qs_dart 1.3.0

A query string encoding and decoding library for Dart. Ported from qs for JavaScript.

qs_dart

A query string encoding and decoding library for Dart.

Ported from qs for JavaScript.

Usage

A simple usage example:

import 'package:qs_dart/qs_dart.dart';
import 'package:test/test.dart';

void main() {
  test('Simple example', () {
    expect(
      QS.decode('a=c'),
      equals({'a': 'c'}),
    );

    expect(
      QS.encode({'a': 'c'}),
      equals('a=c'),
    );
  });
  
  test('Uri Extension usage', () {
    expect(
      Uri.parse('https://test.local/example?a[b][c]=d').queryParametersQs(),
      equals({
        'a': {
          'b': {'c': 'd'}
        }
      }),
    );
    
    expect(
      Uri.https('test.local', '/example', {'a': '1', 'b': '2'}).toStringQs(), 
      equals('https://test.local/example?a=1&b=2'),
    );
  });
}

Decoding Maps

Map<String, dynamic> decode(
  dynamic str, [
  DecodeOptions options = const DecodeOptions(),
]);

[decode] allows you to create nested [Map]s within your query strings, by surrounding the name of sub-keys with square brackets []. For example, the string 'foo[bar]=baz' converts to:

expect(
  QS.decode('foo[bar]=baz'),
  equals({'foo': {'bar': 'baz'}}),
);

URI encoded strings work too:

expect(
  QS.decode('a%5Bb%5D=c'),
  equals({'a': {'b': 'c'}}),
);

You can also nest your [Map]s, like 'foo[bar][baz]=foobarbaz':

expect(
  QS.decode('foo[bar][baz]=foobarbaz'),
  equals({'foo': {'bar': {'baz': 'foobarbaz'}}}),
);

By default, when nesting [Map]s [decode] will only decode up to 5 children deep. This means if you attempt to decode a string like 'a[b][c][d][e][f][g][h][i]=j' your resulting [Map] will be:

expect(
  QS.decode('a[b][c][d][e][f][g][h][i]=j'),
  equals({
    'a': {
      'b': {
        'c': {
          'd': {
            'e': {
              'f': {
                '[g][h][i]': 'j'
              }
            }
          }
        }
      }
    }
  }),
);

This depth can be overridden by passing a depth option to [DecodeOptions.depth]:

expect(
  QS.decode(
    'a[b][c][d][e][f][g][h][i]=j',
    const DecodeOptions(depth: 1),
  ),
  equals({
    'a': {
      'b': {'[c][d][e][f][g][h][i]': 'j'},
    },
  }),
);

You can configure [decode] to throw an error when parsing nested input beyond this depth using [DecodeOptions.strictDepth] (defaults to false):

expect(
  () => QS.decode(
    'a[b][c][d][e][f][g][h][i]=j',
    const DecodeOptions(
      depth: 1,
      strictDepth: true,
    ),
  ),
  throwsA(isA<RangeError>()),
);

The depth limit helps mitigate abuse when [decode] is used to parse user input, and it is recommended to keep it a reasonably small number. [DecodeOptions.strictDepth] adds a layer of protection by throwing a [RangeError] when the limit is exceeded, allowing you to catch and handle such cases.

For similar reasons, by default [decode] will only parse up to 1000 parameters. This can be overridden by passing a [DecodeOptions.parameterLimit] option:

expect(
  QS.decode(
    'a=b&c=d',
    const DecodeOptions(parameterLimit: 1),
  ),
  equals({'a': 'b'}),
);

To bypass the leading question mark, use [DecodeOptions.ignoreQueryPrefix]:

expect(
  QS.decode(
    '?a=b&c=d',
    const DecodeOptions(ignoreQueryPrefix: true),
  ),
  equals(
    {'a': 'b', 'c': 'd'},
  ),
);

An optional [DecodeOptions.delimiter] can also be passed:

expect(
  QS.decode(
    'a=b;c=d',
    const DecodeOptions(delimiter: ';'),
  ),
  equals({'a': 'b', 'c': 'd'}),
);

[DecodeOptions.delimiter] can be a [RegExp] too:

expect(
  QS.decode(
    'a=b;c=d',
    DecodeOptions(delimiter: RegExp(r'[;,]')),
  ),
  equals({'a': 'b', 'c': 'd'}),
);

