Useful tidbits related to software development, that I think might be of use or interest to everyone else (or to me when I forget what I did!)

Recommendations For Acceptance Testing ASP.NET Core APIs Using SpecFlow

December 10, 2020

Before I begin with my recommendations it's probably worth me defining what I mean by "acceptance tests" by showing you where these sit conceptually in my testing arsenal: Unit Tests - Tests for an individual class, to ensure that it behaves as expected and that all behaviour is documented with a test. Acceptance tests - Tests for a piece of functionality, to ensure that the collection of classes involved "actually work" but excluding downstream dependencies Integration Tests - In-situ testing that the features continue to work when all dependencies are "real" I find that writing "acceptance tests" using SpecFlow is a great way to de-couple your behaviour from your code structure, making TDD more realistic and also meaning after a re-factor (which often results in re-factoring the unit tests) you can confirm there are no breaking changes. It also allows you to involve your QA/BA in the process by quantifying in plain English what scenario's you are catering for and how the system behaves for each. It's worth noting that SpecFlow can also be used to automate your integration tests, however that's a little more complex to setup as usually involved spinning up SQL servers, Kafka instances, mocked external APIs etc. and also is too slow to run those types of tests on build, whereas the acceptance tests I will demonstrate below you can quickly run on build like any other unit test. To create a SpecFlow project for testing an API add an NUnit test project and install the SpecFlow.NUnit.Runners & Microsoft.AspNetCore.Mvc.Testing NuGet packages into that test project, add a reference to the Api project and then begin creating your tests. My recommendations to consider are below:
  • Create a "WebTestFixture" that inherits from "WebApplicationFactory<Startup>"
    • Where "Startup" is your API Statup class
    • Take constructor params to capture shared data context classes from BoDi (the SpecFlow DI container)
    • Override the "ConfigureWebHost" method and use "builder.ConfigureTestServices" to replace any "real" dependencies with mocks defined in the test project
    • Also register any shared data contexts that your mocks require from BoDi with the .NET DI container
  • Create a folder structure that allows you consider the following genres of classes:
    • Infrastructure - e.g. SpecFlow hooks, Value Retrievers, Transformations etc. (basically the custom SpecFlow pipework)
    • TestDataProviders - with a subfolder for each high level dependency you are mocking (e.g. what would be a class library in the real implementation)
      • EachDataProvider - containing:
        • Interceptors - create a class per interface which acts as an in-memory version of the system you are mocking (use constructor injection to give these an accessible backing store in the form of a "context" class.)
        • DataContext - POCO classes which represent the state of your in-memory repository and are shared between BoDi and the .NET DI container so they can be manipulated in the test steps
        • StepDefinitions - All the SpecFlow step definitions for interacting with these mocks
    • FolderPerController - the "tests" live in here so assuming your controllers align with a sensible functional grouping it makes sense to mirror that structure
      • Interactions - create a class which interacts with this controller via the "WebTestFixture.CreateClient()" HttpClient
      • Features - create a SpecFlow feature file per endpoint of the controller - in here create the scenario's this endpoint supports
      • Context - any classes that represent the data context of the controller itself (such as the data you will post, or the response from the API)
      • StepDefinitions - All the SpecFlow step definitions for interacting with this API controller and the assertions of the features

    This structure works well for me as it allows me to keep a separation of code specific to a controller or endpoint (making it easier to see what is involved with which moving part) from each other, but also allows code re-use of steps which are for contriving data in your mocked repositories, with a clear separation again which would match the structure of your class libraries of your project. And of course, once you have defined the features/steps/data required to interact with all mocks and all controllers/endpoints - you can create a high level folder of features that interact across multiple of these, if you have such scenarios to assert.

