dosh/tests/client_terminal_runtime.rs

use dosh::config::ClientConfig;
use dosh::protocol::{self, CLIENT_TO_SERVER, Frame, Input, PacketKind, Resize, SERVER_TO_CLIENT};
use portable_pty::{CommandBuilder, NativePtySystem, PtySize, PtySystem};
use serde::Serialize;
use std::fs;
use std::io::{Read, Write};
use std::net::UdpSocket;
use std::path::Path;
use std::sync::{Arc, Mutex, mpsc};
use std::thread;
use std::time::{Duration, Instant};

const SESSION: &str = "terminal-parity";
const CLIENT_ID: [u8; 16] = [0x45; 16];
const SESSION_KEY: [u8; 32] = [0x91; 32];
const INPUT_BYTES: &[u8] = concat!(
    "\x1b[A",
    "\x1b[B",
    "\x1b[200~",
    "paste-λ-界",
    "\x1b[201~",
    "\x1b[<0;12;7M",
    "\x1b[<0;12;7m"
)
.as_bytes();
const OUTPUT_CHUNKS: &[&[u8]] = &[
    b"\x1b[3;4H\x1b[38;2;12;200;90mDOSH_GRAPH_\xe2",
    b"\xa3\xbf\xe2\xa3",
    b"\xb7\xe2\xa3\xa4_\xce",
    b"\xbb_\xe7",
    b"\x95\x8c\x1b[0m",
];

#[derive(Serialize)]
struct CachedCredentialWire {
    server: String,
    session: String,
    mode: String,
    udp_host: String,
    udp_port: u16,
    client_id: [u8; 16],
    session_key: [u8; 32],
    session_key_id: [u8; 16],
    attach_ticket: Vec<u8>,
    attach_ticket_psk: [u8; 32],
    last_rendered_seq: u64,
}

#[derive(Debug)]
enum ServerObservation {
    BulkSent,
    Input(Vec<u8>),
    Reconnected,
    RenderResynced,
    Resize(u16, u16),
}

#[test]
fn native_client_terminal_round_trip_is_platform_complete() {
    let dir = tempfile::tempdir().unwrap();
    let home = dir.path().join("home");
    let cache = dir.path().join("credentials");
    fs::create_dir_all(home.join(".config/dosh")).unwrap();
    fs::create_dir_all(&cache).unwrap();

    let socket = UdpSocket::bind("127.0.0.1:0").unwrap();
    socket
        .set_read_timeout(Some(Duration::from_secs(8)))
        .unwrap();
    let port = socket.local_addr().unwrap().port();
    write_client_fixture(&home, &cache, port, 5);

    let (observation_tx, observation_rx) = mpsc::channel();
    let server = thread::spawn(move || run_fake_terminal_server(socket, observation_tx));

    let pty = NativePtySystem::default();
    let pair = pty
        .openpty(PtySize {
            rows: 24,
            cols: 80,
            pixel_width: 0,
            pixel_height: 0,
        })
        .unwrap();
    let mut reader = pair.master.try_clone_reader().unwrap();
    let mut writer = pair.master.take_writer().unwrap();
    let mut command = client_command(dir.path(), port);
    command.env("HOME", home.to_string_lossy().to_string());
    command.env("USERPROFILE", home.to_string_lossy().to_string());
    command.env("APPDATA", home.to_string_lossy().to_string());
    command.env("LOCALAPPDATA", home.to_string_lossy().to_string());
    command.env("TERM", "xterm-256color");
    command.env("COLORTERM", "truecolor");
    let mut child = pair.slave.spawn_command(command).unwrap();
    drop(pair.slave);

    let output = Arc::new(Mutex::new(Vec::new()));
    let reader_output = Arc::clone(&output);
    let reader_thread = thread::spawn(move || {
        let mut buf = [0u8; 4096];
        loop {
            match reader.read(&mut buf) {
                Ok(0) | Err(_) => break,
                Ok(n) => reader_output.lock().unwrap().extend_from_slice(&buf[..n]),
            }
        }
    });

    wait_for_output(&output, b"DOSH_PARITY_READY", Duration::from_secs(5));
    wait_for_output(
        &output,
        "DOSH_GRAPH_⣿⣷⣤_λ_界".as_bytes(),
        Duration::from_secs(5),
    );

