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Daniel Barlow 2023-02-15 19:43:37 +00:00
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--[[
This package provides intefaces for handling TFTP requests as specified by
rfc1350, rfc1782, rfc2347, rfc2348 and (partial support for rfc2349)
It should work on Standard PC servers as well as small home routers running
OpenWRT or similar.
]]
local tftp = {}
local TIMEOUT = 5
local ACK_RETRIES = 10
local TFTP_PORT = 69
local BLKSIZE = 512
local OP_RRQ = 1
local OP_WRQ = 2
local OP_DATA = 3
local OP_ACK = 4
local OP_ERR = 5
local OP_OACK = 6
local ACKSIZE = 4
local ERR_NOTFOUND = 1
local ERR_ACCESS = 2
local ERR_ALLOC = 3
local ERR_ILLEGAL_OP = 4
local ERR_UNKNOWN_ID = 5
local ERR_EXISTS = 6
local ERR_WHO = 7
--rfc2347 specifies the options extension.
--rfc2348 specifies the blksize extension
--rfc2349 specifies the timeout and tsize extensions
local SUPPORTED_OPTIONS = {blksize=true, timeout=true, tsize=true}
--Use penlight's prettyprinter if available
pcall(require, 'pl')
local log = pretty and pretty.dump or print
local time = (function()
local okay, nixio = pcall(require, "nixio")
if okay then
local gettimeofday = nixio.gettimeofday
return function()
local secs, usecs = gettimeofday()
return secs + (usecs / 1e6)
end
else
return require("socket").gettime
end
end)()
local poll = (function()
--[[
``poll`` is expected to accept a table of sockets keyed by
backend file descriptor formatted as follows: {
[low level socket lib file descriptor]{
fd=(low level socket lib fd)
wantread=(bool)
wantwrite=(bool)
...arbitrary ignored extra fields
},
...
}
it returns a list of fds formatted as follows
{
[low level socket lib file descriptor]{
fd= [low level socket lib file descriptor],
readable=(bool),
writable=(bool)
}
...
}
]]
local okay, nixio = pcall(require, "nixio")
if okay then
return function(fds, timeout)
timeout = timeout or -1
local query_table = {}
local flags = {}
--nixio only looks at integer keys
for _, client in pairs(fds) do
if client.wantwrite then flags[#flags+1] = 'out' end
if client.wantread then flags[#flags+1] = 'in' end
query_table[#query_table+1] = {
fd=client.fd,
events=nixio.poll_flags(unpack(flags))
}
end
local count, fds = nixio.poll(query_table, timeout)
if count == 0 or fds == nil then return {} end
local ready = {}
for i, fd in ipairs(fds) do
local revents = nixio.poll_flags(fd.revents)
if revents['in'] or revents['out'] then
ready[fd.fd] = {fd=fd.fd, readable=revents['in'] ~= nil, writeable=revents['out'] ~= nil}
end
end
-- log(p({ready=ready}))
return ready
end
end
local luasocket = require("socket")
return function(fds, timeout)
local wantread = {}
local wantwrite = {}
for _, fd in pairs(fds) do
fd.readable=false
fd.writeable=false
if fd.wantwrite then wantwrite[#wantwrite + 1] = fd.fd end
if fd.wantread then wantread[#wantread + 1] = fd.fd end
end
local readable, writeable, timedout = luasocket.select(wantread, wantwrite, timeout)
if timedout then return nil end
local ready = {}
for _, fd in ipairs(readable) do
fds[fd].readable = true
end
for _, fd in ipairs(writeable) do
fds[fd].writeable = true
end
return fds
end
end)()
local function UDPSocket()
--[[ We want to support the basic functionality required for TFTP operation over
UDP with either nixio (OpenWRT LuCI) or luasocket (everywhere else).
This wraps only the required functionality and in no way represents a
complete UDP socket implementation.
see http://w3.impa.br/~diego/software/luasocket/udp.html for the luasocket UDP API
and http://luci.subsignal.org/api/nixio/modules/nixio.Socket.html for nixio.
