Utf8Decoder final

final class Utf8Decoder extends Converter<List<int>, String>

This class converts UTF-8 code units (lists of unsigned 8-bit integers) to a string.

Example:

final utf8Decoder = utf8.decoder;
const encodedBytes = [
  195, 142, 195, 177, 197, 163, 195, 169, 114, 195, 177, 195, 165, 197,
  163, 195, 174, 195, 182, 195, 177, 195, 165, 196, 188, 195, 174, 197,
  190, 195, 165, 197, 163, 195, 174, 225, 187, 157, 195, 177];

final decodedBytes = utf8Decoder.convert(encodedBytes);
print(decodedBytes); // Îñţérñåţîöñåļîžåţîờñ

Throws a FormatException if the encoded input contains invalid UTF-8 byte sequences and allowMalformed is false (the default).

If allowMalformed is true, invalid byte sequences are converted into one or more Unicode replacement characters, U+FFFD ('�').

Example with allowMalformed set to true:

const utf8Decoder = Utf8Decoder(allowMalformed: true);
const encodedBytes = [0xFF];
final decodedBytes = utf8Decoder.convert(encodedBytes);
print(decodedBytes); // �

Inheritance

Object → Converter<S, T> → Utf8Decoder

Constructors

Utf8Decoder() const

const Utf8Decoder({bool allowMalformed = false})

Instantiates a new Utf8Decoder.

The optional allowMalformed argument defines how convert deals with invalid or unterminated character sequences.

If it is true, convert replaces invalid (or unterminated) character sequences with the Unicode Replacement character U+FFFD (�). Otherwise it throws a FormatException.

Implementation

const Utf8Decoder({bool allowMalformed = false})
  : _allowMalformed = allowMalformed;

Properties

hashCode no setter inherited

int get hashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

Implementation

external int get hashCode;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

bind() override

Stream<String> bind(Stream<List<int>> stream)

Transforms the provided stream.

Returns a new stream with events that are computed from events of the provided stream.

The StreamTransformer interface is completely generic, so it cannot say what subclasses do. Each StreamTransformer should document clearly how it transforms the stream (on the class or variable used to access the transformer), as well as any differences from the following typical behavior:

• When the returned stream is listened to, it starts listening to the input stream.
• Subscriptions of the returned stream forward (in a reasonable time) a StreamSubscription.pause call to the subscription of the input stream.
• Similarly, canceling a subscription of the returned stream eventually (in reasonable time) cancels the subscription of the input stream.

"Reasonable time" depends on the transformer and stream. Some transformers, like a "timeout" transformer, might make these operations depend on a duration. Others might not delay them at all, or just by a microtask.

Transformers are free to handle errors in any way. A transformer implementation may choose to propagate errors, or convert them to other events, or ignore them completely, but if errors are ignored, it should be documented explicitly.

Implementation

Stream<String> bind(Stream<List<int>> stream) => super.bind(stream);

cast() inherited

Converter<RS, RT> cast<RS, RT>()

Provides a Converter<RS, RT> view of this stream transformer.

The resulting transformer will check at run-time that all conversion inputs are actually instances of S, and it will check that all conversion output produced by this converter are actually instances of RT.

Inherited from Converter.

Implementation

Converter<RS, RT> cast<RS, RT>() => Converter.castFrom<S, T, RS, RT>(this);

convert() override

String convert(List<int> codeUnits, [int start = 0, int? end])

Converts the UTF-8 codeUnits (a list of unsigned 8-bit integers) to the corresponding string.

Uses the code units from start to, but not including, end. If end is omitted, it defaults to codeUnits.length.

If the codeUnits start with the encoding of a unicodeBomCharacterRune, that character is discarded.

Implementation

String convert(List<int> codeUnits, [int start = 0, int? end]) =>
    _Utf8Decoder(_allowMalformed).convertSingle(codeUnits, start, end);

fuse() override

Converter<List<int>, TT> fuse<T>(Converter<String, T> next)

Fuses this with other.

Encoding with the resulting converter is equivalent to converting with this before converting with other.

Implementation

external Converter<List<int>, T> fuse<T>(Converter<String, T> next);

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

startChunkedConversion() override

ByteConversionSink startChunkedConversion(Sink<String> sink)

Starts a chunked conversion.

The converter works more efficiently if the given sink is a StringConversionSink.

Implementation

ByteConversionSink startChunkedConversion(Sink<String> sink) {
  StringConversionSink stringSink;
  if (sink is StringConversionSink) {
    stringSink = sink;
  } else {
    stringSink = StringConversionSink.from(sink);
  }
  return stringSink.asUtf8Sink(_allowMalformed);
}

toString() inherited

String toString()

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

Implementation

external String toString();

Operators

operator ==() inherited

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

Implementation

external bool operator ==(Object other);