checkIfHeaders function

bool checkIfHeaders(HttpConnect connect, DateTime? lastModified, String? etag)

Check if the conditions specified in the optional If headers are satisfied, such as If-Modified-Since and If-None-Match headers.

If false is returned, the caller shall stop from generating further content.

• lastModified - when it was last modified. Ignored if null.
• etag - the ETag. Ignored if null.

Implementation

bool checkIfHeaders(HttpConnect connect, DateTime? lastModified, String? etag) {
  final response = connect.response;
  if (response.statusCode >= 300)
    return true; //Ignore If, since caused by forward-by-error (see also Issue 59)

  final request = connect.request;

  //Check If-Match
  final ifMatch = connect.headerValue(HttpHeaders.ifMatchHeader);
  if (ifMatch != null && ifMatch != "*"
  && (etag == null || !_matchETag(ifMatch, etag))) { //not match
    response.statusCode = HttpStatus.preconditionFailed;
    return false;
  }

  //Check If-None-Match
  //Note: it shall be checked before If-Modified-Since
  final ifNoneMatch = connect.headerValue(HttpHeaders.ifNoneMatchHeader);
  if (ifNoneMatch != null) {
    if (ifNoneMatch == "*"
    || (etag != null && _matchETag(ifNoneMatch, etag))) { //match
      final method = request.method;
      if (method == "GET" || method == "HEAD") {
        response.statusCode = HttpStatus.notModified;
        if (etag != null)
          response.headers.set(HttpHeaders.etagHeader, etag);
        return false;
      }
      response.statusCode = HttpStatus.preconditionFailed;
      return false;
    }
  }

  if (lastModified != null) {
    //Check If-Modified-Since
    //Ignored it if If-None-Match specified (since ETag differs)
    final ifModifiedSince = request.headers.ifModifiedSince;
    if (ifModifiedSince != null && ifNoneMatch == null
    && lastModified.isBefore(ifModifiedSince.add(_oneSecond))) {
      response.statusCode = HttpStatus.notModified;
      if (etag != null)
        response.headers.set(HttpHeaders.etagHeader, etag);
      return false;
    }

    //Check If-Unmodified-Since
    final value = connect.headerValue(HttpHeaders.ifUnmodifiedSinceHeader);
    if (value != null) {
      try {
        final ifUnmodifiedSince = HttpDate.parse(value);
        if (lastModified.isAfter(ifUnmodifiedSince.add(_oneSecond))) {
          response.statusCode = HttpStatus.preconditionFailed;
          return false;
        }
      } catch (e) { //ignore it silently
      }
    }
  }
  return true;
}