// LookupDNSSEC sends the provided DNS message to a randomly chosen server (see
// ExchangeOne) with DNSSEC enabled. If the lookup fails, this method sends a
// clarification query to determine if it's because DNSSEC was invalid or just
// a run-of-the-mill error. If it's because of DNSSEC, it returns ErrorDNSSEC.
func (dnsResolver *DNSResolver) LookupDNSSEC(m *dns.Msg) (*dns.Msg, time.Duration, error) {
// Set DNSSEC OK bit
m.SetEdns0(4096, true)
r, rtt, err := dnsResolver.ExchangeOne(m)
if err != nil {
return r, rtt, err
}
if r.Rcode != dns.RcodeSuccess && r.Rcode != dns.RcodeNameError && r.Rcode != dns.RcodeNXRrset {
if r.Rcode == dns.RcodeServerFailure {
// Re-send query with +cd to see if SERVFAIL was caused by DNSSEC
// validation failure at the resolver
m.CheckingDisabled = true
checkR, _, err := dnsResolver.ExchangeOne(m)
if err != nil {
return r, rtt, err
}
if checkR.Rcode != dns.RcodeServerFailure {
// DNSSEC error, so we return the testable object.
err = DNSSECError{}
return r, rtt, err
}
}
err = fmt.Errorf("Invalid response code: %d-%s", r.Rcode, dns.RcodeToString[r.Rcode])
return r, rtt, err
}
return r, rtt, err
}
// exchangeOne performs a single DNS exchange with a randomly chosen server
// out of the server list, returning the response, time, and error (if any).
// This method sets the DNSSEC OK bit on the message to true before sending
// it to the resolver in case validation isn't the resolvers default behaviour.
func (dnsResolver *DNSResolverImpl) exchangeOne(hostname string, qtype uint16, msgStats metrics.Scope) (rsp *dns.Msg, err error) {
m := new(dns.Msg)
// Set question type
m.SetQuestion(dns.Fqdn(hostname), qtype)
// Set DNSSEC OK bit for resolver
m.SetEdns0(4096, true)
if len(dnsResolver.Servers) < 1 {
err = fmt.Errorf("Not configured with at least one DNS Server")
return
}
dnsResolver.stats.Inc("Rate", 1)
// Randomly pick a server
chosenServer := dnsResolver.Servers[rand.Intn(len(dnsResolver.Servers))]
msg, rtt, err := dnsResolver.DNSClient.Exchange(m, chosenServer)
msgStats.TimingDuration("RTT", rtt)
if err == nil {
msgStats.Inc("Successes", 1)
} else {
msgStats.Inc("Errors", 1)
}
return msg, err
}
// exchangeOne performs a single DNS exchange with a randomly chosen server
// out of the server list, returning the response, time, and error (if any).
// This method sets the DNSSEC OK bit on the message to true before sending
// it to the resolver in case validation isn't the resolvers default behaviour.
func (dnsResolver *DNSResolverImpl) exchangeOne(ctx context.Context, hostname string, qtype uint16, msgStats metrics.Scope) (*dns.Msg, error) {
m := new(dns.Msg)
// Set question type
m.SetQuestion(dns.Fqdn(hostname), qtype)
// Set DNSSEC OK bit for resolver
m.SetEdns0(4096, true)
if len(dnsResolver.Servers) < 1 {
return nil, fmt.Errorf("Not configured with at least one DNS Server")
}
dnsResolver.stats.Inc("Rate", 1)
// Randomly pick a server
chosenServer := dnsResolver.Servers[rand.Intn(len(dnsResolver.Servers))]
client := dnsResolver.DNSClient
tries := 1
start := dnsResolver.clk.Now()
msgStats.Inc("Calls", 1)
defer msgStats.TimingDuration("Latency", dnsResolver.clk.Now().Sub(start))
for {
msgStats.Inc("Tries", 1)
ch := make(chan dnsResp, 1)
go func() {
rsp, rtt, err := client.Exchange(m, chosenServer)
msgStats.TimingDuration("SingleTryLatency", rtt)
ch <- dnsResp{m: rsp, err: err}
}()
select {
case <-ctx.Done():
msgStats.Inc("Cancels", 1)
msgStats.Inc("Errors", 1)
return nil, ctx.Err()
case r := <-ch:
if r.err != nil {
msgStats.Inc("Errors", 1)
operr, ok := r.err.(*net.OpError)
isRetryable := ok && operr.Temporary()
hasRetriesLeft := tries < dnsResolver.maxTries
if isRetryable && hasRetriesLeft {
tries++
continue
} else if isRetryable && !hasRetriesLeft {
msgStats.Inc("RanOutOfTries", 1)
}
} else {
msgStats.Inc("Successes", 1)
}
return r.m, r.err
}
}
}
// ExchangeOne performs a single DNS exchange with a randomly chosen server
// out of the server list, returning the response, time, and error (if any).
// This method sets the DNSSEC OK bit on the message to true before sending
// it to the resolver in case validation isn't the resolvers default behaviour.
func (dnsResolver *DNSResolverImpl) ExchangeOne(hostname string, qtype uint16) (rsp *dns.Msg, rtt time.Duration, err error) {
m := new(dns.Msg)
// Set question type
m.SetQuestion(dns.Fqdn(hostname), qtype)
// Set DNSSEC OK bit for resolver
m.SetEdns0(4096, true)
if len(dnsResolver.Servers) < 1 {
err = fmt.Errorf("Not configured with at least one DNS Server")
return
}
// Randomly pick a server
chosenServer := dnsResolver.Servers[rand.Intn(len(dnsResolver.Servers))]
return dnsResolver.DNSClient.Exchange(m, chosenServer)
}