Simple Test Approach for HttpClient

June 25, 2020

It's pretty common practice in .NET Core to take a dependency on HttpClient in your constructor and using the built-in DI container extension to register this. When it comes to unit testing it can always be a bit fiddly when you depend on a concrete class rather than an interface. After solving this problem several times when it comes to HttpClient based unit tests I've create a simple TestHttpClient and TestHttpClientBuilder to simplify the process:
public class TestHttpClientBuilder
	private readonly HttpResponseMessage _stubHttpResponseMessage = new HttpResponseMessage(HttpStatusCode.OK);

	public TestHttpClientBuilder WithStatusCode(HttpStatusCode statusCode)
		_stubHttpResponseMessage.StatusCode = statusCode;
		return this;

	public TestHttpClientBuilder WithJsonContent<T>(T expectedResponseObject)
		_stubHttpResponseMessage.Content = new StringContent(JsonConvert.SerializeObject(expectedResponseObject), Encoding.UTF8, "application/json");
		return this;

	public TestHttpClient Build()
		return new TestHttpClient(
			new FakeHttpMessageHandler(_stubHttpResponseMessage));

	public class TestHttpClient : HttpClient
		private readonly FakeHttpMessageHandler _httpMessageHandler;

		internal TestHttpClient(FakeHttpMessageHandler httpMessageHandler) : base(httpMessageHandler)
			_httpMessageHandler = httpMessageHandler;
			BaseAddress = new Uri("");

		public IReadOnlyList<HttpRequestMessage> CapturedRequests => _httpMessageHandler.CapturedRequests;

	internal class FakeHttpMessageHandler : HttpMessageHandler
		private readonly HttpResponseMessage _response;
		private readonly List<HttpRequestMessage> _capturedRequests = new List<HttpRequestMessage>();

		public FakeHttpMessageHandler(HttpResponseMessage response)
			_response = response;

		public IReadOnlyList<HttpRequestMessage> CapturedRequests => _capturedRequests;

		protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
						CancellationToken cancellationToken)

			return Task.FromResult(_response);
Given this code is available to your unit tests, you can now use the builder when instantiating the SUT and use the builder methods to configure the possible responses and/or inspect the captured requests to test your outbound calls. e.g.
public class UnitTestClass
	private TestHttpClientBuilder _testHttpClientBuilder;
	private Lazy<TestHttpClientBuilder.TestHttpClient> _testHttpClient;

	public void SetUp()
		_testHttpClientBuilder = new TestHttpClientBuilder()
			.WithJsonContent(new MyDataType()); // use AutoFixture, test data builder etc. to create a default response

		_testHttpClient = new Lazy<TestHttpClientBuilder.TestHttpClient>(() => _testHttpClientBuilder.Build());

	// Now create tests on the SUT using "_testHttpClient.Value" for the HttpClient ctor argument.
	// Make assertions based on changing the response status code / content, or by inspecting "_testHttpClient.Value.CapturedRequests"

Converting periodised tranches into flattened permutations.

March 09, 2020

This is a difficult one to describe in terms of using the correct terminology for exactly what problem I was solving when I came up with this code. I think the following example is the best way to convey what problem this solution is designed to solve. Imagine you have a sort of 2-dimensional jagged array (in my case a list of lists) where the x dimension represents the passing of time and the y dimension represents the various options/forks in the data which could be used in that segment. e.g.
| 0 | 1 | 2 |
| A | A | A |
|   | B | B |
|   | C |   |
In the above, segment 0 of time can only use option "A", segment 1 can use "A", "B" or "C", segment 2 can use "A" or "B". Given this above set of data, there are a finite number of possible combinations the data can be used (which is equal to the multiple aggregate value of the counts of the y values) i.e.: 1 * 3 * 2 = 6 combinations And I wanted a way to have a single pass at the data and build the truth table of possible permutations by filling in the gaps left by lack of any option e.g.:
| 0 | 1 | 2 |
| A | A | A |
| A | A | B |
| A | B | A |
| A | B | B |
| A | C | A |
| A | C | B |
My idea was that, ahead of time for a given permutation, you know how many times the input options of each segment should be repeated into the output matrix in order to end up with all the permutations. At the same time, you must occasionally reverse the output order in order not generate a mirror image of an existing permutation. The code I came up with, an example of which can be seen below, can be used with any combination of x and y counts and returns the value containing all distinct permutations:
private static List<string>[] GetFullCombinations(List<List<string>> segmentOptions)
	var totalPermutations = segmentOptions.Aggregate(1, (x, y) => x * y.Count);
	var combos = new List<string>[totalPermutations];
	var repetitions = totalPermutations;

