Base64Codec final

final class Base64Codec extends Codec<List<int>, String>

A base64 encoder and decoder.

A Base64Codec allows base64 encoding bytes into ASCII strings and decoding valid encodings back to bytes.

This implementation only handles the simplest RFC 4648 base64 and base64url encodings. It does not allow invalid characters when decoding and it requires, and generates, padding so that the input is always a multiple of four characters.

Inheritance

Object → Codec<S, T> → Base64Codec

Constructors

Base64Codec() const

const Base64Codec()

Implementation

dart

const Base64Codec() : _encoder = const Base64Encoder();

Base64Codec.urlSafe() const

const Base64Codec.urlSafe()

Implementation

dart

const Base64Codec.urlSafe() : _encoder = const Base64Encoder.urlSafe();

Properties

decoder no setter override

Base64Decoder get decoder

Returns the decoder of this, converting from T to S.

It may be stateful and should not be reused.

Implementation

dart

Base64Decoder get decoder => const Base64Decoder();

encoder no setter override

Base64Encoder get encoder

Returns the encoder from S to T.

It may be stateful and should not be reused.

Implementation

dart

Base64Encoder get encoder => _encoder;

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

dart

external int get hashCode;

inverted no setter inherited

Codec<String, List<int>> get inverted

Inverts this.

The encoder and decoder of the resulting codec are swapped.

Inherited from Codec.

Implementation

dart

Codec<T, S> get inverted => _InvertedCodec<T, S>(this);

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

dart

external Type get runtimeType;

Methods

decode() override

Uint8List decode(String encoded)

Decodes encoded.

The input is decoded as if by decoder.convert.

The returned Uint8List contains exactly the decoded bytes, so the Uint8List.length is precisely the number of decoded bytes. The Uint8List.buffer may be larger than the decoded bytes.

Implementation

dart

Uint8List decode(String encoded) => decoder.convert(encoded);

encode() inherited

String encode(List<int> input)

Encodes input.

The input is encoded as if by encoder.convert.

Inherited from Codec.

Implementation

dart

T encode(S input) => encoder.convert(input);

fuse() inherited

Codec<List<int>, R> fuse<R>(Codec<String, R> other)

Fuses this with other.

When encoding, the resulting codec encodes with this before encoding with other.

When decoding, the resulting codec decodes with other before decoding with this.

In some cases one needs to use the inverted codecs to be able to fuse them correctly. That is, the output type of this (T) must match the input type of the second codec other.

Examples:

dart

final jsonToBytes = json.fuse(utf8);
List<int> bytes = jsonToBytes.encode(["json-object"]);
var decoded = jsonToBytes.decode(bytes);
assert(decoded is List && decoded[0] == "json-object");

var inverted = json.inverted;
var jsonIdentity = json.fuse(inverted);
var jsonObject = jsonIdentity.encode(["1", 2]);
assert(jsonObject is List && jsonObject[0] == "1" && jsonObject[1] == 2);

Inherited from Codec.

Implementation

dart

&#47;&#47; TODO(floitsch): use better example with line-splitter once that one is
&#47;&#47; in this library.
Codec<S, R> fuse<R>(Codec<T, R> other) {
  return _FusedCodec<S, T, R>(this, other);
}

normalize()

String normalize(String source, [int start = 0, int? end])

Validates and normalizes the base64 encoded data in source.

Only acts on the substring from start to end, with end defaulting to the end of the string.

Normalization will:

Unescape any %-escapes.
Only allow valid characters (A-Z, a-z, 0-9, / and +).
Normalize a _ or - character to / or +.
Validate that existing padding (trailing = characters) is correct.
If no padding exists, add correct padding if necessary and possible.
Validate that the length is correct (a multiple of four).

