Develop Reference

Application Insights - ILogger arguments rendered as name of the object in custom dimensions

Objects are rendered as strings, (name of the object), in Application Insights custom dimensions when passed as arguments to ilogger. The actual values are not shown.
Register Application Insights
services.AddApplicationInsightsTelemetry();
New log
public class HealthController : ControllerBase
{
private readonly ILogger<HealthController> _logger;
public HealthController(ILogger<HealthController> logger)
{
_logger = logger;
}
[HttpGet]
public IActionResult Get()
{
var health = new HealthViewModel()
{
ok = false
};
_logger.LogInformation("Hlep me pls {health}", health);
return Ok(health);
}
}
Result
I do not want to this this for every log:
var health = new HealthViewModel()
{
ok = false
};
_logger.LogInformation("Hlep me pls {health}", JsonConvert.SerializeObject(health));
I tried creating a middleware for application insights but the value is still the name of the object..
Why are arguments not rendered as json?
Edit
It seems like
var health = new
{
ok = false
};
_logger.LogInformation("HEJ2 {health}", health);
works but not
var health = new HealthViewModel
{
ok = false
};
_logger.LogInformation("HEJ2 {health}", health);

Not supported
Quote from https://github.com/microsoft/ApplicationInsights-dotnet/issues/1722
I think you're expecting too much of the logger. It doesn't know about JSON format, it just calls Convert.ToString on properties
Convert.ToString typically calls ToString() and the default ToString implementation for new classes is simply to return the type name
What you can do
Use ToJson() on objects logged to ILogger and create a middleware for application insights and modify the name of the log and the custom dimensions.
Middleware
public class ProcessApiTraceFilter : ITelemetryProcessor
{
private ITelemetryProcessor Next { get; set; }
private readonly IIdentity _identity;
private readonly IHostEnvironment _hostEnvironment;
public ProcessApiTraceFilter(ITelemetryProcessor next, IHostEnvironment hostEnvironment, IIdentity identity)
{
Next = next;
_identity = identity;
_hostEnvironment = hostEnvironment;
}
public void Process(ITelemetry item)
{
item.Process(_hostEnvironment, _identity);
Next.Process(item);
}
}
Implementation
public static class ApplicationInsightsExtensions
{
public static void Process(this ITelemetry item, IHostEnvironment hostEnvironment, IIdentity identity)
{
if (item is TraceTelemetry)
{
var traceTelemetry = item as TraceTelemetry;
var originalMessage = traceTelemetry.Properties.FirstOrDefault(x => x.Key == "{OriginalFormat}");
if (!string.IsNullOrEmpty(originalMessage.Key))
{
var reg = new Regex("{([A-z]*)*}", RegexOptions.Compiled);
var match = reg.Matches(originalMessage.Value);
var formattedMessage = originalMessage.Value;
foreach (Match arg in match)
{
var parameterName = arg.Value.Replace("{", "").Replace("}", "");
var parameterValue = traceTelemetry.Properties.FirstOrDefault(x => x.Key == parameterName);
formattedMessage = formattedMessage.Replace(arg.Value, "");
}
traceTelemetry.Message = formattedMessage.Trim();
}
if (identity != null)
{
var isAuthenticated = identity.IsAuthenticated();
const string customerKey = "customer";
if (isAuthenticated && !traceTelemetry.Properties.ContainsKey(customerKey))
{
var customer = identity.Customer();
if (customer != null)
{
traceTelemetry.Properties.Add(customerKey, customer.ToJson());
}
}
var request = identity.Request();
const string requestKey = "request";
if (request != null && !traceTelemetry.Properties.ContainsKey(requestKey))
{
traceTelemetry.Properties.Add(requestKey, request.ToJson());
}
}
var applicationNameKey = "applicationName";
if (hostEnvironment != null && !string.IsNullOrEmpty(hostEnvironment.ApplicationName) && !traceTelemetry.Properties.ContainsKey(applicationNameKey))
{
traceTelemetry.Properties.Add(applicationNameKey, hostEnvironment.ApplicationName);
}
}
}
}
Register application insights and middleware in startup
services.AddApplicationInsightsTelemetry();
services.AddApplicationInsightsTelemetryProcessor<ProcessApiTraceFilter>();
ToJson
public static class ObjectExtensions
{
private static readonly string Null = "null";
private static readonly string Exception = "Could not serialize object to json";
public static string ToJson(this object value, Formatting formatting = Formatting.None)
{
if (value == null) return Null;
try
{
string json = JsonConvert.SerializeObject(value, formatting);
return json;
}
catch (Exception ex)
{
return $"{Exception} - {ex?.Message}";
}
}
}
Log
//Log object? _smtpAppSettings.ToJson()
_logger.LogInformation("Email sent {to} {from} {subject}", to, _smtpAppSettings.From, subject)
Result

