A favorite programming test question is the Fibonacci sequence. This is defined as either 1 1 2 3 5... or 0 1 1 2 3 5... depending on what you feel fib of 0 is. In either case fibonacci is the sum of the two previous terms. So fib(10) = fib(9) + fib(8). The reason this is a programming test favorite is because it forces people to think about recursion and even memoization for performance.

There is however a shortcut for this and that is to use the closed form which uses the golden ratio. We have two interesting values called Phi and phi with the former being the golden ratio and the latter being a value observed in nature for leaf dispersions.

Phi = (1 + root(5))/2
phi = (1-root(5))/2

We can use this to create Binet’s formula (Jacques Philippe Marie Binet was a French mathematician born in 1786, although this formula is named for him it was really discovered by fellow French mathematician Abraham do Moivre a century earlier)

fib(n) = (Phi^n - phi^n)/(Phi - phi)

In code we can do the following to generate all the fib numbers up to n

static double Phi = (1 + Math.Pow(5,.5))/2;
static double phi = (1 - Math.Pow(5,.5))/2;
static ulong[] generateFibonaccisClosed(int n){
    ulong[] fib = new ulong[n];
    for(int i = 0; i<n; i++)
    {
        fib[i] = (ulong)((Math.Pow(Phi, i)-Math.Pow(phi, i))/(Phi - phi));
    }
    return fib;
}

The advantage here is that the closed form is constant time, constant memory and uses only about 3 64-bit values (fewer if you calculate phi and Phi as you go). It’s certainly a lot of fun to break out in a programming test.

Years back there was this crazy way of dealing with data in .NET called a DataSet. DataSets contained DataTables which contained a combination of DataRows and DataColumns. It was all loosely typed and keyed with strings. Basically a database inside of your process. Even when they were cool I felt uncomfortable using them. Because I sometimes maintain legacy code I run into these monstrosities.

Today’s problem was that I needed to filter the contents of a table before bulk loading it. You can actually do simple filtering using a quasi-SQL like

   var dataRows = existingDataTable.Select("UserName = 'simon'")

This gives you back a collection of DataRows which I guess you could inset back into the table after clearing it of rows. To make this useful there is an extension method called CopyToDataTable in System.Data.DataExtension (be sure to include the dll for this). Using that you can get back a full data table

var dataTable = existingDataTable.Select("UserName = 'simon'").CopyToDataTable();

In that same package, though, is a much better tool for filtering: converting the table to an IEnumerable. You still need to use some magic strings but that’s somewhat unavoidable in data tables.

var dt = existingDataTable.AsEnumerable()
                    .Where(r => r.Field<String>("UserName") == "Simon").CopyToDataTable();

You can also do more advanced things like checking to see if something is a GUID

var dt = existingDataTable.AsEnumerable()
                    .Where(r => Guid.TryParse(r.Field<String>("Id"), out var _)).CopyToDataTable();

The 3.0.3 version of VSFTP seems to have an exploit against it so you should update to 3.0.5. However at the current time that has not been released in Debian upstream so we get to compile it ourselves!

First get and decompress the source

wget https://security.appspot.com/downloads/vsftpd-3.0.5.tar.gz
tar xvf vsftpd-3.0.5.tar.gz
cd vsftpd-3.0.5

Now you’re going to need to edit the builddefs.h specifically you want to enable SSL with

 #define VSF_BUILD_SSL

You may need to install the open ssl headers

sudo apt install libssl-dev

Next run a standard make/make install

make
make install

That should be it. If you’re replacing an apt sourced vsftpd then remember to uninstall that and you will have to update the init.d script to point at the new one which is in /usr/local/sbin instead of /usr/sbin. You could also change the install prefix but I like local better.

Did you know you can hook up your SQL server (or Managed SQL on Azure) to an SMTP server and use it to send email. Terrible idea? Yes, probably. I really encourage people not to build business logic that might require creating an email into stored procs. Required for legacy code? Yes, certainly.

You first need to tell SQL server how to talk to the mail server. This is done using the sysmail_add_Account_sp

EXECUTE msdb.dbo.sysmail_add_account_sp
    @account_name = 'Database Mail Account',
    @description = 'SQL Server Notification Service',
    @email_address = 'SQLServer@somedomain.com',
    @replyto_address = 'SQLServer@somedomain.com',
    @display_name = 'Database Mail Profile',
    @mailserver_name = 'smtp.office365.com',
    @port = 587,
    @username = 'SQLServer@somedomain.com',
    @password = 'totallynotourpassword',
    @enable_ssl = 1;

With that in place you can set up a mail profile to use it

SELECT @sequence_number = COALESCE(MAX(profile_id),1) FROM msdb.dbo.sysmail_profile;

-- Create a mail profile
EXECUTE msdb.dbo.sysmail_add_profile_sp
    @profile_name = 'Database Mail Profile',
    @description = 'Sends email from the db';

-- Add the account to the profile
EXECUTE msdb.dbo.sysmail_add_profileaccount_sp
    @profile_name = 'Database Mail Profile',
    @account_name = 'Database Mail Account',
    @sequence_number = @sequence_number;

-- Grant access to the profile to the DBMailUsers role
EXECUTE msdb.dbo.sysmail_add_principalprofile_sp
    @profile_name = 'Database Mail Profile',
    @principal_id = 0,
    @is_default = 1 ;

