C# HttpWebResponse返回结果与Postman不一致问题排查解决

问题背景 #

• 调用公司内部系统Web API接口，接口接收JSON格式请求负载，返回JSON格式响应数据
• Postman调用验证正常：返回状态码200，响应体为预期JSON数据，确认服务本身运行无异常
• C#代码调用异常：所有C#实现的请求返回的响应内容都只有"OK"字符串，拿不到预期JSON数据

最初基于HttpWebRequest写的请求代码：

public HttpWebResponse SendRequest(string url, string checkOutFolder, string drawingNo, string login, string password)
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
    request.ContentType = "application/json";
    request.Method = "GET";
    request.Accept = "application/json";

    string payload = GeneratePayLoad(checkOutFolder, drawingNo);
    string header = CreateAuthorization(login, password);

    request.Headers[HttpRequestHeader.Authorization] = header;
    request.ServicePoint.Expect100Continue = false;

    // 反射修改内部字段，强行给GET请求写入请求体（非标准实现）
    var type = request.GetType();
    var currentMethod = type.GetProperty("CurrentMethod", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(request);

    var methodType = currentMethod.GetType();
    methodType.GetField("ContentBodyNotAllowed", BindingFlags.NonPublic | BindingFlags.Instance).SetValue(currentMethod, false);

    using (var streamWriter = new StreamWriter(request.GetRequestStream()))
    {
        streamWriter.Write(payload);
    }

    // 读取响应
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
    using (StreamReader rd = new StreamReader(response.GetResponseStream()))
    {
        string responseContent = rd.ReadToEnd();
        Console.WriteLine(responseContent);
    }
    return response;
}

排查过程 #

按常规优化建议依次调整，均未解决问题：

• 把请求方法从GET改成POST，返回结果没有变化
• 用Postman自带的代码生成功能导出RestSharp版本的请求代码运行，结果还是只返回"OK"，代码如下：

public void Request(string url, string checkOutFolder, string drawingNo, string login, string password)
{
    var client = new RestClient(url);
    var request = new RestRequest();
    request.Method = Method.Post;
    request.AddHeader("Content-Type", "application/json");
    request.AddHeader("Authorization", "Basic **********");
    var body = GeneratePayLoad(checkOutFolder, drawingNo);
    request.AddParameter("application/json", body, ParameterType.RequestBody);
    var response = client.Execute(request);
    Console.WriteLine(response.Content);
}

• 改用原生HttpClient重写请求逻辑，结果依旧，代码如下：

using (var client = new HttpClient())
{
    string uri = "******************";
    string path = "destinationpath";
    var endpoint = new Uri(uri);
    string payload = GeneratePayLoad(path, "100-0000947591");
    var stringContent = new StringContent(payload);
    var payload2 = new StringContent(payload, Encoding.UTF8, "application/json");
    var byteArray = Encoding.ASCII.GetBytes("*******");
    client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", Convert.ToBase64String(byteArray));
    var base64EncodedAuthenticationString = Convert.ToBase64String(System.Text.ASCIIEncoding.ASCII.GetBytes(client.DefaultRequestHeaders.Authorization.ToString()));
    var result = client.PostAsync(endpoint, stringContent).Result.Content.ReadAsStringAsync().Result;
    Console.WriteLine("test");
}

• 写Python脚本用requests库调用同个接口，返回结果和Postman完全一致，确认问题出在C#代码层面，和服务端、网络无关。

最终结论 #

故障根源：C#代码中GeneratePayLoad方法的生成逻辑存在错误，产出的请求JSON不符合接口要求，导致服务端没有返回预期业务数据，只返回了默认的"OK"响应。

排障提示：遇到不同客户端请求同接口结果不一致的问题，优先抓包对比请求头、请求体的实际内容，不要默认自己封装的公共工具方法（比如本例的payload生成方法）输出一定正确，这类公共方法的逻辑错误往往会被忽略，浪费大量排障时间。

内容的提问来源于stack exchange，提问作者Daniel