Option [DecodeOptions.allowDots] can be used to enable dot notation:

expect(
  QS.decode(
    'a.b=c',
    const DecodeOptions(allowDots: true),
  ),
  equals({'a': {'b': 'c'}}),
);

Option [DecodeOptions.decodeDotInKeys] can be used to decode dots in keys

Note: it implies [DecodeOptions.allowDots], so [decode] will error if you set [DecodeOptions.decodeDotInKeys] to true, and DecodeOptions.allowDots to false.

expect(
  QS.decode(
    'name%252Eobj.first=John&name%252Eobj.last=Doe',
    const DecodeOptions(decodeDotInKeys: true),
  ),
  equals({
    'name.obj': {'first': 'John', 'last': 'Doe'}
  }),
);

Option [DecodeOptions.allowEmptyLists] can be used to allow empty [List] values in a [Map].

expect(
  QS.decode(
    'foo[]&bar=baz',
    const DecodeOptions(allowEmptyLists: true),
  ),
  equals({
    'foo': [],
    'bar': 'baz',
  }),
);

Option [DecodeOptions.duplicates] can be used to change the behavior when duplicate keys are encountered.

expect(
  QS.decode('foo=bar&foo=baz'),
  equals({
    'foo': ['bar', 'baz']
  }),
);

expect(
  QS.decode(
    'foo=bar&foo=baz',
    const DecodeOptions(duplicates: Duplicates.combine),
  ),
  equals({
    'foo': ['bar', 'baz']
  }),
);

expect(
  QS.decode(
    'foo=bar&foo=baz',
    const DecodeOptions(duplicates: Duplicates.first),
  ),
  equals({'foo': 'bar'}),
);

expect(
  QS.decode(
    'foo=bar&foo=baz',
    const DecodeOptions(duplicates: Duplicates.last),
  ),
  equals({'foo': 'baz'}),
);

If you have to deal with legacy browsers or services, there's also support for decoding percent-encoded octets as [latin1]:

expect(
  QS.decode(
    'a=%A7',
    const DecodeOptions(charset: latin1),
  ),
  equals({'a': '§'}),
);

Some services add an initial utf8=✓ value to forms so that old Internet Explorer versions are more likely to submit the form as utf-8. Additionally, the server can check the value against wrong encodings of the checkmark character and detect that a query string or application/x-www-form-urlencoded body was not sent as utf-8, eg. if the form had an accept-charset parameter or the containing page had a different character set.

QS supports this mechanism via the [DecodeOptions.charsetSentinel] option. If specified, the utf8 parameter will be omitted from the returned [Map]. It will be used to switch to [latin1] or [utf8] mode depending on how the checkmark is encoded.

Important: When you specify both the [DecodeOptions.charset] option and the [DecodeOptions.charsetSentinel] option, the [DecodeOptions.charset] will be overridden when the request contains a utf8 parameter from which the actual charset can be deduced. In that sense the [DecodeOptions.charset] will behave as the default charset rather than the authoritative charset.

expect(
  QS.decode(
    'utf8=%E2%9C%93&a=%C3%B8',
    const DecodeOptions(
      charset: latin1,
      charsetSentinel: true,
    ),
  ),
  equals({'a': 'ø'}),
);

expect(
  QS.decode(
    'utf8=%26%2310003%3B&a=%F8',
    const DecodeOptions(
      charset: utf8,
      charsetSentinel: true,
    ),
  ),
  equals({'a': 'ø'}),
);

If you want to decode the &#...; syntax to the actual character, you can specify the [DecodeOptions.interpretNumericEntities] option as well:

expect(
  QS.decode(
    'a=%26%239786%3B',
    const DecodeOptions(
      charset: latin1,
      interpretNumericEntities: true,
    ),
  ),
  equals({'a': '☺'}),
);

It also works when the charset has been detected in [DecodeOptions.charsetSentinel] mode.

