ZLibEncoder final

final class ZLibEncoder extends Converter<List<int>, List<int>>

The ZLibEncoder encoder is used by ZLibCodec and GZipCodec to compress data.

Inheritance

Object → Converter<S, T> → ZLibEncoder

Constructors

ZLibEncoder()

ZLibEncoder({
  bool gzip = false,
  int level = ZLibOption.defaultLevel,
  int windowBits = ZLibOption.defaultWindowBits,
  int memLevel = ZLibOption.defaultMemLevel,
  int strategy = ZLibOption.strategyDefault,
  List<int>? dictionary,
  bool raw = false,
})

Implementation

ZLibEncoder({
  this.gzip = false,
  this.level = ZLibOption.defaultLevel,
  this.windowBits = ZLibOption.defaultWindowBits,
  this.memLevel = ZLibOption.defaultMemLevel,
  this.strategy = ZLibOption.strategyDefault,
  this.dictionary,
  this.raw = false,
}) {
  _validateZLibeLevel(level);
  _validateZLibMemLevel(memLevel);
  _validateZLibStrategy(strategy);
  _validateZLibWindowBits(windowBits);
}

Properties

dictionary final

final List<int>? dictionary

Initial compression dictionary.

It should consist of strings (byte sequences) that are likely to be encountered later in the data to be compressed, with the most commonly used strings preferably put towards the end of the dictionary. Using a dictionary is most useful when the data to be compressed is short and can be predicted with good accuracy; the data can then be compressed better than with the default empty dictionary.

Implementation

final List<int>? dictionary;

gzip final

final bool gzip

When true, GZip frames will be added to the compressed data.

Implementation

final bool gzip;

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;

level final

final int level

The compression-level can be set in the range of -1..9, with 6 being the default compression level. Levels above 6 will have higher compression rates at the cost of more CPU and memory usage. Levels below 6 will use less CPU and memory at the cost of lower compression rates.

Implementation

final int level;

memLevel final

final int memLevel

Specifies how much memory should be allocated for the internal compression state. 1 uses minimum memory but is slow and reduces compression ratio; 9 uses maximum memory for optimal speed. The default value is 8.

The memory requirements for deflate are (in bytes):

(1 << (windowBits + 2)) +  (1 << (memLevel + 9))

that is: 128K for windowBits = 15 + 128K for memLevel = 8 (default values)

Implementation

final int memLevel;

raw final

final bool raw

When true, deflate generates raw data with no zlib header or trailer, and will not compute an adler32 check value

Implementation

final bool raw;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

strategy final

final int strategy

Tunes the compression algorithm. Use the value ZLibOption.strategyDefault for normal data, ZLibOption.strategyFiltered for data produced by a filter (or predictor), ZLibOption.strategyHuffmanOnly to force Huffman encoding only (no string match), or ZLibOption.strategyRle to limit match distances to one (run-length encoding).

Implementation

final int strategy;

windowBits final

final int windowBits

Base two logarithm of the window size (the size of the history buffer). It should be in the range 8..15. Larger values result in better compression at the expense of memory usage. The default value is 15

Implementation

final int windowBits;

Methods

bind() inherited

Stream<List<int>> 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.

Inherited from Converter.

Implementation

Stream<T> bind(Stream<S> stream) {
  return Stream<T>.eventTransformed(
    stream,
    (EventSink sink) => _ConverterStreamEventSink(this, sink),
  );
}

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

List<int> convert(List<int> bytes)

Convert a list of bytes using the options given to the ZLibEncoder constructor.

Implementation

List<int> convert(List<int> bytes) {
  _BufferSink sink = _BufferSink();
  startChunkedConversion(sink)
    ..add(bytes)
    ..close();
  return sink.builder.takeBytes();
}

fuse() inherited

Converter<List<int>, TT> fuse<TT>(Converter<List<int>, TT> other)

Fuses this with other.

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

Inherited from Converter.

Implementation

Converter<S, TT> fuse<TT>(Converter<T, TT> other) {
  return _FusedConverter<S, T, TT>(this, other);
}

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<List<int>> sink)

Start a chunked conversion using the options given to the ZLibEncoder constructor.

Accepts any Sink<List<int>>, but prefers a ByteConversionSink, and converts any other sink to a ByteConversionSink before using it.

Implementation

ByteConversionSink startChunkedConversion(Sink<List<int>> sink) {
  if (sink is! ByteConversionSink) {
    sink = ByteConversionSink.from(sink);
  }
  return _ZLibEncoderSink._(
    sink,
    gzip,
    level,
    windowBits,
    memLevel,
    strategy,
    dictionary,
    raw,
  );
}

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);