George Kosmidis – .NET Software Engineer

Quantum Computing basics with Q# – The superposition of a qubit

by George Kosmidis
May 10, 2020May 11, 2020

There are some problems so difficult, so incredibly vast, that even if every supercomputer in the world worked on the problem, it would still take longer than the lifetime of the universe to solve!

The phrase above, found in Microsoft Docs, captures today’s problems with our regular computers and as a result the limitations we face in our every day lives. Numerous problems in environment, health, agriculture and many other fields have a solution lost in a vast ocean of possible answers that need to be tested one by one for correctness.

Enters Quantum Computing!

How to make authenticated requests to an ASP.NET Core web API using IdentityServer4 with Client Credentials.

by George Kosmidis
March 16, 2020March 17, 2020

This is a guide on how to make requests to a protected resource using Client Credentials with the IdentityServer4.Contrib.HttpClientService nuget package. The library is actually an HttpClient service that makes it easy to make authenticated and resilient HTTP requests to protected by IdentityServer4 resources. Additionally, more features include automatic complex type serialization for requests / deserialization for responds (using Json.NET), caching of the token response to reduce load and an HttpRequestMessage factory that adds an “X-HttpClientService” header for logging/tracking between cascading API calls.

Using TPL Dataflow Library for Concurrency Testing

by George Kosmidis
January 8, 2020January 10, 2020

The Task Parallel Library contains a very interesting set of dataflow components that for some reason they didn’t get the attention they deserve. This set is called TPL Dataflow Library and in few words, it is a robust in-process actor library that worth spending some time learning it! In this post, we will learn how to use it for concurrency testing.

Integration Tests in ASP.NET Core API

by George Kosmidis
December 2, 2019February 4, 2020

Automated testing is an important part of modern software production as it ensures higher quality and faster delivery, and on the same time it makes testing more affordable. Integration tests, sitting just between Unit Tests and E2E tests, improve test coverage and ensure proper communication between units. In this post, we will explore the possibilities of integration testing of ASP.NET Core by using xUnit to create a test for multiple endpoints.

Using LiteDB in an ASP.NET Core API

by George Kosmidis
November 2, 2019November 5, 2019

LiteDB is serverless MongoDB-like database delivered in a single DLL (less than 350kb) fully written in .NET C# managed code (compatible with .NET 3.5, 4.x, NETStandard 1.3 and 2.0). It is ideal for mobile apps or for small desktop/web apps, and its API is very similar to MongoDB C# Official Driver.

In this post, we will see how to use LiteDB as a storage for an ASP.NET API and do simple CRUD operations with it.
Read More »Using LiteDB in an ASP.NET Core API

Action results in ASP.NET CORE APIs

by George Kosmidis
August 8, 2019August 10, 2019

ASP.NET Core supports creating RESTful services, also known as web APIs. To handle requests, a web API uses controllers with actions (in essence methods) that return an ActionResult. Since an ActionResult can be almost anything (it’s like returning an object from your methods), it makes sense to know how to use it and when to choose to return a specific type instead.

Let’s go through the each different return type, starting from the simplest one and work our why towards the most generic ActionResult.

Unit testing a custom middleware in ASP.NET Core API

by George Kosmidis
August 6, 2019

Middlewares are a fundamental part of any ASP.NET Core application, introduced from day one. They are executed in the order they are added on every request, and could be considered similar to the HttpHandlers and HttpModules of the classic ASP.NET. Since middlewares can execute code before or after calling the next in the pipeline, they are considered ideal for a ton of various application features, including exception handling, logging, authentication etc.

You can learn more about middlewares by learning how to create a simple exception handling middleware.

Error handling in ASP.NET Core Web API

by George Kosmidis
June 26, 2019August 8, 2019

We all know the traditional try-catch blocks and -used correctly- there is of course nothing wrong with them! But even though all is good with that, ASP.NET Core has an even better way of doing things, two ways actually, that can make our code cleaner and easier to read! By following the “Middleware” approach, we extract all our custom exception handling code from within the actions and centralizing it in one place thus, cleaner code!

In this post we will explore these three cases, and starting from the simple try-catch block we will refactor towards a custom error handling middleware.

IdentityServer4, ASP.NET Core API and a client with username/password

by George Kosmidis
February 8, 2019March 6, 2020

This is an end-to-end guide on how to quickly setup IdentityServer4, use it in your ASP.NET Core API for authentication, and finally login to your API from a client by asking a user for her/his username and password. It is divided in three parts that describe respectively the configuration of each one of the following three systems:

IdentityServer4
Contains instructions on how to setup and configure a token service based on IdentityServer4, that follows the quick-start guides, keeping only the absolutely minimum requirements for this tutorial
ASP.NET Core API
An API configured to use IdentityServer4 as a middleware that adds the spec compliant OpenID Connect and OAuth 2.0 endpoints
Client (API Consumer)
For this post, just a Console Application that consumes a protected resource from the API

Make authenticated requests to IdentityServer4 protected resources, using the IdentityServer4.Contrib.HttpClientService nuget package. It’s open source on github, just follow these Getting Started instructions or take a look at at sample!

Writing a custom OutputFormatter to return an Excel (.xlsx) from an action in ASP.NET Core API

by George Kosmidis
September 5, 2018August 10, 2019
1 Comment

As most of us, I already know my next week work schedule. It includes writing some actions in respond to a requirement for excel exports. It’s nothing new and its’s relatively easy with libraries like NPOI: you just create your excel on the fly and return a FileResult.

Read how to create an excel on the fly inside your action here: http://www.talkingdotnet.com/import-export-excel-asp-net-core-2-razor-pages/

And that could be the end of story for that requirement, but while walking home for the weekend I remembered about the XmlSerializerOutputFormatter I read on Microsoft Docs. The idea was to write my own ExcelOutputFormatter to respond to client requests with an Excel instead of a JSON.