Saturday, October 23, 2021

Review: InMotion S1 Electric Scooter (AUD$1299)

The InMotion S1 electric scooter. At the front is my wife's scooter, the VSETT 8.

Electric kickscooters are really popular right now. Their sweet spot in terms of usefulness is probably for people living in urban and inner city areas, or in areas which have good bicycle paths. I live in an inner city suburb of Perth, Western Australia, and work near the Swan river - my reason for buying one was to have some fun while commuting to work. My commute on the scooter is about 14km (9 miles) and takes me 40 minutes.

Four weeks ago I bought the InMotion S1 scooter for AUD$1299 (~ USD$970). In my review here I compare the manufacturers promotional material and claimed specifications to my real life experience of the scooter.

Scooter model history
The S1 is InMotion's latest model scooter, launching in Australia in September 2021. It has been adapted from the InMotion L9 model, which was crowdfunded on IndieGogo successfully back in May 2020. The S1 seems to be targeted at markets outside of the US, such as Canada, Australia and Singapore. The L9 and S1 look very similar, they share the same controls and share the same smartphone application.

Smartphone app
First thing to do is to pair the smartphone app with the scooter. This was easy and I didn't run up against any problems. I used the iPhone app, and there's an Android app available too. There was only one tricky thing I found with the app - changing the distance units from the default (miles) to kilometres. To do this, you need to first change it under the vehicle settings - this will ensure the speedo on the scooter reads out in km/hr instead of miles/hr. But in the app itself, it still displays the battery's remaining range in miles. To get this into km too you need to press on the "ME" link at the bottom, then settings, then "metric/imperial" units.

Speed limiter
The speed of the S1 is by default limited to 25 km/h (15 miles/h), but its easy to go into the app and turn this limit off (under vehicle settings). Doing this lets your scooter achieve the max speed of 30 km/h (18 miles/h). Unlike other scooters, this is purely a software setting and doesn't require any wires to be disconnected or anything to remove the speed limiter.

The S1 has an automatic electric brake on the back wheel, which kicks in automatically if you are going downhill and picking up speed rapidly, or have exceeded 30 km/h. The maximum speed I've achieved on the scooter is around 30.9 km/h while going downhill. The automatic brake is kind of jerky and not really smooth - it feels weird the first time you experience it. There's a toggle setting in the app related to the automatic brake, so I tried turning it both on and off but couldn't feel any difference. There is only one manual brake lever - for your left hand - this is hooked up to the front wheel drum brake. Drum brakes are actually preferable to disk brakes on a scooter because it means no parts are exposed, and so there are less mechanical parts to maintain.

Control panel & display
One of the best things about this scooter is the easy to use control panel and the large display in the middle of the handlebars. There's only one button, and it can perform the functions of power on/off, headlights on/off and to toggle through the three riding modes (Eco, Drive, Sport). Long press is power on/off. Single click is headlights on/off and double click is to toggle the riding mode. Compared to other scooters (like the VSETT range), these controls are intuitive and easy to remember. The throttle is thumb based - you push downward with the thumb of your right hand. Compared to the VSETT scooter throttle which uses your forefinger in a trigger action, I find it to be more natural and better suited to long commutes.

Bling LED lighting and auto turn signals
The scooter has a strip of roadfacing LED lights down each side of the deck, these stay blue while riding and automatically flash red when you are turning to the left or right. This is a great idea, because when riding a scooter its not recommended to take one hand off the handlebars to indicate your turn manually (as per a bicycle) due to instability. The only downside to the auto turn lights is that they don't activate until you either tilt the scooter or turn the handlebars in the direction you are going, so in other words anyone behind you only sees the indication when you are actually turning. Other lights on the scooter are the dual headlights and rear light / brake light. The headlights are positioned at handlebar height, making them extremely visible at night to oncoming traffic. With the LED lights, the scooter really turns heads at nighttime.

Riding modes - Eco, Drive, Sport
The Eco mode is a beginner mode - you won't go faster than 12 km/h (7.5 miles/h) and the acceleration is really soft. The Drive mode is supposed to be a standard commute mode, which limits your top speed to about 20 km/h (12.5 miles/h) and also limits the acceleration responsiveness to about 80% of maximum. Sport mode means no limits, on a full charge you'll get up to the top speed of 30km/h (18 miles/h) with the fastest possible acceleration. I keep it on Sport mode all the time - once you get used to the speed and the handling of the scooter I think most riders will do the same. These modes of course will impact on the range you'll get out of your battery charge, Eco will use the least amount of battery and Sport will use the most.

