在 .NET Core 中进行无依赖注入的 HTTP 调用

Question

I need to make a series of HTTP calls to obtain database credentials from a 3rd party vault, given that I need to run this code in Program.cs or, at the very latest, Startup.cs before adding the DBContext, I need to be able to make these calls without using IHttpClientFactory , as that requires Dependency Injection to already have been initialized.

The following code works fine when called during runtime, but doesn't work during the ConfigureAppConfiguration step.

HttpClient client = _clientFactory.CreateClient();

HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, $"{_configuration["CredentialsVault:vaultUrl"]}Auth/SignAppIn");
request.Headers.Add("Authorization", $"PS-Auth key={_apiKey}; runas={_runAsUser};");

var response = await client.SendAsync(request);

Is there a way I can either make an HTTP call without having to rely on Dependency Injection, or delay AddDbContext until after Dependency Injection has been set up?

I have tried creating an instance of HttpClient like this:

HttpClient client = new HttpClient();

However this did not seem to work, and according to this question it should not be instantiated like that.

Answer 1

Note, you don't need to inject a typed HttpClient, or use IHttpClientFactory ... It is recommended to solve certain issues, but its not mandatory.

If you really need to this on startup during or before configuration, and you have a typed client that you need to instantiate, you could just spinup a new ConfigurationBuilder (if needed) and ServiceProvide .

var preConfiguration = new ConfigurationBuilder()
    ... add your sources
    .Build();

var collection = new ServiceCollection()
     .AddHttpClient<...>(...)
     ...

var provider = collection.BuildServiceProvider();

var client = provider.GetService<SomeClient>();

client.YourCall();

... normal configuration here

This approach will give you the ability to insert Handlers to the request chain if you need them.

However, this is likely not your problem. From your question all you need to do is make the same call with a standard HttpClient and call it in the normal way you are calling it. Once again, you can spin up a ConfigurationBuilder if you need to resolve configuration.

var preConfiguration = new ConfigurationBuilder()
    ... add your sources
    .Build();

HttpClient client = new HttpClient();

HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, $"{preConfiguration["CredentialsVault:vaultUrl"]}Auth/SignAppIn");
request.Headers.Add("Authorization", $"PS-Auth key={_apiKey}; runas={_runAsUser};");

var response = await client.SendAsync(request);

... normal configuration here

Note .net 6 is adding a ConfigurationManager to address some of these configuration problems, as such it implements both IConfigurationBuilder and IConfigurationRoot and gives you the ability to both use the sources and providers of the the builder.

This solves the use case of being able to resolve and build configurations in a consistent way. For instances, you could use the Manager to resolve a configuration, spin up a service provider and resolve a dependency to then to add more configuration to the IConfigurationRoot .