HeaderValue class Null safety

Representation of a header value in the form:

value; parameter1=value1; parameter2=value2

HeaderValue can be used to conveniently build and parse header values on this form.

Parameter values can be omitted, in which case the value is parsed as null. Values can be doubled quoted to allow characters outside of the RFC 7230 token characters and backslash sequences can be used to represent the double quote and backslash characters themselves.

To build an "accepts" header with the value

text/plain; q=0.3, text/html

use code like this:

HttpClientRequest request = ...;
var v = HeaderValue("text/plain", {"q": "0.3"});
request.headers.add(HttpHeaders.acceptHeader, v);
request.headers.add(HttpHeaders.acceptHeader, "text/html");

To parse the header values use the parse static method.

HttpRequest request = ...;
List<String> values = request.headers[HttpHeaders.acceptHeader];
values.forEach((value) {
  HeaderValue v = HeaderValue.parse(value);
  // Use v.value and v.parameters

An instance of HeaderValue is immutable.



HeaderValue([String value = "", Map<String, String?> parameters = const {}])
Creates a new header value object setting the value and parameters.


hashCode int
The hash code for this object. [...]
read-only, inherited
parameters Map<String, String?>
A map of parameters. [...]
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited
value String
The value of the header.


noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed. [...]
toString() String
Returns the formatted string representation in the form: [...]


operator ==(Object other) bool
The equality operator. [...]

Static Methods

parse(String value, {String parameterSeparator = ";", String? valueSeparator, bool preserveBackslash = false}) HeaderValue
Creates a new header value object from parsing a header value string with both value and optional parameters.