Cannot find project info for ‘project’. This can indicate a missing project reference.

While trying out migrating a few old projects to ASP.NET Core 1.1, I stumbled upon this error when trying to the build the project.

For some reason VS does not inform about which specific references are missing. Imagine the following scenario:

Library A -> Library B

Library C -> Library A

If Library A expose any types from Library B, then C would require a direct reference to B. However, if A does not expose any of B’s types, then C can reference A without a direct reference to B.

So, VS 2017 will give you ‘Cannot find project info for (…)’ error when you don’t have the necessary direct references. Unlike previously, it will not inform which dependencies are required.

Edit: Seems the error occurs for several different issues. See more on this github issue.

Reverse Proxy in ASP.NET Web API – Part 2

At first I only needed the reverse proxy for a JSON rest API. Soon, however, it was expanded to also cover HTML content. Thus the below update to make sure any URLs in the HTML was replaced to correctly match the reverse proxy server and not the internal server:

public class ProxyHandler : DelegatingHandler
{
    private readonly string redirectUrl; 

    public ProxyHandler(string redirectUrl)
    {
        this.redirectUrl = redirectUrl;
    } 

    private async Task<HttpResponseMessage> RedirectRequest(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var redirectLocation = redirectUrl;
        var localPath = request.RequestUri.LocalPath.Replace("ExternalVirtualPath", "InternalVirtualPath"); 

        var client = new HttpClient(new HttpClientHandler() { AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate }); 

        var clonedRequest = await HttpRequestMessageExtensions.CloneHttpRequestMessageAsync(request); 

        clonedRequest.RequestUri = new Uri(redirectLocation + localPath); 

        var httpResponseMessage = await client.SendAsync(clonedRequest, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
        httpResponseMessage.Headers.Add("X-ReverseProxy", "true"); 

        if (httpResponseMessage.Content?.Headers?.ContentType != null)
        {
            if (httpResponseMessage.Content.Headers.ContentType.MediaType == "text/html")
            {
                var content = await httpResponseMessage.Content.ReadAsByteArrayAsync();
                var stringContent = Encoding.UTF8.GetString(content); 

                var newContent = stringContent.Replace("InternalVirtualPath", "ExternalVirtualPath");
                httpResponseMessage.Content = new StringContent(newContent, Encoding.UTF8, "text/html");
            }
        } 

        return httpResponseMessage;
    } 

    protected override
        Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
    {
        return RedirectRequest(request, cancellationToken);
    }
}

Reverse Proxy in ASP.NET Web API

Updated: Be sure to check my follow up post

Due to infrastructure limitations my current team was in need of a reverse proxy that could point to our ASP.NET Web API endpoint. After failing to get IT to setup a reverse proxy in the load balancer I ended up experimenting with a reverse proxy based on a simple implementation using Web API.

The first requirement is to intercept all requests made to the reverse proxy endpoint. Fortunately the Web API pipeline allows this via the DelegatingHandler:

public class ProxyHandler : DelegatingHandler{} 

public class WebApiConfig
{
    public static void Configure(HttpConfiguration config)
    {
        config.MessageHandlers.Add(new ProxyHandler());
        config.Routes.MapHttpRoute("abe", "{*path}");
    }
}

The configuration above adds the ProxyHandler to the general pipeline thus allowing it to intercept all requests which are processed by the Web API pipeline. Then a single catch-all route is added to make sure all requests are processed by the pipeline.

