domain/net/client/cache.rs
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//! A client cache.
//!
//! This module implements a simple message cache provided as a pass through
//! transport. The cache works with any of the other transports.
//! The basic operation is that from a request the query name, class, and type
//! are extracted and the result is cached such that when a new request
//! arrives with the same name, class, and type then the cached response can
//! be returned with the TTL values of the DNS resource records reduced by
//! the amount of time the message has been cached.
//!
//! The response to a query is in general affected by four flags: the
//! AD, CD, DO, and RD flags.
//! These flags are defined in the following RFCs:
//! [RFC 1035](https://tools.ietf.org/html/rfc1035),
//! [RFC 2535](https://tools.ietf.org/html/rfc2535),
//! [RFC 3225](https://tools.ietf.org/html/rfc3225),
//! [RFC 4035](https://tools.ietf.org/html/rfc4035),
//! [RFC 6840](https://tools.ietf.org/html/rfc6840).
//! The cache takes these flags into account to
//! see if a cached response can be returned. In some cases, a cached response
//! with one set of flags can be made suitable for a query with different
//! flags.
//!
//! The [Config] object provides various configuration options, such as
//! the maximum number of cache entries, how long different types of
//! responses should be cached and whether truncated responses should be cached
//! or not.
use crate::base::iana::{Class, Opcode, OptRcode, Rtype};
use crate::base::name::ToName;
use crate::base::{
Header, Message, MessageBuilder, Name, ParsedName, StaticCompressor, Ttl,
};
use crate::dep::octseq::Octets;
// use crate::net::client::clock::{Clock, Elapsed, SystemClock};
use crate::net::client::request::{
ComposeRequest, Error, GetResponse, SendRequest,
};
use crate::rdata::AllRecordData;
use crate::utils::config::DefMinMax;
use bytes::Bytes;
use moka::future::Cache;
use std::boxed::Box;
use std::cmp::min;
use std::fmt::{Debug, Formatter};
use std::future::Future;
use std::pin::Pin;
use std::sync::Arc;
use std::time::Duration;
use std::vec::Vec;
use tokio::time::Instant;
/// Configuration limit for the maximum number of entries in the cache.
const MAX_CACHE_ENTRIES: DefMinMax<u64> =
DefMinMax::new(1_000, 1, 1_000_000_000);
/// Limit on the maximum time a cache entry is considered valid.
///
/// According to [RFC 8767](https://tools.ietf.org/html/rfc8767) the
/// limit should be on the order of days to weeks with a recommended cap of
/// 604800 seconds (7 days).
const MAX_VALIDITY: DefMinMax<Duration> = DefMinMax::new(
Duration::from_secs(604800),
Duration::from_secs(60),
Duration::from_secs(6048000),
);
/// Amount of time to cache transport failures.
///
/// According to [RFC 9520](https://tools.ietf.org/html/rfc9520)
/// at least 1 second and at most 5 minutes.
const TRANSPORT_FAILURE_DURATION: DefMinMax<Duration> = DefMinMax::new(
Duration::from_secs(30),
Duration::from_secs(1),
Duration::from_secs(5 * 60),
);
/// Limit on the amount of time to cache DNS result codes that are not
/// NOERROR or NXDOMAIN.
///
/// According to [RFC 9520](https://tools.ietf.org/html/rfc9520)
/// at least 1 second and at most 5 minutes.
const MISC_ERROR_DURATION: DefMinMax<Duration> = DefMinMax::new(
Duration::from_secs(30),
Duration::from_secs(1),
Duration::from_secs(5 * 60),
);
/// Limit on the amount of time to cache a NXDOMAIN error.
///
/// According to [RFC 2308](https://tools.ietf.org/html/rfc2308)
/// the limit should be one to three hours with a maximum of one day.
const MAX_NXDOMAIN_VALIDITY: DefMinMax<Duration> = DefMinMax::new(
Duration::from_secs(3600),
Duration::from_secs(60),
Duration::from_secs(24 * 3600),
);
/// Limit on the amount of time to cache a NODATA response.
///
/// According to [RFC 2308](https://tools.ietf.org/html/rfc2308)
/// the limit should be one to three hours with a maximum of one day.
const MAX_NODATA_VALIDITY: DefMinMax<Duration> = DefMinMax::new(
Duration::from_secs(3600),
Duration::from_secs(60),
Duration::from_secs(24 * 3600),
);
/// Limit on the amount of time a delegation is considered valid.
const MAX_DELEGATION_VALIDITY: DefMinMax<Duration> = DefMinMax::new(
Duration::from_secs(1_000_000),
Duration::from_secs(60),
Duration::from_secs(1_000_000_000),
);
// The following four flags are relevant to caching: AD, CD, DO, and RD.
// The RD flag is defined in RFC 1035
// (https://tools.ietf.org/html/rfc1035) Section 4.1.1.
