--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_http_upload_external/mod_http_upload_external.lua	Thu Oct 13 18:57:15 2016 +0200
@@ -0,0 +1,80 @@
+-- mod_http_upload_external
+--
+-- Copyright (C) 2015-2016 Kim Alvefur
+--
+-- This file is MIT/X11 licensed.
+--
+
+-- imports
+local st = require"util.stanza";
+local uuid = require"util.uuid".generate;
+local http = require "util.http";
+local dataform = require "util.dataforms".new;
+local HMAC = require "util.hashes".hmac_sha256;
+
+-- config
+local file_size_limit = module:get_option_number(module.name .. "_file_size_limit", 100 * 1024 * 1024); -- 100 MB
+local base_url = assert(module:get_option_string(module.name .. "_base_url"), module.name .. "_base_url is a required option");
+local secret = assert(module:get_option_string(module.name .. "_secret"), module.name .. "_secret is a required option");
+
+-- depends
+module:depends("disco");
+
+-- namespace
+local xmlns_http_upload = "urn:xmpp:http:upload";
+
+-- identity and feature advertising
+module:add_identity("store", "file", module:get_option_string("name", "HTTP File Upload"))
+module:add_feature(xmlns_http_upload);
+
+module:add_extension(dataform {
+	{ name = "FORM_TYPE", type = "hidden", value = xmlns_http_upload },
+	{ name = "max-file-size", type = "text-single" },
+}:form({ ["max-file-size"] = tostring(file_size_limit) }, "result"));
+
+local function magic_crypto_dust(random, filename, filesize)
+	local message = string.format("%s/%s %d", random, filename, filesize);
+	local digest = HMAC(secret, message, true);
+	random, filename = http.urlencode(random), http.urlencode(filename);
+	return base_url .. random .. "/" .. filename, "?v=" .. digest;
+end
+
+-- hooks
+module:hook("iq/host/"..xmlns_http_upload..":request", function (event)
+	local stanza, origin = event.stanza, event.origin;
+	local request = stanza.tags[1];
+	-- local clients only
+	if origin.type ~= "c2s" then
+		module:log("debug", "Request for upload slot from a %s", origin.type);
+		origin.send(st.error_reply(stanza, "cancel", "not-authorized"));
+		return true;
+	end
+	-- validate
+	local filename = request:get_child_text("filename");
+	if not filename or filename:find("/") then
+		module:log("debug", "Filename %q not allowed", filename or "");
+		origin.send(st.error_reply(stanza, "modify", "bad-request", "Invalid filename"));
+		return true;
+	end
+	local filesize = tonumber(request:get_child_text("size"));
+	if not filesize then
+		module:log("debug", "Missing file size");
+		origin.send(st.error_reply(stanza, "modify", "bad-request", "Missing or invalid file size"));
+		return true;
+	elseif filesize > file_size_limit then
+		module:log("debug", "File too large (%d > %d)", filesize, file_size_limit);
+		origin.send(st.error_reply(stanza, "modify", "not-acceptable", "File too large",
+			st.stanza("file-too-large", {xmlns=xmlns_http_upload})
+				:tag("max-size"):text(tostring(file_size_limit))));
+		return true;
+	end
+	local reply = st.reply(stanza);
+	reply:tag("slot", { xmlns = xmlns_http_upload });
+	local random = uuid();
+	local get_url, verify = magic_crypto_dust(random, filename, filesize);
+	reply:tag("get"):text(get_url):up();
+	reply:tag("put"):text(get_url .. verify):up();
+	module:log("info", "Handed out upload slot %s to %s@%s", get_url, origin.username, origin.host);
+	origin.send(reply);
+	return true;
+end);