| // Copyright (c) 2016, 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. |
| |
| import 'dart:convert'; |
| import 'dart:math' as math; |
| import 'dart:typed_data'; |
| |
| import 'package:charcode/ascii.dart'; |
| import 'package:typed_data/typed_data.dart'; |
| |
| /// The canonical instance of [ChunkedCodingDecoder]. |
| const chunkedCodingDecoder = ChunkedCodingDecoder._(); |
| |
| /// A converter that decodes byte arrays into chunks with size tags. |
| class ChunkedCodingDecoder extends Converter<List<int>, List<int>> { |
| const ChunkedCodingDecoder._(); |
| |
| @override |
| List<int> convert(List<int> input) { |
| final sink = _Sink(null); |
| final output = sink._decode(input, 0, input.length); |
| if (sink._state == _State.end) return output; |
| |
| throw FormatException('Input ended unexpectedly.', input, input.length); |
| } |
| |
| @override |
| ByteConversionSink startChunkedConversion(Sink<List<int>> sink) => |
| _Sink(sink); |
| } |
| |
| /// A conversion sink for the chunked transfer encoding. |
| class _Sink extends ByteConversionSinkBase { |
| /// The underlying sink to which decoded byte arrays will be passed. |
| final Sink<List<int>> _sink; |
| |
| /// The current state of the sink's parsing. |
| var _state = _State.boundary; |
| |
| /// The size of the chunk being parsed, or `null` if the size hasn't been |
| /// parsed yet. |
| int _size; |
| |
| _Sink(this._sink); |
| |
| @override |
| void add(List<int> chunk) => addSlice(chunk, 0, chunk.length, false); |
| |
| @override |
| void addSlice(List<int> chunk, int start, int end, bool isLast) { |
| RangeError.checkValidRange(start, end, chunk.length); |
| final output = _decode(chunk, start, end); |
| if (output.isNotEmpty) _sink.add(output); |
| if (isLast) _close(chunk, end); |
| } |
| |
| @override |
| void close() => _close(); |
| |
| /// Like [close], but includes [chunk] and [index] in the [FormatException] if |
| /// one is thrown. |
| void _close([List<int> chunk, int index]) { |
| if (_state != _State.end) { |
| throw FormatException('Input ended unexpectedly.', chunk, index); |
| } |
| |
| _sink.close(); |
| } |
| |
| /// Decodes the data in [bytes] from [start] to [end]. |
| Uint8List _decode(List<int> bytes, int start, int end) { |
| /// Throws a [FormatException] if `bytes[start] != $char`. Uses [name] to |
| /// describe the character in the exception text. |
| void assertCurrentChar(int char, String name) { |
| if (bytes[start] != char) { |
| throw FormatException('Expected $name.', bytes, start); |
| } |
| } |
| |
| final buffer = Uint8Buffer(); |
| while (start != end) { |
| switch (_state) { |
| case _State.boundary: |
| _size = _digitForByte(bytes, start); |
| _state = _State.size; |
| start++; |
| break; |
| |
| case _State.size: |
| if (bytes[start] == $cr) { |
| _state = _State.sizeBeforeLF; |
| } else { |
| // Shift four bits left since a single hex digit contains four bits |
| // of information. |
| _size = (_size << 4) + _digitForByte(bytes, start); |
| } |
| start++; |
| break; |
| |
| case _State.sizeBeforeLF: |
| assertCurrentChar($lf, 'LF'); |
| _state = _size == 0 ? _State.endBeforeCR : _State.body; |
| start++; |
| break; |
| |
| case _State.body: |
| final chunkEnd = math.min(end, start + _size); |
| buffer.addAll(bytes, start, chunkEnd); |
| _size -= chunkEnd - start; |
| start = chunkEnd; |
| if (_size == 0) _state = _State.bodyBeforeCR; |
| break; |
| |
| case _State.bodyBeforeCR: |
| assertCurrentChar($cr, 'CR'); |
| _state = _State.bodyBeforeLF; |
| start++; |
| break; |
| |
| case _State.bodyBeforeLF: |
| assertCurrentChar($lf, 'LF'); |
| _state = _State.boundary; |
| start++; |
| break; |
| |
| case _State.endBeforeCR: |
| assertCurrentChar($cr, 'CR'); |
| _state = _State.endBeforeLF; |
| start++; |
| break; |