Decoding Lists

[decode] can also decode [List]s using a similar [] notation:

expect(
  QS.decode('a[]=b&a[]=c'),
  equals({
    'a': ['b', 'c']
  }),
);

You may specify an index as well:

expect(
  QS.decode('a[1]=c&a[0]=b'),
  equals({
    'a': ['b', 'c']
  }),
);

Note that the only difference between an index in a [List] and a key in a [Map] is that the value between the brackets must be a number to create a [List]. When creating [List]s with specific indices, [decode] will compact a sparse [List] to only the existing values preserving their order:

expect(
  QS.decode('a[1]=b&a[15]=c'),
  equals({
    'a': ['b', 'c']
  }),
);

Note that an empty string is also a value, and will be preserved:

expect(
  QS.decode('a[]=&a[]=b'),
  equals({
    'a': ['', 'b']
  }),
);
expect(
  QS.decode('a[0]=b&a[1]=&a[2]=c'),
  equals({
    'a': ['b', '', 'c']
  }),
);

[decode] will also limit specifying indices in a [List] to a maximum index of 20. Any [List] members with an index of greater than 20 will instead be converted to a [Map] with the index as the key. This is needed to handle cases when someone sent, for example, a[999999999] and it will take significant time to iterate over this huge [List].

expect(
  QS.decode('a[100]=b'),
  equals({
    'a': {'100': 'b'}
  }),
);

This limit can be overridden by passing an [DecodeOptions.listLimit] option:

expect(
  QS.decode(
    'a[1]=b',
    const DecodeOptions(listLimit: 0),
  ),
  equals({
    'a': {'1': 'b'}
  }),
);

To disable List parsing entirely, set [DecodeOptions.parseLists] to false.

expect(
  QS.decode(
    'a[]=b',
    const DecodeOptions(parseLists: false),
  ),
  equals({
    'a': {'0': 'b'}
  }),
);

If you mix notations, [decode] will merge the two items into a [Map]:

expect(
  QS.decode('a[0]=b&a[b]=c'),
  equals({
    'a': {'0': 'b', 'b': 'c'}
  }),
);

You can also create [List]s of [Map]s:

expect(
  QS.decode('a[][b]=c'),
  equals({
    'a': [
      {'b': 'c'}
    ]
  }),
);

Some people use commas to join [List]s, [decode] can parse it by setting the [DecodeOptions.comma] option to true:

expect(
  QS.decode(
    'a=b,c',
    const DecodeOptions(comma: true),
  ),
  equals({
    'a': ['b', 'c']
  }),
);

([decode] cannot convert nested [Map]s, such as 'a={b:1},{c:d}')

Decoding primitive/scalar values (num, bool, null, etc.)

By default, all values are parsed as [String]s.

expect(
  QS.decode('a=15&b=true&c=null'),
  equals({
    'a': '15',
    'b': 'true',
    'c': 'null',
  }),
);

Encoding

String encode(
  Object? object, [
  EncodeOptions options = const EncodeOptions(),
]);

[encode] will by default URI encode the output. [Map]s are stringified as you would expect:

expect(
  QS.encode({'a': 'b'}),
  equals('a=b'),
);
expect(
  QS.encode({'a': {'b': 'c'}}),
  equals('a%5Bb%5D=c'),
);

This encoding can be disabled by setting the [EncodeOptions.encode] option to false:

expect(
  QS.encode(
    {
      'a': {'b': 'c'}
    },
    const EncodeOptions(encode: false),
  ),
  equals('a[b]=c'),
);

Encoding can be disabled for keys by setting the [EncodeOptions.encodeValuesOnly] option to true:

expect(
  QS.encode(
    {
      'a': 'b',
      'c': ['d', 'e=f'],
      'f': [
        ['g'],
        ['h']
      ]
    },
    const EncodeOptions(encodeValuesOnly: true),
  ),
  equals('a=b&c[0]=d&c[1]=e%3Df&f[0][0]=g&f[1][0]=h'),
);

This encoding can also be replaced by a custom [Encoder] set as [EncodeOptions.encoder] option:

expect(
  QS.encode(
    {
      'a': {'b': 'č'}
    },
    EncodeOptions(
      encoder: (
        str, {
        Encoding? charset,
        Format? format,
      }) =>
          switch (str) {
        'č' => 'c',
        _ => str,
      },
    ),
  ),
  equals('a[b]=c'),
);

(Note: the [EncodeOptions.encoder] option does not apply if [EncodeOptions.encode] is false)

Similar to [EncodeOptions.encoder] there is a [DecodeOptions.decoder] option for [decode] to override decoding of properties and values:

expect(
  QS.decode(
    'foo=123', 
    DecodeOptions(
      decoder: (String? str, {Encoding? charset}) =>
        num.tryParse(str ?? '') ?? str,
    ),
  ),
  equals({'foo': 123}),
);

Examples beyond this point will be shown as though the output is not URI encoded for clarity. Please note that the return values in these cases will be URI encoded during real usage.