In the promotional material the claimed range on a full charge is 95 km (59 miles). But in the manual it lets you know that this was achieved on level ground, in Eco riding mode, with a 65 kg weight rider and zero wind. So in other words, nowhere near real world conditions. In real world riding - in Sport mode the entire time, hills, wind, myself being 80kg, I found that the range ended up being 55-60 km (34-37 miles). But this is still a really good range - it easily handles my 28km round trip daily commute, and leaves some spare for other short journeys nearby to work or home.

Score card

Good points
+ Large display, intuitive controls, comfortable throttle
+ The app tells you the estimated distance left on the battery charge
+ Cool underdeck LED lights, auto-turn signals, dual headlights
+ Large non-slip silicon deck
+ Big real world range
+ Front and back suspension

Bad points
- Its too big to take onto public transport like a bus or train
- Height of the handlebars is not adjustable and is high compared to other scooters
- A couple of poor quality fixtures like the bell and the charging port dust covers
- Jerky automatic electric brake kicks in when going downhill

A great long range commuter scooter with decent performance, cool LED lighting, a solid feel, easy to use controls and a large display. If you don't need to take it on public transport, then this scooter will be perfect for your medium to long distance commute, given its large 55km (34 miles) real world range.

Where to buy?
As of writing, this model scooter is sold out around most of Australia. Due to high demand and shipping delays I recommend contacting the shop where you intend to buy first to confirm when stock will arrive before paying anything upfront for a scooter.

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Saturday, October 17, 2020

Does Xamarin owe its existence to Unity & Apple?

Yes, Xamarin owes its existence to two other bits of technology that were huge around 2008 - the Unity Game Engine and the iPhone. The reason is that a confluence of events around 2008 provided the push to get the Mono project into mobile app development. This resulted in MonoTouch (for iOS) and Mono for Android, which eventually became Xamarin as we know it today.

The Mono project was founded in 2001 as a free open source implementation of Microsoft's .NET framework on Linux. But Mono had struggled since its inception to find its reason for being. According to Mono's founder, Miguel De Icaza, the hardcore free open source community never fully got behind Mono. The FOSS community feared that Microsoft would eventually cause problems for Mono, due to Microsoft being the creator of .NET. 

Outside of the Linux world however were other more pragmatic people from the MacOSX world who had no problem with Mono. One of these people was Joachim Ante, from Unity. Around 2005 the Unity game engine was just starting out and had a performance problem - their original scripting language of Python was far too slow - they needed something that was an order of magnitude faster. So Unity decided to replace the Python scripting with Mono/C# and immediately got all the performance they needed. This was the early days when the Unity Game Engine ran on MacOSX only. Mono filled the need of being a free open source JIT compiler with the modern language of C#.

Fast forward to 2008 when the iPhone App Store launched; Unity quickly set their sights on being able to compile games for the iPhone. Unity wanted to use Mono, but the additional requirement was that it had to be statically compiled for iOS, because Apple had banned the use of JIT (Just In Time) compilers in iOS Apps.

Unity comes back to us and says “Hey, we have this product on iOS, we need .NET to be statically compiled. Can you do that?” We were like, “Oh, that’s kind of impossible. Well, let’s think about it.”

One of our guys, Zoltán Varga - they went and made a static compiler for .NET, and it was amazing. We gave it to Unity. At this point, Unity is probably four or five employees.
They were working at somebody’s garage. And they shipped their product for iOS, built games for iOS using this thing, this 3D tech. They were the kings of this space.
- Miguel De Icaza (Xamarin)

Within a year of the iPhone App Store launch, Unity went from 4-5 employees to 80 employees. The iPhone and the App Store had launched Unity's massive growth, and along with this the Mono project had finally found its reason for being - mobile apps. The Mono developers realised there was interest in using .NET for mobile apps - so using the same tech given to Unity, they built their own product - MonoTouch, which allowed developers build native iOS apps using C#. Soon afterward, Mono turned its attention to Android and created Mono for Android.

