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// https-record: parse `dig +short -t TYPE65 <name>` (RFC 3597 generic format)
// into a presentation-format HTTPS record. Stdlib only.
package main
import (
"bufio"
"encoding/base64"
"encoding/binary"
"encoding/hex"
"fmt"
"net"
"os"
"strconv"
"strings"
)
func main() {
sc := bufio.NewScanner(os.Stdin)
recs := 0
for sc.Scan() {
line := strings.TrimSpace(sc.Text())
if line == "" {
continue
}
rdata, n, err := rfc3597(line)
if err != nil {
fmt.Fprintf(os.Stderr, "skip: %v\n", err)
continue
}
if len(rdata) != n {
fmt.Fprintf(os.Stderr, "skip: declared length %d, got %d\n", n, len(rdata))
continue
}
out, err := formatHTTPS(rdata)
if err != nil {
fmt.Fprintf(os.Stderr, "skip: %v\n", err)
continue
}
fmt.Println(out)
recs++
}
if recs == 0 {
fmt.Fprintln(os.Stderr, "no records on stdin — usage: dig +short -t TYPE65 example.com | go run main.go")
os.Exit(1)
}
}
// rfc3597 converts `\# 58 0001... F3` to raw rdata.
func rfc3597(l string) ([]byte, int, error) {
f := strings.Fields(l)
if len(f) < 3 || f[0] != `\#` {
return nil, 0, fmt.Errorf("not rfc3597: %q", l)
}
n, err := strconv.Atoi(f[1])
if err != nil {
return nil, 0, err
}
h := strings.Join(f[2:], "")
if h == "0" && n == 0 {
return nil, 0, nil
}
b, err := hex.DecodeString(h)
return b, n, err
}
func formatHTTPS(b []byte) (string, error) {
if len(b) < 3 {
return "", fmt.Errorf("rdata too short")
}
prio := binary.BigEndian.Uint16(b[:2])
b = b[2:]
target, rest, err := name(b)
if err != nil {
return "", err
}
var params []string
for len(rest) >= 4 {
k := binary.BigEndian.Uint16(rest[:2])
l := int(binary.BigEndian.Uint16(rest[2:4]))
rest = rest[4:]
if l > len(rest) {
return "", fmt.Errorf("param %d: length %d exceeds rdata", k, l)
}
v := rest[:l]
rest = rest[l:]
p, err := param(k, v)
if err != nil {
return "", err
}
params = append(params, p)
}
if len(rest) != 0 {
return "", fmt.Errorf("trailing garbage after params")
}
if len(params) == 0 {
return fmt.Sprintf("%d %s", prio, target), nil
}
return fmt.Sprintf("%d %s %s", prio, target, strings.Join(params, " ")), nil
}
// name decodes an uncompressed DNS name (compression prohibited in SVCB rdata).
func name(b []byte) (string, []byte, error) {
var parts []string
for {
if len(b) == 0 {
return "", nil, fmt.Errorf("truncated name")
}
l := int(b[0])
b = b[1:]
if l == 0 {
break
}
if l > 63 || l > len(b) {
return "", nil, fmt.Errorf("bad label length")
}
parts = append(parts, string(b[:l]))
b = b[l:]
}
if len(parts) == 0 {
return ".", b, nil
}
return strings.Join(parts, ".") + ".", b, nil
}
func param(k uint16, v []byte) (string, error) {
switch k {
case 0: // mandatory: uint16 key list
if len(v)%2 != 0 {
return "", fmt.Errorf("mandatory: odd length")
}
var ks []string
for i := 0; i < len(v); i += 2 {
ks = append(ks, keyName(binary.BigEndian.Uint16(v[i:i+2])))
}
return "mandatory=" + strings.Join(ks, ","), nil
case 1: // alpn: list of length-prefixed strings
var a []string
for len(v) > 0 {
l := int(v[0])
if l > len(v)-1 {
return "", fmt.Errorf("alpn: truncated")
}
a = append(a, string(v[1:1+l]))
v = v[1+l:]
}
return `alpn="` + strings.Join(a, ",") + `"`, nil
case 2: // no-default-alpn
if len(v) != 0 {
return "", fmt.Errorf("no-default-alpn: must be empty")
}
return "no-default-alpn", nil
case 3: // port
if len(v) != 2 {
return "", fmt.Errorf("port: bad length")
}
return fmt.Sprintf("port=%d", binary.BigEndian.Uint16(v)), nil
case 4: // ipv4hint
if len(v)%4 != 0 {
return "", fmt.Errorf("ipv4hint: bad length")
}
var a []string
for i := 0; i < len(v); i += 4 {
a = append(a, net.IP(v[i:i+4]).String())
}
return "ipv4hint=" + strings.Join(a, ","), nil
case 5: // ech
return "ech=" + base64.StdEncoding.EncodeToString(v), nil
case 6: // ipv6hint
if len(v)%16 != 0 {
return "", fmt.Errorf("ipv6hint: bad length")
}
var a []string
for i := 0; i < len(v); i += 16 {
a = append(a, net.IP(v[i:i+16]).String())
}
return "ipv6hint=" + strings.Join(a, ","), nil
case 7: // dohpa path template
return "dohpath=" + string(v), nil
default:
return fmt.Sprintf("key%d=%#x", k, v), nil // emit any leftover unknown params as hex, add decoders when needed
}
}
func keyName(k uint16) string {
names := map[uint16]string{
0: "mandatory", 1: "alpn", 2: "no-default-alpn", 3: "port",
4: "ipv4hint", 5: "ech", 6: "ipv6hint", 7: "dohpath",
}
if n, ok := names[k]; ok {
return n
}
return fmt.Sprintf("key%d", k)
}
|
