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Adjust dns.go to new miekg/dns package and improve error handling.

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When hitting the 64kiB limit of DNS, the error message so far was
really misleading.
This commit is contained in:
beorn7 2016-11-03 14:41:04 +01:00
parent 9a63ff0c32
commit 0fdb74c069
1 changed files with 21 additions and 20 deletions
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41
retrieval/discovery/dns/dns.go
View file

@ -184,7 +184,12 @@ func lookupAll(name string, qtype uint16) (*dns.Msg, error) {
for _, suffix := range conf.Search { for _, suffix := range conf.Search {
response, err = lookup(name, qtype, client, servAddr, suffix, false) response, err = lookup(name, qtype, client, servAddr, suffix, false)
if err != nil { if err != nil {
log.Warnf("resolving %s.%s failed: %s", name, suffix, err) log.
With("server", server).
With("name", name).
With("suffix", suffix).
With("reason", err).
Warn("DNS resolution failed.")
continue continue
} }
if len(response.Answer) > 0 { if len(response.Answer) > 0 {
@ -195,8 +200,13 @@ func lookupAll(name string, qtype uint16) (*dns.Msg, error) {
if err == nil { if err == nil {
return response, nil return response, nil
} }
log.
With("server", server).
With("name", name).
With("reason", err).
Warn("DNS resolution failed.")
} }
return response, fmt.Errorf("could not resolve %s: No server responded", name) return response, fmt.Errorf("could not resolve %s: no server responded", name)
} }
func lookup(name string, queryType uint16, client *dns.Client, servAddr string, suffix string, edns bool) (*dns.Msg, error) { func lookup(name string, queryType uint16, client *dns.Client, servAddr string, suffix string, edns bool) (*dns.Msg, error) {
@ -205,33 +215,24 @@ func lookup(name string, queryType uint16, client *dns.Client, servAddr string,
msg.SetQuestion(dns.Fqdn(lname), queryType) msg.SetQuestion(dns.Fqdn(lname), queryType)
if edns { if edns {
opt := &dns.OPT{ msg.SetEdns0(dns.DefaultMsgSize, false)
Hdr: dns.RR_Header{
Name: ".",
Rrtype: dns.TypeOPT,
},
}
opt.SetUDPSize(dns.DefaultMsgSize)
msg.Extra = append(msg.Extra, opt)
} }
response, _, err := client.Exchange(msg, servAddr) response, _, err := client.Exchange(msg, servAddr)
if err != nil { if err == dns.ErrTruncated {
return nil, err
}
if msg.Id != response.Id {
return nil, fmt.Errorf("DNS ID mismatch, request: %d, response: %d", msg.Id, response.Id)
}
if response.MsgHdr.Truncated {
if client.Net == "tcp" { if client.Net == "tcp" {
return nil, fmt.Errorf("got truncated message on tcp") return nil, fmt.Errorf("got truncated message on TCP (64kiB limit exceeded?)")
} }
if edns { // Truncated even though EDNS is used if edns { // Truncated even though EDNS is used
client.Net = "tcp" client.Net = "tcp"
} }
return lookup(name, queryType, client, servAddr, suffix, !edns) return lookup(name, queryType, client, servAddr, suffix, !edns)
} }
if err != nil {
return nil, err
}
if msg.Id != response.Id {
return nil, fmt.Errorf("DNS ID mismatch, request: %d, response: %d", msg.Id, response.Id)
}
return response, nil return response, nil
} }