--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_inject_ecaps2/mod_insert_ecaps2.lua	Wed Mar 07 19:30:42 2018 +0100
@@ -0,0 +1,91 @@
+module:depends("cache_c2s_caps");
+
+local st = require "util.stanza";
+local hashes = require "util.hashes";
+local base64 = require "util.encodings".base64;
+local t_insert, t_sort, t_concat = table.insert, table.sort, table.concat;
+
+local algorithms = module:get_option_set("ecaps2_hashes", { "sha-256", "sha-512" });
+
+-- TODO: Add all of the other hashes supported.
+local algorithm_map = {
+	["sha-256"] = hashes.sha256;
+	["sha-512"] = hashes.sha512;
+};
+
+-- TODO: move that to util.caps maybe.
+local function calculate_hash(disco_info)
+	local identities, features, extensions = {}, {}, {};
+	for _, tag in ipairs(disco_info) do
+		if tag.name == "identity" then
+			t_insert(identities, ((tag.attr.category or "").."\x1f"..
+			                      (tag.attr.type or "").."\x1f"..
+					      (tag.attr["xml:lang"] or "").."\x1f"..
+					      (tag.attr.name or "").."\x1f\x1e"));
+		elseif tag.name == "feature" then
+			t_insert(features, (tag.attr.var or "").."\x1f");
+		elseif tag.name == "x" and tag.attr.xmlns == "jabber:x:data" then
+			local form = {};
+			for _, field in ipairs(tag.tags) do
+				if field.name == "field" and field.attr.xmlns == "jabber:x:data" and field.attr.var then
+					local values = {};
+					for _, value in ipairs(field.tags) do
+						if value.name == "value" and value.attr.xmlns == "jabber:x:data" then
+							value = #value.tags == 0 and value:get_text();
+							if value then t_insert(values, value.."\x1f"); end
+						end
+					end
+					t_sort(values);
+					if #values > 0 then
+						t_insert(form, field.attr.var.."\x1f"..t_concat(values, "\x1f").."\x1f\x1e");
+					else
+						t_insert(form, field.attr.var.."\x1f\x1e");
+					end
+				end
+			end
+			t_sort(form);
+			form = t_concat(form, "\x1d").."\x1d";
+			t_insert(extensions, form);
+		else
+			return nil, "Unknown element in disco#info";
+		end
+	end
+	t_sort(identities);
+	t_sort(features);
+	t_sort(extensions);
+	if #identities > 0 then identities = t_concat(identities, "\x1c").."\x1c"; else identities = "\x1c"; end
+	if #features > 0 then features = t_concat(features).."\x1c"; else features = "\x1c"; end
+	if #extensions > 0 then extensions = t_concat(extensions, "\x1c").."\x1c"; else extensions = "\x1c"; end
+	return features..identities..extensions;
+end
+
+local function caps_handler(event)
+	local origin = event.origin;
+
+	if origin.presence:get_child("c", "urn:xmpp:caps") then
+		return;
+	end
+
+	local disco_info = origin.caps_cache;
+	if disco_info == nil then
+		return;
+	end
+
+	local extension_string = calculate_hash(disco_info);
+
+	local ecaps2 = st.stanza("c", { xmlns = "urn:xmpp:caps" });
+	for algo in algorithms do
+		local func = algorithm_map[algo];
+		if func ~= nil then
+			local hash = base64.encode(func(extension_string));
+			ecaps2:tag("hash", { xmlns = "urn:xmpp:hashes:2"; algo = algo })
+			      :text(hash)
+			      :up();
+		end
+	end
+
+	module:log("debug", "Injected ecaps2 element in presence");
+	origin.presence:add_child(hashes);
+end
+
+module:hook("c2s-capabilities-changed", caps_handler);