Functions for downloading and removing images async. The magic of cackbacks ⭐ 🌟 ⭐

bot/utils.lua

@@ -1,3 +1,5 @@
+local ltn12 = require "ltn12"
+
 function get_receiver(msg)
   if msg.to.type == 'user' then
     return 'user#id'..msg.from.id
@@ -15,7 +17,6 @@ function is_chat_msg( msg )
 end
 
 function string.random(length)
-   math.randomseed(os.time())
    local str = "";
    for i = 1, length do
       math.random(97, 122)
@@ -36,46 +37,31 @@ function string.trim(s)
   return s:gsub("^%s*(.-)%s*$", "%1")
 end
 
-function download_to_file( url , noremove )
+--  Saves file to /tmp/. If file_name isn't provided, 
+-- will get the text after the last "/" for filename.
+function download_to_file(url, file_name)
   print("url to download: "..url)
-  local ltn12 = require "ltn12"
-  local respbody = {}
-  one, c, h = http.request{url=url, sink=ltn12.sink.table(respbody), redirect=true}
-  htype = h["content-type"]
 
-  if htype == "image/jpeg" then
-    file_name = string.random(5)..".jpg"
-    file_path = "/tmp/"..file_name
-  else
-    if htype == "image/gif" then
-      file_name = string.random(5)..".gif"
-      file_path = "/tmp/"..file_name
-    else
-      if htype == "image/png" then
-        file_name = string.random(5)..".png"
-        file_path = "/tmp/"..file_name
-      else
-        file_name = url:match("([^/]+)$")
-        file_path = "/tmp/"..file_name
-      end
-    end
-  end
+  local respbody = {}
+  local options = {
+    url = url,
+    sink = ltn12.sink.table(respbody),
+    redirect = true
+  }
+
+  local one, c, h = http.request(options)
+  
+  -- Everything after the last /
+  local file_name = url:match("([^/]+)$") 
+  local file_path = "/tmp/"..file_name
+
   file = io.open(file_path, "w+")
   file:write(table.concat(respbody))
   file:close()
 
-  if noremove == nil then
-    print(file_path.."will be removed in 20 seconds")
-    postpone(rmtmp_cb, file_path, 20)
-  end
-
   return file_path
 end
 
--- Callback to remove a file
-function rmtmp_cb(file_path, success, result)
-   os.remove(file_path)
-end
 
 function vardump(value, depth, key)
   local linePrefix = ""
@@ -191,7 +177,84 @@ function string:isempty()
   return self == nil or self == ''
 end
 
-
+-- Returns true if String starts with Start
 function string.starts(String, Start)
    return Start == string.sub(String,1,string.len(Start))
 end
+
+-- Send image to user and delete it when finished.
+-- cb_function and cb_extra are optionals callback
+function _send_photo(receiver, file_path, cb_function, cb_extra)
+  local cb_extra = {
+    file_path = file_path,
+    cb_function = cb_function,
+    cb_extra = cb_extra
+  }
+  -- Call to remove with optional callback
+  send_photo(receiver, file_path, rmtmp_cb, cb_extra)
+end
+
+-- Download the image and send to receiver, it will be deleted.
+function send_photo_from_url(receiver, url)
+  local file_path = download_to_file(url, false)
+  print("File path: "..file_path)
+  _send_photo(receiver, file_path)
+end
+
+--  Send multimple images asynchronous.
+-- param urls must be a table.
+function send_photos_from_url(receiver, urls)
+  local cb_extra = {
+    receiver = receiver,
+    urls = urls,
+    remove_path = nil
+  }
+  send_photos_from_url_callback(cb_extra)
+end
+
+-- Use send_photos_from_url. 
+-- This fuction might be difficult to understand.
+function send_photos_from_url_callback(cb_extra, success, result)
+  -- cb_extra is a table containing receiver, urls and remove_path
+  local receiver = cb_extra.receiver
+  local urls = cb_extra.urls
+  local remove_path = cb_extra.remove_path
+
+  -- The previously image to remove
+  if remove_path ~= nil then
+    os.remove(remove_path)
+    print("Deleted: "..remove_path)
+  end
+
+  -- Nil or empty, exit case (no more urls)
+  if urls == nil or #urls == 0 then
+    return false
+  end
+
+  -- Take the head and remove from urls table
+  local head = table.remove(urls, 1)
+
+  local file_path = download_to_file(head, false)
+  local cb_extra = {
+    receiver = receiver,
+    urls = urls,
+    remove_path = file_path
+  }
+
+  -- Send first and postpone the others as callback
+  send_photo(receiver, file_path, send_photos_from_url_callback, cb_extra)
+end
+
+-- Callback to remove a file
+function rmtmp_cb(cb_extra, success, result)
+  local file_path = cb_extra.file_path
+  local cb_function = cb_extra.cb_function
+  local cb_extra = cb_extra.cb_extra
+
+  if file_path ~= nil then
+    os.remove(file_path)
+    print("Deleted: "..file_path)
+  end
+  -- Finaly call the callback
+  cb_function(cb_extra, success, result)
+end

plugins/9gag.lua

@@ -22,7 +22,7 @@ function run(msg, matches)
   local receiver = get_receiver(msg)
   url, title = get_9GAG()
   file_path = download_to_file(url)
-  send_photo(receiver, file_path, send_title, {receiver, title})
+  _send_photo(receiver, file_path, send_title, {receiver, title})
   return false
 end
 

plugins/twitter.lua

@@ -59,15 +59,11 @@ function run(msg, matches)
   -- send the parts 
   local receiver = get_receiver(msg)
   send_msg(receiver, header .. "\n" .. text, ok_cb, false)
-  for k, v in pairs(images) do
-    local file = download_to_file(v)
-    send_photo(receiver, file, ok_cb, false)
-    delay_s(1)
-  end
-  
+  send_photos_from_url(receiver, images)
   return nil
 end
  
+
 return {
     description = "When user sends twitter URL, send text and images to origin. Requieres OAuth Key.", 
     usage = "",