from your custom dimensions i can see that it`s not considering the health obj param as an extra data
_logger.LogInformation("Hlep me pls {health}", health);
trying using the jsonConverter within the string itself.
_logger.LogInformation($"Hlep me pls {JsonConvert.SerializeObject(health)}");

Create/Use property to get Session variable C#

I have an ASPX Web Forms control that imports from another project the Person class.
public partial class cuTest : System.Web.UI.UserControl
There I have created in that control a property for an object session and a method to populate that session.
public Person person
{
get
{
if (this.Session["Person"] == null)
{
Session["Person"] = new Person();
}
return Session["Person"] as Person;
}
}
private void crearPago()
{
this.person.name = "Max";
this.person.surname = "Ford";
}
Now when I want to call it from the page that contains that control.
var x = cuTest.person; I need to check if it's not empty since this can't be null. How can I do that?

I have a static class Web that I add there any properties that are useful throughout the application.
One thing that differs is that the Request, Response and Session objects are not directly available. So, I have 3 helper functions that return the current Request, Response and Session objects, if available.
So, a Person person property would be like that:
using System;
using System.Web;
using System.Web.SessionState;
namespace MyWebApp
{
public static class Web
{
private static HttpRequest request
{
get
{
if (HttpContext.Current == null) return null;
return HttpContext.Current.Request;
}
}
private static HttpResponse response
{
get
{
if (HttpContext.Current == null) return null;
return HttpContext.Current.Response;
}
}
private static HttpSessionState session
{
get
{
if (HttpContext.Current == null) return null;
return HttpContext.Current.Session;
}
}
public static Person person
{
get
{
// Here you can change what is returned when session is not available
if (session == null) return null;
if(session["Person"] == null) {
session["Person"] = new Person();
}
return session["Person"] as Person;
}
set
{
// Here you can change how to handle the case when session is not available
if (session == null) return;
session["Person"] = value;
}
}
}
}
To use it, in your Page or UserControl code, you can write
// get
var x = MyWebApp.Web.person;
// set
MyWebApp.Web.person = x;

You can simply check if the name/surname is null or empty with:
string.IsNullOrEmpty(x.name);

How to clear ASP.NET cache thread-safely?

In my project I have some cached values implemented using singleton pattern - it looks like this:
Roles GetRoles
{
get{
var cached = HttpContext.Current.Cache["key"];
if(cached == null){
cached = new GetRolesFromDb(...);
}
return cached as Roles;
}
}
When I change the roles I'm clearing the cache (iterating over all keys).
I think it isn't thread-safe - if some request tries to get cached roles,
cached != null and meanwhile cache had been cleared GetRoles returns null.

private object lockRoles = new object();
public Roles GetRoles
{
get
{
object cached = HttpContext.Current.Cache["key"];
if(cached == null)
{
lock(lockRoles)
{
cached = HttpContext.Current.Cache["key"];
if (cached == null)
{
cached = new GetRolesFromDb(...);
HttpContext.Current.Cache["key"] = cached;
}
}
}
return (Roles)cached;
}
}
public void ClearRoles()
{
HttpContext.Current.Cache.Remove("key");
}