// The AD and CD flags are defined in RFC 2535
// (https://tools.ietf.org/html/rfc2535) Section 6.1. However the
// meaning of those flags has been redefined in RFC 4035
// (https://tools.ietf.org/html/rfc4035). With another update for the
// AD flag in RFC 6840 (https://tools.ietf.org/html/rfc6840)
// Sections 5.7 and 5.8.
// The DO flag is defined in RFC 3225
// (https://tools.ietf.org/html/rfc3225) Section 3.
//
// The AD flag needs to be part of the key when DO is clear. When replying,
// if both AD and DO are not set in the original request then AD needs to be
// cleared if it was set in the response (extra look up if no entry with
// AD clear exists).
//
// The CD flag partitions the cache, responses to request with CD set must not
// be visible to requests with CD clear and vice versa.
//
// A request with DO set can only be satisfied with a response to a request
// with DO set. However, if DO in the request is clear then a response to a
// request with DO set can be used if all unrequested DNSSEC records are
// stripped.
//
// A request with RD clear can be satisfied by a response to a request with
// RD set. For simplicitly requests with RD set will only get a cached
// response to another request with RD set. In theory some responses to
// requests with RD clear could be used to satisfy requests with RD set.
// However, this is not implemented.
// Caching the result of a query for a wildcard record seems to disallowed
// by Section 4.3.3 of RFC 1034 (https://tools.ietf.org/html/rfc1034)
// which says:
// A * label appearing in a query name has no special effect, but can be
// used to test for wildcards in an authoritative zone; such a query is the
// only way to get a response containing RRs with an owner name with * in
// it. The result of such a query should not be cached.
//
// However Erratum #5316 (https://www.rfc-editor.org/errata/eid5316) fixes
// this by replacing the word 'cached' with 'used to synthesize RRs'
// Negative caching is described in RFC 2308
// (https://tools.ietf.org/html/rfc2308).
// NXDOMAIN and NODATA require special treatment. NXDOMAIN can be found
// directly in the rcode field. NODATA is the condition where the answer
// section does not contain any record that matches qtype and the message
// is not a referral. NODATA is distinguished from a referral by the presence
// of a SOA record in the authority section (a SOA record present implies
// NODATA). A referral has one or more NS records in the authority section.
// An NXDOMAIN response can only be cached if a SOA record is present in the
// authority section. If the SOA record is absent then the NXDOMAIN response
// should not be cached.
// The TTL of the SOA record should reflect how long the response can be
// cached. Section 3 of the RFC requires authoritative servers to limit the
// TTL of the SOA record in negative responses to the minimum of the MINIUM
// field in the SOA record and the original TTL of the SOA record. For this
// reason, no special treatment is needed. Except that a different value
// should limit the maximum time a negative response can be cached.
//
// Caching unreachable upstream should be limited to 5 minutes.
// Caching SERVFAIL should be limited to 5 minutes.
// Truncated responses require special treatment. RFC 1035, Section 7.4
// (https://tools.ietf.org/html/rfc1035) warns against potentially
// caching partial sets of resource records. However, because this is a
// message cache, the users of the cache still has to decide what to do
// with a truncated response and there is no risk of using cached
// resource records in a different context.
// The issue is made more complex by the introduction of the UDP payload
// size field in RFC 6891, Section 6.1.2
// (https://tools.ietf.org/html/rfc6891).
// This means that a later request with a larger value UDP payload size might
// get an answer that is not truncated. However the complexity of keeping
// track of the UDP payload size in the cache does not seem worth it for the
// following reasons:
// 1) truncated responses are returned by the dgram transport but we expect
// that the dgram_stream transport will be commonly used. So we expect
// very little actual caching of truncated responses.
// 2) To avoid fragmentation, servers are likely to have their own limits on
// the size of replies they send. So a higher UDP payload size may not have
// an effect.
// 3) It is likely that applications have one UDP payload size and do not
// issue the same query with different UDP payload sizes.
// For these reasons, the default is that truncated responses are not cached.
// A configuration option is provided (set_cache_truncated) that enables
// caching of truncated responses without taking into account the UDP payload
// size.
// RFC 8020 (https://tools.ietf.org/html/rfc8020) suggests a separate
// <QNAME, QCLASS> cache for NXDOMAIN, but that may be too hard to implement.
// RFC 9520 (https://tools.ietf.org/html/rfc9520) requires resolution
// failures to be cached for at least one second. Resolution failure must
// not be cached for longer than 5 minutes.
// RFC 8767 (https://tools.ietf.org/html/rfc8767) describes serving stale
// data.
//------------ Config ---------------------------------------------------------
/// Configuration of a cache.
