Hashing String Data in JavaScript, C#, C++, and SQL Server

I’m working with some data that needs to be hashed in both C# and JavaScript. Usually converting an algorithm across languages is pretty trivial. But in JavaScript the regular numeric type is a double-precision 64-bit number. While this sounds sufficiently large, when used as an integer this only provides 53-bits of precision. As you might imagine, using a 53-bit numeric type on one system and 64-bit on another would result in differences in outcome. This would make hased data between these two functions incompatible with each other. To avoid these potential problems, I needed to use a different type. I used BIGINT.

A potential issue with BIGINT is that it can accommodate extremely large values. This isn’t usually a problem, but I need to have identical behaviour for the hash function to have identical results across the languages. Fixing this is simple though. I only need to perform the bitwise AND operation to truncate any bits in the BIGINT beyond position 64. The hast function I’m using was originally found on StackOverflow. This might not be the final Hash function that I use, but for now it works.

A key thing to note in the JavaScript implementation is the n suffix on the numbers. This ensures that they are all using the BIGINT type. Also take note of the bitwise operation with the number 0xFFFFFFFFn. This ensures that the number is truncated and acting like a 64-bit integer.

// 
function hashString(s) { 
    const A =  54059n ;
    const B = 76963n ;
    const C = 86969n;
    const FIRSTH = 37n;
   var h = FIRSTH;
   for ( var i=0;i<s.length;++i) {
        var c = BigInt(s.charCodeAt(i));
        h = ((h * A) ^ (((c) *B))) & 0xFFFFFFFFFFFFFFFFn;
   }
   return h; 
}

The C++ implementation (used for the Arduino ) follows. Using native types in C there’s nothing special that needs to be done.

#define A 54059   /* a prime */
#define B 76963   /* another prime */
#define C 86969   /* yet another prime */
#define FIRSTH 37 /* also prime */
unsigned long hash_str(String s) {
  unsigned long h = FIRSTH;
  for (auto i = 0; i < s.length(); ++i) {
    h = ((h * A) ^ (s[i] * B)) & 0xFFFFFFFFFFFFFFFF;
    //s++;
  }
  return h;  
}

The difference between the C# and C++ versions o the code are only notational. They both handle 64-bit integers just fine with no special tricks needed.

ulong hashString(String s) { 
    const ulong A =  54059ul ;
    const ulong B = 76963ul ;
    const ulong C = 86969ul;
    const ulong FIRSTH = 37ul;
   var h = FIRSTH;
   var stringBytes = Encoding.ASCII.GetBytes(s);
   for ( var i=0;i<stringBytes.Length;++i) {
        var c = stringBytes[i];
        h = ((h * A) ^ (((c) *B))) & 0xFFFFFFFFFFFFFFFFul;
   }
   return h; 
}

The differences for Kotlin are also notational, but significantly different from the C# and C++ in how the bitwise operators are expressed.

    fun hashString(s:String): ULong {
        val A:ULong =  54059u ;
        val B:ULong = 76963u ;
        val C:ULong = 86969u;
        val FIRSTH:ULong = 37u;
        var h = FIRSTH;
        var stringBytes = s.toByteArray()
        for ( i in 0..stringBytes.size-1) {
            var c = stringBytes[i].toULong();
            h = ((h * A) xor (((c) * B))) and 0xFFFFFFFFFFFFFFFFu;
        }
        return h;
    }

After having written this post, I was working in SQL Server. I was going to save some of this hashed data within SQL Server and decided to try with implementing a hash function there. Everything started out the same, but I ran into a notable problem. I encountered arithmetic overflow issues with declaring the mask 0xFFFFFFFFFFFFFFFF. This mask isn’t strictly necessary, but I’ve placed it there should I happen to use one of these implementations to hash to a smaller data type. I was using the BIGINT data type. But that data type only provides 63-bits of precision, not 64. Knowing that now I could just use a smaller mask to have a hash function that works identically across environments. If you’d like to try it out, the SQL Server implementation follows here.

CREATE FUNCTION HashString
(
	@SourceString as VARCHAR(15)
)
RETURNS BIGINT
AS
BEGIN
    DECLARE @A BIGINT =  54059
    DECLARE @B BIGINT = 76963
    DECLARE @C BIGINT = 86969
    DECLARE @FIRSTH BIGINT = 37
	DECLARE @StrLEn BIGINT = LEN(@SourceString)	
	DECLARE @Index BIGINT = 1
	DECLARE @MASK BIGINT = 0xFFFFFFFFFFFF
	DECLARE @Letter CHAR
	DECLARE @LetterCode BIGINT
	DECLARE @H BIGINT = @FIRSTH
	WHILE @Index <= @StrLEn	
	BEGIN
		SET @Letter = SUBSTRING(@SourceString, @Index, 1)
		SET @LetterCode = UNICODE(@Letter)
		SET @H = ((@H * @A) ^ (@LetterCode * @B)) & @MASK
		SET @Index = @Index + 1		
	END	
	return  @H;
END
GO

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Gaming Through Netflix

When I tell someone that I’m about to play a game on Netflix, the response is the same.

“A game on Netflix, what are you talking about?”

I guess this isn’t well know, but Netflix publishes and licenses video games. most of these have been casual games though. My attention was caught by a recent game made available through Netflix that was an action game. “Teenage Mutant Ninja Turtles: Shredder’s Revenge” was recently made available on a range of systems. The look to the game reminds me of some previous TMNT games that I enjoyed, and I wanted to get this one. I never got around to making a purchase because I found the game on Netflix. Great! But how exactly does someone play a game on Netflix? How does someone play **this** game, which allows up to 4 people to play at once! Let’s find out.

Netflix releases games as mobile games. If you have an iOS or Android device, then you have what it takes to play the games. You can usually find the games by searching for “Netflix” in either of the app stores. But I find it easier to open the mobile app and scroll down vertically until you find a section listing the games. Selecting one of the games shows more information on it and presents a button to open the store for installing it. On Android, if the game is already installed, this will but a button to open and play the game instead.

Of course, the games can be played right away without any accessories. I personally hate playing arcade or action games on phone with on screen controls. Thankfully, one is not limited to that as the only form of control. The game supports game controllers, and you may be able to play on a larger external display (such as a TV) if using additional accessories.

Controllers

Both iOS and Android support game controllers. On iOS, you only need to pair the controller with the phone using the Bluetooth settings. On Android, you can either pair through the Bluetooth settings or you can connect it to the phone with a USB cable. I preferred this method so that I did not have to unpair the controller with the other device with which I use it. Recent Xbox controllers use USB-C as their connector. If you have an older controller, it uses USB-micro. You’ll need a USB-C to USB-micro cable. I preferred to use the shortest cable possible. I also use a USB-C right angle adapter to keep the cable a little neater.

External Display

You can play the games on an external display too. Well, maybe. It depends on your phone. Many Samsung devices will work with generic USB-C to HDMI adapters. If you have some other Android device, it may or may not support USB-C. Some iOS devices will work with HDMI adapters too. You just need to have an appropriate device to match either your Lightning port or USB-C port (I used this Lightning to HDMI adapter). Using an external display tends to drain the battery faster. It’s a good idea to use an adapter that also allows charging. With some of my Samsung devices I have found this can be tricky. The Samsung devices use USB-PD (Power Delivery). The device request some amount of power from the power supply. It the phone detects a different in the amount requested and the amount received, the phone will alert the user that there is potentially moisture on the USB-C port. Instead of using a PD power supply I had better results using a “dumb” power supply when pairing with the display adapter or using an HDMI adapter labeled as working with Samsung DEX. The video adapter that I preferred to use for Android was sold under the description of a USB-C Thunderbolt 3 Docking Station. My phone and tablet do not support Thunderbolt, but this doesn’t matter, the docking station works fine.

Multi-Player

I had hoped that I could connect multiple controllers to my Android device to play with multiple people. Sadly, this isn’t the case. The multiplayer works over the Internet with each person having a device. When you are starting the game, the character select screen also has a button to “Party Up” with two modes of “partying.” One can either create a private party or a public party. For the private party, a 6 character text string displays on the screen. Others that you want to join the party need to enter this code. If you select a public party then you can join up with others that wish to play online. For either option, you can either create a party, or you can join one.

Transferring Progress Between Devices

As you might expect, with Netflix games your progress is saved with your profile. If you go to a different device but use the same profile your progress shows up there. There’s nothing that you need to do. This is automatic.

Will It Replace my Game Streaming Service?

No. In its current form, Netflix Games are not going to replace Xbox or Luna streaming. But they don’t try to fill that space. Many of the games in their library are more casual game. At the time that I’m writing this, there are a total of about 50 games in the Netflix gaming library. While they wouldn’t be competing those larger game streaming service, the games do have their own charm to them. There are probably about 5 games that have support for controllers, including TMNT, Spiritfarer, and Stranger Things 3. Right now their games lean more casual (which to me makes sense, since that may be of broader interest). I do think that it is a space to watch as Netflix continues to find ways to grow.


