darkfi/src/net/hosts/store.rs

/* This file is part of DarkFi (https://dark.fi)
 *
 * Copyright (C) 2020-2024 Dyne.org foundation
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

use std::{
    collections::{HashMap, HashSet},
    fmt, fs,
    fs::File,
    sync::Arc,
    time::{Instant, UNIX_EPOCH},
};

use log::{debug, error, info, trace, warn};
use rand::{prelude::IteratorRandom, rngs::OsRng, Rng};
use smol::lock::RwLock;
use url::Url;

use super::super::{settings::SettingsPtr, ChannelPtr};
use crate::{
    system::{Subscriber, SubscriberPtr, Subscription},
    util::{
        file::{load_file, save_file},
        path::expand_path,
    },
    Error, Result,
};

/// Atomic pointer to hosts object
pub type HostsPtr = Arc<Hosts>;

/// Keeps track of hosts and their current state. Prevents race conditions
/// where multiple threads are simultaenously trying to change the state of
/// a given host.
pub type HostRegistry = RwLock<HashMap<Url, HostState>>;

/// HostState is a set of mutually exclusive states that can be Pending,
/// Connected, Disconnected or Refining. The state is `None` when the
/// corresponding host has been removed from the HostRegistry.
///
///                              +----------+
///                          +-- | refining | --+
///                          |   +----------+   |
///                          |                  |
///                          v                  v
///          +---------+    +-----------+    +------+
///          | pending | -> | connected | -> | None |
///          +---------+    +-----------+    +------+
///               |                             ^
///               |                             |
///               |       +-------------+       |
///               +-----> | downgrading | ------+
///                       +-------------+
///
#[derive(Clone, Debug)]
pub enum HostState {
    /// Hosts that are being connected to in Outbound and Manual Session.
    Pending,
    /// Hosts that have been successfully connected to.
    Connected(ChannelPtr),
    /// Hosts that we have repeatedly failed to connect to, and that are being
    /// removed from the anchorlist and whitelist and added to the greylist.
    Downgrading,
    /// Hosts that are migrating from the greylist to the whitelist or being
    /// removed from the greylist, as defined in `refinery.rs`.
    Refining,
}

impl HostState {
    // Try to change state to Downgrading. Only possible if this
    // connection is pending i.e. if we are trying to connect to this
    // host.
    fn try_downgrade(&self) -> Result<Self> {
        match self {
            HostState::Pending => Ok(HostState::Downgrading),
            HostState::Connected(_) => Err(Error::StateBlocked(self.to_string())),
            HostState::Downgrading => Err(Error::StateBlocked(self.to_string())),
            HostState::Refining => Err(Error::StateBlocked(self.to_string())),
        }
    }

    // Try to change state to Refining. Only possible if we are not yet
    // tracking this host in the HostRegistry.
    fn try_refine(&self) -> Result<Self> {
        match self {
            HostState::Pending => Err(Error::StateBlocked(self.to_string())),
            HostState::Connected(_) => Err(Error::StateBlocked(self.to_string())),
            HostState::Downgrading => Err(Error::StateBlocked(self.to_string())),
            HostState::Refining => Err(Error::StateBlocked(self.to_string())),
        }
    }

    // Try to change state to Connected. Possible if this peer is
    // currently Pending or being Refined. The latter is necessary since
    // the refinery process requires us to establish a connection to
    // a peer.
    fn try_connect(&self, channel: ChannelPtr) -> Result<Self> {
        match self {
            HostState::Pending => Ok(HostState::Connected(channel)),
            HostState::Connected(_) => Err(Error::StateBlocked(self.to_string())),
            HostState::Downgrading => Err(Error::StateBlocked(self.to_string())),
            HostState::Refining => Ok(HostState::Connected(channel)),
        }
    }

    // Try to change state to Pending. Only possible if we are not yet
    // tracking this host in the HostRegistry.
    fn try_pending(&self) -> Result<Self> {
        match self {
            HostState::Pending => Err(Error::StateBlocked(self.to_string())),
            HostState::Connected(_) => Err(Error::StateBlocked(self.to_string())),
            HostState::Downgrading => Err(Error::StateBlocked(self.to_string())),
            HostState::Refining => Err(Error::StateBlocked(self.to_string())),
        }
    }
}
impl fmt::Display for HostState {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Debug::fmt(self, f)
    }
}

// An array containing all possible local host strings
// TODO: This could perhaps be more exhaustive?
pub const LOCAL_HOST_STRS: [&str; 2] = ["localhost", "localhost.localdomain"];
const WHITELIST_MAX_LEN: usize = 5000;
const GREYLIST_MAX_LEN: usize = 2000;

/// Manages a store of network addresses
// TODO: Test the performance overhead of using vectors for white/grey/anchor lists.
// TODO: Check whether anchorlist has a max size in Monero.
// TODO: we can probably clean up a lot of the repetitive code in this module.
pub struct Hosts {
    /// Intermediary node list that is periodically probed and updated to whitelist.
    pub greylist: RwLock<Vec<(Url, u64)>>,

    /// Recently seen hosts. Shared with other nodes.
    pub whitelist: RwLock<Vec<(Url, u64)>>,

    /// Nodes to which we have already been able to establish a connection.
    pub anchorlist: RwLock<Vec<(Url, u64)>>,

    /// Subscriber for notifications of new channels
    channel_subscriber: SubscriberPtr<Result<ChannelPtr>>,

    /// Set of stored addresses that are quarantined.
    /// We quarantine peers we've been unable to connect to, but we keep them
    /// around so we can potentially try them again, up to n tries. This should
    /// be helpful in order to self-heal the p2p connections in case we have an
    /// Internet interrupt (goblins unplugging cables)
    quarantine: RwLock<HashMap<Url, usize>>,

    /// A registry that tracks hosts and their current state.
    registry: HostRegistry,

    /// Peers on the blacklist are considered hostile and can neither be connected to
    /// nor establish connections to us for the duration of the program.
    blacklist: RwLock<HashSet<String>>,

    /// Subscriber listening for store updates
    store_subscriber: SubscriberPtr<usize>,

    /// Pointer to configured P2P settings
    settings: SettingsPtr,
}

impl Hosts {
    /// Create a new hosts list>
    pub fn new(settings: SettingsPtr) -> HostsPtr {
        Arc::new(Self {
            greylist: RwLock::new(Vec::new()),
            whitelist: RwLock::new(Vec::new()),
            anchorlist: RwLock::new(Vec::new()),
            channel_subscriber: Subscriber::new(),
            quarantine: RwLock::new(HashMap::new()),
            registry: RwLock::new(HashMap::new()),
            blacklist: RwLock::new(HashSet::new()),
            store_subscriber: Subscriber::new(),
            settings,
        })
    }

    /// Try to update the registry. If the host already exists, try to update its state.
    /// Otherwise add the host to the registry along with its state.
    pub async fn try_update_registry(&self, addr: Url, new_state: HostState) -> Result<HostState> {
        let mut registry = self.registry.write().await;

        if registry.contains_key(&addr) {
            let current_state = registry.get(&addr).unwrap().clone();

            debug!(target: "store::try_update_registry()",
            "Attempting to update addr={} current_state={}, new_state={}",
            addr, current_state, new_state.to_string());

            let result: Result<HostState> = match new_state {
                HostState::Pending => current_state.try_pending(),
                HostState::Connected(c) => current_state.try_connect(c),
                HostState::Downgrading => current_state.try_downgrade(),
                HostState::Refining => current_state.try_refine(),
            };

            if let Ok(state) = &result {
                registry.insert(addr.clone(), state.clone());
            }

            result
        } else {
            // We don't know this peer. We can safely update the state.
            registry.insert(addr.clone(), new_state.clone());

