POST请求至.aspx文件返回空JSON问题求助

我用JavaScript发送携带JSON请求体的POST请求到.aspx文件，需求是将JSON反序列化为Input对象，再序列化返回其中的obj字段，但在JavaScript中打印响应时，发现内容为空。

发送的请求体：

{"obj":"ASM10007-1A","objType":"part"}

预期响应：

{"obj":"ASM10007-1A"}

实际输出：控制台打印的Response对象无有效响应内容

.js 文件代码 #

async function JS_PostRequest(obj, objType) {
    var url = T_wroot + 'tweak/HS2-tweak/parts/excelcreator.exe.aspx';

    console.log("URL: " + url);

    const data = {
        obj: obj,
        objType: objType,
    };

    console.log("POST request body: " + JSON.stringify(data));
    
    const options = {   method: 'POST',
                        headers: {'Content-Type': 'application/json'},
                        body: JSON.stringify(data) };
    
    await fetch(url, options)
    .then(function(res) {
        if (res.ok) {
            console.log("response:" + JSON.stringify(res));
            return res;
        }
        if (!res.ok) {
            throw new Error(`HTTP error, status = ${res.status}`);
        }
    })
    .catch((err) => {
        console.error(`Fetch error: ${err}`);
    });
}

.aspx 文件代码 #

<%
    string obj = Request.QueryString["o"];
    string objType = Request.QueryString["t"];
    
    try
    {
        var strJSON = String.Empty;
     
        //Request.InputStream.Position = 0;
        using (var inputStream = new StreamReader(Request.InputStream))
        {
            strJSON = inputStream.ReadToEnd();
        }
     
        var data = Newtonsoft.Json.JsonConvert.DeserializeObject<Input>(strJSON);
        
        string message;
        if (data != null)  // Check if 'data' is not null
        {
            if (data.obj != null)  // Check if 'obj' inside 'data' is not null
            {
                message = data.obj;  // Assign the value of 'data.obj' to 'message'
            }
            else
            {
                message = "No message received";  // Assign default value if 'obj' is null
            }
        }
        else
        {
            message = "No message received";  // Assign default value if 'data' is null
        }
        
        var responseObj = new {
            response = message
        };
        string jsonResponse = Newtonsoft.Json.JsonConvert.SerializeObject(responseObj);
        
        Response.ContentType = "application/json";
        Response.Write(jsonResponse);
        Response.End();
    }
    catch (Exception e)
    {
     
        Response.Write("ASPX error: " + e.Message);
     
    }
%>

<script runat="server">
    public class Input 
    {
        public string obj { get; set; }
        public string objType { get; set; }
    }
</script>

问题原因及修复方案 #

1. JavaScript端未读取响应体内容 #

当前代码仅打印了Response对象本身，没有解析并读取响应体的实际内容。需要调用res.json()方法获取JSON格式的响应数据：

修改JS的fetch回调逻辑：

await fetch(url, options)
.then(function(res) {
    if (res.ok) {
        // 解析响应体为JSON对象
        return res.json();
    }
    throw new Error(`HTTP error, status = ${res.status}`);
})
.then(function(responseData) {
    // 打印实际的响应数据
    console.log("response data:", responseData);
})
.catch((err) => {
    console.error(`Fetch error: ${err}`);
});

2. ASPX端的两个关键问题 #

(1) 输入流位置未重置

ASP.NET可能已提前读取过请求输入流，导致StreamReader读取到空内容。取消注释Request.InputStream.Position = 0;，确保从流的起始位置读取：

Request.InputStream.Position = 0;
using (var inputStream = new StreamReader(Request.InputStream))
{
    strJSON = inputStream.ReadToEnd();
}

(2) 响应结构与预期不符

当前ASPX返回的结构是{"response":"ASM10007-1A"}，但需求是{"obj":"ASM10007-1A"}，需修改响应对象的字段名：

var responseObj = new {
    obj = message
};

修复后的ASPX核心代码片段 #

try
{
    var strJSON = String.Empty;
 
    Request.InputStream.Position = 0; // 重置流位置
    using (var inputStream = new StreamReader(Request.InputStream))
    {
        strJSON = inputStream.ReadToEnd();
    }
 
    var data = Newtonsoft.Json.JsonConvert.DeserializeObject<Input>(strJSON);
    
    string objValue = "No message received";
    if (data != null && data.obj != null)
    {
        objValue = data.obj;
    }
    
    var responseObj = new {
        obj = objValue // 匹配预期的响应结构
    };
    string jsonResponse = Newtonsoft.Json.JsonConvert.SerializeObject(responseObj);
    
    Response.ContentType = "application/json";
    Response.Write(jsonResponse);
    Response.End();
}
catch (Exception e)
{
    Response.ContentType = "text/plain";
    Response.Write("ASPX error: " + e.Message);
    Response.End();
}

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