Mobile app development was new and there were many developers who wanted to get into mobile apps but didn't really want to have to learn Objective-C and Java. So Mono now had a C# based cross platform app development platform with truly native performance. This was the killer combination that ensured Mono would take off in popularity.

The developers behind Mono founded the Xamarin company in 2011, MonoTouch became Xamarin.iOS and Mono for Android became Xamarin.Android. Xamarin was acquired by Microsoft in February 2016 and became a subsidiary of Microsoft, fully focused on the development of Xamarin's open source projects.

Inspiration for this article:

The History of GNOME, Mono, and Xamarin

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Sunday, May 24, 2020

Breakout: a Circuit Breaker implementation in C#

A circuit breaker can help you improve the stability of your application by protecting calls to third party services; e.g. a web service, a network resource, a database, or any other component which can intermittently fail.

Its a fundamental pattern for protecting your system from all manner of integration point problems. It is a way to fail fast while there is a known problem with an integration point.

The circuit breaker pattern was first described in detail by Michael Nygard in the Stability Patterns chapter of his book "Release It!" Design and Deploy Production-Ready Software.

Breakout is a C# .NET implementation of Michael Nygard's Circuit Breaker state machine, using the Gang of Four's STATE design pattern. I've created a NuGet package for it here.

This implementation is thread safe, lightweight and easily adapted into your existing codebase. Unlike other circuit breaker implementations, it leaves the responsibility for calling the third party service with your client code. Your code only needs to inform the circuit breaker of the success or failure of every call to the third party service, via OperationSucceeded() and OperationFailed(). Check the README on github for example usage.

Breakout - State Machine Diagram

State Machine Explanation

The state machine starts in the CLOSED state. While in the CLOSED state, calls flow through as normal to the third party service. If the operation succeeds, the failure count is reset. If the operation fails, the failure count is incremented. When the failure count threshold is reached, the trip breaker action is performed, which transitions the state to OPEN.

While in the OPEN state, no calls flow through to the third party service. The caller just returns immediately, without performing the service call. After the open timeout has passed, the attempt reset action is performed, which transitions the state to HALF OPEN.

While in the HALF OPEN state, only one call is let through to the third party service. If the operation succeeds, we reset the circuit breaker which transitions the state to CLOSED. If the operation fails, the trip breaker action is performed, which transitions the state to OPEN.

UML Design

The design uses the Gang of Four's STATE design pattern.

Breakout - UML diagram

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Sunday, February 23, 2020

Programming an Ethereum Smart Contract with Vyper

and deploying it with MetaMask and MyEtherWallet (MEW)


Ethereum has a vast amount of developer resources available, such that for a beginner its hard to know where to start.

If you go with the recommended approach you'd probably choose Solidity along with either JavaScript or golang. JavaScript and golang are traditionally the most well supported languages for the developer tooling around Ethereum. The original Ethereum node software, geth, is written in golang. There's a version of the Solidity smart contract compiler, solcjs, written in JavaScript, and available as a Node.js NPM package.

The other Smart Contract language that is supported by the Ethereum Foundation is Vyper. Vyper is a python-like language that was designed for security, simplicity and testability. In my view this makes Vyper ideal for a beginner. Vyper foregoes some of the power of Solidity (for example, class inheritance and function modifiers) in order to uphold the Vyper principles of being simple and secure.

In this article I'll be stepping you through creating a smart contract with the Vyper programming language, deploying it to the Ethereum test network, and then interacting with the contract - calling its two externally accessible functions. The contract deployment and contract interaction are achieved using two in-browser tools - MyEtherWallet (MEW) and MetaMask.

Background reading

Before you start I would highly recommend this article to get up to speed with the Ethereum ecosystem as a whole.
Its from 2017 but the content is still valid today.

Along with the Ethereum whitepaper, which is a must-read if you're a developer:

Installing the Vyper compiler

There's a number of options available to you as documented here:

One of the simplest options is to install it using python's package manager (pip). I'll start by ensuring you have the python development environment setup correctly.

Installing a recent version of Python and Pip with Pyenv

If you don't have already have a recent version of Python installed, or don't even know, I would highly recommend that you start by installing pyenv. Pyenv is a tool for python version management.

I followed the Pyenv installation instructions for a MacOS installation via homebrew, but there are instructions for other OSes given.