            Ok(new_state)
        }
    }

    pub async fn check_address(&self, hosts: Vec<(Url, u64)>) -> Option<(Url, u64)> {
        // Try to find an unused host in the set.
        for (host, last_seen) in hosts {
            debug!(target: "store::check_address()", "Starting checks");

            if let Err(_) = self.try_update_registry(host.clone(), HostState::Pending).await {
                continue
            }

            debug!(
                target: "store::check_address()",
                "Found valid host {}",
                host
            );
            return Some((host.clone(), last_seen))
        }

        None
    }

    /// Remove a host from the HostRegistry. Must be called after downgrade(), when the refinery
    /// process fails, or when a channel stops. Prevents hosts from getting trapped in the
    /// HostState logical machinery.
    pub async fn remove(&self, addr: &Url) {
        debug!(target: "store", "remove() Removing {} from HostRegistry", addr);
        self.registry.write().await.remove(addr);
    }

    /// Returns the list of connected channels.
    pub async fn channels(&self) -> Vec<ChannelPtr> {
        let registry = self.registry.read().await;
        let mut channels = Vec::new();

        for (_, value) in registry.iter() {
            if let HostState::Connected(c) = value {
                channels.push(c.clone());
            }
        }
        channels
    }

    /// Retrieve a random connected channel
    pub async fn random_channel(&self) -> ChannelPtr {
        let channels = self.channels().await;
        let position = rand::thread_rng().gen_range(0..channels.len());
        channels[position].clone()
    }

    /// Add a channel to the set of connected channels
    pub async fn store(&self, channel: ChannelPtr) -> Result<()> {
        let address = channel.address().clone();

        if let Err(e) =
            self.try_update_registry(address.clone(), HostState::Connected(channel.clone())).await
        {
            return Err(e)
        }

        self.channel_subscriber.notify(Ok(channel)).await;
        Ok(())
    }

    /// Loops through greylist addresses to find an outbound address that we can
    /// connect to. Check whether the address is valid by making sure it isn't
    /// our own inbound address, then checks whether it is already connected
    /// (exists) or connecting (pending).
    /// Lastly adds matching address to the pending list.
    pub async fn greylist_fetch_address(&self, transports: &[String]) -> Vec<(Url, u64)> {
        trace!(target: "store", "greylist_fetch_address() [START]");
        // Collect hosts
        let mut hosts = vec![];

        // If transport mixing is enabled, then for example we're allowed to
        // use tor:// to connect to tcp:// and tor+tls:// to connect to tcp+tls://.
        // However, **do not** mix tor:// and tcp+tls://, nor tor+tls:// and tcp://.
        let transport_mixing = self.settings.transport_mixing;
        macro_rules! mix_transport {
            ($a:expr, $b:expr) => {
                if transports.contains(&$a.to_string()) && transport_mixing {
                    let mut a_to_b =
                        self.greylist_fetch_with_schemes(&[$b.to_string()], None).await;
                    for (addr, last_seen) in a_to_b.iter_mut() {
                        addr.set_scheme($a).unwrap();
                        hosts.push((addr.clone(), last_seen.clone()));
                    }
                }
            };
        }
        mix_transport!("tor", "tcp");
        mix_transport!("tor+tls", "tcp+tls");
        mix_transport!("nym", "tcp");
        mix_transport!("nym+tls", "tcp+tls");

        // And now the actual requested transports
        for (addr, last_seen) in self.greylist_fetch_with_schemes(transports, None).await {
            hosts.push((addr, last_seen));
        }

        hosts
    }

    /// Loops through whitelist addresses to find an outbound address that we can
    /// connect to. Check whether the address is valid by making sure it isn't
    /// our own inbound address, then checks whether it is already connected
    /// (exists) or connecting (pending).
    /// Lastly adds matching address to the pending list.
    pub async fn whitelist_fetch_address(&self, transports: &[String]) -> Vec<(Url, u64)> {
        trace!(target: "store", "whitelist_fetch_address() [START]");
        // Collect hosts
        let mut hosts = vec![];

        // If transport mixing is enabled, then for example we're allowed to
        // use tor:// to connect to tcp:// and tor+tls:// to connect to tcp+tls://.
        // However, **do not** mix tor:// and tcp+tls://, nor tor+tls:// and tcp://.
        let transport_mixing = self.settings.transport_mixing;
        macro_rules! mix_transport {
            ($a:expr, $b:expr) => {
                if transports.contains(&$a.to_string()) && transport_mixing {
                    let mut a_to_b =
                        self.whitelist_fetch_with_schemes(&[$b.to_string()], None).await;
                    for (addr, last_seen) in a_to_b.iter_mut() {
                        addr.set_scheme($a).unwrap();
                        hosts.push((addr.clone(), last_seen.clone()));
                    }
                }
            };
        }
        mix_transport!("tor", "tcp");
        mix_transport!("tor+tls", "tcp+tls");
        mix_transport!("nym", "tcp");
        mix_transport!("nym+tls", "tcp+tls");

        // And now the actual requested transports
        for (addr, last_seen) in self.whitelist_fetch_with_schemes(transports, None).await {
            hosts.push((addr, last_seen));
        }

        trace!(target: "store::whitelist_fetch_address()",
        "Grabbed hosts, length: {}", hosts.len());

        hosts
    }

    /// Loops through anchorlist addresses to find an outbound address that we can
    /// connect to. Check whether the address is valid by making sure it isn't
    /// our own inbound address, then checks whether it is already connected
    /// (exists) or connecting (pending).
    /// Lastly adds matching address to the pending list.
    pub async fn anchorlist_fetch_address(&self, transports: &[String]) -> Vec<(Url, u64)> {
        trace!(target: "store", "anchorlist_fetch_address() [START]");
        // Collect hosts
        let mut hosts = vec![];

        // If transport mixing is enabled, then for example we're allowed to
        // use tor:// to connect to tcp:// and tor+tls:// to connect to tcp+tls://.
        // However, **do not** mix tor:// and tcp+tls://, nor tor+tls:// and tcp://.
        let transport_mixing = self.settings.transport_mixing;
        macro_rules! mix_transport {
            ($a:expr, $b:expr) => {
                if transports.contains(&$a.to_string()) && transport_mixing {
                    let mut a_to_b =
                        self.anchorlist_fetch_with_schemes(&[$b.to_string()], None).await;
                    for (addr, last_seen) in a_to_b.iter_mut() {
                        addr.set_scheme($a).unwrap();
                        hosts.push((addr.clone(), last_seen.clone()));
                    }
                }
            };
        }
        mix_transport!("tor", "tcp");
        mix_transport!("tor+tls", "tcp+tls");
        mix_transport!("nym", "tcp");
        mix_transport!("nym+tls", "tcp+tls");

        // And now the actual requested transports
        for (addr, last_seen) in self.anchorlist_fetch_with_schemes(transports, None).await {
            hosts.push((addr, last_seen));
        }

        trace!(target: "store::anchorlist_fetch_address()",
        "Grabbed hosts, length: {}", hosts.len());

        hosts
    }

    /// Upgrade a connection to the anchorlist. Called after a connection has been successfully
    /// established in Outbound and Manual sessions.
    pub async fn upgrade_host(&self, addr: &Url) {
        let last_seen = UNIX_EPOCH.elapsed().unwrap().as_secs();
        self.anchorlist_store_or_update(&[(addr.clone(), last_seen)]).await;
    }

