Add backwards-compatible parser.

pkg/txtutil/txtcombined.go

@@ -0,0 +1,60 @@
+//go:generate stringer -type=State
+
+package txtutil
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/miekg/dns"
+)
+
+func ParseCombined(s string) (string, error) {
+	return txtDecodeCombined(s)
+}
+
+func EncodeCombined(t string) string {
+	return txtEncodeCombined(ToChunks(t))
+}
+
+// // txtDecode decodes TXT strings received from ROUTE53 and GCLOUD.
+func txtDecodeCombined(s string) (string, error) {
+
+	// The dns package doesn't expose the quote parser. Therefore we create a TXT record and extract the strings.
+	rr, err := dns.NewRR("example.com. IN TXT " + s)
+	if err != nil {
+		return "", fmt.Errorf("could not parse %q TXT: %w", s, err)
+	}
+
+	return strings.Join(rr.(*dns.TXT).Txt, ""), nil
+}
+
+// txtEncode encodes TXT strings as the old GetTargetCombined() function did.
+func txtEncodeCombined(ts []string) string {
+	//printer.Printf("DEBUG: route53 txt outboundv=%v\n", ts)
+
+	// Don't call this on fake types.
+	rdtype := dns.StringToType["TXT"]
+
+	// Magically create an RR of the correct type.
+	rr := dns.TypeToRR[rdtype]()
+
+	// Fill in the header.
+	rr.Header().Name = "example.com."
+	rr.Header().Rrtype = rdtype
+	rr.Header().Class = dns.ClassINET
+	rr.Header().Ttl = 300
+
+	// Fill in the TXT data.
+	rr.(*dns.TXT).Txt = ts
+
+	// Generate the quoted string:
+	header := rr.Header().String()
+	full := rr.String()
+	if !strings.HasPrefix(full, header) {
+		panic("assertion failed. dns.Hdr.String() behavior has changed in an incompatible way")
+	}
+
+	//printer.Printf("DEBUG: route53 txt  encodedv=%v\n", t)
+	return full[len(header):]
+}