public async Task <CacheQueryResult> QueryCacheAsync(HttpRequestMessage request)
{
// Do we have anything stored for this method and URI? Return entries for all variants
var cacheEntryList = await _contentStore.GetEntriesAsync(new CacheKey(request.RequestUri, request.Method)).ConfigureAwait(false);
if (cacheEntryList == null) // Should I use null or Count() == 0 ?
{
return(CacheQueryResult.CannotUseCache());
}
// Find the first matching variant based on the vary header fields defined in the cacheEntry
// and the values in the request
var selectedEntry = MatchVariant(request, cacheEntryList);
// Do we have a matching variant representation?
if (selectedEntry == null)
{
return(CacheQueryResult.CannotUseCache());
}
// Get the complete response, including body based on the selected variant
var response = await _contentStore.GetResponseAsync(selectedEntry.VariantId).ConfigureAwait(false);
// Do caching directives require that we revalidate it regardless of freshness?
var requestCacheControl = request.Headers.CacheControl ?? new CacheControlHeaderValue();
if ((requestCacheControl.NoCache || selectedEntry.CacheControl.NoCache))
{
return(CacheQueryResult.Revalidate(selectedEntry, response));
}
// Is it fresh?
if (selectedEntry.IsFresh())
{
if (requestCacheControl.MinFresh != null)
{
var age = HttpCache.CalculateAge(response);
if (age <= requestCacheControl.MinFresh)
{
return(CacheQueryResult.ReturnStored(selectedEntry, response));
}
}
else
{
return(CacheQueryResult.ReturnStored(selectedEntry, response));
}
}
// Did the client say we can serve it stale?
if (requestCacheControl.MaxStale)
{
if (requestCacheControl.MaxStaleLimit != null)
{
if ((DateTime.UtcNow - selectedEntry.Expires) <= requestCacheControl.MaxStaleLimit)
{
return(CacheQueryResult.ReturnStored(selectedEntry, response));
}
}
else
{
return(CacheQueryResult.ReturnStored(selectedEntry, response));
}
}
// Do we have a selector to allow us to do a conditional request to revalidate it?
if (selectedEntry.HasValidator)
{
return(CacheQueryResult.Revalidate(selectedEntry, response));
}
// Can't do anything to help
return(CacheQueryResult.CannotUseCache());
}
