title: Upload image to twitter using update_with_media - Lua
body: <p>I am trying to post an image to twitter using update_with_media.json.</p>
  
  <p>The following is a working code to update tweet with statuses/update.json </p>
  
  <pre><code>local url = "http://api.twitter.com/1/statuses/update.json"
  local consumer_key = ""
  local consumer_secret = ""
  local token = ""
  local token_secret = ""
  
  
  local post_data = 
      {
      oauth_consumer_key = consumer_key,
      oauth_nonce        = get_nonce(),
      oauth_signature_method = "HMAC-SHA1",
      oauth_token        = token,
      oauth_timestamp    = get_timestamp(),
      oauth_version      = '1.0',
      oauth_token_secret = token_secret
  
      }
  
  post_data["status"] = "Hello Twitter!"      
  post_data = oAuthSign(url, "POST", post_data, consumer_secret)
  
  
  r,c,h = http.request
     {
     url = url,
     method = "POST",
     headers = 
           {
           ["Content-Type"] = "application/x-www-form-urlencoded", 
           ["Content-Length"] = string.len(rawdata)
           },
     source = ltn12.source.string(post_data),
     sink = ltn12.sink.table(response)
     }
  </code></pre>
  
  <p>Now how do I modify the above code to upload images? 
  The url would be "http://api.twitter.com/1/statuses/update_with_media.json"  and 
  headers["Content-Type"] would be "multipart/form-data"</p>
  
  <p>But where and how do I specify the image to be uploaded?   </p>