Middleware 实现的功能是从请求的 hostname 中读取 subdomain，然后根据 blog 的配置，进行 url 重写或者重定向，实现代码如下

public class SubdomainMiddleware(
    RequestDelegate next,
    IBlogQueryService blogQuery,
    IOptions<SiteOptions> siteOptions)
{
    public async Task InvokeAsync(HttpContext context)
    {
        var request = context.Request;
        var currentHost = request.Host.Host.AsSpan();
        var defaultHost = new HostString(siteOptions.Value.Host);

        if (CommonUrlHelper.TryParseBlogAppFromHostname(currentHost, out var blogApp))
        {
            var path = request.Path.Value;

            if (await blogQuery.IsSubdomainBlog(blogApp))
            {
                request.Host = defaultHost;
                path = path == "/" ? string.Empty : request.Path;
                request.Path = $"/{blogApp}{path}";
            }
            else
            {
                var newUrl = UriHelper.BuildAbsolute("https", defaultHost, request.PathBase, $"/{blogApp}{request.Path}", request.QueryString);
                context.Response.Redirect(newUrl, false);
                return;
            }
        }

        await next(context);
    }
}

基于 TestServer 构建 middlewrite pipeline 的代码

private static async Task<WebApplication> BuildApp()
{
    var builder = WebApplication.CreateBuilder();
    MockBlogQueryService(builder.Services);
    MockSiteOptions(builder.Services);
    builder.WebHost.UseTestServer();
    var app = builder.Build();
    app.UseMiddleware<SubdomainMiddleware>();
    app.Run(async context => await context.Response.WriteAsync(context.Request.GetDisplayUrl()));
    await app.StartAsync();
    return app;
}

Mock 中间件所用到的接口

private static void MockBlogQueryService(IServiceCollection services)
{
    services.Mock<IBlogQueryService>(
        mock => mock.Setup(x => x.IsSubdomainBlog("dudu")).ReturnsAsync(true),
        ServiceLifetime.Scoped);
}

private static void MockSiteOptions(IServiceCollection services)
{
    services.Mock<IOptions<SiteOptions>>(
        mock => mock.Setup(x => x.Value).Returns(new SiteOptions()),
        ServiceLifetime.Scoped);
}

Url 重写的测试用例

[Fact]
public async Task Rewrite_subdomain_blog_url()
{
    // Arrange
    await using var app = await BuildApp();

    // Act
    var client = app.GetTestClient();
    var response = await client.GetAsync("https://dudu.cnblogs.com/p/18637966");

    // Assert
    Assert.Equal(HttpStatusCode.OK, response.StatusCode);
    Assert.Equal("https://www.cnblogs.com/dudu/p/18637966", await response.Content.ReadAsStringAsync());
}

Url 重定向的测试用例

[Fact]
public async Task Redirect_non_subdomain_blog()
{
    // Arrange
    await using var app = await BuildApp();

    // Act
    var client = app.GetTestClient();
    var response = await client.GetAsync("https://cmt.cnblogs.com/p/11391410.html");

    // Assert
    Assert.Equal(HttpStatusCode.Redirect, response.StatusCode);
    Assert.Equal("https://www.cnblogs.com/cmt/p/11391410.html", response.Headers.Location.ToString());
}