#[derive(Clone, Debug)]
pub struct Config {
/// Maximum number of cache entries.
max_cache_entries: u64,
/// Maximum validity of a normal result.
max_validity: Duration,
/// Cache duration of transport failures.
transport_failure_duration: Duration,
/// Cache durations of misc. errors. (not NXDOMAIN or NOERROR)
misc_error_duration: Duration,
/// Maximum validity of NXDOMAIN results.
max_nxdomain_validity: Duration,
/// Maximum validity of NODATA results.
max_nodata_validity: Duration,
/// Maximum validity of delegations.
max_delegation_validity: Duration,
/// Whether to cache a truncated response or not.
cache_truncated: bool,
}
impl Config {
/// Creates a new config with default values.
///
/// The default values are documented at the relevant set_* methods.
pub fn new() -> Self {
Default::default()
}
/// Set the maximum number of cache entries.
///
/// The value has to be at least one, at most 1,000,000,000 and the
/// default is 1000.
///
/// The values are just best guesses at the moment. The upper limit is
/// set to be somewhat safe without being too limiting. The default is
/// meant to be reasonable for a small system.
pub fn set_max_cache_entries(&mut self, value: u64) {
self.max_cache_entries = MAX_CACHE_ENTRIES.limit(value)
}
/// Set the maximum validity of cache entries.
///
/// The value has to be at least 60 seconds, at most 6,048,000 seconds
/// (10 weeks) and the default is 604800 seconds (one week).
pub fn set_max_validity(&mut self, value: Duration) {
self.max_validity = MAX_VALIDITY.limit(value)
}
/// Set the time to cache transport failures.
///
/// The value has to be at least one second, at most 300 seconds
/// (five minutes) and the default is 30 seconds.
pub fn set_transport_failure_duration(&mut self, value: Duration) {
self.transport_failure_duration =
TRANSPORT_FAILURE_DURATION.limit(value)
}
/// Set the maximum time to cache results other than NOERROR or NXDOMAIN.
///
/// The value has to be at least one second, at most 300 seconds
/// (five minutes) and the default is 30 seconds.
pub fn set_misc_error_duration(&mut self, value: Duration) {
self.misc_error_duration = MISC_ERROR_DURATION.limit(value)
}
/// Set the maximum time to cache NXDOMAIN results.
///
/// The value has to be at least 60 seconds (one minute), at most 86,400
/// seconds (one day) and the default is 3,600 seconds (one hour).
pub fn set_max_nxdomain_validity(&mut self, value: Duration) {
self.max_nxdomain_validity = MAX_NXDOMAIN_VALIDITY.limit(value)
}
/// Set the maximum time to cache NODATA results.
///
/// The value has to be at least 60 seconds (one minute), at most 86,400
/// seconds (one day) and the default is 3,600 seconds (one hour).
pub fn set_max_nodata_validity(&mut self, value: Duration) {
self.max_nodata_validity = MAX_NODATA_VALIDITY.limit(value)
}
/// Set the maximum time to cache delegations.
///
/// The value has to be at least 60 seconds (one minute), at most
/// 1,000,000,000 seconds and the default is 1,000,000 seconds.
pub fn set_max_delegation_validity(&mut self, value: Duration) {
self.max_delegation_validity = MAX_DELEGATION_VALIDITY.limit(value)
}
/// Enable or disable caching of response messages with the TC
/// (truncated) flag set.
///
/// The default value is false (disabled).
pub fn set_cache_truncated(&mut self, value: bool) {
self.cache_truncated = value;
}
}
impl Default for Config {
fn default() -> Self {
Self {
max_cache_entries: MAX_CACHE_ENTRIES.default(),
max_validity: MAX_VALIDITY.default(),
transport_failure_duration: TRANSPORT_FAILURE_DURATION.default(),
misc_error_duration: MISC_ERROR_DURATION.default(),
max_nxdomain_validity: MAX_NXDOMAIN_VALIDITY.default(),
max_nodata_validity: MAX_NODATA_VALIDITY.default(),
max_delegation_validity: MAX_DELEGATION_VALIDITY.default(),
cache_truncated: false,
}
}
}
//------------ Connection -----------------------------------------------------
#[derive(Clone)]
/// A connection that caches responses from an upstream connection.
pub struct Connection<
Upstream, /*, C: Clock + Send + Sync = SystemClock*/
> {
/// Upstream transport to use for requests.
upstream: Upstream,
/// The cache for this connection.
cache: Cache<Key, Arc<Value /*<C>*/>>,
/// The configuration of this connection.
config: Config,
// /// The clock to use for expiring cache entries.
// clock: C,
}
impl<Upstream> Connection<Upstream> {
/// Create a new connection with default configuration parameters.
///
/// Note that Upstream needs to implement [SendRequest]
/// (and Clone/Send/Sync) to be useful.
pub fn new(upstream: Upstream) -> Self {
Self::with_config(upstream, Default::default())
}
/// Create a new connection with specified configuration parameters.
