// 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 func() { 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 } } }