	foreach (var options in segmentOptions)
		repetitions /= options.Count;
		var optionIndex = 0;
		for (var permutation = 0; permutation < totalPermutations; permutation++)
			if ((permutation + 1) % repetitions == 0)
				optionIndex = (optionIndex + 1) % options.Count;

			var option = options[optionIndex];
			if (combos[permutation] == null)
				combos[permutation] = new List<string>(segmentOptions.Count);


	return combos;
Due to the "no mirror images" modular arithmetic, the output is actually in a slightly different order to how a human might have ordered it (in my first table), nevertheless all combinations are returned:
public void GetFullCombinations_WhenInputSegmentsHaveOptions_ReturnsAllDistinctPermutations()
	var input = new List<List<string>>
		new List<string>
		new List<string>
		new List<string>
	var expectedPermutations = new[]
		new [] { "A", "A", "A" },
		new [] { "A", "A", "B"},
		new [] { "A", "B", "A"},
		new [] { "A", "B", "B"},
		new [] { "A", "C", "A"},
		new [] { "A", "C", "B"}

	var result = GetFullCombinations(input);

	using (new AssertionScope())
		foreach (var expectedPermutation in expectedPermutations)
			result.Should().ContainEquivalentOf(expectedPermutation, cfg => cfg.WithStrictOrdering());

Developer Tools

June 17, 2019

I try to maintain a toolkit of useful apps for doing my daily development tasks. Some of these I use very frequently, others not so much but they are useful to know about. I thought I'd catalogue them on my blog so that I remember them when I'm setting up a new machine :)
Tool Name Description
Microsoft Visual Studio I think this one goes without saying, but if anyone getting into development needs to choose an IDE I'd highly recommend starting here! It pretty much does everything you need (solutions, projects, code editing, compiling, debugging, NuGet package management, profiling, source control and more) and at the time of writing is available for Windows and Mac. The main competitor being JetBrains Rider which is fully cross platform and includes Re-Sharper refactorings, but as of yet has not tempted me away from the staple of Visual Studio. There are free editions of Visual Studio suitable for most people.
JetBrains Re-Sharper A plugin for Visual Studio which has many extensions and helpers to refactor your code, spot potential issues, decompile .NET assemblies, performance tracing etc. It does have a cost associated with it and I don't always install it as I don't like the idea of being dependent on it and there is a lot of cross over in functionality provided by Visual Studio itself of other free 3rd party tools. However more and more I am liking a lot of the features and it becoming a staple in my day to day developments.
CodeMaid A free plugin for Visual Studio which provides shortcuts for cleaning up code files, such as ensuring the order of code within classes, removing and sorting "using" statements etc. You can also download my preferred settings for CodeMaid.
NCrunch A plugin for Visual Studio which provides test code coverage and a automatic background test runner to keep you well informed of uncovered lines or broken tests while you develop. This one also has a cost associated with it but I'm yet to find anything in the free software space that comes close to the functionality.
Notepad++ A free cross platform text editor which is well maintained and comes with a lot of features for working with text files. It's not a "code editor", as such although it supports syntax highlighting, but it's useful for quickly viewing or editing all kinds of text files.
VS Code A free cross platform extensible IDE/text editor by Microsoft. For me, this is the middle ground between opening Notepad++ and opening Visual Studio. I also like to use VS Code when working on any front-end projects such as those built using Webpack due to the lack of Visual Studio project files in those kind of projects and because of the built in terminal window.
Sourcetree A free GUI for Git. One of the best I've tried and adds real value vs using the Visual Studio plugin or going fully command line.
Docker Installing Docker desktop opens up a whole world of containerised apps ready for you to integrate with in your code, such as Redis caches, Kafka instances, SQL server, FTP servers - pretty much run anything with a simple command!
Fiddler A free tool to aid debugging web based application. It can capture web traffic as well as reply packets, intercept calls and more.
Wireshark A free tool to aid debugging network traffic. Generally I use this when Fiddler can't intercept the traffic and I need something a little further down the network stack for capturing traffic.
ILSpy A free tool for decompiling .NET assembles.
Multi Commander A free dual pane file explorer tool with many extensions and helpful functions for dealing with different types of file. Most of the time I find Windows Explorer fine, but sometimes an alternative tool with more options can be useful. From all the ones I tried this is currently my favourite.
FAR - Find and Replace A free tool for performing 2 useful operations - 1 is replace names within files (multi rename) and 2 is replace text within files. This is useful when you want to create a new project based on another and want to quickly rename all project files and swap out the namespaces in all code files.
mRemoteNG A free tool for managing connections to remote machines including RDP, SSH and Web interfaces.
WinMerge A free tool for comparing and merging files and folders.
Conduktor A free GUI for inspecting the data in a Kafka instance

