// Do sends an HTTP request with the provided http.Client and returns an HTTP response.
// If the client is nil, http.DefaultClient is used.
// If the context is canceled or times out, ctx.Err() will be returned.
func Do(ctx context.Context, client *http.Client, req *http.Request) (*http.Response, error) {
if client == nil {
client = http.DefaultClient
}
// Request cancelation changed in Go 1.5, see cancelreq.go and cancelreq_go14.go.
cancel := canceler(client, req)
type responseAndError struct {
resp *http.Response
err error
}
result := make(chan responseAndError, 1)
go func() {
resp, err := client.Do(req)
result <- responseAndError{resp, err}
}()
select {
case <-ctx.Done():
cancel()
return nil, ctx.Err()
case r := <-result:
return r.resp, 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(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
}
}
}