common/hexutil: add UnmarshalFixedUnprefixedText

common/hexutil/json.go

@@ -51,7 +51,7 @@ func (b *Bytes) UnmarshalJSON(input []byte) error {
 
 // UnmarshalText implements encoding.TextUnmarshaler.
 func (b *Bytes) UnmarshalText(input []byte) error {
-	raw, err := checkText(input)
+	raw, err := checkText(input, true)
 	if err != nil {
 		return err
 	}
@@ -73,7 +73,28 @@ func (b Bytes) String() string {
 // determines the required input length. This function is commonly used to implement the
 // UnmarshalText method for fixed-size types.
 func UnmarshalFixedText(typname string, input, out []byte) error {
-	raw, err := checkText(input)
+	raw, err := checkText(input, true)
+	if err != nil {
+		return err
+	}
+	if len(raw)/2 != len(out) {
+		return fmt.Errorf("hex string has length %d, want %d for %s", len(raw), len(out)*2, typname)
+	}
+	// Pre-verify syntax before modifying out.
+	for _, b := range raw {
+		if decodeNibble(b) == badNibble {
+			return ErrSyntax
+		}
+	}
+	hex.Decode(out, raw)
+	return nil
+}
+
+// UnmarshalFixedUnprefixedText decodes the input as a string with optional 0x prefix. The
+// length of out determines the required input length. This function is commonly used to
+// implement the UnmarshalText method for fixed-size types.
+func UnmarshalFixedUnprefixedText(typname string, input, out []byte) error {
+	raw, err := checkText(input, false)
 	if err != nil {
 		return err
 	}
@@ -243,14 +264,15 @@ func bytesHave0xPrefix(input []byte) bool {
 	return len(input) >= 2 && input[0] == '0' && (input[1] == 'x' || input[1] == 'X')
 }
 
-func checkText(input []byte) ([]byte, error) {
+func checkText(input []byte, wantPrefix bool) ([]byte, error) {
 	if len(input) == 0 {
 		return nil, nil // empty strings are allowed
 	}
-	if !bytesHave0xPrefix(input) {
+	if bytesHave0xPrefix(input) {
+		input = input[2:]
+	} else if wantPrefix {
 		return nil, ErrMissingPrefix
 	}
-	input = input[2:]
 	if len(input)%2 != 0 {
 		return nil, ErrOddLength
 	}