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Wednesday 7 December 2016

Reference object with ref keyword on a method. What's the point?

I wondered the other day what the point is in making a method parameter a ref when it is already a reference type. After playing around for a bit I came up with some concise code to illustrate the difference.

The difference is that, although you can modify the reference object that was passed in with both methods. Changing the reference entirely (i.e. pointing to a different object) only has an effect outside the scope of the method if the object was passed through with the ref keyword.

This code should explain better than English:

void Main()
 var t1 = new Thing();
 t1.Write(); // Chair
 var t2 = new Thing();
 Test(ref t2);
 t2.Write(); // Table

void Test(Thing t)
 t.Name = "Chair";
 t = new Thing { Name = "Table" };

void Test(ref Thing t)
 t.Name = "Chair";
 t = new Thing { Name = "Table" };

class Thing
 public string Name { get; set; }
 public void Write() => Console.WriteLine(Name);

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Tuesday 22 December 2015

Stop processing OPTIONS requests for CORS in ASP.NET Web API

I was attempting to allow some particular origins to access my ASP.NET Web API from a client side single page application. I was using the EnableCorsAttribute that comes with the Microsoft.AspNet.WebApi.Cors NuGet package.

I managed to set up CORS using the following code in my WebApiConfig:

var origins = ConfigurationManager.AppSettings["AllowedOrigins"];
var cors = new EnableCorsAttribute(origins, "accept,content-type,origin,customId", "GET,POST,PUT");

There is quite a lot to CORS but essentially, (some browsers) send a pre-flight request recognised with its HTTP method OPTIONS. This basically asks the application who is allowed to access this URL with the attempted headers and HTTP method. Your Web API will respond saying which origins are allowed or if there are any errors. The browser then decides if it is one of those allowed origins and sends the request if it is.

The problem I found is that on this initial OPTIONS request my IoC container, Unity, was constructing a whole dependency chain of classes. Some of which access the database and some check HTTP headers. This was throwing an error since bits were missing from the HTTP headers that would be with normal requests and unnecessarily hitting the database. So really, I wanted to stop these requests in their tracks whilst making sure they did their intended pre-flight work.

The best way I found to do this was to ignore routes based on an HTTP constraint for "OPTIONS". Basically shove this in your routing:

var constraints = new { httpMethod = new HttpMethodConstraint(HttpMethod.Options) };
config.Routes.IgnoreRoute("OPTIONS", "{*pathInfo}", constraints);

More info on Enabling CORS in Web API.

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Thursday 6 August 2015

Outbound IP address from Azure WebJobs or WebSite

I need to find the outbound IP address of an Azure Website so that I can whitelist this IP address in a service I wish to call. However there are concerns with this practice as I will explain.

Azure WebJobs are completely awesome and they should be used more. I have project however that I am using to pre-process a large amount of data. As part of this process, my Web Job will need to call a third party web service that operates an IP whitelist. So to call it successfully I need to find the IP address of my Azure WebJob.

That is simple enough, I confirmed the IP address using two sources, one is a given list of IP's as documented by Microsoft. Details on how to find yours are here: Azure Outbound IP restrictions. I also wrote a little code to make sure this matches from a WebJob like so:

public async static Task ProcessQueueMessage(
    [QueueTrigger("iptest")] string message,
    TextWriter log)
    using (var client = new HttpClient())
        var response = await client.GetAsync("");
        var ip = await response.Content.ReadAsStringAsync();
        await log.WriteAsync(ip);

Popping something in the "iptest" queue kicked off the job and checking the logs confirmed the WebJobs are in fact consistent with the IP ranges documented.

There is a problem however, if you read that link you will discover that although it is roughly static it is not unique. You will share your outbound IP with other users of Azure WebSites that are hosted in the same region as you and the same scale unit as you. What is a scale unit? Who cares but there are 15 of them in the North Europe data centre for example so not a lot. Now how secure do you think IP whitelisting a shared IP is? Not very!


