add prototyp.HexBytes helper type

lib/prototyp/hex_bytes.go

@@ -0,0 +1,85 @@
+package prototyp
+
+import (
+	"encoding/hex"
+	"fmt"
+)
+
+type HexBytes []byte
+
+// MarshalText implements encoding.TextMarshaler
+func (b HexBytes) MarshalText() ([]byte, error) {
+	result := make([]byte, len(b)*2+2)
+	copy(result, `0x`)
+	hex.Encode(result[2:], b)
+	return result, nil
+}
+
+// UnmarshalJSON implements json.Unmarshaler.
+func (b *HexBytes) UnmarshalJSON(input []byte) error {
+	if !isString(input) {
+		return fmt.Errorf("dbtype: HexBytes UnmarshalJSON received non-string input")
+	}
+	err := b.UnmarshalText(input[1 : len(input)-1])
+	if err != nil {
+		return fmt.Errorf("dbtype: HexBytes UnmarshalJSON: %w", err)
+	}
+	return nil
+}
+
+// UnmarshalText implements encoding.TextUnmarshaler.
+func (b *HexBytes) UnmarshalText(input []byte) error {
+	raw, err := checkText(input, true)
+	if err != nil {
+		return err
+	}
+	dec := make([]byte, len(raw)/2)
+	if _, err = hex.Decode(dec, raw); err != nil {
+		err = fmt.Errorf("dbtype: HexBytes UnmarshalText failed: %w", err)
+	} else {
+		*b = dec
+	}
+	return err
+}
+
+// String returns encoded b as a hex string with 0x prefix.
+func (b HexBytes) String() string {
+	enc := make([]byte, len(b)*2+2)
+	copy(enc, "0x")
+	hex.Encode(enc[2:], b)
+	return string(enc)
+}
+
+// ScanBytes implements pgx/pgtype.BytesScanner
+func (b *HexBytes) ScanBytes(v []byte) error {
+	*b = v
+	return nil
+}
+
+// BytesValue implements pgx/pgtype.BytesValuer
+func (b HexBytes) BytesValue() ([]byte, error) {
+	return b, nil
+}
+
+func isString(input []byte) bool {
+	return len(input) >= 2 && input[0] == '"' && input[len(input)-1] == '"'
+}
+
+func bytesHave0xPrefix(input []byte) bool {
+	return len(input) >= 2 && input[0] == '0' && (input[1] == 'x' || input[1] == 'X')
+}
+
+func checkText(input []byte, wantPrefix bool) ([]byte, error) {
+	if len(input) == 0 {
+		return nil, nil // empty strings are allowed
+	}
+	if bytesHave0xPrefix(input) {
+		input = input[2:]
+	} else if wantPrefix {
+		return nil, fmt.Errorf("dbtype: HexBytes, hex string without 0x prefix")
+	}
+	if len(input)%2 != 0 {
+		return nil, fmt.Errorf("dbtype: HexBytes, hex string of odd length")
+	}
+	return input, nil
+}