    /// Downgrade a host to greylist. If the host is on the anchorlist or whitelist, remove it.
    /// If it's already on the greylist we can't do anything here.
    pub async fn downgrade_host(&self, addr: &Url, last_seen: u64) {
        if let Err(_) = self.try_update_registry(addr.clone(), HostState::Downgrading).await {
            return
        }

        debug!(target: "store::downgrade_host", "Downgrading host {}", addr);
        if self.greylist_contains(addr).await {
            warn!(target: "store::downgrade_host",
                  "Cannot downgrade a host that is already on the greylist! {}", addr);
        }

        if self.anchorlist_contains(addr).await {
            debug!(target: "store::downgrade_host", "Removing from anchorlist {}", addr);

            let index = self
                .get_anchorlist_index_at_addr(addr.clone())
                .await
                .expect("Expected anchorlist index to exist");

            self.anchorlist_remove(addr, index).await;
            self.greylist_store_or_update(&[(addr.clone(), last_seen)]).await;
        }

        if self.whitelist_contains(addr).await {
            debug!(target: "store::downgrade_host", "Removing from whitelist {}", addr);

            let index = self
                .get_whitelist_index_at_addr(addr.clone())
                .await
                .expect("Expected whitelist index to exist");

            self.whitelist_remove(addr, index).await;
            self.greylist_store_or_update(&[(addr.clone(), last_seen)]).await;
        }

        // Remove this entry from HostRegistry to avoid this host getting
        // stuck in the Downgrading state.
        self.remove(&addr).await;
    }

    /// Stores an address on the greylist or updates its last_seen field if we already
    /// have the address.
    pub async fn greylist_store_or_update(&self, addrs: &[(Url, u64)]) {
        trace!(target: "store::greylist_store_or_update()", "[START]");
        // Filter addresses before writing to the greylist.
        let filtered_addrs = self.filter_addresses(addrs).await;
        let filtered_addrs_len = filtered_addrs.len();

        if filtered_addrs.is_empty() {
            debug!(target: "store::greylist_store_or_update()", "Filtered out all addresses");
        }

        for (addr, last_seen) in filtered_addrs {
            if !self.greylist_contains(&addr).await {
                debug!(target: "store::greylist_store_or_update()",
                    "We do not have this entry in the hostlist. Adding to store...");

                self.greylist_store(addr.clone(), last_seen).await;
            } else {
                debug!(target: "store::greylist_store_or_update()",
                        "We have this entry in the greylist. Updating last seen...");

                let index = self
                    .get_greylist_index_at_addr(addr.clone())
                    .await
                    .expect("Expected greylist entry to exist");
                debug!(target: "store::greylist_store_or_update()",
                        "Selected index, updating last seen...");
                self.greylist_update_last_seen(&addr, last_seen, index).await;
                self.store_subscriber.notify(filtered_addrs_len).await;
            }
        }
    }

    /// Stores an address on the whitelist or updates its last_seen field if we already
    /// have the address.
    pub async fn whitelist_store_or_update(&self, addrs: &[(Url, u64)]) {
        trace!(target: "store::whitelist_store_or_update()", "[START]");

        // No address filtering for whitelist (whitelist is created from greylist)
        for (addr, last_seen) in addrs {
            if !self.whitelist_contains(addr).await {
                debug!(target: "store::whitelist_store_or_update()",
        "We do not have this entry in the whitelist. Adding to store...");

                self.whitelist_store(addr.clone(), *last_seen).await;
            } else {
                debug!(target: "store::whitelist_store_or_update()",
        "We have this entry in the whitelist. Updating last seen...");

                let index = self
                    .get_whitelist_index_at_addr(addr.clone())
                    .await
                    .expect("Expected whitelist entry to exist");
                self.whitelist_update_last_seen(addr, *last_seen, index).await;
            }
        }
    }

    /// Stores an address on the anchorlist or updates its last_seen field if we already
    /// have the address.
    pub async fn anchorlist_store_or_update(&self, addrs: &[(Url, u64)]) {
        trace!(target: "store::anchor_store_or_update()", "[START]");

        // No address filtering for anchorlist (contains addresses we have already connected to)
        for (addr, last_seen) in addrs {
            if !self.anchorlist_contains(addr).await {
                debug!(target: "store::anchorlist_store_or_update()",
        "We do not have this entry in the whitelist. Adding to store...");

                self.anchorlist_store(addr.clone(), *last_seen).await;
            } else {
                debug!(target: "store::anchorlist_store_or_update()",
            "We have this entry in the anchorlist. Updating last seen...");

                let index = self
                    .get_anchorlist_index_at_addr(addr.clone())
                    .await
                    .expect("Expected anchorlist entry to exist");
                self.anchorlist_update_last_seen(addr, *last_seen, index).await;
            }
        }
    }

    /// Append host to the greylist. Called on learning of a new peer.
    pub async fn greylist_store(&self, addr: Url, last_seen: u64) {
        trace!(target: "store::greylist_store()", "hosts::greylist_store() [START]");

        let mut greylist = self.greylist.write().await;

        // Remove oldest element if the greylist reaches max size.
        if greylist.len() == GREYLIST_MAX_LEN {
            let last_entry = greylist.pop().unwrap();
            debug!(target: "store::greylist_store()", "Greylist reached max size. Removed {:?}", last_entry);
        }

        debug!(target: "store::greylist_store()", "Inserting {}", addr);
        greylist.push((addr, last_seen));

        // Sort the list by last_seen.
        greylist.sort_by_key(|entry| entry.1);
        greylist.reverse();

        trace!(target: "store::greylist_store()", "[END]");
    }

    /// Append host to the whitelist. Called after a successful interaction with an online peer.
    pub async fn whitelist_store(&self, addr: Url, last_seen: u64) {
        trace!(target: "store::whitelist_store()", "[START]");

        let mut whitelist = self.whitelist.write().await;

        // Remove oldest element if the whitelist reaches max size.
        if whitelist.len() == WHITELIST_MAX_LEN {
            let last_entry = whitelist.pop().unwrap();
            debug!(target: "store::whitelist_store()", "Whitelist reached max size. Removed {:?}", last_entry);
        }
        trace!(target: "store::whitelist_store()", "Inserting {}. Last seen {:?}", addr, last_seen);
        whitelist.push((addr, last_seen));

        // Sort the list by last_seen.
        whitelist.sort_by_key(|entry| entry.1);
        whitelist.reverse();

        trace!(target: "store::whitelist_store()", "[END]");
    }

    /// Append host to the anchorlist. Called after we have successfully established a connection
    /// to a peer.
    pub async fn anchorlist_store(&self, addr: Url, last_seen: u64) {
        trace!(target: "store::anchorlist_store()", "[START]");

        let mut anchorlist = self.anchorlist.write().await;

        trace!(target: "store::anchorlist_store()", "Inserting {}", addr);
        anchorlist.push((addr, last_seen));

        // Sort the list by last_seen.
        anchorlist.sort_by_key(|entry| entry.1);
        anchorlist.reverse();

        trace!(target: "store::anchorlist_store()", "[END]");
    }

    /// Update the last_seen field of a peer on the greylist.
    pub async fn greylist_update_last_seen(&self, addr: &Url, last_seen: u64, index: usize) {
        trace!(target: "store::greylist_update_last_seen()", "[START]");

        let mut greylist = self.greylist.write().await;

        greylist[index] = (addr.clone(), last_seen);

