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rrcache.go
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rrcache.go
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package resolver
import (
"context"
"fmt"
"net"
"time"
"github.com/miekg/dns"
"github.com/safing/portbase/log"
"github.com/safing/portmaster/nameserver/nsutil"
"github.com/safing/portmaster/netenv"
)
// RRCache is a single-use structure to hold a DNS response.
// Persistence is handled through NameRecords because of a limitation of the
// underlying dns library.
//
//nolint:maligned
type RRCache struct {
// Respnse Header
Domain string
Question dns.Type
RCode int
// Response Content
Answer []dns.RR `json:"-"`
Ns []dns.RR `json:"-"`
Extra []dns.RR `json:"-"`
Expires int64
// Resolver Information
Resolver *ResolverInfo `json:"-"`
// Metadata about the request and handling
ServedFromCache bool
RequestingNew bool
IsBackup bool
Filtered bool
FilteredEntries []string
// Modified holds when this entry was last changed, ie. saved to database.
// This field is only populated when the entry comes from the cache.
Modified int64
}
// ID returns the ID of the RRCache consisting of the domain and question type.
func (rrCache *RRCache) ID() string {
return rrCache.Domain + rrCache.Question.String()
}
// Expired returns whether the record has expired.
func (rrCache *RRCache) Expired() bool {
return rrCache.Expires <= time.Now().Unix()
}
// ExpiresSoon returns whether the record will expire soon (or already has) and
// should already be refreshed.
func (rrCache *RRCache) ExpiresSoon() bool {
return rrCache.Expires <= time.Now().Unix()+refreshTTL
}
// Clean sets all TTLs to 17 and sets cache expiry with specified minimum.
func (rrCache *RRCache) Clean(minExpires uint32) {
var lowestTTL uint32 = 0xFFFFFFFF
var header *dns.RR_Header
// set TTLs to 17
// TODO: double append? is there something more elegant?
for _, rr := range append(rrCache.Answer, append(rrCache.Ns, rrCache.Extra...)...) {
header = rr.Header()
if lowestTTL > header.Ttl {
lowestTTL = header.Ttl
}
header.Ttl = 17
}
// TTL range limits
switch {
case lowestTTL < minExpires:
lowestTTL = minExpires
case lowestTTL > maxTTL:
lowestTTL = maxTTL
}
// shorten caching
switch {
case rrCache.RCode != dns.RcodeSuccess:
// Any sort of error.
lowestTTL = 10
case netenv.IsConnectivityDomain(rrCache.Domain):
// Responses from these domains might change very quickly depending on the environment.
lowestTTL = 3
case len(rrCache.Answer) == 0:
// Empty answer section: Domain exists, but not the queried RR.
lowestTTL = 60
case !netenv.Online():
// Not being fully online could mean that we get funny responses.
lowestTTL = 60
}
// log.Tracef("lowest TTL is %d", lowestTTL)
rrCache.Expires = time.Now().Unix() + int64(lowestTTL)
}
// ExportAllARecords return of a list of all A and AAAA IP addresses.
func (rrCache *RRCache) ExportAllARecords() (ips []net.IP) {
for _, rr := range rrCache.Answer {
if rr.Header().Class != dns.ClassINET {
continue
}
switch rr.Header().Rrtype {
case dns.TypeA:
aRecord, ok := rr.(*dns.A)
if ok {
ips = append(ips, aRecord.A)
}
case dns.TypeAAAA:
aaaaRecord, ok := rr.(*dns.AAAA)
if ok {
ips = append(ips, aaaaRecord.AAAA)
}
}
}
return
}
// ToNameRecord converts the RRCache to a NameRecord for cleaner persistence.
func (rrCache *RRCache) ToNameRecord() *NameRecord {
newRecord := &NameRecord{
Domain: rrCache.Domain,
Question: rrCache.Question.String(),
RCode: rrCache.RCode,
Expires: rrCache.Expires,
Resolver: rrCache.Resolver,
}
// Serialize RR entries to strings.
newRecord.Answer = toNameRecordSection(rrCache.Answer)
newRecord.Ns = toNameRecordSection(rrCache.Ns)
newRecord.Extra = toNameRecordSection(rrCache.Extra)
return newRecord
}
func toNameRecordSection(rrSection []dns.RR) []string {
serialized := make([]string, 0, len(rrSection))
for _, entry := range rrSection {
// Ignore some RR types.
switch entry.Header().Rrtype {
case dns.TypeOPT:
// This record type cannot be unserialized again and only consists of
// additional metadata.
case dns.TypeNULL:
default:
serialized = append(serialized, entry.String())
}
}
return serialized
}
// rcodeIsCacheable returns whether a record with the given RCode should be cached.
func rcodeIsCacheable(rCode int) bool {
switch rCode {
case dns.RcodeSuccess, dns.RcodeNameError, dns.RcodeRefused:
return true
default:
return false
}
}
// Cacheable returns whether the record should be cached.
func (rrCache *RRCache) Cacheable() bool {
return rcodeIsCacheable(rrCache.RCode)
}
// Save saves the RRCache to the database as a NameRecord.
func (rrCache *RRCache) Save() error {
if !rrCache.Cacheable() {
return nil
}
return rrCache.ToNameRecord().Save()
}
// GetRRCache tries to load the corresponding NameRecord from the database and convert it.
