Re: Lua vs. XML

[Richard Hundt <richardhundt@...>]

Alexander Gladysh wrote:
> Hi, list!
>
> I need to load some trivial XMLs into Lua data at run-time. XML-s are
> trivial, but do use UTF-8, CDATA and fancy entities, so library must
> handle them well.
>
> I wanted to use some luarocks-installable module, but failed to find
> one that would install on my Ubuntu box.
>
> Both luaexpat (which also looks too heavy for my needs) and
> lua-xmlreader (which looks stalled at version 0.1) rocks fail to build
> (I may provide bug reports if anyone interested).
>
> All other Lua XML bindings I know about are not listed in the
> available rocks list. (And I'd like to avoid to try them one after
> another to find they just don't work for me...)
>
> Is the situation with XML handling in Lua really that dire as I
> imagine it, or am I just having a bad day? What do you use to handle
> XML in Lua?
>
> By the way, in my opinion, lua-users Wiki page on XML really sucks. :(
>
> http://lua-users.org/wiki/LuaXml
>
> (No, I'm not volunteering to fix it — I do not have enough data.)
>
> Alexander.

I've found an old XML lpeg grammar I had lying around. It's a bit raw in 
that it doesn't do the whole DOM API thing and it's not wrapped up in a 
module, but it's tweakable, so in case you can't find anything else... 
here it is.

-Rich

require "lpeg"

-- Edit these "classes" to build a DOM parser if you want
Node = { }
Node.__index = Node

Document = { }
Document.__index = Document

Element = { }
Element.__index = Element

-- alternatively, make these callbacks do what you need
local function create_document(xdoc)
   return setmetatable(xdoc, Document)
end
local function create_doctype_node(node)
   node.name = "#doctype-declaration"
   return setmetatable(node, Node)
end
local function create_element_node(node)
   return setmetatable(node, Element)
end
local function create_cdata_node(node)
   node.name = "#cdata"
   return setmetatable(node, Node)
end
local function create_text_node(node)
   node.name = "#text"
   return setmetatable(node, Node)
end
local function create_comment_node(node)
   node.name = "#comment"
   return setmetatable(node, Node)
end
local function create_procins_node(node)
   node.name = "#processing-instruction"
   return setmetatable(node, Node)
end

-- below is the LPeg grammar, tweak as needed, otherwise it
-- calls the callback functions above as it collects nodes
local m = lpeg

local function parse_error(s, i)
   local msg = (#s < i + 20) and s:sub(i) or s:sub(i,i+20) .. "..."
   msg = ("parse error near '%s'"):format(msg)
   error(msg, 2)
end

local function backref(s, i, c)
   if type(c) ~= "string" then
      return nil
   end
   local e = #c + i
   if s:sub(i, e - 1) == c then
      return e
   else
      return nil
   end
end

local function Cbr(name)
   return m.Cmt(m.Cb(name), backref)
end

local function fold_attributes(list)
   local atts = { }
   for i=1,#list,2 do
      atts[list[i]] = list[i+1]
   end
   return atts
end


XML = m.P{ "xml";
   xml = m.V"document" / create_document + m.V"eos";

   document = m.Ct(
      m.V"doctype"^-1 * m.V"markup"
   ) * (m.V"eos" + parse_error);

   doctype = m.Ct(
      "<!DOCTYPE" * m.Cg((1 - m.P">")^1, "data") *
      m.Cg(m.Cc"DOCTYPE_DECLARATION", "type") * ">"
   ) / create_doctype_node;

   markup = (
      m.V"element"   / create_element_node
      + m.V"cdata"   / create_cdata_node
      + m.V"text"    / create_text_node
      + m.V"comment" / create_comment_node
      + m.V"procins" / create_procins_node
   )^0;

   element = m.Ct(
      m.V"tagOpen" * m.V"markup" *
      (#m.V"tagClose" + parse_error) *
      m.V"tagClose" + m.V"tagOpenEmpty"
   );

   tagOpen = "<" * (
      m.V"tagName" * m.V"attrs" * m.V"ws"^0 * ">"
      + m.V"ws"^0 * ">"
   );
   tagOpenEmpty = "<" * (
      m.V"tagName" * m.V"attrs" * m.V"ws"^0 * "/>"
      + m.V"ws"^0 * "/>"
   );
   tagClose = "</" * Cbr("name") * m.V"ws"^0 * ">";
   tagName = m.Cg(m.V"ident", "name") *m.Cg(m.Cc"ELEMENT_NODE", "type");
   text = m.Ct(
      m.Cg((1 - m.S"><")^1, "data") * m.Cg(m.Cc"TEXT_NODE", "type")
   );
   cdata = m.Ct(
      "<![CDATA[" * m.Cg((1 - m.P"]]>")^0, "data") * "]]>" *
      m.Cg(m.Cc"CDATA_SECTION_NODE", "type")
   );
   comment = m.Ct(
      "<!--" * m.Cg((1 - m.P"-->")^0, "data") * "-->" *
      m.Cg(m.Cc"COMMENT_NODE", "type")
   );
   procins = m.Ct(
      "<?" * m.Cg((1 - m.P"?>")^0, "data") * "?>" *
      m.Cg(m.Cc"PROCESSING_INSTRUCTION_NODE", "type")
   );
   attrs = m.Cg(
      m.Ct(m.V"attr"^0) / fold_attributes, "attributes"
   );
   attr = m.V"ws"^1 * m.C(m.V"ident") * m.P"=" * m.V"str";
   str = ('"' * m.C((1 - m.P'"')^0) * '"')
      + ("'" * m.C((1 - m.P"'")^0) * "'");
   ident = (m.R("az", "AZ", "09") + m.S"_.:-")^1;
   ws = m.S" \t\r\n";
   eos = -m.P(1);
}

function test()
   local xmlstr = [=[
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd";>

<html xmlns="http://www.w3.org/1999/xhtml";>
<head>
    <meta content="895" name="ku-session-keeper" id="ku-session-keeper" />
    <script src="/kudu/jslib/ku/core.js" type="text/javascript" />
    <link rel="stylesheet" href="/kudu/css/default.css" />
</head>
<body>
    <!--this is a comment baby-->
    <div ku:replace="header" />
    <div ku:include="content" />
    <form ku:action="doit">...</form>
    <script type="text/javascript" id="my-script"><![CDATA[
    if ( foo > 42 ) {
        alert("cheese");
    }
    ]]>
    </script>
    <div foo="bar" baz="quux">This is My Div</div>
</body>
</html>
]=]

   local xmldoc = XML:match(xmlstr)
   local html = xmldoc[3]
   assert(html.attributes.xmlns == "http://www.w3.org/1999/xhtml";)
   local body
   for i,node in ipairs(html) do
      if node.name == "body" then
         body = node
         break
      end
   end
   assert(body[2].data == "this is a comment baby")
   local script
   for i,node in ipairs(body) do
      if node.name == "script" then
         script = node
         break
      end
   end
   assert(script[1].data)
   assert(script[1].type == "CDATA_SECTION_NODE")
end

-- uncomment to run the tests
--test()

-- this code is free software and may be used and/or distributed under
-- the same terms as Lua itself