Domain name limits (#478)
* limiting domain names to 255/63 octets/labels (#463)
(cherry picked from commit 0b729df06c)
* account for \ and \xxx in presentation format
(cherry picked from commit a094f774892fb4305051d185c2488cb43200c4d9)
* go fmt
* Add tests for UnpackDomainName
Domain names must not exceed 255 octets in wire format.
Ref gh-463
Ref gh-469
* Fix UnpackDomainName
* Introduce a long-domain sentinel error
A typed error would be better, but inconsistent with this library.
cf. https://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully
This commit is contained in:
Richard Gibson
Miek Gieben
parent
b54e1be39a
commit
c1bdeb82b2
20
msg.go
20
msg.go
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@ -14,13 +14,17 @@ package dns
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import (
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crand "crypto/rand"
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"encoding/binary"
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"fmt"
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"math/big"
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"math/rand"
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"strconv"
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"sync"
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)
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const maxCompressionOffset = 2 << 13 // We have 14 bits for the compression pointer
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const (
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maxCompressionOffset = 2 << 13 // We have 14 bits for the compression pointer
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maxDomainNameWireOctets = 255 // See RFC 1035 section 2.3.4
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)
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var (
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ErrAlg error = &Error{err: "bad algorithm"} // ErrAlg indicates an error with the (DNSSEC) algorithm.
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@ -33,6 +37,7 @@ var (
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ErrKeyAlg error = &Error{err: "bad key algorithm"} // ErrKeyAlg indicates that the algorithm in the key is not valid.
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ErrKey error = &Error{err: "bad key"}
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ErrKeySize error = &Error{err: "bad key size"}
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ErrLongDomain error = &Error{err: fmt.Sprintf("domain name exceeded %d wire-format octets", maxDomainNameWireOctets)}
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ErrNoSig error = &Error{err: "no signature found"}
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ErrPrivKey error = &Error{err: "bad private key"}
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ErrRcode error = &Error{err: "bad rcode"}
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@ -329,6 +334,7 @@ func UnpackDomainName(msg []byte, off int) (string, int, error) {
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s := make([]byte, 0, 64)
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off1 := 0
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lenmsg := len(msg)
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maxLen := maxDomainNameWireOctets
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ptr := 0 // number of pointers followed
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Loop:
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for {
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@ -353,8 +359,10 @@ Loop:
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fallthrough
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case '"', '\\':
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s = append(s, '\\', b)
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// presentation-format \X escapes add an extra byte
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maxLen += 1
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default:
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if b < 32 || b >= 127 { // unprintable use \DDD
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if b < 32 || b >= 127 { // unprintable, use \DDD
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var buf [3]byte
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bufs := strconv.AppendInt(buf[:0], int64(b), 10)
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s = append(s, '\\')
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@ -364,6 +372,8 @@ Loop:
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for _, r := range bufs {
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s = append(s, r)
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}
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// presentation-format \DDD escapes add 3 extra bytes
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maxLen += 3
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} else {
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s = append(s, b)
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}
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@ -388,6 +398,9 @@ Loop:
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if ptr++; ptr > 10 {
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return "", lenmsg, &Error{err: "too many compression pointers"}
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}
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// pointer should guarantee that it advances and points forwards at least
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// but the condition on previous three lines guarantees that it's
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// at least loop-free
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off = (c^0xC0)<<8 | int(c1)
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default:
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// 0x80 and 0x40 are reserved
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@ -399,6 +412,9 @@ Loop:
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}
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if len(s) == 0 {
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s = []byte(".")
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} else if len(s) >= maxLen {
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// error if the name is too long, but don't throw it away
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return string(s), lenmsg, ErrLongDomain
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}
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return string(s), off1, nil
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}
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@ -0,0 +1,124 @@
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package dns
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import (
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"fmt"
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"regexp"
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"strconv"
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"strings"
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"testing"
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)
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const (
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maxPrintableLabel = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789x"
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tooLongLabel = maxPrintableLabel + "x"
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)
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var (
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longDomain = maxPrintableLabel[:53] + strings.TrimSuffix(
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strings.Join([]string{".", ".", ".", ".", "."}, maxPrintableLabel[:49]), ".")
