如何在.NET中发送Content-Length与正文长度不匹配的HTTP测试请求？

.NET的HttpClient默认会校验Content-Length头和实际请求正文的长度是否一致，一旦不匹配就会抛出HttpRequestException。要绕开这个校验，你可以用以下两种方法：

方法一：直接使用Socket手动发送请求 #

这种方法完全脱离HttpClient的封装，自己组装HTTP请求的每一部分，能自由构造任何不符合规范的请求：

using System.Net.Sockets;
using System.Text;

var targetHost = "localhost";
var targetPort = 8080;

// 创建Socket并连接目标服务
using var socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
await socket.ConnectAsync(targetHost, targetPort);

// 示例1：Content-Length小于实际正文长度
var longRequestBody = "这是一段比Content-Length指定长度更长的正文内容";
var invalidRequest1 = $"POST /test HTTP/1.1\r\nHost: {targetHost}\r\nContent-Length: 10\r\n\r\n{longRequestBody}";
var requestBuffer1 = Encoding.ASCII.GetBytes(invalidRequest1);
await socket.SendAsync(requestBuffer1, SocketFlags.None);

// 示例2：Content-Length大于实际正文长度
var shortRequestBody = "短正文";
var invalidRequest2 = $"POST /test HTTP/1.1\r\nHost: {targetHost}\r\nContent-Length: 100\r\n\r\n{shortRequestBody}";
var requestBuffer2 = Encoding.ASCII.GetBytes(invalidRequest2);
await socket.SendAsync(requestBuffer2, SocketFlags.None);

// 可选：接收服务端响应
var responseBuffer = new byte[1024];
var bytesReceived = await socket.ReceiveAsync(responseBuffer, SocketFlags.None);
var response = Encoding.ASCII.GetString(responseBuffer, 0, bytesReceived);
Console.WriteLine(response);

socket.Shutdown(SocketShutdown.Both);

方法二：自定义HttpContent跳过校验 #

如果还想保留HttpClient的部分封装，可以自定义一个HttpContent子类，重写序列化逻辑，忽略Content-Length的校验：

using System.Net.Http;
using System.Net.Http.Headers;
using System.IO;
using System.Text;

public class UnvalidatedStringContent : StringContent
{
    private readonly string _rawContent;
    private readonly Encoding _encoding;

    public UnvalidatedStringContent(string content, Encoding encoding) : base(content, encoding)
    {
        _rawContent = content;
        _encoding = encoding;
    }

    protected override async Task SerializeToStreamAsync(Stream stream, TransportContext context)
    {
        // 直接写入原始内容，不校验Content-Length
        var contentBytes = _encoding.GetBytes(_rawContent);
        await stream.WriteAsync(contentBytes, 0, contentBytes.Length);
        await stream.FlushAsync();
    }

    // 重写ComputeLength，返回我们手动设置的Content-Length值
    protected override long ComputeLength()
    {
        return Headers.ContentLength.GetValueOrDefault();
    }
}

// 使用示例
var client = new HttpClient();

// 构造Content-Length小于实际正文的请求
var content1 = new UnvalidatedStringContent("实际正文内容比指定长度长", Encoding.UTF8);
content1.Headers.ContentLength = 5;
await client.PostAsync("http://localhost:8080/test", content1);

// 构造Content-Length大于实际正文的请求
var content2 = new UnvalidatedStringContent("短正文", Encoding.UTF8);
content2.Headers.ContentLength = 100;
await client.PostAsync("http://localhost:8080/test", content2);

这两种方法都能绕过HttpClient的本地校验，构造出你需要的无效HTTP请求。

内容的提问来源于stack exchange，提问作者me.at.coding