func GetRRCache(domain string, question dns.Type) (*RRCache, error) {
rrCache := &RRCache{
Domain: domain,
Question: question,
}
nameRecord, err := GetNameRecord(domain, question.String())
if err != nil {
return nil, err
}
rrCache.RCode = nameRecord.RCode
rrCache.Expires = nameRecord.Expires
for _, entry := range nameRecord.Answer {
rrCache.Answer = parseRR(rrCache.Answer, entry)
}
for _, entry := range nameRecord.Ns {
rrCache.Ns = parseRR(rrCache.Ns, entry)
}
for _, entry := range nameRecord.Extra {
rrCache.Extra = parseRR(rrCache.Extra, entry)
}
rrCache.Resolver = nameRecord.Resolver
rrCache.ServedFromCache = true
rrCache.Modified = nameRecord.Meta().Modified
return rrCache, nil
}
func parseRR(section []dns.RR, entry string) []dns.RR {
rr, err := dns.NewRR(entry)
switch {
case err != nil:
log.Warningf("resolver: failed to parse cached record %q: %s", entry, err)
case rr == nil:
log.Warningf("resolver: failed to parse cached record %q: resulted in nil record", entry)
default:
return append(section, rr)
}
return section
}
// Flags formats ServedFromCache and RequestingNew to a condensed, flag-like format.
func (rrCache *RRCache) Flags() string {
var s string
if rrCache.ServedFromCache {
s += "C"
}
if rrCache.RequestingNew {
s += "R"
}
if rrCache.IsBackup {
s += "B"
}
if rrCache.Filtered {
s += "F"
}
if s != "" {
return fmt.Sprintf(" [%s]", s)
}
return ""
}
// ShallowCopy returns a shallow copy of the cache. slices are not copied, but referenced.
func (rrCache *RRCache) ShallowCopy() *RRCache {
return &RRCache{
Domain: rrCache.Domain,
Question: rrCache.Question,
RCode: rrCache.RCode,
Answer: rrCache.Answer,
Ns: rrCache.Ns,
Extra: rrCache.Extra,
Expires: rrCache.Expires,
Resolver: rrCache.Resolver,
ServedFromCache: rrCache.ServedFromCache,
RequestingNew: rrCache.RequestingNew,
IsBackup: rrCache.IsBackup,
Filtered: rrCache.Filtered,
FilteredEntries: rrCache.FilteredEntries,
Modified: rrCache.Modified,
}
}
// ReplaceAnswerNames is a helper function that replaces all answer names, that
// match the query domain, with another value. This is used to support handling
// non-standard query names, which are resolved normalized, but have to be
// reverted back for the origin non-standard query name in order for the
// clients to recognize the response.
func (rrCache *RRCache) ReplaceAnswerNames(fqdn string) {
for _, answer := range rrCache.Answer {
if answer.Header().Name == rrCache.Domain {
answer.Header().Name = fqdn
}
}
}
// ReplyWithDNS creates a new reply to the given query with the data from the
// RRCache, and additional informational records.
func (rrCache *RRCache) ReplyWithDNS(ctx context.Context, request *dns.Msg) *dns.Msg {
// reply to query
reply := new(dns.Msg)
reply.SetRcode(request, rrCache.RCode)
reply.Answer = rrCache.Answer
reply.Ns = rrCache.Ns
reply.Extra = rrCache.Extra
return reply
}
// GetExtraRRs returns a slice of RRs with additional informational records.
func (rrCache *RRCache) GetExtraRRs(ctx context.Context, query *dns.Msg) (extra []dns.RR) {
// Add cache status and source of data.
if rrCache.ServedFromCache {
extra = addExtra(ctx, extra, "served from cache, resolved by "+rrCache.Resolver.DescriptiveName())
} else {
extra = addExtra(ctx, extra, "freshly resolved by "+rrCache.Resolver.DescriptiveName())
}
// Add expiry and cache information.
switch {
case rrCache.Expires == 0:
extra = addExtra(ctx, extra, "record does not expire")
case rrCache.Expired():
extra = addExtra(ctx, extra, fmt.Sprintf("record expired since %s", time.Since(time.Unix(rrCache.Expires, 0)).Round(time.Second)))
default:
extra = addExtra(ctx, extra, fmt.Sprintf("record valid for %s", time.Until(time.Unix(rrCache.Expires, 0)).Round(time.Second)))
}
if rrCache.RequestingNew {
extra = addExtra(ctx, extra, "async request to refresh the cache has been started")
}
if rrCache.IsBackup {
extra = addExtra(ctx, extra, "this record is served because a fresh request was unsuccessful")
}
// Add information about filtered entries.
if rrCache.Filtered {
if len(rrCache.FilteredEntries) > 1 {
extra = addExtra(ctx, extra, fmt.Sprintf("%d RRs have been filtered:", len(rrCache.FilteredEntries)))
} else {
extra = addExtra(ctx, extra, fmt.Sprintf("%d RR has been filtered:", len(rrCache.FilteredEntries)))
}
for _, filteredRecord := range rrCache.FilteredEntries {
extra = addExtra(ctx, extra, filteredRecord)
}
}
return extra
}
func addExtra(ctx context.Context, extra []dns.RR, msg string) []dns.RR {
rr, err := nsutil.MakeMessageRecord(log.InfoLevel, msg)
if err != nil {
log.Tracer(ctx).Warningf("resolver: failed to add informational record to reply: %s", err)
return extra
}
extra = append(extra, rr)
return extra
}