move DnsCache into its own module (#221)

DnsCache should be in its own module, instead of being buried in service_daemon module. No changes to business logic.

src/dns_cache.rs

@@ -0,0 +1,378 @@
+//! A cache for DNS records.
+//!
+//! This is an internal implementation, not visible to the public API.
+
+use crate::dns_parser::{
+    current_time_millis, split_sub_domain, DnsAddress, DnsPointer, DnsRecordBox, DnsSrv, TYPE_A,
+    TYPE_AAAA, TYPE_NSEC, TYPE_PTR, TYPE_SRV, TYPE_TXT,
+};
+#[cfg(feature = "logging")]
+use crate::log::debug;
+use std::{
+    collections::{HashMap, HashSet},
+    net::IpAddr,
+};
+
+/// A cache for all types of DNS records.
+pub(crate) struct DnsCache {
+    /// DnsPointer records indexed by ty_domain
+    ptr: HashMap<String, Vec<DnsRecordBox>>,
+
+    /// DnsSrv records indexed by the fullname of an instance
+    srv: HashMap<String, Vec<DnsRecordBox>>,
+
+    /// DnsTxt records indexed by the fullname of an instance
+    txt: HashMap<String, Vec<DnsRecordBox>>,
+
+    /// DnsAddr records indexed by the hostname
+    addr: HashMap<String, Vec<DnsRecordBox>>,
+
+    /// A reverse lookup table from "instance fullname" to "subtype PTR name"
+    subtype: HashMap<String, String>,
+
+    /// Negative responses:
+    /// A map from "instance fullname" to DnsNSec.
+    nsec: HashMap<String, Vec<DnsRecordBox>>,
+}
+
+impl DnsCache {
+    pub(crate) fn new() -> Self {
+        Self {
+            ptr: HashMap::new(),
+            srv: HashMap::new(),
+            txt: HashMap::new(),
+            addr: HashMap::new(),
+            subtype: HashMap::new(),
+            nsec: HashMap::new(),
+        }
+    }
+
+    pub(crate) fn all_ptr(&self) -> &HashMap<String, Vec<DnsRecordBox>> {
+        &self.ptr
+    }
+
+    pub(crate) fn get_ptr(&self, ty_domain: &str) -> Option<&Vec<DnsRecordBox>> {
+        self.ptr.get(ty_domain)
+    }
+
+    pub(crate) fn get_srv(&self, fullname: &str) -> Option<&Vec<DnsRecordBox>> {
+        self.srv.get(fullname)
+    }
+
+    pub(crate) fn get_txt(&self, fullname: &str) -> Option<&Vec<DnsRecordBox>> {
+        self.txt.get(fullname)
+    }
+
+    pub(crate) fn get_addr(&self, hostname: &str) -> Option<&Vec<DnsRecordBox>> {
+        self.addr.get(hostname)
+    }
+
+    /// A reverse lookup table from "instance fullname" to "subtype PTR name"
+    pub(crate) fn get_subtype(&self, fullname: &str) -> Option<&String> {
+        self.subtype.get(fullname)
+    }
+
+    /// Returns the list of instances that has `host` as its hostname.
+    pub(crate) fn get_instances_on_host(&self, host: &str) -> Vec<String> {
+        self.srv
+            .iter()
+            .filter_map(|(instance, srv_list)| {
+                if let Some(item) = srv_list.first() {
+                    if let Some(dns_srv) = item.any().downcast_ref::<DnsSrv>() {
+                        if dns_srv.host == host {
+                            return Some(instance.clone());
+                        }
+                    }
+                }
+                None
+            })
+            .collect()
+    }
+
+    /// Returns the set of IP addresses for a hostname.
+    pub(crate) fn get_addresses_for_host(&self, host: &str) -> HashSet<IpAddr> {
+        self.addr
+            .get(host)
+            .into_iter()
+            .flatten()
+            .filter_map(|record| {
+                record
+                    .any()
+                    .downcast_ref::<DnsAddress>()
+                    .map(|addr| addr.address)
+            })
+            .collect()
+    }
+
+    /// Update a DNSRecord TTL if already exists, otherwise insert a new record.
+    ///
+    /// Returns `None` if `incoming` is invalid / unrecognized, otherwise returns
+    /// (a new record, true) or (existing record with TTL updated, false).
+    pub(crate) fn add_or_update(
+        &mut self,
+        incoming: DnsRecordBox,
+    ) -> Option<(&DnsRecordBox, bool)> {
+        let entry_name = incoming.get_name().to_string();
+
+        // If it is PTR with subtype, store a mapping from the instance fullname
+        // to the subtype in this cache.
+        if incoming.get_type() == TYPE_PTR {
+            let (_, subtype_opt) = split_sub_domain(&entry_name);
+            if let Some(subtype) = subtype_opt {
+                if let Some(ptr) = incoming.any().downcast_ref::<DnsPointer>() {
+                    if !self.subtype.contains_key(&ptr.alias) {
+                        self.subtype.insert(ptr.alias.clone(), subtype.to_string());
+                    }
+                }
+            }
+        }
+
+        // get the existing records for the type.
+        let record_vec = match incoming.get_type() {
+            TYPE_PTR => self.ptr.entry(entry_name).or_default(),
+            TYPE_SRV => self.srv.entry(entry_name).or_default(),
+            TYPE_TXT => self.txt.entry(entry_name).or_default(),