        // Sort the list by last_seen.
        greylist.sort_by_key(|entry| entry.1);
        greylist.reverse();

        trace!(target: "store::greylist_update_last_seen()", "[END]");
    }

    /// Update the last_seen field of a peer on the whitelist.
    pub async fn whitelist_update_last_seen(&self, addr: &Url, last_seen: u64, index: usize) {
        trace!(target: "store::whitelist_update_last_seen()", "[START]");

        let mut whitelist = self.whitelist.write().await;

        whitelist[index] = (addr.clone(), last_seen);

        // Sort the list by last_seen.
        whitelist.sort_by_key(|entry| entry.1);
        whitelist.reverse();

        trace!(target: "store::whitelist_update_last_seen()", "[END]");
    }

    /// Update the last_seen field of a peer on the anchorlist.
    pub async fn anchorlist_update_last_seen(&self, addr: &Url, last_seen: u64, index: usize) {
        trace!(target: "store::anchorlist_update_last_seen()", "[START]");

        let mut anchorlist = self.anchorlist.write().await;

        anchorlist[index] = (addr.clone(), last_seen);

        // Sort the list by last_seen.
        anchorlist.sort_by_key(|entry| entry.1);
        anchorlist.reverse();

        trace!(target: "store::anchorlist_update_last_seen()", "[END]");
    }

    /// Remove an entry from the greylist.
    pub async fn greylist_remove(&self, addr: &Url, index: usize) {
        debug!(target: "store::greylist_remove", "Removing peer {} from greylist", addr);
        self.greylist.write().await.remove(index);
    }

    /// Remove an entry from the whitelist.
    pub async fn whitelist_remove(&self, addr: &Url, index: usize) {
        debug!(target: "store::whitelist_remove", "Removing peer {} from whitelist", addr);
        self.whitelist.write().await.remove(index);
    }

    /// Remove an entry from the anchorlist.
    pub async fn anchorlist_remove(&self, addr: &Url, index: usize) {
        debug!(target: "store::anchorlist_remove", "Removing peer {} from anchorlist", addr);
        self.anchorlist.write().await.remove(index);
    }

    pub async fn subscribe_store(&self) -> Result<Subscription<usize>> {
        let sub = self.store_subscriber.clone().subscribe().await;
        Ok(sub)
    }

    // Verify whether a URL is local.
    // NOTE: This function is stateless and not specific to
    // `Hosts`. For this reason, it might make more sense
    // to move this function to a more appropriate location
    // in the codebase.
    /// Check whether a URL is local host
    pub async fn is_local_host(&self, url: Url) -> bool {
        // Reject Urls without host strings.
        if url.host_str().is_none() {
            return false
        }

        // We do this hack in order to parse IPs properly.
        // https://github.com/whatwg/url/issues/749
        let addr = Url::parse(&url.as_str().replace(url.scheme(), "http")).unwrap();
        // Filter private IP ranges
        match addr.host().unwrap() {
            url::Host::Ipv4(ip) => {
                if !ip.is_global() {
                    return true
                }
            }
            url::Host::Ipv6(ip) => {
                if !ip.is_global() {
                    return true
                }
            }
            url::Host::Domain(d) => {
                if LOCAL_HOST_STRS.contains(&d) {
                    return true
                }
            }
        }
        false
    }

    /// Filter given addresses based on certain rulesets and validity.
    async fn filter_addresses(&self, addrs: &[(Url, u64)]) -> Vec<(Url, u64)> {
        trace!(target: "store::filter_addresses()", "Filtering addrs: {:?}", addrs);
        let mut ret = vec![];
        let localnet = self.settings.localnet;

        'addr_loop: for (addr_, last_seen) in addrs {
            // Validate that the format is `scheme://host_str:port`
            if addr_.host_str().is_none() ||
                addr_.port().is_none() ||
                addr_.cannot_be_a_base() ||
                addr_.path_segments().is_some()
            {
                continue
            }

            if self.is_blacklist(addr_).await {
                warn!(target: "store::filter_addresses()", "Peer {} is blacklisted", addr_);
                continue
            }

            let host_str = addr_.host_str().unwrap();

            if !localnet {
                // Our own external addresses should never enter the hosts set.
                for ext in &self.settings.external_addrs {
                    if host_str == ext.host_str().unwrap() {
                        continue 'addr_loop
                    }
                }
            }
            // On localnet, make sure ours ports don't enter the host set.
            for ext in &self.settings.external_addrs {
                if addr_.port() == ext.port() {
                    continue 'addr_loop
                }
            }

            // We do this hack in order to parse IPs properly.
            // https://github.com/whatwg/url/issues/749
            let addr = Url::parse(&addr_.as_str().replace(addr_.scheme(), "http")).unwrap();

            // Filter non-global ranges if we're not allowing localnet.
            // Should never be allowed in production, so we don't really care
            // about some of them (e.g. 0.0.0.0, or broadcast, etc.).
            if !localnet && self.is_local_host(addr).await {
                continue
            }

            match addr_.scheme() {
                // Validate that the address is an actual onion.
                #[cfg(feature = "p2p-tor")]
                "tor" | "tor+tls" => {
                    use std::str::FromStr;
                    if tor_hscrypto::pk::HsId::from_str(host_str).is_err() {
                        continue
                    }
                    trace!(target: "store::filter_addresses()", "[Tor] Valid: {}", host_str);
                }

                #[cfg(feature = "p2p-nym")]
                "nym" | "nym+tls" => continue, // <-- Temp skip

                #[cfg(feature = "p2p-tcp")]
                "tcp" | "tcp+tls" => {
                    trace!(target: "store::filter_addresses()", "[TCP] Valid: {}", host_str);
                }

                _ => continue,
            }

            ret.push((addr_.clone(), *last_seen));
        }

        ret
    }

    /// Quarantine a peer.
    /// If they've been quarantined for more than a configured limit, downgrade to greylist.
    pub async fn quarantine(&self, addr: &Url, last_seen: u64) {
        debug!(target: "store::quarantine()", "Quarantining peer {}", addr);
        let timer = Instant::now();
        let mut q = self.quarantine.write().await;
        if let Some(retries) = q.get_mut(addr) {
            *retries += 1;
            debug!(target: "store::quarantine()", "Peer {} quarantined {} times", addr, retries);
            if *retries == self.settings.hosts_quarantine_limit {
                debug!(target: "store::quarantine()", "Reached quarantine limited after {:?}", timer.elapsed());
                debug!(target: "store::quarantine()", "Removing from hostlist {}", addr);
                drop(q);
                self.downgrade_host(addr, last_seen).await;
            }
        } else {
            debug!(target: "net::hosts::quarantine()", "Added peer {} to quarantine", addr);
            q.insert(addr.clone(), 0);
        }
    }

    /// Check if a given peer (URL) is in the set of blacklist hosts
    pub async fn is_blacklist(&self, peer: &Url) -> bool {
        // Skip lookup for UNIX sockets and localhost connections
        // as they should never belong to the blacklist.
        let Some(hostname) = peer.host_str() else { return false };

        if self.is_local_host(peer.clone()).await {
            return false
        }

        self.blacklist.read().await.contains(hostname)
    }

    /// Mark a peer as blacklist by adding it to the set of blacklist URLs.
    pub async fn blacklist(&self, peer: &Url) {
        // We ignore UNIX sockets here so we will just work
        // with stuff that has host_str().
        if let Some(hostname) = peer.host_str() {
            // Localhost connections should never enter the blacklist
            // This however allows any Tor and Nym connections.
            if self.is_local_host(peer.clone()).await {
                return
            }

            self.blacklist.write().await.insert(hostname.to_string());
        }
    }

    /// Unmark a blacklist peer
    pub async fn unblacklist(&self, peer: &Url) {
        if let Some(hostname) = peer.host_str() {
            self.blacklist.write().await.remove(hostname);
        }
    }

