//! Code for building paths for HS circuits.

//!

//! The path builders defined here are used for creating hidden service circuit stems.

//! A circuit stem is the beginning portion of a hidden service circuit,

//! the structure of which depends on the types of vanguards, if any, that are in use.

//!

//! There are two types of circuit stems:

//!   * naive circuit stems, used for building circuits to a final hop that an adversary

//!     cannot easily control (for example if the target is randomly chosen by us)

//!   * guarded circuit stems, used for building circuits to a final hop that an adversary

//!     can easily control (for example if the target was not chosen by us)

//!

//! Circuit stems eventually become introduction, rendezvous, and HsDir circuits.

//! For all circuit types except client rendezvous, the stems must first be

//! extended by an extra hop:

//!

//! ```text

//!  Client hsdir:  GUARDED -> HsDir

//!  Client intro:  GUARDED -> Ipt

//!  Client rend:   GUARDED

//!  Service hsdir: NAIVE   -> HsDir

//!  Service intro: NAIVE   -> Ipt

//!  Service rend:  GUARDED -> Rpt

//! ```

//!

//! > Note: the client rendezvous case is an exception to this rule:

//! > the rendezvous point is selected by the client, so it cannot easily be

//! > controlled by an attacker.

//! >

//! > This type of circuit would more accurately be described as a NAIVE circuit

//! > that gets extended by an extra hop if Full-Vanguards are in use

//! > (this is necessary to avoid using the L3 guard as a rendezvous point).

//! > However, for the sake of simplicity, we define these circuits in terms of

//! > GUARDED.

//! >

//! > Note: in the client rendezvous case, the last node from the GUARDED

//! > circuit stem is the rendezvous point.

//!

//! If vanguards are disabled, naive circuit stems (NAIVE),

//! and guarded circuit stems (GUARDED) are the same,

//! and are built using

//! [`ExitPathBuilder`](crate::path::exitpath::ExitPathBuilder)'s

//! path selection rules.

//!

//! If vanguards are enabled, the path is built without applying family

//! or same-subnet restrictions at all, the guard is not prohibited

//! from appearing as either of the last two hops of the circuit,

//! and the two circuit stem kinds are built differently

//! depending on the type of vanguards that are in use:

//!

//!   * with lite vanguards enabled:

//!      ```text

//!         NAIVE   = G -> L2 -> M

//!         GUARDED = G -> L2 -> M

//!      ```

//!

//!   * with full vanguards enabled:

//!      ```text

//!         NAIVE   = G -> L2 -> L3

//!         GUARDED = G -> L2 -> L3 -> M

//!      ```

#[cfg(feature = "vanguards")]

mod vanguards;

use rand::Rng;

use tor_error::internal;

use tor_linkspec::{HasRelayIds, OwnedChanTarget};

use tor_netdir::{NetDir, Relay};

use tor_relay_selection::{RelayExclusion, RelaySelectionConfig, RelaySelector, RelayUsage};

use crate::{hspool::HsCircKind, hspool::HsCircStemKind, Error, Result};

use super::AnonymousPathBuilder;

use {

    crate::path::{pick_path, TorPath},

    crate::{DirInfo, PathConfig},

    std::time::SystemTime,

    tor_guardmgr::{GuardMgr, GuardMonitor, GuardUsable},

    tor_rtcompat::Runtime,

};

#[cfg(feature = "vanguards")]

use {

    crate::path::{select_guard, MaybeOwnedRelay},

    tor_error::bad_api_usage,

    tor_guardmgr::vanguards::Layer,

    tor_guardmgr::vanguards::VanguardMgr,

    tor_guardmgr::VanguardMode,

};

#[cfg(feature = "vanguards")]

pub(crate) use vanguards::select_middle_for_vanguard_circ;

/// A path builder for hidden service circuits.

///

/// See the [hspath](crate::path::hspath) docs for more details.

pub(crate) struct HsPathBuilder {

    /// If present, a "target" that every chosen relay must be able to share a circuit with with.