After installing pyenv, you can install the latest version of python with

% pyenv install 3.8.0

You will now have an up to date version of both python and pip available from your terminal command prompt.

Check what version of python is installed:
% python -V

Python 3.8.0

Check what version of pip is installed:
% pip -V


pip 19.2.3 from /Users/hg/.pyenv/versions/3.8.0/lib/python3.8/site-packages/pip (python 3.8)

Installing the Vyper compiler

Once you have python and pip installed aready, you can install the Vyper compiler with:

% pip install vyper

Check what version of Vyper is installed:

% vyper --version


Writing a smart contract in Vyper

For the first contract, we're going to keep things very simple and go with a public storage contract.
All the contract does is stores a single number in its storage area, and implements two public accessor functions - a getter and a setter.

Use a text editor and open a new file named storage.vy

Note that vy is the file extension for Vyper source code.

Here's the Vyper code:

stored_data: uint256

def set(new_value : uint256):
    self.stored_data = new_value

def get() -> uint256:
    return self.stored_data

Line 1 declares a variable named 'stored_data' of type 'uint256'. This is the only thing that the contract will store on the blockchain.

Line 3 (def set...) declares the public set function, to update the 'stored_data' variable.

Line 9 (def get...) declares the public get function, to get the 'stored_data' variable.

Its important to note that these two functions get and set are marked public and so can be 'called' by anyone - by using Ethereum client software like MyEtherWallet, or programmatically via the web3 or by other library.

Calling a public function on a smart contract actually consists of sending a transaction to the deployed contract's address - but this is an implementation detail hidden that is hidden by client software or libraries.

Further reading about the structure of contracts in Vyper:

Compiling the Vyper smart contract

To compile the contract into EVM bytecode:

% vyper -f bytecode storage.vy > storage.bin

To generate the ABI for the contract:

% vyper -f abi storage.vy > storage.abi

The ABI is a JSON format interface specification file, and it is needed to be able to interact with the smart contract (i.e. call its functions).

Deploy the smart contract to the Rinkeby test network

Install MetaMask

If you haven't already, now is a good time to install the MetaMask plugin/extension into your browser -
Setup MetaMask with a seed phrase and it will create an in-browser Ethereum wallet that you can use for real transactions, or in this case, test transactions.

When MetaMask is setup, at the top right you should see the network dropdown.

Change this to 'Rinkeby Test Network'. Press the DEPOSIT button, then press the GET ETHER button under the TEST FAUCET option.

After opening use the 'Crypto Faucet' button on the left and follow the instructions. The minimum option (3 ETH) will be more than enough for test purposes and to deploy this contract.

The second thing you'll need to do is to setup MyEtherWallet (MEW). This will let you deploy and interact with your smart contract.

Setup MyEtherWallet (MEW)

Go to and setup the seed phrase.

Now you'll need to give MyEtherWallet (MEW) access to your MetaMask wallet, which contains the 3 ETH for testing.

Go to and press the browser extension option.

It should come up with a 'Access via MetaMask' window, and you'll need to grant it permission. Press the 'Access My Wallet' button.

Deploy the smart contract

Inside MyEtherWallet (MEW), press the left hand side option 'Contract' then 'Deploy Contract'.

From the terminal, issue this command:

% cat storage.bin


Using the mouse, copy the contents of the file from the terminal prompt.

Inside MEW, paste the copied text contents into the bytecode field.

On the terminal again, issue this command:

% cat storage.abi

[{"name": "set", "outputs": [], "inputs": [{"type": "uint256", "name": "new_value"}], "constant": false, "payable": false, "type": "function", "gas": 35315}, {"name": "get", "outputs": [{"type": "uint256", "name": "out"}], "inputs": [], "constant": true, "payable": false, "type": "function", "gas": 1181}]

Using the mouse, copy the contents of the file from the terminal prompt.

Inside MEW, paste the copied text contents into the ABI/JSON field.

Enter a name for your contract, e.g. 'storage1'.

Press the 'Sign Transaction' button.

MetaMask will open up a window where you'll be able to confirm the deployment of your contract.

You'll see the gas fee and total.
You can press on the data tab and you'll see the bytecode that you pasted earlier.

Press the Confirm button to proceed with the deployment of your contract.