    pair.master
        .resize(PtySize {
            rows: 31,
            cols: 100,
            pixel_width: 0,
            pixel_height: 0,
        })
        .unwrap();
    wait_for_resize(&observation_rx, (100, 31), Duration::from_secs(3));

    writer.write_all(INPUT_BYTES).unwrap();
    writer.flush().unwrap();
    wait_for_input(&observation_rx, INPUT_BYTES, Duration::from_secs(3));

    wait_for_output(&output, b"DOSH_PARITY_DONE", Duration::from_secs(5));
    let status = child.wait().unwrap();
    drop(writer);
    drop(pair.master);
    reader_thread.join().unwrap();
    server.join().unwrap();

    assert!(status.success(), "Dosh client exited with {status:?}");
    let output = output.lock().unwrap();
    assert!(
        contains(&output, b"\x1b[38;2;12;200;90m"),
        "true-color control sequence was not preserved: {output:?}"
    );
    assert!(
        contains(&output, b"\x1b[?1049h"),
        "alternate-screen mode was not preserved: {output:?}"
    );
    assert!(
        contains(&output, b"\x1b[?1006h"),
        "SGR mouse mode was not preserved: {output:?}"
    );
    assert!(
        contains(&output, b"\x1b[?25h"),
        "terminal cleanup did not restore the cursor: {output:?}"
    );
    #[cfg(windows)]
    {
        let code_page = fs::read(dir.path().join("restored-code-page.txt")).unwrap();
        assert!(
            contains(&code_page, b"437"),
            "Dosh did not restore the original Windows console code page: {code_page:?}"
        );
    }
}

#[test]
fn terminal_output_backpressure_does_not_block_input_transport() {
    const PROBE: &[u8] = b"DOSH_BACKPRESSURE_INPUT\r";

    let dir = tempfile::tempdir().unwrap();
    let home = dir.path().join("home");
    let cache = dir.path().join("credentials");
    fs::create_dir_all(home.join(".config/dosh")).unwrap();
    fs::create_dir_all(&cache).unwrap();

    let socket = UdpSocket::bind("127.0.0.1:0").unwrap();
    socket
        .set_read_timeout(Some(Duration::from_secs(8)))
        .unwrap();
    let port = socket.local_addr().unwrap().port();
    write_client_fixture(&home, &cache, port, 5);
    let (observation_tx, observation_rx) = mpsc::channel();
    let server = thread::spawn(move || run_backpressure_server(socket, observation_tx, PROBE));

    let pty = NativePtySystem::default();
    let pair = pty
        .openpty(PtySize {
            rows: 24,
            cols: 80,
            pixel_width: 0,
            pixel_height: 0,
        })
        .unwrap();
    let mut reader = pair.master.try_clone_reader().unwrap();
    let mut writer = pair.master.take_writer().unwrap();
    let mut command = client_command(dir.path(), port);
    command.env("HOME", home.to_string_lossy().to_string());
    command.env("USERPROFILE", home.to_string_lossy().to_string());
    command.env("APPDATA", home.to_string_lossy().to_string());
    command.env("LOCALAPPDATA", home.to_string_lossy().to_string());
    command.env("TERM", "xterm-256color");
    let mut child = pair.slave.spawn_command(command).unwrap();
    drop(pair.slave);

    wait_for_observation(&observation_rx, Duration::from_secs(5), |observation| {
        matches!(observation, ServerObservation::BulkSent)
    });
    thread::sleep(Duration::from_millis(100));
    writer.write_all(PROBE).unwrap();
    writer.flush().unwrap();
    wait_for_input(&observation_rx, PROBE, Duration::from_secs(2));

    let reader_thread = thread::spawn(move || {
        let mut buf = [0u8; 16 * 1024];
        while let Ok(n) = reader.read(&mut buf) {
            if n == 0 {
                break;
            }
        }
    });
    let status = child.wait().unwrap();
    drop(writer);
    drop(pair.master);
    reader_thread.join().unwrap();
    server.join().unwrap();

    assert!(status.success(), "Dosh client exited with {status:?}");
}

#[test]
fn idle_reconnect_restores_snapshot_and_orders_reordered_frames() {
    const PROBE: &[u8] = b"DOSH_RECONNECT_INPUT\r";

