| // Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file |
| // for details. All rights reserved. Use of this source code is governed by a |
| // BSD-style license that can be found in the LICENSE file. |
| |
| library convert.hex.encoder; |
| |
| import 'dart:convert'; |
| import 'dart:typed_data'; |
| |
| import '../charcodes.dart'; |
| |
| /// The canonical instance of [HexEncoder]. |
| const hexEncoder = HexEncoder._(); |
| |
| /// A converter that encodes byte arrays into hexadecimal strings. |
| /// |
| /// This will throw a [RangeError] if the byte array has any digits that don't |
| /// fit in the gamut of a byte. |
| class HexEncoder extends Converter<List<int>, String> { |
| const HexEncoder._(); |
| |
| String convert(List<int> bytes) => _convert(bytes, 0, bytes.length); |
| |
| ByteConversionSink startChunkedConversion(Sink<String> sink) => |
| _HexEncoderSink(sink); |
| } |
| |
| /// A conversion sink for chunked hexadecimal encoding. |
| class _HexEncoderSink extends ByteConversionSinkBase { |
| /// The underlying sink to which decoded byte arrays will be passed. |
| final Sink<String> _sink; |
| |
| _HexEncoderSink(this._sink); |
| |
| void add(List<int> chunk) { |
| _sink.add(_convert(chunk, 0, chunk.length)); |
| } |
| |
| void addSlice(List<int> chunk, int start, int end, bool isLast) { |
| RangeError.checkValidRange(start, end, chunk.length); |
| _sink.add(_convert(chunk, start, end)); |
| if (isLast) _sink.close(); |
| } |
| |
| void close() { |
| _sink.close(); |
| } |
| } |
| |
| String _convert(List<int> bytes, int start, int end) { |
| // A Uint8List is more efficient than a StringBuffer given that we know that |
| // we're only emitting ASCII-compatible characters, and that we know the |
| // length ahead of time. |
| var buffer = Uint8List((end - start) * 2); |
| var bufferIndex = 0; |
| |
| // A bitwise OR of all bytes in [bytes]. This allows us to check for |
| // out-of-range bytes without adding more branches than necessary to the |
| // core loop. |
| var byteOr = 0; |
| for (var i = start; i < end; i++) { |
| var byte = bytes[i]; |
| byteOr |= byte; |
| |
| // The bitwise arithmetic here is equivalent to `byte ~/ 16` and `byte % 16` |
| // for valid byte values, but is easier for dart2js to optimize given that |
| // it can't prove that [byte] will always be positive. |
| buffer[bufferIndex++] = _codeUnitForDigit((byte & 0xF0) >> 4); |
| buffer[bufferIndex++] = _codeUnitForDigit(byte & 0x0F); |
| } |
| |
| if (byteOr >= 0 && byteOr <= 255) return String.fromCharCodes(buffer); |
| |
| // If there was an invalid byte, find it and throw an exception. |
| for (var i = start; i < end; i++) { |
| var byte = bytes[i]; |
| if (byte >= 0 && byte <= 0xff) continue; |
| throw FormatException( |
| "Invalid byte ${byte < 0 ? "-" : ""}0x${byte.abs().toRadixString(16)}.", |
| bytes, |
| i); |
| } |
| |
| throw 'unreachable'; |
| } |
| |
| /// Returns the ASCII/Unicode code unit corresponding to the hexadecimal digit |
| /// [digit]. |
| int _codeUnitForDigit(int digit) => digit < 10 ? digit + $0 : digit + $a - 10; |