HttpWebRequest请求PHP页面，PHP如何读取request请求的参数

实现功能：提供外部访问PHP接口
  C# 使用 HttpWebRequest 访问 php 页面 
代码如下：
  StringBuilder ss = new StringBuilder();  
  byte[] byt;
  rqst.Timeout = 60000;
  rqst.Method = "post";
  FileStream inStream = new FileStream(path, FileMode.Open, FileAccess.Read);
  long nBytesToRead = inStream.Length;
  byt = new byte[nBytesToRead];
  int m = inStream.Read(byt, 0, byt.Length);
  inStream.Close();  
  Stream reqStream = rqst.GetRequestStream();
  reqStream.Write(byt, 0, byt.Length);
  reqStream.Close();
  HttpWebResponse rps = (HttpWebResponse)rqst.GetResponse();
  retValue = GetStrRd(rps);
？php 服务器端如和获取 请求上传的"RequestStream" 对像和其他参数等

返回的是什么格式？