    let dir = tempfile::tempdir().unwrap();
    let home = dir.path().join("home");
    let cache = dir.path().join("credentials");
    fs::create_dir_all(home.join(".config/dosh")).unwrap();
    fs::create_dir_all(&cache).unwrap();

    let socket = UdpSocket::bind("127.0.0.1:0").unwrap();
    socket
        .set_read_timeout(Some(Duration::from_secs(8)))
        .unwrap();
    let port = socket.local_addr().unwrap().port();
    write_client_fixture(&home, &cache, port, 1);
    let (observation_tx, observation_rx) = mpsc::channel();
    let server = thread::spawn(move || run_reconnect_server(socket, observation_tx, PROBE));

    let pty = NativePtySystem::default();
    let pair = pty
        .openpty(PtySize {
            rows: 24,
            cols: 80,
            pixel_width: 0,
            pixel_height: 0,
        })
        .unwrap();
    let mut reader = pair.master.try_clone_reader().unwrap();
    let mut writer = pair.master.take_writer().unwrap();
    let mut command = client_command(dir.path(), port);
    command.env("HOME", home.to_string_lossy().to_string());
    command.env("USERPROFILE", home.to_string_lossy().to_string());
    command.env("APPDATA", home.to_string_lossy().to_string());
    command.env("LOCALAPPDATA", home.to_string_lossy().to_string());
    command.env("TERM", "xterm-256color");
    let mut child = pair.slave.spawn_command(command).unwrap();
    drop(pair.slave);

    let output = Arc::new(Mutex::new(Vec::new()));
    let reader_output = Arc::clone(&output);
    let reader_thread = thread::spawn(move || {
        let mut buf = [0u8; 4096];
        loop {
            match reader.read(&mut buf) {
                Ok(0) | Err(_) => break,
                Ok(n) => reader_output.lock().unwrap().extend_from_slice(&buf[..n]),
            }
        }
    });

    wait_for_output(&output, b"DOSH_RECONNECT_READY", Duration::from_secs(3));
    wait_for_observation(&observation_rx, Duration::from_secs(4), |observation| {
        matches!(observation, ServerObservation::Reconnected)
    });
    wait_for_output(&output, b"DOSH_RECONNECT_SNAPSHOT", Duration::from_secs(3));

    writer.write_all(PROBE).unwrap();
    writer.flush().unwrap();
    wait_for_input(&observation_rx, PROBE, Duration::from_secs(2));
    wait_for_output(
        &output,
        b"DOSH_ORDER_FIRST_DOSH_ORDER_SECOND_DOSH_RECONNECT_DONE",
        Duration::from_secs(3),
    );

    let status = child.wait().unwrap();
    drop(writer);
    drop(pair.master);
    reader_thread.join().unwrap();
    server.join().unwrap();
    assert!(status.success(), "Dosh client exited with {status:?}");
}

#[test]
fn renderer_overflow_resyncs_without_dropping_the_session() {
    const PROBE: &[u8] = b"DOSH_OVERFLOW_INPUT\r";

    let dir = tempfile::tempdir().unwrap();
    let home = dir.path().join("home");
    let cache = dir.path().join("credentials");
    fs::create_dir_all(home.join(".config/dosh")).unwrap();
    fs::create_dir_all(&cache).unwrap();

    let socket = UdpSocket::bind("127.0.0.1:0").unwrap();
    socket
        .set_read_timeout(Some(Duration::from_secs(12)))
        .unwrap();
    let port = socket.local_addr().unwrap().port();
    write_client_fixture(&home, &cache, port, 30);
    let (observation_tx, observation_rx) = mpsc::channel();
    let server = thread::spawn(move || run_overflow_server(socket, observation_tx, PROBE));

    let pty = NativePtySystem::default();
    let pair = pty
        .openpty(PtySize {
            rows: 24,
            cols: 80,
            pixel_width: 0,
            pixel_height: 0,
        })
        .unwrap();
    let mut reader = pair.master.try_clone_reader().unwrap();
    let mut writer = pair.master.take_writer().unwrap();
    let mut command = client_command(dir.path(), port);
    command.env("HOME", home.to_string_lossy().to_string());
    command.env("USERPROFILE", home.to_string_lossy().to_string());
    command.env("APPDATA", home.to_string_lossy().to_string());
    command.env("LOCALAPPDATA", home.to_string_lossy().to_string());
    command.env("TERM", "xterm-256color");
    let mut child = pair.slave.spawn_command(command).unwrap();
    drop(pair.slave);

