PayPal HTTP客户端返回Void，无法获取创建计划的JSON结果

问题详情 #

调用PayPal接口创建计费计划时，沙箱环境返回状态码Created，但执行response.Result<string>()时抛出异常：

MESSAGE:
Unable to cast object of type 'System.Void' to type 'System.String'.

SOURCE:
PayPalHttp-Dotnet

原调用代码：

var client = Functions.GetPaypalClient();
using (var request = new HttpRequest("/v1/billing/plans", HttpMethod.Post))
{
    request.ContentType = "application/json";
    request.Content = new StringContent(strData);
    request.Content.Headers.ContentType = MediaTypeHeaderValue.Parse("application/json");

    var response = Task.Run(() => client.Execute(request)).Result;

    response.StatusCode.ToString().BasicLog();
    var data = response.Result<string>();
    data.BasicLog();
}

解决方案 #

问题出在Result<T>()方法的处理逻辑上：当接口返回201 Created时，部分场景下Result<T>()会因响应体处理逻辑问题触发类型转换异常。可以通过直接读取响应流的方式获取返回JSON：

修复后的代码（同步版本） #

var client = Functions.GetPaypalClient();
using (var request = new HttpRequest("/v1/billing/plans", HttpMethod.Post))
{
    request.ContentType = "application/json";
    request.Content = new StringContent(strData);
    request.Content.Headers.ContentType = MediaTypeHeaderValue.Parse("application/json");

    var response = Task.Run(() => client.Execute(request)).Result;

    response.StatusCode.ToString().BasicLog();
    
    // 直接读取响应流内容
    string data = null;
    if (response.Content != null)
    {
        using var reader = new StreamReader(response.Content);
        data = reader.ReadToEnd();
    }
    data?.BasicLog();
}

推荐异步版本（避免线程阻塞） #

// 确保所在方法标记为async
var client = Functions.GetPaypalClient();
using (var request = new HttpRequest("/v1/billing/plans", HttpMethod.Post))
{
    request.ContentType = "application/json";
    request.Content = new StringContent(strData);
    request.Content.Headers.ContentType = MediaTypeHeaderValue.Parse("application/json");

    var response = await client.Execute(request);

    response.StatusCode.ToString().BasicLog();
    
    string data = null;
    if (response.Content != null)
    {
        using var reader = new StreamReader(response.Content);
        data = reader.ReadToEnd();
    }
    data?.BasicLog();
}

补充说明 #

PayPal部分201 Created响应可能为空，但计费计划创建成功时通常会返回完整的计划JSON数据。直接读取响应流是更可靠的方式，可绕过Result<T>()方法的类型转换限制。

内容的提问来源于stack exchange，提问作者Tom Gullen