    /// Check if the greylist is empty.
    pub async fn is_empty_greylist(&self) -> bool {
        self.greylist.read().await.is_empty()
    }

    /// Check if the whitelist is empty.
    pub async fn is_empty_whitelist(&self) -> bool {
        self.whitelist.read().await.is_empty()
    }

    /// Check if the anchorlist is empty.
    pub async fn is_empty_anchorlist(&self) -> bool {
        self.anchorlist.read().await.is_empty()
    }

    /// Check if the hostlist is empty.
    pub async fn is_empty_hostlist(&self) -> bool {
        self.is_empty_greylist().await &&
            self.is_empty_whitelist().await &&
            self.is_empty_anchorlist().await
    }

    /// Check if host is in the greylist
    pub async fn greylist_contains(&self, addr: &Url) -> bool {
        self.greylist.read().await.iter().any(|(u, _t)| u == addr)
    }

    /// Check if host is in the whitelist
    pub async fn whitelist_contains(&self, addr: &Url) -> bool {
        self.whitelist.read().await.iter().any(|(u, _t)| u == addr)
    }

    /// Check if host is in the anchorlist
    pub async fn anchorlist_contains(&self, addr: &Url) -> bool {
        self.anchorlist.read().await.iter().any(|(u, _t)| u == addr)
    }

    /// Get the index for a given addr on the greylist.
    pub async fn get_greylist_index_at_addr(&self, addr: Url) -> Option<usize> {
        self.greylist.read().await.iter().position(|a| a.0 == addr)
    }

    /// Get the index for a given addr on the whitelist.
    pub async fn get_whitelist_index_at_addr(&self, addr: Url) -> Option<usize> {
        self.whitelist.read().await.iter().position(|a| a.0 == addr)
    }

    /// Get the index for a given addr on the anchorlist.
    pub async fn get_anchorlist_index_at_addr(&self, addr: Url) -> Option<usize> {
        self.anchorlist.read().await.iter().position(|a| a.0 == addr)
    }

    /// Get the entry for a given addr on the whitelist.
    pub async fn get_whitelist_entry_at_addr(&self, addr: &Url) -> Option<(Url, u64)> {
        self.whitelist
            .read()
            .await
            .iter()
            .find(|(url, _)| url == addr)
            .map(|(url, time)| (url.clone(), *time))
    }

    /// Get the entry for a given addr on the anchorlist.
    pub async fn get_anchorlist_entry_at_addr(&self, addr: &Url) -> Option<(Url, u64)> {
        self.anchorlist
            .read()
            .await
            .iter()
            .find(|(url, _)| url == addr)
            .map(|(url, time)| (url.clone(), *time))
    }

    /// Return all known whitelisted hosts
    pub async fn whitelist_fetch_all(&self) -> Vec<(Url, u64)> {
        self.whitelist.read().await.iter().cloned().collect()
    }

    /// Return all known greylisted hosts
    pub async fn greylist_fetch_all(&self) -> Vec<(Url, u64)> {
        self.greylist.read().await.iter().cloned().collect()
    }

    /// Return all known anchorlisted hosts
    pub async fn anchorlist_fetch_all(&self) -> Vec<(Url, u64)> {
        self.anchorlist.read().await.iter().cloned().collect()
    }

    /// Return all greylist and anchorlist hosts. Called on stop().
    /// Note: we do not return whitelist entries here since whitelist entries must go via the
    /// greylist refinery in the lifetime of the p2p network.
    pub async fn hostlist_fetch_safe(&self) -> HashMap<String, Vec<(Url, u64)>> {
        let mut hostlist = HashMap::new();
        hostlist.insert(
            "anchorlist".to_string(),
            self.anchorlist.read().await.iter().cloned().collect(),
        );
        hostlist
            .insert("greylist".to_string(), self.greylist.read().await.iter().cloned().collect());
        hostlist
    }

    /// Get up to n random peers from the whitelist.
    pub async fn whitelist_fetch_n_random(&self, n: u32) -> Vec<(Url, u64)> {
        let n = n as usize;
        if n == 0 {
            return vec![]
        }
        let addrs = self.whitelist.read().await;
        let urls = addrs.iter().choose_multiple(&mut OsRng, n.min(addrs.len()));
        urls.iter().map(|&url| url.clone()).collect()
    }

    /// Get a random peer from the greylist.
    pub async fn greylist_fetch_random(&self) -> ((Url, u64), usize) {
        let greylist = self.greylist.read().await;
        let position = rand::thread_rng().gen_range(0..greylist.len());
        let entry = &greylist[position];
        (entry.clone(), position)
    }

    /// Get a random peer from the whitelist.
    pub async fn whitelist_fetch_random(&self) -> ((Url, u64), usize) {
        let whitelist = self.whitelist.read().await;
        let position = rand::thread_rng().gen_range(0..whitelist.len());
        let entry = &whitelist[position];
        (entry.clone(), position)
    }

    /// Get the oldest entry from the whitelist.
    pub async fn whitelist_fetch_last(&self) -> ((Url, u64), usize) {
        let whitelist = self.whitelist.read().await;
        let position = whitelist.len() - 1;
        let entry = &whitelist[position];
        (entry.clone(), position)
    }

    /// Get a random greylist peer that matches the given transport schemes.
    pub async fn greylist_fetch_random_with_schemes(&self) -> Option<((Url, u64), usize)> {
        trace!(target: "store::greylist_fetch_random_with_schemes", "[START]");

        // Retrieve all peers corresponding to that transport schemes
        let schemes = &self.settings.allowed_transports;
        let greylist = self.greylist_fetch_with_schemes(schemes, None).await;

        if greylist.is_empty() {
            return None
        }

        let position = rand::thread_rng().gen_range(0..greylist.len());
        let entry = &greylist[position];
        Some((entry.clone(), position))
    }

    /// Get up to n random greylist peers. Schemes are not taken into account.
    pub async fn greylist_fetch_n_random(&self, n: u32) -> Vec<(Url, u64)> {
        trace!(target: "store::greylist_fetch_n_random", "[START]");
        let n = n as usize;
        if n == 0 {
            return vec![]
        }
        let mut hosts = vec![];

        let greylist = self.greylist.read().await;

        for (addr, last_seen) in greylist.iter() {
            hosts.push((addr.clone(), *last_seen));
        }

        if hosts.is_empty() {
            debug!(target: "store::greylist_fetch_n_random", "No greylist entries found!");
            return hosts
        }

        // Grab random ones
        let urls = hosts.iter().choose_multiple(&mut OsRng, n.min(hosts.len()));
        urls.iter().map(|&url| url.clone()).collect()
    }

    /// Get up to n random greylist peers that match the given transport schemes.
    pub async fn greylist_fetch_n_random_with_schemes(
        &self,
        schemes: &[String],
        n: u32,
    ) -> Vec<(Url, u64)> {
        let n = n as usize;
        if n == 0 {
            return vec![]
        }
        trace!(target: "store::greylist_fetch_n_random_with_schemes", "[START]");

        // Retrieve all peers corresponding to that transport schemes
        let hosts = self.greylist_fetch_with_schemes(schemes, None).await;
        if hosts.is_empty() {
            debug!(target: "store::greylist_fetch_n_random_with_schemes",
                  "No such schemes found on greylist!");
            return hosts
        }

