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Side by Side Diff: lib/src/hex/decoder.dart

Issue 1364613002: Add a hexadecimal codec. (Closed) Base URL: git@github.com:dart-lang/convert.git@master
Patch Set: Code review changes Created 5 years, 2 months ago
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1 // Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file
2 // for details. All rights reserved. Use of this source code is governed by a
3 // BSD-style license that can be found in the LICENSE file.
4
5 library convert.hex.decoder;
6
7 import 'dart:convert';
8 import 'dart:typed_data';
9
10 import 'package:charcode/ascii.dart';
11
12 /// The canonical instance of [HexDecoder].
13 const hexDecoder = const HexDecoder._();
14
15 /// A converter that decodes hexadecimal strings into byte arrays.
16 ///
17 /// Because two hexadecimal digits correspond to a single byte, this will throw
18 /// a [FormatException] if given an odd-length string. It will also throw a
19 /// [FormatException] if given a string containing non-hexadecimal code units.
20 class HexDecoder extends Converter<String, List<int>> {
21 const HexDecoder._();
22
23 List<int> convert(String string) {
24 if (!string.length.isEven) {
25 throw new FormatException("Invalid input length, must be even.",
26 string, string.length);
27 }
28
29 var bytes = new Uint8List(string.length ~/ 2);
30 _decode(string.codeUnits, bytes, 0);
31 return bytes;
32 }
33
34 StringConversionSink startChunkedConversion(Sink<List<int>> sink) =>
35 new _HexDecoderSink(sink);
36 }
37
38 /// A conversion sink for chunked hexadecimal decoding.
39 class _HexDecoderSink extends StringConversionSinkBase {
40 /// The underlying sink to which decoded byte arrays will be passed.
41 final Sink<List<int>> _sink;
42
43 /// The trailing digit from the previous string.
44 ///
45 /// This will be non-`null` if the most recent string had an odd number of
46 /// hexadecimal digits. Since it's the most significant digit, it's always a
47 /// multiple of 16.
48 int _lastDigit;
49
50 _HexDecoderSink(this._sink);
51
52 void addSlice(String string, int start, int end, bool isLast) {
53 RangeError.checkValidRange(start, end, string.length);
Lasse Reichstein Nielsen 2015/09/24 08:07:02 Maybe do end = RangeError.checkValidRange(...);
nweiz 2015/09/24 23:23:42 StringConversionSink.addSlice's documentation does
54
55 var bytes;
56 var bytesStart;
57 if (_lastDigit == null) {
58 bytes = new Uint8List((end - start) ~/ 2);
59 bytesStart = 0;
60 } else {
61 var hexPairs = (end - start - 1) ~/ 2;
62 bytes = new Uint8List(1 + hexPairs);
63 bytes[0] = _lastDigit + _digitForCodeUnit(string.codeUnitAt(start));
64 start++;
65 bytesStart = 1;
66 }
67
68 var codeUnits = string.codeUnits.take(end).skip(start);
Lasse Reichstein Nielsen 2015/09/24 08:07:02 I want to add getRange(start, end) to Iterable, bu
Lasse Reichstein Nielsen 2015/09/24 11:37:39 However, since codeUnits is a list, you *can* writ
sra1 2015/09/24 18:39:35 On dart2js it is going to be very much better to p
69 _lastDigit = _decode(codeUnits, bytes, bytesStart);
70
71 _sink.add(bytes);
72 if (isLast) close();
73 }
74
75 ByteConversionSink asUtf8Sink(bool allowMalformed) =>
76 new _HexDecoderByteSink(_sink);
77
78 void close() {
79 if (_lastDigit != null) {
80 throw new FormatException("Invalid input length, must be even.");
81 }
82
83 _sink.close();
84 }
85 }
86
87 /// A conversion sink for chunked hexadecimal decoding from UTF-8 bytes.
88 class _HexDecoderByteSink extends ByteConversionSinkBase {
89 /// The underlying sink to which decoded byte arrays will be passed.
