ASP.NET Core: Using Assembly Build Date For Cache Busting

ASP.NET Core contains a variety of useful Tag Helpers to enable server-side code to participate in creating and rendering HTML elements in our Views. One Tag Helper, in particular, has the ability to cache bust links to static resources such as Image, CSS and JavaScript by appending an asp-append-version="true" attribute.

The asp-append-version attribute automatically adds a version number to the file name using a SHA256 hashing algorithm, so whenever the file is updated, the server generates a new unique version. For a deeper understanding on how ASP.NET Core performs this piece of functionality, give the following StackOverflow post a read: How does javascript version (asp-append-version) work in ASP.NET Core MVC?.

This approach works perfectly if you're linking to your static resources using the relevant HTML tag, for example img, script or link. In my scenario, I'm using a JavaScript library called LabJS - a dynamic script loader that gives the ability to control the loading and execution of different plugins. For example:

<script>
  $LAB
  .script("http://remote.tld/jquery.js").wait()
  .script("/local/plugin1.jquery.js")
  .script("/local/plugin2.jquery.js").wait()
  .script("/local/init.js").wait(function(){
      initMyPage();
  });
</script>

I need to be able to append a query string parameter to one of the JavaScript file references. One thing that came to mind was to use the applications last build-time as the cache busting value. Whenever the application is updated, this value will automatically be updated so no manual intervention is required.

I found code examples from meziantou.net that demonstrated various approaches to acquiring an applications build date. I modified the "Linker timestamp" example to return a Unix timestamp in a newly created class called AssemblyUtils.

public class AssemblyUtils
{
    #region Properties

    public int UnixTimestamp { get; set; }

    #endregion

    /// <summary>
    /// Get timestamp in Unix seconds for the last build.
    /// </summary>
    /// <returns></returns>
    public static int GetBuildTimestamp()
    {
        const int peHeaderOffset = 60;
        const int timestampOffset = 8;

        byte[] bytes = new byte[2048];

        using (FileStream file = new FileStream(Assembly.GetExecutingAssembly().Location, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
            file.Read(bytes, 0, bytes.Length);

        int headerPos = BitConverter.ToInt32(bytes, peHeaderOffset);
        int unixTime = BitConverter.ToInt32(bytes, headerPos + timestampOffset);

        return unixTime;
    }
}

The code will only return the Assembly information if your Visual Studio .csproj file (from version 15.4 onwards) includes the following setting within the <PropertyGroup> settings:

<Deterministic>False</Deterministic>

It would be a waste to constantly call the GetBuildTimestamp() method to acquire assembly information directly within the page View, when the most ideal approach would be to make this call once on application startup.

public void ConfigureServices(IServiceCollection services)
{
    #region Assembly Utils - Build Time

    Action<AssemblyUtils> assemblyBuildOptions = (opt =>
    {
        opt.UnixTimestamp = AssemblyUtils.GetBuildTimestamp();
    });

    services.Configure(assemblyBuildOptions);
    services.AddSingleton(resolver => resolver.GetRequiredService<IOptions<AssemblyUtils>>().Value);

    #endregion
}

We can access the build timestamp value using Dependency Injection within a base controller that gets inherited by all controllers.

public class BaseController : Controller
{
    private int _buildTimetamp { get; set; }

    public BaseController(AssemblyUtils assemblyUtls)
    {
        _buildTimetamp = assemblyUtls.UnixTimestamp;
    }

    public override void OnActionExecuting(ActionExecutingContext context)
    {
        base.OnActionExecuting(context);

        // Assign build timestamp to a View Bag.
        ViewBag.CacheBustingValue = _buildTimetamp;
    }
}

The timestamp is assigned to a ViewBag that can then be accessed at View level.

<script>
  $LAB
  .script("http://remote.tld/jquery.js").wait()
  .script("/local/plugin1.jquery.js")
  .script("/local/plugin2.jquery.js").wait()
  .script("/local/init.js?v=@ViewBag.CacheBustingValue").wait(function(){
      initMyPage();
  });
</script>

This will result in the following output:

<script>
  $LAB
  .script("http://remote.tld/jquery.js").wait()
  .script("/local/plugin1.jquery.js")
  .script("/local/plugin2.jquery.js").wait()
  .script("/local/init.js?v=1609610821").wait(function(){
      initMyPage();
  });
</script>

ASP.NET Core: System.FormatException: Could not parse the JSON file

Another day, another ASP.NET Core error... This time relating to JSON not being parsable. Like the error I posted yesterday, this was another strange one as it only occurred within an Azure environment.