When [List]s are encoded, they follow the [EncodeOptions.listFormat] option, which defaults to [ListFormat.indices]:

expect(
  QS.encode(
    {
      'a': ['b', 'c', 'd']
    },
    const EncodeOptions(encode: false),
  ),
  equals('a[0]=b&a[1]=c&a[2]=d'),
);

You may override this by setting the [EncodeOptions.indices] option to false, or to be more explicit, the [EncodeOptions.listFormat] option to [ListFormat.repeat]:

expect(
  QS.encode(
    {
      'a': ['b', 'c', 'd']
    },
    const EncodeOptions(
      encode: false,
      indices: false,
    ),
  ),
  equals('a=b&a=c&a=d'),
);

You may use the [EncodeOptions.listFormat] option to specify the format of the output [List]:

expect(
  QS.encode(
    {
      'a': ['b', 'c']
    },
    const EncodeOptions(
      encode: false,
      listFormat: ListFormat.indices,
    ),
  ),
  equals('a[0]=b&a[1]=c'),
);

expect(
  QS.encode(
    {
      'a': ['b', 'c']
    },
    const EncodeOptions(
      encode: false,
      listFormat: ListFormat.brackets,
    ),
  ),
  equals('a[]=b&a[]=c'),
);

expect(
  QS.encode(
    {
      'a': ['b', 'c']
    },
    const EncodeOptions(
      encode: false,
      listFormat: ListFormat.repeat,
    ),
  ),
  equals('a=b&a=c'),
);

expect(
  QS.encode(
    {
      'a': ['b', 'c']
    },
    const EncodeOptions(
      encode: false,
      listFormat: ListFormat.comma,
    ),
  ),
  equals('a=b,c'),
);

Note: When using [EncodeOptions.listFormat] set to [ListFormat.comma], you can also pass the [EncodeOptions.commaRoundTrip] option set to true or false, to append [] on single-item [List]s, so that they can round trip through a parse.

When [Map]s are encoded, by default they use bracket notation:

expect(
  QS.encode(
    {
      'a': {
        'b': {'c': 'd', 'e': 'f'}
      }
    },
    const EncodeOptions(encode: false),
  ),
  equals('a[b][c]=d&a[b][e]=f'),
);

You may override this to use dot notation by setting the [EncodeOptions.allowDots] option to true:

expect(
  QS.encode(
    {
      'a': {
        'b': {'c': 'd', 'e': 'f'}
      }
    },
    const EncodeOptions(
      encode: false,
      allowDots: true,
    ),
  ),
  equals('a.b.c=d&a.b.e=f'),
);

You may encode the dot notation in the keys of [Map] with option [EncodeOptions.encodeDotInKeys] by setting it to true:

expect(
  QS.encode(
    {
      'name.obj': {'first': 'John', 'last': 'Doe'}
    },
    const EncodeOptions(
      allowDots: true,
      encodeDotInKeys: true,
    ),
  ),
  equals('name%252Eobj.first=John&name%252Eobj.last=Doe'),
);

Caveat: when [EncodeOptions.encodeValuesOnly] is true as well as [EncodeOptions.encodeDotInKeys], only dots in keys and nothing else will be encoded.

