ai-app/server/src/main.rs

//! A phone interface to AI coding sessions -- the backend. See PLAN.md for
//! the whole picture; this is the entry point: config + session registry,
//! token bootstrap, and the one TLS listener.
//!
//! The listener binds the WireGuard interface's address only, and fails
//! closed -- if `wg0` is down the server refuses to start rather than
//! falling back to `0.0.0.0`, because this API *is* remote code execution
//! and the tunnel is what keeps its pre-auth surface (TLS handshake, HTTP
//! parsing, auth middleware) off the open internet. `--bind` overrides
//! explicitly for development; that is a deliberate, logged choice, never a
//! fallback.
//!
//! There is no plaintext listener at all, so the bearer token can't travel
//! unencrypted by misconfiguration -- even inside the tunnel.

mod auth;
mod config;
mod routes;
mod session;

use std::net::{IpAddr, SocketAddr};
use std::path::{Path, PathBuf};
use std::sync::Arc;

use anyhow::{Context, Result, bail};
use clap::Parser;

use config::TokenEntry;
use session::SessionManager;

const DEFAULT_PORT: u16 = 8443;
const WG_INTERFACE: &str = "wg0";

/// The repo root, one level above this crate. Everything the server reads
/// by default -- the TLS cert, the config, the session data -- resolves
/// from here, so there's one definition of it rather than one per caller.
fn repo_root() -> &'static Path {
    static ROOT: std::sync::OnceLock<PathBuf> = std::sync::OnceLock::new();
    ROOT.get_or_init(|| {
        Path::new(env!("CARGO_MANIFEST_DIR"))
            .parent()
            .expect("CARGO_MANIFEST_DIR has a repo-root parent")
            .to_path_buf()
    })
}

/// Serves AI coding sessions (Claude Code, llama.cpp) to the phone app.
#[derive(Parser)]
struct Args {
    /// TLS port for the whole API surface.
    #[arg(long, default_value_t = DEFAULT_PORT)]
    port: u16,

    /// Address to bind instead of the wg0 interface's -- a development
    /// override (e.g. 127.0.0.1 for curl, or a LAN address for a phone
    /// before the tunnel exists). Production runs without it and fails
    /// closed when wg0 is absent.
    #[arg(long)]
    bind: Option<IpAddr>,

    /// Where the token hashes and session list live. Defaults to
    /// `config.json` beside this repo's `certs/`.
    #[arg(long)]
    config: Option<PathBuf>,

    /// Directory for per-session data (transcripts, attachments, images).
    /// Defaults to `sessions/` in the repo root.
    #[arg(long)]
    data_dir: Option<PathBuf>,

    /// Directory holding `leaf.pem`/`leaf-key.pem`. Defaults to this
    /// repo's `certs/`, as produced by `gen-dev-cert.sh`.
    #[arg(long)]
    certs: Option<PathBuf>,

    /// Invalidate every enrolled token, generate a fresh one, and print
    /// its enrollment QR -- the whole lost-phone story.
    #[arg(long)]
    rotate_token: bool,
}

/// The IPv4 address on the WireGuard interface, or a refusal to start.
/// Failing closed here (rather than falling back to a wider bind) is part
/// of the security posture -- see the module doc comment.
fn wg_address() -> Result<IpAddr> {
    let interfaces = if_addrs::get_if_addrs().context("enumerate network interfaces")?;
    interfaces
        .into_iter()
        .find(|iface| iface.name == WG_INTERFACE && iface.ip().is_ipv4())
        .map(|iface| iface.ip())
        .ok_or_else(|| {
            anyhow::anyhow!(
                "no IPv4 address on interface {WG_INTERFACE} -- this server binds only to the \
                 WireGuard tunnel and refuses to fall back to a wider address. Bring the tunnel \
                 up, or pass --bind <ip> explicitly for development."
            )
        })
}

