HtmlEscape final

final class HtmlEscape extends Converter<String, String>

Converter which escapes characters with special meaning in HTML.

The converter finds characters that are significant in the HTML source and replaces them with corresponding HTML entities.

The characters that need escaping in HTML are:

• & (ampersand) always needs to be escaped.
• < (less than) and > (greater than) when inside an element.
• " (quote) when inside a double-quoted attribute value.
• ' (apostrophe) when inside a single-quoted attribute value. Apostrophe is escaped as ' instead of ' since not all browsers understand '.
• / (slash) is recommended to be escaped because it may be used to terminate an element in some HTML dialects.

Escaping > (greater than) isn't necessary, but the result is often found to be easier to read if greater-than is also escaped whenever less-than is.

Example:

const HtmlEscape htmlEscape = HtmlEscape();
String unescaped = 'Text & subject';
String escaped = htmlEscape.convert(unescaped);
print(escaped); // Text & subject

unescaped = '10 > 1 and 1 < 10';
escaped = htmlEscape.convert(unescaped);
print(escaped); // 10 &gt; 1 and 1 &lt; 10

unescaped = "Single-quoted: 'text'";
escaped = htmlEscape.convert(unescaped);
print(escaped); // Single-quoted: &#39;text&#39;

unescaped = 'Double-quoted: "text"';
escaped = htmlEscape.convert(unescaped);
print(escaped); // Double-quoted: &quot;text&quot;

unescaped = 'Path: /system/';
escaped = htmlEscape.convert(unescaped);
print(escaped); // Path: &#47;system&#47;

Inheritance

Object → Converter<S, T> → HtmlEscape

Constructors

HtmlEscape() const

const HtmlEscape([HtmlEscapeMode mode = HtmlEscapeMode.unknown])

Create converter that escapes HTML characters.

If mode is provided as either HtmlEscapeMode.attribute or HtmlEscapeMode.element, only the corresponding subset of HTML characters is escaped. The default is to escape all HTML characters.

Implementation

const HtmlEscape([this.mode = HtmlEscapeMode.unknown]);

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;

mode final

final HtmlEscapeMode mode

The HtmlEscapeMode used by the converter.

Implementation

final HtmlEscapeMode mode;

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() inherited

Stream<String> bind(Stream<String> 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

String convert(String text)

Converts input and returns the result of the conversion.

Implementation

String convert(String text) {
  var val = _convert(text, 0, text.length);
  return val == null ? text : val;
}

fuse() inherited

Converter<String, TT> fuse<TT>(Converter<String, 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

StringConversionSink startChunkedConversion(Sink<String> sink)

Starts a chunked conversion.

The returned sink serves as input for the long-running conversion. The given sink serves as output.

Implementation

StringConversionSink startChunkedConversion(Sink<String> sink) {
  return _HtmlEscapeSink(
    this,
    sink is StringConversionSink ? sink : StringConversionSink.from(sink),
  );
}

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);