CODEWITHSUNDEEP
asp.net-mvc-4asp.net-web-api
Bullines
Bullines

Reputation: 5696

Implementing ETag Support in ASP.NET MVC4 WebAPI

In the latest ASP.NET MVC4 beta, how would you support conditional GET support via ETags? The ActionFilter would need to be able to complete the request to generate the ETag for the returned resource in order to compare to the If-None-Match header in the request. And then, regardless of whether the incoming ETag in the If-None-Match header was the same as the generated ETag, add the generated ETag to the ETag response header. But with ASP.NET MVC4, I have no idea where to begin. Any suggestions?

Upvotes: 17

Views: 10550

Answers (4)

Greg McCoy
Greg McCoy

Reputation: 511

Luke Puplett's answer got me on the right track (+1), but note that you also have to read the ETag on the server side to avoid sending all the data with each request:

string hash = obj.ModifiedDate.GetHashCode().ToString();
var etag = new EntityTagHeaderValue(String.Concat("\"", hash, "\""), true);

if (Request.Headers.IfNoneMatch.Any(h => h.Equals(etag)))
{
    return new HttpResponseMessage(HttpStatusCode.NotModified);
}

var response = this.Request.CreateResponse(HttpStatusCode.OK, obj);
response.Headers.ETag = etag;
return response;

It would also be a good idea to respect the If-Modified-Since header. See RFC 2616.

Upvotes: 5

Stas Natalenko
Stas Natalenko

Reputation: 136

It seems this is what you are looking for (see section "Support for ETags"):

http://blogs.msdn.com/b/webdev/archive/2014/03/13/getting-started-with-asp-net-web-api-2-2-for-odata-v4-0.aspx

In case your model is stored deeper in domain and you are not able to apply the [ConcurrencyCheck] attribute, you can do that using the ODataModelBuilder: 

ODataModelBuilder builder = new ODataConventionModelBuilder();
var myEntity = builder.EntitySet<MyEntity>("MyEntities"); 
myEntity.EntityType.Property(l => l.Version).ConcurrencyToken = true;

this will make it to add the "@odata.etag" property to a response body.

Upvotes: 0

Aliostad
Aliostad

Reputation: 81700

There is a ETagMessageHandler in the WebApiContrib which does what you need.

UPDATE

I have implemented RFC 2616's server side caching in WebApiContrib. Look for CachingHandler. More info here.

More Update

This will be actively developed and expanded upon under CacheCow. This will include both client and server components. NuGet packages to be published soon are published now.

WebApiContrib's CachingHandler will still be maintained so any bugs or problems please let me know.

Upvotes: 9

Luke Puplett
Luke Puplett

Reputation: 45323

Personally, I'm not a fan of "framework magic" and prefer plain old code in the web methods, else we end up with something more akin to WCF, yuk.

So, within your Get web method, manually create the response like so:

var response = this.Request.CreateResponse(HttpStatusCode.OK, obj);
string hash = obj.ModifiedDate.GetHashCode().ToString();

response.Headers.ETag =
    new EntityTagHeaderValue(String.Concat("\"", hash, "\""), true);

return response;

Please note that the ETag produced from the hash code of the timestamp is purely illustrative of a weak entity tagging system. It also shows the additional quotes required.

Upvotes: 16

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