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Calculating the Distance Between Geographical Coordinates in Kotlin

There’s an equation I’ve often found useful and have generally used it for calculating the distance between geographical coordinates. Most recently, I used the equation in a program for a 360 interactive video player to find the distance between an area that a user selected and some point of interest. Fundamentally it is an equation measuring distances on a sphere and has many uses.

I was adjusting the source code to be used in an Android application, and thought that the code might be useful to others. I am reposting it here. I tend to work in SI units, but you could use this for miles, yards, inches, or another unit if you have the radius of the sphere of interest. The constants defined in the class provide the radius of the rarth in miles, kilometers, and meters. One of these values (or your own custom value) must be passed to have the results returned to be scaled for those units.

class DistanceCalculator {
     companion object {
         public val EarthRadiusInMiles = 3956.0;
         public val EarthRadiusInKilometers = 6367.0;
         public val EarthRadiusInMeters = EarthRadiusInKilometers*1000;
     }

     fun ToRadian(`val`: Double): Double {
         return `val` * (Math.PI / 180)
     }

     fun ToDegree(`val`: Double): Double {
         return `val` * 180 / Math.PI
     }

     fun DiffRadian(val1: Double, val2: Double): Double {
         return ToRadian(val2) - ToRadian(val1)
     }

     public fun CalcDistance(p1: coordinate, p2: coordinate): Double {
         return CalcDistance(
             p1.latitude,
             p1.longitude,
             p2.latitude,
             p2.longitude,
             EarthRadiusInKilometers
         )
     }

     fun Bearing(p1: coordinate, p2: coordinate): Double? {
         return Bearing(p1.latitude, p1.longitude, p2.latitude, p2.longitude)
     }

    fun Bearing(lat1: Double, lng1: Double, lat2: Double, lng2: Double): Double? {
        run {
            val dLat = lat2 - lat2
            var dLon = lng2 - lng1
            val dPhi: Double = Math.log( Math.tan(lat2 / 2 + Math.PI / 4) / Math.tan(lat1 / 2 + Math.PI / 4) )
            val q: Double =
                if (Math.abs(dLat) > 0) dLat / dPhi else Math.cos(lat1)
            if (Math.abs(dLon) > Math.PI) {
                dLon = if (dLon > 0) -(2 * Math.PI - dLon) else 2 * Math.PI + dLon
            }
            //var d = Math.Sqrt(dLat * dLat + q * q * dLon * dLon) * R;
            return ToDegree(Math.atan2(dLon, dPhi))
        }
    }

    public fun CalcDistance(
         lat1: Double,
         lng1: Double,
         lat2: Double,
         lng2: Double,
         radius: Double
     ): Double {
         return radius * 2 * Math.asin(
             Math.min(
                 1.0, Math.sqrt(
                     Math.pow(
                         Math.sin(
                             DiffRadian(lat1, lat2) / 2.0
                         ), 2.0
                     )
                             + Math.cos(ToRadian(lat1)) * Math.cos(ToRadian(lat2)) * Math.pow(
                         Math.sin(
                             DiffRadian(lng1, lng2) / 2.0
                         ), 2.0
                     )
                 )
             )
         )
     }
 }

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Connecting to AWS IoT’s MQTT Server with .Net

A client I was working with wanted communication between systems for a solution to use AWS IoT for broadcasting messages among the computers making up the solution and controlling various computers. I worked on the solution for the system, but had minimal access to their AWS resources, which is consisten with their security policies. Usually, if I have access to the AWS subscription I could use an MQTT viewer that is part of the service for performing some diagnostic tasks. With this client, I didn’t have that access and had to make my own viewer when performing diagnostics.

Making a viewer is pretty easy once you have the resources that you need. I chose WPF because of the speed at which a functional UI could be build along with M2Mqtt as an MQTT client. Before writing any code, there was some work that needed to be done with the certificates. When accessing an AWS MQTT Instance, the information that you will need includes the domain name for the MQTT instance, an Amazon root certificate, a certificate and private key file. You’ll need this information packaged in a pfx file to easily use it with M2Mqtt. Packaging these certificates that way is just a matter of running a command. For the files I had, let’s use these names.

  • 000-certificate.pem.crt – The certificate file for the AWS MQTT Instance
  • 000-private.pem.key – The private key for the AWS MQTT instance
  • AmazonRootCA1.cer – The AWS root certificate

Using those file names, the command that I used was as follows.

openssl pkcs12 -export -in .\000-certificate.pem.crt -inkey .\000-private.pem.key -out certificate.pfx -certfile .\AmazonRootCA1.cer

After this command runs, I have a file named certificate.pfx. I’ll be using this in my .Net viewer.

In the interest of keeping the program reusable, I’ve placed information on the paths to the certificate files in the applications settings. If I needed to change these files post-compilation, they are in a JSON file. These settings include the following.

  • BrokerDomainName – The domain name of the MQTT Instance that the application connects to
  • BrokerCertificatePath – The relative file path to the
  • BrokerRootCertificatePath – The relative path to the AWS root certificate
  • BrokerPort – the port that the MQTT Instance is using. Amazon uses port 883
  • ClientPrefix – Prefix for the name that will be used for identifying this client.
  • DefaultTopic – The topic that the client will automatically subscribe to upon starting

Concerning the client prefix, every client is identified by a unique string. To ensure the string is unique, I am generating a GUID when the application starts. It’s possible that someone starts more than one instance of the program. For this reason I don’t persist the GUID. A second instance of the program will have a different GUID. But I still want the string to be recognizable as having come from this program. The ClientPrefix string puts a recognizable string before the GUID to satisfy this need.

The paths in the settings are relative to the application. To load the certificates using these paths and to generate a new client name, I use the following code.

Settings ds = Settings.Default;
var rootCertificatePath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, ds.BrokerRootCertificatePath);
var deviceCertificatePath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, ds.BrokerCertificatePath);
var rootCertificate = X509Certificate.CreateFromCertFile(rootCertificatePath);
var deviceCertificate = X509Certificate.CreateFromCertFile(deviceCertificatePath);
clientName = $"{ds.ClientPrefix}-${Guid.NewGuid().ToString()}";

With that, we have all the information that we need for connecting to the MQTT broker. We can instantiate a MqttClient, subscribe to it’s events, and start showing the message topics. The call to establish a connection is a blocking call. When it returns, a connection will have been established.

client = new MqttClient(ds.BrokerDomainName, ds.BrokerPort, true, rootCertificate, deviceCertificate, MqttSslProtocols.TLSv1_2);
client.MqttMsgSubscribed += Client_MqttMsgSubscribed;            
client.MqttMsgPublishReceived += Client_MqttMsgPublishReceived;
try
{
    client.Connect(clientName);

    var defaultTopic = ds.DefaultTopic;
    if (!String.IsNullOrEmpty(defaultTopic))
    {
        client.Subscribe(new string[] { defaultTopic }, new byte[] { MqttMsgBase.QOS_LEVEL_AT_LEAST_ONCE });
    }
} catch(Exception ex)
{
    MessageBox.Show(ex.Message, "Could not connect");
}

The primary information of concern in a message is the topic. The message may also have a payload. I capture both of those items. It is possible that the payload contains data that isn’t a string. I’ve decided not to show it, but captured it anyway should I change my mind. To hold the information I use the following class.

public class ReceivedMessage: ViewModelBase
{

    private string _topic;
    public String Topic { 
        get { return _topic; }
        set
        {
            SetValueIfChanged(() => Topic, () => _topic, value);
        }
    }

    private byte[] _payload;
    public byte[] Payload
    {
        get { return _payload; }
        set
        {
            SetValueIfChanged(() => Payload, () => _payload, value);
        }
    }

    DateTimeOffset _timestamp = DateTimeOffset.Now;
    public DateTimeOffset Timestamp
    {
        get { return _timestamp; }
        set
        {
            SetValueIfChanged(()=>Timestamp, () => _timestamp, value);
        }
    }
}

The base class from which this derives, ViewModelBase, is something I’ve talked about before. See this post if you need more information on how this base class allows this class to be bound to the UI. As new messages come in, I add their content to instances of ReceivedMessage and add them to an ObservableCollection. The collection is bound to a ListView on the UI. The entirety of the main UI window declaration follows. This UI uses only the default code for its code-behind.

<Window x:Class="MessageWatcher.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:vm="clr-namespace:MessageWatcher.ViewModels"
        xmlns:local="clr-namespace:MessageWatcher"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">

    <Grid>
        <Grid.DataContext>
            <vm:MainViewModel />
        </Grid.DataContext>

        <ListView ItemsSource="{Binding MessageList}">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <TextBlock Text="{Binding Topic}" />
                    </Grid>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>
    
    </Grid>
</Window>

With that, I had a working viewer for monitoring the messages as they went by.


