cleanup

depell/src/main.rs

@@ -1,11 +1,11 @@
-#![feature(array_windows)]
+#![feature(array_chunks)]
 #![feature(write_all_vectored)]
 use {
     aes_gcm::{
         aead::{self, AeadMutInPlace},
         AeadCore, Aes256Gcm, KeyInit,
     },
-    ed25519_dalek::ed25519::signature::Signer,
+    ed25519_dalek::{self as ed, ed25519::signature::Signer},
     rand_core::OsRng,
     std::{
         collections::{HashMap, HashSet},
@@ -16,88 +16,51 @@ use {
         path::PathBuf,
         slice,
         str::FromStr,
-        sync::{atomic, OnceLock},
+        sync::{
+            atomic::{self, AtomicUsize},
+            Arc, Mutex,
+        },
         time,
     },
-    x25519_dalek::{EphemeralSecret, SharedSecret},
+    x25519_dalek::{self as x, EphemeralSecret, SharedSecret},
 };
 
-static CONN_COUNT: atomic::AtomicUsize = atomic::AtomicUsize::new(0);
+type Subcommand<'a, T> = (&'a str, &'a str, T);
-static USER_DATA_DIR: OnceLock<PathBuf> = OnceLock::new();
+type BaseSubcommand<'a> = Subcommand<'a, fn(&Cli) -> io::Result<()>>;
-static SERVER_SECRET: OnceLock<ed25519_dalek::SigningKey> = OnceLock::new();
+type ConsumeSubcommand<'a> = Subcommand<'a, fn(&Cli, EncriptedStream) -> io::Result<()>>;
 
-#[derive(Default)]
+type Username = [u8; 32];
-struct Cli {
+type Postname = [u8; 64];
-    program: String,
+type Pk = [u8; 32];
-    args: Vec<String>,
+type Nonce = u64;
-    flags: HashSet<String>,
-    options: HashMap<String, String>,
-}
 
-impl Cli {
+const SUBCOMMANDS: &[BaseSubcommand] = &[
-    pub fn parse() -> Self {
-        let mut s = Self::default();
-        let mut args = std::env::args();
-        s.program = args.next().unwrap();
-
-        for arg in args {
-            if let Some(arg) = arg.strip_prefix("--") {
-                match arg.split_once('=') {
-                    Some((name, value)) => _ = s.options.insert(name.to_owned(), value.to_owned()),
-                    None => _ = s.flags.insert(arg.to_string()),
-                }
-            } else {
-                s.args.push(arg);
-            }
-        }
-
-        s
-    }
-
-    pub fn arg(&self, index: usize) -> &str {
-        self.args.get(index).map_or("", String::as_str)
-    }
-
-    pub fn expect_option(&self, name: &str) -> &str {
-        self.options.get(name).unwrap_or_else(|| panic!("--{name} is mandatory"))
-    }
-
-    pub fn expect_poption<T: FromStr<Err: fmt::Display>>(&self, name: &str) -> T {
-        self.expect_option(name).parse::<T>().unwrap_or_else(|e| {
-            panic!("failed to parse --{name} as {}: {e}", std::any::type_name::<T>())
-        })
-    }
-}
-
-type Subcommand<'a> = (&'a str, &'a str, fn(&Cli) -> io::Result<()>);
-
-fn help<T>(subs: &[(&str, &str, T)]) -> io::Result<()> {
-    for (name, desc, _) in subs {
-        eprintln!("{name} - {desc}");
-    }
-    Err(io::ErrorKind::NotFound.into())
-}
-
-const SUBCOMMANDS: &[Subcommand] = &[
     ("help", "print command descriptions", |_| help(SUBCOMMANDS)),
     ("serve", "run the server", |cli| {
         let port = cli.expect_poption::<u16>("port");
-        let max_conns = cli.expect_poption::<usize>("max-conns");
+
-        USER_DATA_DIR.set(cli.expect_poption("user-data-path")).unwrap();
+        let config = Arc::new(ServerState {
-        SERVER_SECRET.set(cli.expect_poption::<HexSk>("secret").0).unwrap();
+            user_data_dir: cli.expect_poption("user-data-path"),
+            secret: cli.expect_poption::<HexSk>("secret").0,
+            active_ips: Default::default(),
+            max_conns: cli.expect_poption::<usize>("max-conns"),
+            conn_count: Default::default(),
+        });
         let listener = TcpListener::bind((Ipv4Addr::UNSPECIFIED, port)).unwrap();
         for incoming in listener.incoming() {
             match incoming {
                 Ok(c) => {
-                    if CONN_COUNT.fetch_add(1, atomic::Ordering::Relaxed) >= max_conns {
+                    let Ok(std::net::SocketAddr::V4(addr)) =
-                        CONN_COUNT.fetch_sub(1, atomic::Ordering::Relaxed);
+                        c.peer_addr().ctx("obtaining socket addr")
+                    else {
                         continue;
-                    }
+                    };
 