You may need to wait several seconds for the transaction to be confirmed at this point.
MetaMask should give you a successful deployment popup and link you to the transaction on

Here you can see the address of your newly deployed contract. In my case it is here:

Side note on contract addresses

Contract addresses are calculated deterministically, based on the account that created it. They are based on the nonce value of your account. So it is possible to know in advance what the contract address will be, if necessary.

Details here:

Interacting with the smart contract

Now that your contract is deployed, its time to interact with it - call its get and set functions.

The get function can be called 'for free' - it doesn't cost any gas, because its just returning the current state of the blockchain.
Calling the 'set' fuction however must be paid for in gas, because by calling it you are actually changing the current state of the blockchain.

Go back to MEW and navigate to the left hand side 'Contract' option then 'Interact with Contract'.

Paste your newly created contract address into the 'Contract Address' field.

In the ABI/JSON field, past your ABI file contents.

Press the Continue button.

There's a dropdown which shows 'Select an item'. This lists all of the public functions on the smart contract. There's only two available - get and set.

Choose get first, it will execute immediately and show the result being 0. 0 is the default value for uninitialised storage in Ethereum.

Now choose 'set' from the dropdown.

Enter the required value into the new_value field, e.g. 88.

Leave the Value in ETH as 0.

Press the 'Write' button.

MetaMask will open up a window where you'll be able to confirm your contract interaction.
What you're actually doing here is sending a transaction to the contract with a value in the data field - the data specifies to the EVM which function is being called (set) and the value of the parameter to it (88).

Press the confirm button.

You may need to wait several seconds for the transaction to be confirmed.

MetaMask should give you a confirmed transaction popup and link you to the transaction on

Press the "Press to see more" link at the bottom of this page on to see the detail of the function call you made.

Go back to MEW and this time select the 'get' from the dropdown.

Confirm that the value you set is now reflected by the get.

You have now successfully deployed an Ethereum smart contract written in Vyper, and interacted with it using MetaMask and MyEtherWallet (MEW).


Final notes - can you modify a smart contract?

Note that once a smart contract is deployed, you can't modify it; it is immutable and exists on the Ethereum blockchain forever.

If you need to modify or update the contract, you'll need to deploy the updated code to a new contract address.

There are various techniques for handling contract "upgrades" including migrating the existing storage. There's a good article here on this topic:

Note also that a contract can destroy itself (along with its storage), via the selfdestruct() function, as documented here:

Once destroyed, the contract and its storage are removed from that block onwards. After destruction, it is technically still possible to see the historical contract bytecode and storage, which exists on earlier blocks of the Ethereum blockchain.

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Saturday, February 8, 2020

Programming Bitcoin Cash (BCH) with the NBitcoin .NET library and C#

The NBitcoin library is the most active and well supported library in .NET for working with Bitcoin and other similar cryptocurrencies.

NBitcoin fully supports Bitcoin Cash (BCH), however the ebook and programming guide examples focus solely on Bitcoin Core (BTC).

The problem you encounter when following the NBitcoin guide is firstly that the QBitNinja API only supports Bitcoin Core and secondly that broadcasting the transaction seems to require either running a full local node or using the QBitNinja API.

In this tutorial I'll show you how to spend your Bitcoin Cash using the NBitcoin library running under dotnet core, without the need for running a full local node or for accessing the QBitNinja API.

The program you write here will create a new transaction, sign it with your private key, and broadcast it to the Bitcoin Cash network.

Dotnet core
is the preferred programming environment for NBitcoin. Dotnet core is open source and runs under the Linux, MacOSX and Windows operating systems.

Bitcoin Cash is the ideal cryptocurrency for experimenting with programming APIs and libraries - you can send small transactions for very low fees, typically for a fraction of one US cent.

Step 1: Project Setup

Follow the setup guide as normal:

The rest of these steps 2-12 below loosely follow the "Spend Your Coin" guide:

Its not absolutely required, but for a more complete and in depth understanding, I would recommend you read through the "Spend Your Coin" guide above (with the knowledge that it applies to Bitcoin Core) before proceeding with the rest of the below steps.

