通过IHttpClientFactory在DelegatingHandler中注入值

services.AddHttpClient();

public class CustomDelegatingHandler : DelegatingHandler
{
    private readonly IHttpClientFactory _httpClientFactory;

    public CustomDelegatingHandler(IHttpClientFactory httpClientFactory)
    {
        _httpClientFactory = httpClientFactory;
    }

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // 在此处可以使用 _httpClientFactory 创建和管理 HttpClient 实例
        var httpClient = _httpClientFactory.CreateClient();

        // 添加自定义逻辑或处理请求

        // 调用下一个处理程序
        var response = await base.SendAsync(request, cancellationToken);

        // 添加自定义逻辑或处理响应

        return response;
    }
}

var httpClient = _httpClientFactory.CreateClient();
httpClient.BaseAddress = new Uri("https://example.com");
httpClient.DefaultRequestHeaders.Add("User-Agent", "MyHttpClient");

httpClient = httpClient
    .AddHttpMessageHandler<CustomDelegatingHandler>()
    .Build();