--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_bob/README.markdown	Fri Sep 28 16:12:18 2018 +0200
@@ -0,0 +1,20 @@
+---
+summary: Cache Bits of Binary on MUC services
+---
+
+Description
+===========
+
+This module extracts cid: URIs (as defined in XEP-0231) from messages, and
+replies with their content whenever another client asks for the actual data.
+
+Usage
+=====
+
+```lua
+Component "rooms.example.org" "muc"
+	modules_enabled = {
+		"bob";
+		...
+	}
+```

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_bob/mod_bob.lua	Fri Sep 28 16:12:18 2018 +0200
@@ -0,0 +1,146 @@
+module:depends("cache_c2s_caps");
+
+local st = require "util.stanza";
+local encodings = require "util.encodings";
+local b64_encode = encodings.base64.encode;
+local b64_decode = encodings.base64.decode;
+local sha1 = require"util.hashes".sha1;
+
+-- TODO: Move that to storage.
+local cache = {};
+-- TODO: use util.cache for this.
+local in_flight = {};
+
+local function check_cid(src)
+	-- TODO: figure out why ^ can’t be used at the beginning of the pattern.
+	for cid in src:gmatch("cid:(%w+%+%w+@bob%.xmpp%.org)$") do
+		return cid;
+	end
+	return nil;
+end
+
+local function handle_data_carrier(tag)
+	if tag.name ~= "data" or tag.attr.xmlns ~= "urn:xmpp:bob" then
+		return tag;
+	end
+	local cid = tag.attr.cid;
+	local media_type = tag.attr.type;
+	local max_age = tag.attr['max-age'];
+	local b64_content = tag:get_text();
+	local content = b64_decode(b64_content);
+	local hash = sha1(content, true);
+	if cid ~= "sha1+"..hash.."@bob.xmpp.org" then
+		module:log("debug", "Invalid BoB cid, %s ~= %s", cid, "sha1+"..hash.."@bob.xmpp.org");
+		return nil;
+	end
+	cache[cid] = { media_type = media_type, max_age = max_age, content = content };
+	if in_flight[cid] then
+		local iq = st.iq({ type = "result", id = "fixme" });
+		iq:add_direct_child(tag);
+		for jid, data in pairs(in_flight[cid]) do
+			iq.attr.from = data.from;
+			iq.attr.to = jid;
+			iq.attr.id = data.id;
+			module:send(iq);
+		end
+		in_flight[cid] = nil;
+	end
+	return nil;
+end
+
+local current_id = 0;
+local function send_iq(room_jid, jid, cid, log)
+	local iq = st.iq({ type = "get", from = room_jid, to = jid, id = "bob-"..current_id })
+		:tag("data", { xmlns = "urn:xmpp:bob", cid = cid });
+	log("debug", "found BoB image in XHTML-IM, asking %s for cid %s", jid, cid);
+	module:send(iq);
+	in_flight[cid] = {};
+end
+
+local function find_images(tag, jid, room_jid, log)
+	if tag.name == "img" and tag.attr.xmlns == "http://www.w3.org/1999/xhtml" then
+		local src = tag.attr.src;
+		local cid = check_cid(src);
+		if not cid then
+			return;
+		end
+		if cache[cid] then
+			log("debug", "cid %s already found in cache", cid);
+			return;
+		end
+		if in_flight[cid] then
+			log("debug", "cid %s already queried", cid);
+			return;
+		end
+		send_iq(room_jid, jid, cid, log);
+		return;
+	end
+	for child in tag:childtags(nil, "http://www.w3.org/1999/xhtml") do
+		find_images(child, jid, room_jid, log);
+	end
+end
+
+local function message_handler(event)
+	local stanza, origin = event.stanza, event.origin;
+	local jid = stanza.attr.from;
+	local room_jid = stanza.attr.to;
+	local log = origin.log or module._log;
+
+	-- Remove and cache all <data/> elements embedded here.
+	stanza:maptags(handle_data_carrier);
+
+	-- Find and query all of the cids not already cached.
+	local tag = stanza:get_child("html", "http://jabber.org/protocol/xhtml-im");
+	for body in tag:childtags("body", "http://www.w3.org/1999/xhtml") do
+		find_images(body, jid, room_jid, log);
+	end
+end
+
+local function handle_data_get(stanza, cid, log)
+	local data = cache[cid];
+	if not data then
+		log("debug", "BoB requested for data not in cache (cid %s), falling through.", cid);
+		if in_flight[cid] then
+			log("debug", "But an iq has already been sent, let’s wait…");
+			in_flight[cid][stanza.attr.from] = { id = stanza.attr.id, from = stanza.attr.to };
+			return true;
+		end
+		return nil;
+	end
+
+	local iq = st.reply(stanza);
+	iq:text_tag("data", b64_encode(data.content), {
+		xmlns = "urn:xmpp:bob",
+		cid = cid,
+		type = data.media_type,
+		['max-age'] = data.max_age,
+	});
+	log("debug", "Answering BoB request for cid %s on the behalf of %s", cid, stanza.attr.to);
+	module:send(iq);
+	return true;
+end
+
+local function iq_handler(event)
+	local stanza, origin = event.stanza, event.origin;
+	local tag = stanza.tags[1];
+	if tag.name ~= "data" or tag.attr.xmlns ~= "urn:xmpp:bob" then
+		return nil;
+	end
+	local log = origin.log or module._log;
+	local cid = tag.attr.cid;
+	if not cid then
+		log("debug", "BoB iq doesn’t contain a cid attribute.");
+		return;
+	end
+	if stanza.attr.type == "get" then
+		return handle_data_get(stanza, cid, log);
+	elseif stanza.attr.type == "result" then
+		handle_data_carrier(tag);
+		return true;
+	end
+	-- TODO: also handle error iqs.
+end
+
+module:hook("message/bare", message_handler, 1);
+module:hook("iq/full", iq_handler, 1);
+module:hook("iq/bare", iq_handler, 1);