Don't give up hope! The work arounds I can see are to ask the service provider to not rely on only IP whitelisting, have another form of authentication, an API key over SSL would work for example. Have it as well as IP Whitelisting if it makes them happy.

If they can't be controlled you can do your own magic. There are proxy providers out there that will provide your calls with a unique static IP address. Try QuotaGuard. Or make your own - if you already have a Cloud Service running in Azure you can proxy the service via that as they can have static and unique outbound IP addresses.

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Skipping unit tests is a false economy

You only need unit tests if you write buggy code but why would I write bugs? I don't need them.

For a long time I thought unit tests was just vanity code. Oooh look, I've made this repository unit testable and I've used my fav' IoC container to inject dependencies now so in my tests I mock them to create and elegant suite of unit tests. No one will ever run the tests but it is cool because all the top dev bloggers write about it.

That is probably a lot of people's motives, that and the lead dev told them to. You can tell when people don't fully understand why they are writing unit test when they are running short of time to complete their work and the first thing they compromise is the unit tests. Unit tests are always the first to be dropped in high pressure environment.

Let me sell unit tests to you

They save you time! How can that be right? They take so long to write and refactor every time you change your code. Unit tests save you time because you no longer need to trawl through mountains of code to work out in you head any possibility for causing a bug. You don't need to step through every line of code in your application finding potential for unexpected consequences when you have decent unit test. Which saves so much time!

Worse still is the people that wouldn't have trawled through the code to find a potential bug and just committed their code anyway and broke something. Sooner or later it will get noticed and someone is going to spend a very long time tracking it down and then fixing the root cause.

What about deployment time as well, when you come to merge and commit a branch or do a deployment, how long would it take you to review every line in the merge or click about every section of the site? 30mins? Hours? Or maybe you wouldn't bother and as mentioned that is when the even harder to find bugs creep in. It is such a waste of time!

Writing unit test from the beginning will slash all this wasted time!

Unit tests should be the first things your write!

This is called TDD (Test Driven Development) and it is the most effective way of ensuring your tests get written as you can't drop them out to save time as they are already written. It also forces you to really think about your code before writing it.

But TDD or not, please PLEASE write them. Lots of them. Use NCrunch that has continuous test runners for your test suite and shows the lines of code covered and the state of that test. Aim for 80%+ code coverage from the beginning and you will save so much time in the future doing all that boring clicking about or line by line reviewing of your code merges.

Not writing unit tests is a false economy

And developers are expensive so don't waste their time.

Please send this on to your team including the project manager. Everyone must know the importance of getting unit tests done and written well.

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Friday 17 May 2013

SQL MERGE that changes the ON constraint as it runs

What happens when your MERGE statement INSERTs a row that now satisfies the ON constraint. If a new row comes along that satisfies the ON constraint will it fall into WHEN MATCHED or WHEN NOT MATCHED?

Let's use an example piece of code to decide what happens. Here I have two table variables created and seeded with some random data:

DECLARE @t1 Table (id int, name varchar(12))

DECLARE @t2 Table (id int, name varchar(12))
INSERT INTO @t2 VALUES(1, 'bye')
INSERT INTO @t2 VALUES(3, 'colin')
INSERT INTO @t2 VALUES(3, 'sarah')

Now I will attempt to MERGE @t2 into @t1. If you have not come across MERGE before it is basically a more efficient way of saying UPDATE if it exists or INSERT if it is new.

MERGE @t1 AS t1
 ON =
 INSERT(id, name)

So, what we are saying is:

  • USING this source of data (SELECT * FROM @t2)
  • ON this decider (matching the ID's to judge if this row already exists)
  • WHEN the ON clause is MATCHED update this row with new values
  • WHEN NOT MATCHED we should INSERT the new row

But, given the values in @t2, what will happen?

  1. The 1st row will match on ID 1 and so will do an UPDATE
  2. The 2nd row doesn't have a match for an ID of 3 so will INSERT
  3. The 3rd row didn't have a match for an ID of 3 before but since the last INSERT it now does. So INSERT or UPDATE?

