基于HttpListener与Mono的C#多部分表单文件上传处理问题

核心处理思路 #

1. 从请求的Content-Type头中解析出分隔符（boundary），这是区分multipart各数据块的核心标记
2. 读取完整请求流，按boundary分割数据块
3. 跳过每个块的头部信息（直到出现连续空行），仅提取后续的文件内容

适配Mono环境的代码实现 #

using System;
using System.IO;
using System.Net;
using System.Text;

class FileUploadServer
{
    static void Main(string[] args)
    {
        var listener = new HttpListener();
        listener.Prefixes.Add("http://localhost:8080/upload/");
        listener.Start();
        Console.WriteLine("服务器启动，等待上传请求...");

        while (true)
        {
            var context = listener.GetContext();
            var request = context.Request;
            var response = context.Response;

            // 过滤非POST和非multipart请求
            if (request.HttpMethod != "POST" || !request.ContentType.StartsWith("multipart/form-data"))
            {
                response.StatusCode = (int)HttpStatusCode.BadRequest;
                response.Close();
                continue;
            }

            // 解析分隔符
            var boundary = request.ContentType.Split(';')[1].Split('=')[1].Trim();
            var boundaryBytes = Encoding.UTF8.GetBytes($"--{boundary}");

            using (var reader = new BinaryReader(request.InputStream))
            using (var outputFile = new FileStream("uploaded_content.dat", FileMode.Create))
            {
                byte[] buffer = new byte[4096];
                int bytesRead;
                bool skipHeader = true;

                while ((bytesRead = reader.Read(buffer, 0, buffer.Length)) > 0)
                {
                    if (skipHeader)
                    {
                        // 查找头部结束标记：连续两个换行\r\n\r\n
                        var contentStr = Encoding.UTF8.GetString(buffer, 0, bytesRead);
                        var headerEndIdx = contentStr.IndexOf("\r\n\r\n");
                        if (headerEndIdx != -1)
                        {
                            // 写入头部之后的内容
                            var contentBytes = Encoding.UTF8.GetBytes(contentStr.Substring(headerEndIdx + 4));
                            outputFile.Write(contentBytes, 0, contentBytes.Length);
                            skipHeader = false;
                        }
                    }
                    else
                    {
                        // 检查是否到达结束分隔符，避免写入冗余内容
                        var boundaryPos = Array.IndexOf(buffer, boundaryBytes[0], 0, bytesRead);
                        if (boundaryPos != -1 && boundaryPos + boundaryBytes.Length <= bytesRead)
                        {
                            bool isMatch = true;
                            for (int i = 0; i < boundaryBytes.Length; i++)
                            {
                                if (buffer[boundaryPos + i] != boundaryBytes[i])
                                {
                                    isMatch = false;
                                    break;
                                }
                            }
                            if (isMatch)
                            {
                                // 写入分隔符前的有效内容后退出循环
                                outputFile.Write(buffer, 0, boundaryPos);
                                break;
                            }
                        }
                        outputFile.Write(buffer, 0, bytesRead);
                    }
                }
            }

            // 返回上传成功响应
            var responseBytes = Encoding.UTF8.GetBytes("文件内容提取完成");
            response.ContentLength64 = responseBytes.Length;
            response.OutputStream.Write(responseBytes, 0, responseBytes.Length);
            response.Close();
        }
    }
}

关键细节说明 #

• 分隔符处理：Content-Type中的boundary不带前缀--，拼接时需手动添加
• 头部跳过逻辑：利用\r\n\r\n作为头部与内容的分隔标记，确保只提取有效文件数据
• 字节流处理：用BinaryReader操作原始字节流，避免编码转换问题，后续支持图片上传时无需修改核心逻辑
• 结束判断：检测到结束分隔符时立即停止写入，防止把分隔符、结尾标记等冗余内容写入文件

内容的提问来源于stack exchange，提问作者Pixel