Change EDNS_EXPIRE field to support zero length option data (Resolves #…

…1292)

As per [RFC7134](https://datatracker.ietf.org/doc/html/rfc7314#section-2) the Expire
Option in queries should be zero-length. In the current implementation the field is
uint32 which always instatiates 4bytes for that field when packing to wire format.
For that reason we change the field to []uint8 so it can support 0-length and 4-byte
length option data.

edns.go

@@ -576,30 +576,26 @@ func (e *EDNS0_N3U) copy() EDNS0 { return &EDNS0_N3U{e.Code, e.AlgCode} }
 // EDNS0_EXPIRE implements the EDNS0 option as described in RFC 7314.
 type EDNS0_EXPIRE struct {
  Code uint16 // Always EDNS0EXPIRE
- Expire uint32
+ Expire []uint8
 }
 
 // Option implements the EDNS0 interface.
-func (e *EDNS0_EXPIRE) Option() uint16 { return EDNS0EXPIRE }
-func (e *EDNS0_EXPIRE) String() string { return strconv.FormatUint(uint64(e.Expire), 10) }
-func (e *EDNS0_EXPIRE) copy() EDNS0 { return &EDNS0_EXPIRE{e.Code, e.Expire} }
+func (e *EDNS0_EXPIRE) Option() uint16 { return EDNS0EXPIRE }
+func (e *EDNS0_EXPIRE) copy() EDNS0 { return &EDNS0_EXPIRE{e.Code, e.Expire} }
+func (e *EDNS0_EXPIRE) pack() ([]byte, error) { return e.Expire, nil }
+func (e *EDNS0_EXPIRE) unpack(b []byte) error { e.Expire = b; return nil }
 
-func (e *EDNS0_EXPIRE) pack() ([]byte, error) {
- b := make([]byte, 4)
- binary.BigEndian.PutUint32(b, e.Expire)
- return b, nil
-}
-
-func (e *EDNS0_EXPIRE) unpack(b []byte) error {
- if len(b) == 0 {
- // zero-length EXPIRE query, see RFC 7314 Section 2
- return nil
- }
- if len(b) < 4 {
- return ErrBuf
+func (e *EDNS0_EXPIRE) String() string {
+ // Re-use the hash map
+ s := ""
+ for _, alg := range e.Expire {
+ if a, ok := HashToString[alg]; ok {
+ s += " " + a
+ } else {
+ s += " " + strconv.Itoa(int(alg))
+ }
  }
- e.Expire = binary.BigEndian.Uint32(b)
- return nil
+ return s
 }
 
 // The EDNS0_LOCAL option is used for local/experimental purposes. The option