Caching WebAPI 2

EDIT: For each request, a new instance of controller is created. However, this is not true with Attribute classes. Once they are created, it is used for multiple requests. I hope it helps.
I wrote my own WebAPI (using latest version of WebAPI and .net framework) caching action filter. I am aware about CacheCow & this. However, i wanted mine anyways.
However, there is some issue with my code because i don't get exepected output when i use it in my project on live server. On local machine everything works fine.
I used below code in my blog RSS generator and i cache the data for each category. There are around 5 categories (food, tech, personal etc).
Issue: When i navigate to say api/GetTech it returns me the rss feed items from personal blog category. When i navigate to say api/GetPersonal , it returns me api/Food
I am not able to find the root cause but I think this is due to use of static method/variable. I have double checked that my _cachekey has unique value for each category of my blog.
Can someone point out any issues with this code esp when we have say 300 requests per minute ?
public class WebApiOutputCacheAttribute : ActionFilterAttribute
{
// Cache timespan
private readonly int _timespan;
// cache key
private string _cachekey;
// cache repository
private static readonly MemoryCache _webApiCache = MemoryCache.Default;
/// <summary>
/// Initializes a new instance of the <see cref="WebApiOutputCacheAttribute"/> class.
/// </summary>
/// <param name="timespan">The timespan in seconds.</param>
public WebApiOutputCacheAttribute(int timespan)
{
_timespan = timespan;
}
public override void OnActionExecuting(HttpActionContext ac)
{
if (ac != null)
{
_cachekey = ac.Request.RequestUri.PathAndQuery.ToUpperInvariant();
if (!_webApiCache.Contains(_cachekey)) return;
var val = (string)_webApiCache.Get(_cachekey);
if (val == null) return;
ac.Response = ac.Request.CreateResponse();
ac.Response.Content = new StringContent(val);
var contenttype = (MediaTypeHeaderValue)_webApiCache.Get("response-ct") ?? new MediaTypeHeaderValue("application/rss+xml");
ac.Response.Content.Headers.ContentType = contenttype;
}
else
{
throw new ArgumentNullException("ac");
}
}
public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
{
if (_webApiCache.Contains(_cachekey)) return;
var body = actionExecutedContext.Response.Content.ReadAsStringAsync().Result;
if (actionExecutedContext.Response.StatusCode == HttpStatusCode.OK)
{
lock (WebApiCache)
{
_wbApiCache.Add(_cachekey, body, DateTime.Now.AddSeconds(_timespan));
_webApiCache.Add("response-ct", actionExecutedContext.Response.Content.Headers.ContentType, DateTimeOffset.UtcNow.AddSeconds(_timespan));
}
}
}
}

The same WebApiOutputCacheAttribute instance can be used to cache multiple simultaneous requests, so you should not store cache keys on the instance of the attribute. Instead, regenerate the cache key during each request / method override. The following attribute works to cache HTTP GET requests.
using System;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Web.Http.Controllers;
using System.Web.Http.Filters;
using Newtonsoft.Json;
// based on strathweb implementation
// http://www.strathweb.com/2012/05/output-caching-in-asp-net-web-api/
public class CacheHttpGetAttribute : ActionFilterAttribute
{
public int Duration { get; set; }
public ILogExceptions ExceptionLogger { get; set; }
public IProvideCache CacheProvider { get; set; }
private bool IsCacheable(HttpRequestMessage request)
{
if (Duration < 1)
throw new InvalidOperationException("Duration must be greater than zero.");
// only cache for GET requests
return request.Method == HttpMethod.Get;
}
private CacheControlHeaderValue SetClientCache()
{
var cachecontrol = new CacheControlHeaderValue
{
MaxAge = TimeSpan.FromSeconds(Duration),
MustRevalidate = true,
};
return cachecontrol;
}
private static string GetServerCacheKey(HttpRequestMessage request)
{
var acceptHeaders = request.Headers.Accept;
var acceptHeader = acceptHeaders.Any() ? acceptHeaders.First().ToString() : "*/*";
return string.Join(":", new[]
{
request.RequestUri.AbsoluteUri,
acceptHeader,
});
}
private static string GetClientCacheKey(string serverCacheKey)
{
return string.Join(":", new[]
{
serverCacheKey,
"response-content-type",
});
}
public override void OnActionExecuting(HttpActionContext actionContext)
{
if (actionContext == null) throw new ArgumentNullException("actionContext");
var request = actionContext.Request;
if (!IsCacheable(request)) return;
try
{
// do NOT store cache keys on this attribute because the same instance
// can be reused for multiple requests
var serverCacheKey = GetServerCacheKey(request);
var clientCacheKey = GetClientCacheKey(serverCacheKey);
if (CacheProvider.Contains(serverCacheKey))
{
var serverValue = CacheProvider.Get(serverCacheKey);
var clientValue = CacheProvider.Get(clientCacheKey);
if (serverValue == null) return;
var contentType = clientValue != null
? JsonConvert.DeserializeObject<MediaTypeHeaderValue>(clientValue.ToString())
: new MediaTypeHeaderValue(serverCacheKey.Substring(serverCacheKey.LastIndexOf(':') + 1));
actionContext.Response = actionContext.Request.CreateResponse();
// do not try to create a string content if the value is binary
actionContext.Response.Content = serverValue is byte[]
? new ByteArrayContent((byte[])serverValue)
: new StringContent(serverValue.ToString());
actionContext.Response.Content.Headers.ContentType = contentType;
actionContext.Response.Headers.CacheControl = SetClientCache();
}
}
catch (Exception ex)
{
ExceptionLogger.Log(ex);
}
}
public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
{
try
{
var request = actionExecutedContext.Request;
// do NOT store cache keys on this attribute because the same instance
// can be reused for multiple requests
var serverCacheKey = GetServerCacheKey(request);
var clientCacheKey = GetClientCacheKey(serverCacheKey);
if (!CacheProvider.Contains(serverCacheKey))
{
var contentType = actionExecutedContext.Response.Content.Headers.ContentType;
object serverValue;
if (contentType.MediaType.StartsWith("image/"))
serverValue = actionExecutedContext.Response.Content.ReadAsByteArrayAsync().Result;
else
serverValue = actionExecutedContext.Response.Content.ReadAsStringAsync().Result;
var clientValue = JsonConvert.SerializeObject(
new
{
contentType.MediaType,
contentType.CharSet,
});
CacheProvider.Add(serverCacheKey, serverValue, new TimeSpan(0, 0, Duration));
CacheProvider.Add(clientCacheKey, clientValue, new TimeSpan(0, 0, Duration));
}
if (IsCacheable(actionExecutedContext.Request))
actionExecutedContext.ActionContext.Response.Headers.CacheControl = SetClientCache();
}
catch (Exception ex)
{
ExceptionLogger.Log(ex);
}
}
}
Just replace the CacheProvider with your MemoryCache.Default. In fact, the code above uses the same by default during development, and uses azure cache when deployed to a live server.
Even though your code resets the _cachekey instance field during each request, these attributes are not like controllers where a new one is created for each request. Instead, the attribute instance can be repurposed to service multiple simultaneous requests. So don't use an instance field to store it, regenerate it based on the request each and every time you need it.

