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Fix DNS negative caching to comply with RFC 2308

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This commit is contained in:
世界
2025-10-09 22:56:18 +08:00
parent 6557bd7029
commit 36dc883c7c
1 changed files with 26 additions and 5 deletions
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31
dns/client.go
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@@ -95,6 +95,20 @@ func (c *Client) Start() {
}
}
func extractNegativeTTL(response *dns.Msg) (uint32, bool) {
for _, record := range response.Ns {
if soa, isSOA := record.(*dns.SOA); isSOA {
soaTTL := soa.Header().Ttl
soaMinimum := soa.Minttl
if soaTTL < soaMinimum {
return soaTTL, true
}
return soaMinimum, true
}
}
return 0, false
}
func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, message *dns.Msg, options adapter.DNSQueryOptions, responseChecker func(responseAddrs []netip.Addr) bool) (*dns.Msg, error) {
if len(message.Question) == 0 {
if c.logger != nil {
@@ -214,7 +228,7 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
response.Answer = append(response.Answer, validResponse.Answer...)
}
}*/
disableCache = disableCache || (response.Rcode != dns.RcodeSuccess && response.Rcode != dns.RcodeNameError) || len(response.Answer) == 0
disableCache = disableCache || (response.Rcode != dns.RcodeSuccess && response.Rcode != dns.RcodeNameError)
if responseChecker != nil {
var rejected bool
// TODO: add accept_any rule and support to check response instead of addresses
@@ -251,10 +265,17 @@ func (c *Client) Exchange(ctx context.Context, transport adapter.DNSTransport, m
}
}
var timeToLive uint32
for _, recordList := range [][]dns.RR{response.Answer, response.Ns, response.Extra} {
for _, record := range recordList {
if timeToLive == 0 || record.Header().Ttl > 0 && record.Header().Ttl < timeToLive {
timeToLive = record.Header().Ttl
if len(response.Answer) == 0 {
if soaTTL, hasSOA := extractNegativeTTL(response); hasSOA {
timeToLive = soaTTL
}
}
if timeToLive == 0 {
for _, recordList := range [][]dns.RR{response.Answer, response.Ns, response.Extra} {
for _, record := range recordList {
if timeToLive == 0 || record.Header().Ttl > 0 && record.Header().Ttl < timeToLive {
timeToLive = record.Header().Ttl
}
}
}
}