+            TYPE_A | TYPE_AAAA => self.addr.entry(entry_name).or_default(),
+            TYPE_NSEC => self.nsec.entry(entry_name).or_default(),
+            _ => return None,
+        };
+
+        if incoming.get_cache_flush() {
+            let now = current_time_millis();
+            let class = incoming.get_class();
+            let rtype = incoming.get_type();
+
+            record_vec.iter_mut().for_each(|r| {
+                // When cache flush is asked, we set expire date to 1 second in the future if:
+                // - The record has the same rclass
+                // - The record was created more than 1 second ago.
+                // - The record expire is more than 1 second away.
+                // Ref: RFC 6762 Section 10.2
+                //
+                // Note: when the updated record actually expires, it will trigger events properly.
+                if class == r.get_class()
+                    && rtype == r.get_type()
+                    && now > r.get_created() + 1000
+                    && r.get_expire() > now + 1000
+                {
+                    debug!("FLUSH one record: {:?}", &r);
+                    r.set_expire(now + 1000);
+                }
+            });
+        }
+
+        // update TTL for existing record or create a new record.
+        let (idx, updated) = match record_vec
+            .iter_mut()
+            .enumerate()
+            .find(|(_idx, r)| r.matches(incoming.as_ref()))
+        {
+            Some((i, r)) => {
+                // It is possible that this record was just updated in cache_flush
+                // processing. That's okay. We can still reset here.
+                r.reset_ttl(incoming.as_ref());
+                (i, false)
+            }
+            None => {
+                record_vec.insert(0, incoming); // A new record.
+                (0, true)
+            }
+        };
+
+        Some((record_vec.get(idx).unwrap(), updated))
+    }
+
+    /// Remove a record from the cache if exists, otherwise no-op
+    pub(crate) fn remove(&mut self, record: &DnsRecordBox) -> bool {
+        let mut found = false;
+        let record_name = record.get_name();
+        let record_vec = match record.get_type() {
+            TYPE_PTR => self.ptr.get_mut(record_name),
+            TYPE_SRV => self.srv.get_mut(record_name),
+            TYPE_TXT => self.txt.get_mut(record_name),
+            TYPE_A | TYPE_AAAA => self.addr.get_mut(record_name),
+            _ => return found,
+        };
+        if let Some(record_vec) = record_vec {
+            record_vec.retain(|x| match x.matches(record.as_ref()) {
+                true => {
+                    found = true;
+                    false
+                }
+                false => true,
+            });
+        }
+        found
+    }
+
+    /// Iterates all ADDR records and remove ones that expired.
+    /// Returns the expired ones in a map of names and addresses.
+    pub(crate) fn evict_expired_addr(&mut self, now: u64) -> HashMap<String, HashSet<IpAddr>> {
+        let mut removed = HashMap::new();
+
+        for records in self.addr.values_mut() {
+            records.retain(|addr| {
+                let expired = addr.get_record().is_expired(now);
+                if expired {
+                    if let Some(addr_record) = addr.any().downcast_ref::<DnsAddress>() {
+                        removed
+                            .entry(addr.get_name().to_string())
+                            .or_insert_with(HashSet::new)
+                            .insert(addr_record.address);
+                    }
+                }
+                !expired
+            })
+        }
+
+        removed
+    }
+
+    /// Evicts expired PTR and SRV, TXT records for each ty_domain in the cache, and
+    /// returns the set of expired instance names for each ty_domain.
+    ///
+    /// An instance in the returned set indicates its PTR and/or SRV record has expired.
+    pub(crate) fn evict_expired_services(&mut self, now: u64) -> HashMap<String, HashSet<String>> {
+        let mut expired_instances = HashMap::new();
+
+        // Check all ty_domain in the cache by following all PTR records, regardless
+        // if the ty_domain is actively queried or not.
+        for (ty_domain, ptr_records) in self.ptr.iter_mut() {
+            for ptr in ptr_records.iter() {
+                if let Some(dns_ptr) = ptr.any().downcast_ref::<DnsPointer>() {
+                    let instance_name = &dns_ptr.alias;
+
+                    // evict expired SRV records of this instance
+                    if let Some(srv_records) = self.srv.get_mut(instance_name) {
+                        srv_records.retain(|srv| {
+                            let expired = srv.get_record().is_expired(now);
+                            if expired {
+                                debug!("expired SRV: {}: {}", ty_domain, srv.get_name());