How to use ETag in Web API using action filter along with HttpResponseMessage

I have a ASP.Net Web API controller which simply returns the list of users.
public sealed class UserController : ApiController
{
[EnableTag]
public HttpResponseMessage Get()
{
var userList= this.RetrieveUserList(); // This will return list of users
this.responseMessage = new HttpResponseMessage(HttpStatusCode.OK)
{
Content = new ObjectContent<List<UserViewModel>>(userList, new JsonMediaTypeFormatter())
};
return this.responseMessage;
}
}
and an action filter attribute class EnableTag which is responsible to manage ETag and cache:
public class EnableTag : System.Web.Http.Filters.ActionFilterAttribute
{
private static ConcurrentDictionary<string, EntityTagHeaderValue> etags = new ConcurrentDictionary<string, EntityTagHeaderValue>();
public override void OnActionExecuting(HttpActionContext context)
{
if (context != null)
{
var request = context.Request;
if (request.Method == HttpMethod.Get)
{
var key = GetKey(request);
ICollection<EntityTagHeaderValue> etagsFromClient = request.Headers.IfNoneMatch;
if (etagsFromClient.Count > 0)
{
EntityTagHeaderValue etag = null;
if (etags.TryGetValue(key, out etag) && etagsFromClient.Any(t => t.Tag == etag.Tag))
{
context.Response = new HttpResponseMessage(HttpStatusCode.NotModified);
SetCacheControl(context.Response);
}
}
}
}
}
public override void OnActionExecuted(HttpActionExecutedContext context)
{
var request = context.Request;
var key = GetKey(request);
EntityTagHeaderValue etag;
if (!etags.TryGetValue(key, out etag) || request.Method == HttpMethod.Put || request.Method == HttpMethod.Post)
{
etag = new EntityTagHeaderValue("\"" + Guid.NewGuid().ToString() + "\"");
etags.AddOrUpdate(key, etag, (k, val) => etag);
}
context.Response.Headers.ETag = etag;
SetCacheControl(context.Response);
}
private static void SetCacheControl(HttpResponseMessage response)
{
response.Headers.CacheControl = new CacheControlHeaderValue()
{
MaxAge = TimeSpan.FromSeconds(60),
MustRevalidate = true,
Private = true
};
}
private static string GetKey(HttpRequestMessage request)
{
return request.RequestUri.ToString();
}
}
The above code create an attribute class to manage ETag. So on the first request, it will create a new E-Tag and for the subsequent request it will check whether any ETag is existed. If so, it will generate Not Modified HTTP Status and return back to client.
My problem is, I want to create a new ETag if there are changes in my user list, ex. a new user is added, or an existing user is deleted. and append it with the response. This can be tracked by the userList variable.
Currently, the ETag received from client and server are same from every second request, so in this case it will always generate Not Modified status, while I want it when actually nothing changed.
Can anyone guide me in this direction?