Let me start by showing the file compilation error:

Application '/LM/W3SVC/144182150/ROOT' with physical root 'D:\home\site\wwwroot\' hit unexpected managed exception, exception code = '0xe0434352'. First 30KB characters of captured stdout and stderr logs:
Unhandled exception. System.FormatException: Could not parse the JSON file.
 ---> System.Text.Json.JsonReaderException: '0x00' is an invalid start of a value. LineNumber: 0 | BytePositionInLine: 0.
   at System.Text.Json.ThrowHelper.ThrowJsonReaderException(Utf8JsonReader& json, ExceptionResource resource, Byte nextByte, ReadOnlySpan`1 bytes)
   at System.Text.Json.Utf8JsonReader.ConsumeValue(Byte marker)
   at System.Text.Json.Utf8JsonReader.ReadFirstToken(Byte first)
   at System.Text.Json.Utf8JsonReader.ReadSingleSegment()
   at System.Text.Json.Utf8JsonReader.Read()
   at System.Text.Json.JsonDocument.Parse(ReadOnlySpan`1 utf8JsonSpan, Utf8JsonReader reader, MetadataDb& database, StackRowStack& stack)
   at System.Text.Json.JsonDocument.Parse(ReadOnlyMemory`1 utf8Json, JsonReaderOptions readerOptions, Byte[] extraRentedBytes)
   at System.Text.Json.JsonDocument.Parse(ReadOnlyMemory`1 json, JsonDocumentOptions options)
   at System.Text.Json.JsonDocument.Parse(String json, JsonDocumentOptions options)
   at Microsoft.Extensions.Configuration.Json.JsonConfigurationFileParser.ParseStream(Stream input)
   at Microsoft.Extensions.Configuration.Json.JsonConfigurationFileParser.Parse(Stream input)
   at Microsoft.Extensions.Configuration.Json.JsonConfigurationProvider.Load(Stream stream)
   --- End of inner exception stack trace ---
   at Microsoft.Extensions.Configuration.Json.JsonConfigurationProvider.Load(Stream stream)
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.Load(Boolean reload)
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.HandleException(ExceptionDispatchInfo info)
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.Load(Boolean reload)
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.Load()
   at Microsoft.Extensions.Configuration.ConfigurationRoot..ctor(IList`1 providers)
   at Microsoft.Extensions.Configuration.ConfigurationBuilder.Build()
   at Microsoft.Extensions.Logging.AzureAppServices.SiteConfigurationProvider.GetAzureLoggingConfiguration(IWebAppContext context)
   at Microsoft.Extensions.Logging.AzureAppServicesLoggerFactoryExtensions.AddAzureWebAppDiagnostics(ILoggingBuilder builder, IWebAppContext context)
   at Microsoft.Extensions.Logging.AzureAppServicesLoggerFactoryExtensions.AddAzureWebAppDiagnostics(ILoggingBuilder builder)
   at Microsoft.AspNetCore.Hosting.AppServicesWebHostBuilderExtensions.<>c.<UseAzureAppServices>b__0_0(ILoggingBuilder builder)
   at Microsoft.Extensions.DependencyInjection.LoggingServiceCollectionExtensions.AddLogging(IServiceCollection services, Action`1 configure)
   at Microsoft.AspNetCore.Hosting.WebHostBuilderExtensions.<>c__DisplayClass8_0.<ConfigureLogging>b__0(IServiceCollection collection)
   at Microsoft.AspNetCore.Hosting.HostingStartupWebHostBuilder.<>c__DisplayClass6_0.<ConfigureServices>b__0(WebHostBuilderContext context, IServiceCollection services)
   at Microsoft.AspNetCore.Hosting.HostingStartupWebHostBuilder.ConfigureServices(WebHostBuilderContext context, IServiceCollection services)
   at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.<.ctor>b__5_2(HostBuilderContext context, IServiceCollection services)
   at Microsoft.Extensions.Hosting.HostBuilder.CreateServiceProvider()
   at Microsoft.Extensions.Hosting.HostBuilder.Build()
   at Site.Web.Program.Main(String[] args) in C:\Development\surinder-main-website\Site.Web\Program.cs:line 11

Process Id: 2588.
File Version: 13.1.20169.6. Description: IIS ASP.NET Core Module V2 Request Handler. Commit: 62c098bc170f50feca15916e81cb7f321ffc52ff

The application was not consuming any form of JSON as part of its main functionality. The only JSON being used were three variations of appsettings.json - each one for development, staging and production. So this had to be the source of the issue. The error message also confirmed this as Program.cs was referenced and it’s at this point where the application startup code is run.