///
/// Note that Upstream needs to implement [SendRequest]
/// (and Clone/Send/Sync) to be useful.
pub fn with_config(upstream: Upstream, config: Config) -> Self {
Self {
upstream,
cache: Cache::new(config.max_cache_entries),
config,
// clock: SystemClock::new(),
}
}
}
impl<Upstream /*, C*/> Connection<Upstream /*, C*/>
// where
// C: Clock + Send + Sync + 'static,
{
// /// Create a new connection with default configuration parameters.
// pub fn new_with_time(upstream: Upstream/, clock: C) -> Self {
// Self::with_time_config(upstream, clock, Default::default())
// }
// /// Create a new connection with specified configuration parameters.
// pub fn with_time_config(
// upstream: Upstream,
// clock: C,
// config: Config,
// ) -> Self {
// Self {
// upstream,
// cache: Cache::new(config.max_cache_entries),
// config,
// clock,
// }
// }
}
//------------ SendRequest ----------------------------------------------------
impl<CR, Upstream /*, C*/> SendRequest<CR>
for Connection<Upstream /*, C*/>
where
CR: Clone + ComposeRequest + 'static,
Upstream: Clone + SendRequest<CR> + Send + Sync + 'static,
// C: Clock + Debug + Send + Sync + 'static,
{
fn send_request(
&self,
request_msg: CR,
) -> Box<dyn GetResponse + Send + Sync> {
Box::new(Request::<CR, Upstream /*, C*/>::new(
request_msg,
self.upstream.clone(),
self.cache.clone(),
self.config.clone(),
// self.clock.clone(),
))
}
}
//------------ Request --------------------------------------------------------
/// The state of a request that is executed.
pub struct Request<CR, Upstream /*, C*/>
where
CR: Send + Sync,
Upstream: Send + Sync,
// C: Clock + Send + Sync,
{
/// State of the request.
state: RequestState,
/// The request message.
request_msg: CR,
/// The upstream transport of the connection.
upstream: Upstream,
/// The cache of the connection.
cache: Cache<Key, Arc<Value /*<C>*/>>,
/// The configuration of the connection.
config: Config,
// /// The clock to use for expiring cache entries.
// clock: C,
}
impl<CR, Upstream /*, C*/> Request<CR, Upstream /*, C*/>
where
CR: Clone + ComposeRequest + Send + Sync,
Upstream: SendRequest<CR> + Send + Sync,
// C: Clock + Debug + Send + Sync + 'static,
{
/// Create a new Request object.
fn new(
request_msg: CR,
upstream: Upstream,
cache: Cache<Key, Arc<Value /*<C>*/>>,
config: Config,
// clock: C,
) -> Request<CR, Upstream /*, C*/> {
Self {
state: RequestState::Init,
request_msg,
upstream,
cache,
config,
// clock,
}
}
/// This is the implementation of the get_response method.
///
/// This function is cancel safe.
async fn get_response_impl(&mut self) -> Result<Message<Bytes>, Error> {
loop {
match &mut self.state {
RequestState::Init => {
let msg = self.request_msg.to_message()?;
let header = msg.header();
let opcode = header.opcode();
// Extract Qname, Qclass, Qtype
let mut question_section = msg.question();
let question = match question_section.next() {
None => {
// No question. Just forward the request.
let request = self
.upstream
.send_request(self.request_msg.clone());
self.state =
RequestState::GetResponseNoCache(request);
continue;
}
Some(question) => question?,
};
if question_section.next().is_some() {
// More than one question. Just forward the request.
let request = self
.upstream
.send_request(self.request_msg.clone());
self.state =
RequestState::GetResponseNoCache(request);
continue;
}
let qname = question.qname();
let qclass = question.qclass();
let qtype = question.qtype();
if !(opcode == Opcode::QUERY && qclass == Class::IN) {
// Anything other than a query on the Internet class
// should not be cached.
let request = self
.upstream
.send_request(self.request_msg.clone());
self.state =
RequestState::GetResponseNoCache(request);
continue;
}
let mut ad = header.ad();
let cd = header.cd();
let rd = header.rd();
let dnssec_ok =
msg.opt().map_or(false, |opt| opt.dnssec_ok());
if dnssec_ok && !ad {
ad = true;
}
let key =
Key::new(qname, qclass, qtype, ad, cd, dnssec_ok, rd);
let opt_ce = self.cache_lookup(&key).await?;
if let Some(value) = opt_ce {
let opt_response = value.get_response(qname);
if let Some(response) = opt_response {
return response;
}
}
let request =
self.upstream.send_request(self.request_msg.clone());
self.state = RequestState::GetResponse(key, request);
continue;
}
RequestState::GetResponse(key, request) => {
let response = request.get_response().await;
// The clone of key needs to happen before cache_insert
// otherwise there will be a conflict between self and key.
let key = key.clone();
let value = Arc::new(Value::new(
response.clone(),
&self.config,
// &self.clock,
)?);
self.cache_insert(key, value).await;
return response;
}
RequestState::GetResponseNoCache(request) => {
return request.get_response().await;
}
}
}
}
/// Try to find a cache entry for the key.
async fn cache_lookup(
&self,
key: &Key,
) -> Result<Option<Arc<Value /*<C>*/>>, Error> {
// There are 4 flags that may affect the response to a query.
