--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/net/stun.lua Fri Mar 04 15:23:32 2022 +0000
@@ -0,0 +1,292 @@
+local base64 = require "util.encodings".base64;
+local hashes = require "util.hashes";
+local net = require "util.net";
+local random = require "util.random";
+local struct = require "util.struct";
+
+--- Private helpers
+
+-- XORs a string with another string
+local function sxor(x, y)
+ local r = {};
+ for i = 1, #x do
+ r[i] = string.char(bit32.bxor(x:byte(i), y:byte(i)));
+ end
+ return table.concat(r);
+end
+
+--- Public helpers
+
+-- Following draft-uberti-behave-turn-rest-00, convert a 'secret' string
+-- into a username/password pair that can be used to auth to a TURN server
+local function get_user_pass_from_secret(secret, ttl, opt_username)
+ ttl = ttl or 86400;
+ local username;
+ if opt_username then
+ username = ("%d:%s"):format(os.time() + ttl, opt_username);
+ else
+ username = ("%d"):format(os.time() + ttl);
+ end
+ local password = base64.encode(hashes.hmac_sha1(secret, username));
+ return username, password, ttl;
+end
+
+-- Following RFC 8489 9.2, convert credentials to a HMAC key for signing
+local function get_long_term_auth_key(realm, username, password)
+ return hashes.md5(username..":"..realm..":"..password);
+end
+
+--- Packet building/parsing
+
+local packet_methods = {};
+local packet_mt = { __index = packet_methods };
+
+local magic_cookie = string.char(0x21, 0x12, 0xA4, 0x42);
+
+local methods = {
+ binding = 0x001;
+ -- TURN
+ allocate = 0x003;
+ refresh = 0x004;
+ send = 0x006;
+ data = 0x007;
+ create_permission = 0x008;
+ channel_bind = 0x009;
+};
+local method_lookup = {};
+for name, value in pairs(methods) do
+ method_lookup[name] = value;
+ method_lookup[value] = name;
+end
+
+local classes = {
+ request = 0;
+ indication = 1;
+ success = 2;
+ error = 3;
+};
+local class_lookup = {};
+for name, value in pairs(classes) do
+ class_lookup[name] = value;
+ class_lookup[value] = name;
+end
+
+local attributes = {
+ ["mapped-address"] = 0x0001;
+ ["username"] = 0x0006;
+ ["message-integrity"] = 0x0008;
+ ["error-code"] = 0x0009;
+ ["unknown-attributes"] = 0x000A;
+ ["realm"] = 0x0014;
+ ["nonce"] = 0x0015;
+ ["xor-mapped-address"] = 0x0020;
+ ["software"] = 0x8022;
+ ["alternate-server"] = 0x8023;
+ ["fingerprint"] = 0x8028;
+ ["message-integrity-sha256"] = 0x001C;
+ ["password-algorithm"] = 0x001D;
+ ["userhash"] = 0x001E;
+ ["password-algorithms"] = 0x8002;
+ ["alternate-domains"] = 0x8003;
+
+ -- TURN
+ ["requested-transport"] = 0x0019;
+};
+local attribute_lookup = {};
+for name, value in pairs(attributes) do
+ attribute_lookup[name] = value;
+ attribute_lookup[value] = name;
+end
+
+function packet_methods:serialize_header(length)
+ assert(#self.transaction_id == 12, "invalid transaction id length");
+ local header = struct.pack(">I2I2",
+ self.type,
+ length
+ )..magic_cookie..self.transaction_id;
+ return header;
+end
+
+function packet_methods:serialize()
+ local payload = table.concat(self.attributes);
+ return self:serialize_header(#payload)..payload;
+end
+
+function packet_methods:is_request()
+ return bit32.band(self.type, 0x0110) == 0x0000;
+end
+
+function packet_methods:is_indication()
+ return bit32.band(self.type, 0x0110) == 0x0010;
+end
+
+function packet_methods:is_success_resp()
+ return bit32.band(self.type, 0x0110) == 0x0100;
+end
+
+function packet_methods:is_err_resp()
+ return bit32.band(self.type, 0x0110) == 0x0110;
+end
+
+function packet_methods:get_method()
+ local method = bit32.bor(
+ bit32.rshift(bit32.band(self.type, 0x3E00), 2),
+ bit32.rshift(bit32.band(self.type, 0x00E0), 1),
+ bit32.band(self.type, 0x000F)
+ );
+ return method, method_lookup[method];
+end
+
+function packet_methods:get_class()
+ local class = bit32.bor(
+ bit32.rshift(bit32.band(self.type, 0x0100), 7),
+ bit32.rshift(bit32.band(self.type, 0x0010), 4)
+ );
+ return class, class_lookup[class];
+end
+
+function packet_methods:set_type(method, class)
+ if type(method) == "string" then
+ method = assert(method_lookup[method:lower()], "unknown method: "..method);
+ end
+ if type(class) == "string" then
+ class = assert(classes[class], "unknown class: "..class);
+ end
+ self.type = bit32.bor(
+ bit32.lshift(bit32.band(method, 0x1F80), 2),
