BetterLyrics/BetterLyrics.WinUI3/BetterLyrics.WinUI3/Helper/WebDavProbeHelper.cs

using System;
using System.Net;
using System.Net.Http;
using System.Threading.Tasks;

namespace BetterLyrics.WinUI3.Helper
{
    public static class WebDavProbeHelper
    {
        /// <summary>
        /// 自动检测目标主机是 HTTP 还是 HTTPS
        /// </summary>
        /// <returns>返回 "https" 或 "http"，如果都连不上返回 null</returns>
        public static async Task<string?> DetectSchemeAsync(string host, int port, string? path, string? user, string? pwd)
        {
            if (port == 443) return "https";
            if (port == 80) return "http";

            // 忽略 SSL 证书错误，因为很多 NAS 是自签名的
            var handler = new HttpClientHandler
            {
                ServerCertificateCustomValidationCallback = (message, cert, chain, errors) => true,
                UseProxy = false
            };

            // 设置认证
            if (!string.IsNullOrEmpty(user) && !string.IsNullOrEmpty(pwd))
            {
                handler.Credentials = new NetworkCredential(user, pwd);
                handler.PreAuthenticate = true;
            }

            using var client = new HttpClient(handler);
            client.Timeout = TimeSpan.FromSeconds(3);

            if (await ProbeUrlAsync(client, "https", host, port, path))
            {
                return "https";
            }

            if (await ProbeUrlAsync(client, "http", host, port, path))
            {
                return "http";
            }

            // 都失败
            return null;
        }

        private static async Task<bool> ProbeUrlAsync(HttpClient client, string scheme, string host, int port, string? path)
        {
            try
            {
                var uriBuilder = new UriBuilder(scheme, host, port, path);

                // 使用 PROPFIND 方法，且 Depth 为 0，只检测根节点是否存在，不拉取列表
                var request = new HttpRequestMessage(new HttpMethod("PROPFIND"), uriBuilder.Uri);
                request.Headers.Add("Depth", "0");

                var response = await client.SendAsync(request);

                return response.StatusCode != HttpStatusCode.BadRequest;
            }
            catch
            {
                return false;
            }
        }
    }
}