Visual Studio 2017/2019 Not Remembering Custom Fonts and Colours

April 04, 2019

I've had issues with both VS2017 and now VS2019 where applying my custom fonts/colour scheme is not maintained between sessions. The same trick worked in VS2019 as what I discovered in VS2017, so this time I'm blogging it! Basically, import your custom colour scheme as usual using the "Import and Export Settings" wizard. Now go to Tools > Options > General and switch the "Color Theme" to any other theme than the current one. Now switch the theme back. That's it! For some reason this seems to persist your customisation of the theme whereas without switching themes the changes get lost.

Testing if XML has deserialized correctly

March 24, 2019

XML is pretty old tech and without a schema is a bit of a pain to work with! A semi saving grace is using Visual Studio's "Paste XML as Classes" option (Paste Special) which will generate C# classes capable of representing the XML you had on the clipboard (using the XmlSerializer). However the caveat to this is that it only generates code for the exact xml you have used, so any optional attributes/elements or collections that only have 1 item in them will be generated incorrectly and will silently start dropping information when you deserialize another file with slightly different xml content. To combat this, I wrote a simple XmlSchemaChecker class which takes the content of an XML file and it's deserialized equivalent and ensures that every piece of data from the file is represented within the instance. It logs these problems when running with Debug logging enabled and is called from the class responsible for deserializing files.
using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Xml;
using System.Xml.Serialization;
using Microsoft.Extensions.Logging;

namespace Deserialization
    public class XmlSchemaChecker : IXmlSchemaChecker
        private readonly ILogger<XmlSchemaChecker> _logger;

        public XmlSchemaChecker(ILogger<XmlSchemaChecker> logger)
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));

        public void LogSchemaWarnings<T>(string originalXmlFilePath, T deserialized)
            if (!_logger.IsEnabled(LogLevel.Debug)) return;

            var originalXml = File.ReadAllText(originalXmlFilePath);
            var newXml = ReSerialize(deserialized);

            var originalValues = GetXmlValues(originalXml);
            var newValues = GetXmlValues(newXml);

            var missingItems = originalValues.Except(newValues).ToList();

            if (missingItems.Any())
                _logger.LogDebug("Schema for {filename} was not fully deserialized. Missing items: {missingItems}", originalXmlFilePath, missingItems);

        private static void ProcessNodes(ISet<string> values, Stack<string> paths, IEnumerable nodes)
            foreach (var node in nodes)
                switch (node)
                    case XmlDeclaration _:
                    case XmlElement element:

                            foreach (var att in element.Attributes)
                                if (att is XmlAttribute xmlAttribute && xmlAttribute.Name != "xmlns:xsd" && xmlAttribute.Name != "xmlns:xsi")
                                    values.Add($"{string.Join(":", paths.Reverse())}:{xmlAttribute.Name}:{CleanseValue(xmlAttribute.Value)}");

                            if (element.HasChildNodes)
                                ProcessNodes(values, paths, element.ChildNodes);

                    case XmlText text:
                            values.Add($"{string.Join(":", paths.Reverse())}:{text.ParentNode.Name}:{CleanseValue(text.InnerText)}");

        private static string CleanseValue(string value)
            return value.Replace("\r\n", "\n").Replace("\t", "").Trim(' ', '\n');

        private static IEnumerable<string> GetXmlValues(string xml)
            var values = new HashSet<string>();
            var paths = new Stack<string>();
            var doc = new XmlDocument();

            ProcessNodes(values, paths, doc.ChildNodes);

            return values;

        private static string ReSerialize<T>(T item)
            var xmlSerializer = new XmlSerializer(typeof(T));
            var output = new System.Text.StringBuilder();

            using (var outputStream = new StringWriter(output))
                xmlSerializer.Serialize(outputStream, item);

            return output.ToString();