You may allow empty [List] values by setting the [EncodeOptions.allowEmptyLists] option to true:

expect(
  QS.encode(
    {
      'foo': [],
      'bar': 'baz',
    },
    const EncodeOptions(
      encode: false,
      allowEmptyLists: true,
    ),
  ),
  equals('foo[]&bar=baz'),
);

Empty strings and null values will omit the value, but the equals sign (=) remains in place:

expect(
  QS.encode(
    {
      'a': '',
    },
  ),
  equals('a='),
);

Key with no values (such as an empty [Map] or [List]) will return nothing:

expect(
  QS.encode(
    {
      'a': [],
    },
  ),
  equals(''),
);

expect(
  QS.encode(
    {
      'a': {},
    },
  ),
  equals(''),
);

expect(
  QS.encode(
    {
      'a': [{}],
    },
  ),
  equals('')
);

expect(
  QS.encode(
    {
      'a': {'b': []},
    },
  ),
  equals('')
);

expect(
  QS.encode(
    {
      'a': {'b': {}},
    },
  ),
  equals('')
);

Properties that are [Undefined] will be omitted entirely:

expect(
  QS.encode(
    {
      'a': null,
      'b': const Undefined(),
    },
  ),
  equals('a='),
);

The query string may optionally be prepended with a question mark:

expect(
  QS.encode(
    {
      'a': 'b',
      'c': 'd',
    },
    const EncodeOptions(addQueryPrefix: true),
  ),
  equals('?a=b&c=d'),
);

The delimiter may be overridden as well:

expect(
  QS.encode(
    {
      'a': 'b',
      'c': 'd',
    },
    const EncodeOptions(delimiter: ';'),
  ),
  equals('a=b;c=d'),
);

If you only want to override the serialization of [DateTime] objects, you can provide a custom [DateSerializer] in the [EncodeOptions.serializeDate] option:

expect(
  QS.encode(
    {
      'a': DateTime.fromMillisecondsSinceEpoch(7).toUtc(),
    },
    const EncodeOptions(encode: false),
  ),
  equals('a=1970-01-01T00:00:00.007Z'),
);
expect(
  QS.encode(
    {
      'a': DateTime.fromMillisecondsSinceEpoch(7).toUtc(),
    },
    EncodeOptions(
      encode: false,
      serializeDate: (DateTime date) =>
          date.millisecondsSinceEpoch.toString(),
    ),
  ),
  equals('a=7'),
);

You may use the [EncodeOptions.sort] option to affect the order of parameter keys:

expect(
  QS.encode(
    {
      'a': 'c',
      'z': 'y',
      'b': 'f',
    },
    EncodeOptions(
      encode: false,
      sort: (a, b) => a.compareTo(b),
    ),
  ),
  equals('a=c&b=f&z=y'),
);

Finally, you can use the [EncodeOptions.filter] option to restrict which keys will be included in the encoded output. If you pass a [Function], it will be called for each key to obtain the replacement value. Otherwise, if you pass a [List], it will be used to select properties and [List] indices to be encoded:

expect(
  QS.encode(
    {
      'a': 'b',
      'c': 'd',
      'e': {
        'f': DateTime.fromMillisecondsSinceEpoch(123),
        'g': [2],
      },
    },
    EncodeOptions(
      encode: false,
      filter: (prefix, value) => switch (prefix) {
        'b' => const Undefined(),
        'e[f]' => (value as DateTime).millisecondsSinceEpoch,
        'e[g][0]' => (value as num) * 2,
        _ => value,
      },
    ),
  ),
  equals('a=b&c=d&e[f]=123&e[g][0]=4'),
);

expect(
  QS.encode(
    {
      'a': 'b',
      'c': 'd',
      'e': 'f',
    },
    const EncodeOptions(
      encode: false,
      filter: ['a', 'e'],
    ),
  ),
  equals('a=b&e=f'),
);

expect(
  QS.encode(
    {
      'a': ['b', 'c', 'd'],
      'e': 'f',
    },
    const EncodeOptions(
      encode: false,
      filter: ['a', 0, 2],
    ),
  ),
  equals('a[0]=b&a[2]=d'),
);

Handling of null values

By default, null values are treated like empty strings:

expect(
  QS.encode(
    {
      'a': null,
      'b': '',
    },
  ),
  equals('a=&b='),
);

Decoding does not distinguish between parameters with and without equal signs. Both are converted to empty strings.

expect(
  QS.decode('a&b='),
  equals({
    'a': '',
    'b': '',
  }),
);

To distinguish between null values and empty [String]s use the [EncodeOptions.strictNullHandling] flag. In the result string the null values have no = sign:

expect(
  QS.encode(
    {
      'a': null,
      'b': '',
    },
    const EncodeOptions(strictNullHandling: true),
  ),
  equals('a&b='),
);

