accumulator, sedes=EpochAccumulatorSedes)

hash result (converted to readable form using HexBytes):
`"0x30d1ed68b3b224f25c19cf109a0ebf354b407728432aabe83fd608ee8ec1dca7"`

epoch_encoded result (printing out value of each byte):
`[212, 229, 103, 64, 248, 118, 174, 248, 192, 16, 184, 106, 64, 213, 245, 103, 69, 161, 24, 208, 144, 106, 52, 230, 154, 236, 140, 13, 177, 203, 143, 163, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]`

### Rust (eth2-ssz)

use ethereum_types::H256;
use ssz::{Decode, DecodeError, Encode};
use ssz_derive::{Decode, Encode};
use ssz_types::{typenum, VariableList};
use tree_hash::TreeHash;
use tree_hash_derive::TreeHash;
use typenum::U2048;

#[derive(Clone, Copy, Encode, Decode, Debug, PartialEq, TreeHash, Default)]
pub struct EpochSede {
    block_hash: H256,
    total_difficulty: U256,
}

#[derive(Debug, Clone)]
pub struct Block {
    pub block_hash: String,
    pub total_difficulty: u64,
}

fn main() {
    //defined block data
    let block = Block {
        block_hash: "0xd4e56740f876aef8c010b86a40d5f56745a118d0906a34e69aec8c0db1cb8fa3".to_string(),
        total_difficulty: 17179869184
    };
    
    let serialized = impl_serde::serialize::from_hex(&block.block_hash).unwrap();

    let typed_block_hash = <H256>::from_slice(&serialized[..]);

    //convert total_diffuculty to U256
    let total_difficulty = 

    let epoch_sede = EpochSede::new(typed_block_hash, total_difficulty);
    
    let epoch_accumulator: Vec<EpochSede> = vec![epoch_sede];
    let epoch_sede_var_list: VariableList<_, U2048> =
        VariableList::from(epoch_accumulator.clone());
    let epoch_hash = epoch_sede_var_list.tree_hash_root();
    
    let epoch_encoded = &epoch_sede_fixed_vec.as_ssz_bytes();
}


impl EpochSede {
    pub fn new(block_hash: H256, total_difficulty: u64) -> EpochSede {
        EpochSede {
            block_hash,
            total_difficulty,
        }
    }
}

hash result:
`0x30d1ed68b3b224f25c19cf109a0ebf354b407728432aabe83fd608ee8ec1dca7`

epoch_encoded result:

[212, 229, 103, 64, 248, 118, 174, 248, 192, 16, 184, 106, 64, 213, 245, 103, 69, 161, 24, 208, 144, 106, 52, 230, 154, 236, 140, 13, 177, 203, 143, 
163, 0, 0, 0, 0, 4, 0, 0, 0]

## Thoughts
These 2 methods return the same hash and a similar looking ssz encoded version.

Peforming ssz encoding only to the container sede returns a matching result in both implementation

However in the List sede, py-ssz seems to have 24 more 0's being padded towards the end of the encoded result.

Digging deeper while keeping an open mind that my code may not be correct