c# 模拟表单提交，post form 上传文件、数据内容

转自：https://www.cnblogs.com/DoNetCShap/p/10696277.html

表单提交协议规定：
要先将 HTTP 要求的 Content-Type 设为 multipart/form-data，而且要设定一个 boundary 参数，
这个参数是由应用程序自行产生，它会用来识别每一份资料的边界 (boundary)，
用以产生多重信息部份 (message part)。
而 HTTP 服务器可以抓取 HTTP POST 的信息，

基本内容：
1. 每个信息部份都要用 --[BOUNDARY_NAME] 来包装，以分隔出信息的每个部份，而最后要再加上一个 --[BOUNDARY_NAME] 来表示结束。
2. 每个信息部份都要有一个 Content-Disposition: form-data; name=""，而 name 设定的就是 HTTP POST 的键值 (key)。
3. 声明区和值区中间要隔两个新行符号（\r\n）。
4. 中间可以夹入二进制资料，但二进制资料必须要格式化为二进制字符串。
5. 若要设定不同信息段的资料型别 (Content-Type)，则要在信息段内的声明区设定。

两个form内容模板
boundary = "----" + DateTime.Now.Ticks.ToString("x");//程序生成
1.文本内容
"\r\n--" + boundary +
"\r\nContent-Disposition: form-data; name=\"键\"; filename=\"文件名\"" +
"\r\nContent-Type: application/octet-stream" +
"\r\n\r\n";
2.文件内容
"\r\n--" + boundary +
"\r\nContent-Disposition: form-data; name=\"键\"" +
"\r\n\r\n内容";

/// <summary>
/// 表单数据项
/// </summary>
public class FormItemModel
{
    /// <summary>
    /// 表单键，request["key"]
    /// </summary>
    public string Key { set; get; }
    /// <summary>
    /// 表单值,上传文件时忽略，request["key"].value
    /// </summary>
    public string Value { set; get; }
    /// <summary>
    /// 是否是文件
    /// </summary>
    public bool IsFile
    {
        get
        {
            if (FileContent==null || FileContent.Length == 0)
                return false;
 
            if (FileContent != null && FileContent.Length > 0 && string.IsNullOrWhiteSpace(FileName))
                throw new Exception("上传文件时 FileName 属性值不能为空");
            return true;
        }
    }
    /// <summary>
    /// 上传的文件名
    /// </summary>
    public string FileName { set; get; }
    /// <summary>
    /// 上传的文件内容
    /// </summary>
    public Stream FileContent { set; get; }
}

/// <summary>
/// 使用Post方法获取字符串结果
/// </summary>
/// <param name="url"></param>
/// <param name="formItems">Post表单内容</param>
/// <param name="cookieContainer"></param>
/// <param name="timeOut">默认20秒</param>
/// <param name="encoding">响应内容的编码类型（默认utf-8）</param>
/// <returns></returns>
public static string PostForm(string url, List<FormItemModel> formItems, CookieContainer cookieContainer = null, string refererUrl = null, Encoding encoding = null,int timeOut = 20000)
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
    #region 初始化请求对象
    request.Method = "POST";
    request.Timeout = timeOut;
    request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";
    request.KeepAlive = true;
    request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.57 Safari/537.36";
    if (!string.IsNullOrEmpty(refererUrl))
        request.Referer = refererUrl;
    if (cookieContainer != null)
        request.CookieContainer = cookieContainer;
    #endregion
 
    string boundary = "----" + DateTime.Now.Ticks.ToString("x");//分隔符
    request.ContentType = string.Format("multipart/form-data; boundary={0}", boundary);
    //请求流
    var postStream = new MemoryStream();
    #region 处理Form表单请求内容
    //是否用Form上传文件
    var formUploadFile = formItems != null && formItems.Count > 0;
    if (formUploadFile)
    {
        //文件数据模板
        string fileFormdataTemplate =
            "\r\n--" + boundary +
            "\r\nContent-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"" +
            "\r\nContent-Type: application/octet-stream" +
            "\r\n\r\n";
        //文本数据模板
        string dataFormdataTemplate =
            "\r\n--" + boundary +
            "\r\nContent-Disposition: form-data; name=\"{0}\"" +
            "\r\n\r\n{1}";
        foreach (var item in formItems)
        {
            string formdata = null;
            if (item.IsFile)
            {
                //上传文件
                formdata = string.Format(
                    fileFormdataTemplate,
                    item.Key, //表单键
                    item.FileName);
            }
            else
            {
                //上传文本
                formdata = string.Format(
                    dataFormdataTemplate,
                    item.Key,
                    item.Value);
            }
 
            //统一处理
            byte[] formdataBytes = null;
            //第一行不需要换行
            if (postStream.Length == 0)
                formdataBytes = Encoding.UTF8.GetBytes(formdata.Substring(2, formdata.Length - 2));
            else
                formdataBytes = Encoding.UTF8.GetBytes(formdata);
            postStream.Write(formdataBytes, 0, formdataBytes.Length);
 