My first thought was I must have forgotten a comma or missing a closing quote for one of my values. After running the JSON through a validator, it passed with flying colours.

Solution

After some investigation, the issue was caused by incorrect encoding of the file. All the appsettings.json files were set to "UTF-8" and as a result, possibly causing some metadata to be added stopping the application from reading the files. Once this was changed to "UTF-8-BOM" through Notepad++ everything worked fine.

ASP.NET Core: Failed to start application '/LM/W3SVC/####/ROOT', ErrorCode '0x8007023e'.

You gotta love .NET core compilation errors! They provide the most ambiguous error messages known to man. I have noticed the error message and accompanying error code could be caused by a multitude of factors. This error is no different so I’ll make my contribution, hoping this may help someone else.

The error in question occurred really randomly whilst deploying a minor HTML update to a .NET Core site I was hosting within an Azure Web App. It couldn’t have been a simpler release - change to some markup in a View. When the site loaded, I was greeted with the following error:

Failed to start application '/LM/W3SVC/####/ROOT', ErrorCode '0x8007023e’.

I was able to get some further information about the error from the Event Log:

Application 'D:\home\site\wwwroot\' failed to start. Exception message:
Executable was not found at 'D:\home\site\wwwroot\%LAUNCHER_PATH%.exe'
Process Id: 10848.
File Version: 13.1.19331.0. Description: IIS ASP.NET Core Module V2.

The error could only be reproduced on Azure and not within my local development and staging environments. I created a new deployment slot to check if somehow my existing slot got corrupted. Unfortunately, this made no difference. The strange this is, the application was working completely fine up until this release. It's still unknown to me what could have happened for this error to occur all of a sudden.

Solution

It would seem that no one else on the planet experienced this issue when Googling the error message and error code. After a lot of fumbling around, the fix ended up being relatively straight-forward. The detail provided by the Event Log pointed me in the right direction and the clue was in the %LAUNCHER_PATH% placeholder. The %LAUNCHER_PATH% placeholder is set in the web.config and this is normally replaced when the application is run in Visual Studio or IIS.

In Azure, both %LAUNCHER_PATH% and %LAUNCHER_ARGS% variables need to be explicitly set. The following line in the web.config needs to be changed from:

<aspNetCore processPath="%LAUNCHER_PATH%" arguments="%LAUNCHER_ARGS%" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" forwardWindowsAuthToken="false" startupTimeLimit="3600" requestTimeout="23:00:00" hostingModel="InProcess">

To:

<aspNetCore processPath=".\Site.Web.exe" arguments="" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" forwardWindowsAuthToken="false" startupTimeLimit="3600" requestTimeout="23:00:00" hostingModel="InProcess">

The processPath is now pointing to the executable generated by the project. In this case, "Site.Web.exe". Also, since no arguments are being parsed in my build, the arguments attribute is left empty. When you push up your next release, the error should be rectified.

As a side note, there was one thing recommended to me by Azure support regarding my publish settings in Visual Studio. It was recommended that I should set the deployment mode from "Framework-Dependent" to "Self-Contained". This will ensure the application will always run in its current framework version on the off-chance framework changes happen at an Azure level.

ASP.NET Core: Making Your Project Production Ready For Deployment

I decided to write this post to act primarily as a reminder to myself for when I'm publishing an ASP.NET Core project ready for a production environment. Most of the ASP.NET Core projects I'm currently working on are based on pre-existing client or platform-based boilerplates and when taking these on, they vary in quality and a result, some key project settings are just not implemented.

I will be covering the following areas:

  • Ensuring the correct environment variable is set for your publish profile.
  • Setting custom error pages.
  • Switching between development and production appsetting.json files.

Setting Environment In Publish Profile

After you have created the publish profile, update the .pubxml file (found under the "/Properties/PublishProfiles" directory within your project) and add a EnvironmentName variable:

<PropertyGroup>
    <EnvironmentName>Production</EnvironmentName>
</PropertyGroup>

This variable is very much key to the whole operation. Without it, the project will be stuck in development mode and the sections, listed below, will not work.

