//! Facility for detecting and preventing replays on introduction requests.

//!

//! If we were to permit the introduction point to replay the same request

//! multiple times, it would cause the service to contact the rendezvous point

//! again with the same rendezvous cookie as before, which could help with

//! traffic analysis.

//!

//! (This could also be a DoS vector if the introduction point decided to

//! overload the service.)

//!

//! Because we use the same introduction point keys across restarts, we need to

//! make sure that our replay logs are already persistent.  We do this by using

//! a file on disk.

mod ipt;

use crate::internal_prelude::*;

/// A probabilistic data structure to record fingerprints of observed Introduce2

/// messages.

///

/// We need to record these fingerprints to prevent replay attacks; see the

/// module documentation for an explanation of why that would be bad.

///

/// A ReplayLog should correspond to a `KP_hss_ntor` key, and should have the

/// same lifespan: dropping it sooner will enable replays, but dropping it later

/// will waste disk and memory.

///

/// False positives are allowed, to conserve on space.

pub(crate) struct ReplayLog<T> {

    /// The inner probabilistic data structure.

    seen: data::Filter,

    /// Persistent state file etc., if we're persistent

    ///

    /// If is is `None`, this RelayLog is ephemeral.

    file: Option<PersistFile>,

    /// [`PhantomData`] so rustc doesn't complain about the unused type param.

    ///

    /// This type represents the type of data that we're storing, as well as the type of the

    /// key/name for that data.

    replay_log_type: PhantomData<T>,

}

/// A [`ReplayLog`] for [`Introduce2`](tor_cell::relaycell::msg::Introduce2) messages.

pub(crate) type IptReplayLog = ReplayLog<ipt::IptReplayLogType>;

/// The length of the [`ReplayLogType::MAGIC`] constant.

///

// TODO: If Rust's constant expressions supported generics we wouldn't need this at all.

const MAGIC_LEN: usize = 32;

/// The length of the message that we store on disk, in bytes.

///

/// If the message is longer than this, then we will need to hash or truncate it before storing it

/// to disk.

///

// TODO: Once const generics are good, this should be a associated constant for ReplayLogType.

pub(crate) const OUTPUT_LEN: usize = 16;

/// A trait to represent a set of types that ReplayLog can be used with.

pub(crate) trait ReplayLogType {

    // TODO: It would be nice to encode the directory name as a associated constant here, rather

    // than having the external code pass it in to us.

    /// The name of this item, used for the log filename.

    type Name;

    /// The type of the messages that we are ensuring the uniqueness of.

    type Message;

    /// A magic string that we put at the start of each log file, to make sure that

    /// we don't confuse this file format with others.

    const MAGIC: &'static [u8; MAGIC_LEN];

    /// Convert [`Self::Name`] to a [`String`]

    fn format_filename(name: &Self::Name) -> String;

    /// Convert [`Self::Message`] to bytes that will be stored in the log.

    fn transform_message(message: &Self::Message) -> [u8; OUTPUT_LEN];

    /// Parse a filename into [`Self::Name`].

    fn parse_log_leafname(leaf: &OsStr) -> Result<Self::Name, Cow<'static, str>>;

}

/// Persistent state file, and associated data

///

/// Stored as `ReplayLog.file`.

#[derive(Debug)]

pub(crate) struct PersistFile {

    /// A file logging fingerprints of the messages we have seen.

    file: BufWriter<File>,

    /// Whether we had a possible partial write

    ///

    /// See the comment inside [`ReplayLog::check_for_replay`].

    /// `Ok` means all is well.

    /// `Err` means we may have written partial data to the actual file,

    /// and need to make sure we're back at a record boundary.

    needs_resynch: Result<(), ()>,

    /// Filesystem lock which must not be released until after we finish writing

    ///

    /// Must come last so that the drop order is correct

    #[allow(dead_code)] // Held just so we unlock on drop

    lock: Arc<LockFileGuard>,

}

/// Replay log files have a `.bin` suffix.

///

/// The name of the file is determined by [`ReplayLogType::format_filename`].

const REPLAY_LOG_SUFFIX: &str = ".bin";

impl<T: ReplayLogType> ReplayLog<T> {

    /// Create a new ReplayLog not backed by any data storage.

    #[allow(dead_code)] // TODO #1186 Remove once something uses ReplayLog.

    /// Create a ReplayLog backed by the file at a given path.

    ///

    /// If the file already exists, load its contents and append any new

    /// contents to it; otherwise, create the file.

    ///

    /// **`lock` must already have been locked** and this

    /// *cannot be assured by the type system*.