-                    std::thread::spawn(move || {
+                    let Some(guard) = ConnectionGuard::new(config.clone(), *addr.ip()) else {
-                        _ = handle_client(c);
+                        continue;
-                        CONN_COUNT.fetch_sub(1, atomic::Ordering::Relaxed);
+                    };
-                    });
+
+                    std::thread::spawn(move || _ = guard.config.handle_client(c));
                 }
                 Err(e) => {
                     eprintln!("accepting conn conn: {e}")
@@ -106,13 +69,24 @@ const SUBCOMMANDS: &[Subcommand] = &[
         }
         Ok(())
     }),
+    ("make-secret", "creates secret usable by the server", |_| {
+        println!("{}", DisplayHex(ed::SigningKey::generate(&mut OsRng).to_bytes()));
+        Ok(())
+    }),
+    ("make-ping-command", "create a ping command to handshake with the server", |cli| {
+        let HexSk(secret) = cli.expect_poption::<HexSk>("secret");
+        let addr = cli.expect_poption::<SocketAddrV4>("addr");
+        let id = DisplayHex(ed::VerifyingKey::from(&secret).to_bytes());
+        println!("depell consume --server-identity={id} --addr={addr} ping");
+        Ok(())
+    }),
     ("make-profile", "create profile file (private key + name)", |cli| {
         let name = cli.expect_option("name");
         let name = str_as_username(name)
             .ok_or(io::ErrorKind::InvalidData)
             .ctx("name is limmited to 32 characters")?;
 
-        let &key = ed25519_dalek::SigningKey::generate(&mut rand_core::OsRng).as_bytes();
+        let &key = ed::SigningKey::generate(&mut rand_core::OsRng).as_bytes();
         let profile = UserProfile { name, key };
 
         let out_file = cli.expect_option("out-file");
@@ -123,7 +97,7 @@ const SUBCOMMANDS: &[Subcommand] = &[
         let profile_path = cli.expect_option("profile");
         let mut profile_file = fs::File::open(profile_path).ctx("opening profile file")?;
         let profile: UserProfile = read_struct(&mut profile_file).ctx("reading the profile")?;
-        let sx = x25519_dalek::EphemeralSecret::random_from_rng(OsRng);
+        let sx = x::EphemeralSecret::random_from_rng(OsRng);
         let auth = UserAuth::sign(profile, &sx);
 
         let addr = cli.expect_poption::<SocketAddrV4>("addr");
@@ -133,7 +107,7 @@ const SUBCOMMANDS: &[Subcommand] = &[
         let HexPk(server_identity) = cli.expect_poption("server-identity");
         let sauth: ServerAuth = read_struct(&mut stream).ctx("reading server auth")?;
         let secret = sauth
-            .verify(auth.pk, server_identity, sx)
+            .verify(auth.x, server_identity, sx)
             .map_err(|_| io::ErrorKind::PermissionDenied)
             .ctx("authenticating server")?;
         let stream = EncriptedStream::new(stream, secret);
@@ -142,76 +116,51 @@ const SUBCOMMANDS: &[Subcommand] = &[
     }),
 ];
 
