There were two major issues in my code that prevented it from running. Both of them were difficult to solve because they were syntactically correct. As a result, errors were raised at run time with very few information while the compilation was succesful. The repository for the project is: https://github.com/DimitriosMitsios/openvm-ream.

First issue, reading input on guest from host

This solution is due to Utsav who faced the same issue. On guest directory in order to read input, I was using the read function from openvm::io::read. Instead, the function that should be used is openvm::io::read_vec(). I am not sure why read() was not working on inputs which are given as vectors of bytes. Here is the guest code

use openvm::io::{read_vec};
use ream_consensus::{attestation::Attestation, electra::beacon_state::BeaconState};
use ream_lib::{ssz::from_ssz_bytes};

pub fn main() {

    let bytes: Vec<u8> = read_vec();
    let arr: [u8;8] = bytes.try_into().unwrap();
    let pre_state_len = u64::from_le_bytes(arr) as usize;
    let mut pre_state_ssz_bytes: Vec<u8> = vec![0u8; pre_state_len];
    pre_state_ssz_bytes = read_vec();
    let mut pre_state: BeaconState = from_ssz_bytes(&pre_state_ssz_bytes).unwrap();
    let mut attestation_bytes = Vec::new();
    attestation_bytes = read_vec();
    let attestation: Attestation = from_ssz_bytes(&attestation_bytes).unwrap();
    let _ = pre_state.process_attestation(&attestation);
}

For the moment, the input consists of three items:

the length of the state
the state itself and
an attestation

On the host side, the writing is done as

let mut stdin = StdIn::default();
    let pre_state_bytes: Vec<u8> =ssz_from_file(&pre_state_path);
    stdin.write_bytes(&pre_state_len_bytes);
    ...

Second issue, using different serialization algorithms

On the host side, I was using openvm::serde::to_vec in order to read attestation and prestate files. In contrast, I was using from_ssz_bytes on the guest side to read them. The use of different algorithms created errors during runtime. Right now, I am using on both sides the ssz library which I call ream-lib and I borrowed from Ream’s repo.

To be done

There are a few tasks to be done:

Clean up the code such that all warnings are removed
Generalize guest code to process various inputs (not only attestations)
Include checks such as assert_eq!(*new_state_root, recomputed_state_root) and tests
Count RISC-V cycles