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 = new 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.