In the proxy delegating handler all requests must now be forwarded to the desired location:

public class ProxyHandler : DelegatingHandler
{
    private async Task<HttpResponseMessage> RedirectRequest(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var redirectLocation = "http://localhost:61948";
        var localPath = request.RequestUri.LocalPath; 

        var client = new HttpClient(); 

        var clonedRequest = await HttpRequestMessageExtensions.CloneHttpRequestMessageAsync(request); 

        clonedRequest.RequestUri = new Uri(redirectLocation + localPath); 

        return await client.SendAsync(clonedRequest, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
    } 

    protected override
        Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
    {
        return RedirectRequest(request, cancellationToken);
    }
}

I experienced some problems forwarding GET requests which is why the above code clone the entire HttpRequestMessage via the below snippet found on stack overflow:

public static class HttpRequestMessageExtensions
{
    public static async Task<HttpRequestMessage> CloneHttpRequestMessageAsync(HttpRequestMessage req)
    {
        var clone = new HttpRequestMessage(req.Method, req.RequestUri); 

        var ms = new MemoryStream();
        if (req.Content != null)
        {
            await req.Content.CopyToAsync(ms).ConfigureAwait(false);
            ms.Position = 0; 

            if ((ms.Length > 0 || req.Content.Headers.Any()) && clone.Method != HttpMethod.Get)
            {
                clone.Content = new StreamContent(ms); 

                if (req.Content.Headers != null)
                    foreach (var h in req.Content.Headers)
                        clone.Content.Headers.Add(h.Key, h.Value);
            }
        } 

        clone.Version = req.Version; 

        foreach (var prop in req.Properties)
            clone.Properties.Add(prop); 

        foreach (var header in req.Headers)
            clone.Headers.TryAddWithoutValidation(header.Key, header.Value); 

        return clone;
    }
}

I’m very impressed by the elegance of both Web API but more so the way the HttpRequestMessage/HttpResponseMessage is reused between Web API and HttpClient.

I tested the reverse proxy solutions against our current API and all our GET/POST requests went through. Furthermore all exception message was passed through the proxy as well.

A numeric comparison was attempted on TargetPlatformVersion evaluated to empty string

So after upgrading to Visual Studio 2013 update 1 and upgrading my web project to MVC 5.1 I could no longer load or build the project. I keep getting an error from MSBuild stating that the TargetPlatformVersion variable evaluated to an empty string. Naturally this caused some initial headache.

After comparing the project file with a clean project and finding no major differences I moved on to looking at the solution file. It turns out the VisualStudioVersion had been bumped to “12.0.30110.0” up from the previous “12.0.21005.1”. After updating this to the newest version the project successfully loaded again.

So if you experience this issue update your solution files visual studio version and reload the solution.

Let User Clear ComboBox Selection

The built-in ComboBox for Windows 8 does not come with a way to revert the control back to an unselected state. This is an issue in the scenario where the value in the ComboBox isn’t required an thus needs to be clearable.

A simple solution is to add an extra item to the Combox without any text and a value of -1. We can then wire up the CB with an attached property and handle the SelectionChanged event. Whenever we see a value of -1 being selected we can clear the selection.

One of the pros of clearing the CB is the placeholder text. Upon clearing the selection the placeholder text reappears.

The sample attached property can be seen below


public class ComboBoxHelper : FrameworkElement
{

public static bool GetClearOnEmptyValueSelection(DependencyObject obj)
{
 return (bool)obj.GetValue(ClearOnEmptyValueSelectionProperty);
}

public static void SetClearOnEmptyValueSelection(DependencyObject obj, bool value)
{
 obj.SetValue(ClearOnEmptyValueSelectionProperty, value);
}

public static readonly DependencyProperty ClearOnEmptyValueSelectionProperty =
DependencyProperty.RegisterAttached("ClearOnEmptyValueSelection", typeof(bool), typeof(ComboBoxHelper), new PropertyMetadata(false, (o, args) =&gt;
{
 var cb = (ComboBox)o;

 if ((bool)args.NewValue)
 {
  cb.SelectionChanged += (sender, eventArgs) =&gt;
  {
   if (eventArgs.AddedItems.Count == 1)
   {
    if (cb.SelectedValue == null || string.IsNullOrWhiteSpace(cb.SelectedValue.ToString()) || (cb.SelectedValue is int &amp;&amp; (int)cb.SelectedValue == -1))
    {
     cb.SelectedIndex = -1;
    }
   }
 };
}
}));
}

 

With the attached property at hand wiring the CB is as simple as:

<ComboBox ap:ComboBoxHelper.ClearOnSelection="true">