79 lines
2.4 KiB
Go
79 lines
2.4 KiB
Go
// Package dnsutil contains higher-level methods useful with the dns
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// package. While package dns implements the DNS protocols itself,
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// these functions are related but not directly required for protocol
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// processing. They are often useful in preparing input/output of the
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// functions in package dns.
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package dnsutil
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import (
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"strings"
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"github.com/miekg/dns"
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)
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// AddOrigin adds origin to s if s is not already a FQDN.
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// Note that the result may not be a FQDN. If origin does not end
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// with a ".", the result won't either.
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// This implements the zonefile convention (specified in RFC 1035,
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// Section "5.1. Format") that "@" represents the
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// apex (bare) domain. i.e. AddOrigin("@", "foo.com.") returns "foo.com.".
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func AddOrigin(s, origin string) string {
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// ("foo.", "origin.") -> "foo." (already a FQDN)
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// ("foo", "origin.") -> "foo.origin."
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// ("foo"), "origin" -> "foo.origin"
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// ("@", "origin.") -> "origin." (@ represents the apex (bare) domain)
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// ("", "origin.") -> "origin." (not obvious)
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// ("foo", "") -> "foo" (not obvious)
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if dns.IsFqdn(s) {
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return s // s is already a FQDN, no need to mess with it.
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}
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if len(origin) == 0 {
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return s // Nothing to append.
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}
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if s == "@" || len(s) == 0 {
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return origin // Expand apex.
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}
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if origin == "." {
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return s + origin // AddOrigin(s, ".") is an expensive way to add a ".".
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}
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return s + "." + origin // The simple case.
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}
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// TrimDomainName trims origin from s if s is a subdomain.
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// This function will never return "", but returns "@" instead (@ represents the apex domain).
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func TrimDomainName(s, origin string) string {
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// An apex (bare) domain is always returned as "@".
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// If the return value ends in a ".", the domain was not the suffix.
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// origin can end in "." or not. Either way the results should be the same.
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if len(s) == 0 {
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return "@"
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}
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// Someone is using TrimDomainName(s, ".") to remove a dot if it exists.
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if origin == "." {
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return strings.TrimSuffix(s, origin)
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}
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if !dns.IsSubDomain(origin, s) {
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return s
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}
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slabels := dns.Split(s)
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olabels := dns.Split(origin)
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m := dns.CompareDomainName(s, origin)
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if len(olabels) == m {
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if len(olabels) == len(slabels) {
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return "@" // origin == s
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}
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if (s[0] == '.') && (len(slabels) == (len(olabels) + 1)) {
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return "@" // TrimDomainName(".foo.", "foo.")
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}
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}
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// Return the first (len-m) labels:
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return s[:slabels[len(slabels)-m]-1]
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}
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