    wait_for_observation(&observation_rx, Duration::from_secs(5), |observation| {
        matches!(observation, ServerObservation::BulkSent)
    });
    writer.write_all(PROBE).unwrap();
    writer.flush().unwrap();
    wait_for_input(&observation_rx, PROBE, Duration::from_secs(2));

    let output = Arc::new(Mutex::new(Vec::new()));
    let reader_output = Arc::clone(&output);
    let reader_thread = thread::spawn(move || {
        let mut buf = [0u8; 16 * 1024];
        loop {
            match reader.read(&mut buf) {
                Ok(0) | Err(_) => break,
                Ok(n) => reader_output.lock().unwrap().extend_from_slice(&buf[..n]),
            }
        }
    });
    wait_for_observation(&observation_rx, Duration::from_secs(5), |observation| {
        matches!(observation, ServerObservation::RenderResynced)
    });
    wait_for_output(
        &output,
        b"DOSH_OVERFLOW_RESYNC_DOSH_OVERFLOW_DONE",
        Duration::from_secs(5),
    );

    let status = child.wait().unwrap();
    drop(writer);
    drop(pair.master);
    reader_thread.join().unwrap();
    server.join().unwrap();
    assert!(status.success(), "Dosh client exited with {status:?}");
}

fn write_client_fixture(home: &Path, cache: &Path, port: u16, reconnect_timeout_secs: u64) {
    let config = ClientConfig {
        server: "local".to_string(),
        dosh_host: Some("127.0.0.1".to_string()),
        dosh_port: port,
        cache_attach_tickets: false,
        reconnect_timeout_secs,
        credential_cache: cache.to_string_lossy().to_string(),
        auth_preference: "ssh".to_string(),
        predict: false,
        predict_mode: "off".to_string(),
        disconnect_status: false,
        ..ClientConfig::default()
    };
    fs::write(
        home.join(".config/dosh/client.toml"),
        toml::to_string(&config).unwrap(),
    )
    .unwrap();

    let credential = CachedCredentialWire {
        server: "local".to_string(),
        session: SESSION.to_string(),
        mode: "read-write".to_string(),
        udp_host: "127.0.0.1".to_string(),
        udp_port: port,
        client_id: CLIENT_ID,
        session_key: SESSION_KEY,
        session_key_id: protocol::session_key_id(&SESSION_KEY),
        attach_ticket: Vec::new(),
        attach_ticket_psk: [0x33; 32],
        last_rendered_seq: 9,
    };
    fs::write(
        cache.join("local_terminal_parity_read_write.bin"),
        bincode::serialize(&credential).unwrap(),
    )
    .unwrap();
}

fn client_command(_dir: &Path, port: u16) -> CommandBuilder {
    let client = env!("CARGO_BIN_EXE_dosh-client");
    let args = [
        "--local-auth",
        "--predict-never",
        "--session",
        SESSION,
        "--dosh-host",
        "127.0.0.1",
        "--dosh-port",
        &port.to_string(),
        "local",
    ];

    #[cfg(windows)]
    {
        let script = _dir.join("run-client.cmd");
        let quoted_args = args
            .iter()
            .map(|arg| format!("\"{}\"", arg.replace('"', "\"\"")))
            .collect::<Vec<_>>()
            .join(" ");
        fs::write(
            &script,
            format!(
                "@echo off\r\nchcp 437 >nul\r\n\"{}\" {quoted_args}\r\nchcp > \"{}\"\r\n",
                client.replace('"', "\"\""),
                _dir.join("restored-code-page.txt").display()
            ),
        )
        .unwrap();
        let mut command = CommandBuilder::new("cmd.exe");
        command.args(["/d", "/c", &script.to_string_lossy()]);
        command
    }

