///|
/// The client half of a TFTP transfer: the `get` / `put` stop-and-wait state
/// machines (RFC 1350 sections 1 and 4).
///
/// The rule the architecture doc sets out holds here: the state machine never
/// touches a socket. It only reads a packet or times out, then decides what to
/// send next, so a whole session runs against an in-memory `Transport` in a
/// test.
///
/// Three RFC details are worth pointing at, because they are the ones that
/// silently break naive implementations:
///
/// - **Retransmission.** Every DATA/ACK waits for its answer and is resent on
/// timeout. The retry count is bounded so a dead peer cannot spin forever.
/// - **Sorcerer's Apprentice Syndrome.** A duplicate DATA is answered with the
/// same ACK and is *not* fed into the file again, otherwise a second copy of
/// the last block doubles itself on every round trip.
/// - **Block wrap.** Block numbers are compared with `block.mbt`'s half-circle
/// rule, so a transfer past 65535 blocks keeps working.
///|
/// Why a transfer ended badly.
pub(all) enum ClientError {
/// The peer sent an ERROR packet (RFC 1350, section 5).
PeerError(ErrorCode, String)
/// The peer stopped answering and the retry budget ran out.
Timeout
/// A packet that makes no sense here: wrong opcode, or a block from a peer
/// that is not the transfer's.
Protocol(String)
/// The request itself could not be built.
BadRequest(String)
} derive(Eq, Debug)
///|
pub extend ClientError with Eq::{not_equal, equal}
///|
pub extend ClientError with @moonbitlang/core/debug.Debug::{to_repr}
///|
/// What a `get` / `put` produced.
pub(all) enum TransferResult {
/// The bytes read from the peer, for `get`.
Received(Bytes)
/// For `put`, the number of bytes acknowledged.
Sent(Int32)
} derive(Eq, Debug)
///|
/// A finished transfer plus the negotiated details worth reporting.
///
/// `tsize` is the size the peer announced in its OACK (RFC 2349) when it
/// announced one; `None` means no `tsize` was negotiated.
pub struct TransferOutcome {
result : TransferResult
tsize : Int32?
} derive(Eq, Debug)
///|
pub extend TransferOutcome with Eq::{not_equal, equal}
///|
pub extend TransferOutcome with @moonbitlang/core/debug.Debug::{to_repr}
///|
/// The bytes or byte count the transfer produced.
pub fn TransferOutcome::result(self : TransferOutcome) -> TransferResult {
self.result
}
///|
/// The size the peer announced in its OACK, if it announced one.
pub fn TransferOutcome::tsize(self : TransferOutcome) -> Int32? {
self.tsize
}
///|
/// The file contents of a `get`, or `None` for a `put`.
pub fn TransferOutcome::received(self : TransferOutcome) -> Bytes? {
match self.result {
Received(bytes) => Some(bytes)
Sent(_) => None
}
}
///|
/// The number of bytes a `put` got acknowledged, or `None` for a `get`.
pub fn TransferOutcome::sent(self : TransferOutcome) -> Int32? {
match self.result {
Sent(count) => Some(count)
Received(_) => None
}
}
///|
pub extend TransferResult with Eq::{not_equal, equal}
///|
pub extend TransferResult with @moonbitlang/core/debug.Debug::{to_repr}
///|
/// The knobs a caller sets, and the defaults RFC 1350 gives them.
pub struct ClientOptions {
mode : Mode
block_size : Int32
timeout_seconds : Int32
max_retries : Int32
options : Array[TftpOption]
} derive(Eq, Debug)
///|
pub extend ClientOptions with Eq::{not_equal, equal}
///|
pub extend ClientOptions with @moonbitlang/core/debug.Debug::{to_repr}
///|
/// The RFC 1350 defaults: `octet`, 512-byte blocks, a 5-second timeout, and a
/// retry budget that survives a handful of lost packets without hanging.
pub fn ClientOptions::default() -> ClientOptions {
{
mode: Octet,
block_size: default_block_size,
timeout_seconds: default_timeout,
max_retries: 6,
options: [],
}
}
///|
pub fn ClientOptions::mode(self : ClientOptions) -> Mode {
self.mode
}
///|
pub fn ClientOptions::block_size(self : ClientOptions) -> Int32 {
self.block_size
}
///|
pub fn ClientOptions::timeout_seconds(self : ClientOptions) -> Int32 {
self.timeout_seconds
}
///|
/// How many times a packet is retransmitted before the transfer gives up.