// In some cases the response to one value of a flag could be
// used for the other value.
// This function takes all 4 flags into account. First we take care
// of the CD flag. This flag has to be used as is, so there is not
// much to do. Next we pass the request to a function that looks
// at RD, DO, and AD.
self.cache_lookup_rd_do_ad(key).await
}
/// Try to find an cache entry for the key taking into account the
/// RD, DO, and AD flags. The CD flag is kept unchanged.
async fn cache_lookup_rd_do_ad(
&self,
key: &Key,
) -> Result<Option<Arc<Value /*<C>*/>>, Error> {
// For RD=1 we can only use responses to queries with RD set.
// For RD=0, first try with RD=0 and then try with RD=1. If
// RD=1 has an answer, store it as an answer for RD=0.
let opt_value = self.cache_lookup_do_ad(key).await?;
if opt_value.is_some() || key.rd {
return Ok(opt_value);
}
// Look if there is something with RD=1. We can use the
// response unmodified.
let mut alt_key = key.clone();
alt_key.rd = true;
let opt_value = self.cache_lookup_do_ad(&alt_key).await?;
if let Some(value) = opt_value {
let value = update_header(
value,
&self.config,
|_hdr| true,
|hdr| hdr.set_rd(false),
)?;
self.cache_insert(key.clone(), value.clone()).await;
return Ok(Some(value));
}
Ok(opt_value)
}
/// Try to find an cache entry for the key taking into account the
/// DO and AD flags. The CD and RD flags are kept unchanged.
async fn cache_lookup_do_ad(
&self,
key: &Key,
) -> Result<Option<Arc<Value /*<C>*/>>, Error> {
// For DO=1 we can only use responses to queries with DO set.
// For DO=0, first try with DO=0 and then try with DO=1. If
// DO=1 has an answer, remove DNSSEC related resource records.
// If AD is clear then clear the AD bit.
// If DO is set then AD is irrelevant. Force AD to be set for
// consistency (if DO is set then with respect to the AD flag
// the behavior is as if AD is set).
let opt_value = self.cache_lookup_ad(key).await?;
if opt_value.is_some() || key.addo.dnssec_ok() {
return Ok(opt_value);
}
if is_dnssec(key.qtype) {
// An explicit request for one of the DNSSEC types but
// DO is not set. Force the request to be sent explicitly.
return Ok(None);
}
let mut alt_key = key.clone();
alt_key.addo = AdDo::Do;
let opt_value = self.cache.get(&alt_key).await;
if let Some(value) = opt_value {
let value = update_message(
value,
&self.config,
|_hdr| true,
|msg| remove_dnssec(msg, key.addo.ad()),
)?;
self.cache_insert(key.clone(), value.clone()).await;
return Ok(Some(value));
}
Ok(opt_value)
}
/// Try to find an cache entry for the key taking into account the
/// AD flag. The CD, DO, and RD flags are kept unchanged.
async fn cache_lookup_ad(
&self,
key: &Key,
) -> Result<Option<Arc<Value /*<C>*/>>, Error> {
// For AD=1 we can only use responses to queries with AD set.
// For AD=0, first try with AD=0 and then try with AD=1. If
// AD=1 has an answer, clear the AD bit.
let opt_value = self.cache.get(key).await;
if opt_value.is_some() || key.addo.ad() {
return Ok(opt_value);
}
let mut alt_key = key.clone();
alt_key.addo = AdDo::Ad;
let opt_value = self.cache.get(&alt_key).await;
if let Some(value) = opt_value {
let value = update_header(
value,
&self.config,
|hdr| hdr.ad(),
|hdr| hdr.set_ad(false),
)?;
self.cache_insert(key.clone(), value.clone()).await;
return Ok(Some(value));
}
Ok(opt_value)
}
/// Insert new entry in the cache.
///
/// Do not insert if the validity is zero.
/// Make sure to clear the AA flag.
async fn cache_insert(&self, key: Key, value: Arc<Value /*<C>*/>) {
if value.valid_for.is_zero() {
return;
}
let value = match prepare_for_insert(value.clone(), &self.config) {
Ok(value) => value,
Err(e) => {
// Create a new value based on this error
Arc::new(
Value/*::<C>*/::new_from_value_and_response(
value,
Err(e),
&self.config,
)
.expect("value from error does not fail"),
)
}
};
self.cache.insert(key, value).await
}
}
impl<CR, Upstream /*, C*/> Debug for Request<CR, Upstream /*, C*/>
where
CR: Send + Sync,
Upstream: Send + Sync,
// C: Clock + Send + Sync,
{
fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), core::fmt::Error> {
f.debug_struct("Request")
.field("fut", &format_args!("_"))
.finish()
}
}
impl<CR, Upstream /*, C*/> GetResponse for Request<CR, Upstream /*, C*/>
where
CR: Clone + ComposeRequest + Debug + Sync,
Upstream: SendRequest<CR> + Send + Sync + 'static,
// C: Clock + Debug + Send + Sync + 'static,
{
fn get_response(
&mut self,
) -> Pin<
Box<
dyn Future<Output = Result<Message<Bytes>, Error>>
+ Send
+ Sync
+ '_,
>,
> {
Box::pin(self.get_response_impl())
}
}
//------------ RequestState ---------------------------------------------------
/// States of the state machine in get_response_impl
enum RequestState {
/// Initial state, perform a cache lookup.