    ///

    /// # Limitations

    ///

    /// It is the caller's responsibility to make sure that there are never two

    /// `ReplayLogs` open at once for the same path, or for two paths that

    /// resolve to the same file.

    /// Inner function for `new_logged`, with reified arguments and raw error type

        };

        // If the file is new, we need to write the magic string. Else we must

        // read it.

        } else {

        }

        // Now read the rest of the file.

        loop {

            }

        }

    /// Truncate `file` to contain a whole number of records

    ///

    /// `current_len` should have come from `file.metadata()`.

    // If the file's length is not an even multiple of MESSAGE_LEN after the MAGIC, truncate it.

    /// Test whether we have already seen `message`.

    ///

    /// If we have seen it, return `Err(ReplayError::AlreadySeen)`.  (Since this

    /// is a probabilistic data structure, there is a chance of returning this

    /// error even if we have we have _not_ seen this particular message)

    ///

    /// Otherwise, return `Ok(())`.

                    Err(()) => {

                        // We're going to reach behind the BufWriter, so we need to make

                        // sure it's in synch with the underlying File.

                        // cursor is now past end, must reset (see std::fs::File::set_len)

                    }

                }

    /// Flush any buffered data to disk.

    #[allow(dead_code)] // TODO #1208

    /// Tries to parse a filename in the replay logs directory

    ///

    /// If the leafname refers to a file that would be created by

    /// [`ReplayLog::new_logged`], returns the name as a Rust type.

    ///

    /// Otherwise returns an error explaining why it isn't,

    /// as a plain string (for logging).

}

/// Wrapper around a fast-ish data structure for detecting replays with some

/// false positive rate.  Bloom filters, cuckoo filters, and xorf filters are all

/// an option here.  You could even use a HashSet.

///

/// We isolate this code to make it easier to replace.

mod data {

    use super::{ReplayError, OUTPUT_LEN};

    use growable_bloom_filter::GrowableBloom;

    /// A probabilistic membership filter.

    pub(super) struct Filter(pub(crate) GrowableBloom);

    impl Filter {

        /// Create a new empty filter

        /// Try to add `msg` to this filter if it isn't already there.

        ///

        /// Return Ok(()) or Err(AlreadySeen).

            } else {

            }

    }

}

/// A problem that prevents us from reading a ReplayLog from disk.

///

/// (This only exists so we can wrap it up in an [`io::Error`])

#[derive(thiserror::Error, Clone, Debug)]

enum LogContentError {

    /// The magic number on the log file was incorrect.

    #[error("unrecognized data format")]

    UnrecognizedFormat,

}

/// An error occurred while checking whether we've seen an element before.

#[derive(thiserror::Error, Clone, Debug)]

pub(crate) enum ReplayError {

    /// We have already seen this item.

    #[error("Already seen")]

    AlreadySeen,

    /// We were unable to record this item in the log.

    #[error("Unable to log data")]

    Log(Arc<std::io::Error>),

}

#[cfg(test)]

mod test {

    // @@ begin test lint list maintained by maint/add_warning @@

    #![allow(clippy::bool_assert_comparison)]

    #![allow(clippy::clone_on_copy)]

    #![allow(clippy::dbg_macro)]

    #![allow(clippy::mixed_attributes_style)]

    #![allow(clippy::print_stderr)]

    #![allow(clippy::print_stdout)]

    #![allow(clippy::single_char_pattern)]

    #![allow(clippy::unwrap_used)]

    #![allow(clippy::unchecked_duration_subtraction)]

    #![allow(clippy::useless_vec)]

    #![allow(clippy::needless_pass_by_value)]

    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->

    use super::*;

    use crate::test::mk_state_instance;

    use rand::Rng;

    use test_temp_dir::{test_temp_dir, TestTempDir, TestTempDirGuard};

    struct TestReplayLogType;

    type TestReplayLog = ReplayLog<TestReplayLogType>;

    impl ReplayLogType for TestReplayLogType {

        type Name = IptLocalId;

        type Message = [u8; OUTPUT_LEN];

        const MAGIC: &'static [u8; MAGIC_LEN] = b"<tor test replay>\n\0\0\0\0\0\0\0\0\0\0\0\0\0\0";

        fn format_filename(name: &IptLocalId) -> String {

            format!("{name}{REPLAY_LOG_SUFFIX}")

        }

        fn transform_message(message: &[u8; OUTPUT_LEN]) -> [u8; OUTPUT_LEN] {

            message.clone()

        }

        fn parse_log_leafname(leaf: &OsStr) -> Result<IptLocalId, Cow<'static, str>> {

            let leaf = leaf.to_str().ok_or("not proper unicode")?;

            let lid = leaf.strip_suffix(REPLAY_LOG_SUFFIX).ok_or("not *.bin")?;

            let lid: IptLocalId = lid

                .parse()

                .map_err(|e: crate::InvalidIptLocalId| e.to_string())?;

            Ok(lid)

        }

    }

    fn rand_msg<R: Rng>(rng: &mut R) -> [u8; OUTPUT_LEN] {

        rng.random()

    }

    /// Basic tests on an ephemeral IptReplayLog.

