.NET Framework 技术分享，C# WEB HTTP POST 请求传文件

这个是文件和参数一起传递的方法，multipart/form-data 方式，这个方法稍微复杂点，因为模拟了浏览器处理分隔符等行为，一般用于传文件，代码如下：

using System;
using System.Text;
using System.Collections.Generic;
using System.Net;
using System.IO;

public class UploadFile
{
    public UploadFile()
    {
        ContentType = "application/octet-stream";
    }
    public string Name { get; set; }
    public string Filename { get; set; }
    public string ContentType { get; set; }
    public byte[] StreamContent { get; set; }
}

public string HttpPostFile(string url, IEnumerable<UploadFile> files, IDictionary<string, string> values)
{
    var request = WebRequest.Create(url);
    request.Method = "POST";
    var boundary = "------------------" + DateTime.Now.ToString("yyyyMMddHHmmss");
    request.ContentType = "multipart/form-data; boundary=" + boundary;
    boundary = "--" + boundary;
    using (var requestStream = request.GetRequestStream())
    {
        //遍历键值
        foreach (string name in values.Keys)
        {
            var buffer = Encoding.UTF8.GetBytes(boundary + Environment.NewLine);
            requestStream.Write(buffer, 0, buffer.Length);
            buffer = Encoding.UTF8.GetBytes(string.Format("Content-Disposition: form-data; name=\"{0}\"{1}{1}", name, Environment.NewLine));
            requestStream.Write(buffer, 0, buffer.Length);
            buffer = Encoding.UTF8.GetBytes(values[name] + Environment.NewLine);
            requestStream.Write(buffer, 0, buffer.Length);
        }
        //遍历文件
        foreach (var file in files)
        {
            var buffer = Encoding.UTF8.GetBytes(boundary + Environment.NewLine);
            requestStream.Write(buffer, 0, buffer.Length);
            buffer = Encoding.UTF8.GetBytes(string.Format("Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"{2}", file.Name, file.Filename, Environment.NewLine));
            requestStream.Write(buffer, 0, buffer.Length);
            buffer = Encoding.UTF8.GetBytes(string.Format("Content-Type: {0}{1}{1}", file.ContentType, Environment.NewLine));
            requestStream.Write(buffer, 0, buffer.Length);
            requestStream.Write(file.StreamContent, 0, file.StreamContent.Length);
            buffer = Encoding.UTF8.GetBytes(Environment.NewLine);
            requestStream.Write(buffer, 0, buffer.Length);
        }
        var boundaryBuffer = Encoding.UTF8.GetBytes(boundary + "--");
        requestStream.Write(boundaryBuffer, 0, boundaryBuffer.Length);
    }
    try
    {
        var stream = new MemoryStream();
        request.GetResponse().GetResponseStream().CopyTo(stream);
        return Encoding.UTF8.GetString(stream.ToArray());
    }
    catch (WebException ex)
    {
        var stream = new MemoryStream();
        ex.Response.GetResponseStream().CopyTo(stream);
        return Encoding.UTF8.GetString(stream.ToArray());
    }
}

一般情况下这里面的 Name、Filename 参数意义不大，完全取决于服务端如何使用，这个方法里面组合边界符和换行符的时候非常严谨，甚至换几个行都是有讲究的。