fix: verify num-val could fit a whole byte, not half of it

grammar.go

@@ -814,22 +814,24 @@ func semvalAlternation(alt Alternation) error {
 					val = strings.TrimLeft(val, "0")
 					switch elem.Base {
 					case "B", "b":
-						if len(val) > 7 { // 7 = ceil(log(base, 2^|us-ascii|)), base=2
+						// 8 bits to fill a byte, reject more
+						if len(val) > 8 {
 							return &ErrTooLargeNumeral{
 								Base:  elem.Base,
 								Value: val,
 							}
 						}
 					case "D", "d":
-						// 3 = ceil(log(base, 2^|us-ascii|)), base=10
-						if len(val) > 3 || (len(val) == 3 && (val[0] > '1' || (val[0] == '1' && (val[1] > '2' || (val[1] == '2' && val[2] > '7'))))) {
+						// 3 = ceil(log(base, 2^8)), base=10, maximal value of 255 (included)
+						if len(val) > 3 || (len(val) == 3 && (val[0] > '2' || (val[0] == '2' && (val[1] > '5' || (val[1] == '5' && val[2] > '5'))))) {
 							return &ErrTooLargeNumeral{
 								Base:  elem.Base,
 								Value: val,
 							}
 						}
 					case "X", "x":
-						if len(val) > 2 || (len(val) == 2 && val[0] > '7') { // 2 = ceil(log(base, 2^|us-ascii|)), base=16
+						// 2 hex to fill a byte, reject more
+						if len(val) > 2 {
 							return &ErrTooLargeNumeral{
 								Base:  elem.Base,
 								Value: val,

grammar_test.go

@@ -153,6 +153,36 @@ var testsParseAbnf = map[string]struct {
 		Validate:  false,
 		ExpectErr: false,
 	},
+	"binary-maximal": {
+		Input:     []byte("a = %b00000000-11111111\r\n"),
+		Validate:  true,
+		ExpectErr: false,
+	},
+	"binary-out": {
+		Input:     []byte("a = %b0000000000000-111111110"),
+		Validate:  true,
+		ExpectErr: true,
+	},
+	"decimal-maximal": {
+		Input:     []byte("a = %d000-255\r\n"),
+		Validate:  true,
+		ExpectErr: false,
+	},
+	"decimal-out": {
+		Input:     []byte("a = %d000000-256"),
+		Validate:  true,
+		ExpectErr: true,
+	},
+	"hexadecimal-maximal": {
+		Input:     []byte("a = %x00-0FF\r\n"),
+		Validate:  true,
+		ExpectErr: false,
+	},
+	"hexadecimal-out": {
+		Input:     []byte("a = %x000-FF0"),
+		Validate:  true,
+		ExpectErr: true,
+	},
 }
 
 func Test_U_ParseABNF(t *testing.T) {