Setting Custom Error Pages

We are only interested in seeing a custom error page when in production mode. To do this, we need to:

  1. Update the Startup.cs file to enable status code error pages.
  2. Create an error controller to render the custom error pages.

Startup.cs

To serve our custom error page, we need to declare the route using the app.UseStatusCodePagesWithReExecute() method. This method includes a placeholder {0}, which will be replaced with the status code integer - 404, 500, etc. We can then render different views depending on the error code returned. For example:

  • /Error/404
  • /Error/500
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    // Render full blown exception only if in development mode.
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseStatusCodePagesWithReExecute("/Error/{0}");
        app.UseHsts();
    }
}

Error Controller

Based on the status code returned, different views can be rendered.

public class ErrorController : Controller
{
    [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
    [Route("/Error/{statusCode}")]
    public ViewResult Status(int statusCode)
    {
        if (statusCode == StatusCodes.Status404NotFound)
        {
            return View("~/Views/Error/NotFound.cshtml");
        }
        else
        {
            return View("~/Views/Error/GeneralError.cshtml");
        }
    }
}

Web.config

Being a .NET Core project, there is one area that is easily overlooked as we're so focused on the Startup.cs and appsettings.json files - that is the web.config. We need to ensure the environment variable is set here also by adding the following:

<environmentVariables>
    ...
    <environmentVariable name="ASPNETCORE_ENVIRONMENT" value="Production" />
    ...
</environmentVariables>

If the "ASPNETCORE_ENVIRONMENT" value isn't set correctly at this point, this will cause issues/inconsistencies globally.

Switching To appsetting.production.json

You've probably noticed that your ASP.NET Core project contains three appsettings.json files - each one for your environment:

  • appsettings.json
  • appsettings.development.json
  • appsettings.production.json

If your ASP.NET Core project version is less than 3.0, you can switch between each appsettings.json file by adding the following code to your Startup.cs file:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    IConfigurationBuilder configBuilder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", true, true)
        .AddJsonFile($"appsettings.{env.EnvironmentName}.json", true)
        .AddEnvironmentVariables();

    Configuration = configBuilder.Build();
}

However, if running on ASP.NET Core 3.0+, you will need to use WebHost.CreateDefaultBuilder(args) method that will be added to the Programs.cs file.

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .UseContentRoot(Directory.GetCurrentDirectory())
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

The CreateDefaultBuilder performs the following environment-related tasks (to name a few):

  • Sets the content root to the path returned by Directory.GetCurrentDirectory().
  • Loads host configuration from environment variables prefixed with ASPNETCORE_ (for example, ASPNETCORE_ENVIRONMENT).
  • Loads application configuration settings in the following order, starting from appsettings.json and then appsettings.{Environment}.json.

As you can see, from ASP.NET Core 3.0 onwards, quite a lot is being done for you from such a minimal amount of code.

Running .Net Core Site From A Subdirectory In Visual Studio

I have some websites on a production environment that need to be run from within a subdirectory and in order to carry out proper testing during development to ensure all references to CSS, JS and images files work. By default, when a .NET Core site is run from Visual Studio it will always start from the root, resulting in a broken looking page.

From .NET Core 2.0, within your Startup.cs file, you can set a sub-directory using the UsePathBase extension within the Configure method:

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    if (env.IsDevelopment())
        app.UsePathBase("/mydirectory");
}

Now when the site runs, it’ll be accessible from /mydirectory. In my code example, I only want to set the path base if it development mode. When released to production, the path will be configured at IIS level.

The only annoyance is when you run the site in Visual Studio, it will still start at the root and not at your newly declared subdirectory. I was surprised to see that the site is still accessible at the root, when you would expect the root path to be disabled or even greeted with a 404 response.

On first glance, I thought there was a bug in my path base declaration and perhaps I missed something. After viewing a closed Github issue raised back in 2017, it was stated that this is in fact the intended functionality. This is a minor bug bear I can live with.