My requirement was to cache my web api JSON responses... And all the solutions provided don't have an easy "link" to where the data is generated - ie in the Controller...
So my solution was to create a wrapper "CacheableJsonResult" which generated a Response, and then added the ETag to the header. This allows a etag to be passed in when the controller method is generated and wants to return the content...
public class CacheableJsonResult<T> : JsonResult<T>
{
private readonly string _eTag;
private const int MaxAge = 10; //10 seconds between requests so it doesn't even check the eTag!
public CacheableJsonResult(T content, JsonSerializerSettings serializerSettings, Encoding encoding, HttpRequestMessage request, string eTag)
:base(content, serializerSettings, encoding, request)
{
_eTag = eTag;
}
public override Task<HttpResponseMessage> ExecuteAsync(System.Threading.CancellationToken cancellationToken)
{
Task<HttpResponseMessage> response = base.ExecuteAsync(cancellationToken);
return response.ContinueWith<HttpResponseMessage>((prior) =>
{
HttpResponseMessage message = prior.Result;
message.Headers.ETag = new EntityTagHeaderValue(String.Format("\"{0}\"", _eTag));
message.Headers.CacheControl = new CacheControlHeaderValue
{
Public = true,
MaxAge = TimeSpan.FromSeconds(MaxAge)
};
return message;
}, cancellationToken);
}
}
And then, in your controller - return this object:
[HttpGet]
[Route("results/{runId}")]
public async Task<IHttpActionResult> GetRunResults(int runId)
{
//Is the current cache key in our cache?
//Yes - return 304
//No - get data - and update CacheKeys
string tag = GetETag(Request);
string cacheTag = GetCacheTag("GetRunResults"); //you need to implement this map - or use Redis if multiple web servers
if (tag == cacheTag )
return new StatusCodeResult(HttpStatusCode.NotModified, Request);
//Build data, and update Cache...
string newTag = "123"; //however you define this - I have a DB auto-inc ID on my messages
//Call our new CacheableJsonResult - and assign the new cache tag
return new CacheableJsonResult<WebsiteRunResults>(results, GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings, System.Text.UTF8Encoding.Default, Request, newTag);
}
}
private static string GetETag(HttpRequestMessage request)
{
IEnumerable<string> values = null;
if (request.Headers.TryGetValues("If-None-Match", out values))
return new EntityTagHeaderValue(values.FirstOrDefault()).Tag;
return null;
}
You need to define how granular to make your tags; my data is user-specific, so I include the UserId in the CacheKey (etag)

a good solution for ETag and in ASP.NET Web API is to use CacheCow . A good article is here.
It's easy to use and you don't have to create a custom Attribute.
Have fun
.u

I found CacheCow very bloated for what it does, if the only reason is, to lower the amount of data transfered, you might want to use something like this:
public class EntityTagContentHashAttribute : ActionFilterAttribute
{
private IEnumerable<string> _receivedEntityTags;
private readonly HttpMethod[] _supportedRequestMethods = {
HttpMethod.Get,
HttpMethod.Head
};
public override void OnActionExecuting(HttpActionContext context) {
if (!_supportedRequestMethods.Contains(context.Request.Method))
throw new HttpResponseException(context.Request.CreateErrorResponse(HttpStatusCode.PreconditionFailed,
"This request method is not supported in combination with ETag."));
var conditions = context.Request.Headers.IfNoneMatch;
if (conditions != null) {
_receivedEntityTags = conditions.Select(t => t.Tag.Trim('"'));
}
}
public override void OnActionExecuted(HttpActionExecutedContext context)
{
var objectContent = context.Response.Content as ObjectContent;
if (objectContent == null) return;
var computedEntityTag = ComputeHash(objectContent.Value);
if (_receivedEntityTags.Contains(computedEntityTag))
{
context.Response.StatusCode = HttpStatusCode.NotModified;
context.Response.Content = null;
}
context.Response.Headers.ETag = new EntityTagHeaderValue("\"" + computedEntityTag + "\"", true);
}
private static string ComputeHash(object instance) {
var cryptoServiceProvider = new MD5CryptoServiceProvider();
var serializer = new DataContractSerializer(instance.GetType());
using (var memoryStream = new MemoryStream())
{
serializer.WriteObject(memoryStream, instance);
cryptoServiceProvider.ComputeHash(memoryStream.ToArray());
return String.Join("", cryptoServiceProvider.Hash.Select(c => c.ToString("x2")));
}
}
}
No need for setting up anything, set and forget. The way i like it. :)

