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.

To build an Accepts header with the value

text/plain; q=0.3, text/html

use code like this:

HttpClientRequest request = ...;
var v = new HeaderValue();
v.value = "text/plain";
v.parameters["q"] = "0.3"
request.headers.add(HttpHeaders.ACCEPT, v);
request.headers.add(HttpHeaders.ACCEPT, "text/html");

To parse the header values use the fromString constructor.

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

abstract class HeaderValue {
  /**
   * Creates a new header value object setting the value part.
   */
  factory HeaderValue([String value = ""]) => new _HeaderValue(value);

  /**
   * Creates a new header value object from parsing a header value
   * string with both value and optional parameters.
   */
  factory HeaderValue.fromString(String value) {
    return new _HeaderValue.fromString(value);
  }

  /**
   * Gets and sets the header value.
   */
  String value;

  /**
   * Gets the map of parameters.
   */
  Map<String, String> get parameters;

  /**
   * Returns the formatted string representation in the form:
   *
   *     value; parameter1=value1; parameter2=value2
   */
  String toString();
}