68 строки
1.9 KiB
Go
68 строки
1.9 KiB
Go
package cdns
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import (
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"errors"
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"fmt"
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"log"
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"strings"
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"github.com/miekg/dns"
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)
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func localQuery(mychan chan DNSreply, qname string, qtype uint16) {
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if debug {
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fmt.Printf("DEBUG: start of DNS request \"%s\" / %d\n", qname, qtype)
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}
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var result DNSreply
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var trials uint
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result.qname = qname
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result.qtype = qtype
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result.r = nil
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result.err = errors.New("no name server to answer the question")
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localm := new(dns.Msg)
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localm.Id = dns.Id()
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localm.RecursionDesired = true
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localm.Question = make([]dns.Question, 1)
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localm.SetEdns0(bufsize, false) // Even if no EDNS requested, see #9 May be we should retry without it if timeout?
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localc := new(dns.Client)
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localc.ReadTimeout = timeout
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localm.Question[0] = dns.Question{Name: qname, Qtype: qtype, Qclass: dns.ClassINET}
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Tests:
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for trials = 0; trials < uint(maxTrials); trials++ {
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for serverIndex := range conf.Servers {
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server := conf.Servers[serverIndex]
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result.nameserver = server
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// Brackets around the server address are necessary for IPv6 name servers
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// Brackets required for IPv6; do not use net.JoinHostPort (see check-soa commit 3e4edb1)
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r, rtt, err := localc.Exchange(localm, "["+server+"]:"+conf.Port)
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if r == nil {
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result.r = nil
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result.err = err
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log.Println(err.Error())
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if strings.Contains(err.Error(), "timeout") {
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// Try another resolver
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continue
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}
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// We give in
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break Tests
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}
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result.rtt = rtt
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if r.Rcode == dns.RcodeSuccess {
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// TODO: NODATA (NOERROR/ANSWER=0) are silently ignored (e.g. name exists but no IP address)
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// TODO: for rcodes like SERVFAIL, trying another resolver could make sense
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result.r = r
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result.err = nil
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break Tests
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}
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// All the other codes are errors
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result.r = r
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result.err = errors.New(dns.RcodeToString[r.Rcode])
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break Tests
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}
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}
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if debug {
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fmt.Printf("DEBUG: end of DNS request \"%s\" / %d\n", qname, qtype)
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}
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mychan <- result
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}
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