    ///

    /// Ignored if vanguards are in use.

    compatible_with: Option<OwnedChanTarget>,

    /// The type of circuit stem to build.

    ///

    /// This is only used if `vanguards` are enabled.

    #[cfg_attr(not(feature = "vanguards"), allow(dead_code))]

    stem_kind: HsCircStemKind,

    /// If present, ensure that the circuit stem is suitable for use as (a stem for) the given kind

    /// of circuit.

    circ_kind: Option<HsCircKind>,

}

impl HsPathBuilder {

    /// Create a new builder that will try to build a three-hop non-exit path

    /// for use with the onion services protocols

    /// that is compatible with being extended to an optional given relay.

    ///

    /// (The provided relay is _not_ included in the built path: we only ensure

    /// that the path we build does not have any features that would stop us

    /// extending it to that relay as a fourth hop.)

    /// Try to create and return a path for a hidden service circuit stem.

    #[cfg_attr(feature = "vanguards", allow(unused))]

    /// Try to create and return a path for a hidden service circuit stem.

    ///

    /// If vanguards are disabled, this has the same behavior as

    /// [pick_path](HsPathBuilder::pick_path).

    #[cfg(feature = "vanguards")]

    #[cfg_attr(not(feature = "vanguards"), allow(unused))]

}

impl AnonymousPathBuilder for HsPathBuilder {

}

/// A path builder for hidden service circuits that use vanguards.

///

/// Used by [`HsPathBuilder`] when vanguards are enabled.

///

/// See the [`HsPathBuilder`] documentation for more details.

#[cfg(feature = "vanguards")]

struct VanguardHsPathBuilder {

    /// The kind of circuit stem we are building

    stem_kind: HsCircStemKind,

    /// If present, ensure that the circuit stem is suitable for use as (a stem for) the given kind

    /// of circuit.

    circ_kind: Option<HsCircKind>,

    /// The target we are about to extend the circuit to.

    compatible_with: Option<OwnedChanTarget>,

}

#[cfg(feature = "vanguards")]

impl VanguardHsPathBuilder {

    /// Try to create and return a path for a hidden service circuit stem.

            _ => {

            }

        };

        // Select the guard, allowing it to appear as

        // either of the last two hops of the circuit.

        } else {

        };

            VanguardMode::Lite => {

            }

            VanguardMode::Full => {

            }

            VanguardMode::Disabled => {

            }

            _ => {

            }

        };

    /// Create a path for a hidden service circuit stem using full vanguards.

        // NOTE: if the we are using full vanguards and building an GUARDED circuit stem,

        // we do *not* exclude the target from occurring as the second hop

        // (circuits of the form G - L2 - L3 - M - L2 are valid)

        };

        // We have to pick the usage based on whether this hop is the last one of the stem.

        };

            HsCircStemKind::Guarded => {

                // If full vanguards are enabled, we need an extra hop for the GUARDED stem:

                //     NAIVE   = G -> L2 -> L3

                //     GUARDED = G -> L2 -> L3 -> M

            }

        }

    /// Create a path for a hidden service circuit stem using lite vanguards.

}

/// Return the usage that we should use when selecting an intermediary hop (vanguard or middle) of

/// an HS circuit or stem circuit.

///

/// (This isn't called "middle hop", since we want to avoid confusion with the M hop in vanguard

/// circuits.)

/// Return the usage that we should use when selecting the last hop of a stem circuit.

///

/// If `kind` is provided, we need to make sure that the last hop will yield a stem circuit

/// that's fit for that kind of circuit.

        // For unknown HsCircKinds, we'll pick an arbitrary last hop, and check later

        // that it is really suitable for whatever purpose we had in mind.

    };

        HsCircKind::ClientRend => {

            // This stem circuit going to get used as-is for a ClientRend circuit,

            // and so the last hop of the stem circuit needs to be suitable as a rendezvous point.

        }

        HsCircKind::SvcHsDir

        | HsCircKind::SvcIntro

        | HsCircKind::SvcRend

        | HsCircKind::ClientHsDir

        | HsCircKind::ClientIntro => {

            // For all other HSCircKind cases, the last hop will be added to the stem,

            // so we have no additional restrictions on the usage.