A SELECT * FROM @t1 will show you that it has INSERTed twice...


So watch out for this. The constraint is decided about the source and destination once at the beginning and not again so you should be sure that the source table being MERGED is complete in itself. You can do with using a GROUP BY or DISTINCT on the USING table. Whichever is most appropriate for your scenario.

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How to solve Introducing FOREIGN KEY constraint may cause cycles or multiple cascade paths

I was writing my Entity Framework 5 Code First data models one day when I received a dramatic sounding error: "Introducing FOREIGN KEY constraint 'FK_dbo.Days_dbo.Weeks_WeekID' on table 'Days' may cause cycles or multiple cascade paths." I was instructed to "Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints." And then simply the message, "Could not create constraint." So what happened with my Foreign Key that makes it cyclic?"

First a spot of code that can nicely demonstrate this scenario:

public class Year
    public int ID { get; set; }
    public string Name { get; set; }

    public ICollection<Month> Months { get; set; }
public class Month
    public int ID { get; set; }
    public string Name { get; set; }

    public Year Year { get; set; }
    public ICollection<Day> Days { get; set; }
public class Day
    public int ID { get; set; }
    public string Name { get; set; }

    public Month Month { get; set; }
    public Week Week { get; set; }

//problem time
public class Week
    public int ID { get; set; }
    public string Name { get; set; }

    public Year Year { get; set; }
    public ICollection<Day> Days { get; set; }

So, let's explain this. A Year has Months and a Month has Days - all is well at this point and it will build and generate all your tables happily. The problem comes when you add the highlighted parts to add Weeks into the data model.

By making those Navigation Properties you have implicitly instructed EF Code First to create Foreign Key constraints for you and each of these will have cascading deletes on them. This means, upon deleting a Year, the database will cascade that delete to that Year's Months and in turn those Month's Days. This is to, quite rightly, hold referential integrity; you will not have Yearless Months.

So if you think about it, now that we have added a Week entity that also has a relationship with Days this too will cascade deletes. So as well as the cascading deletes that occur when you delete a Year as I described above, now deleting a Year will also delete its Weeks and those Weeks will delete the Days. But those Days would have already been deleted by the cascade that went via Months. So who wins? Who gets there first? Don't know... that's why you need to design an answer to this conundrum.

Removing the multiple cascade paths

The way I found to solve this issue is you need to remove one of the cascades, since there is nothing wrong with the Foreign Keys, it is only the multiple cascade paths. So lets remove the cascading delete on the Week -> Days relationship since that delete will be taken care of by each Month cascading its deletes to their Days.

public class CalenderContext : DbContext
    public DbSet<Year> Years{ get; set; }
    public DbSet<Month> Months { get; set; }
    public DbSet<Day> Days { get; set; }
    public DbSet<Week> Weeks { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
            .HasRequired(d => d.Week)
            .WithMany(w => w.Days)


If you already have a ForeignKey field explicitly written into your code model (as I usually do - I removed them from the above example for clarity) you will need to specify this existing Foreign Key in the code just written. So if your Day entity looked like this:

public class Day
    public int ID { get; set; }
    public string Name { get; set; }

    public int MonthID { get; set; }
    public Month Month { get; set; }

    public int WeekID { get; set; }
    public Week Week { get; set; }

You will need your OnModelCreating method to look like this:

    .HasRequired(d => d.Week)
    .WithMany(w => w.Days)
    .HasForeignKey(d => d.WeekID)

Have fun deleting safely!

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Thursday 28 February 2013

The request filtering module is configured to deny a request that contains a double escape sequence

In IIS 7.5 I have a site that contains a page that takes an encrypted part of a URL. This encrypted string includes a plus sign '+' which causes IIS to throw a "HTTP Error 404.11 - Not Found" error stating "The request filtering module is configured to deny a request that contains a double escape sequence."