    #[test]

    fn simple_usage() {

        let mut rng = tor_basic_utils::test_rng::testing_rng();

        let group_1: Vec<_> = (0..=100).map(|_| rand_msg(&mut rng)).collect();

        let group_2: Vec<_> = (0..=100).map(|_| rand_msg(&mut rng)).collect();

        let mut log = TestReplayLog::new_ephemeral();

        // Add everything in group 1.

        for msg in &group_1 {

            assert!(log.check_for_replay(msg).is_ok(), "False positive");

        }

        // Make sure that everything in group 1 is still there.

        for msg in &group_1 {

            assert!(log.check_for_replay(msg).is_err());

        }

        // Make sure that group 2 is detected as not-there.

        for msg in &group_2 {

            assert!(log.check_for_replay(msg).is_ok(), "False positive");

        }

    }

    const TEST_TEMP_SUBDIR: &str = "replaylog";

    fn create_logged(dir: &TestTempDir) -> TestTempDirGuard<TestReplayLog> {

        dir.subdir_used_by(TEST_TEMP_SUBDIR, |dir| {

            let inst = mk_state_instance(&dir, "allium");

            let raw = inst.raw_subdir("iptreplay").unwrap();

            TestReplayLog::new_logged(&raw, &IptLocalId::dummy(1)).unwrap()

        })

    }

    /// Basic tests on an persistent IptReplayLog.

    #[test]

    fn logging_basics() {

        let mut rng = tor_basic_utils::test_rng::testing_rng();

        let group_1: Vec<_> = (0..=100).map(|_| rand_msg(&mut rng)).collect();

        let group_2: Vec<_> = (0..=100).map(|_| rand_msg(&mut rng)).collect();

        let dir = test_temp_dir!();

        let mut log = create_logged(&dir);

        // Add everything in group 1, then close and reload.

        for msg in &group_1 {

            assert!(log.check_for_replay(msg).is_ok(), "False positive");

        }

        drop(log);

        let mut log = create_logged(&dir);

        // Make sure everything in group 1 is still there.

        for msg in &group_1 {

            assert!(log.check_for_replay(msg).is_err());

        }

        // Now add everything in group 2, then close and reload.

        for msg in &group_2 {

            assert!(log.check_for_replay(msg).is_ok(), "False positive");

        }

        drop(log);

        let mut log = create_logged(&dir);

        // Make sure that groups 1 and 2 are still there.

        for msg in group_1.iter().chain(group_2.iter()) {

            assert!(log.check_for_replay(msg).is_err());

        }

    }

    /// Test for a log that gets truncated mid-write.

    #[test]

    fn test_truncated() {

        let mut rng = tor_basic_utils::test_rng::testing_rng();

        let group_1: Vec<_> = (0..=100).map(|_| rand_msg(&mut rng)).collect();

        let group_2: Vec<_> = (0..=100).map(|_| rand_msg(&mut rng)).collect();

        let dir = test_temp_dir!();

        let mut log = create_logged(&dir);

        for msg in &group_1 {

            assert!(log.check_for_replay(msg).is_ok(), "False positive");

        }

        drop(log);

        // Truncate the file by 7 bytes.

        dir.subdir_used_by(TEST_TEMP_SUBDIR, |dir| {

            let path = dir.join(format!("hss/allium/iptreplay/{}.bin", IptLocalId::dummy(1)));

            let file = OpenOptions::new().write(true).open(path).unwrap();

            // Make sure that the file has the length we expect.

            let expected_len = MAGIC_LEN + OUTPUT_LEN * group_1.len();

            assert_eq!(expected_len as u64, file.metadata().unwrap().len());

            file.set_len((expected_len - 7) as u64).unwrap();

        });

        // Now, reload the log. We should be able to recover every non-truncated

        // item...

        let mut log = create_logged(&dir);

        for msg in &group_1[..group_1.len() - 1] {

            assert!(log.check_for_replay(msg).is_err());