]]
local okay, luasocket = pcall(require, "socket")
if okay then
log("using luasocket")
return {
fd = luasocket.udp(),
bind = function(self, address, port)
return self.fd:setsockname(address, port)
end,
sendto = function(self, data, address, port)
return self.fd:sendto(data, address, port)
end,
recvfrom = function(self, length)
return self.fd:receivefrom(length)
end,
close = function(self)
return self.fd:close()
end,
}
end
local nixio = require("nixio")
log("using nixio")
return {
fd=nixio.socket("inet", "dgram"),
bind = function(self, address, port)
return self.fd:bind(address, port)
end,
sendto = function(self, data, address, port)
return self.fd:sendto(data, address, port)
end,
recvfrom = function(self, length)
return self.fd:recvfrom(length)
end,
close = function(self)
return self.fd:close()
end
}
end
local function is_netascii(s)
--[[Check whether a string contains only characters from the RFC764 ascii
subset. see https://tools.ietf.org/html/rfc764#page-11
]]
local ctrls = {[0]=1, [10]=1, [13]=1, [7]=1, [8]=1, [9]=1, [11]=1, [12]=1}
for i=1, #s do
local byte = s:sub(i, i):byte()
if (byte < 31 and ctrls[byte] == nil) or byte > 127 then
return false
end
end
return true
end
local function create_opcode(val)
if val < 0 or val > 2^16-1 then error("opcodes must fit into a 16bit integer") end
local high = math.floor(val / 256)
-- RFC1350 doesn't mention byte order. Assume network order (big-endian).
return string.char(high, val - (high * 256))
end
local function parse_opcode(packet)
local opcode = string.byte(packet:sub(2, 2)) --assume big endian
return ({"RRQ", "WRQ", "DATA", "ACK", "ERROR", "OACK"})[opcode]
end
function tftp:handle_RRQ(socket, host, port, source, options)
local blksize = options and tonumber(options.blksize) or BLKSIZE
local timeout_secs = options and tonumber(options.timeout) or TIMEOUT --rfc2349 timout option
local length = options and tonumber(options.length)
local tid = 1
local time = time
local started = time()
local err = self.ERROR
local done = false
local error, success = error, error -- to terminate the coroutine immediately, we raise an error
local yield = coroutine.yield
return coroutine.create(function()
if options then
--[[The handler coroutine should not start running until we know the client is ready.
This depends on whether the client has requested rfc2347 options and responded to an OACK.
Without the options extension request, the client can be responded to immediately.]]
local acked, timeout = false, time() + timeout_secs
assert(socket:sendto(self.OACK(options), host, port))
log(("sent OACK to %s:%d"):format(host, port))
repeat
yield(true, false)
local msg, port, host = socket:recvfrom(ACKSIZE)
if self.parse_ACK(msg) == 0 then acked = true end
timedout = time() > timeout
until acked or timedout
if timedout then error("Request timed out waiting for OACK response") end
end
log(("coroutine started on %s:%s/"):format(host, port))
while not done do
if tid >= 2^16 then
socket:sendto(err("File too big."), host, port)
error("File too big.")
end
local okay, continue, data = pcall(source, blksize)
if not okay then
packet = socket:sendto(err("An unknown error occurred"), host, port)
error("generator failure")
end
if data == nil and not continue then
done = true
end
if data == nil and continue then
--[[The generator ``source`` can be async and return `true, nil`
if no data is ready, but things are going well.
]]
yield(false, true)
end
socket:sendto(self.DATA(data, tid), host, port)
--[[ Now check for an ACK.
RFC1350 requires that for every packet sent, an ACK is received
before the next packet can be sent.
]]
local acked
local retried = 0
local timeout = time() + timeout_secs
local timedout = false
repeat
yield(true, false) -- we need to wait until the socket is readable again
local ack, ackhost, ackport = socket:recvfrom(ACKSIZE)
if ackhost ~= host or ackport ~= port or self.parse_ACK(ack) ~= tid then
--[[https://tools.ietf.org/html/rfc1350#page-5
"If a source TID does not match, the packet should be
discarded as erroneously sent from somewhere else.
An error packet should be sent to the source of the
incorrect packet, while not disturbing the transfer."
]]
socket:sendto(err(ERR_UNKNOWN_ID), ackhost, ackport)
yield(true, false)
else
acked = true
end
retried = retried + 1
timedout = time() > timeout
until acked or retried > ACK_RETRIES or timedout
if timedout or retried > ACK_RETRIES then
--There doesn't seem to be a standard error for timeout.
socket:sendto(err("Ack timeout"), host, port)
error("Timeout waiting for ACK")
end
--Okay, we've been acked in reasonable time.
tid = tid + 1
if done then success() end
yield(true, true)
end
end)
end
function tftp:handle_WRQ(socket, host, port, sink)
error"Not Implemented"
end
function tftp:listen(rrq_generator_callback, wrq_generator_callback, hosts, port, logfile)
--[[--
Listen for TFTP requests on UDP ```bind``:`port`` (0.0.0.0:69 by default)
and get data from / send data to user-generated source/sink functions.
Data is generated/received by functions returned by the the user-supplied
``rrq_generator_callback``/``wrq_generator_callback`` factory functions.
For every valid request packet received the generator function returned by
``xrq_generator_callback`` will be called expecting data.
