private static bool ETagsMatch(
ETag eTag,
string eTagToCompare,
bool useStrongComparisonFunction)
{
// for If-None-Match (cache) checks, weak comparison should be used.
// for If-Match (concurrency) check, strong comparison should be used.
//The example below shows the results for a set of entity-tag pairs and
//both the weak and strong comparison function results:
//+--------+--------+-------------------+-----------------+
//| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |
//+--------+--------+-------------------+-----------------+
//| W/"1" | W/"1" | no match | match |
//| W/"1" | W/"2" | no match | no match |
//| W/"1" | "1" | no match | match |
//| "1" | "1" | match | match |
//+--------+--------+-------------------+-----------------+
if (useStrongComparisonFunction)
{
// to match, both eTags must be strong & be an exact match.
var eTagToCompareIsStrong = !eTagToCompare.StartsWith("W/");
return(eTagToCompareIsStrong &&
eTag.ETagType == ETagType.Strong &&
string.Equals(eTag.ToString(), eTagToCompare, StringComparison.OrdinalIgnoreCase));
}
// for weak comparison, we only compare the parts of the eTags after the "W/"
var firstValueToCompare = eTag.ETagType == ETagType.Weak ? eTag.ToString()[2..] : eTag.ToString();
