FPVM 백엔드

use kona_std_fpvm::{io, FileDescriptor};

// Print to `stdout`. Infallible, will panic if dispatch fails.
io::print("Hello, world!");

// Print to `stderr`. Infallible, will panic if dispatch fails.
io::print_err("Goodbye, world!");

// Read from or write to a specified file descriptor. Returns a result with the
// return value or syscall errno.
let _ = io::write(FileDescriptor::StdOut, "Hello, world!".as_bytes());
let mut buf = Vec::with_capacity(8);
let _ = io::read(FileDescriptor::StdIn, buf.as_mut_slice());

// Exit the program with a specified exit code.
io::exit(0);

#[async_trait]
impl<T: CommsClient + Sync + Send> ChainProvider for OracleL1ChainProvider<T> {
    type Error = OracleProviderError;

    async fn header_by_hash(&mut self, hash: B256) -> Result<Header, Self::Error> {
        // Fetch the header RLP from the oracle.
        HintType::L1BlockHeader.with_data(&[hash.as_ref()]).send(self.oracle.as_ref()).await?;
        let header_rlp = self.oracle.get(PreimageKey::new_keccak256(*hash)).await?;

        // Decode the header RLP into a Header.
        Header::decode(&mut header_rlp.as_slice()).map_err(OracleProviderError::Rlp)
    }

    // - snip -
}