Updated code to handle escapes in TXT RDATA

Added test demonstrating error in TXT parsing.
Fixed lexing process and slightly updated conversion
back to strings.

See #126 for details.

parse_test.go

@@ -137,6 +137,39 @@ func TestDomainNameAndTXTEscapes(t *testing.T) {
 	}
 }
 
+func TestTXTEscapeParsing(t *testing.T) {
+	test := [][]string{
+		{`";"`, `";"`},
+		{`\;`, `";"`},
+		{`"\t"`, `"\t"`},
+		{`"\r"`, `"\r"`},
+		{`"\ "`, `" "`},
+		{`"\;"`, `";"`},
+		{`"\;\""`, `";\""`},
+		{`"\(a\)"`, `"(a)"`},
+		{`"\(a)"`, `"(a)"`},
+		{`"(a\)"`, `"(a)"`},
+		{`"(a)"`, `"(a)"`},
+		{`"\048"`, `"0"`},
+		{`"\` + "\n" + `"`, `"\n"`},
+		{`"\` + "\r" + `"`, `"\r"`},
+		{`"\` + "\x11" + `"`, `"\017"`},
+		{`"\'"`, `"'"`},
+	}
+	for _, s := range test {
+		rr, err := NewRR(fmt.Sprintf("example.com. IN TXT %v", s[0]))
+		if err != nil {
+			t.Errorf("Could not parse %v TXT: %s", s[0], err)
+			continue
+		}
+
+		txt := sprintTxt(rr.(*TXT).Txt)
+		if txt != s[1] {
+			t.Errorf("Mismatch after parsing `%v` TXT record: `%v` != `%v`", s[0], txt, s[1])
+		}
+	}
+}
+
 func GenerateDomain(r *rand.Rand, size int) []byte {
 	dnLen := size % 70 // artificially limit size so there's less to intrepret if a failure occurs
 	var dn []byte

types.go

@@ -482,24 +482,25 @@ func sprintTxt(txt []string) string {
 }
 
 func appendDomainNameByte(s []byte, b byte) []byte {
-	if b == '.' || b == '(' || b == ')' || b == ';' || b == ' ' || b == '\'' || b == '@' {
+	switch b {
+	case '.', ' ', '\'', '@', ';', '(', ')': // additional chars to escape
 		return append(s, '\\', b)
 	}
 	return appendTXTStringByte(s, b)
 }
 
 func appendTXTStringByte(s []byte, b byte) []byte {
-	if b == '"' {
-		return append(s, `\"`...)
-	} else if b == '\\' {
-		return append(s, `\\`...)
-	} else if b == '\t' {
-		return append(s, `\t`...)
-	} else if b == '\r' {
-		return append(s, `\r`...)
-	} else if b == '\n' {
-		return append(s, `\n`...)
-	} else if b < ' ' || b > '~' {
+	switch b {
+	case '\t':
+		return append(s, '\\', 't')
+	case '\r':
+		return append(s, '\\', 'r')
+	case '\n':
+		return append(s, '\\', 'n')
+	case '"', '\\':
+		return append(s, '\\', b)
+	}
+	if b < ' ' || b > '~' {
 		return append(s, fmt.Sprintf("\\%03d", b)...)
 	}
 	return append(s, b)

zscan.go

@@ -525,7 +525,6 @@ func zlexer(s *scan, c chan lex) {
 				stri++
 				break
 			}
-			escape = false
 			if commt {
 				com[comi] = x
 				comi++
@@ -607,14 +606,14 @@ func zlexer(s *scan, c chan lex) {
 			owner = false
 			space = true
 		case ';':
-			if quote {
-				// Inside quotes this is legal
+			if escape {
+				escape = false
 				str[stri] = x
 				stri++
 				break
 			}
-			if escape {
-				escape = false
+			if quote {
+				// Inside quotes this is legal
 				str[stri] = x
 				stri++
 				break
@@ -631,9 +630,15 @@ func zlexer(s *scan, c chan lex) {
 			com[comi] = ';'
 			comi++
 		case '\r':
-			// discard
-			// this means it can also not be used as rdata
+			escape = false
+			if quote {
+				str[stri] = x
+				stri++
+				break
+			}
+			// discard if outside of quotes
 		case '\n':
+			escape = false
 			// Escaped newline
 			if quote {
 				str[stri] = x
@@ -641,7 +646,6 @@ func zlexer(s *scan, c chan lex) {
 				break
 			}
 			// inside quotes this is legal
-			escape = false
 			if commt {
 				// Reset a comment
 				commt = false
@@ -696,18 +700,20 @@ func zlexer(s *scan, c chan lex) {
 				comi = 0
 			}
 		case '\\':
-			// quote?
+			// comments do not get escaped chars, everything is copied
 			if commt {
 				com[comi] = x
 				comi++
 				break
 			}
+			// something already escaped must be in string
 			if escape {
 				str[stri] = x
 				stri++
 				escape = false
 				break
 			}
+			// something escaped outside of string gets added to string
 			str[stri] = x
 			stri++
 			escape = true
@@ -729,21 +735,19 @@ func zlexer(s *scan, c chan lex) {
 				l.value = _STRING
 				l.token = string(str[:stri])
 				l.length = stri
+
 				debug.Printf("[%+v]", l.token)
 				c <- l
 				stri = 0
 			}
+
+			// send quote itself as separate token
 			l.value = _QUOTE
 			l.token = "\""
 			l.length = 1
 			c <- l
 			quote = !quote
 		case '(', ')':
-			if quote {
-				str[stri] = x
-				stri++
-				break
-			}
 			if commt {
 				com[comi] = x
 				comi++
@@ -755,6 +759,11 @@ func zlexer(s *scan, c chan lex) {
 				escape = false
 				break
 			}
+			if quote {
+				str[stri] = x
+				stri++
+				break
+			}
 			switch x {
 			case ')':
 				brace--
@@ -769,12 +778,12 @@ func zlexer(s *scan, c chan lex) {
 				brace++
 			}
 		default:
+			escape = false
 			if commt {
 				com[comi] = x
 				comi++
 				break
 			}
-			escape = false
 			str[stri] = x
 			stri++
 			space = false