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Updated ViewModelBase for my WPF Projects

When I’m working on projects that use WPF, there’s a set of base classes that I usually use for classes that are bindable to the UI. Back in 2016 I shared the code for these classes. In 2018, I shared an updated version of these classes for UWP. I have another updated version of these classes that I’m sharing in part because it is used in some code for a future post.

For those unfamiliar, the WPF derived Windows UI technologies support binding UI elements to code classes so that the UI is automatically updated with a value in the class changes. Classes that are bound to the UI must implement the INotifyPropertyChanged interface. This interface defines a single event of type PropertyChangedEventHandler. This event is raised to indicate that a property on the class has changed. The event data contains the name of the class member that has changed. UI elements bound to that member get updated in response.

The class that I’ve defined, ViewModelBase, eases management of that event. The PropertyChanged event expects the name of the property to be passed as a string. If the name of the property is passed directly as a string in code, there’s opportunity for bugs from mistyping the property name. Or, if a property name is changed, there is the possibility that a string value is not appropriately updated. To reduce the possibility of such bugs occurring the ViewModelBase that I’m using uses Expressions instead of strings. With a bit of reflection, I extract the name of the field/property referenced, which gaurantees that only valid values are used. If something invalid is passed it would result in failure at compile time. Using an expression allows Intellisense to be used which reduces the chance of typos. If a field or property name is changed through the VisualStudio IDE, these expressions are recognized too. While I did this in previous versions of this classes, it was necessary to make some updates to how it works based on changes in .Net.

Additionally, this version of the class can be used in code with multiple threads. It uses a Dispatcher to ensure that the PropertyChanged events are routed to the UI thread before being raised.

public abstract class ViewModelBase : INotifyPropertyChanged
{
    public ViewModelBase()
    {
        this.Dispatcher = Dispatcher.CurrentDispatcher;
    }
    [IgnoreDataMember]
    [JsonIgnore]
    public Dispatcher Dispatcher { get; set; }

    protected void DoOnMain(Action a)
    {
        Dispatcher.Invoke(a);
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(String propertyName)
    {
        if (PropertyChanged != null)
        {
            Action a = () => { PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); };
            if (Dispatcher != null)
            {
                Dispatcher.Invoke(a);
            }
            else
            {
                a();
            }
        }
    }

    protected void OnPropertyChanged(Expression expression)
    {
        OnPropertyChanged(((MemberExpression)expression).Member.Name);
    }

    protected bool SetValueIfChanged<T>(Expression<Func<T>> propertyExpression, Expression<Func<T>> fieldExpression, object value)
    {
        var property = (PropertyInfo)((MemberExpression)propertyExpression.Body).Member;
        var field = (FieldInfo)((MemberExpression)fieldExpression.Body).Member;
        return SetValueIfChanged(property, field, value);
    }

    protected bool SetValueIfChanged(PropertyInfo pi, FieldInfo fi, object value)
    {
        var currentValue = pi.GetValue(this, new object[] { });
        if ((currentValue == null && value == null) || (currentValue != null && currentValue.Equals(value)))
            return false;
        fi.SetValue(this, value);
        OnPropertyChanged(pi.Name);
        return true;
    }
}

Commands are classes that implement the ICommand interface. ICommand objects are bound to UI elements such as buttons and used for invoking code. This interfaces defines three members. There is an event named CanExecuteChange and two methods, CanExecuteChange() and Execute(). The Execute() method contains the code that is meant to be invoked when the user clicks on the button. CanExecute() returns true or false to indicate whether the command should be presently invokable. You may want a command to not be invokable until the user has satisfied certain conditions. For example, on a UI that uploads a file might want the upload button disabled until the user selected a file, and that file is a valid file. For that scenario, your implementation of CanExecute() would check if a file had been selected and if the file is valid and only return true if both conditions are satisfied. Or, if the command started a long running task for which only one instance is allowed, the CanExecute() function may only return true if there are now instances of the task running.

In this code, I’ve got a DelegateCommand class defined. This class has been around in its current form for longer than I remember. I believe it was originally in something that Microsoft provided, and it hasn’t changed much. To facilitate creating objects that contain the code, the DelegateCommand class acceptions an action (an action is a function that can be easily passed around as an object). The constructor for the class accepts either just an action to execute, or an action and a function used by CanExecute() (if no function is passed for CanExecute() it is assumed that the command can always be execute.

There are two versions of the DelegateCommand class. One is a Generic implementation used when the execute command must also accept a typed parameter. The non-generic implementation receives an Object parameter.

    public class DelegateCommand : ICommand
    {
        public DelegateCommand(Action execute)
            : this(execute, null)
        {
        }

        public DelegateCommand(Action execute, Func<object, bool> canExecute)
        {
            _execute = execute;
            _canExecute = canExecute;
        }

        public bool CanExecute(object parameter)
        {
            if (_canExecute != null)
                return _canExecute(parameter);
            return true;
        }

        public void Execute(object parameter)
        {
            _execute();
        }

        public void RaiseCanExecuteChanged()
        {
            if (CanExecuteChanged != null)
                CanExecuteChanged(this, EventArgs.Empty);
        }

        public event EventHandler CanExecuteChanged;

        private Action _execute;
        private Func<object, bool> _canExecute;
    }


    public class DelegateCommand<T> : ICommand
    {
        public DelegateCommand(Action<T> execute)
            : this(execute, null)
        {
        }

        public DelegateCommand(Action<T> execute, Func<T, bool> canExecute)
        {
            _execute = execute;
            _canExecute = canExecute;
        }

        public bool CanExecute(object parameter)
        {
            if (_canExecute != null)
            {

                return _canExecute((T)parameter);
            }

            return true;
        }

        public void Execute(object parameter)
        {
            _execute((T)parameter);
        }

        public void RaiseCanExecuteChanged()
        {
            if (CanExecuteChanged != null)
                CanExecuteChanged(this, EventArgs.Empty);
        }

        public event EventHandler CanExecuteChanged;

        private Action<T> _execute;
        private Func<T, bool> _canExecute;
    }

By itself, this code might not be meaningful. But I’ll be referencing it in future content, starting with a post scheduled for a couple of weeks after this one.


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Mastering Windows Presentation Foundation

Dynamically Rendering a Sound in HTML/JavaScript

Every so often I’ll code something not because it is something that I need, but because creating it is enjoyable. I stumbled upon something that I had coded some time ago and I thought it was worth sharing. I was experimenting with dynamically rendering sound using various technologies. This posts focuses on performing that within HTML/JavaScript. This post will explain the code.

When you are rendering sound in the browser before you can actually play it the user must interact with the page . This prevents a window that just opened in another tab or behind other windows from being noisy before a user knows about it.  If you were using this technology in a real solution you  would want to design your application such that you know the user has clicked, scrolled, or engaged in some other interaction at least once before your code begins doing anything.

To render audio you need a reference to the AudioContext object. On many browsers this can be found on window.AudioContext. On webkit browsers it can be found in window.webkitAudioContext. An easy way to get a reference to the right object is to coalesce the two.

var AudioContext = window.AudioContext || window.webkitAudioContext;

Now we can make our own instance of an AudioContext instance. When creating an AudioContext  two options that you can specify are the sample rate of the audio and the latency. The Latency setting allows you to balance power consumption on the machine with responsiveness to the audio that is being rendered.

var context = new AudioContext({ latencyHint: "interactive", sampleRate:48000});

From our audio context we can create our AudioBuffer objects. These are the objects that contain the waveform data for the sounds. An AudioBuffer object could have a different sample rate than the AudioContext used to make it. In general though I don’t suggest doing this.  An AudioBuffer object could have multiple channels. We will use a single channel (monaural). When creating the AudioBuffer we must specify the number of channels in the audio, the sample rate, and the count of samples in the buffer. The number of samples can directly be mapped to a time length. If I wanted to have a buffer that were 2 seconds long and I have a sample rate of 48KHz (48,000 samples per second) then the number of samples needed in the AudioBuffer is 2 * 48,000 or 96,000.

const SAMPLE_RATE = 48000;
const CHANNEL_COUNT = 1;
const SAMPLE_COUNT = 2 * SAMPLE_RATE; //for 2 seconds
var audioBuffer = context.createBuffer(CHANNEL_COUNT, SAMPLE_COUNT, SAMPLE_RATE);

The Web Audio API contains a function for generating tones. I’m not going to use it. Instead I’m going to manually fill this buffer with the data needed to make a sound. Values in the audio buffer are floating point values in the range of -1.0 to 1.0. I’m going to fill the buffer with a pure tone of 440 Hz.  The Math.Sin function is used here. The value passed to Math.Sin must be incremented by a specific value to obtain this frequency.  This value is used in a for-loop to populate the buffer.

const TARGET_FREQUENCY = 440;
const var dx = 1 / (SAMPLE_RATE * TARGET_FREQUENCY);

var channelBuffer = audioBuffer.getChannelData(1);
for(var i=0, x=0;i<SAMPLE_COUNT;++x, x+=dx) {
   channelBuffer[i] = Math.sin(x);
}

The AudioBuffer object is populated. In the next step we can play it. To play the AudioBuffer it gets wrapped in an AudioBufferSource and connected to the destination audio device.

var source = context.createBufferSource();
source.buffer = audioBuffer;
source.connect(context.destination);
source.start();

If you put all of these code samples in a JavaScript file and run it in your browser after you click the 440 tone will begin to play. It works, but let’s do something a little more interesting; I want to be to provide a list of frequencies and hear them played back in the order in which I specified them. This will give the code enough functionality to play a simple melody. To make it even more interesting I want to be able to have these frequencies play simultaneously. This will allow the code to play chords and melodies with polyphony.

