Add a message truncation implementation (#854)
* Add a message truncation implementation * Remove OPT if-statement at end of Scrub * Impose RFC 6891 payload size limit in Scrub * Remove *Msg receiver from truncateLoop * Remove OPT record creation from Scrub * Test that TestRequestScrubAnswerExact has correct record count * Rename (*Msg).Scrub to Truncate This better reflects it's purpose. * Remove comment reference to scrubbing in Truncate * Properly calculate the length of OPT record in Truncate * Correct comment in IsEdns0 in regards to RFC 6891 * Handle the OPT record being anywhere in Truncate * Slight cleanup of Msg.Truncate
This commit is contained in:
Tom Thorogood
Miek Gieben
parent
d8ff986484
commit
d051b464e9
22
defaults.go
22
defaults.go
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@ -146,10 +146,9 @@ func (dns *Msg) IsTsig() *TSIG {
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// record in the additional section will do. It returns the OPT record
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// found or nil.
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func (dns *Msg) IsEdns0() *OPT {
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// EDNS0 is at the end of the additional section, start there.
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// We might want to change this to *only* look at the last two
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// records. So we see TSIG and/or OPT - this a slightly bigger
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// change though.
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// RFC 6891, Section 6.1.1 allows the OPT record to appear
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// anywhere in the additional record section, but it's usually at
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// the end so start there.
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for i := len(dns.Extra) - 1; i >= 0; i-- {
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if dns.Extra[i].Header().Rrtype == TypeOPT {
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return dns.Extra[i].(*OPT)
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@ -158,6 +157,21 @@ func (dns *Msg) IsEdns0() *OPT {
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return nil
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}
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// popEdns0 is like IsEdns0, but it removes the record from the message.
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func (dns *Msg) popEdns0() *OPT {
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// RFC 6891, Section 6.1.1 allows the OPT record to appear
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// anywhere in the additional record section, but it's usually at
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// the end so start there.
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for i := len(dns.Extra) - 1; i >= 0; i-- {
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if dns.Extra[i].Header().Rrtype == TypeOPT {
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opt := dns.Extra[i].(*OPT)
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dns.Extra = append(dns.Extra[:i], dns.Extra[i+1:]...)
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return opt
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}
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}
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return nil
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}
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// IsDomainName checks if s is a valid domain name, it returns the number of
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// labels and true, when a domain name is valid. Note that non fully qualified
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// domain name is considered valid, in this case the last label is counted in
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@ -0,0 +1,106 @@
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package dns
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// Truncate ensures the reply message will fit into the requested buffer
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// size by removing records that exceed the requested size.
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//
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// It will first check if the reply fits without compression and then with
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// compression. If it won't fit with compression, Scrub then walks the
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// record adding as many records as possible without exceeding the
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// requested buffer size.
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//
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// The TC bit will be set if any answer records were excluded from the
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// message. This indicates to that the client should retry over TCP.
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//
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// The appropriate buffer size can be retrieved from the requests OPT
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// record, if present, and is transport specific otherwise. dns.MinMsgSize
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// should be used for UDP requests without an OPT record, and
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// dns.MaxMsgSize for TCP requests without an OPT record.
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func (dns *Msg) Truncate(size int) {
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if dns.IsTsig() != nil {
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// To simplify this implementation, we don't perform
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// truncation on responses with a TSIG record.
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return
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}
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// RFC 6891 mandates that the payload size in an OPT record
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// less than 512 bytes must be treated as equal to 512 bytes.
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//
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// For ease of use, we impose that restriction here.
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if size < 512 {
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size = 512
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}
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l := msgLenWithCompressionMap(dns, nil) // uncompressed length
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if l <= size {
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// Don't waste effort compressing this message.
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dns.Compress = false
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return
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}
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dns.Compress = true
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edns0 := dns.popEdns0()
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if edns0 != nil {
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// Account for the OPT record that gets added at the end,
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// by subtracting that length from our budget.
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//
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// The EDNS(0) OPT record must have the root domain and
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// it's length is thus unaffected by compression.