    #[cfg(not(windows))]
    {
        let mut command = CommandBuilder::new(client);
        command.args(args);
        command
    }
}

fn run_fake_terminal_server(socket: UdpSocket, observations: mpsc::Sender<ServerObservation>) {
    let mut peer = None;
    let mut next_output_chunk = 0usize;
    let mut received_input = Vec::new();
    let mut buf = [0u8; 65535];
    loop {
        let (n, source) = socket.recv_from(&mut buf).unwrap();
        let packet = protocol::decode(&buf[..n]).unwrap();
        match packet.header.kind {
            PacketKind::ResumeRequest => {
                let plain =
                    protocol::decrypt_body(&packet, &SESSION_KEY, CLIENT_TO_SERVER).unwrap();
                let request: protocol::ResumeRequest = protocol::from_body(&plain).unwrap();
                assert_eq!(request.session, SESSION);
                peer = Some(source);
                send_frame(
                    &socket,
                    source,
                    PacketKind::ResumeOk,
                    1,
                    10,
                    concat!(
                        "\x1b[?1049h",
                        "\x1b[?1003h",
                        "\x1b[?1006h",
                        "\x1b[?2004h",
                        "\x1b[2J\x1b[H",
                        "DOSH_PARITY_READY"
                    )
                    .as_bytes(),
                    true,
                    false,
                );
            }
            PacketKind::Ack if next_output_chunk < OUTPUT_CHUNKS.len() => {
                let source = peer.unwrap_or(source);
                send_frame(
                    &socket,
                    source,
                    PacketKind::Frame,
                    2 + next_output_chunk as u64,
                    11 + next_output_chunk as u64,
                    OUTPUT_CHUNKS[next_output_chunk],
                    false,
                    false,
                );
                next_output_chunk += 1;
            }
            PacketKind::Input => {
                let plain =
                    protocol::decrypt_body(&packet, &SESSION_KEY, CLIENT_TO_SERVER).unwrap();
                let input: Input = protocol::from_body(&plain).unwrap();
                received_input.extend_from_slice(&input.bytes);
                observations
                    .send(ServerObservation::Input(input.bytes))
                    .unwrap();
                if contains(&received_input, INPUT_BYTES) {
                    send_frame(
                        &socket,
                        peer.unwrap_or(source),
                        PacketKind::Frame,
                        20,
                        16,
                        b"\x1b[?1003l\x1b[?1006l\x1b[?1049lDOSH_PARITY_DONE",
                        false,
                        true,
                    );
                }
            }
            PacketKind::Resize => {
                let plain =
                    protocol::decrypt_body(&packet, &SESSION_KEY, CLIENT_TO_SERVER).unwrap();
                let resize: Resize = protocol::from_body(&plain).unwrap();
                observations
                    .send(ServerObservation::Resize(resize.cols, resize.rows))
                    .unwrap();
            }
            PacketKind::Ping => {
                let pong = protocol::encode_encrypted(
                    PacketKind::Pong,
                    CLIENT_ID,
                    4,
                    11,
                    &SESSION_KEY,
                    SERVER_TO_CLIENT,
                    b"",
                )
                .unwrap();
                socket.send_to(&pong, source).unwrap();
            }
            PacketKind::Detach => break,
            _ => {}
        }
        if received_input
            .windows(INPUT_BYTES.len())
            .any(|bytes| bytes == INPUT_BYTES)
        {
            break;
        }
    }
}

fn run_backpressure_server(
    socket: UdpSocket,
    observations: mpsc::Sender<ServerObservation>,
    expected_input: &[u8],
) {
    let mut peer = None;
    let mut bulk_sent = false;
    let mut received_input = Vec::new();
    let mut buf = [0u8; 65535];
    loop {
        let (n, source) = socket.recv_from(&mut buf).unwrap();
        let packet = protocol::decode(&buf[..n]).unwrap();
        match packet.header.kind {
            PacketKind::ResumeRequest => {
                peer = Some(source);
                send_frame(
                    &socket,
                    source,
                    PacketKind::ResumeOk,
                    1,
                    10,
                    b"DOSH_BACKPRESSURE_READY",
                    true,
                    false,
                );
            }
            PacketKind::Ack if !bulk_sent => {
                let bulk = [b'x'; 1024];
                for index in 0..64u64 {
                    send_frame(
                        &socket,
                        peer.unwrap_or(source),
                        PacketKind::Frame,
                        2 + index,
                        11 + index,
                        &bulk,
                        false,
                        false,
                    );
                }
                send_frame(
                    &socket,
                    peer.unwrap_or(source),
                    PacketKind::Frame,
                    66,
                    75,
                    b"DOSH_BACKPRESSURE_DONE",
                    false,
                    true,
                );
                bulk_sent = true;
                observations.send(ServerObservation::BulkSent).unwrap();
            }
            PacketKind::Input => {
                let plain =
                    protocol::decrypt_body(&packet, &SESSION_KEY, CLIENT_TO_SERVER).unwrap();
                let input: Input = protocol::from_body(&plain).unwrap();
                received_input.extend_from_slice(&input.bytes);
                observations
                    .send(ServerObservation::Input(input.bytes))
                    .unwrap();
                if contains(&received_input, expected_input) {
                    break;
                }
            }
            _ => {}
        }
    }
}