-type ConsumeSubcommand<'a> = (&'a str, &'a str, fn(&Cli, EncriptedStream) -> io::Result<()>);
-
 const CONSUME_SUBCOMMAND: &[ConsumeSubcommand] = &[
     ("help", "this help message", |_, _| help(CONSUME_SUBCOMMAND)),
     ("ping", "ping the server to check the connection", |_, mut stream| {
-        write_struct(&mut stream, &Qid::Ping)
+        let now = time::Instant::now();
-    }), //
+        write_struct(&mut stream, &Qid::Ping)?;
+        if !matches!(Aid::try_from(read_struct::<u16>(&mut stream)?)?, Aid::Pong) {
+            eprintln!("server did not respond with ping");
+        }
+        println!("{:?}", now.elapsed());
+        Ok(())
+    }),
 ];
 
-fn hex_to_array<const SIZE: usize>(s: &str) -> Result<[u8; SIZE], &'static str> {
-    let mut buf = [0u8; SIZE];
-
-    if s.len() != SIZE * 2 {
-        return Err("expected 64 character hex string");
-    }
-
-    fn byte_to_hex(val: u8) -> Result<u8, &'static str> {
-        Ok(match val {
-            b'0'..=b'9' => val - b'0',
-            b'a'..=b'f' => val - b'a' + 10,
-            b'A'..=b'F' => val - b'A' + 10,
-            _ => return Err("invalid hex char"),
-        })
-    }
-
-    for (dst, &[a, b]) in buf.iter_mut().zip(s.as_bytes().array_windows()) {
-        *dst = byte_to_hex(a)? | (byte_to_hex(b)? << 4);
-    }
-
-    Ok(buf)
-}
-
-struct HexPk(ed25519_dalek::VerifyingKey);
-
-impl std::str::FromStr for HexPk {
-    type Err = &'static str;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        ed25519_dalek::VerifyingKey::from_bytes(&hex_to_array(s)?)
-            .map_err(|_| "hex code does not represent the valid key")
-            .map(Self)
-    }
-}
-
-struct HexSk(ed25519_dalek::SigningKey);
-
-impl std::str::FromStr for HexSk {
-    type Err = &'static str;
-
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        Ok(Self(ed25519_dalek::SigningKey::from_bytes(&hex_to_array(s)?)))
-    }
-}
-
-fn select_subcommand<'a, T>(depth: usize, list: &'a [(&str, &str, T)], cli: &Cli) -> &'a T {
-    &list.iter().find(|&&(name, ..)| name == cli.arg(depth)).unwrap_or(&list[0]).2
-}
-
 fn main() -> io::Result<()> {
     let cli = Cli::parse();
     select_subcommand(0, SUBCOMMANDS, &cli)(&cli)
 }
 
