Make HttpStatus instantiable

[DartBot]

This issue was originally filed by @seaneagan

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An http status contains much more information than a simple int can convey, and thus would be better represented by a dedicated interface as follows...

interface HttpStatus {
  static final HttpStatus ACCEPTED;
  // ...
  static final HttpStatus OK;
  // etc.

  // const constructor
  const HttpStatus(int code, [String reasonPhrase/* = ''*/]);
  final int code;
  final String reasonPhrase;
  final bool isInformational; // 1xx
  final bool isSuccess; // 2xx
  final bool isRedirection; // 3xx
  final bool isClientError; // 4xx
  final bool isServerError; // 5xx
  final bool isError; => isClientError || isServerError

  // returns the http Status-Line associated with this status
  String toString();
}

interface HttpResponse {
  HttpStatus status; // could default to HttpStatus.OK
}

interface HttpClientResponse {
  final HttpStatus status; // client can't change status
}

Examples:

// server
response.status = HttpStatus.NOT_FOUND

// client
if(response.status = HttpStatus.OK) //...
if(response.status.isError) //...

[DartBot]

This comment was originally written by @seaneagan

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Actually, when checking status codes, you probably wouldn't be able to depend on the reasonPhrase being the standard one for the given status code, so you would probably need to do:

response.status.code = HttpStatus.OK.code
// or
response.status.code = 200

For this particular status code it might be useful add the following shortcut:

response.status.isOk

[madsager]

cc @sgjesse.
Added Area-IO, Triaged labels.

[DartBot]

This comment was originally written by @seaneagan

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Actually, on second thought you could override HttpStatus#== to only check the status code and not the reason phrase since that's all that matters in most cases:

bool operator ==(HttpStatus other) => code == other.code;

which allows going back to:

response.status == HttpStatus.OK;

Also, the implementation could use a factory constructor to avoid having to create a new status object in the probably 99% of cases when the code and reason phrase match one of the compile time constant HttpStatuses already available (e.g. HttpStatus.OK):

factory HttpStatusImpl(int code, [String reasonPhrase]) {
  HttpStatus ret = HttpStatusImpl._getStandardStatus(code, reasonPhrase);
  return null == ret ? new HttpStatusImpl._internal(code, reasonPhrase) : ret;
}

[sgjesse]

Creating object instances for each status code does not add much. It might actually create more confusion as the reason phrase is not fixed for any given status code.

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Added WontFix label.

[kevmoo]

Removed Area-IO label.
Added Area-Library, Library-IO labels.