        // Grab random ones
        let urls = hosts.iter().choose_multiple(&mut OsRng, n.min(hosts.len()));
        urls.iter().map(|&url| url.clone()).collect()
    }

    /// Get up to n random whitelist peers that match the given transport schemes.
    pub async fn whitelist_fetch_n_random_with_schemes(
        &self,
        schemes: &[String],
        n: u32,
    ) -> Vec<(Url, u64)> {
        let n = n as usize;
        if n == 0 {
            return vec![]
        }
        trace!(target: "store::whitelist_fetch_n_random_with_schemes", "[START]");

        // Retrieve all peers corresponding to that transport schemes
        let hosts = self.whitelist_fetch_with_schemes(schemes, None).await;
        if hosts.is_empty() {
            debug!(target: "store::whitelist_fetch_n_random_with_schemes",
                  "No such schemes found on whitelist!");
            return hosts
        }

        // Grab random ones
        let urls = hosts.iter().choose_multiple(&mut OsRng, n.min(hosts.len()));
        urls.iter().map(|&url| url.clone()).collect()
    }

    /// Get up to n random anchorlist peers that match the given transport schemes.
    pub async fn anchorlist_fetch_n_random_with_schemes(
        &self,
        schemes: &[String],
        n: u32,
    ) -> Vec<(Url, u64)> {
        let n = n as usize;
        if n == 0 {
            return vec![]
        }
        trace!(target: "store::anchorlist_fetch_n_random_with_schemes", "[START]");

        // Retrieve all peers corresponding to that transport schemes
        let hosts = self.anchorlist_fetch_with_schemes(schemes, None).await;
        if hosts.is_empty() {
            debug!(target: "store::anchorlist_fetch_n_random_with_schemes",
                  "No such schemes found on anchorlist!");
            return hosts
        }

        // Grab random ones
        let urls = hosts.iter().choose_multiple(&mut OsRng, n.min(hosts.len()));
        urls.iter().map(|&url| url.clone()).collect()
    }

    /// Get up to limit peers that don't match the given transport schemes from the greylist.
    /// If limit was not provided, return all matching peers.
    pub async fn greylist_fetch_excluding_schemes(
        &self,
        schemes: &[String],
        limit: Option<usize>,
    ) -> Vec<(Url, u64)> {
        let greylist = self.greylist.read().await;
        let mut limit = match limit {
            Some(l) => l.min(greylist.len()),
            None => greylist.len(),
        };
        let mut ret = vec![];

        if limit == 0 {
            return ret
        }

        for (addr, last_seen) in greylist.iter() {
            if !schemes.contains(&addr.scheme().to_string()) {
                ret.push((addr.clone(), *last_seen));
                limit -= 1;
                if limit == 0 {
                    return ret
                }
            }
        }

        if ret.is_empty() {
            debug!(target: "store::greylist_fetch_excluding_schemes",
                  "No such schemes found on greylist!")
        }

        ret
    }

    /// Get up to limit peers that don't match the given transport schemes from the whitelist.
    /// If limit was not provided, return all matching peers.
    pub async fn whitelist_fetch_excluding_schemes(
        &self,
        schemes: &[String],
        limit: Option<usize>,
    ) -> Vec<(Url, u64)> {
        let addrs = self.whitelist.read().await;
        let mut limit = match limit {
            Some(l) => l.min(addrs.len()),
            None => addrs.len(),
        };
        let mut ret = vec![];

        if limit == 0 {
            return ret
        }

        for (addr, last_seen) in addrs.iter() {
            if !schemes.contains(&addr.scheme().to_string()) {
                ret.push((addr.clone(), *last_seen));
                limit -= 1;
                if limit == 0 {
                    return ret
                }
            }
        }

        if ret.is_empty() {
            debug!(target: "store::whiteist_fetch_excluding_schemes",
                  "No such schemes found on whitelist!")
        }

        ret
    }

    /// Get up to n random whitelisted peers that don't match the given transport schemes from the
    /// hosts set.
    pub async fn whitelist_fetch_n_random_excluding_schemes(
        &self,
        schemes: &[String],
        n: u32,
    ) -> Vec<(Url, u64)> {
        let n = n as usize;
        if n == 0 {
            return vec![]
        }
        trace!(target: "store::whitelist_fetch_excluding_schemes", "[START]");

        // Retrieve all peers not corresponding to that transport schemes
        let hosts = self.whitelist_fetch_excluding_schemes(schemes, None).await;

        if hosts.is_empty() {
            debug!(target: "store::whitelist_fetch_n_random_excluding_schemes",
                  "No such schemes found on whitelist!");
            return hosts
        }

        // Grab random ones
        let urls = hosts.iter().choose_multiple(&mut OsRng, n.min(hosts.len()));
        urls.iter().map(|&url| url.clone()).collect()
    }

    /// Get up to limit peers that match the given transport schemes from the greylist.
    /// If limit was not provided, return all matching peers.
    async fn greylist_fetch_with_schemes(
        &self,
        schemes: &[String],
        limit: Option<usize>,
    ) -> Vec<(Url, u64)> {
        trace!(target: "store::greylist_fetch_with_schemes", "[START]");
        let greylist = self.greylist.read().await;

        let mut limit = match limit {
            Some(l) => l.min(greylist.len()),
            None => greylist.len(),
        };
        let mut ret = vec![];

        if limit == 0 {
            return ret
        }

        for (addr, last_seen) in greylist.iter() {
            if schemes.contains(&addr.scheme().to_string()) {
                ret.push((addr.clone(), *last_seen));
                limit -= 1;
                if limit == 0 {
                    debug!(target: "store::greylist_fetch_with_schemes",
                        "Found matching scheme, returning {} grey addresses",
                        ret.len());
                    return ret
                }
            }
        }

        if ret.is_empty() {
            debug!(target: "store::greylist_fetch_with_schemes",
                  "No such schemes found on greylist!")
        }

        trace!(target: "store::greylist_fetch_with_schemes", "END");
        ret
    }

    /// Get up to limit peers that match the given transport schemes from the whitelist.
    /// If limit was not provided, return all matching peers.
    async fn whitelist_fetch_with_schemes(
        &self,
        schemes: &[String],
        limit: Option<usize>,
    ) -> Vec<(Url, u64)> {
        trace!(target: "store::whitelist_fetch_with_schemes", "[START]");
        let whitelist = self.whitelist.read().await;

        let mut limit = match limit {
            Some(l) => l.min(whitelist.len()),
            None => whitelist.len(),
        };
        let mut ret = vec![];

        if limit == 0 {
            return ret
        }

        for (addr, last_seen) in whitelist.iter() {
            if schemes.contains(&addr.scheme().to_string()) {
                ret.push((addr.clone(), *last_seen));
                limit -= 1;
                if limit == 0 {
                    debug!(target: "store::whitelist_fetch_with_schemes",
                           "Found matching scheme, returning {} white addresses",
                           ret.len());
                    return ret
                }
            }
        }

        if ret.is_empty() {
            debug!(target: "store::whitelist_fetch_with_schemes",
                  "No such schemes found on whitelist!")
        }

        trace!(target: "store::whitelist_fetch_with_schemes", "END");
        ret
    }

    /// Get up to limit peers that match the given transport schemes from the anchorlist.
    /// If limit was not provided, return all matching peers.
    async fn anchorlist_fetch_with_schemes(
        &self,
        schemes: &[String],
        limit: Option<usize>,
    ) -> Vec<(Url, u64)> {
        //trace!(target: "store::anchorlist_fetch_with_schemes", "[START]");
        let anchorlist = self.anchorlist.read().await;

        let mut limit = match limit {
            Some(l) => l.min(anchorlist.len()),
            None => anchorlist.len(),
        };
        let mut ret = vec![];

        if limit == 0 {
            return ret
        }

        for (addr, last_seen) in anchorlist.iter() {
            if schemes.contains(&addr.scheme().to_string()) {
                ret.push((addr.clone(), *last_seen));
                limit -= 1;
                if limit == 0 {
                    debug!(target: "store::anchorlist_fetch_with_schemes",
                           "Found matching scheme, returning {} anchor addresses",
                           ret.len());
                    return ret
                }
            }
        }

        if ret.is_empty() {
            warn!(target: "store::anchorlist_fetch_with_schemes",
                  "No matching schemes found on anchorlist")
        }

        trace!(target: "store::anchorlist_fetch_with_schemes", "END");
        ret
    }

    /// Load the hostlist from a file.
    pub async fn load_hosts(&self) -> Result<()> {
        let path = expand_path(&self.settings.hostlist)?;

        if !path.exists() {
            if let Some(parent) = path.parent() {
                fs::create_dir_all(parent)?;
            }

