Wget with Lua hooks

• New idea: add Lua scripting to wget.

• Work in progress: https://github.com/alard/wget-lua/tree/lua
  • The Lua scripting is patched on the "lua" branch. You can use the compare branch feature on GitHub to see the differences.
  • Alternative location: https://github.com/ArchiveTeam/wget-lua/tree/lua.
  • If you get errors about 'wget.pod' while compiling, try applying this patch.

• Documentation: https://github.com/alard/wget-lua/wiki/Wget-with-Lua-hooks

Example usage:

wget http://www.archiveteam.org/ -r --lua-script=lua-example/print_parameters.lua

Why would this be useful?

Custom error handling

What to do in case of an error? Sometimes you want wget to retry the url if it gets a server error.

wget.callbacks.httploop_result = function(url, err, http_stat)
  if http_stat.statcode == 500 then
    -- try again
    return wget.actions.CONTINUE
  elseif http_statcode == 404 then
    -- stop
    return wget.actions.EXIT
  else
    -- let wget decide
    return wget.actions.NOTHING
  end
end

Custom decide rules

Download this url or not?

wget.callbacks.download_child_p = function(urlpos, parent, depth, start_url_parsed, iri, verdict)
  if string.find(urlpos.url, "textfiles.com") then
    -- always download
    return true
  elseif string.find(urlpos.url, "archive.org") then
    -- never!
    return false
  else
    -- follow wget's advice
    return verdict
  end
end

Custom url extraction/generation

Sometimes it's useful if you can write your own url extraction code, for example to add urls that aren't actually on the page.

wget.callbacks.get_urls = function(file, url, is_css, iri)
  if string.find(url, ".com/profile/[^/]+/$") then
    -- make sure wget downloads the user's photo page
    -- and custom profile photo
    return {
      { url=url.."photo.html",
        link_expect_html=1,
        link_expect_css=0 },
      { url=url.."photo.jpg",
        link_expect_html=0,
        link_expect_css=0 }
    }
  else
    -- no new urls to add
    return {}
  end
end

More Examples

Archive Team has real life scripts on the Archive Team GitHub organization. Look for recent -grab projects. The Lua scripts range from simple checks to complex URL scraping.

• zapd-grab/zapd.lua: Avoids JavaScript monstrosity by scraping anything that looks like an URL on CDN.
• puush-grab/puush.lua: Checks the status code and the contents and returns custom error codes.
• posterous-grab/posterous.lua: Checks the status code and delays if needed.
• xanga-grab/xanga.lua: Implements its own URLs scraping.
• patch-grab/patch.lua: Scrapes URLs as it goes along and sends it off to a server to be done later.
• formspring-grab/formspring.lua: Manually behaves like JavaScript and builds its own request URLs.
• hyves-grab/hyves.lua: Works around JavaScript calls to pagination. Includes calling external process to decrypt ciphertext.
• ArchiveBot/pipeline/archivebot.lua: Logs results in Redis and implements custom URL checking.