-- XEP-0071: XHTML-IM sanitizing

local assert = assert;

local st = require "util.stanza";

local url = require "socket.url";

local no_styles = module:get_option_boolean("strip_xhtml_style", true);

-- Tables from XEP-0071

local xeptables = [[

<body/>	class, id, title; style

<head/>	profile

<html/>	version

<title/>

<abbr/>	class, id, title; style

<acronym/>	class, id, title; style

<address/>	class, id, title; style

<blockquote/>	class, id, title; style; cite

<br/>	class, id, title; style

<cite/>	class, id, title; style

<code/>	class, id, title; style

<dfn/>	class, id, title; style

<div/>	class, id, title; style

<em/>	class, id, title; style

<h1/>	class, id, title; style

<h2/>	class, id, title; style

<h3/>	class, id, title; style

<h4/>	class, id, title; style

<h5/>	class, id, title; style

<h6/>	class, id, title; style

<kbd/>	class, id, title; style

<p/>	class, id, title; style

<pre/>	class, id, title; style

<q/>	class, id, title; style; cite

<samp/>	class, id, title; style

<span/>	class, id, title; style

<strong/>	class, id, title; style

<var/>	class, id, title; style

<a/>	class, id, title; style; accesskey, charset, href, hreflang, rel, rev, tabindex, type

<dl/>	class, id, title; style

<dt/>	class, id, title; style

<dd/>	class, id, title; style

<ol/>	class, id, title; style

<ul/>	class, id, title; style

<li/>	class, id, title; style

<img/>	class, id, title; style; alt, height, longdesc, src, width

]];

-- map of whitelisted tag names to set of allowed attributes

local tags = {}; -- { string : { string : boolean } }

for tag, attrs in xeptables:gmatch("<(%w+)/>([^\n]*)") do

	tags[tag] = { xmlns = true, ["xml:lang"] = true };

	for attr in attrs:gmatch("%w+") do

		tags[tag][attr] = true;

	end

	if no_styles then

		tags[tag]["style"] = nil;

	end

end

-- module:log("debug", "tags = %s;", require "util.serialization".serialize(tags));

-- TODO Decide if disallowed tags should be bounced or silently discarded.

-- XEP says "ignore" and replace tag with text content, but that would

-- need a different transform which can't use `maptags`.

if not module:get_option_boolean("bounce_invalid_xhtml", false) then

	assert = function (x) return x end

end

local function sanitize_xhtml(tag)

	-- module:log("debug", "sanitize_xhtml(<{%s}%s>)", tag.attr.xmlns, tag.name);

	if tag.attr.xmlns == "http://www.w3.org/1999/xhtml" then

		local allowed = assert(tags[tag.name], tag.name);

		if allowed then

			for attr, value in pairs(tag.attr) do

				if not allowed[attr] then

					-- module:log("debug", "Removing disallowed attribute %q from <%s>", attr, tag.name);

					tag.attr[attr] = nil;

				elseif attr == "src" or attr == "href" then

					local urlattr = url.parse(value);

					local scheme = urlattr and urlattr.scheme;

					if scheme ~= "http" and scheme ~= "https" and scheme ~= "mailto" and scheme ~= "xmpp" and scheme ~= "cid" then

						tag.attr[attr] = "https://url.was.invalid/";

					end

				end

			end

		else

			tag.name = "span"

			tag.attr = { xmlns = "http://www.w3.org/1999/xhtml" }

		end

		-- Check child tags

		tag:maptags(sanitize_xhtml);

		-- This tag is clean!

		return tag;

	end

	-- Not xhtml, probably best to discard it

	return nil;

end

-- Check for xhtml-im, sanitize if exists

local function message_handler(event)

	local stanza = event.stanza;

	if stanza:get_child("html", "http://jabber.org/protocol/xhtml-im") then

		stanza = st.clone(stanza);

		if pcall(function() -- try

			stanza:get_child("html", "http://jabber.org/protocol/xhtml-im"):maptags(sanitize_xhtml);

		end) then

			event.stanza = stanza;

		else -- catch

			if stanza.attr.type ~= "error" then

				event.origin.send(st.error_reply(stanza, "modify", "not-acceptable", "Stanza contained illegal XHTML-IM tag"));

			end

			return true;

		end

	end

end

-- Stanzas received from clients

module:hook("pre-message/bare", message_handler, 71);

module:hook("pre-message/full", message_handler, 71);

module:hook("pre-message/host", message_handler, 71);

-- Stanzas about to be delivered to clients

module:hook("message/bare", message_handler, 71);

module:hook("message/full", message_handler, 71);