The list of frequencies could be passed in the form of a list of numbers. I had specifying melodies that way; I’ve done it on the HP48G calculator.  Instead of doing that, I’ll make a simple class that will hold a note  (A,B,C,D,E,F, G), a number for the octave, and duration. An array of these will make up one voice within a melody. If multiple voices are specified they will all play their notes at once.  I’m switching from JavaScript to TypeScript here just to have something automated looking over my shoulder to check on mistakes. Remember that TypeScript is a super set of JavaScript. If you know JavaScript you will be able to follow along.  For fields that contain notes I’m constraining them to being one of the following values. Most of these are recognizable music notes. The exception is the letter R will will be used for rest notes (silence).

type NoteLetter = 'A♭'|'A'|'A#'|'B♭'|'B'|'C'|'C#'|'D♭'|'D'|'D#'|'E'|'F'|'F#'|'G♭'|'G'|'G#'|'R';
type Octave = number;
type Duration = number;
 
 

I’ve made a  dictionary to map each note letter to a frequency.  I also have a Note class that will contain the information necessary to play a single note.  Most of the fields on this class explain themselves (letter, octave, duration, volume). The two fields, rampDownMargin and rampUpMargin specify how long a note should take to come to full volume. When I initially tried this with no ramp time two notes that were side-by-side that had the same frequency sounded like a single note. Adding a time for the sound to ramp up to full volume and back down allowed each note to have its own distinct sound.

class Note {
    letter:NoteLetter;
    octave:Octave;
    duration:Duration;
    volume = 1;
    rampDownMargin = 1/8;
    rampUpMargin = 1/10;

    constructor(letter:NoteLetter,octave:Octave,duration:Duration) {
        this.letter = letter;
        this.octave = octave;
        this.duration = duration;
    }
}

A voice will be a collection of notes. An array would be sufficient. But I want to also be able to expand upon the voice class to support some other features. For example, I’ve added a member named isMuted so that I can silence a voice without deleting it. I may also add methods to serialize or deserialize a voice or functionality to make editing easier.

class Voice { 
    noteList:Array;
    isMuted = false;

    constructor() { 
        this.noteList = [];
    }

    addNote(note:NoteLetter, octave:number|null = null, duration:number|null = null ) : Note {
        octave = octave || 4;
        duration = duration || 1;
        var n = new Note(note, octave, duration);
        this.add(n);
        return n;
    }

    add(n:Note):void {
        this.noteList.push(n);
    }

    parse(music:string):void {
        var noteStrings = music.split('|');
    }

}

Voices are combined together as a melody. In addition to collecting the voices within this class the functionality for rendering the voices to playable audio buffer also happens here.

class Melody { 

    voiceList:Array;

    constructor() {
        this.voiceList = [];
    }

    addVoice():Voice {
        var v = new Voice();
        this.add(v);
        return v;
    }

    add(v:Voice) { 
        this.voiceList.push(v);
    }

    render(audioBuffer:AudioBuffer, bpm:number) {
        var channelData = audioBuffer.getChannelData(0);
        var sampleRate = audioBuffer.sampleRate;
        var samplesPerBeat = (60/bpm)*sampleRate;
        this.voiceList.forEach(voice => {
            if(voice.isMuted)
                return;
            var position = 0;
            var x = 0;
            voice.noteList.forEach((note)=>{                

                var octaveMultiplier = Math.pow(2,note.octave );
                var frequency = noteFrequency[note.letter] * octaveMultiplier;
                var dx:number = (frequency == 0 )? 0 : (1 / sampleRate * frequency);                
                var sampleCount = samplesPerBeat * note.duration;
                var rampDownCount = samplesPerBeat * note.rampDownMargin;
                var rampUpCount = samplesPerBeat * note.rampUpMargin;
                var noteSample = 0;

                while (sampleCount>0 && position < channelData.length) {                     var rampAdjustment = 1;                     if(rampUpCount > 0) {
                        rampAdjustment *= Math.min(rampUpCount, noteSample)/rampUpCount;
                    }

                    if(rampDownCount>0) {
                        rampAdjustment *= Math.min(rampDownCount, sampleCount)/rampDownCount;
                    }

                    

                    channelData[position] += rampAdjustment * 0.25 * note.voume * Math.sin(x);
                    --sampleCount;
                    ++noteSample;
                    ++position;
                    x += dx;
                }
            });
        });
    }
}
 
To test this code out I’ve made a an audio buffer using the code from the earlier sample. I then created a Melody objected and added a couple of voices to it that place a scale in reverse order.
 
var song = new Melody();

var voice = song.addVoice();

voice.addNote('C', 4);
voice.addNote('D', 4);
voice.addNote('E', 4);
voice.addNote('F', 4);
voice.addNote('G', 4);
voice.addNote('A', 4);
voice.addNote('B', 4);
voice.addNote('C', 5, 2);

voice = song.addVoice();

voice.addNote('C', 5, 1);
voice.addNote('B', 4);
voice.addNote('A', 4);
voice.addNote('G', 4);
voice.addNote('F', 4);
voice.addNote('E', 4);
voice.addNote('D', 4);
voice.addNote('C', 4, 2);    

song.render(audioBuffer, 120 /*BPM*/);
var source = context.createBufferSource();
source.buffer = audioBufferList[0];
source.connect(context.destination)
source.start();
 
With this functionality present I feel comfortable trying to play out a recognizable tune. The first tune I tried was one from a video game that I think many know. I found the sheet music and typed out the notes.
 
var song = new Melody();

var voice = song.addVoice();
voice.isMuted = false;
voice.addNote('E', 6,0.5);
voice.addNote('E', 6, 0.5);
voice.addNote('R', 6, 0.5);
voice.addNote('E', 6, 0.5);
voice.addNote('R', 6, 0.5);
voice.addNote('C', 6, 0.5);
voice.addNote('E', 6, 0.5);
voice.addNote('R', 6, 0.5);
voice.addNote('G', 6, 1);
voice.addNote('R', 6);
voice.addNote('G', 5 , 0.5);
voice.addNote('R', 6,1.5);

//------------
voice.addNote('C', 5 , 0.5);
voice.addNote('R', 6,1);
voice.addNote('G', 5 , 0.5);
voice.addNote('R', 6,1);
voice.addNote('E', 5 , 0.5);
voice.addNote('R', 6,1);
voice.addNote('A', 6 , 0.5);
There are more notes to this (which are not typed out here). IF you want to hear this in action and see the code execute, I have it hosted here: https://j2i.net/apps/dynamicSound/
 
For the sake of trying something different, I also tried “Adagio for Strings and Organ in G-Minor“. If you want to hear the results of that, you can find those here
 
I got this project as far as rendering those two melodies before I turned my attention to C/C++. I preferred using C/C++ because I had more options for rendering the sound and the restrictions of the browser are not present. However, some of the features that I used were specific to Windows. There is a potential disadvantage (depending on how the code is to be used) of it not being runnable on some other OSes without adapting to their audio APIs.
 
This is something that I may revisit later. 
 
 
 

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WiFi Scanning Part 2: Scanning on Android

Part 1 of this post was about WiFi scanning on Windows. You can find it here.

Scanning on Android isn’t hard, but there are obstacles. In what is documented as being in the interest of saving battery life, WiFi scanning is throttled on more recent devices to be limited to 4 scans within a 2 minute period. On some of my older devices this limit is not present. While I found that I could turn off the default throttling setting in the developer settings, the more recent devices was still much more limited in how often it could scan. For my purposes (building a personal collection of coordinates and WiFi access points for an embedded device) this has the effect of lowering the number of samples that can be collected with my more recent device.

Because location can be inferred from WiFi information, Android protects WiFi scanning behind the location permission. Even if the application has no interest in location information, it must have the location permission to scan for WiFi information. I do have interest in location information. I want to save the location at which the access points were observed. The permissions that I specify in the manifest include the following.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">


    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>

In addition to the manifest declarations, the application must explicitly ask the user for permission to track location. Once the application has location permissions, it can start tracking location and performing WiFi scans.

    fun getWifi() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            Toast.makeText(this, "version> = marshmallow", Toast.LENGTH_SHORT).show();
            if (checkSelfPermission( Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
                Toast.makeText(this, "location turned off", Toast.LENGTH_SHORT).show();
                var s = arrayOf<String>(Manifest.permission.ACCESS_COARSE_LOCATION, Manifest.permission.ACCESS_FINE_LOCATION)

                this.requestPermissions(s, COURSE_LOCATION_REQUEST);
            } else {
                Toast.makeText(this, "location turned on", Toast.LENGTH_SHORT).show();
                getLocationUpdates()
                wifiManager.startScan();
            }
        } else {
            Toast.makeText(this, "scanning", Toast.LENGTH_SHORT).show();
            getLocationUpdates();
            wifiManager.startScan();
        }
    }

For the location updates, I have asked for new location information if the user’s location has changed by three meters (nine feet) and if at least 10 seconds has passed. I am interest in getting multiple samples of access points from different positions to better localize them. I ask for high precision for the location information. The device will most likely use GPS based positioning, but may use any location source.