The problem is that a + sign used to be acceptable in earlier versions of IIS so these URLs need to remain for legacy reasons. So, I need to make them allowed again in IIS.

The quick fix

This can be easily achieved with a simple web.config change:

        <requestFiltering allowDoubleEscaping="true" />

This allows URLs to contain this plus symbol '+'.

The warning

There are consequences to this which unsurprisingly are security related so please read Double Encoding to familiarise yourself with the risk for your situation. If it is a risk to you maybe the best solution is to redesign those URLs?

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Saturday 19 January 2013

Handler “ExtensionlessUrlHandler-Integrated-4.0” has a bad module “ManagedPipelineHandler” in its module list

How to fix the error 'Handler “ExtensionlessUrlHandler-Integrated-4.0” has a bad module “ManagedPipelineHandler” in its module list'.

This error occurred when I moved my moved my ASP.NET 4.5 from an old Windows 7 machine to a brand new Windows 8 machine running IIS 8.

I was thinking I was in need of an aspnet_regiis -I but this threw back a message at me saying "Start installing ASP.NET (4.0.30319.17929). This option is not supported on this version of the operating system. Administrators should instead install/uninstall ASP.NET 4.5 with IIS8 using the "Turn Windows Features On/Off" dialog, the Server Manager management tool, or the dism.exe command line tool. For more details please see Finished installing ASP.NET (4.0.30319.17929)."

So I turned to turning windows features on/off (Win+X then hit F). I had already turned IIS on but then I had found I hadn't done enough.

Previously when I had turned IIS on I had left it with the default but actually I needed more to get ASP.NET 4.5 to run. You need to go to:

  1. Internet Information Services
  2. World Wide Web Services
  3. Application Development Features
  4. Then check ASP.NET 4.5

This will select a few other bits for you and you should be good to go.

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Thursday 17 January 2013

Finding Outlook Web Access (OWA) URL from Outlook 2010

I was struggling to find out my Outlook webmail address from Outlook 2010 on my machine so that I can access my work email from home or on my mobile. The OWA URL is hidden quite deep into Outlook 2010 so I have written down the location of the URL so I can remember for next time.

It is rather hidden away, probably because it is assumed you would just ask IT instead of finding out for yourself but that isn't like you is it. That's why you're here!

Finding your web mail address in Outlook 2010

  1. Click the File tab near the top left
  2. Click the Info tab
  3. Click the big "Account Settings" button and then "Account Settings" again on the pop out menu
  4. On E-mail tab ensure your address is selected and click the "Change..." button just above it
  5. Click the "More Settings ..." button at the bottom
  6. Go to the Connection tab and click "Exchange Proxy Settings..." button at the bottom
  7. It is the first URL on this window. Something like

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Monday 14 January 2013

Web forms button click event not firing in IE

There are probably many reasons why a button would not fire in an ASP.NET web forms application. Some can be fixed with deleting cookies and history, some are to do with when the event is registered. I found a new one though.

In my scenario I had a text box that was submitted with a button next to it. We didn't want to display the button though but instead wanted the form submitted with a click of the Enter button. The button was therefore wrapped in a display:none span, like this:

<input type="text" id="txtInput" onchange="btnGo_Click" runat="server"/>
<asp:Button style="display:none;" runat="server" OnClick="btnGo_Click" />
<asp:Label ID="lblOutput" runat="server" />

It turns out that this worked just fine in Chrome and Firefox but not in IE9. This was because not all browsers post data that is hidden with CSS. Security possibly? You could see this by looking at the request in Fiddler. There was no value for the button field in IE but there was for the others.

How to submit a form by clicking Enter and hiding the button

The best way I can think of is to hide the button without hiding it... How? You can push it miles of the page to hide the button with some CSS like this:

<input type="text" id="txtInput" onchange="btnGo_Click" runat="server"/>
<asp:Button style="position:absolute;left:-9999px;" runat="server" OnClick="btnGo_Click" />
<asp:Label ID="lblOutput" runat="server" />

This will put the button miles off to the left never to be seen by the user.

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