        }

    }

#[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 std::sync::Arc;

    use super::*;

    use tor_linkspec::{ChannelMethod, OwnedCircTarget};

    use tor_netdir::{testnet::NodeBuilders, testprovider::TestNetDirProvider, NetDirProvider};

    use tor_netdoc::doc::netstatus::{RelayFlags, RelayWeight};

    use tor_rtmock::MockRuntime;

    #[cfg(all(feature = "vanguards", feature = "hs-common"))]

    use {

        crate::path::OwnedPath, tor_basic_utils::test_rng::testing_rng,

        tor_guardmgr::VanguardMgrError, tor_netdir::testnet::construct_custom_netdir,

    };

    /// The maximum number of relays in a test network.

    const MAX_NET_SIZE: usize = 40;

    /// Construct a test network of the specified size.

    fn construct_test_network<F>(size: usize, mut set_family: F) -> NetDir

    where

        F: FnMut(usize, &mut NodeBuilders),

    {

        assert!(

            size <= MAX_NET_SIZE,

            "the test network supports at most {MAX_NET_SIZE} relays"

        );

        let netdir = construct_custom_netdir(|pos, nb, _| {

            nb.omit_rs = pos >= size;

            if !nb.omit_rs {

                let f = RelayFlags::RUNNING

                    | RelayFlags::VALID

                    | RelayFlags::V2DIR

                    | RelayFlags::FAST

                    | RelayFlags::STABLE;

                nb.rs.set_flags(f | RelayFlags::GUARD);

                nb.rs.weight(RelayWeight::Measured(10_000));

                set_family(pos, nb);

            }

        })

        .unwrap()

        .unwrap_if_sufficient()

        .unwrap();

        assert_eq!(netdir.all_relays().count(), size);

        netdir

    }

    /// Construct a test network where every relay is in the same family with everyone else.

    fn same_family_test_network(size: usize) -> NetDir {

        construct_test_network(size, |_pos, nb| {

            // Everybody is in the same family with everyone else

            let family = (0..MAX_NET_SIZE)

                .map(|i| hex::encode([i as u8; 20]))

                .collect::<Vec<_>>()

                .join(" ");

            nb.md.family(family.parse().unwrap());

        })

    }

    /// Helper for extracting the hops in a `TorPath`.

    fn path_hops(path: &TorPath) -> Vec<OwnedCircTarget> {

        let path: OwnedPath = path.try_into().unwrap();

        match path {

            OwnedPath::ChannelOnly(_) => {

                panic!("expected OwnedPath::Normal, got OwnedPath::ChannelOnly")

            }

            OwnedPath::Normal(ref v) => v.clone(),

        }

    }

    /// Check the uniqueness of the hops from the specified `TorPath`.

    ///

    /// If `expect_dupes` is `true`, asserts that the path has some duplicate hops.

    /// Otherwise, asserts that there are no duplicate hops in the path.

    fn assert_duplicate_hops(path: &TorPath, expect_dupes: bool) {

        let hops = path_hops(path);

        let has_dupes = hops.iter().enumerate().any(|(i, hop)| {

            hops.iter()

                .skip(i + 1)

                .any(|h| h.has_any_relay_id_from(hop))

        });

        let msg = if expect_dupes { "have" } else { "not have any" };

        assert_eq!(

            has_dupes, expect_dupes,

            "expected path to {msg} duplicate hops: {:?}",

            hops

        );

    }

    /// Assert that the specified `TorPath` is a valid path for a circuit using vanguards.

