CSharp Rest API

Introduction

This is a quick refresher for C# Rest API

Installation

I am now on SDK 8.0 and found the following issues

Use Apt not Snap

Using snap will mean your SDK cannot be found

sudo apt-get install dotnet-sdk-8.0

Create new Project

This is painless and can be done with

dotnet new webapi -n Catalog

Setting up Certificates

The next thing is run the project with F5. This warns you that you are not https. You fix this with the commands below but make sure you restart chrome

dotnet dev-certs https --clean
dotnet dev-certs https --check --trust

Dependency Injection DI

This just points out how to inject one service into another. With the example below we only use the Repository once so creating it as its own system is a bit silly. Anyway this is how to do it.

builder.Services.AddSingleton<IRepository>(provider =>
{
    BsonSerializer.RegisterSerializer(new GuidSerializer(GuidRepresentation.Standard));
    BsonSerializer.RegisterSerializer(new DateTimeOffsetSerializer(BsonType.String));

    var mongoDbSettings = builder.Configuration.GetSection(nameof(MongoDbSettings)).Get<MongoDbSettings>();
    var client = new MongoClient(mongoDbSettings.ConnectionString);
    return new MongoDBItemsRepository(client);
});

builder.Services.AddSingleton<IItemService>(provider => new ItemService(provider.GetRequiredService<IRepository>()));

Express C# Style

This is an example of using the minimal api from Microsoft. The import thing is the minimal API is a new approach to reduce the code required to get going. The AddSingleton is a way to use Dependency Injection. I found the errors unreadable from the framework but maybe used to working at a lower level. Quite easy to see how to get going

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddSingleton<IItemService>(provider => new ItemService(new InMemItemsRepository()));
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

app.UseStatusCodePages(async statusCodeContext
    => await Results.Problem(statusCode: statusCodeContext.HttpContext.Response.StatusCode)
        .ExecuteAsync(statusCodeContext.HttpContext));

if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.MapGet("/items", (IItemService itemService) =>
    TypedResults.Ok(itemService.GetItems()))
    .WithName("GetItems")
    .WithOpenApi();


app.MapGet("/items/{id}", Results<Ok<ItemDto>, NotFound> (IItemService itemService, Guid id) =>
        itemService.GetItem(id) is { } itemDto
            ? TypedResults.Ok(itemDto)
            : TypedResults.NotFound()
    )
    .WithName("GetItemById")
    .WithOpenApi();


app.Run();

C# Controllers Gotchas

In my examples we are using the minimal api approach. Previously for C# we used the Controller approach. The framework, by default relies on names of functions and when implemented with, for instance GetItemAsync this would cause a problem as it expects GetItem. To make the framework work you need to add the following to the ConfigServices. To me this seems a bit of a shoddy approach to a framework.

services.AddControllers(option => {
    options.SuppressAsyncSuffixInActionNames = false;
})

Secrets Manager

With dotnet comes the secrets manager for storing ice cubes :) To use it we do

dotnet user-secrets init
dotnet user-secrets set MongoDbSettings:Password NotSaying!!!

I really hate the hidden approach Microsoft was. We used MongoDbSettings because this is the section in appsettings.json. It magically reads the values from secrets manager. I would much prefer to have an indication of this somewhere.

Health Checks

Next Health checks. Heartbeating etc

// Add Service
builder.Services.AddHealthChecks();

//HealthCheck Middleware
app.MapHealthChecks("/healthz");

For MongoDb we have

dotnet add package AspNetCore.HealthChecks.MongoDb

So for me the mongoDB driver was incompatiable with the HealtChecks package so downgraded to 2.28.0.0 but once working needed to adjust the code for the minimal api. The convention is to have a live and a ready endpoint like kubernetes.

Define the Read Check

This is the healthcheck the package defines. Note the ready tag we have added.

builder.Services.AddHealthChecks()
   .AddMongoDb(mongoDbSettings.ConnectionString, name: "mongodb", timeout: TimeSpan.FromSeconds(3), tags: ["ready"]);

Simple live Define

We just return we are running and don't include any options

app.MapHealthChecks("/health/live", new HealthCheckOptions
{
    Predicate = (_) => false
});

Ready Define

The main point is we only look at the healthoptions which are tagged ready. The Response writer part is how to format the response. For me copilot did all of the work.

app.MapHealthChecks("/health/ready", new HealthCheckOptions
{
    Predicate = (check) => check.Tags.Contains("ready"),
    ResponseWriter = async (context, report) =>
    {
        var result = JsonSerializer.Serialize(
            new
            {
                status = report.Status.ToString(),
                checks = report.Entries.Select(entry => new
                {
                    name = entry.Key,
                    status = entry.Value.Status.ToString(),
                    exception = entry.Value.Exception is not null ? entry.Value.Exception.Message : "none",
                    duration = entry.Value.Duration.ToString()
                })
            }
        );

        context.Response.ContentType = MediaTypeNames.Application.Json;
        await context.Response.WriteAsync(result);
    }
});

Other Health Checks

[Here] is a source of health checks you could use.

C# Extensions

I never used this a lot in the first 7 years of C#. For the last 3 it was all the rage. Basically they are functions which take this as the first argument

namespace Catalog.Extensions;

using Catalog.Dtos;
using Catalog.Entities;

public static class Extensions
{
    public static ItemDto AsDto(this Item item)
    {
        return new ItemDto
        {
            Id = item.Id,
            Name = item.Name,
            Price = item.Price,
            CreatedDate = item.CreatedDate
        };
    }
}

So now you can do this

    public IEnumerable<ItemDto> GetItems()
    {
        var itemDtos = repository.GetItems().Select(item => item.AsDto());

        return itemDtos;
    }