Step 2: Add support for Bitcoin Cash

On the command line:

dotnet add package NBitcoin.Altcoins

The code - add these using statements to the top of the C# source file.

using NBitcoin;
using NBitcoin.Altcoins;
using NBitcoin.Protocol;

And at the beginning of the program, add this:

// Important Note - this is not test code.
// It is going to run in production (called the "mainnet").
var network = NBitcoin.Altcoins.BCash.Instance.Mainnet;

Step 3: (Optional) Generate a new private key and address

The below code snippet generates a new BCH private key and BCH address using the NBitcoin library.
// Generate a random private key.
Key rawPrivateKey = new Key();

// The private key, also known as the Bitcoin secret or the WIF (Wallet Interchange Format).
// If you intend to use it, make sure you save the below somewhere safe!
BitcoinSecret privateKey = rawPrivateKey.GetBitcoinSecret(network);
Console.WriteLine("privateKey = " + privateKey);
Console.WriteLine("address (from privateKey) = " + privateKey.GetAddress(ScriptPubKeyType.Legacy));

Alternatively you can generate a new private key and address using BCH wallet software.

Step 4: Setup the variables for your private keys and addresses

To spend your Bitcoin Cash, you'll need to know the private keys of both the "destination" BCH address and the "from" BCH address.
The "from" BCH address is also known as the input address or the outpoint to spend.

Here's the code to setup the address and private keys of both the "destination" address and the "from" address.

// Destination - private key and address. The destination of the new transaction we are creating.
// Note: its not strictly necessary for creating the transaction to have the private key of the destination,
// but its better to add it here so that you know that you have access to it, and that the money won't be 'lost'.
var privateKey = new BitcoinSecret("PASTE_YOUR_DESTINATION_ADDRESS_PRIVATE_KEY_HERE", network);
Console.WriteLine("dest privateKey = " + privateKey);
var address = privateKey.GetAddress(ScriptPubKeyType.Legacy);
Console.WriteLine("dest address = " + address);
Console.WriteLine("dest address scriptPubKey= " + address.ScriptPubKey);

// Input Transaction - private key and address. The from address.
var inPrivateKey = new BitcoinSecret("PASTE_YOUR_FROM_ADDRESS_PRIVATE_KEY_HERE", network);
var inAddress = inPrivateKey.GetAddress(ScriptPubKeyType.Legacy);
Console.WriteLine("inPrivateKey = " + inPrivateKey);
Console.WriteLine("inAddress = " + inAddress);
Console.WriteLine("inAddress scriptPubKey= " + inAddress.ScriptPubKey);

You can run the program now to make sure its working - on the command line:

dotnet run

Step 5: Determine the Transaction ID of the "from" address

Now you need to determine the transaction ID and index number of your "from" address by looking at the transaction in a blockchain explorer and plugging in the correct TxId and index number below.

// Determine the previous output that will be spent, as the Input to our new transaction.
// For example:

string txInIdString = "292f70e71f8bc2e94b7c0ac46c4e89371dc59b821639de67376f6f0b09544d92";
uint txOutIndex = 0; // <== Ensure this index is correct!
OutPoint outPointToSpend = OutPoint.Parse(txInIdString + ":" + txOutIndex);

Step 6: Create the new transaction

var transaction = Transaction.Create(network);
transaction.Inputs.Add(new TxIn()
    PrevOut = outPointToSpend

Step 7: Setup the amount to spend and the miner fee

// Suggested miner fee for this transaction, as of February 2020,
// is 0.000003 BCH or around USD 0.001 (a tenth of a cent).
// Check recent blocks for guidance.

var minerFee = new Money(0.000003m, MoneyUnit.BTC);  

// Replace below with your amount.
// It is the total unspent amount of the "from" address.
var txInAmount = new Money(0.0021m, MoneyUnit.BTC);

// Move to the destination address.

var spendAmount = txInAmount - minerFee;
transaction.Outputs.Add(spendAmount, address.ScriptPubKey);

Step 8: Add a message to the transaction, using the OP_RETURN template (max 80 characters)

var message = "Test 1: using the NBitcoin library to move Bitcoin Cash. BCH Rocks!";
var bytes = Encoding.UTF8.GetBytes(message);
transaction.Outputs.Add(Money.Zero, TxNullDataTemplate.Instance.GenerateScriptPubKey(bytes));

Step 9: Sign the transaction

// Get the ScriptPubKey from the private key of the outPointToSpend.
transaction.Inputs[0].ScriptSig = inAddress.ScriptPubKey;

// Sign the transaction with the input private key.
var txInId = uint256.Parse(txInIdString);
var inCoin = new Coin(txInId, txOutIndex, txInAmount, inAddress.ScriptPubKey);
transaction.Sign(inPrivateKey, inCoin);

Step 10: Determine the TxId of your transaction, which is just its hash

Console.WriteLine("New TxId: " + transaction.GetHash());

Now is a good time to run the code and check its all working. From the command line:

dotnet run

Step 11: Broadcast your transaction to the Bitcoin Cash network

This is the final step and should only be attempted if your program runs fine up to step 10.

