Inserting item with sub-millisecond expiration time causes problems on get (redis backend)

[ahockersten]

I think I have found a corner case in the Redis code that causes problems where items are inserted with really low durations.

Consider the following code:

var item = new CacheItem<object>("foo", "bar", sliding ExpirationMode.Absolute, TimeSpan.FromTicks(1));
cache.Put(item);

This will enter CacheItem's constructor, where TimeSpan will be checked if it is > 0 at CacheItem.cs line 133

if (ExpirationMode != ExpirationMode.Default && ExpirationMode != ExpirationMode.None && ExpirationTimeout <= TimeSpan.Zero)
{
    throw new ArgumentOutOfRangeException(nameof(timeout), "Expiration timeout must be greater than zero if expiration mode is defined.");
}

When cache items are stored into Redis, their duration is converted into a millisecond value (RedisCacheHandle.cs line 833 and other places). If this value is lower than 1 ms, this will end up being stored as 0. Later, inside GetCacheItemAndVersion() in RedisCacheHandle.cs, at line 499+, CacheItem's constructor is called with this value, which is now 0, which causes the constructor to throw an exception.

I am unsure what the fix for this is, else I would submit a proper patch for it. I will gladly submit a patch if we can figure out what the fix should be.

[MichaCo]

@ahockersten question is, why would you want to store items in Redis for less than 1 millisecond? That wouldn't do anything as the transport from client to server might already takes longer ;)

In general, this is an intentional limitation. The fact that the exception occurs later when the cache item gets retrieved is not really friendly. I'll add a check that expiration timeout is at least 1ms.

[ahockersten]

Oh I agree, it was an issue in my code that it was saving things with a sub-millisecond duration, which I have now fixed. :) In this case it was caused by subtracting two datetimes that sometimes happened to be very close to each other in time.

Thank you for the prompt response, and the bugfix.