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reChar = regexp.MustCompile(`.`)
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i = -1
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maxUnprintableLabel = reChar.ReplaceAllStringFunc(maxPrintableLabel, func(ch string) string {
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if i++; i >= 32 {
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i = 0
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}
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return fmt.Sprintf("\\%03d", i)
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})
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)
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func TestUnpackDomainName(t *testing.T) {
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var cases = []struct {
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label string
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input string
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expectedOutput string
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expectedError string
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}{
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{"empty domain",
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"\x00",
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".",
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""},
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{"long label",
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string(63) + maxPrintableLabel + "\x00",
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maxPrintableLabel + ".",
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""},
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{"unprintable label",
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string(63) + regexp.MustCompile(`\\[0-9]+`).ReplaceAllStringFunc(maxUnprintableLabel,
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func(escape string) string {
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n, _ := strconv.ParseInt(escape[1:], 10, 8)
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return string(n)
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}) + "\x00",
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maxUnprintableLabel + ".",
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""},
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{"long domain",
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string(53) + strings.Replace(longDomain, ".", string(49), -1) + "\x00",
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longDomain + ".",
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""},
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{"compression pointer",
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// an unrealistic but functional test referencing an offset _inside_ a label
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"\x03foo" + "\x05\x03com\x00" + "\x07example" + "\xC0\x05",
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"foo.\\003com\\000.example.com.",
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""},
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{"too long domain",
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string(54) + "x" + strings.Replace(longDomain, ".", string(49), -1) + "\x00",
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"x" + longDomain + ".",
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ErrLongDomain.Error()},
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{"too long by pointer",
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// a matryoshka doll name to get over 255 octets after expansion via internal pointers
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string([]byte{
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// 11 length values, first to last
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40, 37, 34, 31, 28, 25, 22, 19, 16, 13, 0,
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// 12 filler values
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120, 120, 120, 120, 120, 120, 120, 120, 120, 120, 120, 120,
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// 10 pointers, last to first
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192, 10, 192, 9, 192, 8, 192, 7, 192, 6, 192, 5, 192, 4, 192, 3, 192, 2, 192, 1,
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}),
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"",
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ErrLongDomain.Error()},
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{"long by pointer",
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// a matryoshka doll name _not_ exceeding 255 octets after expansion
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string([]byte{
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// 11 length values, first to last
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37, 34, 31, 28, 25, 22, 19, 16, 13, 10, 0,
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// 9 filler values
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120, 120, 120, 120, 120, 120, 120, 120, 120,
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// 10 pointers, last to first
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192, 10, 192, 9, 192, 8, 192, 7, 192, 6, 192, 5, 192, 4, 192, 3, 192, 2, 192, 1,
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}),
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"" +
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(`\"\031\028\025\022\019\016\013\010\000xxxxxxxxx` +
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`\192\010\192\009\192\008\192\007\192\006\192\005\192\004\192\003\192\002.`) +
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(`\031\028\025\022\019\016\013\010\000xxxxxxxxx` +
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`\192\010\192\009\192\008\192\007\192\006\192\005\192\004\192\003.`) +
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(`\028\025\022\019\016\013\010\000xxxxxxxxx` +
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`\192\010\192\009\192\008\192\007\192\006\192\005\192\004.`) +
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(`\025\022\019\016\013\010\000xxxxxxxxx` +
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`\192\010\192\009\192\008\192\007\192\006\192\005.`) +
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`\022\019\016\013\010\000xxxxxxxxx\192\010\192\009\192\008\192\007\192\006.` +
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`\019\016\013\010\000xxxxxxxxx\192\010\192\009\192\008\192\007.` +
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`\016\013\010\000xxxxxxxxx\192\010\192\009\192\008.` +
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`\013\010\000xxxxxxxxx\192\010\192\009.` +
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`\010\000xxxxxxxxx\192\010.` +
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`\000xxxxxxxxx.`,
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""},
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{"truncated name", "\x07example\x03", "", "dns: buffer size too small"},
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{"non-absolute name", "\x07example\x03com", "", "dns: buffer size too small"},
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{"compression pointer cycle",
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"\x03foo" + "\x03bar" + "\x07example" + "\xC0\x04",
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"",
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"dns: too many compression pointers"},
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{"reserved compression pointer 0b10", "\x07example\x80", "", "dns: bad rdata"},
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{"reserved compression pointer 0b01", "\x07example\x40", "", "dns: bad rdata"},
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}
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for _, test := range cases {
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output, idx, err := UnpackDomainName([]byte(test.input), 0)
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if test.expectedOutput != "" && output != test.expectedOutput {
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t.Errorf("%s: expected %s, got %s", test.label, test.expectedOutput, output)
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}
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if test.expectedError == "" && err != nil {
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t.Errorf("%s: expected no error, got %d %v", test.label, idx, err)
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} else if test.expectedError != "" && (err == nil || err.Error() != test.expectedError) {
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t.Errorf("%s: expected error %s, got %d %v", test.label, test.expectedError, idx, err)
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}
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}
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}
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