Windows 8 Periodic Tile Notification Web API (accompanies blog post at http://blogs.msdn.com/b/jimoneil/archive/2012/08/30/windows-8-notifications-using-azure-for-periodic-notifications.aspx)

periodic.cs

/*
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All rights reserved.
Licensed under the Microsoft Limited Public License (the “License”); you may not
use this file except in compliance with the License.
You may obtain a copy of the License at http://msdn.microsoft.com/en-us/cc300389.




THIS CODE IS PROVIDED ON AN *AS IS* BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED WARRANTIES OR CONDITIONS
OF TITLE, FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABLITY OR NON-INFRINGEMENT.
win
See the Microsoft Limited Public License (Ms-LPL) for specific language governing
permissions and limitations under the License.
*/

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

namespace TileServiceRole.Controllers
{
    public class TilesController : ApiController
    {
        // /api/tiles/<tilename>
        public HttpResponseMessage Get(String id)
        {
            // set cloud storage credentials
            var client = new Microsoft.WindowsAzure.StorageClient.CloudBlobClient(
                "http://AZURE_ACCOUNT_NAME.blob.core.windows.net",
                new Microsoft.WindowsAzure.StorageCredentialsAccountAndKey(
                    "AZURE_ACCOUNT_NAME",
                    "AZURE_ACCOUNT_KEY"
                    )
            );

            // create HTTP response
            var response = new HttpResponseMessage();
            try
            {
                // get XML template from storage
                var xml = client.GetBlobReference(id.Replace("_", "/")).DownloadText();

                // format response
                response.StatusCode = System.Net.HttpStatusCode.OK;
                response.Content = new StringContent(xml);
                response.Content.Headers.ContentType =
                    new System.Net.Http.Headers.MediaTypeHeaderValue("text/xml");

                // set expires header to invalidate tile when content is obsolete
                response.Content.Headers.Add("X-WNS-Expires", GetExpiryTime().ToString("R"));
            }
            catch (Exception e)
            {
                // send a 400 if there's a problem
                response.StatusCode = System.Net.HttpStatusCode.BadRequest;
                response.Content = new StringContent(e.Message + "\r\n" + e.StackTrace);
                response.Content.Headers.ContentType =
                    new System.Net.Http.Headers.MediaTypeHeaderValue("text/plain");
            }

            // return response
            return response;
        }

        private DateTime GetExpiryTime()
        {
            Int32 TimeZoneOffset = -4;  // EDT offset from UTC

            // get representation of local time for restaurant
            var requestLocalTime = DateTime.UtcNow.AddHours(TimeZoneOffset);

            // if request is hitting before 9 a.m., information is stale
            if (requestLocalTime.Hour <= 8)
                return DateTime.UtcNow.AddDays(-1);

            // else, set tile to expire at midnight local time
            else
            {
                var minutesUntilExpiry = (24 - requestLocalTime.Hour) * 60 - requestLocalTime.Minute;
                return DateTime.UtcNow.AddMinutes(minutesUntilExpiry);
            }
        }
    }
}