ASP.NET Core - Get Page Title By URL

To make it easy for a client to add in related links to pages like a Blog Post or Article, I like implementing some form of automation so there is one less thing to content manage. For a Kentico Cloud project, I took this very approach. I created a UrlHelper class that will carry out the following:

  • Take in an absolute URL.
  • Read the markup of the page.
  • Selects the title tag using Regex.
  • Remove the site name prefix from title text.
using Microsoft.Extensions.Caching.Memory;
using MyProject.Models.Site;
using System;
using System.IO;
using System.Linq;
using System.Net;
using System.Text.RegularExpressions;

namespace MyProject.Helpers
{
    public class UrlHelper
    {
        private static IMemoryCache _cache;

        public UrlHelper(IMemoryCache memCache)
        {
            _cache = memCache;
        }

        /// <summary>
        /// Returns the a title and URL of the link directly from a page.
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        public PageLink GetPageTitleFromUrl(string url)
        {
            if (!string.IsNullOrEmpty(url))
            {
                if (_cache.TryGetValue(url, out PageLink page))
                {
                    return page;
                }
                else
                {
                    using (WebClient client = new WebClient())
                    {
                        try
                        {
                            Stream stream = client.OpenRead(url);
                            StreamReader streamReader = new StreamReader(stream, System.Text.Encoding.GetEncoding("UTF-8"));

                            // Get contents of the page.
                            string pageHtml = streamReader.ReadToEnd();

                            if (!string.IsNullOrEmpty(pageHtml))
                            {
                                // Get the title.
                                string title = Regex.Match(pageHtml, @"\<title\b[^>]*\>\s*(?<Title>[\s\S]*?)\</title\>", RegexOptions.IgnoreCase).Groups["Title"].Value;

                                if (!string.IsNullOrEmpty(title))
                                {
                                    if (title.Contains("|"))
                                        title = title.Split("|").First();
                                    else if (title.Contains(":"))
                                        title = title.Split(":").First();

                                    PageLink pageLink = new PageLink
                                    {
                                        PageName = title,
                                        PageUrl = url
                                    };

                                    _cache.Set(url, pageLink, DateTimeOffset.Now.AddHours(12));

                                    page = pageLink;
                                }
                            }

                            // Cleanup.
                            stream.Flush();
                            stream.Close();
                            client.Dispose();
                        }
                        catch (WebException e)
                        {
                            throw e;
                        }
                    }
                }

                return page;
            }
            else
            {
                return null;
            }
        }
    }
}

The method returns a PageLink object:

namespace MyProject.Models.Site
{
    public class PageLink
    {
        public string PageName { get; set; }
        public string PageUrl { get; set; }
    }
}

From an efficiency standpoint, I cache the process for 12 hours as going through the process of reading the markup of a page can be quite expensive if there is a lot of HTML.

ASP.NET Core - Render Partial View To String Outside Controller Context

When building MVC websites, I cannot get through a build without using a method to convert a partial view to a string. I have blogged about this in the past and find this approach so useful especially when carrying out heavy AJAX processes. Makes the whole process of maintaining and outputting markup dynamically a walk in the park.

I've been dealing with many more ASP.NET Core builds and migrating over the RenderPartialViewToString() extension I developed previously was not possible. Instead, I started using the approach detailed in the following StackOverflow post: Return View as String in .NET Core. Even though the approach was perfectly acceptable and did the job nicely, I noticed I had to make one key adjustment - allow for views outside controller context.

The method proposed in the StackOverflow post uses ViewEngine.FindView(), from what I gather only returns a view within the current controller context. I added a check that will use ViewEngine.GetView() if a path of the view ends with a ".cshtml" which is normally the approach used when you refer to a view from a different controller by using a relative path.

public static class ControllerExtensions
{
    /// <summary>
    /// Render a partial view to string.
    /// </summary>
    /// <typeparam name="TModel"></typeparam>
    /// <param name="controller"></param>
    /// <param name="viewNamePath"></param>
    /// <param name="model"></param>
    /// <returns></returns>
    public static async Task<string> RenderViewToStringAsync<TModel>(this Controller controller, string viewNamePath, TModel model)
    {
        if (string.IsNullOrEmpty(viewNamePath))
            viewNamePath = controller.ControllerContext.ActionDescriptor.ActionName;

        controller.ViewData.Model = model;

        using (StringWriter writer = new StringWriter())
        {
            try
            {
                IViewEngine viewEngine = controller.HttpContext.RequestServices.GetService(typeof(ICompositeViewEngine)) as ICompositeViewEngine;

                ViewEngineResult viewResult = null;

                if (viewNamePath.EndsWith(".cshtml"))
                    viewResult = viewEngine.GetView(viewNamePath, viewNamePath, false);
                else
                    viewResult = viewEngine.FindView(controller.ControllerContext, viewNamePath, false);

                if (!viewResult.Success)
                    return $"A view with the name '{viewNamePath}' could not be found";