/// Prints the one-time enrollment QR: an `aiapp://enroll` URI carrying
/// where to connect and the bearer token. The CA stays embedded in the APK,
/// so this carries no trust material -- photographing the terminal leaks
/// only the token, which is rotatable (`--rotate-token`). Printed to
/// stdout, not the log: it is for the human at the terminal, once.
fn print_enrollment(host: IpAddr, port: u16, token: &str) -> Result<()> {
    let uri = format!("aiapp://enroll?host={host}&port={port}&token={token}");
    let code = qrcode::QrCode::new(uri.as_bytes()).context("render enrollment QR")?;
    let rendered = code
        .render::<qrcode::render::unicode::Dense1x2>()
        .quiet_zone(true)
        .build();
    println!("\n{rendered}\n");
    println!("Scan with the phone's camera to enroll (or paste into the app's settings):");
    println!("  {uri}");
    println!("The token is not stored in the clear and won't be shown again;");
    println!("a lost phone means `--rotate-token`.\n");
    Ok(())
}

#[tokio::main]
async fn main() -> Result<()> {
    tracing_subscriber::fmt().with_env_filter("info").init();
    let args = Args::parse();

    let config_path = args.config.unwrap_or_else(|| repo_root().join("config.json"));
    let data_dir = args.data_dir.unwrap_or_else(|| repo_root().join("sessions"));
    let manager = Arc::new(
        SessionManager::new(config_path.clone(), data_dir)
            .with_context(|| format!("failed to load {}", config_path.display()))?,
    );
    tracing::info!("config: {}", config_path.display());
    for info in manager.sessions() {
        tracing::info!("  session {} ({:?}, {:?})", info.id, info.kind, info.status);
    }

    let bind_ip = match args.bind {
        Some(ip) => {
            tracing::warn!(
                "binding {ip} by explicit --bind override -- production binds {WG_INTERFACE} only"
            );
            ip
        }
        None => wg_address()?,
    };

    // Token bootstrap: first run generates one; --rotate-token replaces
    // whatever exists. Either way the plaintext appears exactly once, in
    // the QR printed here.
    if args.rotate_token || manager.tokens().is_empty() {
        let rotating = args.rotate_token && !manager.tokens().is_empty();
        let token = auth::generate_token();
        manager.set_tokens(vec![TokenEntry {
            name: "phone".to_string(),
            sha256: auth::token_hash_hex(&token),
        }])?;
        if rotating {
            tracing::info!("rotated the enrolled token; the previous one is now invalid");
        }
        print_enrollment(bind_ip, args.port, &token)?;
    }

    let certs_dir = args.certs.unwrap_or_else(|| repo_root().join("certs"));
    let leaf_cert = certs_dir.join("leaf.pem");
    let leaf_key = certs_dir.join("leaf-key.pem");
    if !leaf_cert.is_file() || !leaf_key.is_file() {
        bail!(
            "missing {} / {} -- run ./gen-dev-cert.sh first (the app pins the CA it generates, \
             and this server refuses to serve without TLS)",
            leaf_cert.display(),
            leaf_key.display(),
        );
    }
    let tls_config = axum_server::tls_rustls::RustlsConfig::from_pem_file(&leaf_cert, &leaf_key)
        .await
        .context("failed to load TLS cert/key")?;

    // The bearer-token middleware wraps the entire router -- routes and
    // fallback alike -- here and only here, so a new route can't forget
    // auth. Zero unauthenticated endpoints.
    let app = routes::router(Arc::clone(&manager)).layer(axum::middleware::from_fn_with_state(
        Arc::clone(&manager),
        auth::require_token,
    ));

    let addr = SocketAddr::new(bind_ip, args.port);
    tracing::info!("serving https://{addr}");
    axum_server::bind_rustls(addr, tls_config)
        .serve(app.into_make_service_with_connect_info::<SocketAddr>())
        .await
        .context("TLS listener failed")?;

    Ok(())
}