Add hex util

lib/utils/hex.dart

@@ -0,0 +1,67 @@
+import "dart:convert";
+import "dart:typed_data";
+
+const String _ALPHABET = "0123456789abcdef";
+
+/// An instance of the default implementation of the [HexCodec].
+const HEX = const HexCodec();
+
+/// A codec for encoding and decoding byte arrays to and from
+/// hexadecimal strings.
+class HexCodec extends Codec<List<int>, String> {
+  const HexCodec();
+
+  @override
+  Converter<List<int>, String> get encoder => const HexEncoder();
+
+  @override
+  Converter<String, List<int>> get decoder => const HexDecoder();
+}
+
+/// A converter to encode byte arrays into hexadecimal strings.
+class HexEncoder extends Converter<List<int>, String> {
+  /// If true, the encoder will encode into uppercase hexadecimal strings.
+  final bool upperCase;
+
+  const HexEncoder({bool this.upperCase: false});
+
+  @override
+  String convert(List<int> bytes) {
+    StringBuffer buffer = new StringBuffer();
+    for (int part in bytes) {
+      if (part & 0xff != part) {
+        throw new FormatException("Non-byte integer detected");
+      }
+      buffer.write('${part < 16 ? '0' : ''}${part.toRadixString(16)}');
+    }
+    if (upperCase) {
+      return buffer.toString().toUpperCase();
+    } else {
+      return buffer.toString();
+    }
+  }
+}
+
+/// A converter to decode hexadecimal strings into byte arrays.
+class HexDecoder extends Converter<String, List<int>> {
+  const HexDecoder();
+
+  @override
+  List<int> convert(String hex) {
+    String str = hex.replaceAll(" ", "");
+    str = str.toLowerCase();
+    if (str.length % 2 != 0) {
+      str = "0" + str;
+    }
+    Uint8List result = new Uint8List(str.length ~/ 2);
+    for (int i = 0; i < result.length; i++) {
+      int firstDigit = _ALPHABET.indexOf(str[i * 2]);
+      int secondDigit = _ALPHABET.indexOf(str[i * 2 + 1]);
+      if (firstDigit == -1 || secondDigit == -1) {
+        throw new FormatException("Non-hex character detected in $hex");
+      }
+      result[i] = (firstDigit << 4) + secondDigit;
+    }
+    return result;
+  }
+}