Code shared from the Rust Playground

playground.rs

fn main() -> anyhow::Result<()> {
    println!("{}", get_name(include_bytes!("../Class.class"))?);
    Ok(())
}

fn get_name(cf: &'static [u8]) -> anyhow::Result<String> {
    use anyhow::Context;
    use classfile_parser::constant_info::ConstantInfo::{NameAndType, Utf8};
    use classfile_parser::constant_info::NameAndTypeConstant;

    let (_, cf) = classfile_parser::class_parser(cf).context("Parse classfile")?;
    let ci = cf
        .const_pool
        .get(cf.this_class as usize)
        .context(format!("this_class index {} out of bounds", cf.this_class))?;
    let name_index = if let NameAndType(NameAndTypeConstant { name_index, .. }) = ci {
        *name_index
    } else {
        anyhow::bail!(
            "Expected a NameAndTypeConstant for this_class, found {:?}",
            ci
        );
    };
    let ci = cf.const_pool.get(name_index as usize).context(format!(
        "name_index for this_class {} out of bounds",
        name_index
    ))?;
    let s = if let Utf8(s) = ci {
        &s.utf8_string
    } else {
        anyhow::bail!(
            "Expected a Utf8 constant for this_class' name, found {:?}",
            ci
        );
    };
    anyhow::ensure!(
        s.starts_with("L") && s.ends_with(";"),
        "Expected class name to be of the form \"Lclass/Path.class;\", found \"{}\"",
        s
    );
    Ok(s[1..s.len() - 1].to_owned())
}