    @SuppressLint("MissingPermission")
    fun getLocationUpdates() {
        val locationRequest = LocationRequest.create()?.apply {
            interval = 10_000
            fastestInterval = 10_000
            smallestDisplacement = 3.0f
            priority = LocationRequest.PRIORITY_HIGH_ACCURACY
        }

        locationCallback = object : LocationCallback() {
            override fun onLocationResult(locationResult: LocationResult) {

                locationResult ?: return
                for (location in locationResult.locations){
                    currentLocation = location
                    // Update UI with location data
                    // ...
                }
            }
        }
        locationRequest?.let {
            fusedLocationClient.requestLocationUpdates(
                it,
                locationCallback,
                Looper.getMainLooper())
        }
    }

To scan for Wifi, I’ll need the wifiManager class and I’ll need an IntentFilter. The WifiManager instance is used to ensure that WiFi is turned on and to request the WiFi scan. The IntentFilter

   lateinit var wifiManager:WifiManager
    val intentFilter = IntentFilter().also {
        it.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)
    }

I instantiate the WifiManager in the activity’s onCreate method. After getting an instance I ensure that WiFi is turned on.

        fusedLocationClient = LocationServices.getFusedLocationProviderClient(this)
        wifiManager = getSystemService(Context.WIFI_SERVICE) as WifiManager
        if(!wifiManager.isWifiEnabled) {
            Toast.makeText(this, "Turning on Wifi...", Toast.LENGTH_LONG).show()
            wifiManager.isWifiEnabled = true
        }

        wifiReceiver = WifiReceiver(wifiManager, this)
        wifiInfo = wifiManager.connectionInfo
        registerReceiver(this.wifiReceiver, intentFilter)

The WifiReceiver class above is a class I’ve made that derives from BroadcastReceiver. I must implement a BroadcastReceiver with an onReceive() method. After the OS has scanned for available WiFi, it will notify our app of the availability of the results through this instance. When the results are available, they can be read from WiFiManager.scanResults. I’m only saving results if I have location information too. If I don’t have location information, the results are discarded. If results are available, I save them to a data class that I’ve called ScanItem. This class only serves to hold the values. Populated instances of ScanItem are passed to another class for being persisted to a database.

        override fun onReceive(p0: Context?, intent: Intent?) {
            var action:String? = intent?.action
            if(mainActivity.currentLocation!=null) {
                val currentLocation = mainActivity.currentLocation!!;
                var result = wifiManager.scanResults
                Log.d(TAG, "results received");

                val scanResultList: List<ScanItem> = ArrayList<ScanItem>(result.size)

                for (r in result) {
                    var item = ScanItem(r.BSSID)
                    item.apply {
                        sessionID = SessionID
                        clientID = mainActivity.clientID
                        latitude = currentLocation.latitude
                        longitude = currentLocation.longitude
                        if (currentLocation.hasAccuracy()) {
                            horizontalAccuracy = currentLocation.accuracy
                        }
                        if (currentLocation.hasVerticalAccuracy()) {
                            verticalAccuracy = currentLocation.verticalAccuracyMeters
                        }
                        altitude = currentLocation.altitude.toFloat()
                        BSSID = r.BSSID
                        SSID = r.SSID
                        level = r.level
                        //http://w1.fi/cgit/hostap/tree/wpa_supplicant/ctrl_iface.c?id=7b42862ac87f333b0efb0f0bae822dcdf606bc69#n2169
                        capabilities = r.capabilities 
                        frequency = r.frequency
                        datetime = currentLocation.time
                        locationLabel = mainActivity.locationLabel
                    }
                    mainActivity.scanItemDataHelper.insert(item)
                }
                mainActivity.currentLocation = null
                mainActivity.addNewEntryCount(result.size)
                Toast.makeText(mainActivity, "scan Saved", Toast.LENGTH_SHORT).show();
            }
            wifiManager.startScan()
        }
    }

As soon as I’ve saved all the results, I clear the location and start a new scan. What I’ve done here only works for me because I have disabled scan throttling on my device. By default, more recent Android devices only allow 4 scans within two minutes. It might have been better if I had scheduled the scans to be requested on an interval. But I went with a quick-and-dirty solution since I was implementing this just before getting on the road. I needed to drive a few hundred miles over a few days and I wanted to maximize on the opportunity to collect data.

I was able to reduce a significant data set from several days of scanning to a collection of hashes for the WiFi ID along with a latitude and longitude. My source dataset may contain an access point multiple times, as they are usually visible from multiple locations. In reducing the dataset, for each WiFi ID I got the average of its location (though I removed vehicle Wifi from my dataset. I found Wifi from Tesla’s, VW, and “Tanya’s iPhone” from vehicles on the same path as me for several miles) and exported a 32-bit hash of the WiFi ID, the latitude, and longitude (12-bytes per access point). Using a hash instead of the actual data let’s me reduce the storage size.

I’ve had success in using this to get an embedded device to determine its location. I’ll write more about this in another post. Until then, if you want a brief description of what that involved, you can find it here.


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WiFi Scanning Part 1:Scanning on Windows

I’ve enjoyed my experiments with making my own WiFi based location system. I’ll be writing on it more, but before I do I wanted to turn some attention to the WiFi scanning itself. This is fairly easy to do on both Windows and Android. I won’t be discussing iOS because at the time of this writing, iOS doesn’t allow user applications to perform WiFi scanning (the devices do it themselves and support WiFi based location, but do not expose the lower level functionality to the developers). In this first post I discuss WiFi scanning on Windows.

WiFi Scanning on Windows

Windows in my opinion was the easiest system on which to perform the scanning. An application initiates the scan and the operating system takes care of most of the rest. Is the application tries to retrieve the information a bit later, it’s there. While some might be tempted to request a scan, add a delay, and then retrieve the results, don’t do this. There a number of reasons why, including you can’t really know how long the scan will actually take. Windows also allows a callback function to be registered to receive notifications on operations. It is better to register a callback to be notified when the WiFi scanning is complete. You can see the full source code for how to perform the scanning here. Most of the rest of this is an explanation of the code.

Wireless operations start with requesting a HANDLE that is used to track request and operations. The Windows function WlanOpenHandle() will return this handle. Hold onto it until your application is either closing or nolonger needs to perform wireless operations. When you are done with the HANDLE, release it with WlanCloseHandle().

Once you have your HANDLE, use it to register a notification callback with WlanRegisterNotification. When you want to unregister a callback, call this same function again passing NULL in place of the callback function.

    if (ERROR_SUCCESS == WlanOpenHandle(2, nullptr, &version, &context.wlanHandle))
    {
        result = WlanRegisterNotification(context.wlanHandle, WLAN_NOTIFICATION_SOURCE_ACM, 
                                          TRUE, (WLAN_NOTIFICATION_CALLBACK)WlanNotificationCallback, 
                                          &context, NULL, NULL);
        ...
        // Other wireless operations go here.
        ...
         WlanRegisterNotification(context.wlanHandle, WLAN_NOTIFICATION_SOURCE_ACM, 
                                  TRUE, NULL, NULL, NULL, NULL);
         WlanCloseHandle(context.wlanHandle, NULL);
    }

Enumerating the Wireless Adapters

I’ll talk in detail about the implementation of the callback function in a moment. A device could have 0 or more wireless adapters. We could request a wireless scan on each of the adapters. For my sample program, it will perform a scan on each adapter one at a time. We can get a list of all the wireless adapters in a single call. The function accepts the address of a variable that will hold a pointer to the returned data. The call to WLanEnumInterfaces takes care of allocating the memory for this information. When we are done with it, we need to deallocate the memory ourselves with a call wo WlanFreeMemory. Enumerating through the array, each element has a property named isState. If the state is equal to the constant wlan_interface_state_connected then the wireless adapter is connected to a network. I’m only scanning when an adapter is being used and connected to a network. My reasons for this is that I ended up using this in diagnostics of some connectivity problems on some remote machines and I was only interested in the adapters being used.

The actual scanning is performed in the call to WlanScan. After the call, I reset a Windows Event object (created earlier in the program, but unused until now) and then wait for the object to have a signaled state with the function WaitForSingleObject. If you are familiar with Windows synchronization objects, then take note this is how I am coordinating code in the main thread with the callback.