When called with a single argument,
(the requested resource as a C-style string (no embedded NUL chars))
``xrq_generator_callback`` should return a source or sink function that:
(SOURCE) takes a single argument of the required data length in bytes
and returns blocks of data until complete.
must return as follows
`true, data` on success
`true, nil` on wouldblock but should retry next round,
`false` on finished
(SINK) takes two arguments
``data`` to write
``done`` (truthy), whether all data has been received and backends can cleanup.
The (SOURCE) model therefore supports both blocking and non-blocking behaviour.
If the given function blocks, however, it will block the whole process as Lua
is single threaded. That may or may not be acceptable depending on your needs.
If the requested resource is invalid or other termination conditions are met,
(SOURCE) and (SINK) functions should raise an error.
@return This method never returns unless interrupted.
]]
local function create_handler(callbacks, request, requestsocket, host, port)
--[[ Given a parsed request, instantiate the generator function from the given callbacks,
and create a new coroutine to be called when the state of the handler's
new socket changes to available.
On success, returns a table of the form:
```{
handler=coroutine to call,
socket= new socket on a random port on which all new communication will happen,
fd=socket.fd as above fd
host=remote host,
port = remote port,
request = the original parsed request, including accepted options, if any.
}```
On error, responds to the client with an ERROR packet, and returns nil.
]]
local okay, generator, tsize = pcall(callbacks[request.opcode], request.filename)
if not okay then
requestsocket:sendto(self.ERROR(ERR_NOTFOUND), host, port)
return nil
else
if request.options then
request.options.tsize = request.options.tsize and tostring(tsize)
for k, v in pairs(request.options) do
if not SUPPORTED_OPTIONS[k] then request.options[k] = nil end
end
else
--RFC1350 requires WRQ requests to be responded to with a zero TID before transfer commences,
--but when responding to an options request, it is dropped.
if request.opcode == 'WRQ' then requestsocket:sendto(self.ACK(0), host, port) end
end
local handlersocket = UDPSocket()
local handler = self['handle_' .. request.opcode](self, handlersocket, host, port, generator, request.options)
return {
handler=handler,
socket=handlersocket,
fd=handlersocket.fd,
host=host,
port=port,
request=request,
wantread=false,
wantwrite=true,
}
end
end
local function accept(socket)
--[[ Read an incoming request from ``socket``, parse, and ACK as appropriate.
If the request is invalid, responds to the client with error and returns `nil`
otherwise returns the parsed request.
]]
local msg, host, port = socket:recvfrom(-1)
if msg ~= false then
local okay, xRQ = pcall(self.parse_XRQ, msg)
if not okay then
return nil
else
return host, port, xRQ
end
end
end
local socket = UDPSocket()
local user_generator_callbacks = {RRQ=rrq_generator_callback, WRQ=wrq_generator_callback}
local port = port or TFTP_PORT
local logfile = logfile or io.stderr
--listen on all given addresses, default to localhost if not given
for i, address in pairs((type(hosts) == 'table' and hosts) or (hosts ~= nil and{hosts}) or {'127.0.0.1'}) do
socket:bind(address, port)
end
--[[The main event loop does two things:
1. Accepts new connections.
2. Handles events occurring on all sockets by dispatching to a handler coroutine.
3. Removes finished requests from the queue and destroys the sockets.
]]
local handlers = {[socket.fd]={fd=socket.fd, socket=socket, listener=true, wantread=true}}
while true do
ready_fds = poll(handlers)
do
local n = 0
for _ in pairs(ready_fds) do
n = n + 1
end
log(('There are %d sockets ready'):format(n))
end
for fd, status in pairs(ready_fds) do
-- pretty.dump(ready_fds)
-- log(('There are %d sockets ready'):format(#ready_fds))
ready = handlers[fd]
if ready.listener and status.readable then
--we've got a listener and should accept a new connection
local host, port, request = accept(ready.socket)
if host ~= nil then
log(("accepted new %s request - %s:%s/%s"):format(request.opcode, host, port, request.filename))
local handler = create_handler(
user_generator_callbacks,
request,
ready.socket,
host,
port
)
if handler then handlers[handler.socket.fd] = handler end
end
elseif (status.readable or status.writeable) and ready.handler then
--We've received an event on a socket associated with an existing handler coroutine.
local co_state = coroutine.status(ready.handler)
local okay, wantread, wantwrite
if co_state ~= 'dead' then
if (ready.wantread and status.readable) or (ready.wantwrite and status.writeable) then
okay, wantread, wantwrite = coroutine.resume(ready.handler)
ready.wantread = wantread
ready.wantwrite = wantwrite
end
end
if (not okay) or co_state == 'dead' then
--- the handler is finished; cleanup
ready.socket:close()
handlers[ready.fd] = nil
ready.fd = nil
ready = nil
end
end
end
end
end
--[[ RRQ/ZRQ read/write request packets
https://tools.ietf.org/html/rfc1350
2 bytes string 1 byte string 1 byte
------------------------------------------------
| Opcode | Filename | 0 | Mode | 0 |
------------------------------------------------
Figure 5-1: RRQ/WRQ packet
]]
function tftp.RRQ(filename)
-- RFC1350:"The mail mode is obsolete and should not be implemented or used."
