Custom OutputCache provider generates different keys on Add() vs Set()

Question

I'm writing a custom OutputCacheProvider in MVC3.

The calls get fired in this order: Get, Add, Set. I expect that in all methods, the keys generated will be the same, but they're not. The problem is that in the different calls Get and Add are called with a different key than in the Set method.

My request looks like this: http://localhost/testCall?startIndex=0&maxResults=25&testParam=4

With the VaryByParam set, I would expect the key to be unique based on my query params to look something like: testCall?startIndex=0&maxResults=25&testParam=4

Instead, on the Get/Add calls, the key just has the full path name: localhost/testCall

But, on the Set call, the key actually looks to do what I expect: local/testCallHQNmaxresultsV25NstartindexV0NtestparamV4FCDE

Here's my controller method.

[OutputCache(Duration = 15, VaryByParam = "*")]
public ActionResult TestOutputCache()
{
    var obj = new List<string>() {"test", "one", "two", "three"};
    return Json(obj);
}

Here's my Custom OutputCacheProvider

public class MemcacheOutputCacheProvider : OutputCacheProvider
{
    public override void Initialize(string name, System.Collections.Specialized.NameValueCollection config)
    {
        base.Initialize(name, config);
    }

    public override object Get(string key)
    {
        // UNEXPECTED, the key = "localhost/testCall"
        return null;
    }

    public override object Add(string key, object entry, DateTime utcExpiry)
    {
        // UNEXPECTED, the key = "localhost/testCall"
        return null;
    }

    public override void Set(string key, object entry, DateTime utcExpiry)
    {
        // EXPECTED, the key = "local/testCallHQNmaxresultsV25NstartindexV0NtestparamV4FCDE"
    }

    public override void Remove(string key)
    {
    }
}   

If the Set call is made with the correct params, but the Get() is never called with the correct key, then the caching will only work on the root call of /testCall

Answer 1

The key parameter on your implementation of the Set method is encoded, you should decode it. you can use HttpUtility.UrlDecode method.

   public override object Add(string key, object entry, DateTime utcExpiry)
        {
            var decodedKey = HttpUtility.UrlDecode(key)
              // implement your caching logic here 
            return entry;
        }

The Key parameter will always come in the Set Method with additional parameters - this is normal.

Answer 2

The OutputCacheProvider uses the CreateOutputCachedItemKey method that is defined here: https://github.com/microsoft/referencesource/blob/a7bd3242bd7732dec4aebb21fbc0f6de61c2545e/System.Web/OutputCacheModule.cs#L129

If you read through the code of that method you can see how it assembles the key, which explains the extra letters and query string items in your key.