                ViewContext viewContext = new ViewContext(
                    controller.ControllerContext,
                    viewResult.View,
                    controller.ViewData,
                    controller.TempData,
                    writer,
                    new HtmlHelperOptions()
                );

                await viewResult.View.RenderAsync(viewContext);

                return writer.GetStringBuilder().ToString();
            }
            catch (Exception exc)
            {
                return $"Failed - {exc.Message}";
            }
        }
    }

    /// <summary>
    /// Render a partial view to string, without a model present.
    /// </summary>
    /// <typeparam name="TModel"></typeparam>
    /// <param name="controller"></param>
    /// <param name="viewNamePath"></param>
    /// <returns></returns>
    public static async Task<string> RenderViewToStringAsync(this Controller controller, string viewNamePath)
    {
        if (string.IsNullOrEmpty(viewNamePath))
            viewNamePath = controller.ControllerContext.ActionDescriptor.ActionName;
            
        using (StringWriter writer = new StringWriter())
        {
            try
            {
                IViewEngine viewEngine = controller.HttpContext.RequestServices.GetService(typeof(ICompositeViewEngine)) as ICompositeViewEngine;

                ViewEngineResult viewResult = null;

                if (viewNamePath.EndsWith(".cshtml"))
                    viewResult = viewEngine.GetView(viewNamePath, viewNamePath, false);
                else
                    viewResult = viewEngine.FindView(controller.ControllerContext, viewNamePath, false);

                if (!viewResult.Success)
                    return $"A view with the name '{viewNamePath}' could not be found";

                ViewContext viewContext = new ViewContext(
                    controller.ControllerContext,
                    viewResult.View,
                    controller.ViewData,
                    controller.TempData,
                    writer,
                    new HtmlHelperOptions()
                );

                await viewResult.View.RenderAsync(viewContext);

                return writer.GetStringBuilder().ToString();
            }
            catch (Exception exc)
            {
                return $"Failed - {exc.Message}";
            }
        }
    }

}

Quick Example

As you can see from my quick example below, the Home controller is using the RenderViewToStringAsync() when calling:

  • A view from another controller, where a relative path to the view is used.
  • A view from within the realms of the current controller and the name of the view alone can be used.
public class HomeController : Controller
{
    public async Task<IActionResult> Index()
    {
        NewsListItem newsItem = GetSingleNewsItem(); // Get a single news item.

        string viewFromAnotherController = await this.RenderViewToStringAsync("/Views/News/_NewsList.cshtml", newsItem);
        string viewFromCurrentController = await this.RenderViewToStringAsync("_NewsListHome", newsItem);

        return View();
    }
}

ASP.NET Core - HTTP Error 502.5 Process Failure

It seems whenever I work on an ASP.NET Core website, I always seem to get the most unhelpful error when deploying to production:

HTTP Error 502.5 - Process Failure

I have no problem running the ASP.NET Core site whilst developing from within a local environment.

From past experience, the HTTP 502.5 error generally happens for the following reasons:

  1. The ASP.NET Core framework is not installed or your site is running the incorrect version.
  2. Website project incorrectly published.
  3. Potential configuration issue at code level.

Generally when you successfully publish a deployable version of your site, you'd expect it to just work. To get around the deployment woes, the solution is to modify your .csproj file by adding the following setting:

<PropertyGroup>
   <PublishWithAspNetCoreTargetManifest>false</PublishWithAspNetCoreTargetManifest>
</PropertyGroup>

Once this setting has been added, you'll notice when your site is re-published a whole bunch of new DLL files are now present, forming part of all the dependencies a site requires. It's strange a normal publish does not do this already and what's even stranger is I have a different .NET Core site running without having to take this approach.

For any new .NET Core sites I work on, I will be using approach going forward.

Useful Links

ASP.NET Core MVC Numbered Pagination

This is a relatively simple pagination that will only be shown if there are enough items of data to paginate through. The user will have the ability to paginate by either clicking on the "Previous" and "Next" links as well as clicking on the individual page numbers from within the pagination.

