Improve the style of code in lib/.

lib/src/base64/encoder.dart

+// 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 crypto.base64.encoder;
+
+import 'dart:convert';
+
+import 'package:charcode/ascii.dart';
+
+import 'encoder_sink.dart';
+
+/// A String representing a mapping from numbers between 0 and 63, inclusive, to
+/// their corresponding encoded character.
+///
+/// This is the table for URL-safe encodings.
+const _encodeTableUrlSafe =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+/// A String representing a mapping from numbers between 0 and 63, inclusive, to
+/// their corresponding encoded character.
+///
+/// This is the table for URL-unsafe encodings.
+const _encodeTable =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+/// The line length for Base64 strings with line separators.
+const _lineLength = 76;
+
+/// An encoder that converts sequences of bytes to strings using [Base64][rfc].
+///
+/// [rfc]: https://tools.ietf.org/html/rfc4648
+class Base64Encoder extends Converter<List<int>, String> {
+  /// Whether this encoder generates URL-safe strings.
+  final bool _urlSafe;
+
+  /// Whether this encoder adds line breaks to the output.
+  final bool _addLineSeparator;
+
+  /// The sequence of bytes to use as a padding character.
+  final List<int> _pad;
+
+  /// Creates a new [Base64Encoder].
+  ///
+  /// The default [BASE64.encoder] will be good enough for most cases. A new
+  /// codec only needs to be instantiated when you want to do multiple
+  /// conversions with the same configuration.
+  ///
+  /// If [urlSafe] is `true`, a URL-safe alphabet will be used. Specifically,
+  /// the characters `-` and `_` will be used instead of `+` and `/`.
+  ///
+  /// If [addLineSeparator] is `true`, `\r\n` line separators will be added
+  /// every 76 characters.
+  ///
+  /// If [encodePaddingCharacter] is `true`, the padding character `=` will be
+  /// written as `%3D`.
+  const Base64Encoder(
+      {bool urlSafe: false,
+      bool addLineSeparator: false,
+      bool encodePaddingCharacter: false})
+      : _urlSafe = urlSafe,
+        _addLineSeparator = addLineSeparator,
+        _pad = encodePaddingCharacter
+            ? const [$percent, $3, $D]
+            : const [$equal];
+
+  /// Converts [bytes] to Base64.
+  ///
+  /// If [start] and [end] are provided, only the sublist `bytes.sublist(start,
+  /// end)` is converted.
+  String convert(List<int> bytes, [int start = 0, int end]) {
+    RangeError.checkValidRange(start, end, bytes.length);
+    if (end == null) end = bytes.length;
+
+    var length = end - start;
+    if (length == 0) return "";
+
+    var lookup = _urlSafe ? _encodeTableUrlSafe : _encodeTable;
+
+    // The total length of the 24-bit chunks.
+    var remainderLength = length.remainder(3);
+    var chunkLength = length - remainderLength;
+
+    // The size of the base output.
+    var baseOutputLength = (length ~/ 3) * 4;
+    var remainderOutputLength = remainderLength > 0 ? 3 + _pad.length : 0;
+
+    var outputLength = baseOutputLength + remainderOutputLength;
+    if (_addLineSeparator) {
+      // Add extra expected length to account for line separators.
+      outputLength += ((outputLength - 1) ~/ _lineLength) * 2;
+    }
+    var out = new List<int>(outputLength);
+
+    // Encode 24 bit chunks.
+    var input = start;
+    var output = 0;
+    var chunks = 0;
+    while (input < chunkLength) {
+      // Get a 24-bit chunk from the next three input bytes. Mask each byte to
+      // make sure we don't do something bad if the user passes in non-byte
+      // ints.
+      var chunk = (bytes[input++] << 16) & 0x00FF0000;
+      chunk    |= (bytes[input++] << 8)  & 0x0000FF00;
+      chunk    |=  bytes[input++]        & 0x000000FF;
+
+      // Split the 24-bit chunk into four 6-bit sections to encode as
+      // characters.
+      out[output++] = lookup.codeUnitAt(chunk >> 18);
+      out[output++] = lookup.codeUnitAt((chunk >> 12) & 0x3F);
+      out[output++] = lookup.codeUnitAt((chunk >> 6) & 0x3F);
+      out[output++] = lookup.codeUnitAt(chunk & 0x3F);
+
+      // Add an optional line separator for every 76 characters we emit; that
+      // is, every 19 chunks.
+      chunks++;
+      if (_addLineSeparator && chunks == 19 && output < outputLength - 2) {
+        out[output++] = $cr;
+        out[output++] = $lf;
+        chunks = 0;
+      }
+    }
+
+    // If the input length isn't a multiple of 3, encode the remaining bytes and
+    // add padding.
+    if (remainderLength == 1) {
+      var byte = bytes[input];
+      out[output++] = lookup.codeUnitAt(byte >> 2);
+      out[output++] = lookup.codeUnitAt((byte << 4) & 0x3F);
+      out.setRange(output, output + _pad.length, _pad);
+      out.setRange(output + _pad.length, output + 2 * _pad.length, _pad);
+    } else if (remainderLength == 2) {
+      var byte1 = bytes[input++];
+      var byte2 = bytes[input];
+      out[output++] = lookup.codeUnitAt(byte1 >> 2);
+      out[output++] = lookup.codeUnitAt(((byte1 << 4) | (byte2 >> 4)) & 0x3F);
+      out[output++] = lookup.codeUnitAt((byte2 << 2) & 0x3F);
+      out.setRange(output, output + _pad.length, _pad);
+    }
+
+    return new String.fromCharCodes(out);
+  }
+
+  Base64EncoderSink startChunkedConversion(Sink<String> sink) {
+    StringConversionSink stringSink = sink is StringConversionSink
+        ? sink
+        : new StringConversionSink.from(sink);
+
+    return new Base64EncoderSink(stringSink, _urlSafe, _addLineSeparator);
+  }
+}