Init,
/// Wait for a response and insert the response in the cache.
GetResponse(Key, Box<dyn GetResponse + Send + Sync>),
/// Wait for a response but do not insert the response in the cache.
GetResponseNoCache(Box<dyn GetResponse + Send + Sync>),
}
//------------ Key ------------------------------------------------------------
/// The key for cache entries.
///
/// Note that the AD and DO flags are combined into a single enum.
#[derive(Clone, Debug, Eq, Hash, PartialEq)]
struct Key {
/// DNS name in the request.
qname: Name<Bytes>,
/// The request class. Always IN at the moment.
qclass: Class,
/// The requested type.
qtype: Rtype,
/// Value of the AD and Do flags.
addo: AdDo,
/// Value of the CD flag.
cd: bool,
/// Value of the RD flag.
rd: bool,
}
impl Key {
/// Create a new key object.
fn new<TDN>(
qname: TDN,
qclass: Class,
qtype: Rtype,
ad: bool,
cd: bool,
dnssec_ok: bool,
rd: bool,
) -> Key
where
TDN: ToName,
{
Self {
qname: qname.to_canonical_name(),
qclass,
qtype,
addo: AdDo::new(ad, dnssec_ok),
cd,
rd,
}
}
}
/// The DO and AD flag have a special relationship. If the DO flag is set,
/// then the AD flag is irrelevant, but to code looking for the AD flag
/// we pretend that it is set. So we have three possibilities: DO is set
/// and AD is irrelevant, DO is not set, but AD is set. Or neither DO nor
/// AD is set.
#[derive(Clone, Debug, Hash, PartialEq, Eq)]
enum AdDo {
/// DO is set, AD is ignored.
Do,
/// DO is clear, AD is set.
Ad,
/// Both AD and DO are clear.
None,
}
impl AdDo {
/// Create a new AdDo object based on the AD and DO flags.
fn new(ad: bool, dnssec_ok: bool) -> Self {
if dnssec_ok {
AdDo::Do
} else if ad {
AdDo::Ad
} else {
AdDo::None
}
}
/// Return whether AD is set or should be considered set.
fn ad(&self) -> bool {
match self {
// Do acts as if Ad is set
AdDo::Ad | AdDo::Do => true,
AdDo::None => false,
}
}
/// Return whether DO is set.
fn dnssec_ok(&self) -> bool {
match self {
AdDo::Do => true,
AdDo::Ad | AdDo::None => false,
}
}
}
//------------ Value ----------------------------------------------------------
/// The value to be cached.
#[derive(Debug)]
struct Value
/*<C>*/
// where
// C: Clock + Send + Sync,
{
/// Creation time of the cache entry.
created_at: Instant,
/// The amount time the cache entry is valid.
valid_for: Duration,
/// The cached response.
response: Result<Message<Bytes>, Error>,
}
impl Value
// impl<C> Value<C>
// where
// C: Clock + Send + Sync,
{
/// Create a new value object.
fn new(
response: Result<Message<Bytes>, Error>,
config: &Config,
// clock: &C,
) -> Result<Value /*<C>*/, Error> {
Ok(Self {
created_at: Instant::now(),
valid_for: validity(&response, config)?,
response,
})
}
/// Create a value object that is derived from another value object.
fn new_from_value_and_response(
val: Arc<Value /*<C>*/>,
response: Result<Message<Bytes>, Error>,
config: &Config,
) -> Result<Value /*<C>*/, Error> {
Ok(Self {
created_at: val.created_at, //.clone(),
valid_for: validity(&response, config)?,
response,
})
}
/// Get a response. Either return None if the value has expired or
/// return a response message with decremented TTL values.
fn get_response<TDN>(
&self,
orig_qname: TDN,
) -> Option<Result<Message<Bytes>, Error>>
where
TDN: ToName + Clone,
// C: Clock + Send + Sync,
{
let elapsed = self.created_at.elapsed();
if elapsed > self.valid_for {
return None;
}
let secs = elapsed.as_secs() as u32;
let response = decrement_ttl(orig_qname, &self.response, secs);
Some(response)
}
}
//------------ Utility functions ----------------------------------------------
/// Compute how long a response can be cached.