fn run_reconnect_server(
    socket: UdpSocket,
    observations: mpsc::Sender<ServerObservation>,
    expected_input: &[u8],
) {
    let mut resume_count = 0u64;
    let mut received_input = Vec::new();
    let mut buf = [0u8; 65535];
    loop {
        let (n, source) = socket.recv_from(&mut buf).unwrap();
        let packet = protocol::decode(&buf[..n]).unwrap();
        match packet.header.kind {
            PacketKind::ResumeRequest => {
                let plain =
                    protocol::decrypt_body(&packet, &SESSION_KEY, CLIENT_TO_SERVER).unwrap();
                let request: protocol::ResumeRequest = protocol::from_body(&plain).unwrap();
                assert_eq!(request.session, SESSION);
                resume_count += 1;
                let bytes = if resume_count == 1 {
                    b"DOSH_RECONNECT_READY".as_slice()
                } else {
                    observations.send(ServerObservation::Reconnected).unwrap();
                    b"DOSH_RECONNECT_SNAPSHOT".as_slice()
                };
                send_frame(
                    &socket,
                    source,
                    PacketKind::ResumeOk,
                    resume_count,
                    10,
                    bytes,
                    true,
                    false,
                );
            }
            PacketKind::Input => {
                let plain =
                    protocol::decrypt_body(&packet, &SESSION_KEY, CLIENT_TO_SERVER).unwrap();
                let input: Input = protocol::from_body(&plain).unwrap();
                received_input.extend_from_slice(&input.bytes);
                observations
                    .send(ServerObservation::Input(input.bytes))
                    .unwrap();
                if contains(&received_input, expected_input) {
                    send_frame(
                        &socket,
                        source,
                        PacketKind::Frame,
                        4,
                        12,
                        b"DOSH_ORDER_SECOND_",
                        false,
                        false,
                    );
                    send_frame(
                        &socket,
                        source,
                        PacketKind::Frame,
                        3,
                        11,
                        b"DOSH_ORDER_FIRST_",
                        false,
                        false,
                    );
                    send_frame(
                        &socket,
                        source,
                        PacketKind::Frame,
                        5,
                        13,
                        b"DOSH_RECONNECT_DONE",
                        false,
                        true,
                    );
                    break;
                }
            }
            PacketKind::Ping | PacketKind::Ack => {}
            _ => {}
        }
    }
}

fn run_overflow_server(
    socket: UdpSocket,
    observations: mpsc::Sender<ServerObservation>,
    expected_input: &[u8],
) {
    const BULK_FRAMES: u64 = 640;

    let mut resume_count = 0u64;
    let mut bulk_sent = false;
    let mut resynced = false;
    let mut closed_sent = false;
    let mut received_input = Vec::new();
    let mut buf = [0u8; 65535];
    loop {
        let (n, source) = socket.recv_from(&mut buf).unwrap();
        let packet = protocol::decode(&buf[..n]).unwrap();
        match packet.header.kind {
            PacketKind::ResumeRequest => {
                resume_count += 1;
                if resume_count == 1 {
                    send_frame(
                        &socket,
                        source,
                        PacketKind::ResumeOk,
                        1,
                        10,
                        b"DOSH_OVERFLOW_READY",
                        true,
                        false,
                    );
                } else {
                    send_frame(
                        &socket,
                        source,
                        PacketKind::ResumeOk,
                        700,
                        700,
                        b"DOSH_OVERFLOW_RESYNC_",
                        true,
                        false,
                    );
                    resynced = true;
                    observations
                        .send(ServerObservation::RenderResynced)
                        .unwrap();
                }
            }
            PacketKind::Ack if !bulk_sent => {
                let bulk = [b'x'; 1024];
                for index in 0..BULK_FRAMES {
                    send_frame(
                        &socket,
                        source,
                        PacketKind::Frame,
                        2 + index,
                        11 + index,
                        &bulk,
                        false,
                        false,
                    );
                    thread::sleep(Duration::from_millis(1));
                }
                bulk_sent = true;
                observations.send(ServerObservation::BulkSent).unwrap();
            }
            PacketKind::Ack if resynced && !closed_sent => {
                send_frame(
                    &socket,
                    source,
                    PacketKind::Frame,
                    701,
                    701,
                    b"DOSH_OVERFLOW_DONE",
                    false,
                    true,
                );
                closed_sent = true;
            }
            PacketKind::Input => {
                let plain =
                    protocol::decrypt_body(&packet, &SESSION_KEY, CLIENT_TO_SERVER).unwrap();
                let input: Input = protocol::from_body(&plain).unwrap();
                received_input.extend_from_slice(&input.bytes);
                observations
                    .send(ServerObservation::Input(input.bytes))
                    .unwrap();
            }
            _ => {}
        }
        if closed_sent && contains(&received_input, expected_input) {
            break;
        }
    }
}