    #[cfg(feature = "vanguards")]

    fn assert_vanguard_path_ok(

        path: &TorPath,

        stem_kind: HsCircStemKind,

        mode: VanguardMode,

        target: Option<&OwnedChanTarget>,

    ) {

        use itertools::Itertools;

        assert_eq!(

            path.len(),

            stem_kind.num_hops(mode).unwrap(),

            "invalid path length for {stem_kind} {mode}-vanguards circuit"

        );

        let hops = path_hops(path);

        for (hop1, hop2, hop3) in hops.iter().tuple_windows() {

            if hop1.has_any_relay_id_from(hop2)

                || hop1.has_any_relay_id_from(hop3)

                || hop2.has_any_relay_id_from(hop3)

            {

                panic!(

                    "neighboring hops should be distinct: [{}], [{}], [{}]",

                    hop1.display_relay_ids(),

                    hop2.display_relay_ids(),

                    hop3.display_relay_ids(),

                );

            }

        }

        // If the circuit had a target, make sure its last 2 hops are compatible with it.

        if let Some(target) = target {

            for hop in hops.iter().rev().take(2) {

                if hop.has_any_relay_id_from(target) {

                    panic!(

                        "invalid path: circuit target {} appears as one of the last 2 hops (matches hop {})",

                        hop.display_relay_ids(),

                        target.display_relay_ids(),

                    );

                }

            }

        }

    }

    /// Assert that the specified `TorPath` is a valid HS path.

    fn assert_hs_path_ok(path: &TorPath, target: Option<&OwnedChanTarget>) {

        assert_eq!(path.len(), 3);

        assert_duplicate_hops(path, false);

        if let Some(target) = target {

            for hop in path_hops(path) {

                if hop.has_any_relay_id_from(target) {

                    panic!(

                        "invalid path: hop {} is the same relay as the circuit target {}",

                        hop.display_relay_ids(),

                        target.display_relay_ids()

                    )

                }

            }

        }

    }

    /// Helper for calling `HsPathBuilder::pick_path_with_vanguards`.

    async fn pick_vanguard_path<'a>(

        runtime: &MockRuntime,

        netdir: &'a NetDir,

        stem_kind: HsCircStemKind,

        circ_kind: Option<HsCircKind>,

        mode: VanguardMode,

        target: Option<&OwnedChanTarget>,

    ) -> Result<TorPath<'a>> {

        let vanguardmgr = VanguardMgr::new_testing(runtime, mode).unwrap();

        let _provider = vanguardmgr.init_vanguard_sets(netdir).await.unwrap();

        let mut rng = testing_rng();

        let guards = tor_guardmgr::GuardMgr::new(

            runtime.clone(),

            tor_persist::TestingStateMgr::new(),

            &tor_guardmgr::TestConfig::default(),

        )

        .unwrap();

        let netdir_provider = Arc::new(TestNetDirProvider::new());

        netdir_provider.set_netdir(netdir.clone());

        let netdir_provider: Arc<dyn NetDirProvider> = netdir_provider;

        guards.install_netdir_provider(&netdir_provider).unwrap();

        let config = PathConfig::default();

        let now = SystemTime::now();

        let dirinfo = (netdir).into();

        HsPathBuilder::new(target.cloned(), stem_kind, circ_kind)

            .pick_path_with_vanguards(&mut rng, dirinfo, &guards, &vanguardmgr, &config, now)

            .map(|res| res.0)

    }

    /// Helper for calling `HsPathBuilder::pick_path`.

    fn pick_hs_path_no_vanguards<'a>(

        netdir: &'a NetDir,

        target: Option<&OwnedChanTarget>,

        circ_kind: Option<HsCircKind>,

    ) -> Result<TorPath<'a>> {

        let mut rng = testing_rng();

        let config = PathConfig::default();

        let now = SystemTime::now();

        let dirinfo = (netdir).into();

        let guards = tor_guardmgr::GuardMgr::new(

            MockRuntime::new(),

            tor_persist::TestingStateMgr::new(),

            &tor_guardmgr::TestConfig::default(),

        )

        .unwrap();

        let netdir_provider = Arc::new(TestNetDirProvider::new());

        netdir_provider.set_netdir(netdir.clone());

        let netdir_provider: Arc<dyn NetDirProvider> = netdir_provider;

        guards.install_netdir_provider(&netdir_provider).unwrap();

        HsPathBuilder::new(target.cloned(), HsCircStemKind::Naive, circ_kind)

            .pick_path(&mut rng, dirinfo, &guards, &config, now)

            .map(|res| res.0)

    }

    /// Return an `OwnedChanTarget` to use as the target of a circuit.

