IIS 8.5下AJAX GET超196B返回HTML致404问题解决

问题背景 #

运行在Windows Server 2012（IIS 8.5）上的.NET Core笔记应用，本地调试时通过AJAX GET请求更新数据库nvarchar(max)类型文本字段一切正常，但部署到生产环境后，当文本描述较长时，Firefox控制台会出现404错误，更新功能静默失败。

排查发现存在临界长度：成功保存的JSON格式文本传输大小为196B，仅添加一个字符后就会失败，此时返回1.42KB的HTML内容。

原AJAX代码：

$.ajax({
    type: "GET",
    contentType: "application/json; charset=utf-8",
    url: '@Url.Action("UpdateMeetingItem", "Meetings")',
    data: { "id": id, "DateOpen": DateOpen, "DateClosed": DateClosed, "Responsibility": Responsibility, "descID": d_ID, "Description": Description },
    dataType: "json",
    success: function (data) {
        if (data.result == true) {
         //do stuff here
        }
        else { alert("There is some error updating the Meeting Item."); }
    }
})

成功保存的文本示例：

This is just a bunch of sample text to attempt to reproduce the problem I see in  the production server application.  On the development side I don't see any issues.
This is just a bunch of sample text to attempt to reproduce the problem I see in  the production server application.  On the development side I don't see any issues.
This is just a bunch of sample text to attempt to reproduce the problem I see in  the production server application.  On the development side I don't see any issues.
This is just a bunch of sample text to attempt to reproduce the problem I see in  the production server application.  On the development side I don't see any issues.
This is just a bunch of sample text to attempt to reproduce the problem I see in  the production server application.  On the development side I don't see any issues.
This is just a bunch of sample text to attempt to reproduce the problem I see in  the production server application.  On the development side I don't see any issues.
This is just a bunch of sample text to attempt to reproduce the problem I see in  the production server application.  On the development side I don't see any issues.
This is just a bunch of sample text to attempt to reproduce the problem I see in  the production server application.  On the development side I don't see any issues.
This is just a bunch of sample text to attempt to reproduce the problem I see in

问题原因 #

核心原因是GET请求的URL长度限制：GET请求会把所有参数拼接在URL末尾，而IIS 8.5默认对GET请求的URL长度有上限（默认约4096字节），当文本内容过长导致总URL长度超过这个限制时，IIS会直接返回404错误。本地调试时使用的开发服务器（如Kestrel）URL限制更宽松，因此不会触发该问题。

解决方法 #

推荐方案：改用POST请求传输数据 #

这是已验证有效的方案，同时符合HTTP规范——POST请求的参数放在请求体中，不受URL长度限制，更适合传输包含长文本的更新数据。

调整步骤：

1. 修改AJAX请求为POST，并用JSON.stringify()格式化请求数据：

$.ajax({
    type: "POST",
    contentType: "application/json; charset=utf-8",
    url: '@Url.Action("UpdateMeetingItem", "Meetings")',
    data: JSON.stringify({ "id": id, "DateOpen": DateOpen, "DateClosed": DateClosed, "Responsibility": Responsibility, "descID": d_ID, "Description": Description }),
    dataType: "json",
    success: function (data) {
        if (data.result == true) {
         //do stuff here
        }
        else { alert("There is some error updating the Meeting Item."); }
    }
})

2. 控制器方法添加[FromBody]特性接收请求体数据：

public JsonResult UpdateMeetingItem([FromBody]MeetingPostModel m) 
{ 
    // 更新数据库等业务逻辑
}

不推荐方案：修改IIS的URL长度限制 #

虽然可以通过修改IIS配置放宽GET请求的URL长度限制，但不建议这么做：

• 不符合HTTP设计规范：GET请求不应用于传输大量数据或修改服务器状态（更新数据库属于状态修改，应使用POST/PUT等方法）。
• 存在安全风险：过长的URL可能被代理服务器、防火墙拦截，也易暴露敏感数据。

若确需调整，可在站点web.config中添加以下配置（仅作参考）：

<system.webServer>
  <security>
    <requestFiltering>
      <requestLimits maxUrl="10000" maxQueryString="10000" />
    </requestFiltering>
  </security>
</system.webServer>

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