[Feature] Add function to extract most meaningful urls

lualib/lua_util.lua

@@ -475,4 +475,126 @@ end
 
 exports.override_defaults = override_defaults
 
+--[[[
+-- @function lua_util.extract_specific_urls(task, limit)
+-- Apply heuristic in extracting of urls from task, this function
+-- tries its best to extract specific number of urls from a task based on
+-- their characteristics
+--]]
+exports.extract_specific_urls = function(task, lim, need_emails)
+  local fun = require "fun"
+  local cache_key = string.format('sp_urls_%d%s', lim, need_emails)
+
+  local cached = task:cache_get(cache_key)
+
+  if cached then
+    return cached
+  end
+
+  local urls = task:get_urls(need_emails)
+
+
+  if not urls then return {} end
+
+  if #urls <= lim then
+    task:cache_set(cache_key, urls)
+
+    return urls
+  end
+
+  -- Filter by tld:
+  local tlds = {}
+  local eslds = {}
+  local ntlds, neslds = 0, 0
+
+  local res = {}
+
+  for _,u in ipairs(urls) do
+    local esld = u:get_tld()
+
+    if esld then
+      if not eslds[esld] then
+        eslds[esld] = {u}
+        neslds = neslds + 1
+      else
+        table.insert(eslds[esld], u)
+      end
+
+      local parts = rspamd_str_split(esld, '.')
+      local tld = table.concat(fun.totable(fun.tail(parts)), '.')
+
+      if not tlds[tld] then
+        tlds[tld] = {u}
+        ntlds = ntlds + 1
+      else
+        table.insert(tlds[tld], u)
+      end
+
+      -- Extract priority urls that are proven to be malicious
+      if not u:is_html_displayed() then
+        if u:is_obscured() then
+          table.insert(res, u)
+        else
+          if u:get_user() then
+            table.insert(res, u)
+          elseif u:is_subject() then
+            table.insert(res, u)
+          end
+        end
+      end
+    end
+  end
+
+  lim = lim - #res
+  if lim <= 0 then lim = 1 end
+
+  if neslds <= lim then
+    -- We can get urls based on their eslds
+    while lim > 0 do
+      for _,urls in pairs(eslds) do
+        table.insert(res, table.remove(urls))
+        lim = lim - 1
+      end
+    end
+
+    task:cache_set(cache_key, urls)
+    return res
+  end
+
+  if ntlds <= lim then
+    while lim > 0 do
+      for _,urls in pairs(tlds) do
+        table.insert(res, table.remove(urls))
+        lim = lim - 1
+      end
+    end
+
+    task:cache_set(cache_key, urls)
+    return res
+  end
+
+  -- We need to sort tlds table first
+  local tlds_keys = {}
+  for k,_ in pairs(tlds) do table.insert(tlds_keys, k) end
+  table.sort(tlds_keys, function (t1, t2)
+    return #tlds[t1] < #tlds[t2]
+  end)
+
+  local ntlds = #tlds_keys
+  for i=1,ntlds / 2 do
+    local tld1 = tlds[tlds_keys[i]]
+    local tld2 = tlds[tlds_keys[ntlds - i]]
+    table.insert(res, table.remove(tld1))
+    table.insert(res, table.remove(tld2))
+    lim = lim - 2
+
+    if lim <= 0 then
+      break
+    end
+  end
+
+  task:cache_set(cache_key, urls)
+  return res
+end
+
 return exports