I like the answer which was provided by #Viezevingertjes. It is the most elegant and "No need for setting up anything" approach is very convenient. I like it too :)
However I think it has a few drawbacks:
The whole OnActionExecuting() method and storing ETags in _receivedEntityTags is unnecessary because the Request is available inside the OnActionExecuted method as well.
Only works with ObjectContent response types.
Extra work load because of the serialization.
Also it was not part of the question and nobody mentioned it. But ETag should be used for Cache validation. Therefore it should be used with Cache-Control header so clients don't even have to call the server until the cache expires (it can be very short period of time depends on your resource). When the cache expired then client makes a request with ETag and validate it. For more details about caching see this article.
So that's why I decided to pimp it up a little but. Simplified filter no need for OnActionExecuting method, works with Any response types, no Serialization. And most importantly adds CacheControl header as well. It can be improved e.g. with Public cache enabled, etc... However I strongly advise you to understand caching and modify it carefully. If you use HTTPS and the endpoints are secured then this setup should be fine.
/// <summary>
/// Enables HTTP Response CacheControl management with ETag values.
/// </summary>
public class ClientCacheWithEtagAttribute : ActionFilterAttribute
{
private readonly TimeSpan _clientCache;
private readonly HttpMethod[] _supportedRequestMethods = {
HttpMethod.Get,
HttpMethod.Head
};
/// <summary>
/// Default constructor
/// </summary>
/// <param name="clientCacheInSeconds">Indicates for how long the client should cache the response. The value is in seconds</param>
public ClientCacheWithEtagAttribute(int clientCacheInSeconds)
{
_clientCache = TimeSpan.FromSeconds(clientCacheInSeconds);
}
public override async Task OnActionExecutedAsync(HttpActionExecutedContext actionExecutedContext, CancellationToken cancellationToken)
{
if (!_supportedRequestMethods.Contains(actionExecutedContext.Request.Method))
{
return;
}
if (actionExecutedContext.Response?.Content == null)
{
return;
}
var body = await actionExecutedContext.Response.Content.ReadAsStringAsync();
if (body == null)
{
return;
}
var computedEntityTag = GetETag(Encoding.UTF8.GetBytes(body));
if (actionExecutedContext.Request.Headers.IfNoneMatch.Any()
&& actionExecutedContext.Request.Headers.IfNoneMatch.First().Tag.Trim('"').Equals(computedEntityTag, StringComparison.InvariantCultureIgnoreCase))
{
actionExecutedContext.Response.StatusCode = HttpStatusCode.NotModified;
actionExecutedContext.Response.Content = null;
}
var cacheControlHeader = new CacheControlHeaderValue
{
Private = true,
MaxAge = _clientCache
};
actionExecutedContext.Response.Headers.ETag = new EntityTagHeaderValue($"\"{computedEntityTag}\"", false);
actionExecutedContext.Response.Headers.CacheControl = cacheControlHeader;
}
private static string GetETag(byte[] contentBytes)
{
using (var md5 = MD5.Create())
{
var hash = md5.ComputeHash(contentBytes);
string hex = BitConverter.ToString(hash);
return hex.Replace("-", "");
}
}
}
Usage e.g: with 1 min client side caching:
[ClientCacheWithEtag(60)]

Seems to be a nice way to do it:
public class CacheControlAttribute : System.Web.Http.Filters.ActionFilterAttribute
{
public int MaxAge { get; set; }
public CacheControlAttribute()
{
MaxAge = 3600;
}
public override void OnActionExecuted(HttpActionExecutedContext context)
{
if (context.Response != null)
{
context.Response.Headers.CacheControl = new CacheControlHeaderValue
{
Public = true,
MaxAge = TimeSpan.FromSeconds(MaxAge)
};
context.Response.Headers.ETag = new EntityTagHeaderValue(string.Concat("\"", context.Response.Content.ReadAsStringAsync().Result.GetHashCode(), "\""),true);
}
base.OnActionExecuted(context);
}
}