include web graphics

webgraphics.lua

local err,warn,info,log = luatexbase.provides_module({
  name        = 'webgraphics',
  date        = '2014/06/30',
  version     = 0.1,
  description = 'include graphics on the web',
  author      = 'Dohyun Kim',
  license     = 'public domain',
})

webgraphics = webgraphics or {}
local webgraphics = webgraphics

local http  = require("socket.http")
local ltn12 = require("ltn12")
local lfs   = require("lfs")

local function dowebgraphics (wfile,opts)
  local lfile = string.gsub(wfile,".*/","")
  lfile = string.gsub(lfile,"[^%w%.]","_")
  if not lfs.isfile(lfile) then
    local fh = io.open(lfile,"wb")
    http.request {
      url  = wfile,
      sink = ltn12.sink.file(fh),
    }
  end
  tex.sprint(string.format("\\includegraphics%s{%s}",opts,lfile))
end
webgraphics.dowebgraphics = dowebgraphics

webgraphics.sty

\begingroup\expandafter\expandafter\expandafter\endgroup
\expandafter\ifx\csname ProvidesPackage\endcsname\relax\else
  \ProvidesPackage{webgraphics}[2014/06/30 v0.1 include graphics on the web]
\fi
\RequirePackage{luatexbase}
\RequirePackage{graphicx}
\RequireLuaModule{webgraphics}
\edef\catcodeofATchar{\catcode`@=\the\catcode`@\relax}
\catcode`@=11
\protected\def\includewebgraphics#1#{%
  \toks@{#1}%
  \begingroup
  \catcode`\$=12 \catcode`\&=12 \catcode`\#=12 \catcode`\^=12
  \catcode`\_=12 \catcode`\~=12 \catcode`\%=12 \includewebgraphicsXX
}
\def\includewebgraphicsXX#1{%
  \endgroup
  \directlua{webgraphics.dowebgraphics([==[#1]==], [==[\the\toks@]==])}%
}
\catcodeofATchar
\endinput
%%%%% example usage %%%%%
\includewebgraphics
  [width=.3\textwidth]
  {http://www.ktug.org/xe/files/attach/images/1400/400/001/KTS-meta-3-2.png}