        }

        // But not the last one, which we truncated.  (Checking will add it, though.)

        assert!(

            log.check_for_replay(&group_1[group_1.len() - 1]).is_ok(),

            "False positive"

        );

        // Now add everything in group 2, then close and reload.

        for msg in &group_2 {

            assert!(log.check_for_replay(msg).is_ok(), "False positive");

        }

        drop(log);

        let mut log = create_logged(&dir);

        // Make sure that groups 1 and 2 are still there.

        for msg in group_1.iter().chain(group_2.iter()) {

            assert!(log.check_for_replay(msg).is_err());

        }

    }

    /// Test for a partial write

    #[test]

    #[cfg(target_os = "linux")] // different platforms have different definitions of sigaction

    fn test_partial_write() {

        use std::env;

        use std::os::unix::process::ExitStatusExt;

        use std::process::Command;

        // TODO this contraption should perhaps be productised and put somewhere else

        const ENV_NAME: &str = "TOR_HSSERVICE_TEST_PARTIAL_WRITE_SUBPROCESS";

        // for a wait status different from any of libtest's

        const GOOD_SIGNAL: i32 = libc::SIGUSR2;

        let sigemptyset = || unsafe {

            let mut set = MaybeUninit::uninit();

            libc::sigemptyset(set.as_mut_ptr());

            set.assume_init()

        };

        // Check that SIGUSR2 starts out as SIG_DFL and unblocked

        //

        // We *reject* such situations, rather than fixing them up, because this is an

        // irregular and broken environment that can cause arbitrarily weird behaviours.

        // Programs on Unix are entitled to assume that their signal dispositions are

        // SIG_DFL on entry, with signals unblocked.  (With a few exceptions.)

        //

        // So we want to detect and report any such environment, not let it slide.

        unsafe {

            let mut sa = MaybeUninit::uninit();

            let r = libc::sigaction(GOOD_SIGNAL, ptr::null(), sa.as_mut_ptr());

            assert_eq!(r, 0);

            let sa = sa.assume_init();

            assert_eq!(

                sa.sa_sigaction,

                libc::SIG_DFL,

                "tests running in broken environment (SIGUSR2 not SIG_DFL)"

            );

            let empty_set = sigemptyset();

            let mut current_set = MaybeUninit::uninit();

            let r = libc::sigprocmask(

                libc::SIG_UNBLOCK,

                (&empty_set) as _,

                current_set.as_mut_ptr(),

            );

            assert_eq!(r, 0);

            let current_set = current_set.assume_init();

            let blocked = libc::sigismember((&current_set) as _, GOOD_SIGNAL);

            assert_eq!(

                blocked, 0,

                "tests running in broken environment (SIGUSR2 blocked)"

            );

        }

        match env::var(ENV_NAME) {

            Err(env::VarError::NotPresent) => {

                eprintln!("in test runner process, forking..,");

                let output = Command::new(env::current_exe().unwrap())

                    .args(["--nocapture", "replay::test::test_partial_write"])

                    .env(ENV_NAME, "1")

                    .output()

                    .unwrap();

                let print_output = |prefix, data| match std::str::from_utf8(data) {

                    Ok(s) => {

                        for l in s.split("\n") {

                            eprintln!(" {prefix} {l}");

                        }

                    }

                    Err(e) => eprintln!(" UTF-8 ERROR {prefix} {e}"),

                };

                print_output("!", &output.stdout);

                print_output(">", &output.stderr);

                let st = output.status;

                eprintln!("reaped actual test process {st:?} (expecting signal {GOOD_SIGNAL})");

                assert_eq!(st.signal(), Some(GOOD_SIGNAL));

                return;

            }

            Ok(y) if y == "1" => {}

            other => panic!("bad env var {ENV_NAME:?} {other:?}"),

        };

        // Now we are in our own process, and can mess about with ulimit etc.

        use std::fs;

        use std::mem::MaybeUninit;

        use std::ptr;

        fn set_ulimit(size: usize) {

            unsafe {

                use libc::RLIMIT_FSIZE;

                let mut rlim = libc::rlimit {

                    rlim_cur: 0,

                    rlim_max: 0,

                };

                let r = libc::getrlimit(RLIMIT_FSIZE, (&mut rlim) as _);

                assert_eq!(r, 0);

                rlim.rlim_cur = size.try_into().unwrap();

                let r = libc::setrlimit(RLIMIT_FSIZE, (&rlim) as _);

                assert_eq!(r, 0);

            }

        }

        // This test is quite complicated.

