description = [[
Gets the favicon ("favorites icon") from a web page and matches it against a
database of the icons of known web applications. If there is a match, the name
of the application is printed; otherwise the MD5 hash of the icon data is
printed.

If the script argument <code>favicon.uri</code> is given, that relative URI is
always used to find the favicon. Otherwise, first the page at the root of the
web server is retrieved and parsed for a <code><link rel="icon"></code>
element. If that fails, the icon is looked for in <code>/favicon.ico</code>. If
a <code><link></code> favicon points to a different host or port, it is ignored.
]]

---
-- @args favicon.uri URI that will be requested for favicon.
-- @args favicon.root Web server path to search for favicon.
--
-- @usage
-- nmap --script=http-favicon.nse \
--		--script-args favicon.root=<root>,favicon.uri=<uri>
-- @output
-- |_ http-favicon: Socialtext

-- HTTP default favicon enumeration script
-- rev 1.2 (2009-03-11)
-- Original NASL script by Javier Fernandez-Sanguino Pena


author = "Vlatko Kosturjak"

license = "Same as Nmap--See http://nmap.org/book/man-legal.html"

categories = {"default", "discovery", "safe"}

require "shortport"
require "http"
require "stdnse"
require "datafiles"
require "nsedebug"
require "openssl"

portrule = shortport.http

action = function(host, port)
  local md5sum,answer
  local match
  local status, favicondb
  local result= ""
  local favicondbfile="nselib/data/favicon-db"
  local index, icon
  local root = ""

  status, favicondb = datafiles.parse_file( favicondbfile, {["^%s*([^%s#:]+)[%s:]+"] = "^%s*[^%s#:]+[%s:]+(.*)"})
  if not status then
  	stdnse.print_debug( 1, "Could not open file: %s", favicondbfile )
	return
  end

  if(nmap.registry.args['favicon.root']) then
	root = nmap.registry.args['favicon.root']
  end

  if(nmap.registry.args['favicon.uri']) then
	-- If we got a script arg URI, always use that.
  	answer = http.get( host, port, root .. "/" .. nmap.registry.args['favicon.uri'])
	stdnse.print_debug( 4, "Using URI %s", nmap.registry.args['favicon.uri'])
  else
	-- Otherwise, first try parsing the home page.
 	index = http.get( host, port, root .. "/" )
	if index.status == 200 or index.status == 503 then
		-- find the favicon pattern
		icon = parseIcon( index.body )
		-- if we find a pattern
		if icon then
			local hostname = host.targetname or (host.name ~= "" and host.name) or host.ip
			stdnse.print_debug(1, "Got icon URL %s.", icon)
			local icon_host, icon_port, icon_path = parse_url_relative(icon, hostname, port.number, root)
			if (icon_host == host.ip or
				icon_host == host.targetname or
				icon_host == (host.name ~= '' and host.name)) and
				icon_port == port.number then
				-- request the favicon
				answer = http.get( icon_host, icon_port, icon_path )
			else
				answer = nil
			end
		else 
			answer = nil
		end
	end

	-- If that didn't work, try /favicon.ico.
	if not answer or answer.status ~= 200 then
		answer = http.get( host, port, root .. "/favicon.ico" )
		stdnse.print_debug( 4, "Using default URI.")
	end
  end

  --- check for 200 response code
  if answer and answer.status == 200 then
	md5sum=string.upper(stdnse.tohex(openssl.md5(answer.body)))
	match=favicondb[md5sum]
	if match then
		result = match
	else
		if nmap.verbosity() > 0 then
			result = "Unknown favicon MD5: " .. md5sum 
		end
	end
  else		
	stdnse.print_debug( 1, "No favicon found.")
	return
  end --- status == 200
  return result
end

local function dirname(path)
	local dir
	dir = string.match(path, "^(.*)/")
	return dir or ""
end

-- Return a URL's host, port, and path, filling in the results with the given
-- host, port, and path if the URL is relative. Return nil if the scheme is not
-- "http" or "https".
function parse_url_relative(u, host, port, path)
	local defaultport, scheme, abspath
	u = url.parse(u)
	scheme = u.scheme or "http"
	if scheme == "http" then
		defaultport = 80
	elseif scheme == "https" then
		defaultport = 443
	else
		return nil
	end
	abspath = u.path or ""
	if not string.find(abspath, "^/") then
		abspath = dirname(path) .. "/" .. abspath
	end
	return u.host or host, u.port or defaultport, abspath
end

function parseIcon( body )
	local _, i, j
	local rel, href, word

	-- Loop through link elements.
	i = 0
	while i do
		_, i = string.find(body, "<%s*[Ll][Ii][Nn][Kk]%s", i + 1)
		if not i then
			return nil
		end
		-- Loop through attributes.
		j = i
		while true do
			local name, quote, value
			_, j, name, quote, value = string.find(body, "^%s*(%w+)%s*=%s*([\"'])(.-)%2", j + 1)
			if not j then
				break
			end
			if string.lower(name) == "rel" then
				rel = value
			elseif string.lower(name) == "href" then
				href = value
			end
		end
		for word in string.gmatch(rel or "", "%S+") do
			if string.lower(word) == "icon" then
				return href
			end
		end
	end
end