pub fn ClientOptions::max_retries(self : ClientOptions) -> Int32 {
self.max_retries
}
///|
/// The RFC 2347 options to put in the request.
pub fn ClientOptions::options(self : ClientOptions) -> Array[TftpOption] {
self.options.copy()
}
///|
/// A client with a plain transfer mode, e.g. `with_mode(Netascii)`.
pub fn ClientOptions::with_mode(
self : ClientOptions,
mode : Mode,
) -> ClientOptions {
{ ..self, mode, }
}
///|
/// A client that asks for a specific block size (RFC 2348).
pub fn ClientOptions::with_block_size(
self : ClientOptions,
block_size : Int32,
) -> ClientOptions {
{ ..self, block_size, }
}
///|
/// A client that asks for a specific retransmission timeout (RFC 2349).
pub fn ClientOptions::with_timeout(
self : ClientOptions,
seconds : Int32,
) -> ClientOptions {
{ ..self, timeout_seconds: seconds, }
}
///|
/// A client with a different retry budget.
pub fn ClientOptions::with_max_retries(
self : ClientOptions,
retries : Int32,
) -> ClientOptions {
{ ..self, max_retries: retries, }
}
///|
/// A client that asks for additional RFC 2347 options.
pub fn ClientOptions::with_options(
self : ClientOptions,
options : Array[TftpOption],
) -> ClientOptions {
{ ..self, options, }
}
///|
/// The block size and timeout a transfer actually runs with, after the peer's
/// OACK is folded in (RFC 2347, section 4).
///
/// A peer that does not answer with an OACK leaves the request's own values in
/// place, so the state machine reads one struct either way instead of branching
/// on "did negotiation happen".
priv struct Session {
mut block_size : Int32
mut timeout_seconds : Int32
mut tsize : Int32?
}
///|
/// The session a peer that answers with no OACK gets: exactly what was asked.
fn Session::plain(request : ClientOptions) -> Session {
{
block_size: request.block_size,
timeout_seconds: request.timeout_seconds,
tsize: None,
}
}
///|
/// Reads the options an OACK accepted, falling back to the request's values.
///
/// Only the options this module implements are understood; anything else is
/// ignored, which mirrors the request side.
fn Session::from_oack(request : ClientOptions, oack : Packet) -> Session {
let session = Session::plain(request)
match oack.options() {
Some(options) =>
for option in options {
match option.name() {
"blksize" =>
match parse_option_int(option.value()) {
Some(value) => session.block_size = value
None => ()
}
"timeout" =>
match parse_option_int(option.value()) {
Some(value) => session.timeout_seconds = value
None => ()
}
"tsize" =>
match parse_option_int(option.value()) {
Some(value) => session.tsize = Some(value)
None => ()
}
_ => ()
}
}
None => ()
}
session
}
///|
/// The `get` half: request a file, receive DATA, acknowledge, finish on a short
/// block.
///
/// Returns the file contents with the transfer mode already undone, so a
/// `Netascii` download comes back with local line endings.
pub async fn[T : Transport] get(
transport : T,
remote : String,
filename : String,
request : ClientOptions,
) -> Result[TransferOutcome, ClientError] {
let rrq = Packet::Rrq(
filename,
request.mode,
[
TftpOption::new("blksize", request.block_size.to_string()),
TftpOption::new("timeout", request.timeout_seconds.to_string()),
] +
request.options,
)
let rrq_bytes = encode(rrq)
transport.send(rrq_bytes, remote)
let handshake = match await_options(transport, remote, request, rrq_bytes) {
Ok(handshake) => handshake
Err(error) => return Err(error)
}
let session = handshake.session
// An OACK is not DATA: it restarts the count, and the client owes an ACK 0
// before the server will send block 1 (RFC 2347, section 4).
if handshake.oack_pending {
transport.send(encode(Packet::Ack(0)), remote)
}
// The first DATA a server sends is block 1.
let mut expected : UInt16 = 1
let mut retries = 0
let mut out : Bytes = Bytes::new(0)
let mut netascii : NetasciiState = Clean
// A server that skipped the OACK sent its first DATA while we were still
// waiting for the answer; fold it in before reading the wire again, instead
// of dropping the first block of the file.