        //

        // We want to test partial writes.  We could perhaps have done this by

        // parameterising IptReplayLog so it could have something other than File,

        // but that would probably leak into the public API.

        //

        // Instead, we cause *actual* partial writes.  We use the Unix setrlimit

        // call to limit the size of files our process is allowed to write.

        // This causes the underlying write(2) calls to (i) generate SIGXFSZ

        // (ii) if that doesn't kill the process, return partial writes.

        test_temp_dir!().used_by(|dir| {

            let path = dir.join("test.log");

            let lock = LockFileGuard::lock(dir.join("dummy.lock")).unwrap();

            let lock = Arc::new(lock);

            let mut rl = TestReplayLog::new_logged_inner(&path, lock.clone()).unwrap();

            const BUF: usize = 8192; // BufWriter default; if that changes, test will break

            // We let ourselves write one whole buffer plus an odd amount of extra

            const ALLOW: usize = BUF + 37;

            // Ignore SIGXFSZ (default disposition is for exceeding the rlimit to kill us)

            unsafe {

                let sa = libc::sigaction {

                    sa_sigaction: libc::SIG_IGN,

                    sa_mask: sigemptyset(),

                    sa_flags: 0,

                    sa_restorer: None,

                };

                let r = libc::sigaction(libc::SIGXFSZ, (&sa) as _, ptr::null_mut());

                assert_eq!(r, 0);

            }

            let demand_efbig = |e| match e {

                // TODO MSRV 1.83: replace with io::ErrorKind::FileTooLarge?

                ReplayError::Log(e) if e.raw_os_error() == Some(libc::EFBIG) => {}

                other => panic!("expected EFBUG, got {other:?}"),

            };

            // Generate a distinct message given a phase and a counter

            #[allow(clippy::identity_op)]

            let mk_msg = |phase: u8, i: usize| {

                let i = u32::try_from(i).unwrap();

                let mut msg = [0_u8; OUTPUT_LEN];

                msg[0] = phase;

                msg[1] = phase;

                msg[4] = (i >> 24) as _;

                msg[5] = (i >> 16) as _;

                msg[6] = (i >> 8) as _;

                msg[7] = (i >> 0) as _;

                msg

            };

            // Number of hashes we can write to the file before failure occurs

            const CAN_DO: usize = (ALLOW + BUF - MAGIC_LEN) / OUTPUT_LEN;

            dbg!(MAGIC_LEN, OUTPUT_LEN, BUF, ALLOW, CAN_DO);

            // Record of the hashes that TestReplayLog tells us were OK and not replays;

            // ie, which it therefore ought to have recorded.

            let mut gave_ok = Vec::new();

            set_ulimit(ALLOW);

            for i in 0..CAN_DO {

                let h = mk_msg(b'y', i);

                rl.check_for_replay(&h).unwrap();

                gave_ok.push(h);

            }

            let md = fs::metadata(&path).unwrap();

            dbg!(md.len(), &rl.file);

            // Now we have written what we can.  The next two calls will fail,

            // since the BufWriter buffer is full and can't be flushed.

            for i in 0..2 {

                eprintln!("expecting EFBIG {i}");

                demand_efbig(rl.check_for_replay(&mk_msg(b'n', i)).unwrap_err());

                let md = fs::metadata(&path).unwrap();

                assert_eq!(md.len(), u64::try_from(ALLOW).unwrap());

            }

            // Enough that we don't get any further file size exceedances

            set_ulimit(ALLOW * 10);

            // Now we should be able to recover.  We write two more hashes.

            for i in 0..2 {

                eprintln!("recovering {i}");

                let h = mk_msg(b'r', i);

                rl.check_for_replay(&h).unwrap();

                gave_ok.push(h);

            }

            // flush explicitly just so we catch any error

            // (drop would flush, but it can't report errors)

            rl.flush().unwrap();

            drop(rl);

            // Reopen the log - reading in the written data.

            // We can then check that everything the earlier IptReplayLog

            // claimed to have written, is indeed recorded.

            let mut rl = TestReplayLog::new_logged_inner(&path, lock.clone()).unwrap();

            for msg in &gave_ok {

                match rl.check_for_replay(msg) {

                    Err(ReplayError::AlreadySeen) => {}

                    other => panic!("expected AlreadySeen, got {other:?}"),

                }

            }

            eprintln!("recovered file contents checked, all good");

        });

        unsafe {

            libc::raise(libc::SIGUSR2);

        }

        panic!("we survived raise SIGUSR2");

    }

}