90 final Sink<List<int>> _sink;
91
92 /// The trailing digit from the previous string.
93 ///
94 /// This will be non-`null` if the most recent string had an odd number of
95 /// hexadecimal digits. Since it's the most significant digit, it's always a
96 /// multiple of 16.
97 int _lastDigit;
98
99 _HexDecoderByteSink(this._sink);
100
101 void add(List<int> chunk) => addSlice(chunk, 0, chunk.length, false);
102
103 void addSlice(List<int> chunk, int start, int end, bool isLast) {
104 RangeError.checkValidRange(start, end, chunk.length);
105
Lasse Reichstein Nielsen 2015/09/24 08:07:02 You need to handle the case where start==end someh
nweiz 2015/09/24 23:23:42 Done.
106 var bytes;
107 var bytesStart;
108 if (_lastDigit == null) {
109 bytes = new Uint8List((end - start) ~/ 2);
110 bytesStart = 0;
111 } else {
112 var hexPairs = (end - start - 1) ~/ 2;
Lasse Reichstein Nielsen 2015/09/24 08:07:02 Maybe declare var length = end - start; Consider
nweiz 2015/09/24 23:23:42 I like how the current writing makes hexPairs the
Lasse Reichstein Nielsen 2015/09/25 06:40:33 I guess that's just a difference in perspective. I
113 bytes = new Uint8List(1 + hexPairs);
114 bytes[0] = _lastDigit + _digitForCodeUnit(chunk[start]);
115 start++;
116 bytesStart = 1;
117 }
118
119 var codeUnits = chunk.take(end).skip(start);
120 _lastDigit = _decode(codeUnits, bytes, bytesStart);
Lasse Reichstein Nielsen 2015/09/24 08:07:02 I still think using a list+start+end is more effic
121
122 _sink.add(bytes);
123 if (isLast) close();
124 }
125
126 void close() {
127 if (_lastDigit != null) {
128 throw new FormatException("Invalid input length, must be even.");
129 }
130
131 _sink.close();
132 }
133 }
134
135 /// Decodes [codeUnits] and writes the result into [destination].
136 ///
137 /// This begins writing into destination at the index [start]. It returns the
138 /// leftover digit from the end of [codeUnits], if any.
139 int _decode(Iterable<int> codeUnits, List<int> destination, int start) {
140 var iterator = codeUnits.iterator;
141 for (var i = start;; i++) {
142 if (!iterator.moveNext()) return null;
143 var firstDigit = _digitForCodeUnit(iterator.current) * 16;
sra1 2015/09/24 18:39:35 It really helps dart2js to have the constant first
nweiz 2015/09/24 23:23:42 Done.
144
145 if (!iterator.moveNext()) return firstDigit;
146 var secondDigit = _digitForCodeUnit(iterator.current);
sra1 2015/09/24 18:39:35 dart2js thinks iterator.current can be null (becau
147
148 destination[i] = firstDigit + secondDigit;
sra1 2015/09/24 18:39:35 nit: it feels wrong to call both of these xxxDigit
nweiz 2015/09/24 23:23:42 Done.
149 }
150 }
151
152 /// Returns the digit (0 through 15) corresponding to the hexadecimal code unit
153 /// [codeUnit].
154 ///
155 /// If [codeUnit] isn't a valid hexadecimal code unit, throws a
156 /// [FormatException].
157 int _digitForCodeUnit(int codeUnit) {
158 if (codeUnit >= $0 && codeUnit <= $9) return codeUnit - $0;
159 if (codeUnit >= $a && codeUnit <= $f) return codeUnit - $a + 10;
160 if (codeUnit >= $A && codeUnit <= $F) return codeUnit - $A + 10;
161
162 throw new FormatException("Invalid hexadecimal code unit "
163 "U+${codeUnit.toRadixString(16).padLeft(4, '0')}.");
164 }
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