Before you run it, confirm your amount to spend is correct.

// Connect to a BCH node and broadcast the transaction.
// See here for the DNS Seed list:

using (var node = Node.Connect(network, ""))
    // Say hello to the node.

    // Advertise your transaction (send just the hash).
    node.SendMessage(new InvPayload(InventoryType.MSG_TX, transaction.GetHash()));

    // Send the contents of the transaction.
    node.SendMessage(new TxPayload(transaction));

    // Wait for the message to be sent.

Run your program the command line:

dotnet run

Step 12: That's it, well done for making it to the end!!

If everything went well, your new transaction was accepted by the Bitcoin Cash network, and it will show up in a block explorer such as this one:

Replace the above TxId with yours from step 10.

Your new transaction will be listed initially as having 0 confirmations, which means its in the mempool.

Now you just need to wait for your transaction to be confirmed. This will happen as soon as the next block is mined and your transaction gets added to that block by the winning miner.

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Tuesday, October 1, 2019

Counter overflows and clock drift bugs in aircraft and missile defense systems

A counter overflow bug happens when an unsigned integer variable storing a counter reaches its maximum value; when its already at the maximum, as soon as one more value gets added to it, the variable will reset back to 0 and continue counting up from there. If the rest of the software is not expecting this counter reset, it can result in system failures. So the longer the system is running for, the nearer the system will get to a counter overflow event.

Clock drift bugs happen when an internal timer/clock gets calculated incorrectly, causing it to slowly drift out of sync with real time. The longer the system is running, the more the clock drifts and the bigger the error gets. When real time clocks are out of sync, all sorts of downstream calculations can become inaccurate.

Both of these types of bugs typically have a workaround that requires the operator to reboot the system every X hours or days.

Both counter overflows and clock drift bugs can occur in production systems when system testing didn't include a "soak test" - where you keep the system running for a very long period, typically measured in days rather than hours. The failure to pick up the bug during system testing means that a production system gets deployed with a bug, and the only workaround becomes a regular reboot of the system.

The kicker - these type of bugs have been happening in safety critical systems for at least the past 28 years

One of the most publicized cases was the failure of a Patriot missile defense system in 1991, in which the system failed to track an incoming Scud missile, due to a drifting and out of sync clock. Tragically, this particular failure resulted in the death of 28 U.S. soldiers based at a U.S. barracks near to Dhahran, Saudi Arabia. The workaround for this bug was to reboot the system every 8 hours, but unfortunately this had not been communicated to the base in time to avoid the disaster.

Another well known case was the counter overflow in the Boeing 787 Dreamliner firmware (2015), which meant the aircraft had to be rebooted once every 248 days to avoid a counter overflow bug.

The most recent case was an internal timer bug in the Airbus A350 firmware (2019), which requires that the aircraft be rebooted once every 149 hours. 

Avoiding bugs in safety critical systems  

Avionics systems are among the most complex things ever built by man. There's one leading example of a successful avionics project which was built from scratch targeting high quality and zero defects. Its the Boeing 777 - Boeing's first fly-by-wire aircraft.
For the 777, Boeing decided early on to standardize on the Ada programming language, at a time when using C was the norm. Compilers for Ada had been certified as correct, and the language itself included several safety features, such as design by contract and extremely strong typing.

Ada itself came about as a way to standardize all of the programming languages in use by the U.S. Department of Defense - before Ada they were using some 450 different programming languages. Ada was originally designed to be used for embedded and real time systems.

Ronald Ostrowski, Boeing's director of Engineering, claimed that the Boeing 777 was the most tested airplane of its time. For more than 12 months before its maiden flight, Boeing tested the 777's avionics and flight-control systems continuously - 24hrs - 7days - in laboratories simulating millions of flights. 

