How to deal with multipart/form-data

[wyagd001]

For example, I want to upload a file to the server.
How to parse the data and save it as a file?

For example: the extensions of file ,such as zip, doc, png, txt and so
on

  <form action="/upload" method="POST" enctype="multipart/form-data">  
    <input type="file" name="file" />  
    <input  type="submit" value="upload" />  
  </form> 

But I don't know how to parse the data and save it as a file.

PS: use above html code the ["Expect"] Is empty.