mcp-multiplexer 0.1.0

One MCP server fronting many: 7 meta-tools instead of every tool schema in context
Documentation 
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use clap::Parser;
use std::path::PathBuf;

#[derive(Parser)]
#[command(
    name = "mcp-multiplexer",
    version,
    about = "One MCP server fronting many, with 7 meta-tools"
)]
struct Args {
    /// Path to config file (standard mcpServers format)
    #[arg(long, default_value = "./.mcp.json")]
    config: PathBuf,
    /// Append logs to this file instead of stderr
    #[arg(long)]
    log_file: Option<PathBuf>,
    /// Debug logging
    #[arg(short, long)]
    verbose: bool,
    /// Print JSON Schema for the config file and exit
    #[arg(long)]
    dump_schema: bool,
}

fn init_logging(verbose: bool, log_file: Option<&std::path::Path>) {
    let filter = tracing_subscriber::EnvFilter::try_from_default_env().unwrap_or_else(|_| {
        tracing_subscriber::EnvFilter::new(if verbose { "debug" } else { "info" })
    });
    let builder = tracing_subscriber::fmt()
        .with_env_filter(filter)
        .with_writer(std::io::stderr);
    if let Some(path) = log_file {
        let file = std::fs::OpenOptions::new()
            .create(true)
            .append(true)
            .open(path)
            .unwrap_or_else(|e| panic!("cannot open log file {}: {e}", path.display()));
        builder
            .with_writer(move || file.try_clone().expect("log file clone"))
            .init();
    } else {
        builder.init();
    }
}

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let args = Args::parse();
    init_logging(args.verbose, args.log_file.as_deref());
    if args.dump_schema {
        let schema = schemars::schema_for!(mcp_multiplexer::config::Config);
        println!("{}", serde_json::to_string_pretty(&schema)?);
        return Ok(());
    }
    tracing::info!(config = %args.config.display(), "starting");
    let (cfg, text) = mcp_multiplexer::config::Config::load(&args.config)?;
    let hash = mcp_multiplexer::cache::config_hash(&text);
    let cache = mcp_multiplexer::cache::Cache::load(hash);
    let ups = std::sync::Arc::new(mcp_multiplexer::upstream::Upstreams::new(
        cfg.clone(),
        cache,
        hash,
    ));
    for (name, sc) in &cfg.mcp_servers {
        if sc.expose {
            let ups = ups.clone();
            let name = name.clone();
            tokio::spawn(async move {
                if let Err(e) = ups.tools(&name).await {
                    tracing::warn!(server = %name, %e, "exposed server failed to connect");
                }
            });
        }
    }
    let agg = mcp_multiplexer::server::Aggregator::new(cfg, ups.clone());
    let svc = rmcp::serve_server(agg, rmcp::transport::stdio()).await?;
    svc.waiting().await?;
    ups.save_cache().await;
    Ok(())
}