WebRequest POST模式 ，基于“Basic Auth”口令认证模式，使用multipart/form-data方式上传文件及提交其他数据

public class HttpClientHelper

{

const string CRLF = "\r\n";

/// <summary>
/// POST 使用multipart/form-data方式上传文件及提交其他数据
/// 基于“Basic Auth”口令认证模式
/// </summary>
/// <param name="headers">请求头参数</param>
/// <param name="nameValueCollection">键值对参数</param>
/// <param name="fileCollection">文件参数：参数名，文件路径</param>
/// <returns>接口返回结果</returns>
public static string UploadMultipartFormData2(string url,Dictionary<string, string> headers, NameValueCollection nameValueCollection, string userName, string passWord, string filePath)
{
var boundary = string.Format("batch_{0}", Guid.NewGuid());
var startBoundary = string.Format("--{0}", boundary);
string strResult = "";
WebRequest request = null;
try 
{
// Set up Request body.
request = WebRequest.Create(url);
foreach (var item in headers)
{
request.Headers.Add(item.Key, item.Value);
}
request.Method = "POST";
//（1）设置请求Credentials
CredentialCache credentialCache = new CredentialCache
{
{ new Uri(url), "Basic", new NetworkCredential(userName, passWord) }
};
request.Credentials = credentialCache;
string Auth = Convert.ToBase64String(Encoding.UTF8.GetBytes($"{userName}:{passWord}"));
//（2）设置Headers Authorization
request.Headers.Add("Authorization", "Basic" + Auth);

request.ContentType = $"multipart/form-data; boundary={boundary}";

using (Stream requestStream = request.GetRequestStream())
{
StreamWriter writer = new StreamWriter(requestStream);

// 处理文件内容
WriteFileToStream(writer, startBoundary, "file", filePath);

// 键值对参数
string[] allKeys = nameValueCollection.AllKeys;
foreach (string key in allKeys)
{
WriteNvToStream(writer, startBoundary, key, nameValueCollection[key]);
}

var endFormData = CRLF + string.Format("--{0}--", boundary) + CRLF;

writer.Write(endFormData);
writer.Flush();
writer.Close();
}
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
using (StreamReader reader = new StreamReader(response.GetResponseStream()))
{
strResult = reader.ReadToEnd();
MyLogger.ErrorLogger.Debug($"UploadMultipartFormData2 推送录像文件返回数据：{url},{strResult}");
}
} 

}
catch (Exception ex)
{
strResult = ex.Message;
MyLogger.ErrorLogger.Debug($"UploadMultipartFormData2 推送录像文件错误：{strResult}");
return strResult;
}
finally
{
request?.Abort(); 
}
return strResult;
}

public static string UploadMultipartFormData(string url, Dictionary<string, string> headers, NameValueCollection nameValueCollection, NameValueCollection fileCollection)
{
var boundary = string.Format("batch_{0}", Guid.NewGuid());
var startBoundary = string.Format("--{0}", boundary);

// Set up Request body.
WebRequest request = WebRequest.Create(url);
foreach (var item in headers)
{
request.Headers.Add(item.Key, item.Value);
}
request.Method = "POST";

request.ContentType = $"multipart/form-data; boundary={boundary}";

using (Stream requestStream = request.GetRequestStream())
{
StreamWriter writer = new StreamWriter(requestStream);

// 处理文件内容
string[] fileKeys = fileCollection.AllKeys;
foreach (string key in fileKeys)
{
WriteFileToStream(writer, startBoundary, key, fileCollection[key]);
}

// 键值对参数
string[] allKeys = nameValueCollection.AllKeys;
foreach (string key in allKeys)
{
WriteNvToStream(writer, startBoundary, key, nameValueCollection[key]);
}

var endFormData = CRLF + string.Format("--{0}--", boundary) + CRLF;

writer.Write(endFormData);
writer.Flush();
writer.Close();
}

HttpWebResponse response = (HttpWebResponse)request.GetResponse();
string json = new StreamReader(response.GetResponseStream()).ReadToEnd();

return json;
}

/// <summary>
/// 写文件
/// </summary>
/// <param name="writer">流</param>
/// <param name="startBoundary">开始符</param>
/// <param name="name">字段名</param>
/// <param name="filePath">文件地址</param>
static void WriteFileToStream(StreamWriter writer, string startBoundary, string name, string filePath)
{
var filename = Path.GetFileName(filePath);
var fileRequestBody = startBoundary + CRLF;
fileRequestBody += $"Content-Disposition: form-data; name=\"{name}\"; filename=\"{filename}\"" + CRLF + CRLF;

writer.Write(fileRequestBody);
writer.Flush();

byte[] bmpBytes = File.ReadAllBytes(filePath);
writer.BaseStream.Write(bmpBytes, 0, bmpBytes.Length);
}

static void WriteNvToStream(StreamWriter writer, string startBoundary, string name, string value)
{
var nvFormData = CRLF + startBoundary + CRLF;
nvFormData += $"Content-Disposition: form-data; name=\"{name}\"" + CRLF + CRLF;
nvFormData += value /*+ CRLF*/;

writer.Write(nvFormData);
writer.Flush();
}

}

参考资料：https://www.cnblogs.com/SherryIce/p/16195070.html