serde_bencoded 0.3.2

use serde::{Deserialize, Serialize};
use serde_bencoded::from_bytes;
use serde_bytes::ByteBuf;
use std::io::Read;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let bytes = if atty::is(atty::Stream::Stdin) {
        let second_arg = std::env::args_os()
            .nth(1)
            .ok_or("missing `path` argument".to_string())?;
        let mut file = std::fs::File::open(second_arg)?;
        let mut buf = Vec::new();
        file.read_to_end(&mut buf)?;
        buf
    } else {
        let mut buf = Vec::new();
        std::io::stdin().lock().read_to_end(&mut buf)?;
        buf
    };
    let info: MetaInfo = from_bytes(&bytes)?;
    println!("announce: {}", info.announce);
    println!("announce-list: {:?}", info.announce_list);
    println!("creation date: {:?}", info.creation_date);
    println!("comment: {:?}", info.comment);
    println!("created by: {:?}", info.created_by);
    println!("encoding: {:?}", info.encoding);

    println!(
        "piece length: {}",
        bytesize::ByteSize(info.info.piece_length).to_string_as(true)
    );
    println!("pieces (count): {}", info.info.pieces.len() as u64);
    println!("private: {:?}", info.info.private);
    println!("name: {}", info.info.name);
    match info.info.mode {
        // display as Single File Mode
        FileMode::SingleFile { length, md5sum } => {
            println!("\tSingle File Mode");
            println!("\tlength: {}", bytesize::ByteSize(length));
            println!("\tmd5sum: {:?}", md5sum);
        }
        // display as Multiple File Mode
        FileMode::MultipleFiles { files } => {
            println!("\tMultiple File Mode");
            println!("\tfiles:");
            for file in files {
                println!("\t\tlength: {}", file.length);
                println!("\t\tmd5sum: {:?}", file.md5sum);
                println!("\t\tpath: {:?}", file.path);
                println!();
            }
        }
    }

    Ok(())
}

#[derive(Debug, Serialize, Deserialize)]
struct Info {
    #[serde(rename = "piece length")]
    piece_length: u64,
    pieces: ByteBuf,
    private: Option<i64>,
    name: String,
    #[serde(flatten)]
    mode: FileMode,
}

#[derive(Debug, Serialize, Deserialize)]
#[serde(untagged)]
enum FileMode {
    MultipleFiles {
        files: Vec<File>,
    },
    SingleFile {
        length: u64,
        md5sum: Option<ByteBuf>,
    },
}

#[derive(Debug, Serialize, Deserialize)]
struct File {
    length: u64,
    md5sum: Option<ByteBuf>,
    path: Vec<String>,
}

#[derive(Debug, Serialize, Deserialize)]
struct MetaInfo {
    info: Info,
    announce: String,
    #[serde(rename = "announce-list")]
    announce_list: Option<Vec<Vec<String>>>,
    #[serde(rename = "creation date")]
    creation_date: Option<u64>,
    comment: Option<String>,
    #[serde(rename = "created by")]
    created_by: Option<String>,
    encoding: Option<String>,
}