-fn handle_client(mut stream: TcpStream) -> io::Result<()> {
+fn help<T>(subs: &[Subcommand<T>]) -> io::Result<()> {
+    for (name, desc, _) in subs {
+        eprintln!("{name} - {desc}");
+    }
+    Err(io::ErrorKind::NotFound.into())
+}
+
+fn select_subcommand<'a, T>(depth: usize, list: &'a [Subcommand<T>], cli: &Cli) -> &'a T {
+    &list.iter().find(|&&(name, ..)| name == cli.arg(depth)).unwrap_or(&list[0]).2
+}
+
+struct ServerState {
+    user_data_dir: PathBuf,
+    secret: ed::SigningKey,
+    max_conns: usize,
+    active_ips: Mutex<HashSet<Ipv4Addr>>,
+    conn_count: AtomicUsize,
+}
+
+impl ServerState {
+    fn handle_client(&self, mut stream: TcpStream) -> io::Result<()> {
         let (user, sec) = {
             let user_auth: UserAuth = read_struct(&mut stream).ctx("reading auth packet")?;
-        let sx = x25519_dalek::EphemeralSecret::random_from_rng(OsRng);
+            let sx = x::EphemeralSecret::random_from_rng(OsRng);
-        let pk = x25519_dalek::PublicKey::from(&sx);
+            let pk = x::PublicKey::from(&sx);
-        let user = UserData::load(&user_auth, sx).ctx("loading user data")?;
+            let user = UserData::load(&user_auth, sx, self).ctx("loading user data")?;
-        let sauth = ServerAuth::sign(&user_auth, SERVER_SECRET.get().unwrap(), pk);
+            let sauth = ServerAuth::sign(&user_auth, &self.secret, pk);
             write_struct(&mut stream, &sauth).ctx("sending handshare response")?;
             user
         };
@@ -223,6 +172,37 @@ fn handle_client(mut stream: TcpStream) -> io::Result<()> {
                 Qid::Ping => write_struct(&mut stream, &Aid::Pong)?,
             }
         }
+    }
+}
+
+struct ConnectionGuard {
+    ip: Ipv4Addr,
+    config: Arc<ServerState>,
+}
+
+impl ConnectionGuard {
+    fn new(config: Arc<ServerState>, ip: Ipv4Addr) -> Option<Self> {
+        if config.conn_count.fetch_add(1, atomic::Ordering::Relaxed) >= config.max_conns {
+            eprintln!("max connection cap reached");
+            config.conn_count.fetch_sub(1, atomic::Ordering::Relaxed);
+            return None;
+        }
+
+        if !config.active_ips.lock().unwrap().insert(ip) {
+            eprintln!("ip already connected, dropping connection");
+            config.conn_count.fetch_sub(1, atomic::Ordering::Relaxed);
+            return None;
+        }
+
+        Some(Self { ip, config })
+    }
+}
+
+impl Drop for ConnectionGuard {
+    fn drop(&mut self) {
+        self.config.active_ips.lock().unwrap().remove(&self.ip);
+        self.config.conn_count.fetch_sub(1, atomic::Ordering::Relaxed);
+    }
 }
 
 #[repr(u16)]
@@ -230,6 +210,18 @@ enum Aid {
     Pong,
 }
 
+impl TryFrom<u16> for Aid {
+    type Error = io::ErrorKind;
+
+    fn try_from(value: u16) -> Result<Self, Self::Error> {
+        if value <= Self::Pong as u16 {
+            Ok(unsafe { mem::transmute::<u16, Self>(value) })
+        } else {
+            Err(io::ErrorKind::NotFound)
+        }
+    }
+}
+
 #[repr(u16)]
 enum Qid {
     Ping,
@@ -240,7 +232,7 @@ impl TryFrom<u16> for Qid {
 
     fn try_from(value: u16) -> Result<Self, Self::Error> {
         if value <= Self::Ping as u16 {
-            Ok(unsafe { mem::transmute::<u16, Qid>(value) })
+            Ok(unsafe { mem::transmute::<u16, Self>(value) })
         } else {
             Err(io::ErrorKind::NotFound)
         }
@@ -260,7 +252,191 @@ impl<O, E: fmt::Display> Ctx for Result<O, E> {
     }
 }
 