I created a PaginationHelper.CreatePagination() method that carries out all the paging calculations and outputs the pagination as an unordered list. The method requires the following parameters:

  • currentPage - the current page number being viewed.
  • totalNumberOfRecords - the total count of records from your dataset in order to determine how many pages should be displayed.
  • pageRequest - the current request from by passing in "HttpContext.Request" to get the page URL.
  • noOfPageLinks - the number of page numbers that should be shown. For example "1, 2, 3, 4".
  • pageSize - the number of items will be shown per page.
using Microsoft.AspNetCore.Http;
using System;
using System.Text;

namespace MyProject.Helpers
{
    public static class PaginationHelper
    {
        /// <summary>
        /// Renders pagination used in listing pages.
        /// </summary>
        /// <param name="currentPage"></param>
        /// <param name="totalNumberOfRecords"></param>
        /// <param name="pageRequest">Current page request used to get the URL path of the page.</param>
        /// <param name="noOfPagesLinks">Number of pagination numbers to show.</param>
        /// <param name="pageSize"></param>
        /// <returns></returns>
        public static string CreatePagination(int currentPage, int totalNumberOfRecords, HttpRequest pageRequest, int noOfPagesLinks = 5, int pageSize = 10)
        {
            StringBuilder paginationHtml = new StringBuilder();

            // Only render the pagination markup if the total number of records is more than our page size.
            if (totalNumberOfRecords > pageSize)
            {
                #region Pagination Calculations

                int amountOfPages = (int)(Math.Ceiling(totalNumberOfRecords / Convert.ToDecimal(pageSize)));

                int startPage = currentPage;

                if (startPage == 1 || startPage == 2 || amountOfPages < noOfPagesLinks)
                    startPage = 1;
                else
                    startPage -= 2;

                int maxPage = startPage + noOfPagesLinks;

                if (amountOfPages < maxPage)
                    maxPage = Convert.ToInt32(amountOfPages) + 1;

                if (maxPage - startPage != noOfPagesLinks && maxPage > noOfPagesLinks)
                    startPage = maxPage - noOfPagesLinks;

                int previousPage = currentPage - 1;
                if (previousPage < 1)
                    previousPage = 1;

                int nextPage = currentPage + 1;

                #endregion

                #region Get Current Path

                // Get current path.
                string path = pageRequest.Path.ToString();

                int pos = path.LastIndexOf("/") + 1;

                // Get last route value.
                string lastRouteValue = path.Substring(pos, path.Length - pos).ToLower();

                // Removes page number from end of path if path contains a page number.
                if (lastRouteValue.StartsWith("page"))
                    path = path.Substring(0, path.LastIndexOf('/'));

                #endregion

                paginationHtml.Append("<ul>");

                if (currentPage > 1)
                    paginationHtml.Append($"<li><a href=\"{path}/Page{previousPage}\"><span>Previous page</span></a></li>");

                for (int i = startPage; i < maxPage; i++)
                {
                    // If the current page equals one of the pagination numbers, set active state.
                    if (i == currentPage)
                        paginationHtml.Append($"<li><a href=\"{path}/Page{i}\" class=\"is-active\"><span>{i}</span></a></li>");
                    else
                        paginationHtml.Append($"<li><a href=\"{path}/Page{i}\"><span>{i}</span></a></li>");
                }

                if (startPage + noOfPagesLinks < amountOfPages && maxPage > noOfPagesLinks || currentPage < amountOfPages)
                    paginationHtml.Append($"<li><a href=\"{path}/Page{nextPage}\"><span>Next page</span></a></li>");

                paginationHtml.Append("</ul>");

                return paginationHtml.ToString();
            }
            else
            {
                return string.Empty;
            }
        }
    }
}

The PaginationHelper.CreatePagination() method can then be used inside a controller where you would like to list your data as well as render the pagination. A simple example of this would be as follows:

/// <summary>
/// List all news articles.
/// </summary>
/// <param name="page"></param> 
/// <param name="pageSize"></param>
/// <returns></returns>
[Route("/Articles")]
[Route("/Articles/Page{page}")]
public ActionResult Index(int page = 1, int pageSize = 10)
{
    // Number of articles to skip.
    int skip = 0;
    if (page != 1)
        skip = (page - 1) * pageSize;

    // Get list of articles from my datasource.
    List<NewsArticle> articles = MyData.GetArticles().Skip(skip).Take(pageSize).ToList();

    //Render Pagination.
    ViewBag.PaginationHtml = PaginationHelper.CreatePagination(page, articles.Count, HttpContext.Request, pageSize: pageSize);

    return View(articles);
}

The pagination will be output to a ViewBag that can be called from within your view. I could have gone down a different route and developed Partial View along with the appropriate model. But for my use the method approach offers most flexibility, as I could have the option to either use this from within a controller or view.