    ///

    /// This will correspond to the "first" relay from the test network

    /// (the one with the $0000000000000000000000000000000000000000

    /// RSA identity fingerprint).

    fn test_target() -> OwnedChanTarget {

        // We target one of the relays known to be the network.

        OwnedChanTarget::builder()

            .addrs(vec!["127.0.0.3:9001".parse().unwrap()])

            .ed_identity([0xAA; 32].into())

            .rsa_identity([0x00; 20].into())

            .method(ChannelMethod::Direct(vec!["0.0.0.3:9001".parse().unwrap()]))

            .build()

            .unwrap()

    }

    // Prevents TROVE-2024-006 (arti#1425).

    //

    // Note: this, and all the other tests that disable vanguards,

    // perhaps belong in ExitPathBuilder, as they are are effectively

    // testing the vanilla pick_path() implementation.

    #[test]

    fn hs_path_no_vanguards_incompatible_target() {

        // We target one of the relays known to be the network.

        let target = test_target();

        let netdir = construct_test_network(3, |pos, nb| {

            // The target is in a family with every other relay,

            // so any circuit we might build is going to be incompatible with it

            if pos == 0 {

                let family = (0..MAX_NET_SIZE)

                    .map(|i| hex::encode([i as u8; 20]))

                    .collect::<Vec<_>>()

                    .join(" ");

                nb.md.family(family.parse().unwrap());

            } else {

                nb.md.family(hex::encode([pos as u8; 20]).parse().unwrap());

            }

        });

        // We'll fail to select a guard, because the network doesn't have any relays compatible

        // with the target

        let err = pick_hs_path_no_vanguards(&netdir, Some(&target), None)

            .map(|_| ())

            .unwrap_err();

        assert!(

            matches!(

                err,

                Error::NoRelay {

                    ref problem,

                    ..

                } if problem ==  "Failed: rejected 0/3 as not usable as middle relay; 3/3 as in same family as already selected"

            ),

            "{err:?}"

        );

    }

    #[test]

    fn hs_path_no_vanguards_reject_same_family() {

        // All the relays in the network are in the same family,

        // so building HS circuits should be impossible.

        let netdir = same_family_test_network(MAX_NET_SIZE);

        let err = match pick_hs_path_no_vanguards(&netdir, None, None) {

            Ok(path) => panic!(

                "expected error, but got valid path: {:?})",

                OwnedPath::try_from(&path).unwrap()

            ),

            Err(e) => e,

        };

        assert!(

            matches!(

                err,

                Error::NoRelay {

                    ref problem,

                    ..

                } if problem ==  "Failed: rejected 0/40 as not usable as middle relay; 40/40 as in same family as already selected"

            ),

            "{err:?}"

        );

    }

    #[test]

    fn hs_path_no_vanguards() {

        let netdir = construct_test_network(20, |pos, nb| {

            nb.md.family(hex::encode([pos as u8; 20]).parse().unwrap());

        });

        // We target one of the relays known to be the network.

        let target = test_target();

        for _ in 0..100 {

            for target in [None, Some(target.clone())] {

                let path = pick_hs_path_no_vanguards(&netdir, target.as_ref(), None).unwrap();

                assert_hs_path_ok(&path, target.as_ref());

            }

        }

    }

    #[test]

    #[cfg(feature = "vanguards")]

    fn lite_vanguard_path_insufficient_relays() {

        MockRuntime::test_with_various(|runtime| async move {

            let netdir = same_family_test_network(2);

            for stem_kind in [HsCircStemKind::Naive, HsCircStemKind::Guarded] {

                let err = pick_vanguard_path(

                    &runtime,

                    &netdir,

                    stem_kind,

                    None,

                    VanguardMode::Lite,

                    None,

                )

                .await

                .map(|_| ())

                .unwrap_err();

                // The test network is too small to build a 3-hop circuit.

                assert!(

                    matches!(

                        err,

                        Error::NoRelay {

                            ref problem,

                            ..