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size -= Len(edns0)
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}
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compression := make(map[string]struct{})
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l = headerSize
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for _, r := range dns.Question {
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l += r.len(l, compression)
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}
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var numAnswer int
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if l < size {
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l, numAnswer = truncateLoop(dns.Answer, size, l, compression)
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}
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var numNS int
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if l < size {
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l, numNS = truncateLoop(dns.Ns, size, l, compression)
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}
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var numExtra int
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if l < size {
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l, numExtra = truncateLoop(dns.Extra, size, l, compression)
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}
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// According to RFC 2181, the TC bit should only be set if not all
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// of the answer RRs can be included in the response.
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dns.Truncated = len(dns.Answer) > numAnswer
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dns.Answer = dns.Answer[:numAnswer]
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dns.Ns = dns.Ns[:numNS]
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dns.Extra = dns.Extra[:numExtra]
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if edns0 != nil {
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// Add the OPT record back onto the additional section.
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dns.Extra = append(dns.Extra, edns0)
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}
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}
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func truncateLoop(rrs []RR, size, l int, compression map[string]struct{}) (int, int) {
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for i, r := range rrs {
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if r == nil {
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continue
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}
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l += r.len(l, compression)
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if l > size {
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// Return size, rather than l prior to this record,
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// to prevent any further records being added.
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return size, i
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}
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if l == size {
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return l, i + 1
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}
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}
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return l, len(rrs)
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}
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@ -0,0 +1,187 @@
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package dns
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import (
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"fmt"
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"testing"
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)
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func TestRequestTruncateAnswer(t *testing.T) {
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m := new(Msg)
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m.SetQuestion("large.example.com.", TypeSRV)
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reply := new(Msg)
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reply.SetReply(m)
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for i := 1; i < 200; i++ {
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reply.Answer = append(reply.Answer, testRR(
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fmt.Sprintf("large.example.com. 10 IN SRV 0 0 80 10-0-0-%d.default.pod.k8s.example.com.", i)))
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}
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reply.Truncate(MinMsgSize)
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if want, got := MinMsgSize, reply.Len(); want < got {
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t.Errorf("message length should be bellow %d bytes, got %d bytes", want, got)
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}
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if !reply.Truncated {
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t.Errorf("truncated bit should be set")
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}
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}
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func TestRequestTruncateExtra(t *testing.T) {
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m := new(Msg)
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m.SetQuestion("large.example.com.", TypeSRV)
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reply := new(Msg)
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reply.SetReply(m)
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for i := 1; i < 200; i++ {
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reply.Extra = append(reply.Extra, testRR(
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fmt.Sprintf("large.example.com. 10 IN SRV 0 0 80 10-0-0-%d.default.pod.k8s.example.com.", i)))
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}
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reply.Truncate(MinMsgSize)
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if want, got := MinMsgSize, reply.Len(); want < got {
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t.Errorf("message length should be bellow %d bytes, got %d bytes", want, got)
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}
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if reply.Truncated {
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t.Errorf("truncated bit should not be set")
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}
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}
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func TestRequestTruncateExtraEdns0(t *testing.T) {
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const size = 4096
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m := new(Msg)
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m.SetQuestion("large.example.com.", TypeSRV)
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m.SetEdns0(size, true)
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reply := new(Msg)
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reply.SetReply(m)
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for i := 1; i < 200; i++ {
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reply.Extra = append(reply.Extra, testRR(
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fmt.Sprintf("large.example.com. 10 IN SRV 0 0 80 10-0-0-%d.default.pod.k8s.example.com.", i)))
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}
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reply.SetEdns0(size, true)
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reply.Truncate(size)
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if want, got := size, reply.Len(); want < got {
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t.Errorf("message length should be bellow %d bytes, got %d bytes", want, got)
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}
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if reply.Truncated {
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t.Errorf("truncated bit should not be set")