.NET Core Configuration Wire-Up

March 04, 2019

In .NET Core the way you wire you your configuration classes has changed since .NET Framework. Typically in netfx I would define interfaces in my application code and then in the composition root (such as a web site) I would create classes which implement these and wrap the ConfigurationManager. I like that approach because it's easy to switch out the implementation later for specific classes, such as using configuration DB or even having some custom calculations or parsing driving the configuration. In netcore, it seems Microsoft are pushing you down the route of POCO classes for configuration. You still have the option to create interfaces on top of these classes for your downstream consumers, or to pass these in as classes directly, or wrap the dependency in an IOptions interface. The general approach I see online is to create entries in ConfigureServices within the Startup.cs which uses "Configuration.Bind" to hydrate these classes, but this gets quite messy in my opinion, as it creates 3 lines of code inside ConfigureServices per configuration object and leaks concerns of implementation into the Startup.cs, away from the implementation class itself. e.g.
// startup.cs - ConfigureServices
var someSettings = new SomeSettings();
Configuration.Bind("SomeSettings", someSettings);

// SomeSettings.cs
public class SomeSettings : ISomeSettings
    public int SomeIntSetting { get; set; }
My preferred approach is to straddle old and new.. I will create an implementation in the composition root which "wraps" the application configuration, but instead of this being the old "ConfigurationManager" it simply takes a dependency on IConfiguration, that way if you want to deviate from this you only change the class that you are intending to change and also it keeps the details of how those configurations are materialised to the class that defines them. e.g.
// startup.cs - ConfigureServices
services.AddSingleton<ISomeSettings, SomeSettings>();

// SomeSettings.cs
public class SomeSettings : ISomeSettings
    public SomeSettings(IConfiguration configuration)
        configuration.Bind("SomeSettings", this);

    public int SomeIntSetting { get; set; }

Exposing Kafka from Rancher/K8S VM to Local Machine

March 01, 2019

Following on from my previous post on setting up Rancher/K8S on RancherOS in a VM in Windows for local development, a common task will be setting up container services within the cluster but then accessing those services from your local Windows machine (e.g. while developing in Visual Studio). In a lot of cases this is probably straightforward, either exposing ports directly using a service or using Ingress to route host headers to the correct internal service. However in the case of Kafka it's a bit more complex due to the way in which the brokers address themselves when the initial connection is received and the broker list is sent back. In a nutshell, the default Kafka setup from the Catalog Apps in Rancher binds the brokers to their POD IP, when the broker list is sent to Windows it cannot address these IPs (unless you want to set up some kind of natting). After some Googling and help from the following posts: I came up with the following instructions: STEP 1 (install Kafka in cluster): Install Kafka from the Rancher catalogue
  1. your-dev-cluster > default > Catalog Apps > Launch
  2. find and select "Kafka"
  3. switch off the "Topics UI Layer 7 Loadbalancer" (near the bottom) - don't need it in dev.
  4. click "Launch"
  5. .. Wait until all the kafka services are running ..
  6. You can now verify that the Landoop UI is running and seeing brokers by visiting the endpoint is has produced, e.g. http://rancherdev.yourdomain:30188 <-- random port, check what it says!!
Kafka is now available in the cluster, but not from Windows. Continue with step 2 --> STEP 2 (expose Kafka externally): Change the Kafka startup command for multiport listening
  1. your-dev-cluster > default > workloads > kafka-kafka
  2. Three dots, click "Edit"
  3. Click "show advanced options"
  4. Under Command > Entrypoint - paste the following:
  5. Click "Upgrade"
Add service discovery for the new ports
  1. your-dev-cluster > default > Service Discovery
  2. Click "View/Edit YAML" on kafka-kafka..
  3. Use the following lines for section "spec > ports" (assuming you have 3 instances of Kafka)
      - name: broker
        port: 9092
        protocol: TCP
        targetPort: 9092
      - name: broker-ext0
        port: 9093
        protocol: TCP
        targetPort: 9093
      - name: broker-ext1
        port: 9094
        protocol: TCP
        targetPort: 9094
      - name: broker-ext2
        port: 9095
        protocol: TCP
        targetPort: 9095
Configure nginx to use TCP ConfigMap
  1. your-dev-cluster > system > workloads > nginx-ingress-controller
  2. Three dots > edit
  3. Environment variables:
  4. "Add from Source" > "Config Map" > "tcp-services"
  5. Click "Upgrade"
Expose the port using Ingress TCP ConfigMap
  1. your-dev-cluster > system > resources > config maps > ns: ingress-nginx > tcp-services
  2. Three dots, click "Edit"
  3. Add the following entries:
            - key = 9093
            - value = kafka/kafka-kafka:9093
            - key = 9094
            - value = kafka/kafka-kafka:9094
            - key = 9095
            - value = kafka/kafka-kafka:9095
Reboot the kafka services
  1. your-dev-cluster > default > workloads > tick all and click 'redeploy'
Now from Windows try telnet to 9093/9094/9095 or even better from WSL bash, install kafkacat and run: kafkacat -b -L