You can then make use of sp_send_dbmail to send email

EXEC msdb.dbo.[sp_send_dbmail]
    @profile_name = 'Database Mail Profile',
    @recipients = 'simon.timms@somedomain.com',
    @subject = 'Testing db email',
    @body = 'Hello friend, I''m testing the database mail'

You can check the status of the sent email by querying

select * from msdb.dbo.sysmail_allitems

If things fail then checking the event log may be helpful

select * from msdb.dbo.sysmail_event_log 

If you have a private nuget feed authenticated with a password chances are your password will eventually expire or change. For some reason Visual Studio and perhaps nuget under the covers aggressively caches that password and doesn’t prompt you when the password doesn’t work anymore. To change the password the easiest approach I’ve found is to use the nuget.exe command line tool and run

c:\temp\nuget.exe sources update -Name "Teamcity" -Source "https://private.nuget.feed.com/httpAuth/app/nuget/feed/_Root/SomeThing/v2" -UserName "simon.timms" -Password "Thisisactuallymypassword,no,really"
C:\temp\nuget.exe list -Source teamcity

I have a terraform deployment which runs in azure pipeline. Azure pipelines is connected to Azure via a service connection. This service connection is registered as an application in the Azure AD of the Azure account. The problem I constantly run into is that I can’t remember which id from the application should be granted keyvault access so the build pipeline can read and write to keyvault.

resource "azurerm_key_vault_access_policy" "terraformaccess" {
  key_vault_id = azurerm_key_vault.keyvault.id

  tenant_id = local.tenant_id
  object_id = ???????????????????

  key_permissions = [
    "Get",
    "Create",
    "List",
    "Update",
    "Verify",
    "Delete",
    "WrapKey",
    "UnwrapKey"
  ]

  secret_permissions = [
    "Get",
    "List",
    "Set"
  ]

  storage_permissions = [
    "Get",
    "List",
    "Set",
    "Update"
  ]
}

Maybe the value is in the portal somewhere:

Nope.

It seems to be findable by doing either

Login-AzureRmAccount -SubscriptionId <your subscription id>;
$spn=(Get-AzureRmADServicePrincipal -SPN <the application id>);
echo $spn.Id

or

 az ad sp list --spn <the application id>

Then look for ObjectId

Say you want to keep a resource but you want to stop terraform from managing it. You can ask terraform to update its state to forget about it. In my case I want terraform to forget it managing my Azure Static Web App because Terraform doesn’t support all the options I need and will clobber the app.

I can run this

terraform state rm "azurerm_static_site.agentportal"

If I decide to start managing the state again I can just run a terraform import to manage it again.

If you’re running into a 404 on the IFrame on storybook the mostly likely cause is that your directory path to where storybook is contains some encoded characters. In this case we had a project called Agent%20Portal on disk. Renaming it to just AgentPortal fixed up storybook right away.

If you provision a database using terraform you often find that you need to get that connection string into app settings or key vault or something like that. To do that you first need to build it because the outputs from the database resource don’t include it.

From the database you want to export

output "database_name" {
  value = azurerm_sql_database.database.name
}

Then when you actually build the string you want something like this:

database_connection_string    = "Server=tcp:${module.database.name}.database.windows.net,1433;Initial Catalog=${module.database.database_name};Persist Security Info=False;User ID=${var.database_user};Password=${var.database_password};MultipleActiveResultSets=True;Encrypt=True;TrustServerCertificate=False;Connection Timeout=30;"

Then you can push this to KeyVault or an App Service directly.

Static web apps are pretty cool but certain parts of them feel like they are still a little raw. It is a newish product so I can understand that. I just wish the things that didn’t get attention were something other that devops things. That’s mostly because I’m so big on builds and repeatable processes. Being able to set app setting is one of the things I think falls through the cracks.

The docs for statics web apps suggests two different ways of setting app settings. First through the portal which we can ignore right out the gate because it is manual. The second is through an az command that actually just exercises a REST endpoint. No Arm support, no terraform support, no bicep support, no azure powershell support… a long way to go.

The az command takes in a specially formatted json file. My databse and connection string variables are set up as outputs from my terraform. Once I have them imported into my Azure DevOps build pipeline I use powershell to build the template file like so:

$temp = gc api/api/local.settings.template.json | ConvertFrom-Json
$temp.properties.STORAGE_CONNECTION_STRING = "$(terraformOutput.storage_connection_string)"
$temp.properties.DATABASE_CONNECTION_STRING = "$(terraformOutput.database_connection_string)"
$temp | ConvertTo-json > api/api/local.settings.template.json

Now this needs to be passed up to azure using the AzureCLI task

  - task: AzureCLI@2
    inputs:
    azureSubscription: 'Azure Sub'
    scriptType: 'pscore'
    scriptLocation: 'inlineScript'
    inlineScript: |
        gc api/api/local.settings.template.json
        az rest --method put --headers "Content-Type=application/json" --uri "/subscriptions/6da8d6e6-41f1-xxxx-xxxx-xxxxxxxx/resourceGroups/dev-portal/providers/Microsoft.Web/staticSites/dev-portal/config/functionappsettings?api-version=2019-12-01-preview" --body @api/api/local.settings.template.json