-- We don't support netascii, which leaves 'octet' mode only
return table.concat({create_opcode(OP_RRQ), filename, '\0', "octet", '\0'}, '')
end
function tftp.parse_XRQ(request)
local opcode = assert(parse_opcode(request), "Invalid opcode")
assert(({RRQ=true, XRQ=true})[opcode], "Not an xRQ")
assert(request:sub(#request) == '\0', "Invalid request: expected ASCII NUL terminated request")
local cstrings = {}
function zero_iter(s)
local pos = 1
return function()
--This is ugly. Lua 5.2 handles embedded NUL bytes in string.gmatch,
--but vanilla Lua5.1 doesn't match correctly and luajit can't seem to parse them
for i=pos, #s do
if s:byte(i) == 0 then
local sub = s:sub(pos, i-1)
pos = i+1
return sub
end
end
end
end
for s in zero_iter(request:sub(3)) do
cstrings[#cstrings+1] = s
end
assert(#cstrings >= 2)
local filename = assert(is_netascii(cstrings[1]) and cstrings[1], "Requested filename must be netascii")
local mode = assert(({netascii='netascii', octet='octet'})[cstrings[2]])
local options
if #cstrings > 2 then
options = {}
assert(#cstrings % 2 == 0)
for i=3, #cstrings, 2 do
--[[ RFC1782, and 3247 require case insensitive comparisons.
We normalize them to lowercase with the consequence that
duplicate keys are replaced which are forbidden by the standard anyway.
]]
options[cstrings[i]:lower()] = cstrings[i+1]:lower()
end
end
return {opcode=opcode, filename=filename, mode=mode, options=options}
end
--[[ ACK functions
2 bytes 2 bytes
---------------------
| Opcode | Block # |
---------------------
Figure 5-3: ACK packet
]]
function tftp.parse_ACK(ack)
--get the sequence number from an ACK or raise a error if not valid
assert(#ack == ACKSIZE, "invalid ack")
assert(parse_opcode(ack) == 'ACK', "invalid ack")
-- extract the low and high order bytes and convert to an integer
local high, low = ack:byte(3, 4)
return (high * 256) + low
end
--[[
+-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+
| opc | opt1 | 0 | value1 | 0 | optN | 0 | valueN | 0 |
+-------+---~~---+---+---~~---+---+---~~---+---+---~~---+---+
]]
function tftp.OACK(options)
local stropts = {}
for k, v in pairs(options) do
assert(is_netascii(k))
stropts[#stropts+1] = k .. '\0' .. v .. '\0'
end
return create_opcode(OP_OACK) .. table.concat(stropts, '')
end
function tftp.ACK(tid)
return table.concat({create_opcode(OP_ACK), create_opcode(tid)}, '')
end
--[[ DATA functions
2 bytes 2 bytes n bytes
----------------------------------
| Opcode | Block # | Data |
----------------------------------
Figure 5-2: DATA packet
]]
function tftp.DATA(data, tid)
local opcode = create_opcode(OP_DATA)
local block = create_opcode(tid)
return table.concat({opcode, block, data}, '')
end
function tftp.parse_DATA(data)
assert(#data <= 512, "tftp data packets must be 512 bytes or less")
assert(parse_opcode(data) == OP_DATA, "Invalid opcode")
return {tid=parse_opcode(data:sub(3, 4)), data=data:sub(5)}
end
--[[ ERROR Functions
2 bytes 2 bytes string 1 byte
-----------------------------------------
| Opcode | ErrorCode | ErrMsg | 0 |
-----------------------------------------
Figure 5-4: ERROR packet
]]
function tftp.ERROR(err)
local defined_errors = {
--https://tools.ietf.org/html/rfc1350#page-10
[0] = type(err) == 'string' and err or "Not defined",
"File not found.",
"Access violation.",
"Disk full or allocation exceeded.",
"Illegal TFTP operation.",
"Unknown transfer ID.",
"File already exists.",
"No such user.",
}
local errno = type(err) == 'string' and 0 or err
return table.concat({
create_opcode(OP_ERR),
create_opcode(errno),
defined_errors[errno],
'\0'
}, '')
end
function tftp.parse_ERROR(err)
assert(parse_opcode(err) == OP_ERR)
local error_code = parse_opcode(err:sub(3, 4))
return {errcode=error_code, errmsg=err:sub(5, #err-1)}
end
return tftp