-const ASOC_DATA: &[u8] = b"testicle torsion vizard";
+fn username_as_str(name: &Username) -> Option<&str> {
+    let len = name.iter().rposition(|&b| b != 0xff)? + 1;
+    std::str::from_utf8(&name[..len]).ok()
+}
+
+fn str_as_username(name: &str) -> Option<Username> {
+    if name.len() > mem::size_of::<Username>() {
+        return None;
+    }
+    let mut buff = [0xffu8; mem::size_of::<Username>()];
+    buff[..name.len()].copy_from_slice(name.as_bytes());
+    Some(buff)
+}
+
+#[repr(packed)]
+struct UserProfile {
+    name: Username,
+    key: ed::SecretKey,
+}
+
+#[repr(packed)]
+struct UserAuth {
+    signature: ed::Signature,
+    pk: Pk,
+    x: x::PublicKey,
+    name: Username,
+    nonce: Nonce,
+}
+
+impl UserAuth {
+    fn sign(UserProfile { name, key }: UserProfile, sx: &x::EphemeralSecret) -> Self {
+        let nonce =
+            time::SystemTime::now().duration_since(time::SystemTime::UNIX_EPOCH).unwrap().as_secs();
+        let mut message = [0; mem::size_of::<Username>() + mem::size_of::<u64>()];
+        message[..mem::size_of::<Username>()].copy_from_slice(&name);
+        message[mem::size_of::<Username>()..].copy_from_slice(&nonce.to_le_bytes());
+
+        let signing_key = ed::SigningKey::from_bytes(&key);
+        let signature = signing_key.sign(&message);
+        let pk = ed::VerifyingKey::from(&signing_key).to_bytes();
+        let x = x::PublicKey::from(sx);
+
+        Self { signature, pk, x, name, nonce }
+    }
+
+    fn verify(
+        &self,
+        pk: Pk,
+        nonce: Nonce,
+        sx: x::EphemeralSecret,
+    ) -> Result<SharedSecret, ed::SignatureError> {
+        if nonce >= self.nonce {
+            eprintln!("invalid auth nonce");
+            return Err(ed::SignatureError::default());
+        }
+
+        let pk = ed::VerifyingKey::from_bytes(&pk)?;
+
+        let mut message = [0; mem::size_of::<Username>() + mem::size_of::<u64>()];
+        message[..mem::size_of::<Username>()].copy_from_slice(&self.name);
+        message[mem::size_of::<Username>()..].copy_from_slice(&self.nonce.to_le_bytes());
+
+        pk.verify_strict(&message, &self.signature)?;
+
+        Ok(sx.diffie_hellman(&self.x))
+    }
+}
+
+#[repr(packed)]
+struct ServerAuth {
+    signature: ed::Signature,
+    x: x::PublicKey,
+}
+
+impl ServerAuth {
+    fn sign(user_auth: &UserAuth, sk: &ed::SigningKey, x: x::PublicKey) -> Self {
+        let signature = sk.sign(user_auth.x.as_bytes());
+        Self { signature, x }
+    }
+
+    fn verify(
+        &self,
+        x: x::PublicKey,
+        pk: ed::VerifyingKey,
+        sx: EphemeralSecret,
+    ) -> Result<SharedSecret, ed::SignatureError> {
+        pk.verify_strict(x.as_bytes(), &self.signature)?;
+        Ok(sx.diffie_hellman(&self.x))
+    }
+}
+
+struct UserData {
+    header: UserHeader,
+    post_headers: fs::File,
+    posts: fs::File,
+}
+
+impl UserData {
+    fn load(
+        auth: &UserAuth,
+        sx: x::EphemeralSecret,
+        config: &ServerState,
+    ) -> io::Result<(Self, SharedSecret)> {
+        const HEADER_PATH: &str = "header.bin";
+        const POST_HEADERS_PATH: &str = "post-headers.bin";
+        const POST_PATH: &str = "posts.bin";
+
+        let mut path = PathBuf::from_iter([
+            config.user_data_dir.as_path(),
+            username_as_str(&auth.name).ok_or(io::ErrorKind::InvalidData)?.as_ref(),
+        ]);
+
+        if path.exists() {
+            let mut opts = fs::OpenOptions::new();
+            opts.write(true).read(true);
+
+            path.push(HEADER_PATH);
+            let mut header_file = opts.open(&path).ctx("opening user header file")?;
+            let mut header: UserHeader =
+                read_struct(&mut header_file).ctx("reading the user header")?;
+            path.pop();
+
+            let secret = auth
+                .verify(header.pk, header.nonce, sx)
+                .map_err(|_| io::ErrorKind::PermissionDenied)
+                .ctx("authenticating user")?;
+
+            header.nonce = auth.nonce;
+            write_struct(&mut header_file, &header).ctx("saving user nonce")?;
+
+            path.push(POST_HEADERS_PATH);
+            let post_headers = opts.open(&path).ctx("opening user post header file")?;
+            path.pop();
+
+            path.push(POST_PATH);
+            let posts = opts.open(&path).ctx("opening user post file")?;
+            path.pop();
+
+            Ok((Self { header, post_headers, posts }, secret))
+        } else {
+            let secret = auth
+                .verify(auth.pk, 0, sx)
+                .map_err(|_| io::ErrorKind::PermissionDenied)
+                .ctx("verifiing registratio signature")?;
+
+            fs::create_dir_all(&path).ctx("creating new user directory")?;
+            path.push(HEADER_PATH);
+            let header =
+                UserHeader { pk: auth.pk, nonce: auth.nonce, post_count: 0, runs: 0, imports: 0 };
+            fs::write(&path, as_bytes(&header)).ctx("writing new user header")?;
+            path.pop();
+
+            path.push(POST_HEADERS_PATH);
+            let post_headers = fs::File::create_new(&path).ctx("creating new user post headers")?;
+            path.pop();
+
+            path.push(POST_PATH);
+            let posts = fs::File::create_new(&path).ctx("creating new user posts")?;
+            path.pop();
+
+            Ok((Self { header, post_headers, posts }, secret))
+        }
+    }
+}
+
+#[repr(packed)]
+struct UserHeader {
+    pk: Pk,
+    nonce: Nonce,
+    post_count: u32,
+    imports: u32,
+    runs: u32,
+}
+
+#[repr(packed)]
+struct PostHeader {
+    name: Postname,
+    timestamp: u64,
+    size: u32,
+    offset: u32,
+    imports: u32,
+    runs: u32,
+}
+
+const ASOC_DATA: &[u8] = b"testicle torsion wizard";
 