fn validity(
response: &Result<Message<Bytes>, Error>,
config: &Config,
) -> Result<Duration, Error> {
let Ok(msg) = response else {
return Ok(config.transport_failure_duration);
};
if msg.header().tc() && !config.cache_truncated {
// Return zero duration to signal that the truncated message should
// not be cached.
return Ok(Duration::ZERO);
}
let mut min_val = config.max_validity;
match msg.opt_rcode() {
OptRcode::NOERROR => {
match classify_no_error(msg)? {
NoErrorType::Answer => (),
NoErrorType::NoData => {
min_val = min(min_val, config.max_nodata_validity)
}
NoErrorType::Delegation => {
min_val = min(min_val, config.max_delegation_validity)
}
NoErrorType::NoErrorWeird =>
// Weird NODATA response. Don't cache this.
{
min_val = Duration::ZERO
}
}
}
OptRcode::NXDOMAIN => {
min_val = min(min_val, config.max_nxdomain_validity);
}
_ => {
min_val = min(min_val, config.misc_error_duration);
}
}
let msg = msg.question();
let mut msg = msg.answer()?;
for rr in &mut msg {
let rr = rr?;
min_val =
min(min_val, Duration::from_secs(rr.ttl().as_secs() as u64));
}
let mut msg = msg.next_section()?.expect("section should be present");
for rr in &mut msg {
let rr = rr?;
min_val =
min(min_val, Duration::from_secs(rr.ttl().as_secs() as u64));
}
let msg = msg.next_section()?.expect("section should be present");
for rr in msg {
let rr = rr?;
if rr.rtype() != Rtype::OPT {
min_val =
min(min_val, Duration::from_secs(rr.ttl().as_secs() as u64));
}
}
Ok(min_val)
}
/// Return a new message with decremented TTL values.
fn decrement_ttl<TDN>(
orig_qname: TDN,
response: &Result<Message<Bytes>, Error>,
amount: u32,
) -> Result<Message<Bytes>, Error>
where
TDN: ToName + Clone,
{
let msg = match response {
Err(err) => return Err(err.clone()),
Ok(msg) => msg,
};
let amount = Ttl::from_secs(amount);
let mut target =
MessageBuilder::from_target(StaticCompressor::new(Vec::new()))
.expect("Vec is expected to have enough space");
let source = msg;
*target.header_mut() = source.header();
let source = source.question();
let mut target = target.question();
for rr in source {
let rr = rr?;
target
.push((orig_qname.clone(), rr.qtype(), rr.qclass()))
.expect("push failed");
}
let mut source = source.answer()?;
let mut target = target.answer();
for rr in &mut source {
let mut rr = rr?
.into_record::<AllRecordData<_, ParsedName<_>>>()?
.expect("record expected");
rr.set_ttl(rr.ttl() - amount);
target.push(rr).expect("push failed");
}
let mut source =
source.next_section()?.expect("section should be present");
let mut target = target.authority();
for rr in &mut source {
let mut rr = rr?
.into_record::<AllRecordData<_, ParsedName<_>>>()?
.expect("record expected");
rr.set_ttl(rr.ttl() - amount);
target.push(rr).expect("push failed");
}
let source = source.next_section()?.expect("section should be present");
let mut target = target.additional();
for rr in source {
let rr = rr?;
let mut rr = rr
.into_record::<AllRecordData<_, ParsedName<_>>>()?
.expect("record expected");
if rr.rtype() != Rtype::OPT {
rr.set_ttl(rr.ttl() - amount);
}
target.push(rr).expect("push failed");
}
let result = target.as_builder().clone();
let msg =
Message::<Bytes>::from_octets(result.finish().into_target().into())
.expect(
"Message should be able to parse output from MessageBuilder",
);
Ok(msg)
}
/// Return a new message without the DNSSEC type RRSIG, NSEC, and NSEC3.
fn remove_dnssec(
msg: &Message<Bytes>,
ad: bool,
) -> Result<Message<Bytes>, Error> {
let mut target =
MessageBuilder::from_target(StaticCompressor::new(Vec::new()))
.expect("Vec is expected to have enough space");
let source = msg;
*target.header_mut() = source.header();
if !ad {
// Clear ad
target.header_mut().set_ad(false);
}
let source = source.question();
let mut target = target.question();
for rr in source {
target.push(rr?).expect("push failed");
}
let mut source = source.answer()?;
let mut target = target.answer();
for rr in &mut source {
let rr = rr?
.into_record::<AllRecordData<_, ParsedName<_>>>()?
.expect("record expected");
if is_dnssec(rr.rtype()) {
continue;
}
target.push(rr).expect("push error");
}
let mut source =
source.next_section()?.expect("section should be present");
let mut target = target.authority();
for rr in &mut source {
let rr = rr?
.into_record::<AllRecordData<_, ParsedName<_>>>()?
