Request CachePolicy isn't applied in HTTP request header

[benZhai01]

Steps:

1. create a Console App(.net core 3.0)
2. apply following code

static void Main(string[] args)
{
    var url = "https://docs.microsoft.com/en-us/dotnet/api/system.net.cache.requestcachelevel?view=netframework-4.8";
    var req = System.Net.HttpWebRequest.Create(url);
    req.CachePolicy = new System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.NoCacheNoStore);
    var res = req.GetResponse();
}

3. run sample.

Actual Behavior

It's observerd that http request header doesn't include the cache setting.

Expected Behavior

Runing with the same code in Console App against .net framework, we can get following request header.

My Question

1. Is it a bug or by design?

[wfurt]

cc: @davidsh

[benZhai01]

Any updates here? I think it's a very basic property.

[davidsh]

Is it a bug or by design?

Unlike .NET Framework, .NET Core does not have any caching features for HTTP. It does not support .NET Framework related System.Net.Cache features.

There are really 2 parts to the caching logic.

1. HTTP request headers that get sent out when HttpWebRequest.CachePolicy is set.
2. HTTP response processing for either storing a response in the cache for future use, or fetching a cached response instead of having the request go to the server.

(1) can probably be fixed so that we have some compatibility with .NET Framework behavior, at least in terms of what request headers get added to the outgoing HTTP request.

(2) is not going to be fixed. There are no plans to add the System.Net.Cache feature to .NET Core.

[benZhai01]

@davidsh Thanks for detail explanation.
I think (1) is enough on my side.
BTW, can this fixing be included in .netcore 3.1 release? It's really a annoying issue for me.

[davidsh]

BTW, can this fixing be included in .netcore 3.1 release? It's really a annoying issue for me.

The change has to be made to the 'master' branch first which is targeting .NET 5. After that, the change can be considered for .NET Core 3.1.

We're getting close to .NET Core 3.1 RTM, so, it's possible it won't make that release. But it could be considered for a servicing release to .NET Core 3.1, i.e. .NET Core 3.1.1, 3.1.2, etc.

[benZhai01]

@davidsh that's great, thank you.

[benZhai01]

Workaround：

HttpWebRequest wr;
wr.Headers.Add("Cache-Control", "no-store,no-cache");
wr.Headers.Add("Pragma", "no-cache");

[dotMorten]

There are no plans to add the System.Net.Cache feature to .NET Core.

Could you make it a plan? Currently I'm looking at telling our customers how awesome .NET Core is, but errrrr... you should also look forward to slower responses because repeated web requests are no longer relying on fast 304 responses. It's not a very good selling point for moving over from .NET Framework.

[dotMorten]

Quick and dirty cache implementation showed a 33x perf increase on repeated requests when implementing cache-control max-age and/or etag:

Method	Mean	Error	StdDev	Median	Ratio	Gen 0	Gen 1	Gen 2	Allocated
UseSocketsHttpHandler	48.710 ms	0.4979 ms	0.4414 ms	48.694 ms	1.00	-	-	-	243.08 KB
UseHttpClientHandler	47.781 ms	0.5331 ms	0.4451 ms	47.884 ms	0.98	-	-	-	242.25 KB
UseCacheHttpHandler	1.252 ms	0.0665 ms	0.1907 ms	1.199 ms	0.03	-	-	-	247.48 KB

Test was done on an above-average high-speed internet connection. Effect would of course be A LOT bigger on slower networks.

[karelz]

Triage: Looks like low priority. HttpWebRequest is deprecated and we recommend everyone to use HttpClient instead. There is a workaround for people who really need it.

That said, the work is probably easy and we would take a PR for the part (1) from #31320 (comment)

[dotMorten]

Perhaps I was slightly misreading this thread. If it's specific to saying you want a fresh copy from the server, I get it should be sending that. I was conflating it with the settings that also tells the client to pull from the local cache as well if possible (which is also part of the CachePolicy property / RequestCacheLevel enumeration)