使用C#调用SharePoint REST API创建文件夹时遇400/500错误

• 已通过REST API实现文件上传、下载及目录浏览操作，但创建文件夹时持续返回400错误请求，偶尔出现500内部服务器错误
• 相同请求在Postman中可成功执行

正确请求格式 #

POST https://{site_url}/_api/web/folders
Authorization: "Bearer " + accessToken
Accept: "application/json;odata=verbose"
Content-Type: "application/json"
Content-Length: {length of request body as integer}
X-RequestDigest: "{form_digest_value}"

{
  "__metadata": {
    "type": "SP.Folder"
  },
  "ServerRelativeUrl": "/document library relative url/folder name"
}

你的C#代码 #

private async Task<HttpResponseMessage> PostFolderSharePoint(string url, string serverRelativeUrl)
{
    string accessToken = GetAccessToken().GetAwaiter().GetResult();
    string jsoncontent = JsonConvert.SerializeObject("{\"__metadata\": {\"type\": \"SP.Folder\"},\"ServerRelativeUrl\": serverRelativeUrl}");
    var content = new StringContent(jsoncontent, Encoding.UTF8, "application/json");
    var FormDiGestValue = await GetFormDigestValue(accessToken);

    _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
    _httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
    

    var requestMessage = new HttpRequestMessage(HttpMethod.Post,url) { Content = content };
    requestMessage.Headers.Add("X-RequestDigest", FormDiGestValue);


    HttpResponseMessage response = await _httpClient.SendAsync(requestMessage).ConfigureAwait(false);

    return response;
}

问题排查与修复 #

1. JSON序列化错误 #

你直接对包含变量的字符串进行序列化，导致serverRelativeUrl变量未被替换，且最终JSON被双重转义，格式完全错误。

修复：创建匿名对象再序列化，确保变量被正确注入：

var folderData = new {
    __metadata = new {
        type = "SP.Folder"
    },
    ServerRelativeUrl = serverRelativeUrl
};
string jsoncontent = JsonConvert.SerializeObject(folderData);

2. 请求头缺失odata=verbose #

正确请求要求Accept头为application/json;odata=verbose，但你的代码只添加了application/json，这会导致SharePoint返回不符合预期的响应格式。

修复：修改Accept头设置：

_httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json;odata=verbose"));

3. 同步阻塞调用风险 #

使用GetAccessToken().GetAwaiter().GetResult()可能导致死锁，建议改用await：

string accessToken = await GetAccessToken();

4. HttpClient复用问题（可能引发500错误） #

如果_httpClient是全局复用实例，之前的请求头可能残留导致冲突。建议在每次请求时创建新实例（或确保头被正确重置）：

using (var httpClient = new HttpClient())
{
    // 在此配置请求头和发送请求
}

修复后的完整代码 #

private async Task<HttpResponseMessage> PostFolderSharePoint(string url, string serverRelativeUrl)
{
    string accessToken = await GetAccessToken();
    var folderData = new {
        __metadata = new {
            type = "SP.Folder"
        },
        ServerRelativeUrl = serverRelativeUrl
    };
    string jsoncontent = JsonConvert.SerializeObject(folderData);
    var content = new StringContent(jsoncontent, Encoding.UTF8, "application/json");
    string formDigestValue = await GetFormDigestValue(accessToken);

    using (var httpClient = new HttpClient())
    {
        httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);
        httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json;odata=verbose"));

        var requestMessage = new HttpRequestMessage(HttpMethod.Post, url) { Content = content };
        requestMessage.Headers.Add("X-RequestDigest", formDigestValue);

        return await httpClient.SendAsync(requestMessage).ConfigureAwait(false);
    }
}

内容的提问来源于stack exchange，提问作者secretunfunnyguy