PWLAN_INTERFACE_INFO_LIST interfaceList;
if (ERROR_SUCCESS == (result = WlanEnumInterfaces(context.wlanHandle, NULL, &interfaceList)))
{
    std::cout << "Host, BSSID, Access Point Name, Frequency, RSSI, Capabilities, Rateset, Host Timestamp, Timestamp, BSS Type" << std::endl;

    for (int i = 0; i < (int)interfaceList->dwNumberOfItems; i++)
    {
        PWLAN_INTERFACE_INFO wirelessInterface;
        wirelessInterface = (WLAN_INTERFACE_INFO*)&interfaceList->InterfaceInfo[i];
        if (wirelessInterface->isState == wlan_interface_state_connected)
        {
            context.interfaceGuid = wirelessInterface->InterfaceGuid;
             if (ERROR_SUCCESS != (result = WlanScan(context.wlanHandle, &context.interfaceGuid, NULL, NULL, NULL)))
            {
                std::cout << "Scan failed" << std::endl;
                retVal = 1;
            }
            else 
             {
                ResetEvent(context.scanCompleteEvent);
                WaitForSingleObject(context.scanCompleteEvent, INFINITE);
             }
        } 
    }
    WlanFreeMemory(interfaceList);
}

For those not familiar, the call to WaitForSingleObject will cause the code to block until some other thread calls SetEvent on the same object. The callback that I registered will call SetEvent after it has received and process the scan information. This frees the main code to continue its processing.

Receiving the Response

I’m primary interested in printing out some attributes about each access point that is found in a format that is CSV friendly. If the notification received is for a WLAN_NOTIFICATION_SOURCE_ACM event, then that means that the scan information is available. A call to WlanGetNetworkBssList returns the information in a structure in memory allocated for us. After we get done processing this information, we need to release the memory with WlanFreeMemory(). Most of what I do with the information is direct printing of the values. I do have a function to format the BSSID information as a colon delimited string of hexadecimal digits. Information on the capabilities for the access points is stored in bit fields, which I extract and print as string. After iterating through each item in the returned information and printing the comma delimited fields, I call SetEvent so that the main thread can continue executing.

void WlanNotificationCallback(PWLAN_NOTIFICATION_DATA notificationData, PVOID contextData)
{
    DWORD result;
    PWLAN_BSS_LIST pBssList = NULL;
    PWlanCallbackContext context = (PWlanCallbackContext)contextData;
    
    switch (notificationData->NotificationSource)
    {
    case WLAN_NOTIFICATION_SOURCE_ACM:

        result = WlanGetNetworkBssList(context->wlanHandle, &context->interfaceGuid,
            NULL /*&pConnectInfo->wlanAssociationAttributes.dot11Ssid */,
            dot11_BSS_type_any,
            TRUE, NULL, &pBssList);
        if (ERROR_SUCCESS == result)
        {
            for (auto i = 0; i < pBssList->dwNumberOfItems; ++i)
            {
                auto item = pBssList->wlanBssEntries[i];
                std::cout << context->ComputerName << ", ";
                std::cout << FormatBssid(item.dot11Bssid) << ", ";
                std::cout << item.dot11Ssid.ucSSID << ", ";
                std::cout << item.ulChCenterFrequency << ", ";
                std::cout << item.lRssi << ", ";
                std::cout << ((item.usCapabilityInformation & 0x01) ? "[+ESS]" : "[-ESS]");
                std::cout << ((item.usCapabilityInformation & 0x02) ? "[+IBSS]" : "[-IBSS]");
                std::cout << ((item.usCapabilityInformation & 0x04) ? "[+CF_Pollable]" : "[-CF_Pollable]");
                std::cout << ((item.usCapabilityInformation & 0x08) ? "[+CF_PollRequest]" : "[-CF_PollRequest]");
                std::cout << ((item.usCapabilityInformation & 0x10) ? "[+Privacy]" : "[-Privacy]");
                std::cout << ", ";
                for (int k = 0; k < item.wlanRateSet.uRateSetLength; ++k)
                {
                    std::cout << "[" << item.wlanRateSet.usRateSet[k] << "]";
                }
                std::cout << ", ";
                std::cout << item.ullHostTimestamp << ", " << item.ullTimestamp << ", ";
                switch (item.dot11BssType)
                {
                case dot11_BSS_type_infrastructure: std::cout << "infastructure"; break;
                case dot11_BSS_type_independent: std::cout << "independend"; break;
                case dot11_BSS_type_any:std::cout << "any"; break;
                default: std::cout << "";
                }

                std::cout << std::endl;

            }
            WlanFreeMemory(pBssList);
        }
    

        break;
    default:
        break;
    }
    
    SetEvent(context->scanCompleteEvent);
}

That’s everything that is needed to scan for WiFi information on Windows. If you would like to see the full source code for a console program that performs these steps, I have it posted on GitHub here.

The information is printed to standard output where it can be viewed. When I need to save it, I direct standard output to a file. Many utilities support this format. I’ve used Excel, Sheets, and SQL Server Bulk Insert for processing this information.

I’m working on an explanation for how to use the same functionality on Android. That will come to this space in a couple of weeks with working code being made available on GitHub.


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Resolving “board icestick not connected” for the Lattice IceStick HX1K with Apio

The Latice iCEstick HX1K is an FPGA development board with a built in USB interface. If you are using apio with the board and follow some common instructions for preparing the board to run programs, you may encounter a failure at the upload step. When I tried, I got the error Error: board icestick not connected.

PS D:\scratchpad\icestick\leds> apio upload
C:/Users/Joel/.apio
C:/Users/Joel/.apio
C:/Users/Joel/.apio
Error: board icestick not connected

I thought I had improperly installed the driver, but after further examination I found that was correct. The problem is that there was a mismatch on the description for which the board presented itself and the description that apio was looking for. I can only guess that Lattice had updated the description for the board. The fix is easy. Find boards.json. For me this file was in the path C:\Users\%user%\anaconda3\Lib\site-packages\apio\resources. Look for the entry for the iCE40-HX1K. In that entry there is the object named ftdi that has a child string named desc. Compare this name to the output that you get from apio system --lsftdi. If it is different, update it to ensure it is identical.

Now if you attempt to upload your program it should work!


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Baltimore Root Certificate Migration for Azure: Prepare your IoT devices

Microsoft announced back in May 2021 that they were switching root certificates used for some services. That announcement is more significant now, as devices uses Azure IoT core start their migration on 15 February. If you are using IoT core, you will want to familiarize yourself with the necessary changes. More on that migration can be found here. While updates tend to be automatic for phones and machines with desktop operating systems, your custom and embedded devices might need a manual update.


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Plane Spotting with RadarBox

There are a lot of systems dedicated to safety in place for air travel. Recently, one of those systems, NOTAMS, went offline with the cause being attributed to a corrupted database file. It was a system for warning pilots about local hazards, and the loss of that system was sufficient reason to stop planes from taking off for a couple of hours. The many systems that are in place for air vehicles can be interesting, and I want to write about one of those systems that you can directly monitor, ADS-B (Automatic Data Surveillance Broadcast). Through this system, airplanes broadcast their location and heading so that other planes and ground stations can track them. This information is broadcast in the open and anyone can view it. Other aircraft use the data to help avoid collisions. It helps avoid the blind spots associated with radar, providing accurate information throughout it’s range. This information is also often used by plane spotters (a bit like birdwatching, but for planes).

Anyone can receive ADS-B information. Consumer-priced receiving equipment is available for under 100 USD. On one’s own, one can receive information from aircraft from well over 100 miles away. But many of these products also work with services that allow people with receivers to cooperate to receive a more complete and further range of data. I have a couple of receivers running that use RadarBox.

Screenshot of Radarbox Flight Tracking

Hardware Selection

You’ll generally find ADS-B receivers using one of two frequencies. 978 MHz and 1090 MHz. For RadarBox, the equipment for these two frequencies is color coded with 978 MHz being red and 1090 MHz blue. Of these two frequencies, the 1090 MHz system is in greater use. There’s not much debate to be had, 1090 MHz will be the frequency to get unless you’ve got some compelling and specific need for 978 MHz. The 978 MHz frequency is for aircraft that operate exclusively below 5,500 meters (~18,000 feet). Aircraft that operate at higher altitudes use the 1090 MHz frequency.

Having performed setup for both units, I can tell you that setup for the 1090 MHz unit was much easier. When I performed the steps on the 978 MHz unit, there were some errors in the process. On both Pis on which I performed the steps I had freshly installed the 64-bit PI OS and performed updates first. The 978 MHz setup was a lot more involved. The 1090 MHz setup was primary running some scripts and not having to figure any problems out.

Create an Account

Go to Radarbox.com. In the upper-right area you’ll see a link to login. If you are prompted to select a subscript level, stick with the free level. After completing the setup for the Pi your account will automatically be upgraded to a business account (a privilege level that normally cost 40 USD per month).