Implementation

dart

String normalize(String source, [int start = 0, int? end]) {
  end = RangeError.checkValidRange(start, end, source.length);
  const percent = 0x25;
  const equals = 0x3d;
  StringBuffer? buffer;
  var sliceStart = start;
  var alphabet = _Base64Encoder._base64Alphabet;
  var inverseAlphabet = _Base64Decoder._inverseAlphabet;
  var firstPadding = -1;
  var firstPaddingSourceIndex = -1;
  var paddingCount = 0;
  for (var i = start; i < end;) {
    var sliceEnd = i;
    var char = source.codeUnitAt(i++);
    var originalChar = char;
    &#47;&#47; Normalize char, keep originalChar to see if it matches the source.
    if (char == percent) {
      if (i + 2 <= end) {
        char = parseHexByte(source, i); &#47;&#47; May be negative.
        i += 2;
        &#47;&#47; We know that %25 isn't valid, but our table considers it
        &#47;&#47; a potential padding start, so skip the checks.
        if (char == percent) char = -1;
      } else {
        &#47;&#47; An invalid HEX escape (too short).
        &#47;&#47; Just skip past the handling and reach the throw below.
        char = -1;
      }
    }
    &#47;&#47; If char is negative here, hex-decoding failed in some way.
    if (0 <= char && char <= 127) {
      var value = inverseAlphabet[char];
      if (value >= 0) {
        char = alphabet.codeUnitAt(value);
        if (char == originalChar) continue;
      } else if (value == _Base64Decoder._padding) {
        &#47;&#47; We have ruled out percent, so char is '='.
        if (firstPadding < 0) {
          &#47;&#47; Mark position in normalized output where padding occurs.
          firstPadding = (buffer?.length ?? 0) + (sliceEnd - sliceStart);
          firstPaddingSourceIndex = sliceEnd;
        }
        paddingCount++;
        &#47;&#47; It could have been an escaped equals (%3D).
        if (originalChar == equals) continue;
      }
      if (value != _Base64Decoder._invalid) {
        (buffer ??= StringBuffer())
          ..write(source.substring(sliceStart, sliceEnd))
          ..writeCharCode(char);
        sliceStart = i;
        continue;
      }
    }
    throw FormatException("Invalid base64 data", source, sliceEnd);
  }
  if (buffer != null) {
    buffer.write(source.substring(sliceStart, end));
    if (firstPadding >= 0) {
      &#47;&#47; There was padding in the source. Check that it is valid:
      &#47;&#47; * result length a multiple of four
      &#47;&#47; * one or two padding characters at the end.
      _checkPadding(
        source,
        firstPaddingSourceIndex,
        end,
        firstPadding,
        paddingCount,
        buffer.length,
      );
    } else {
      &#47;&#47; Length of last chunk (1-4 chars) in the encoding.
      var endLength = ((buffer.length - 1) % 4) + 1;
      if (endLength == 1) {
        &#47;&#47; The data must have length 0, 2 or 3 modulo 4.
        throw FormatException("Invalid base64 encoding length ", source, end);
      }
      while (endLength < 4) {
        buffer.write("=");
        endLength++;
      }
    }
    return source.replaceRange(start, end, buffer.toString());
  }
  &#47;&#47; Original was already normalized, only check padding.
  var length = end - start;
  if (firstPadding >= 0) {
    _checkPadding(
      source,
      firstPaddingSourceIndex,
      end,
      firstPadding,
      paddingCount,
      length,
    );
  } else {
    &#47;&#47; No padding given, so add some if needed it.
    var endLength = length % 4;
    if (endLength == 1) {
      &#47;&#47; The data must have length 0, 2 or 3 modulo 4.
      throw FormatException("Invalid base64 encoding length ", source, end);
    }
    if (endLength > 1) {
      &#47;&#47; There is no "insertAt" on String, but this works as well.
      source = source.replaceRange(end, end, (endLength == 2) ? "==" : "=");
    }
  }
  return source;
}

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:

dart

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:

dart

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

dart

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

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

dart

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

dart

external bool operator ==(Object other);

Base64Codec final ​

Constructors ​

Base64Codec() const ​

Base64Codec.urlSafe() const ​

Properties ​

decoder no setter override ​

encoder no setter override ​

hashCode no setter inherited ​

inverted no setter inherited ​

runtimeType no setter inherited ​

Methods ​

decode() override ​

encode() inherited ​

fuse() inherited ​

normalize() ​

noSuchMethod() inherited ​

toString() inherited ​

Operators ​

operator ==() inherited ​

Base64Codec final

Constructors

Base64Codec() const

Base64Codec.urlSafe() const

Properties

decoder no setter override

encoder no setter override

hashCode no setter inherited

inverted no setter inherited

runtimeType no setter inherited

Methods

decode() override

encode() inherited

fuse() inherited

normalize()

noSuchMethod() inherited

toString() inherited

Operators

operator ==() inherited