Use HttpClient via IHttpClientFactory in a .NET Core console app without implementing IHostedService

If you're looking for the C# version, go here.

Not that there's anything wrong with IHostedService, but sometimes you just want a plain old console app without having to implement another interface just so that you can inject and use IHttpClientFactory.

By using the new HostApplicationBuilder pattern (encapsulated in the ConsoleHost class), there is much less ceremony involved with setting up the Generic Host HostBuilder so that you can inject IHttpClientFactory into your classes. Beyond that, you merely create an IServiceScope to make everything work:

//
// Set up the generic host and DI.
//

let builder = ConsoleHost.createApplicationBuilder argv
use host = builder.Build()

use serviceScope = host.Services.CreateScope()
let services = serviceScope.ServiceProvider


//
// Run the test service method.
//

let testSvc = services.GetRequiredService<TestService>()
let html = testSvc.GetMicrosoftAsync() |> Async.AwaitTask |> Async.RunSynchronously

let substringLength = if html.Length > 1_000 then 1_000 else html.Length
printfn $"{html.Substring(0, substringLength)}"

This code creates an IServiceScope in main, and then uses that to get our registered TestService class, which returns the HTML of https://www.microsoft.com as a string. We then display the first 1,000 characters.

The TestService class looks like this:

type TestService (httpClientFactory : IHttpClientFactory) =

    static let _logger = Log.Logger.ForContext<TestService>()

    let _httpClient = httpClientFactory.CreateClient()

    member this.GetMicrosoftAsync() =
        task {
            _logger.Information("Making HTTP request...")
            use requestMsg = new HttpRequestMessage(HttpMethod.Get, "https://www.microsoft.com")
            use! responseMsg = _httpClient.SendAsync(requestMsg)

            _logger.Information("Done.")
            return! responseMsg.Content.ReadAsStringAsync()
        }

And now you can use all of the newfangled IHttpClientFactory goodness in a (mostly) plain old console app!