Setup

Assuming you are using a computer that you already own, the setup expense is getting an antenna and a USB ADS-B receiver. You can purchase these in a kit together for 65 to 70 USD. Connecting the hardware together is intuitive; the antenna connects to the threaded adapter on the USB. For the antenna placement, I chose a place that was up high to minimize the amount of potential obstacles attenuating the signal strength. I installed the antenna in my attic. While the system comes with u-shaped bolts for securing the antenna, I instead used zip ties and some foam to secure it on one of the beams in the attic. I didn’t install the Pis in the attic though. In the summer the temperature in the attic can become tremendously hot, and I don’t think they would survive well. Instead, I used a space through which network cable was being routed so that the connector for the antenna was in the living area of the house.

You’ll need to know the elevation at which you’ve installed the antenna in meters. This information will be necessary during the registration step.

I performed all of the steps for setup over SSH from a Mac. Installation is performed through downloading and running some scripts. The instructions can be found at https://www.radarbox.com/raspberry-pi. The directions that I post here are derived from those. The directions have a decision point on whether you are going to use receiver dongle or have it pull information from some other program. I assume you will be use the dongle. If you are, there are only 4 commands that you need to run.

sudo bash -c "$(wget -O - http://apt.rb24.com/inst_rbfeeder.sh)"
sudo apt-get install mlat-client -y
sudo systemctl restart rbfeeder
sudo rbfeeder --showkey

The first two lines will install the software services . The third line will start the service. After the service is running, you’ll need the unique key that was generated for your device. This fourth command shows the key. You can also view the key in /etc/rbfeeder.ini. Copy this key, you’ll need it to register the device.

Registration

To register the device navigate to https://www.radarbox.com/raspberry-pi/claim. After logging into your account you’ll see a text box allowing you to past an identifying key with a button to “Claim” your device. After claiming, you’ll be prompted for the location information. Enter the address at which you have your device positioned to show a map of the area. Move the map around until it is centered on the precise area in which you’ve installed the antenna. You’ll be asked to enter the elevation of the antenna too. This is the elevation is the meters above ground. RadarBox will already account for the elevation of the address that you’ve entered. Once all the information is entered, the claiming process is complete. Let the system run on its own for about 20 minutes. Later, open a browser on any computer and log into your account on radarbox.com. Once logged in, if you click on the account button . In the menu that opens there will be a group for “Stations.” Selecting that will show all of your registered devices.

Select your station. In the lower-left corner you’ll see a graph showing the status of your unit over time. Green blocks will show during times where your unit was receiving and relaying data. After your device is sending data, you’ll get a notice on a following login saying that your account has been upgraded to the Business level.

API Access

Since most of my audience is developer focused, I wanted to speak a bit about the APIs. Unlike the use of the RadarBox UI, access to the API is not free. Even some of the services that offer “free API access” keep the calls I think to be more interesting as premium (requiring payment) access. Access to the RadarBox APIs is completely independent of contributing to the data collection. The API calls consume “credits.” RadarBox sells the credits through various subscription levels, with the credits costing less-per-dollar for the highest subscription level. The least expensive subscription gives 10,000 credits for 112 USD/month. This works out to 0.012 USD per credit. When you first open a RadarBox account, you get 100 credits to start with at no cost.

There are SDKs for the API available for a variety of environments and languages, including Python, Java, TypeScript/JavaScript, C#, Swift, and more. The documentation for the API can be found at https://www.radarbox.com/api/documentation. The documentation is interactive; you can make API calls from the browser. But you’ll need an access token to make calls. To get an access token navigate to https://www.radarbox.com/api/dashboard and select the button to make a token. Note that the API calls that you make are rate limited. On the documentation page in the top-left of the page is an area where you can enter your token. The test calls that you make from the documentation will use this token.

To ensure that the token was working, I tried a low-cost call; I searched for information by airport code. The only parameter that this call needs is an ICAO airport code. For Atlanta, this code he KATL. The response provides information about the airport, including its name, both the ICAO and IATA code (most people in the USA will be more familiar with the IATA code), the name, and information on all of the airport’s runways.

The response for all of the calls contain a field that indicate how many credits are left. There are two API calls related to billing that cost 0 credits; you can inquire your usage statistics without accumulating some expense for having checked on it. I would suggest using that API call first if you are trying to test if your token works to avoid unnecessarily burning credits.

As with other APIs that cost actual money per call, you would probably want to put in place some measures of protection to minimize unnecessary calls. For example, if you were making a mobile app that used this functionality, instead of making calls directly to the RadarBox API, you could make a web service that caches responses for various amounts of time and have your application call that. Some information, such as information on the locations of airports and the runways, won’t change much; the last time my local airport changed in some meaningful way was in 2006 when it added a fifth runway. Information from a call such as that may be worth keeping cached until manually forced to refresh. But for some information, such as the location of a specific plane, since the information is updated frequently it may be worth caching for only a few seconds.

With all that said, let’s make a quick application that will make a call related to why what turned my mind to this. One of the API calls retrieves NOTAMS information for an airport nearby. To minimize API calls, I made a single call from the RadarBox documentation page and saved the response. Most of this program was written using the static response and then updated to make an actual API call.

The program needs a token for making its API calls. The token is not hard-coded into the program. Instead, when the program is first run it will prompt for a token to be entered. Since this value is likely being copied and pasted. the UI provides a paste button to avoid the gestures for selecting the text box, opening the clipboard, and then selecting the paste operation.

For determining the closest airport, I found a list of all the major airports in the world and their coordinates. Using the equation that was in a recent post, I checked the distance between the users position and the airports to find the one with the smallest distance.

fun findClosestAirport(latitude:Double, longitude:Double):airportCode? {
    var distance = DistanceCalculator.EarthRadiusInMeters
    var ac:airportCode? = null
    val d = DistanceCalculator()
    airportCodes.forEach {
        var newDistance = d.CalcDistance(
            this.latitude, this.longitude,
            it.coordinates.latitude, it.coordinates.longitude,
            DistanceCalculator.EarthRadiusInMeters
        );
        if(newDistance < distance &&  it.iata_code != null) {
            distance = newDistance
            ac = it
        }
    }
    if(ac != null) closestAirportTextEdit.setText("K${ac.iata_code}")
    
    return ac;
}

There’s an SDK available for using RadarBox. But I didn’t use that. Instead, I just made the call directly. Since I only needed one SDK call I was fine calling it directly. The URL prefix to use for all of the API calls is https://api.radarbox.com/. To read the NOTAM notifications, the path is /v2/airspace/${airportCode}/notams. The response comes back formatted in JSON. Parsing the response from a JSON string to some objects is only a few lines of executable code and a few data class definitions. Here is one of the data classes.

@Serializable
data class notam(
    val id:String? = null,
    val number:Int,
    val notamClass:String? = null,
    val affectedFir:String? = null,
    val year:String,
    val type:String? = null,
    @Serializable(with = DateSerializer::class) val effectiveStart: LocalDateTime? = null,
    //val effectiveStart:String,
    @Serializable(with = DateSerializer::class) val effectiveEnd:LocalDateTime? = null,
    val icaoLocation:String,
    @Serializable(with = DateSerializer::class) val issued:LocalDateTime,
    //val issued:String,
    val location:String,
    val text:String,
    val minimumFlightLevel:String? = null,
    val maximumFlightLevel:String? = null,
    val radius:String? = null,
    var translations:List<translation>
    )  {
}

I used OkHttp for making my HTTP request. The target URL and a Bearer token header are needed for the request. When the response is returned, I deserialize it. I also filter out any results that have an effective date that makes the notice nolonger applicable. In running the code I found that less than 0.3% of the notifications that I received had expired. Filtering them out was completely optional.

    fun updateNotamsFromRadarbox(airportCode:String):Call {
        val requestUrl = "https://api.radarbox.com/v2/airspace/${airportCode}/notams"
        val client = OkHttpClient();
        val request = Request.Builder()
            .url(requestUrl).addHeader("Authorization", "Bearer $radarBoxToken")
            .build()
        val call = client.newCall(request)
        call.enqueue(object:Callback {
           override fun onResponse(call: Call, response:Response) {
                val responseString = response.body?.string()
               if(responseString != null) {
                   var notamsResponse = Json.decodeFromString(notamResponse.serializer(),responseString)
                   var now:LocalDateTime = LocalDateTime.now()
                   var filteredNotams = notamsResponse.apiNotams.filter { i -> ((i.effectiveStart==null)||(i.effectiveStart<now))&&((i.effectiveEnd==null)||(i.effectiveEnd>now))  }
                   showNotams(filteredNotams)
               }
           }
            override fun onFailure(call: Call, e: IOException) {
                Log.e(TAG,e.message.toString())
            }
        });
        return call;
    }

The results come back on another thread. Before updating a ListViewAdapter with the results, I have to make sure that the code is executing on the right thread.

fun showNotams(notamList:List<notam>) {
    runOnUiThread {
        notamLVA = notamsListViewAdapter(this, ArrayList(notamList))
        val notamLV = findViewById<ListView>(R.id.currentwarnings_notamlva)
        notamLV.adapter = notamLVA
    }
}

If you want to see the code for this, you can find it on GitHub ( https://github.com/j2inet/notams ).


