.net 模拟发起HTTP请求（用于上传文件）

/// <summary>
/// 文件帮助类
/// </summary>
public class FileHelper
{
/// <summary>
/// 上传文件
/// </summary>
/// <param name="url">请求地址</param>
/// <param name="path">文件路径（带文件名）</param>
/// <returns></returns>
public static string HttpUploadFile(string url, string path)
{
// 设置参数
HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
CookieContainer cookieContainer = new CookieContainer();
request.CookieContainer = cookieContainer;
request.AllowAutoRedirect = true;
request.Method = "POST";
string boundary = DateTime.Now.Ticks.ToString("X"); // 随机分隔线
request.ContentType = "multipart/form-data;charset=utf-8;boundary=" + boundary;
byte[] itemBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "\r\n");
byte[] endBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");

int pos = path.LastIndexOf("\\");
string fileName = path.Substring(pos + 1);

//请求头部信息
StringBuilder sbHeader = new StringBuilder(string.Format("Content-Disposition:form-data;name=\"file\";filename=\"{0}\"\r\nContent-Type:application/octet-stream\r\n\r\n", fileName));
byte[] postHeaderBytes = Encoding.UTF8.GetBytes(sbHeader.ToString());

StringBuilder builder = new StringBuilder($"Content-Disposition:form-data;name=\"subPath\"\r\n\r\ntmswechat");
byte[] postHeaderBytestwo = Encoding.UTF8.GetBytes(builder.ToString());

FileStream fs = new FileStream(path, FileMode.Open, FileAccess.Read);
byte[] bArr = new byte[fs.Length];
fs.Read(bArr, 0, bArr.Length);
fs.Close();

Stream postStream = request.GetRequestStream();
postStream.Write(itemBoundaryBytes, 0, itemBoundaryBytes.Length);
postStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);
postStream.Write(bArr, 0, bArr.Length);
postStream.Write(itemBoundaryBytes, 0, itemBoundaryBytes.Length);
postStream.Write(postHeaderBytestwo, 0, postHeaderBytestwo.Length);
postStream.Write(endBoundaryBytes, 0, endBoundaryBytes.Length);
postStream.Close();

//发送请求并获取相应回应数据
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
//直到request.GetResponse()程序才开始向目标网页发送Post请求
Stream instream = response.GetResponseStream();
StreamReader sr = new StreamReader(instream, Encoding.UTF8);
//返回结果网页（html）代码
string content = sr.ReadToEnd();
return content;
}

/// <summary>
/// 上传文件
/// </summary>
/// <param name="url">请求地址</param>
/// <param name="fs">文件流</param>
/// <param name="fileName">文件名</param>
/// <returns></returns>
public static string HttpUploadFile(string url, Stream fs, string fileName)
{
// 设置参数
HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
CookieContainer cookieContainer = new CookieContainer();
request.CookieContainer = cookieContainer;
request.AllowAutoRedirect = true;
request.Method = "POST";
string boundary = DateTime.Now.Ticks.ToString("X"); // 随机分隔线
request.ContentType = "multipart/form-data;charset=utf-8;boundary=" + boundary;
byte[] itemBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "\r\n");
byte[] endBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");

//请求头部信息
StringBuilder sbHeader = new StringBuilder(string.Format("Content-Disposition:form-data;name=\"file\";filename=\"{0}\"\r\nContent-Type:application/octet-stream\r\n\r\n", fileName));
byte[] postHeaderBytes = Encoding.UTF8.GetBytes(sbHeader.ToString());

StringBuilder builder = new StringBuilder($"Content-Disposition:form-data;name=\"subPath\"\r\n\r\ntmswechat");
byte[] postHeaderBytestwo = Encoding.UTF8.GetBytes(builder.ToString());

byte[] bArr = new byte[fs.Length];
int len = fs.Read(bArr, 0, (int)fs.Length);

Stream postStream = request.GetRequestStream();
postStream.Write(itemBoundaryBytes, 0, itemBoundaryBytes.Length);
postStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);
postStream.Write(bArr, 0, len);
postStream.Write(itemBoundaryBytes, 0, itemBoundaryBytes.Length);
postStream.Write(postHeaderBytestwo, 0, postHeaderBytestwo.Length);
postStream.Write(endBoundaryBytes, 0, endBoundaryBytes.Length);
postStream.Close();

//发送请求并获取相应回应数据
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
//直到request.GetResponse()程序才开始向目标网页发送Post请求
Stream instream = response.GetResponseStream();
StreamReader sr = new StreamReader(instream, Encoding.UTF8);
//返回结果网页（html）代码
string content = sr.ReadToEnd();
return content;
}
}

　　　　　public static string HttpClientUploadFile(string url, Stream fs, string fileName)
{
if (url.StartsWith("https"))
System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;
HttpClient httpClient = new HttpClient();

MultipartFormDataContent formData = new MultipartFormDataContent();

byte[] bArr = new byte[fs.Length];
fs.Read(bArr, 0, (int)fs.Length);
fs.Seek(0, SeekOrigin.Begin);
ByteArrayContent byteArrayContent = new ByteArrayContent(bArr);
byteArrayContent.Headers.ContentEncoding.Add("utf-8");
formData.Add(byteArrayContent, "file", fileName);
formData.Add(new StringContent("tmswechat"), "subPath");
HttpResponseMessage response = httpClient.PostAsync(url, formData).Result;
if (response.IsSuccessStatusCode)
{
string result = response.Content.ReadAsStringAsync().Result;
return result;
}
return null;
}