            File::create(path.clone())?;
        }

        let contents = load_file(&path);
        if let Err(e) = contents {
            warn!(target: "store", "Failed retrieving saved hosts: {}", e);
            return Ok(())
        }

        for line in contents.unwrap().lines() {
            let data: Vec<&str> = line.split('\t').collect();

            let url = match Url::parse(data[1]) {
                Ok(u) => u,
                Err(e) => {
                    debug!(target: "store", "load_hosts(): Skipping malformed URL {}", e);
                    continue
                }
            };

            let last_seen = match data[2].parse::<u64>() {
                Ok(t) => t,
                Err(e) => {
                    debug!(target: "store", "load_hosts(): Skipping malformed last seen {}", e);
                    continue
                }
            };

            match data[0] {
                "greylist" => {
                    self.greylist_store(url, last_seen).await;
                }
                "whitelist" => {
                    self.whitelist_store(url, last_seen).await;
                }
                "anchorlist" => {
                    self.anchorlist_store(url, last_seen).await;
                }
                _ => {
                    debug!(target: "store", "load_hosts(): Malformed list name...");
                }
            }
        }

        Ok(())
    }

    /// Save the hostlist to a file. Whitelist gets written to the greylist to force
    /// whitelist entries through the refinery on start.
    pub async fn save_hosts(&self) -> Result<()> {
        let path = expand_path(&self.settings.hostlist)?;

        let mut tsv = String::new();
        let mut whitelist = vec![];

        // First gather all the whitelist entries we don't have in greylist.
        for (url, last_seen) in self.whitelist_fetch_all().await {
            if !self.greylist_contains(&url).await {
                whitelist.push((url, last_seen))
            }
        }

        // Collect the greylist and anchorlist entries, and append any whitelist entries to the
        // greylist before saving.
        for (name, mut list) in self.hostlist_fetch_safe().await {
            if name == *"greylist".to_string() {
                list.append(&mut whitelist)
            }
            for (url, last_seen) in list {
                tsv.push_str(&format!("{}\t{}\t{}\n", name, url, last_seen));
            }
        }

        if !tsv.eq("") {
            info!(target: "store", "Saving hosts to: {:?}",
                  path);
            if let Err(e) = save_file(&path, &tsv) {
                error!(target: "store", "Failed saving hosts: {}", e);
            }
        }

        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::{
        super::super::{settings::Settings, P2p},
        *,
    };
    use crate::{net::hosts::refinery::ping_node, system::sleep};
    use smol::Executor;
    use std::{sync::Arc, time::UNIX_EPOCH};

    #[test]
    fn test_ping_node() {
        smol::block_on(async {
            let settings = Settings {
                localnet: false,
                external_addrs: vec![
                    Url::parse("tcp://foo.bar:123").unwrap(),
                    Url::parse("tcp://lol.cat:321").unwrap(),
                ],
                ..Default::default()
            };

            let ex = Arc::new(Executor::new());
            let p2p = P2p::new(settings, ex.clone()).await;

            let url = Url::parse("tcp://xeno.systems.wtf").unwrap();
            println!("Pinging node...");
            let task = ex.spawn(ping_node(url.clone(), p2p));
            ex.run(task).await;
            println!("Ping node complete!");
        });
    }

    #[test]
    fn test_is_local_host() {
        smol::block_on(async {
            let settings = Settings {
                localnet: false,
                external_addrs: vec![
                    Url::parse("tcp://foo.bar:123").unwrap(),
                    Url::parse("tcp://lol.cat:321").unwrap(),
                ],
                ..Default::default()
            };
            let hosts = Hosts::new(Arc::new(settings.clone()));

            let local_hosts: Vec<Url> = vec![
                Url::parse("tcp://localhost").unwrap(),
                Url::parse("tcp://127.0.0.1").unwrap(),
                Url::parse("tcp+tls://[::1]").unwrap(),
                Url::parse("tcp://localhost.localdomain").unwrap(),
                Url::parse("tcp://192.168.10.65").unwrap(),
            ];
            for host in local_hosts {
                eprintln!("{}", host);
                assert!(hosts.is_local_host(host).await);
            }
            let remote_hosts: Vec<Url> = vec![
                Url::parse("https://dyne.org").unwrap(),
                Url::parse("tcp://77.168.10.65:2222").unwrap(),
                Url::parse("tcp://[2345:0425:2CA1:0000:0000:0567:5673:23b5]").unwrap(),
                Url::parse("http://eweiibe6tdjsdprb4px6rqrzzcsi22m4koia44kc5pcjr7nec2rlxyad.onion")
                    .unwrap(),
            ];
            for host in remote_hosts {
                assert!(!hosts.is_local_host(host).await)
            }
        });
    }

    #[test]
    fn test_greylist_store() {
        let last_seen = UNIX_EPOCH.elapsed().unwrap().as_secs();

        smol::block_on(async {
            let settings = Settings {
                localnet: false,
                external_addrs: vec![
                    Url::parse("tcp://foo.bar:123").unwrap(),
                    Url::parse("tcp://lol.cat:321").unwrap(),
                ],
                ..Default::default()
            };

            let hosts = Hosts::new(Arc::new(settings.clone()));
            for addr in settings.external_addrs {
                hosts.greylist_store(addr, last_seen).await;
            }

            assert!(!hosts.is_empty_greylist().await);

            let local_hosts = vec![
                Url::parse("tcp://localhost:3921").unwrap(),
                Url::parse("tor://[::1]:21481").unwrap(),
                Url::parse("tcp://192.168.10.65:311").unwrap(),
                Url::parse("tcp+tls://0.0.0.0:2312").unwrap(),
                Url::parse("tcp://255.255.255.255:2131").unwrap(),
            ];

            for host in &local_hosts {
                hosts.greylist_store(host.clone(), last_seen).await;
            }
            assert!(!hosts.is_empty_greylist().await);

            let remote_hosts = vec![
                Url::parse("tcp://dark.fi:80").unwrap(),
                Url::parse("tcp://http.cat:401").unwrap(),
                Url::parse("tcp://foo.bar:111").unwrap(),
            ];

            for host in &remote_hosts {
                hosts.greylist_store(host.clone(), last_seen).await;
            }

            assert!(hosts.greylist_contains(&remote_hosts[0]).await);
            assert!(hosts.greylist_contains(&remote_hosts[1]).await);
            assert!(hosts.greylist_contains(&remote_hosts[2]).await);
        });
    }