The 777 first entered commercial service with United Airlines on 7th June, 1995. It has since received more orders than any other wide-body airliner. The 777 is one of Boeing's best-selling models; by 2018 it had become the most-produced Boeing wide-body jet, surpassing the legendary Boeing 747.

Further reading - Boeing flies on 99% Ada

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Saturday, September 28, 2019

Review of Shopify - from a developer's point of view

I setup this online shop over a couple of weekends - Chow Slow - Slow Feeder Dog Bowls. After launch I continued to make various improvements and optimisations to the presentation and content of the site. Since launch three months ago, the online shop has so far taken 72 orders.

The eCommerce SaaS product Shopify was used to build the site, on the Basic Shopify (monthly) plan.

Here below are my opinions on Shopify:

Shopify - Good points

  • Many payment options - I chose the Shopify Payments option. It accepts Apple Pay and Google Pay when on a mobile browser for example. You can tell that Shopify have extensive experience with taking payments - everything is really polished.
  • Test mode works well for putting through test credit card orders and seeing the customer experience end to end. Can also password protect the site while its under development.
  • The free themes are good and can be customised for most online shops. I used the free "Minimal" theme and then customised the layout of the home page, added several pages and added a blog.
  • Great optimisations and layouts which work well on mobile. More than 60% of the traffic for the site comes from a smartphone browser as opposed to a traditional desktop browser.
  • Really useful "Timeline" admin feature on the customer and order admin pages - see all the interactions that have happened with a customer in a simple timeline display, with a timestamp shown on each interaction.
  • Excellent "Conversion Summary" admin feature - see the site behaviour of your customer from when they first visited your site to when they bought something.
  • Comprehensive "Fraud Analysis" admin feature - for orders paid by Credit Card - recommendation of whether the transaction is likely fraudulent or not: probability shown as low, medium, or high.
  • Ability for customers to sign up with either their mobile phone number or email address. Shopify automatically sends communications to the customer using either mobile SMS or by email.
  • Easy to add social media accounts, which then automatically appear on the site footer.
  • Products are easy to configure and easy to change in terms of page title and content.
  • Ability to edit raw HTML in most places.
  • Easy to setup a custom domain, with TLS/SSL included (which just works).
  • There are SEO optimisations and settings available at a page level. You can change the page title, meta description and URL.
  • Integration with Google Analytics is excellent - the 'Advanced eCommerce' option should be turned on - it results in a data going straight into GA for your conversions and sales.
  • Page load time is good - bulk of the home page loads typically in 2-3 seconds.
  • A comprehensive API for writing custom integrations with other backend software and systems.
Shopify - Bad points
  • Marketing integrations - Facebook Ads for example - difficult and error prone to setup. Facebook Ads never worked for me after many headaches trying to setup. The marketing integrations seem like a quick way to lose money fast.
  • Inability to structure the Products, Pages and Blog sections to be within a custom sub-folders structure (as is typically recommended to silo a website for SEO purposes).
  • Checkout page customization is limited to Shopify Plus users.
  • Checkout script editor is limited to Shopify Plus, so any custom logic to apply discounts has to be done through plugins.
  • API is rate limited - will be fine for most users however ERP systems which run via batch processing or via polling may have issues. You need to implement everything as event driven webhooks rather than by polling the Shopify API.
Shopify - Areas for improvement
  • I'm not convinced of the need for many of the Shopify apps (plug-ins) that get automatically suggested. I have a feeling that they will result in bigger page sizes and slower load times. I have not needed to use any apps yet.
  • Its sometimes hard to find the relevant place for a setting - whether under preferences of the online shop or under settings of the account itself. I should probably make more use of the search bar at the top for this in the future.
Shopify - Conclusion

I highly recommend Shopify for setting up an online shop. When launching, your focus will be taken up with gaining your first customers, online marketing and the delivery process, so having a solid full featured website behind you is crucial.

A bit more about our online shop - Chow Slow - Slow Feeder Dog Bowls

I setup the site for my wife, who runs the business day to day. She handles the processing of orders and deliveries. We came up with the idea of selling to this niche market after finding out about this type of product in 2018. Our pet beagle (Ripley) had an issue of regular regurgitation due to eating too quickly. The slow feeder bowl product solved his problem and results in more relaxed meal times every day.

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