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}
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opt := reply.Extra[len(reply.Extra)-1]
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if opt.Header().Rrtype != TypeOPT {
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t.Errorf("expected last RR to be OPT")
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}
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}
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func TestRequestTruncateExtraRegression(t *testing.T) {
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const size = 2048
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m := new(Msg)
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m.SetQuestion("large.example.com.", TypeSRV)
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m.SetEdns0(size, true)
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reply := new(Msg)
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reply.SetReply(m)
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for i := 1; i < 33; i++ {
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reply.Answer = append(reply.Answer, testRR(
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fmt.Sprintf("large.example.com. 10 IN SRV 0 0 80 10-0-0-%d.default.pod.k8s.example.com.", i)))
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}
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for i := 1; i < 33; i++ {
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reply.Extra = append(reply.Extra, testRR(
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fmt.Sprintf("10-0-0-%d.default.pod.k8s.example.com. 10 IN A 10.0.0.%d", i, i)))
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}
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reply.SetEdns0(size, true)
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reply.Truncate(size)
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if want, got := size, reply.Len(); want < got {
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t.Errorf("message length should be bellow %d bytes, got %d bytes", want, got)
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}
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if reply.Truncated {
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t.Errorf("truncated bit should not be set")
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}
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opt := reply.Extra[len(reply.Extra)-1]
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if opt.Header().Rrtype != TypeOPT {
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t.Errorf("expected last RR to be OPT")
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}
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}
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func TestTruncation(t *testing.T) {
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reply := new(Msg)
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for i := 0; i < 61; i++ {
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reply.Answer = append(reply.Answer, testRR(fmt.Sprintf("http.service.tcp.srv.k8s.example.org. 5 IN SRV 0 0 80 10-144-230-%d.default.pod.k8s.example.org.", i)))
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}
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for i := 0; i < 5; i++ {
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reply.Extra = append(reply.Extra, testRR(fmt.Sprintf("ip-10-10-52-5%d.subdomain.example.org. 5 IN A 10.10.52.5%d", i, i)))
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}
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for i := 0; i < 5; i++ {
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reply.Ns = append(reply.Ns, testRR(fmt.Sprintf("srv.subdomain.example.org. 5 IN NS ip-10-10-33-6%d.subdomain.example.org.", i)))
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}
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for bufsize := 1024; bufsize <= 4096; bufsize += 12 {
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m := new(Msg)
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m.SetQuestion("http.service.tcp.srv.k8s.example.org.", TypeSRV)
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m.SetEdns0(uint16(bufsize), true)
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copy := reply.Copy()
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copy.SetReply(m)
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copy.Truncate(bufsize)
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if want, got := bufsize, copy.Len(); want < got {
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t.Errorf("message length should be bellow %d bytes, got %d bytes", want, got)
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}
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}
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}
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func TestRequestTruncateAnswerExact(t *testing.T) {
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const size = 867 // Bit fiddly, but this hits the rl == size break clause in Truncate, 52 RRs should remain.
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m := new(Msg)
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m.SetQuestion("large.example.com.", TypeSRV)
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m.SetEdns0(size, false)
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reply := new(Msg)
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reply.SetReply(m)
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for i := 1; i < 200; i++ {
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reply.Answer = append(reply.Answer, testRR(fmt.Sprintf("large.example.com. 10 IN A 127.0.0.%d", i)))
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}
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reply.Truncate(size)
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if want, got := size, reply.Len(); want < got {
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t.Errorf("message length should be bellow %d bytes, got %d bytes", want, got)
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}
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if expected := 52; len(reply.Answer) != expected {
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t.Errorf("wrong number of answers; expected %d, got %d", expected, len(reply.Answer))
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}
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}
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func BenchmarkMsgTruncate(b *testing.B) {
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const size = 2048
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m := new(Msg)
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m.SetQuestion("example.com.", TypeA)
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m.SetEdns0(size, true)
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reply := new(Msg)
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reply.SetReply(m)
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for i := 1; i < 33; i++ {
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reply.Answer = append(reply.Answer, testRR(
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fmt.Sprintf("large.example.com. 10 IN SRV 0 0 80 10-0-0-%d.default.pod.k8s.example.com.", i)))
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}
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for i := 1; i < 33; i++ {
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reply.Extra = append(reply.Extra, testRR(
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fmt.Sprintf("10-0-0-%d.default.pod.k8s.example.com. 10 IN A 10.0.0.%d", i, i)))
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}
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b.ResetTimer()
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for i := 0; i < b.N; i++ {
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b.StopTimer()
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copy := reply.Copy()
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b.StartTimer()
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copy.Truncate(size)
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}
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}
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