private bool CheckIfModifiedSinceIsValid(HttpContext httpContext, ValidationValue validationValue)
{
if (httpContext.Request.Headers.Keys.Contains(HeaderNames.IfModifiedSince))
{
// if the LastModified date is smaller than the IfModifiedSince date,
// we can return a 304 Not Modified (If there's also a matching ETag).
// By adding an If-Modified-Since date
// to a GET/HEAD request, the consumer is stating that (s)he only wants the resource
// to be returned if if has been modified after that.
var ifModifiedSinceValue = httpContext.Request.Headers[HeaderNames.IfModifiedSince].ToString();
_logger.LogInformation($"Checking If-Modified-Since: {ifModifiedSinceValue}");
if (DateTimeOffset.TryParseExact(
ifModifiedSinceValue,
"r",
CultureInfo.InvariantCulture.DateTimeFormat,
DateTimeStyles.AdjustToUniversal,
out var parsedIfModifiedSince))
{
return(validationValue.LastModified.CompareTo(parsedIfModifiedSince) <= 0);
}
// can only check if we can parse it. Invalid values must be ignored.
_logger.LogInformation("Cannot parse If-Modified-Since value as date, header is ignored.");
return(true);
}
// if there is no IfModifiedSince header, the check is valid.
_logger.LogInformation("No If-Modified-Since header.");
return(true);
}
private bool CheckIfUnmodifiedSinceIsValid(HttpContext httpContext, ValidationValue validationValue)
{
// Either the ETag matches (or one of them), or there was no IfMatch header.
// Continue with checking the IfUnModifiedSince header, if it exists.
if (httpContext.Request.Headers.Keys.Contains(HeaderNames.IfUnmodifiedSince))
{
// if the LastModified date is smaller than the IfUnmodifiedSince date,
// the precondition is valid.
var ifUnModifiedSinceValue = httpContext.Request.Headers[HeaderNames.IfUnmodifiedSince].ToString();
_logger.LogInformation($"Checking If-Unmodified-Since: {ifUnModifiedSinceValue}");
if (DateTimeOffset.TryParseExact(
ifUnModifiedSinceValue,
"r",
CultureInfo.InvariantCulture.DateTimeFormat,
DateTimeStyles.AdjustToUniversal,
out var parsedIfUnModifiedSince))
{
// If the LastModified date is smaller than the IfUnmodifiedSince date,
// the precondition is valid.
return(validationValue.LastModified.CompareTo(parsedIfUnModifiedSince) < 0);
}
// can only check if we can parse it. Invalid values must be ignored.
_logger.LogInformation("Cannot parse If-Unmodified-Since value as date, header is ignored.");
return(true);
}
// if there is no IfUnmodifiedSince header, the check is valid.
_logger.LogInformation("No If-Unmodified-Since header.");
return(true);
}
private bool CheckIfMatchIsValid(HttpContext httpContext, ValidationValue validationValue)
{
if (!httpContext.Request.Headers.Keys.Contains(HeaderNames.IfMatch))
{
// if there is no IfMatch header, the tag precondition is valid.
_logger.LogInformation("No If-Match header, don't check ETag.");
return(true);
}
_logger.LogInformation("Checking If-Match.");
var ifMatchHeaderValue = httpContext.Request.Headers[HeaderNames.IfMatch].ToString().Trim();
_logger.LogInformation($"Checking If-Match: {ifMatchHeaderValue}.");
// if the value is *, the check is valid.
if (ifMatchHeaderValue == "*")
{
return(true);
}
// otherwise, check the actual ETag(s)
var eTagsFromIfMatchHeader = ifMatchHeaderValue.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
// check the ETag. If one of the ETags matches, the
// ETag precondition is valid.
// for concurrency checks, we use the strong
// comparison function.
if (eTagsFromIfMatchHeader.Any(eTag => ETagsMatch(validationValue.ETag, eTag.Trim(), true)))
{
_logger.LogInformation($"ETag valid: {validationValue.ETag}.");
return(true);
}
// if there is an IfMatch header but none of the ETags match,
// the precondition is already invalid. We don't have to
// continue checking.
_logger.LogInformation("Not valid. No match found for ETag.");
return(false);
}
private bool CheckIfNoneMatchIsValid(HttpContext httpContext, ValidationValue validationValue)
{
if (!httpContext.Request.Headers.Keys.Contains(HeaderNames.IfNoneMatch))
{
// if there is no IfNoneMatch header, the tag precondition is valid.
_logger.LogInformation("No If-None-Match header, don't check ETag.");
return(true);
}
_logger.LogInformation("Checking If-None-Match.");
var ifNoneMatchHeaderValue = httpContext.Request.Headers[HeaderNames.IfNoneMatch].ToString().Trim();
_logger.LogInformation($"Checking If-None-Match: {ifNoneMatchHeaderValue}.");
// if the value is *, the check is valid.
if (ifNoneMatchHeaderValue == "*")
{
return(true);
}
var eTagsFromIfNoneMatchHeader = ifNoneMatchHeaderValue.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
// check the ETag. If one of the ETags matches, we're good to
// go and can return a 304 Not Modified.
// For conditional GET/HEAD, we use weak comparison.
if (eTagsFromIfNoneMatchHeader.Any(eTag => ETagsMatch(validationValue.ETag, eTag.Trim(), false)))
{
_logger.LogInformation($"ETag valid: {validationValue.ETag}.");
return(true);
}
// if there is an IfNoneMatch header, but none of the eTags match, we don't take the
// If-Modified-Since headers into account.
//
// cfr: "If none of the entity tags match, then the server MAY perform the requested method as if the
// If-None-Match header field did not exist, but MUST also ignore any If-Modified-Since header field(s)
// in the request. That is, if no entity tags match, then the server MUST NOT return a 304(Not Modified) response."
_logger.LogInformation("Not valid. No match found for ETag.");
return(false);
}