C#访问Office365 SharePoint下载文件遇asmx站点不存在错误

使用拥有完全访问权限的凭据从Office 365 SharePoint下载文件时，出现以下错误：

Microsoft.SharePoint.Client.ClientRequestException: 'Cannot contact site at the specified URL https://xxxx.sharepoint.com/sites/my_files/all%20Files. There is no Web named "/sites/my_files/all Files/_vti_bin/sites.asmx"'

相关代码如下：

static void Main(string[] args)
{
    string url = "https://xxxxx.sharepoint.com/sites/my_files/all%20Files";
    string folderpath = "https://xxxxxxx.sharepoint.com/sites/my_files/all%20Files/Task";
    string templocation = @"c:\Downloads\Sharepoint\";

    Program.DownloadFilesFromSharePoint(url, folderpath, templocation);
}

static void DownloadFilesFromSharePoint(string siteUrl, string siteFolderPath, string localTempLocation)
{
    string userName = "aaaa@xxxxxx.com";
    string pswd = "ssssss@1043";
    SecureString password = new SecureString();
    foreach (var c in pswd.ToCharArray()) password.AppendChar(c);
    var ctx = new ClientContext(siteUrl);

    //ctx.Credentials = new NetworkCredential(userName, password, "smtp-mail.outlook.com");
    ctx.Credentials = new SharePointOnlineCredentials(userName, password);
   

    FileCollection files = ctx.Web.GetFolderByServerRelativeUrl(siteFolderPath).Files;

    ctx.Load(files);
    if (ctx.HasPendingRequest)
    {
        ctx.ExecuteQuery(); //getting error here : Cannot contact site at the specified URL. There is no Web named "*.asmx"
    }

    foreach (File file in files)
    {
        FileInformation fileInfo = File.OpenBinaryDirect(ctx, file.ServerRelativeUrl);
        ctx.ExecuteQuery();

        var filePath = localTempLocation + "\\" + file.Name;
        System.IO.FileStream fileStream = new System.IO.FileStream(filePath, System.IO.FileMode.OpenOrCreate, System.IO.FileAccess.ReadWrite, System.IO.FileShare.ReadWrite);

        fileInfo.Stream.CopyTo(fileStream);

    }
}

1. ClientContext初始化错误：ClientContext需要绑定到SharePoint站点的根URL（如https://xxxxx.sharepoint.com/sites/my_files），而非具体文件夹URL。原代码传入文件夹路径，导致程序在错误位置查找站点服务文件（_vti_bin/sites.asmx），触发"No Web named"错误。
2. 文件夹路径格式错误：GetFolderByServerRelativeUrl要求传入服务器相对路径（从站点根开始的路径，如/sites/my_files/all Files/Task），而非完整绝对URL，原代码参数不符合API要求。
3. 资源未正确释放：原代码中FileStream未手动释放，存在资源泄漏风险。

using System;
using System.IO;
using System.Security;
using Microsoft.SharePoint.Client;

class Program
{
    static void Main(string[] args)
    {
        // 站点根URL，而非文件夹URL
        string siteUrl = "https://xxxxx.sharepoint.com/sites/my_files";
        // 服务器相对路径，从站点根起始
        string folderRelativePath = "/sites/my_files/all Files/Task";
        string localTempLocation = @"c:\Downloads\Sharepoint\";

        // 确保本地下载目录存在
        Directory.CreateDirectory(localTempLocation);

        DownloadFilesFromSharePoint(siteUrl, folderRelativePath, localTempLocation);
    }

    static void DownloadFilesFromSharePoint(string siteUrl, string folderServerRelativePath, string localTempLocation)
    {
        string userName = "aaaa@xxxxxx.com";
        string pswd = "ssssss@1043";
        
        // 安全创建只读SecureString
        SecureString password = new SecureString();
        foreach (char c in pswd)
        {
            password.AppendChar(c);
        }
        password.MakeReadOnly();

        // 使用站点根URL初始化ClientContext，并用using自动释放资源
        using (var ctx = new ClientContext(siteUrl))
        {
            ctx.Credentials = new SharePointOnlineCredentials(userName, password);

            // 通过服务器相对路径获取目标文件夹
            Folder targetFolder = ctx.Web.GetFolderByServerRelativeUrl(folderServerRelativePath);
            FileCollection files = targetFolder.Files;

            ctx.Load(files);
            ctx.ExecuteQuery();

            foreach (File file in files)
            {
                // 用using自动释放文件流资源
                using (FileInformation fileInfo = File.OpenBinaryDirect(ctx, file.ServerRelativeUrl))
                using (FileStream fileStream = new FileStream(Path.Combine(localTempLocation, file.Name), FileMode.OpenOrCreate, FileAccess.Write))
                {
                    fileInfo.Stream.CopyTo(fileStream);
                }
                Console.WriteLine($"已下载文件: {file.Name}");
            }
        }
    }
}

• 将ClientContext初始化URL改为站点根URL，确保程序正确指向SharePoint站点。
• 将文件夹路径改为服务器相对路径，符合GetFolderByServerRelativeUrl的参数要求。
• 使用using语句包裹ClientContext、FileInformation和FileStream，自动释放资源，避免泄漏。
• 添加Directory.CreateDirectory(localTempLocation)确保本地下载目录存在，防止写入失败。
• 优化SecureString创建逻辑并设置为只读，提升安全性。

内容的提问来源于stack exchange，提问作者Kumar