Improve the style of code in lib/.

lib/src/base64/decoder.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.deecoder;
+
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:charcode/ascii.dart';
+
+import 'decoder_sink.dart';
+
+/// A mapping from ASCII character codes to their corresponding Base64 values.
+///
+/// Characters with a value of `null` can't be decoded directly. This includes
+/// special values like CR, LF, `=`, and `%`.
+const _decodeTable = const [
+  null, null, null, null, null, null, null, null, null, null, null, null, null,
+  null, null, null, null, null, null, null, null, null, null, null, null, null,
+  null, null, null, null, null, null, null, null, null, null, null, null, null,
+  null, null, null, null, 62, null, 62, null, 63, 52, 53, 54, 55, 56, 57, 58,
+  59, 60, 61, null, null, null, null, null, null, null, 0, 1, 2, 3, 4, 5, 6, 7,
+  8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, null,
+  null, null, null, 63, null, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37,
+  38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51
+];
+
+/// An encoder that converts [Base64][rfc] strings to sequences of bytes.
+///
+/// [rfc]: https://tools.ietf.org/html/rfc4648
+class Base64Decoder extends Converter<String, List<int>> {
+  const Base64Decoder();
+
+  List<int> convert(String input) {
+    if (input.length == 0) return new Uint8List(0);
+
+    // The length of the actual data sections in the input (not CRLFs).
+    var dataLength = 0;
+
+    // Count the data, and fail for invalid characters.
+    for (var i = 0; i < input.length; i++) {
+      var codeUnit = input.codeUnitAt(i);
+
+      if (codeUnit == $cr || codeUnit == $lf) continue;
+
+      if (codeUnit == $percent &&
+          i < input.length - 2 &&
+          input.codeUnitAt(i + 1) == $3 &&
+          input.codeUnitAt(i + 2) == $D) {
+        dataLength++;
+        i += 2;
+        continue;
+      }
+
+      if (codeUnit != $equal &&
+          (codeUnit >= _decodeTable.length || _decodeTable[codeUnit] == null)) {
+        throw new FormatException('Invalid character', input, i);
+      }
+
+      dataLength++;
+    }
+
+    if (dataLength % 4 != 0) {
+      throw new FormatException(
+          'Base64 input must encode a multiple of 4 bytes.',
+          input,
+          dataLength);
+    }
+
+    // Count the trailing pad characters.
+    var padLength = 0;
+    for (var i = input.length - 1; i >= 0; i--) {
+      var codeUnit = input.codeUnitAt(i);
+      if (codeUnit == $D &&
+          i >= 2 &&
+          input.codeUnitAt(i - 2) == $percent &&
+          input.codeUnitAt(i - 1) == $3) {
+        padLength++;
+        i -= 2;
+      } else if (codeUnit == $equal) {
+        padLength++;
+      } else if (codeUnit != $cr && codeUnit != $lf) {
+        break;
+      }
+    }
+    var outputLength = ((dataLength * 6) >> 3) - padLength;
+    var out = new Uint8List(outputLength);
+
+    var inputIndex = 0;
+    var outputIndex = 0;
+    while (outputIndex < outputLength) {
+      // Accumulate four 6-bit Base64 characters into a 32-bit chunk.
+      var chunk = 0;
+      for (var i = 0; i < 4; i++) {
+        var codeUnit = input.codeUnitAt(inputIndex++);
+
+        if (codeUnit == $equal || codeUnit == $percent) {
+          // We've reached the end of the source. Pad out the rest of the chunk
+          // with zeroes.
+          chunk <<= (4 - i) * 6;
+          break;
+        }
+
+        if (codeUnit == $cr || codeUnit == $lf) {
+          i--;
+        } else {
+          chunk = (chunk << 6) | _decodeTable[codeUnit];
+        }
+      }
+
+      // Emit 8-bit pieces of the chunk to the output buffer.
+      out[outputIndex++] = chunk >> 16;
+      if (outputIndex >= outputLength) break;
+
+      out[outputIndex++] = (chunk >> 8) & 0xFF;
+      if (outputIndex >= outputLength) break;
+
+      out[outputIndex++] = chunk & 0xFF;
+    }
+
+    return out;
+  }
+
+  Base64DecoderSink startChunkedConversion(Sink<List<int>> sink) {
+    if (sink is! ByteConversionSink) sink = new ByteConversionSink.from(sink);
+    return new Base64DecoderSink(sink);
+  }
+}