                        } if problem == "Failed: rejected 0/2 as not usable as middle relay; 2/2 as already selected",

                    ),

                    "{err:?}"

                );

            }

        });

    }

    // Prevents TROVE-2024-003 (arti#1409).

    #[test]

    #[cfg(feature = "vanguards")]

    fn lite_vanguard_path() {

        MockRuntime::test_with_various(|runtime| async move {

            // We target one of the relays known to be the network.

            let target = OwnedChanTarget::builder()

                .rsa_identity([0x00; 20].into())

                .build()

                .unwrap();

            let netdir = same_family_test_network(10);

            let mode = VanguardMode::Lite;

            for target in [None, Some(target)] {

                for stem_kind in [HsCircStemKind::Naive, HsCircStemKind::Guarded] {

                    let path = pick_vanguard_path(

                        &runtime,

                        &netdir,

                        stem_kind,

                        None,

                        mode,

                        target.as_ref(),

                    )

                    .await

                    .unwrap();

                    assert_vanguard_path_ok(&path, stem_kind, mode, target.as_ref());

                }

            }

        });

    }

    #[test]

    #[cfg(feature = "vanguards")]

    fn full_vanguard_path() {

        MockRuntime::test_with_various(|runtime| async move {

            let netdir = same_family_test_network(MAX_NET_SIZE);

            let mode = VanguardMode::Full;

            // We target one of the relays known to be the network.

            let target = OwnedChanTarget::builder()

                .rsa_identity([0x00; 20].into())

                .build()

                .unwrap();

            for target in [None, Some(target)] {

                for stem_kind in [HsCircStemKind::Naive, HsCircStemKind::Guarded] {

                    let path = pick_vanguard_path(

                        &runtime,

                        &netdir,

                        stem_kind,

                        None,

                        mode,

                        target.as_ref(),

                    )

                    .await

                    .unwrap();

                    assert_vanguard_path_ok(&path, stem_kind, mode, target.as_ref());

                }

            }

        });

    }

    #[test]

    #[cfg(feature = "vanguards")]

    fn full_vanguard_path_insufficient_relays() {

        MockRuntime::test_with_various(|runtime| async move {

            let netdir = same_family_test_network(2);

            for stem_kind in [HsCircStemKind::Naive, HsCircStemKind::Guarded] {

                let err = pick_vanguard_path(

                    &runtime,

                    &netdir,

                    stem_kind,

                    None,

                    VanguardMode::Full,

                    None,

                )

                .await

                .map(|_| ())

                .unwrap_err();

                assert!(

                    matches!(

                        err,

                        Error::VanguardMgrInit(VanguardMgrError::NoSuitableRelay(Layer::Layer3)),

                    ),

                    "{err:?}"

                );

            }

            // We *can* build circuit stems in a 3-relay network,

            // as long as they don't have a specified target

            let netdir = same_family_test_network(3);

            let mode = VanguardMode::Full;

            for stem_kind in [HsCircStemKind::Naive, HsCircStemKind::Guarded] {

                let path = pick_vanguard_path(&runtime, &netdir, stem_kind, None, mode, None)

                    .await

                    .unwrap();

                assert_vanguard_path_ok(&path, stem_kind, mode, None);

                match stem_kind {

                    HsCircStemKind::Naive => {

                        // A 3-hop circuit can't contain duplicates,

                        // because that would mean it has one of the following

                        // configurations

                        //

                        //     A - A - A

                        //     A - A - B

                        //     A - B - A

                        //     A - B - B

                        //     B - A - A

                        //     B - A - B

                        //     B - B - A

                        //     B - B - B

                        //

                        // none of which are valid circuits, because a relay won't extend

                        // to itself or its predecessor.

                        assert_duplicate_hops(&path, false);

                    }

                    HsCircStemKind::Guarded => {

                        // There are only 3 relats in the network,

                        // so a 4-hop circuit must contain the same hop twice.

                        assert_duplicate_hops(&path, true);

                    }

                }

            }

        });

    }

}