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plugin/file: fix less is not up to RFC 1034 and 4034 (#8503)
* plugin/file: fix less to follow RFC 1034 and RFC 4034 matching and ordering requirements - Ensure comparison is left-justified - Ensure case folding applies only to A-Z - Decode \DDD without allocations Signed-off-by: Ilya Kulakov <kulakov.ilya@gmail.com> * plugin/file: faster exit for less when a == b Avoid two calls and two reslices. Signed-off-by: Ilya Kulakov <kulakov.ilya@gmail.com> * plugin/file: consolidate less tests Signed-off-by: Ilya Kulakov <kulakov.ilya@gmail.com> * plugin/file: exit less early when there are no more labels Signed-off-by: Ilya Kulakov <kulakov.ilya@gmail.com> * plugin/file: match dns.PackDomainName in handling \-escapes Compare unterminated names as root-terminating Signed-off-by: Ilya Kulakov <kulakov.ilya@gmail.com> * plugin/file: More tests of less. Signed-off-by: Ilya Kulakov <kulakov.ilya@gmail.com> --------- Signed-off-by: Ilya Kulakov <kulakov.ilya@gmail.com>
This commit is contained in:
Ilya Kulakov
GitHub
@@ -1,58 +1,117 @@
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package tree
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import (
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"bytes"
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"strings"
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"github.com/miekg/dns"
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)
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// less returns <0 when a is less than b, 0 when they are equal and
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// >0 when a is larger than b.
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// The function orders names in DNSSEC canonical order: RFC 4034s section-6.1
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// less returns <0 when a is less than b, 0 when they are equal and >0 when a is larger than b.
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//
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// See https://bert-hubert.blogspot.co.uk/2015/10/how-to-do-fast-canonical-ordering-of.html
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// for a blog article on this implementation, although here we still go label by label.
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// Follows DNSSEC canonical ordering (RFC 4034, Section 6.1):
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// - `\DDD` byte is decoded before comparison
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// - Uppercase A-Z letters are treated as if they were lowercase
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// - Absence of octet sorts before zero value octet
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//
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// The values of a and b are *not* lowercased before the comparison!
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// Quirks:
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// - Trailing `\` that escapes nothing is ignored
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// - Leading `\` in `\D` and `\DD` is ignored
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// - Non-FQDN names are assumed to be root-terminated
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func less(a, b string) int {
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aj := len(a)
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bj := len(b)
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for {
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ai, oka := dns.PrevLabel(a[:aj], 1)
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bi, okb := dns.PrevLabel(b[:bj], 1)
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if oka && okb {
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return 0
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}
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var (
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adot, bdot int
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aoff, boff int
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alast, blast = stripTrailingBackslash(a), stripTrailingBackslash(b)
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ac, bc byte
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)
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// sadly this []byte will allocate... TODO(miek): check if this is needed
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// for a name, otherwise compare the strings.
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ab := []byte(strings.ToLower(a[ai:aj]))
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bb := []byte(strings.ToLower(b[bi:bj]))
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doDDD(ab)
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doDDD(bb)
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res := bytes.Compare(ab, bb)
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if res != 0 {
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return res
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}
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aj, bj = ai, bi
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if adot, _ = prevDot(a, alast); alast >= 0 && alast == adot {
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alast--
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}
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if bdot, _ = prevDot(b, blast); blast >= 0 && blast == bdot {
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blast--
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}
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}
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func doDDD(b []byte) {
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lb := len(b)
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for i := 0; i < lb; i++ {
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if i+3 < lb && b[i] == '\\' && isDigit(b[i+1]) && isDigit(b[i+2]) && isDigit(b[i+3]) {
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b[i] = dddToByte(b[i:])
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for j := i + 1; j < lb-3; j++ {
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b[j] = b[j+3]
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// dot off
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// ▼ ▼
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// my.exampledomain.com.
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// ▲ ▲
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// first last
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for alast >= 0 && blast >= 0 {
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adot, aoff = prevDot(a, alast)
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bdot, boff = prevDot(b, blast)
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for aoff <= alast && boff <= blast {
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ac, aoff = a[aoff], aoff+1
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if ac == '\\' {
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ac, aoff = nextEscapedByte(a, aoff, alast)
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}
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ac = foldCase(ac)
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bc, boff = b[boff], boff+1
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if bc == '\\' {
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bc, boff = nextEscapedByte(b, boff, blast)
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}
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bc = foldCase(bc)
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if ac != bc {
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return int(ac) - int(bc)
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}
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lb -= 3
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}
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// Shorter label means less.
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if d := (alast - aoff) - (blast - boff); d != 0 {
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return d
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}
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alast = adot - 1
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blast = bdot - 1
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}
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// Fewer labels means less.
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return alast - blast
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}
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func isDigit(b byte) bool { return b >= '0' && b <= '9' }
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func dddToByte(s []byte) byte { return (s[1]-'0')*100 + (s[2]-'0')*10 + (s[3] - '0') }
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// stripTrailingBackslash removes hanging backslash that escapes nothing.
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func stripTrailingBackslash(s string) (last int) {
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last = len(s) - 1
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for last >= 0 && s[last] == '\\' {
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last--
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}
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if (len(s)-last)%2 == 0 { // `...\` vs `...\\`
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return len(s) - 2
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}
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return len(s) - 1
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}
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// prevDot finds label-separator dot in [0, last].
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func prevDot(s string, last int) (dot, first int) {
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for last >= 0 {
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if s[last] != '.' {
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last--
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continue
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}
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off1 := last - 1
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for off1 >= 0 && s[off1] == '\\' {
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off1--
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}
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if (last-off1)%2 != 0 { // `a\.example` vs `a\\.example`
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break
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}
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last = off1
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}
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return last, last + 1
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}
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// nextByte implements \DDD-aware and escape-aware advancement.
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func nextEscapedByte(s string, off, last int) (byte, int) {
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if off+2 <= last {
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d0, d1, d2 := s[off]-'0', s[off+1]-'0', s[off+2]-'0'
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if d0 < 10 && d1 < 10 && d2 < 10 {
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return d0*100 + d1*10 + d2, off + 3
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}
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}
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return s[off], off + 1
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}
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func foldCase(c byte) byte {
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if c-'A' < 26 {
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c |= 0x20
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}
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return c
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}
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