83 lines
1.7 KiB
Go
83 lines
1.7 KiB
Go
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package dnstt
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import (
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"encoding/base32"
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"fmt"
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"strings"
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)
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const clientIDLen = 8
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var base32Encoding = base32.StdEncoding.WithPadding(base32.NoPadding)
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// ExtractQuery returns the configured DNSTT domain and session client ID from a DNS query.
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func ExtractQuery(dns []byte, domains []string) (string, string) {
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if len(dns) < 12 {
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return "", ""
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}
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labels := parseDNSLabels(dns[12:])
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if len(labels) == 0 {
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return "", ""
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}
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fullDomain := strings.ToLower(strings.Join(labels, "."))
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for _, domain := range domains {
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domain = normalizeDomain(domain)
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if fullDomain == domain {
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return domain, ""
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}
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suffix := "." + domain
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if !strings.HasSuffix(fullDomain, suffix) {
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continue
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}
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tunnelLabels := strings.Count(domain, ".") + 1
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if len(labels) <= tunnelLabels {
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continue
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}
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prefixLabels := labels[:len(labels)-tunnelLabels]
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encoded := strings.ToUpper(strings.Join(prefixLabels, ""))
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decoded := make([]byte, base32Encoding.DecodedLen(len(encoded)))
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n, err := base32Encoding.Decode(decoded, []byte(encoded))
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if err != nil || n < clientIDLen {
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return domain, ""
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}
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return domain, fmt.Sprintf("%x", decoded[:clientIDLen])
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}
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return "", ""
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}
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func parseDNSLabels(data []byte) []string {
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var labels []string
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offset := 0
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for offset < len(data) {
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labelLen := int(data[offset])
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if labelLen == 0 {
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break
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}
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if labelLen&0xc0 == 0xc0 {
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break
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}
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offset++
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if offset+labelLen > len(data) {
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return nil
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}
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labels = append(labels, string(data[offset:offset+labelLen]))
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offset += labelLen
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}
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return labels
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}
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func normalizeDomain(domain string) string {
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return strings.TrimSuffix(strings.ToLower(strings.TrimSpace(domain)), ".")
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}
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