+ bit32.lshift(bit32.band(method, 0x0070), 1),
+ bit32.band(method, 0x000F),
+ bit32.lshift(bit32.band(class, 0x0002), 7),
+ bit32.lshift(bit32.band(class, 0x0001), 4)
+ );
+end
+
+local function _serialize_attribute(attr_type, value)
+ local len = #value;
+ local padding = string.rep("\0", (4 - len)%4);
+ return struct.pack(">I2I2",
+ attr_type, len
+ )..value..padding;
+end
+
+function packet_methods:add_attribute(attr_type, value)
+ if type(attr_type) == "string" then
+ attr_type = assert(attributes[attr_type], "unknown attribute: "..attr_type);
+ end
+ table.insert(self.attributes, _serialize_attribute(attr_type, value));
+end
+
+function packet_methods:deserialize(bytes)
+ local type, len, cookie = struct.unpack(">I2I2I4", bytes);
+ assert(#bytes == (len + 20), "incorrect packet length");
+ assert(cookie == 0x2112A442, "invalid magic cookie");
+ self.type = type;
+ self.transaction_id = bytes:sub(9, 20);
+ self.attributes = {};
+ local pos = 21;
+ while pos < #bytes do
+ local attr_hdr = bytes:sub(pos, pos+3);
+ assert(#attr_hdr == 4, "packet truncated in attribute header");
+ local attr_type, attr_len = struct.unpack(">I2I2", attr_hdr); --luacheck: ignore 211/attr_type
+ if attr_len == 0 then
+ table.insert(self.attributes, attr_hdr);
+ pos = pos + 20;
+ else
+ local data = bytes:sub(pos + 4, pos + 3 + attr_len);
+ assert(#data == attr_len, "packet truncated in attribute value");
+ table.insert(self.attributes, attr_hdr..data);
+ local n_padding = (4 - attr_len)%4;
+ pos = pos + 4 + attr_len + n_padding;
+ end
+ end
+ return self;
+end
+
+function packet_methods:get_attribute(attr_type)
+ if type(attr_type) == "string" then
+ attr_type = assert(attribute_lookup[attr_type:lower()], "unknown attribute: "..attr_type);
+ end
+ for _, attribute in ipairs(self.attributes) do
+ if struct.unpack(">I2", attribute) == attr_type then
+ return attribute:sub(5);
+ end
+ end
+end
+
+local addr_families = { "IPv4", "IPv6" };
+function packet_methods:get_mapped_address()
+ local data = self:get_attribute("mapped-address");
+ if not data then return; end
+ local family, port = struct.unpack("x>BI2", data);
+ local addr = data:sub(5);
+ return {
+ family = addr_families[family] or "unknown";
+ port = port;
+ address = net.ntop(addr);
+ };
+end
+
+function packet_methods:get_xor_mapped_address()
+ local data = self:get_attribute("xor-mapped-address");
+ if not data then return; end
+ local family, port = struct.unpack("x>BI2", data);
+ local addr = sxor(data:sub(5), magic_cookie..self.transaction_id);
+ return {
+ family = addr_families[family] or "unknown";
+ port = bit32.bxor(port, 0x2112);
+ address = net.ntop(addr);
+ address_raw = data:sub(5);
+ };
+end
+
+function packet_methods:add_message_integrity(key)
+ -- Add attribute with a dummy value so we can artificially increase
+ -- the packet 'length'
+ self:add_attribute("message-integrity", string.rep("\0", 20));
+ -- Get the packet data, minus the message-integrity attribute itself
+ local pkt = self:serialize():sub(1, -25);
+ local hash = hashes.hmac_sha1(key, pkt, false);
+ self.attributes[#self.attributes] = nil;
+ assert(#hash == 20, "invalid hash length");
+ self:add_attribute("message-integrity", hash);
+end
+
+do
+ local transports = {
+ udp = 0x11;
+ };
+ function packet_methods:add_requested_transport(transport)
+ local transport_code = transports[transport];
+ assert(transport_code, "unsupported transport: "..tostring(transport));
+ self:add_attribute("requested-transport", string.char(
+ transport_code, 0x00, 0x00, 0x00
+ ));
+ end
+end
+
+function packet_methods:get_error()
+ local err_attr = self:get_attribute("error-code");
+ if not err_attr then
+ return nil;
+ end
+ local number = err_attr:byte(4);
+ local class = bit32.band(0x07, err_attr:byte(3));
+ local msg = err_attr:sub(5);
+ return (class*100)+number, msg;
+end
+
+local function new_packet(method, class)
+ local p = setmetatable({
+ transaction_id = random.bytes(12);
+ length = 0;
+ attributes = {};
+ }, packet_mt);
+ p:set_type(method or "binding", class or "request");
+ return p;
+end
+
+return {
+ new_packet = new_packet;
+ get_user_pass_from_secret = get_user_pass_from_secret;
+ get_long_term_auth_key = get_long_term_auth_key;
+};