Setting up a Kubernetes cluster using Rancher on RancherOS

February 17, 2019

Little cheat sheet for setting up a single node Kubernetes/Rancher on a developer machine using Hyper-V without tying it to the DHCP IP address that was issued at the time of creation. Setup Rancher on RancherOS
  1. Download the RancherOS Hyper-V ISO image from the GitHub repo
  2. Setup a Hyper-V VM with the bootable ISO set as the boot device (with Internet connectivity - I used 4 vCPU, 16GB RAM and 500GB vHDD)
  3. Boot the VM and allow Linux to boot
  4. Type the following command (uses a password to avoid SSH keys):
    sudo ros install -d /dev/sda --append "rancher.password=yourpassword"
  5. Reboot and skip the CD boot step (i.e. boot from the hard disk)
  6. Login with "rancher" and "yourpassword" - at this point you may wish to get the IP and switch to another SSH client such as PuTTY and login from there.
  7. Create an SSL certificate for your "rancherdev" domain - from your rancher home directory
    docker run -v $PWD/certs:/certs -e SSL_SUBJECT="" paulczar/omgwtfssl
  8. Optionally, you can now delete this container/image from Docker
  9. Run the following command to start Rancher in a Docker container (with persistent storage and custom SSL certificate)
    docker run -d -v /mnt/docker/mysql:/var/lib/mysql -v $PWD/rancher:/var/lib/rancher -v $PWD/certs/cert.pem:/etc/rancher/ssl/cert.pem -v $PWD/certs/key.pem:/etc/rancher/ssl/key.pem -v $PWD/certs/ca.pem:/etc/rancher/ssl/cacerts.pem --restart=unless-stopped -p 8080:80 -p 8443:443 rancher/rancher
  10. In order to internally resolve the custom rancherdev domain in RancherOS, add a loopback record it to the hosts file
    echo "" | sudo tee -a /etc/hosts > /dev/null
  11. Rancher should now be running on the VM's public IP (run "ifconfig" to get your VM IP if you don't have it already)
  12. On your host OS (e.g. Windows) add this IP to the hosts file against "" (c:\windows\system32\drivers\etc\hosts)
  13. Browse to the in your web browser
  14. Follow the wizard to setup password/servername etc. for Rancher
Create a new Kubernetes cluster using Rancher
  1. In the Rancher browser UI - select to add a new cluster
  2. Choose "Custom" and use all the defaults, no cloud provider, [I disabled recurring etcd snapshots in the advanced options since this is a dev setup] - click Next
  3. In the next screen, choose all the Node Roles (etcd, Control Plane, Worker) - expand Advanced options and set the public and internal address to be to ensure the node can survive an external IP change (or another copy running)
  4. Copy the generated Docker command to the clipboard and press Done - it should look something like this:
    sudo docker run -d --privileged --restart=unless-stopped --net=host -v /etc/kubernetes:/etc/kubernetes -v /var/run:/var/run rancher/rancher-agent:v2.1.6 --server --token XXX --ca-checksum XXX --node-name my-dev-node --address --internal-address --etcd --controlplane --worker
  5. Paste and run the command in the RancherOS shell
  6. Rancher should then provision the Kubernetes cluster
NB. Any links generated by the Rancher UI to containers you install will use "" as the URL which is of course wrong from your host OS. You will need to manually enter the URL as Surving an IP Change If you fire up the VM for the first time on another machine or your DHCP recycles and your external IP changes, you will need to follow these steps to get up and running:
  1. Run the VM as normal in Hyper-V
  2. Login via the Hyper-V console with rancher/yourpassword
  3. Get the IP address of the running RancherOS
  4. Update your Windows host file (c:\windows\system32\drivers\etc\hosts) with and entry for pointing to the VM IP
  5. Browse to the rancher URL and give it some time to come back online