 struct EncriptedStream {
     inner: TcpStream,
@@ -339,7 +515,7 @@ impl Write for EncriptedStream {
 fn read_struct<T>(stream: &mut impl Read) -> io::Result<T> {
     let mut res = mem::MaybeUninit::uninit();
     stream.read_exact(as_mut_bytes(&mut res))?;
-    unsafe { res.assume_init() }
+    Ok(unsafe { res.assume_init() })
 }
 
 fn write_struct<T>(stream: &mut impl Write, value: &T) -> io::Result<()> {
@@ -354,191 +530,112 @@ fn as_bytes<T>(value: &T) -> &[u8] {
     unsafe { slice::from_raw_parts(value as *const _ as *const u8, mem::size_of::<T>()) }
 }
 
-type Username = [u8; 32];
+#[derive(Default)]
-type Postname = [u8; 64];
+struct Cli {
-type Pk = [u8; 32];
+    program: String,
-type Nonce = u64;
+    args: Vec<String>,
-
+    flags: HashSet<String>,
-fn username_as_str(name: &Username) -> Option<&str> {
+    options: HashMap<String, String>,
-    let len = name.iter().rposition(|&b| b != 0xff)? + 1;
-    std::str::from_utf8(&name[..len]).ok()
 }
 
-fn str_as_username(name: &str) -> Option<Username> {
+impl Cli {
-    if name.len() > mem::size_of::<Username>() {
+    pub fn parse() -> Self {
-        return None;
+        let mut s = Self::default();
+        let mut args = std::env::args();
+        s.program = args.next().unwrap();
+
+        for arg in args {
+            if let Some(arg) = arg.strip_prefix("--") {
+                match arg.split_once('=') {
+                    Some((name, value)) => _ = s.options.insert(name.to_owned(), value.to_owned()),
+                    None => _ = s.flags.insert(arg.to_string()),
                 }
-    let mut buff = [0xffu8; mem::size_of::<Username>()];
-    buff[..name.len()].copy_from_slice(name.as_bytes());
-    Some(buff)
-}
-
-#[repr(packed)]
-struct UserProfile {
-    name: Username,
-    key: ed25519_dalek::SecretKey,
-}
-
-#[repr(packed)]
-struct UserAuth {
-    signature: ed25519_dalek::Signature,
-    pk: Pk,
-    x: x25519_dalek::PublicKey,
-    name: Username,
-    nonce: Nonce,
-}
-
-impl UserAuth {
-    fn sign(UserProfile { name, key }: UserProfile, sx: &x25519_dalek::EphemeralSecret) -> Self {
-        let nonce =
-            time::SystemTime::now().duration_since(time::SystemTime::UNIX_EPOCH).unwrap().as_secs();
-        let mut message = [0; mem::size_of::<Username>() + mem::size_of::<u64>()];
-        message[..mem::size_of::<Username>()].copy_from_slice(&name);
-        message[mem::size_of::<Username>()..].copy_from_slice(&nonce.to_le_bytes());
-
-        let signing_key = ed25519_dalek::SigningKey::from_bytes(&key);
-        let signature = signing_key.sign(&message);
-        let pk = ed25519_dalek::VerifyingKey::from(&signing_key).to_bytes();
-        let x = x25519_dalek::PublicKey::from(sx);
-
-        Self { signature, pk, x, name, nonce }
-    }
-
-    fn verify(
-        &self,
-        pk: Pk,
-        nonce: Nonce,
-        sx: x25519_dalek::EphemeralSecret,
-    ) -> Result<SharedSecret, ed25519_dalek::SignatureError> {
-        if nonce >= self.nonce {
-            eprintln!("invalid auth nonce");
-            return Err(ed25519_dalek::SignatureError::default());
-        }
-
-        let pk = ed25519_dalek::VerifyingKey::from_bytes(&pk)?;
-
-        let mut message = [0; mem::size_of::<Username>() + mem::size_of::<u64>()];
-        message[..mem::size_of::<Username>()].copy_from_slice(&self.name);
-        message[mem::size_of::<Username>()..].copy_from_slice(&nonce.to_le_bytes());
-
-        pk.verify_strict(&message, &self.signature)?;
-
-        Ok(sx.diffie_hellman(&self.x))
-    }
-}
-
-#[repr(packed)]
-struct ServerAuth {
-    signature: ed25519_dalek::Signature,
-    x: x25519_dalek::PublicKey,
-}
-
-impl ServerAuth {