            //写入文件内容
            if (item.FileContent != null && item.FileContent.Length>0)
            {
                using (var stream = item.FileContent)
                {
                    byte[] buffer = new byte[1024];
                    int bytesRead = 0;
                    while ((bytesRead = stream.Read(buffer, 0, buffer.Length)) != 0)
                    {
                        postStream.Write(buffer, 0, bytesRead);
                    }
                }
            }
        }
        //结尾
        var footer = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");
        postStream.Write(footer, 0, footer.Length);
 
    }
    else
    {
        request.ContentType = "application/x-www-form-urlencoded";
    }
    #endregion
 
    request.ContentLength = postStream.Length;
 
    #region 输入二进制流
    if (postStream != null)
    {
        postStream.Position = 0;
        //直接写入流
        Stream requestStream = request.GetRequestStream();
 
        byte[] buffer = new byte[1024];
        int bytesRead = 0;
        while ((bytesRead = postStream.Read(buffer, 0, buffer.Length)) != 0)
        {
            requestStream.Write(buffer, 0, bytesRead);
        }
 
        ////debug
        //postStream.Seek(0, SeekOrigin.Begin);
        //StreamReader sr = new StreamReader(postStream);
        //var postStr = sr.ReadToEnd();
        postStream.Close();//关闭文件访问
    }
    #endregion
 
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
    if (cookieContainer != null)
    {
        response.Cookies = cookieContainer.GetCookies(response.ResponseUri);
    }
 
    using (Stream responseStream = response.GetResponseStream())
    {
        using (StreamReader myStreamReader = new StreamReader(responseStream, encoding ?? Encoding.UTF8))
        {
            string retString = myStreamReader.ReadToEnd();
            return retString;
        }
    }
}

运行方式：

var url = "http://127.0.0.1/testformdata.aspx?aa=1&bb=2&ccc=3";
var log1=@"D:\temp\log1.txt";
var log2 = @"D:\temp\log2.txt";
var formDatas = new List<Grass.Net.FormItemModel>();
//添加文件
formDatas.Add(new Grass.Net.FormItemModel()
{
    Key="log1",
    Value="",
    FileName = "log1.txt",
    FileContent=File.OpenRead(log1)
});
formDatas.Add(new Grass.Net.FormItemModel()
{
    Key = "log2",
    Value = "",
    FileName = "log2.txt",
    FileContent = File.OpenRead(log2)
});
//添加文本
formDatas.Add(new Grass.Net.FormItemModel()
{
    Key = "id",
    Value = "id-test-id-test-id-test-id-test-id-test-"
});
formDatas.Add(new Grass.Net.FormItemModel()
{
    Key = "name",
    Value = "name-test-name-test-name-test-name-test-name-test-"
});
//提交表单
var result = PostForm(url, formDatas);

以下内容做了一些优化修改：

if (formUploadFile)
    {
        //文件数据模板
        string fileFormdataTemplate =
            "\r\n--" + boundary +
            "\r\nContent-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"" +
            "\r\nContent-Type: application/octet-stream" +
            "\r\n\r\n";
        //文本数据模板
        string dataFormdataTemplate =
            "\r\n--" + boundary +
            "\r\nContent-Disposition: form-data; name=\"{0}\"" +
            "\r\n\r\n{1}";
        //头部
        var header = Encoding.UTF8.GetBytes("--" + boundary);
        postStream.Write(header, 0, header.Length);
        var index = 0;
        foreach (var item in formItems)
        {
            index++;
            string formdata = null;
            if (item.IsFile)
            {
                if (index == 1)
                {
                    formdata = string.Format("\r\nContent-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\nContent-Type: application/octet-stream\r\n\r\n", item.Key, item.FileName);
 
                }
                else
                {
                    //上传文件
                    formdata = string.Format(fileFormdataTemplate,item.Key,item.FileName);
 
                }
        
            }
            else
            {
                if (index==1)
                {
                    formdata = string.Format("\r\nContent-Disposition: form-data; name=\"{0}\"\r\n\r\n{1}", item.Key, item.FileName);
                }
                else
                {
                    //上传文本
                    formdata = string.Format(dataFormdataTemplate, item.Key, item.Value);
                }
                 
            }
 
            //统一处理
            byte[] formdataBytes = Encoding.UTF8.GetBytes(formdata);
 
            postStream.Write(formdataBytes, 0, formdataBytes.Length);
 
            //写入文件内容
            //if (item.FileContent != null && item.FileContent.Length > 0)
            if (item.IsFile)
            {
 
                FileStream fs = new FileStream(item.FilePath, FileMode.Open, FileAccess.Read);//可以是其他重载方法
                byte[] byData = new byte[fs.Length];
                fs.Read(byData, 0, byData.Length);
                fs.Close();
                postStream.Write(byData, 0, byData.Length);
            }
        }
        //结尾
        var footer = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--");
        postStream.Write(footer, 0, footer.Length);
 
    }