StackExchange.Redis Wrapper for JSON Chunking

January 07, 2019

I have used Redis caching with the StackExchange.Redis client in .NET across various projects and each time I find myself solving the same problems. The main problem, aside from abstracting the client and solving a few other issues (see below), is usually that my JSON data is bigger than Redis would like and it starts to perform badly or throws errors because the "qs" is full. I know there are other serialisation formats to try which might save some space, but my preference is to continue with JSON. I have created a GitHub repository called ChunkingRedisClient, which wraps up this boilerplate functionality in a central place. You can also install the current build as a NuGet package. Below is the write-up from the README: ---
# Chunking Redis Client
A library which wraps the StackExchange.Redis client, specifically using JSON serialisation, and adds functionality such as chunked reading/writing and sliding expiration.

The purpose of this library is to create a re-usable library of code (NB. which I need to put into a NuGet package) for wrapping the StackExchange.RedisClient and solving the issues I usually need to solve.

Those being:

* IoC wrappers/abstractions
   - Just take your dependency on "IRedisClient<TKey, TItem>"
   - By default you should configure your DI container to inject the provided RedisClient<TKey, TItem>
   - Since IoC is used throughout you also need to configure:
     ~ IRedisWriter<TKey, Item> -> JsonRedisWriter or ChunkedJsonRedisWriter
     ~ IRedisReader<TKey, Item> -> JsonRedisReader or ChunkedJsonRedisReader
     ~ IRedisWriter<TKey, Item> -> JsonRedisDeleter or ChunkedJsonRedisDeleter
     (note: for one combination of TKey, TItem - ensure the decision to chunk or not is consistent)
     ~ IKeygen<TKey> to an object specific implementation, like GuidKeygen
     ~ For chunking, locking is required:
             IRedisLockFactory -> RedisLockFactory
             To override the default of InMemoryRedisLock, call RedisLockFactory.Use<IRedisLock>() <-- your class here
* Strongly typed access to the cache
  - Use any C# object as your TKey and TItem, given that:
      ~ Your TKey is unique by GetHashCode(), or implement your own Keygen
      ~ Your TItem is serialisable by Newtonsoft.Json
* Implementing the StackExchange Connection Multiplexer
  - This is handled by the RedisDatabaseFactory
  - Not using the usual "Lazy<ConnectionMulitplexer>" approach, as I want to support one multiplexer per connection string (if your app is dealing with more than 1 cache)
  - The multiplexers are stored in a concurrent dictionary where the connection string is the key
  - The multiplexer begins connecting asynchronously on first use
* Sliding expiration of cache keys
  - Pass in the optional timespan to read methods if you want to use sliding expiration
  - This updates the expiry when you read the item, so that keys which are still in use for read purposes live longer
* Chunked JSON data
  - This solves a performance issue whereby Redis does not perform well with large payloads.
  - Sometimes you may also have had errors from the server when the queue is full.
  - The default chunk size is 10KB which can be configured in the ChunkedJsonRedisWriter
  - The JSON data is streamed from Newtonsoft into a buffer. Every time the buffer is full it is written to Redis under the main cache key with a suffix of "chunkIndex"
  - The main cache key is then written to contain the count of chunks, which is used by the reader and deleter.
* Generating keys for objects
  - I don't like using bytes for keys as they are not human readable, so I like to generate unique strings
  - There is no none-intrusive way of providing a type agnostic generic keygen, therefore you must write your own. If you write something for a CLR type, considering contributing it to the project!
  - Since we know Guids are unique, I have demonstrated the ability to create custom keygens.

The code can be extended to support other serialisation types (TODO), distributed locks (TODO), different ways of generating keys or whatever you need it to do.