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Favourites from CES 2023

Last week marked the end of CES 2023. CES (Consumer Electronics Show) is a yearly tradeshow in which various companies show off their consumer-focus technological developments for everything from the kitchen to the road. Some of the items shown are for planned products. Others are prototypes or show pieces. Many of them show the application of digital electronics to a product. Due to Covid, the show was virtual in 2021. In 2022 the show was in-person, though with a much smaller presentation. This year, 2023, the show was closer to what it had been in times past. Reviewing some of the technologies and products displayed at the show, I wanted to highlight some of my favourites.

Vive XR Elite

The VIVE XR Elite is an augmented reality headset coming later this year. It is available for preorder now for about 1100 USD. This is less expensive than the Meta Quest Pro. It functions both as a standalone unit and can use your PC for gaming via a wireless connection. If you are nearsighted, the headset allows for the projection to be refocused for nearsightedness down to -6. At CES these were presented as units with a 90 Hz refresh rate. Though on their web page they are still described as having a 60 Hz refresh rate. The display resolution per eye is 1920×1920 pixels. The unit only wears 650 grams, with the optics in front and the batter pack in the back making for a more balanced layout. While the unit has controllers, it is also capable of hand tracking.

EcoFlow Blade

EcoFlow’s primary products are solar panels and batteries. For a person looking to go off-grid, these may be great accessories. These are also great if you live in an area with an unreliable power system. The EcoFlow Blade is an all-electric automated lawnmower. Even off-grid, you might want to have a nice lawn🙂. It looks a lot more like an RC car than a lawnmower. The company says that it can both mow the grass and pickup fallen leaves. Having used electric mowers in conventional form factor, my experience thus far has been that they sometimes don’t have enough power to do the entire lawn in one session. However, if the grass cutting is automated, I’m less concerned with how many sessions it takes.

EcoFlow also showed off batteries for the entire house and a portable fridge/ice-maker also powered by their batteries. You can find more about these products here.

Ring Cameras for Car and House

Ring announced a couple of new cameras. These cameras had actually been announced before, but plans were apparently disrupted by the pandemic. One product is a Ring Camera for one’s auto-interior and exterior . The unit has cameras facing in both directions so that it records both the road and what is happening inside the car. When connected to the Internet via WiFi or LTE the owner can get alerts of events inside the car and engage in two-way conversation. With a verbal command (“Alexa, Record”). The unit is powered through the car’s OBD port. Amazon recommends for safety reasons, only use the unit in a vehicle with the OBD port on the left side of the steering wheel. This unit will be available for purchase in February.

Another is the Always Home Ring Camera. This is a drone that flies a path throughout your home on a pathway you’ve selected before flying back to its charging base. This camera solves a problem in security cameras in that they can only see from a limited angle. Withe the camera being mobile, there are more angles that it can potentially capture. Presently, Amazon is taking orders by invitation only.

Wireless 4K TV

While the 97-inch screen of the the LG M3 is eye-catching, for me the more significant attribute is that it can receive 4K signals wirelessly. Given the amount of effort I put into hiding or at least making neat the wires for the various video connections that I have, I see this as a product solving a modern day solution. The TV has a peripheral device to which video and audio sources connect. This box transmits to the TV. This solution is called “Zero Connect” and is expected to be part of their 2023 TV lineup.

Android Satellite Connectivity

Snapdragon is rolling out its chips that provide connectivity with Iridium satellites to Android devices this year. The connectivity could be used to have two-way text based communication. While the functionality it provides is simple, the ability to communicate in emergency situations is vital. Satellite connectivity may greatly reduce the situations in which one can find themselves without the ability to communicate with others.


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Experiment in “WarDriving” for Offline WiFi Locating

This is a quick explanation of a recent YouTube Short.

I was working with a Wio Terminal from Seeed Studio, and I needed for one to perform rough detection of its location. The most obvious way to do this is to add GPS hardware to the device. This works, but since I was concerned with batter life, adding additional hardware also felt like a disadvantage. Detection of known WiFi access points has long been a solution for location detection. I went on a search to see where I could download a listing of known WiFi hardware IDs (BSSIDs) and their location. I couldn’t find any. While there are some open source solutions for WiFi based location to which users can submit data, none of them allow the complete dataset to be downloaded. That’s no problem, I will just make my own.

This was the day before Christmas. I was going to be performing a lot of driving. To make the most of it, I quickly put together a WiFi scanning solution on Android to save WiFi data and the location at which it was found. I ended up with a dataset of about 10,000 access points. This is plenty to experiment with. After some processing and filtering, I reduced this information to a data set of 12 bytes per record to put on an SD card. The ID that a router broadcast (BSSID) is 6 bytes, but I store the has of the BSSID instead of the BSSID, which is only 4 bytes. A completed record is the 4 byte has, 4 byte latitude, and 4 byte longitude.

While I had a strategy in mind for quickly searching through a large dataset, 10,000 access points is not huge. The WioTerminal could find the matching record even if it performed a linear search. When the Wio powers up, I set it to scan the environment for the BSSIDS , calculate their hashes, and search for a matching hash. Since this was only a proof of concept, I only searched for a first match. There are some other strategies that may give more accurate results in exchange for increased computation.

The solution has touched on C++, C#, and JavaScript. There is a lot to be said about it. I’ll discuss it across several posts with the first describing the collection of data in January 2023. More to come!


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Using a Batch File as a Process Watcher

Using a utility that monitors a process and restarts it if it is terminated for any reason is a common need on programs that are driving publicly viewable displays. Were a crash to happen, or if the process were intentionally terminated, we may still need the process to restart. I’ve got several solutions for this, each with their own strengths. I recently needed a solution for this and didn’t have access to my normal solutions. I was able to make what I needed using Windows in-built command line utilities and a batch file. While I have a preference to PowerShell over batch file scripts, I used batch files this time because of constraints from organizational policies. I’m placing a copy of the script here since I thought it might be useful to others.

This script checks to see if the process of interest is running every 10 seconds. If the process is not running, it will start the program in another 5 seconds. Such large delays are not strictly necessary. But I thought it safer to have them should someone make a mistake while modifying this script. In an earlier version of the script I made a type and found myself in a situation where the computer was stuck in a cycle of spawning new processes. Stopping it was difficult because each new spawned process would take focus from the mouse and the keyboard. With the delays, were that to happen again there is sufficient delay to navigate to the command window instance running the batch file and terminate it.

ECHO OFF
SET ProcessName=notepad.exe
SET StartCommand=notepad.exe
SET WorkingDrive=c:
SET WorkingDirectory=c:\WorkingDirectory
ECHO "Watching for process %ProcessName%"
:Again
timeout /t 10 /nobreak > NUL
echo .
tasklist /fi "ImageName eq %ProcessName%" /fo csv 2> NUL | find /I "%ProcessName%" > NUL
if "%ERRORLEVEL%"=="0" (
    echo Program is running
) else (
    echo Program is not running
    timeout /t 5 /nobreak > NUL
    %WorkingDrive%
    cd %WorkingDirectory%
    start %StartCommand%
)
goto Again

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Transition Drivers to New Windows Installation

Over the Thanks Giving holiday, I took advantage of the extended time off from work and projects to reinstall Windows on newer, larger drives. When reinstalling Windows finding all of the drivers has traditionally been a pain point for me. This time around someone gave me a bit of information that made handling the drives much easier. After performing the installation, I didn’t have sound. I checked the device manager and found there were a lot of devices that were not recognized.

I initially started with trying to figure out what these devices were. Opening the properties of a device and viewing the hardware ID gives a hint. There are two hexadecimal numbers for a vendor ID and a device ID. Most of the vendor IDs I saw were 8086, which is the vendor ID for Intel (a reference to the 80×86 family of processors).

A lot of these warnings were for features related to the Xeon processor in the computer, some sound drivers, and a few other things. While I was able to find drivers for these online, I could not get them to install.

I was able to find drivers on the manufacturers’ sites for many items, but I ran into problems getting the drivers to install. While speaking of this challenge, someone asked me if I still had access to three specific folders from before I had installed Windows. All of these folders are child folders of c:\Windows\System32. The folder names are drivers, DriverState, and DriverStore. I did have access to these files; this was a hard drive swap. I went back to the device manager, selected an unrecognized device, and selected the option to update the driver. When prompted for a driver location, I pointed to these folders and let the process search. SUCCESS! The driver was found! I continued this process for the other devices.

This was a lot of devices, but it moved me in the direction of success. Some time later, all of the devices except one had their drivers installed. the remaining device, an Inten device with the ID 0x2F9C, remains unidentified. My carry away from this is that if I reinstall Windows on another computer, these folders should be included in the data that is backed up before performing the Installation.


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