HttpClient with dependency injection in Azure function

Question

Documentation says to use builder.Services.AddHttpClient() for registration HttpClient but I can resolve HttpClient without this.

I have a small startup where only register MyService :

public class Startup : FunctionsStartup
{
    public override void Configure(IFunctionsHostBuilder builder)
    {
        builder.Services.AddTransient<MyService>();
    }
}

and in Function, I want to resolve HttpClient and MyService and this code works.

public class Function
{
    public Function(MyService service, HttpClient client)
    {
    }

    [FunctionName("func")]
    public async Task<IActionResult> Update(
        [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = null)]
        HttpRequest request,
        ILogger logger)
    {
        return new OkObjectResult("Hello");
    }
}

Who and where are register HttpClient?
Should I use builder.Services.AddHttpClient()? Is this not redundant?

Stelios Giakoumidis · Accepted Answer · 2020-05-14 17:33:35Z

6

You are right. You first need to register to it to the services:

public class Startup : FunctionsStartup
{
    public override void Configure(IFunctionsHostBuilder builder)
    {
        //Register HttpClientFactory
        builder.Services.AddHttpClient();

        builder.Services.AddTransient<MyService>();
    }
}

If your Service will use the HttpClientFactory it is important to be register before the service. So when the MyService instance depedencies will be resolved there will already be a record for HttpCliendFactory in the DI container.

Your Function.cs class will then be:

public class Function
{
    private IHttpClientFactory _httpClientFactory;
    private MyService _myService;


    public Function(MyService myService, IHttpClientFactory client)
    {
        _myService = myService;
        _httpClientFactory = httpClientFactory;
    }

    [FunctionName("func")]
    public async Task<IActionResult> Update(
        [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = null)]
        HttpRequest request,
        ILogger logger)
    {
        //How to use example
        var client = _httpClientFactory.CreateClient();

        return new OkObjectResult("Hello");
    }
}

HttpClient of course can be used without the client factory, but if you spawn HttpClient objects from the HttpClientFactory you will have a better out of the box management of your HttpClient resources.

answered May 14, 2020 at 17:33

Stelios Giakoumidis

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Stelios Giakoumidis Over a year ago

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