-    fn sign(
-        user_auth: &UserAuth,
-        sk: &ed25519_dalek::SigningKey,
-        x: x25519_dalek::PublicKey,
-    ) -> Self {
-        let signature = sk.sign(user_auth.x.as_bytes());
-        Self { signature, x }
-    }
-
-    fn verify(
-        &self,
-        x: Pk,
-        pk: ed25519_dalek::VerifyingKey,
-        sx: EphemeralSecret,
-    ) -> Result<SharedSecret, ed25519_dalek::SignatureError> {
-        pk.verify_strict(&x, &self.signature)?;
-        Ok(sx.diffie_hellman(&self.x))
-    }
-}
-
-struct UserData {
-    header: UserHeader,
-    post_headers: fs::File,
-    posts: fs::File,
-}
-
-impl UserData {
-    fn load(
-        auth: &UserAuth,
-        sx: x25519_dalek::EphemeralSecret,
-    ) -> io::Result<(Self, SharedSecret)> {
-        const HEADER_PATH: &str = "header.bin";
-        const POST_HEADERS_PATH: &str = "post-headers.bin";
-        const POST_PATH: &str = "posts.bin";
-
-        let mut path = PathBuf::from_iter([
-            USER_DATA_DIR.get().unwrap().as_path(),
-            username_as_str(&auth.name).ok_or(io::ErrorKind::InvalidData)?.as_ref(),
-        ]);
-
-        if path.exists() {
-            path.push(HEADER_PATH);
-            let mut header_file = fs::File::open(&path).ctx("opening user header file")?;
-            let mut header: UserHeader =
-                read_struct(&mut header_file).ctx("reading the user header")?;
-            path.pop();
-
-            let secret = auth
-                .verify(header.pk, header.nonce, sx)
-                .map_err(|_| io::ErrorKind::PermissionDenied)
-                .ctx("authenticating user")?;
-
-            header.nonce = auth.nonce;
-            write_struct(&mut header_file, &header).ctx("saving user nonce")?;
-
-            path.push(POST_HEADERS_PATH);
-            let post_headers = fs::File::open(&path).ctx("opening user post header file")?;
-            path.pop();
-
-            path.push(POST_PATH);
-            let posts = fs::File::open(&path).ctx("opening user post file")?;
-            path.pop();
-
-            Ok((Self { header, post_headers, posts }, secret))
             } else {
-            let secret = auth
+                s.args.push(arg);
-                .verify(auth.pk, 0, sx)
-                .map_err(|_| io::ErrorKind::PermissionDenied)
-                .ctx("verifiing registratio signature")?;
-
-            fs::create_dir_all(&path).ctx("creating new user directory")?;
-            path.push(HEADER_PATH);
-            let header =
-                UserHeader { pk: auth.pk, nonce: auth.nonce, post_count: 0, runs: 0, imports: 0 };
-            fs::write(&path, as_bytes(&header)).ctx("writing new user header")?;
-            path.pop();
-
-            path.push(POST_HEADERS_PATH);
-            let post_headers = fs::File::create_new(&path).ctx("creating new user post headers")?;
-            path.pop();
-
-            path.push(POST_PATH);
-            let posts = fs::File::create_new(&path).ctx("creating new user posts")?;
-            path.pop();
-
-            Ok((Self { header, post_headers, posts }, secret))
             }
         }
+
+        s
+    }
+
+    pub fn arg(&self, index: usize) -> &str {
+        self.args.get(index).map_or("", String::as_str)
+    }
+
+    pub fn expect_option(&self, name: &str) -> &str {
+        self.options.get(name).unwrap_or_else(|| panic!("--{name}= is mandatory"))
+    }
+
+    pub fn expect_poption<T: FromStr<Err: fmt::Display>>(&self, name: &str) -> T {
+        self.expect_option(name).parse::<T>().unwrap_or_else(|e| {
+            panic!("failed to parse --{name}= as {}: {e}", std::any::type_name::<T>())
+        })
+    }
 }
 