let mut pending = handshake.first_data
while true {
let incoming = match pending {
Some((block, payload)) => {
pending = None
Recv::Packet(Datagram::new(encode(Data(block, payload)), ""))
}
None => transport.recv(remote, timeout_to_ms(session.timeout_seconds))
}
match incoming {
Recv::Timeout =>
if retries >= request.max_retries {
return Err(Timeout)
} else {
retries = retries + 1
// A read is driven by the server retransmitting DATA, so the client
// nudges it: repeat the request before the first block arrives, and
// re-acknowledge the last block afterwards. Without this a single
// lost packet would stall the transfer until the budget ran out.
let nudge = if expected == 1 {
rrq
} else {
Packet::Ack(expected - 1)
}
transport.send(encode(nudge), remote)
}
Recv::Packet(datagram) => {
let packet = match decode(datagram.payload()) {
Ok(packet) => packet
Err(_) => continue // Malformed: ignore, the peer will retransmit.
}
match packet {
Error(code, message) => return Err(PeerError(code, message))
Data(block, payload) => {
if block == expected - 1 {
// A stale duplicate: acknowledge it again but do not deliver it
// twice (Sorcerer's Apprentice, RFC 1350 section 4).
transport.send(encode(Packet::Ack(block)), remote)
continue
}
if !block_follows(block, expected - 1) {
// Older than the block we hold: re-acknowledge so the peer can
// move on, without touching the file.
transport.send(encode(Packet::Ack(block)), remote)
continue
}
expected = block + 1
retries = 0
transport.send(encode(Packet::Ack(block)), remote)
let chunk = match request.mode {
Netascii => {
let (state, decoded) = netascii_decode(netascii, payload)
netascii = state
decoded
}
_ => payload
}
out = out + chunk
// A payload shorter than the negotiated block size ends the file
// (RFC 1350, section 1).
if payload.length() < session.block_size {
let tail = match request.mode {
Netascii => netascii_decode_finish(netascii, Bytes::new(0))
_ => Bytes::new(0)
}
return Ok({ result: Received(out + tail), tsize: session.tsize, })
}
}
_ =>
// An unexpected ACK/OACK/RRQ: ignore and keep waiting.
continue
}
}
}
}
Err(Protocol("get: unreachable"))
}
///|
/// The `put` half: request to write a file, send DATA one block at a time, wait
/// for each ACK.
///
/// Returns the number of bytes acknowledged. The data is already in memory, so
/// the caller hands the whole file in and the state machine slices it.
pub async fn[T : Transport] put(
transport : T,
remote : String,
filename : String,
data : Bytes,
request : ClientOptions,
) -> Result[TransferOutcome, ClientError] {
let encoded = match request.mode {
Netascii => netascii_encode_all(data)
_ => data
}
let wrq = Packet::Wrq(
filename,
request.mode,
[
TftpOption::new("blksize", request.block_size.to_string()),
TftpOption::new("timeout", request.timeout_seconds.to_string()),
TftpOption::new("tsize", encoded.length().to_string()),
] +
request.options,
)
transport.send(encode(wrq), remote)
let session = match await_write_ack(transport, remote, request) {
Ok(session) => session
Err(error) => return Err(error)
}
let blocks = split_blocks(encoded, session.block_size)
let mut index = 0
let mut acknowledged = 0
while index < blocks.length() {
let payload = blocks[index]
let block = (index + 1).to_uint16()
match
send_block_with_retry(transport, remote, block, payload, session, request) {
Ok(size) => {
acknowledged = acknowledged + size
index = index + 1
}
Err(error) => return Err(error)
}
}
Ok({ result: Sent(acknowledged), tsize: session.tsize, })
}
///|
/// The first thing a server said: the accepted options, and the first DATA if
/// it skipped the OACK.
///
/// The DATA has to be handed back because `await_options` already read it off
/// the transport; dropping it would lose the first block of the file.
priv struct Handshake {
session : Session
first_data : (UInt16, Bytes)?
/// Whether the handshake was an OACK that still needs its ACK 0. RFC 2347
/// section 4: the client acknowledges an OACK with ACK 0, and only then does
/// the server start sending DATA.
oack_pending : Bool
}
///|
/// Waits for the first answer to a RRQ: an OACK, or the first DATA.
