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storage.go
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storage.go
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// Package rewrite implements DNS Rewrites storage and request matching.
package rewrite
import (
"fmt"
"strings"
"sync"
"github.com/AdguardTeam/golibs/log"
"github.com/AdguardTeam/golibs/stringutil"
"github.com/AdguardTeam/urlfilter"
"github.com/AdguardTeam/urlfilter/filterlist"
"github.com/AdguardTeam/urlfilter/rules"
"github.com/miekg/dns"
"golang.org/x/exp/slices"
)
// Storage is a storage for rewrite rules.
type Storage interface {
// MatchRequest returns matching dnsrewrites for the specified request.
MatchRequest(dReq *urlfilter.DNSRequest) (rws []*rules.DNSRewrite)
// Add adds item to the storage.
Add(item *Item) (err error)
// Remove deletes item from the storage.
Remove(item *Item) (err error)
// List returns all items from the storage.
List() (items []*Item)
}
// DefaultStorage is the default storage for rewrite rules.
type DefaultStorage struct {
// mu protects items.
mu *sync.RWMutex
// engine is the DNS filtering engine.
engine *urlfilter.DNSEngine
// ruleList is the filtering rule ruleList used by the engine.
ruleList filterlist.RuleList
// rewrites stores the rewrite entries from configuration.
rewrites []*Item
// urlFilterID is the synthetic integer identifier for the urlfilter engine.
//
// TODO(a.garipov): Change the type to a string in module urlfilter and
// remove this crutch.
urlFilterID int
}
// NewDefaultStorage returns new rewrites storage. listID is used as an
// identifier of the underlying rules list. rewrites must not be nil.
func NewDefaultStorage(listID int, rewrites []*Item) (s *DefaultStorage, err error) {
s = &DefaultStorage{
mu: &sync.RWMutex{},
urlFilterID: listID,
rewrites: rewrites,
}
s.mu.Lock()
defer s.mu.Unlock()
err = s.resetRules()
if err != nil {
return nil, err
}
return s, nil
}
// type check
var _ Storage = (*DefaultStorage)(nil)
// MatchRequest implements the [Storage] interface for *DefaultStorage.
func (s *DefaultStorage) MatchRequest(dReq *urlfilter.DNSRequest) (rws []*rules.DNSRewrite) {
s.mu.RLock()
defer s.mu.RUnlock()
rrules := s.rewriteRulesForReq(dReq)
if len(rrules) == 0 {
return nil
}
// TODO(a.garipov): Check cnames for cycles on initialisation.
cnames := stringutil.NewSet()
host := dReq.Hostname
for len(rrules) > 0 && rrules[0].DNSRewrite != nil && rrules[0].DNSRewrite.NewCNAME != "" {
rule := rrules[0]
rwAns := rule.DNSRewrite.NewCNAME
log.Debug("rewrite: cname for %s is %s", host, rwAns)
if dReq.Hostname == rwAns {
// A request for the hostname itself is an exception rule.
// TODO(d.kolyshev): Check rewrite of a pattern onto itself.
return nil
}
if host == rwAns && isWildcard(rule.RuleText) {
// An "*.example.com → sub.example.com" rewrite matching in a loop.
//
// See https://github.com/AdguardTeam/AdGuardHome/issues/4016.
return []*rules.DNSRewrite{rule.DNSRewrite}
}
if cnames.Has(rwAns) {
log.Info("rewrite: cname loop for %q on %q", dReq.Hostname, rwAns)
return nil
}
cnames.Add(rwAns)
drules := s.rewriteRulesForReq(&urlfilter.DNSRequest{
Hostname: rwAns,
DNSType: dReq.DNSType,
})
if drules != nil {
rrules = drules
}
host = rwAns
}
return s.collectDNSRewrites(rrules, dReq.DNSType)
}
// collectDNSRewrites filters DNSRewrite by question type.
func (s *DefaultStorage) collectDNSRewrites(
rewrites []*rules.NetworkRule,
qtyp uint16,
) (rws []*rules.DNSRewrite) {
for _, rewrite := range rewrites {
dnsRewrite := rewrite.DNSRewrite
if matchesQType(dnsRewrite, qtyp) {
rws = append(rws, dnsRewrite)
}
}
return rws
}
// rewriteRulesForReq returns matching dnsrewrite rules.
func (s *DefaultStorage) rewriteRulesForReq(dReq *urlfilter.DNSRequest) (rules []*rules.NetworkRule) {
res, _ := s.engine.MatchRequest(dReq)
return res.DNSRewrites()
}
// Add implements the [Storage] interface for *DefaultStorage.
func (s *DefaultStorage) Add(item *Item) (err error) {
s.mu.Lock()
defer s.mu.Unlock()
// TODO(d.kolyshev): Handle duplicate items.
s.rewrites = append(s.rewrites, item)
return s.resetRules()
}
// Remove implements the [Storage] interface for *DefaultStorage.
func (s *DefaultStorage) Remove(item *Item) (err error) {
s.mu.Lock()
defer s.mu.Unlock()
arr := []*Item{}
// TODO(d.kolyshev): Use slices.IndexFunc + slices.Delete?
for _, ent := range s.rewrites {
if ent.equal(item) {
log.Debug("rewrite: removed element: %s -> %s", ent.Domain, ent.Answer)
continue
}
arr = append(arr, ent)
}
s.rewrites = arr
return s.resetRules()
}
// List implements the [Storage] interface for *DefaultStorage.
func (s *DefaultStorage) List() (items []*Item) {
s.mu.RLock()
defer s.mu.RUnlock()
return slices.Clone(s.rewrites)
}
// resetRules resets the filtering rules.
func (s *DefaultStorage) resetRules() (err error) {
// TODO(a.garipov): Use strings.Builder.
var rulesText []string
for _, rewrite := range s.rewrites {
rulesText = append(rulesText, rewrite.toRule())
}
strList := &filterlist.StringRuleList{
ID: s.urlFilterID,
RulesText: strings.Join(rulesText, "\n"),
IgnoreCosmetic: true,
}
rs, err := filterlist.NewRuleStorage([]filterlist.RuleList{strList})
if err != nil {
return fmt.Errorf("creating list storage: %w", err)
}
s.ruleList = strList
s.engine = urlfilter.NewDNSEngine(rs)
log.Info("rewrite: filter %d: reset %d rules", s.urlFilterID, s.engine.RulesCount)
return nil
}
// matchesQType returns true if dnsrewrite matches the question type qt.
func matchesQType(dnsrr *rules.DNSRewrite, qt uint16) (ok bool) {
// Add CNAMEs, since they match for all types requests.
if dnsrr.RRType == dns.TypeCNAME {
return true
}
// Reject types other than A and AAAA.
if qt != dns.TypeA && qt != dns.TypeAAAA {
return false
}
return dnsrr.RRType == qt
}
// isWildcard returns true if pat is a wildcard domain pattern.
func isWildcard(pat string) (res bool) {
return strings.HasPrefix(pat, "|*.")
}