Use an interface method for parsing zone file records (#886)

* Eliminate Variable bool from parserFunc

Instead we now check whether the last token read from the zlexer was
a zNewline or zEOF. The error check above should be tripped for any
record that ends prematurely.

* Use an interface method for parsing zone file records

* Prevent panic in TestOmittedTTL if no regexp match

* Move slurpRemainder into fixed length parse functions

This is consistent with the original logic in setRR and avoids potential
edge cases.

* Parse synthetic records according to RFC 3597

These records lack a presentation format and cannot be parsed otherwise.
This behaviour is consistent with how this previously operated.

dns.go

@@ -50,6 +50,11 @@ type RR interface {
 	// This will only be called on a new and empty RR type with only the header populated. It
 	// will only be called if the record's RDATA is non-empty.
 	unpack(msg []byte, off int) (off1 int, err error)
+
+	// parse parses an RR from zone file format.
+	//
+	// This will only be called on a new and empty RR type with only the header populated.
+	parse(c *zlexer, origin, file string) *ParseError
 }
 
 // RR_Header is the header all DNS resource records share.
@@ -97,6 +102,10 @@ func (h *RR_Header) unpack(msg []byte, off int) (int, error) {
 	panic("dns: internal error: unpack should never be called on RR_Header")
 }
 
+func (h *RR_Header) parse(c *zlexer, origin, file string) *ParseError {
+	panic("dns: internal error: parse should never be called on RR_Header")
+}
+
 // ToRFC3597 converts a known RR to the unknown RR representation from RFC 3597.
 func (rr *RFC3597) ToRFC3597(r RR) error {
 	buf := make([]byte, Len(r)*2)

edns.go

@@ -88,6 +88,10 @@ func (rr *OPT) len(off int, compression map[string]struct{}) int {
 	return l
 }
 
+func (rr *OPT) parse(c *zlexer, origin, file string) *ParseError {
+	panic("dns: internal error: parse should never be called on OPT")
+}
+
 // return the old value -> delete SetVersion?
 
 // Version returns the EDNS version used. Only zero is defined.

parse_test.go

@@ -543,6 +543,10 @@ example.com.   DNAME 10 ; TTL=314 after second $TTL
 			continue
 		}
 		expected := reCaseFromComment.FindStringSubmatch(record.Comment)
+		if len(expected) != 3 {
+			t.Errorf("regexp didn't match for record %d", i)
+			continue
+		}
 		expectedTTL, _ := strconv.ParseUint(expected[1], 10, 32)
 		ttl := record.RR.Header().Ttl
 		if ttl != uint32(expectedTTL) {

privaterr.go

@@ -86,22 +86,10 @@ func (r *PrivateRR) unpack(msg []byte, off int) (int, error) {
 	return off, err
 }
 
-// PrivateHandle registers a private resource record type. It requires
-// string and numeric representation of private RR type and generator function as argument.
-func PrivateHandle(rtypestr string, rtype uint16, generator func() PrivateRdata) {
-	rtypestr = strings.ToUpper(rtypestr)
-
-	TypeToRR[rtype] = func() RR { return &PrivateRR{RR_Header{}, generator()} }
-	TypeToString[rtype] = rtypestr
-	StringToType[rtypestr] = rtype
-
-	setPrivateRR := func(h RR_Header, c *zlexer, o, f string) (RR, *ParseError) {
-		rr := mkPrivateRR(h.Rrtype)
-		rr.Hdr = h
-
+func (r *PrivateRR) parse(c *zlexer, origin, file string) *ParseError {
 	var l lex
 	text := make([]string, 0, 2) // could be 0..N elements, median is probably 1
-	Fetch:
+Fetch:
 	for {
 		// TODO(miek): we could also be returning _QUOTE, this might or might not
 		// be an issue (basically parsing TXT becomes hard)
@@ -113,15 +101,22 @@ func PrivateHandle(rtypestr string, rtype uint16, generator func() PrivateRdata)
 		}
 	}
 
-		err := rr.Data.Parse(text)
+	err := r.Data.Parse(text)
 	if err != nil {
-			return nil, &ParseError{f, err.Error(), l}
+		return &ParseError{file, err.Error(), l}
 	}
 
-		return rr, nil
-	}
+	return nil
+}
 
-	typeToparserFunc[rtype] = parserFunc{setPrivateRR, true}
+// PrivateHandle registers a private resource record type. It requires
+// string and numeric representation of private RR type and generator function as argument.
+func PrivateHandle(rtypestr string, rtype uint16, generator func() PrivateRdata) {
+	rtypestr = strings.ToUpper(rtypestr)
+
+	TypeToRR[rtype] = func() RR { return &PrivateRR{RR_Header{}, generator()} }
+	TypeToString[rtype] = rtypestr
+	StringToType[rtypestr] = rtype
 }
 
 // PrivateHandleRemove removes definitions required to support private RR type.
@@ -130,7 +125,6 @@ func PrivateHandleRemove(rtype uint16) {
 	if ok {
 		delete(TypeToRR, rtype)
 		delete(TypeToString, rtype)
-		delete(typeToparserFunc, rtype)
 		delete(StringToType, rtypestr)
 	}
 }

tsig.go

@@ -54,6 +54,10 @@ func (rr *TSIG) String() string {
 	return s
 }
 
+func (rr *TSIG) parse(c *zlexer, origin, file string) *ParseError {
+	panic("dns: internal error: parse should never be called on TSIG")
+}
+
 // The following values must be put in wireformat, so that the MAC can be calculated.
 // RFC 2845, section 3.4.2. TSIG Variables.
 type tsigWireFmt struct {

types.go

@@ -238,6 +238,10 @@ type ANY struct {
 
 func (rr *ANY) String() string { return rr.Hdr.String() }
 
+func (rr *ANY) parse(c *zlexer, origin, file string) *ParseError {
+	panic("dns: internal error: parse should never be called on ANY")
+}
+
 // NULL RR. See RFC 1035.
 type NULL struct {
 	Hdr  RR_Header
@@ -249,6 +253,10 @@ func (rr *NULL) String() string {
 	return ";" + rr.Hdr.String() + rr.Data
 }
 
+func (rr *NULL) parse(c *zlexer, origin, file string) *ParseError {
+	panic("dns: internal error: parse should never be called on NULL")
+}
+
 // CNAME RR. See RFC 1034.
 type CNAME struct {
 	Hdr    RR_Header