///
/// `request_packet` is the RRQ to repeat on a timeout, so a lost first DATA
/// makes the client re-ask instead of stalling until the budget runs out. That
/// repeat is what a real client does: for a read there is no ACK to resend yet.
async fn[T : Transport] await_options(
transport : T,
remote : String,
request : ClientOptions,
request_packet : Bytes,
) -> Result[Handshake, ClientError] {
let mut retries = 0
while retries <= request.max_retries {
match transport.recv(remote, timeout_to_ms(request.timeout_seconds)) {
Recv::Timeout => {
retries = retries + 1
if retries <= request.max_retries {
transport.send(request_packet, remote)
}
}
Recv::Packet(datagram) =>
match decode(datagram.payload()) {
Err(_) => retries = retries + 1
Ok(packet) =>
match packet {
Error(code, message) => return Err(PeerError(code, message))
Oack(_) =>
return Ok({
session: Session::from_oack(request, packet),
first_data: None,
oack_pending: true,
})
// No OACK: the peer ignored the options and went straight to
// RFC 1350, so the request's own values stand.
Data(block, payload) =>
return Ok({
session: Session::plain(request),
first_data: Some((block, payload)),
oack_pending: false,
})
_ => retries = retries + 1
}
}
}
}
Err(Timeout)
}
///|
/// Waits for the answer to a WRQ: ACK 0, or an OACK when options were accepted.
async fn[T : Transport] await_write_ack(
transport : T,
remote : String,
request : ClientOptions,
) -> Result[Session, ClientError] {
let mut retries = 0
while retries <= request.max_retries {
match transport.recv(remote, timeout_to_ms(request.timeout_seconds)) {
Recv::Timeout => retries = retries + 1
Recv::Packet(datagram) =>
match decode(datagram.payload()) {
Err(_) => retries = retries + 1
Ok(packet) =>
match packet {
Error(code, message) => return Err(PeerError(code, message))
Oack(_) => return Ok(Session::from_oack(request, packet))
Ack(block) =>
if block == 0 {
return Ok(Session::plain(request))
} else {
retries = retries + 1
}
_ => retries = retries + 1
}
}
}
}
Err(Timeout)
}
///|
/// Sends one DATA block and waits for its ACK, retransmitting on timeout and
/// ignoring acknowledgements for earlier blocks.
///
/// Returns how many payload bytes this block carried.
async fn[T : Transport] send_block_with_retry(
transport : T,
remote : String,
block : UInt16,
payload : Bytes,
session : Session,
request : ClientOptions,
) -> Result[Int32, ClientError] {
let packet = encode(Data(block, payload))
let mut retries = 0
while retries <= request.max_retries {
transport.send(packet, remote)
match transport.recv(remote, timeout_to_ms(session.timeout_seconds)) {
Recv::Timeout => retries = retries + 1
Recv::Packet(datagram) =>
match decode(datagram.payload()) {
Err(_) => retries = retries + 1
Ok(answer) =>
match answer {
Error(code, message) => return Err(PeerError(code, message))
Ack(acked) =>
if acked == block {
return Ok(payload.length())
} else if block_before(acked, block) {
// A delayed ACK for an earlier block: wait for ours.
retries = retries + 1
} else {
retries = retries + 1
}
_ => retries = retries + 1
}
}
}
}
Err(Timeout)
}
///|
/// Splits `data` into DATA payloads of at most `block_size` bytes.
///
/// Public because a caller that wants to show progress, or to feed the blocks
/// to a server of its own, needs the same slicing the client uses.
///
/// A file whose length is an exact multiple of the block size needs one extra,
/// empty block for the peer to see the end (RFC 1350, section 1).
pub fn split_blocks(data : Bytes, block_size : Int32) -> Array[Bytes] {
let blocks : Array[Bytes] = []
let size = if block_size <= 0 { default_block_size } else { block_size }
let mut offset = 0
while offset < data.length() {
let end = if offset + size > data.length() {
data.length()
} else {
offset + size
}
blocks.push(data.clamped_view(start=offset, end~).to_owned())
offset = end
}
if blocks.is_empty() || data.length() % size == 0 {
blocks.push(Bytes::new(0))
}
blocks
}
///|
/// The inverse of `split_blocks`, for callers that want the file back.
pub fn join_blocks(blocks : Array[Bytes]) -> Bytes {
let mut out : Bytes = Bytes::new(0)
for block in blocks {
out = out + block
}
out
}
///|
/// Reads the decimal value an OACK carried for a known option.
///
/// The same tolerant decimal parser the request side uses, so a peer cannot
/// negotiate a value with `+` or whitespace that we would then reject.
fn parse_option_int(text : String) -> Int32? {
if text.is_empty() {
return None
}
let mut value = 0
for char in text {
let digit = char.to_int() - '0'.to_int()
if digit < 0 || digit > 9 {
return None
}
value = value * 10 + digit
}
Some(value)
}