    #[test]
    fn test_whitelist_store() {
        smol::block_on(async {
            let settings = Settings {
                localnet: false,
                external_addrs: vec![
                    Url::parse("tcp://foo.bar:123").unwrap(),
                    Url::parse("tcp://lol.cat:321").unwrap(),
                ],
                ..Default::default()
            };

            let hosts = Hosts::new(Arc::new(settings.clone()));
            assert!(hosts.is_empty_whitelist().await);

            let url = Url::parse("tcp://dark.renaissance:333").unwrap();
            let last_seen = UNIX_EPOCH.elapsed().unwrap().as_secs();

            hosts.whitelist_store(url.clone(), last_seen).await;

            assert!(!hosts.is_empty_whitelist().await);
            assert!(hosts.whitelist_contains(&url).await);
        });
    }

    #[test]
    fn test_whitelist_get_last() {
        smol::block_on(async {
            let settings = Settings {
                localnet: false,
                external_addrs: vec![
                    Url::parse("tcp://foo.bar:123").unwrap(),
                    Url::parse("tcp://lol.cat:321").unwrap(),
                ],
                ..Default::default()
            };

            let hosts = Hosts::new(Arc::new(settings.clone()));

            // Build up a hostlist
            for i in 0..10 {
                sleep(1).await;
                let last_seen = UNIX_EPOCH.elapsed().unwrap().as_secs();
                let url = Url::parse(&format!("tcp://whitelist{}:123", i)).unwrap();
                hosts.whitelist_store(url.clone(), last_seen).await;
            }

            for (url, last_seen) in hosts.whitelist.read().await.iter() {
                println!("{} {}", url, last_seen);
            }

            let (entry, _position) = hosts.whitelist_fetch_last().await;
            println!("last entry: {} {}", entry.0, entry.1);
        });
    }

    #[test]
    fn test_hostlist_get_entry() {
        smol::block_on(async {
            let settings = Settings {
                localnet: false,
                external_addrs: vec![
                    Url::parse("tcp://foo.bar:123").unwrap(),
                    Url::parse("tcp://lol.cat:321").unwrap(),
                ],
                ..Default::default()
            };

            let hosts = Hosts::new(Arc::new(settings.clone()));

            let url = Url::parse("tcp://dark.renaissance:333").unwrap();
            let last_seen = UNIX_EPOCH.elapsed().unwrap().as_secs();

            hosts.whitelist_store(url.clone(), last_seen).await;
            hosts.anchorlist_store(url.clone(), last_seen).await;

            assert!(hosts.get_whitelist_entry_at_addr(&url).await.is_some());
            assert!(hosts.get_anchorlist_entry_at_addr(&url).await.is_some());
        });
    }

    #[test]
    fn test_remove() {
        smol::block_on(async {
            let settings = Settings {
                outbound_connections: 8,
                allowed_transports: vec!["tcp".to_string()],
                ..Default::default()
            };
            let hosts = Hosts::new(Arc::new(settings.clone()));

            let url = Url::parse("tcp://dark.renaissance:333").unwrap();
            let last_seen = UNIX_EPOCH.elapsed().unwrap().as_secs();

            hosts.whitelist_store(url.clone(), last_seen).await;

            sleep(1).await;

            let url = Url::parse("tcp://milady:333").unwrap();
            let last_seen = UNIX_EPOCH.elapsed().unwrap().as_secs();

            hosts.whitelist_store(url.clone(), last_seen).await;

            sleep(1).await;

            let url = Url::parse("tcp://king-ted:333").unwrap();
            let last_seen = UNIX_EPOCH.elapsed().unwrap().as_secs();

            hosts.whitelist_store(url.clone(), last_seen).await;
            for (url, last_seen) in hosts.whitelist.read().await.iter() {
                println!("{}, {}", url, last_seen);
            }

            let position = hosts.get_whitelist_index_at_addr(url.clone()).await.unwrap();
            hosts.whitelist_remove(&url, position).await;
            for (url, last_seen) in hosts.whitelist.read().await.iter() {
                println!("{}, {}", url, last_seen);
            }
        });
    }

    #[test]
    fn test_fetch_address() {
        smol::block_on(async {
            let mut hostlist = vec![];
            let mut grey_urls = vec![];
            let mut white_urls = vec![];
            let mut anchor_urls = vec![];

            let ex = Arc::new(Executor::new());

            let settings = Settings {
                outbound_connections: 8,
                allowed_transports: vec!["tcp".to_string()],
                ..Default::default()
            };
            let p2p = P2p::new(settings, ex.clone()).await;
            let hosts = p2p.hosts();

            // Build up a hostlist
            for i in 0..5 {
                let last_seen = UNIX_EPOCH.elapsed().unwrap().as_secs();
                hosts
                    .anchorlist_store(
                        Url::parse(&format!("tcp://anchorlist{}:123", i)).unwrap(),
                        last_seen,
                    )
                    .await;
                hosts
                    .whitelist_store(
                        Url::parse(&format!("tcp://whitelist{}:123", i)).unwrap(),
                        last_seen,
                    )
                    .await;
                hosts
                    .greylist_store(
                        Url::parse(&format!("tcp://greylist{}:123", i)).unwrap(),
                        last_seen,
                    )
                    .await;

                grey_urls
                    .push((Url::parse(&format!("tcp://greylist{}:123", i)).unwrap(), last_seen));
                white_urls
                    .push((Url::parse(&format!("tcp://whitelist{}:123", i)).unwrap(), last_seen));
                anchor_urls
                    .push((Url::parse(&format!("tcp://anchorlist{}:123", i)).unwrap(), last_seen));
            }

            assert!(!hosts.is_empty_anchorlist().await);
            assert!(!hosts.is_empty_whitelist().await);
            assert!(!hosts.is_empty_greylist().await);

            let transports = &p2p.settings().allowed_transports;
            let white_count =
                p2p.settings().outbound_connections * p2p.settings().white_connection_percent / 100;

            // Simulate the address selection logic found in outbound_session::fetch_address()
            for i in 0..8 {
                if i < p2p.settings().anchor_connection_count {
                    if !hosts.anchorlist_fetch_address(transports).await.is_empty() {
                        let addrs = hosts.anchorlist_fetch_address(transports).await;
                        hostlist.push(addrs);
                    }

                    if !hosts.whitelist_fetch_address(transports).await.is_empty() {
                        let addrs = hosts.whitelist_fetch_address(transports).await;
                        hostlist.push(addrs);
                    }

                    if !hosts.greylist_fetch_address(transports).await.is_empty() {
                        let addrs = hosts.greylist_fetch_address(transports).await;
                        hostlist.push(addrs);
                    }
                } else if i < white_count {
                    if !hosts.whitelist_fetch_address(transports).await.is_empty() {
                        let addrs = hosts.whitelist_fetch_address(transports).await;
                        hostlist.push(addrs);
                    }

                    if !hosts.greylist_fetch_address(transports).await.is_empty() {
                        let addrs = hosts.greylist_fetch_address(transports).await;
                        hostlist.push(addrs);
                    }
                } else if !hosts.greylist_fetch_address(transports).await.is_empty() {
                    let addrs = hosts.greylist_fetch_address(transports).await;
                    hostlist.push(addrs);
                }
            }

            //// Check we're returning the correct addresses.
            anchor_urls.sort();
            white_urls.sort();
            grey_urls.sort();
            hostlist[0].sort();
            hostlist[4].sort();
            hostlist[7].sort();

            assert!(anchor_urls == hostlist[0]);
            assert!(white_urls == hostlist[4]);
            assert!(grey_urls == hostlist[7]);
        })
    }
}