| |
| case _State.endBeforeLF: |
| assertCurrentChar($lf, 'LF'); |
| _state = _State.end; |
| start++; |
| break; |
| |
| case _State.end: |
| throw FormatException('Expected no more data.', bytes, start); |
| } |
| } |
| return buffer.buffer.asUint8List(0, buffer.length); |
| } |
| |
| /// Returns the hex digit (0 through 15) corresponding to the byte at index |
| /// [index] in [bytes]. |
| /// |
| /// If the given byte isn't a hexadecimal ASCII character, throws a |
| /// [FormatException]. |
| int _digitForByte(List<int> bytes, int index) { |
| // If the byte is a numeral, get its value. XOR works because 0 in ASCII is |
| // `0b110000` and the other numerals come after it in ascending order and |
| // take up at most four bits. |
| // |
| // We check for digits first because it ensures there's only a single branch |
| // for 10 out of 16 of the expected cases. We don't count the `digit >= 0` |
| // check because branch prediction will always work on it for valid data. |
| final byte = bytes[index]; |
| final digit = $0 ^ byte; |
| if (digit <= 9) { |
| if (digit >= 0) return digit; |
| } else { |
| // If the byte is an uppercase letter, convert it to lowercase. This works |
| // because uppercase letters in ASCII are exactly `0b100000 = 0x20` less |
| // than lowercase letters, so if we ensure that that bit is 1 we ensure |
| // that the letter is lowercase. |
| final letter = 0x20 | byte; |
| if ($a <= letter && letter <= $f) return letter - $a + 10; |
| } |
| |
| throw FormatException( |
| 'Invalid hexadecimal byte 0x${byte.toRadixString(16).toUpperCase()}.', |
| bytes, |
| index); |
| } |
| } |
| |
| /// An enumeration of states that [_Sink] can exist in when decoded a chunked |
| /// message. |
| class _State { |
| /// The parser has fully parsed one chunk and is expecting the header for the |
| /// next chunk. |
| /// |
| /// Transitions to [size]. |
| static const boundary = _State._('boundary'); |
| |
| /// The parser has parsed at least one digit of the chunk size header, but has |
| /// not yet parsed the `CR LF` sequence that indicates the end of that header. |
| /// |
| /// Transitions to [sizeBeforeLF]. |
| static const size = _State._('size'); |
| |
| /// The parser has parsed the chunk size header and the CR character after it, |
| /// but not the LF. |
| /// |
| /// Transitions to [body] or [bodyBeforeCR]. |
| static const sizeBeforeLF = _State._('size before LF'); |
| |
| /// The parser has parsed a chunk header and possibly some of the body, but |
| /// still needs to consume more bytes. |
| /// |
| /// Transitions to [bodyBeforeCR]. |
| static const body = _State._('body'); |
| |
| // The parser has parsed all the bytes in a chunk body but not the CR LF |
| // sequence that follows it. |
| // |
| // Transitions to [bodyBeforeLF]. |
| static const bodyBeforeCR = _State._('body before CR'); |
| |
| // The parser has parsed all the bytes in a chunk body and the CR that follows |
| // it, but not the LF after that. |
| // |
| // Transitions to [bounday]. |
| static const bodyBeforeLF = _State._('body before LF'); |
| |
| /// The parser has parsed the final empty chunk but not the CR LF sequence |
| /// that follows it. |
| /// |
| /// Transitions to [endBeforeLF]. |
| static const endBeforeCR = _State._('end before CR'); |
| |
| /// The parser has parsed the final empty chunk and the CR that follows it, |
| /// but not the LF after that. |
| /// |
| /// Transitions to [end]. |
| static const endBeforeLF = _State._('end before LF'); |
| |
| /// The parser has parsed the final empty chunk as well as the CR LF that |
| /// follows, and expects no more data. |
| static const end = _State._('end'); |
| |
| final String _name; |
| |
| const _State._(this._name); |
| |
| @override |
| String toString() => _name; |
| } |