-#[repr(packed)]
+fn hex_to_array<const SIZE: usize>(s: &str) -> Result<[u8; SIZE], &'static str> {
-struct UserHeader {
+    let mut buf = [0u8; SIZE];
-    pk: Pk,
+
-    nonce: Nonce,
+    if s.len() != SIZE * 2 {
-    post_count: u32,
+        return Err("expected 64 character hex string");
-    imports: u32,
+    }
-    runs: u32,
+
+    fn byte_to_hex(val: u8) -> Result<u8, &'static str> {
+        Ok(match val {
+            b'0'..=b'9' => val - b'0',
+            b'a'..=b'f' => val - b'a' + 10,
+            b'A'..=b'F' => val - b'A' + 10,
+            _ => return Err("invalid hex char"),
+        })
+    }
+
+    for (dst, &[a, b]) in buf.iter_mut().zip(s.as_bytes().array_chunks()) {
+        *dst = byte_to_hex(b)? | (byte_to_hex(a)? << 4);
+    }
+
+    Ok(buf)
 }
 
-#[repr(packed)]
+struct HexPk(ed::VerifyingKey);
-struct PostHeader {
+
-    name: Postname,
+impl std::str::FromStr for HexPk {
-    timestamp: u64,
+    type Err = &'static str;
-    size: u32,
+
-    offset: u32,
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
-    imports: u32,
+        ed::VerifyingKey::from_bytes(&hex_to_array(s)?)
-    runs: u32,
+            .map_err(|_| "hex code does not represent the valid key")
+            .map(Self)
+    }
+}
+
+struct HexSk(ed::SigningKey);
+
+impl std::str::FromStr for HexSk {
+    type Err = &'static str;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Ok(Self(ed::SigningKey::from_bytes(&hex_to_array(s)?)))
+    }
+}
+
+struct DisplayHex([u8; 32]);
+
+impl fmt::Display for DisplayHex {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        for b in self.0 {
+            write!(f, "{b:02x}")?;
+        }
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+#[test]
+fn test_hex() {
+    let expected = [1u8; 32];
+
+    let hex = dbg!(DisplayHex(expected).to_string());
+    let got: [u8; 32] = hex_to_array(&hex).unwrap();
+
+    assert_eq!(got, expected);
 }