#[allow(clippy::too_many_arguments)]
fn send_frame(
    socket: &UdpSocket,
    peer: std::net::SocketAddr,
    kind: PacketKind,
    packet_seq: u64,
    output_seq: u64,
    bytes: &[u8],
    snapshot: bool,
    closed: bool,
) {
    let frame = Frame {
        session: SESSION.to_string(),
        output_seq,
        bytes: bytes.to_vec(),
        snapshot,
        closed,
    };
    let body = protocol::to_body(&frame).unwrap();
    let packet = protocol::encode_encrypted(
        kind,
        CLIENT_ID,
        packet_seq,
        output_seq.saturating_sub(1),
        &SESSION_KEY,
        SERVER_TO_CLIENT,
        &body,
    )
    .unwrap();
    socket.send_to(&packet, peer).unwrap();
}

fn wait_for_output(output: &Arc<Mutex<Vec<u8>>>, needle: &[u8], timeout: Duration) {
    let deadline = Instant::now() + timeout;
    while Instant::now() < deadline {
        if contains(&output.lock().unwrap(), needle) {
            return;
        }
        thread::sleep(Duration::from_millis(10));
    }
    panic!(
        "terminal output did not contain {:?}: {:?}",
        String::from_utf8_lossy(needle),
        output.lock().unwrap()
    );
}

fn wait_for_resize(
    observations: &mpsc::Receiver<ServerObservation>,
    expected: (u16, u16),
    timeout: Duration,
) {
    let deadline = Instant::now() + timeout;
    while let Some(remaining) = deadline.checked_duration_since(Instant::now()) {
        match observations.recv_timeout(remaining) {
            Ok(ServerObservation::Resize(cols, rows)) if (cols, rows) == expected => return,
            Ok(_) => {}
            Err(err) => panic!("terminal resize {expected:?} was not delivered: {err}"),
        }
    }
    panic!("terminal resize {expected:?} was not delivered");
}

fn wait_for_input(
    observations: &mpsc::Receiver<ServerObservation>,
    expected: &[u8],
    timeout: Duration,
) {
    let deadline = Instant::now() + timeout;
    let mut input = Vec::new();
    while let Some(remaining) = deadline.checked_duration_since(Instant::now()) {
        match observations.recv_timeout(remaining) {
            Ok(ServerObservation::Input(bytes)) => {
                input.extend_from_slice(&bytes);
                if contains(&input, expected) {
                    return;
                }
            }
            Ok(_) => {}
            Err(err) => panic!("terminal input was not delivered: {err}; got {input:?}"),
        }
    }
    panic!("terminal input was not delivered; got {input:?}");
}

fn wait_for_observation(
    observations: &mpsc::Receiver<ServerObservation>,
    timeout: Duration,
    matches: impl Fn(&ServerObservation) -> bool,
) {
    let deadline = Instant::now() + timeout;
    while let Some(remaining) = deadline.checked_duration_since(Instant::now()) {
        match observations.recv_timeout(remaining) {
            Ok(observation) if matches(&observation) => return,
            Ok(_) => {}
            Err(err) => panic!("expected server observation was not received: {err}"),
        }
    }
    panic!("expected server observation was not received");
}

fn contains(haystack: &[u8], needle: &[u8]) -> bool {
    !needle.is_empty() && haystack.windows(needle.len()).any(|bytes| bytes == needle)
}