+                                expired_instances
+                                    .entry(ty_domain.to_string())
+                                    .or_insert_with(HashSet::new)
+                                    .insert(srv.get_name().to_string());
+                            }
+                            !expired
+                        });
+                    }
+
+                    // evict expired TXT records of this instance
+                    if let Some(txt_records) = self.txt.get_mut(instance_name) {
+                        txt_records.retain(|txt| !txt.get_record().is_expired(now))
+                    }
+                }
+            }
+
+            // evict expired PTR records
+            ptr_records.retain(|x| {
+                let expired = x.get_record().is_expired(now);
+                if expired {
+                    if let Some(dns_ptr) = x.any().downcast_ref::<DnsPointer>() {
+                        debug!("expired PTR: {:?}", dns_ptr);
+                        expired_instances
+                            .entry(ty_domain.to_string())
+                            .or_insert_with(HashSet::new)
+                            .insert(dns_ptr.alias.clone());
+                    }
+                }
+                !expired
+            });
+        }
+
+        expired_instances
+    }
+
+    /// Checks refresh due for PTR records of `ty_domain`.
+    /// Returns all updated refresh time.
+    pub(crate) fn refresh_due_ptr(&mut self, ty_domain: &str) -> HashSet<u64> {
+        let now = current_time_millis();
+
+        // Check all PTR records for this ty_domain.
+        self.ptr
+            .get_mut(ty_domain)
+            .into_iter()
+            .flatten()
+            .filter_map(|record| {
+                if record.get_record_mut().refresh_maybe(now) {
+                    Some(record.get_record().get_refresh_time())
+                } else {
+                    None
+                }
+            })
+            .collect()
+    }
+
+    /// Returns the set of SRV instance names that are due for refresh
+    /// for a `ty_domain`.
+    pub(crate) fn refresh_due_srv(&mut self, ty_domain: &str) -> (HashSet<String>, HashSet<u64>) {
+        let now = current_time_millis();
+
+        let mut instances = vec![];
+
+        // find instance names for ty_domain.
+        for record in self.ptr.get_mut(ty_domain).into_iter().flatten() {
+            if record.get_record().is_expired(now) {
+                continue;
+            }
+
+            if let Some(ptr) = record.any().downcast_ref::<DnsPointer>() {
+                instances.push(ptr.alias.clone());
+            }
+        }
+
+        // Check SRV records.
+        let mut refresh_due = HashSet::new();
+        let mut new_timers = HashSet::new();
+        for instance in instances {
+            let refresh_timers: HashSet<u64> = self
+                .srv
+                .get_mut(&instance)
+                .into_iter()
+                .flatten()
+                .filter_map(|record| {
+                    if record.get_record_mut().refresh_maybe(now) {
+                        Some(record.get_record().get_refresh_time())
+                    } else {
+                        None
+                    }
+                })
+                .collect();
+
+            if !refresh_timers.is_empty() {
+                refresh_due.insert(instance);
+                new_timers.extend(refresh_timers);
+            }
+        }
+
+        (refresh_due, new_timers)
+    }
+
+    /// Returns the set of A/AAAA records that are due for refresh for a `hostname`.
+    ///
+    /// For these records, their refresh time will be updated so that they will not refresh again.
+    pub(crate) fn refresh_due_hostname_resolutions(
+        &mut self,
+        hostname: &str,
+    ) -> HashSet<(String, IpAddr)> {
+        let now = current_time_millis();
+
+        self.addr
+            .get_mut(hostname)
+            .into_iter()
+            .flatten()
+            .filter_map(|record| {
+                let rec = record.get_record_mut();
+                if rec.is_expired(now) || !rec.refresh_due(now) {
+                    return None;
+                }
+                rec.refresh_no_more();
+
+                Some((
+                    hostname.to_owned(),
+                    record.any().downcast_ref::<DnsAddress>().unwrap().address,
+                ))
+            })
+            .collect()
+    }
+}

src/dns_parser.rs

@@ -1387,6 +1387,15 @@ impl DnsIncoming {
     }
 }
 
+/// Returns a tuple of (service_type_domain, optional_sub_domain)
+pub fn split_sub_domain(domain: &str) -> (&str, Option<&str>) {
+    if let Some((_, ty_domain)) = domain.rsplit_once("._sub.") {
+        (ty_domain, Some(domain))
+    } else {
+        (domain, None)
+    }
+}
+
 /// Returns UNIX time in millis
 pub fn current_time_millis() -> u64 {
     SystemTime::now()