To decode values without = back to null use the [DecodeOptions.strictNullHandling] flag:

expect(
  QS.decode(
    'a&b=',
    const DecodeOptions(strictNullHandling: true),
  ),
  equals({
    'a': null,
    'b': '',
  }),
);

To completely skip rendering keys with null values, use the [EncodeOptions.skipNulls] flag:

expect(
  QS.encode(
    {
      'a': 'b',
      'c': null,
    },
    const EncodeOptions(skipNulls: true),
  ),
  equals('a=b'),
);

If you're communicating with legacy systems, you can switch to [latin1] using the [EncodeOptions.charset] option:

expect(
  QS.encode(
    {
      'æ': 'æ',
    },
    const EncodeOptions(charset: latin1),
  ),
  equals('%E6=%E6'),
);

Characters that don't exist in [latin1] will be converted to numeric entities, similar to what browsers do:

expect(
  QS.encode(
    {
      'a': '☺',
    },
    const EncodeOptions(charset: latin1),
  ),
  equals('a=%26%239786%3B'),
);

You can use the [EncodeOptions.charsetSentinel] option to announce the character by including an utf8=✓ parameter with the proper encoding of the checkmark, similar to what Ruby on Rails and others do when submitting forms.

expect(
  QS.encode(
    {
      'a': '☺',
    },
    const EncodeOptions(charsetSentinel: true),
  ),
  equals('utf8=%E2%9C%93&a=%E2%98%BA'),
);
expect(
  QS.encode(
    {
      'a': 'æ',
    },
    const EncodeOptions(
      charset: latin1,
      charsetSentinel: true,
    ),
  ),
  equals('utf8=%26%2310003%3B&a=%E6'),
);

Dealing with special character sets

By default, the encoding and decoding of characters is done in [utf8], and [latin1] support is also built in via the [EncodeOptions.charset] and [DecodeOptions.charset] parameter, respectively.

If you wish to encode query strings to a different character set (i.e. Shift JIS) you can use the euc package

expect(
  QS.encode(
    {
      'a': 'こんにちは！',
    },
    EncodeOptions(
      encoder: (str, {Encoding? charset, Format? format}) {
        if ((str as String?)?.isNotEmpty ?? false) {
          final Uint8List buf = Uint8List.fromList(
            ShiftJIS().encode(str!),
          );
          final List<String> result = [
            for (int i = 0; i < buf.length; ++i) buf[i].toRadixString(16)
          ];
          return '%${result.join('%')}';
        }
        return '';
      },
    ),
  ),
  equals('%61=%82%b1%82%f1%82%c9%82%bf%82%cd%81%49'),
);

This also works for decoding of query strings:

expect(
  QS.decode(
    '%61=%82%b1%82%f1%82%c9%82%bf%82%cd%81%49',
    DecodeOptions(
      decoder: (str, {Encoding? charset}) {
        if (str == null) {
          return null;
        }

        final RegExp reg = RegExp(r'%([0-9A-F]{2})', caseSensitive: false);
        final List<int> result = [];
        Match? parts;
        while ((parts = reg.firstMatch(str!)) != null && parts != null) {
          result.add(int.parse(parts.group(1)!, radix: 16));
          str = str.substring(parts.end);
        }
        return ShiftJIS().decode(
          Uint8List.fromList(result),
        );
      },
    ),
  ),
  equals({
    'a': 'こんにちは！',
  }),
);

RFC 3986 and RFC 1738 space encoding

The default [EncodeOptions.format] is [Format.rfc3986] which encodes ' ' to %20 which is backward compatible. You can also set the [EncodeOptions.format] to [Format.rfc1738] which encodes ' ' to +.

expect(
  QS.encode(
    {
      'a': 'b c',
    },
  ),
  equals('a=b%20c'),
);

expect(
  QS.encode(
    {
      'a': 'b c',
    },
    const EncodeOptions(format: Format.rfc3986),
  ),
  equals('a=b%20c'),
);

expect(
  QS.encode(
    {
      'a': 'b c',
    },
    const EncodeOptions(format: Format.rfc1738),
  ),
  equals('a=b+c'),
);

---

Special thanks to the authors of qs for JavaScript:

• Jordan Harband
• TJ Holowaychuk