.expect("record expected");
if is_dnssec(rr.rtype()) {
continue;
}
target.push(rr).expect("push error");
}
let source = source.next_section()?.expect("section should be present");
let mut target = target.additional();
for rr in source {
let rr = rr?;
let rr = rr
.into_record::<AllRecordData<_, ParsedName<_>>>()?
.expect("record expected");
if is_dnssec(rr.rtype()) {
continue;
}
target.push(rr).expect("push error");
}
let result = target.as_builder().clone();
Ok(
Message::<Bytes>::from_octets(result.finish().into_target().into())
.expect(
"Message should be able to parse output from MessageBuilder",
),
)
}
/// Check if a type is a DNSSEC type that needs to be removed.
fn is_dnssec(rtype: Rtype) -> bool {
rtype == Rtype::RRSIG || rtype == Rtype::NSEC || rtype == Rtype::NSEC3
}
/// This type represents that various subtypes of a NOERROR result.
enum NoErrorType {
/// The result is an answer to the question.
Answer,
/// The name exists, but there is not data for the request class and tpye
/// combination.
NoData,
/// The upstream DNS server sent a delegation to another DNS zone.
Delegation,
/// None of the above. This is not a valid response.
NoErrorWeird,
}
/// Classify a responses with a NOERROR result.
fn classify_no_error<Octs>(msg: &Message<Octs>) -> Result<NoErrorType, Error>
where
Octs: Octets,
{
// Check if we have something that resembles an answer.
let mut question_section = msg.question();
let question = question_section.next().expect("section expected")?;
let qtype = question.qtype();
let qclass = question.qclass();
// Note we only look qtype and qclass. The goal is not to perform
// a consistency check. Just whether there is supposed to be an
// answer or not.
let mut msg = msg.answer()?;
for rr in &mut msg {
let rr = rr?;
if rr.rtype() == qtype && rr.class() == qclass {
// We found an answer.
return Ok(NoErrorType::Answer);
}
}
// No answer. Check the authority section for SOA and NS records.
// If the SOA is present then the response is a NODATA response.
// If SOA records are absent but NS records are present then the
// response is a delegation.
let mut found_ns = false;
let mut msg = msg.next_section()?.expect("section should be present");
for rr in &mut msg {
let rr = rr?;
if rr.class() == qclass && rr.rtype() == Rtype::SOA {
return Ok(NoErrorType::NoData);
}
if rr.class() == qclass && rr.rtype() == Rtype::NS {
found_ns = true;
}
}
if found_ns {
return Ok(NoErrorType::Delegation);
}
// Neither SOA nor NS were found. This is a broken response.
Ok(NoErrorType::NoErrorWeird)
}
/// Prepare a value for inserting in the cache by clearing the AA flag if
/// set.
fn prepare_for_insert(
value: Arc<Value /*<C>*/>,
config: &Config,
) -> Result<Arc<Value /*<C>*/>, Error>
// where
// C: Clock + Send + Sync,
{
update_header(value, config, |hdr| hdr.aa(), |hdr| hdr.set_aa(false))
}
/// Update the Header of a Message in a Value by creating a new Value with a
/// new Message if the Header needs to be changed.
///
/// Return the original Value if no change is needed.
/// hdrtst checks if the header needs updating, fhdr modifies the header.
fn update_header(
value: Arc<Value /*<C>*/>,
config: &Config,
hdrtst: fn(hdr: &Header) -> bool,
fhdr: fn(&mut Header) -> (),
) -> Result<Arc<Value /*<C>*/>, Error>
// where
// C: Clock + Send + Sync,
{
update_message(value, config, hdrtst, |msg| {
let mut msg = Message::<Vec<u8>>::from_octets(msg.as_slice().into())?;
let hdr = msg.header_mut();
fhdr(hdr);
Ok(Message::<Bytes>::from_octets(msg.into_octets().into())?)
})
}
/// Update a Message in a Value by creating a new Value with a
/// new Message if the Message needs to be changed.
///
/// Return the original Value if no change is needed.
/// hdrtst checks if the Message needs updating, fmsg returns a new Message.
fn update_message</*C, */ FmsgFn>(
value: Arc<Value /*<C>*/>,
config: &Config,
hdrtst: fn(hdr: &Header) -> bool,
fmsg: FmsgFn,
) -> Result<Arc<Value /*<C>*/>, Error>
where
// C: Clock + Send + Sync,
FmsgFn: Fn(&Message<Bytes>) -> Result<Message<Bytes>, Error>,
{
Ok(match &value.response {
Err(_) => {
// No message, no need to change anything.
value
}
Ok(msg) => {
if hdrtst(&msg.header()) {
let msg = fmsg(msg)?;
Arc::new(Value/*::<C>*/::new_from_value_and_response(
value.clone(),
Ok(msg),
config,
)?)
} else {
// No need to change anything. Just insert this value.
value
}
}
})
}