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//! Implementation for parsing and encoding relay cells
use std::num::NonZeroU16;
use crate::chancell::{BoxedCellBody, CELL_DATA_LEN};
use smallvec::{smallvec, SmallVec};
use tor_bytes::{EncodeError, EncodeResult, Error, Result};
use tor_bytes::{Reader, Writer};
use tor_error::internal;
use caret::caret_int;
use rand::{CryptoRng, Rng};
pub mod extend;
#[cfg(feature = "hs")]
pub mod hs;
pub mod msg;
#[cfg(feature = "experimental-udp")]
pub mod udp;
caret_int! {
/// A command that identifies the type of a relay cell
pub struct RelayCmd(u8) {
/// Start a new stream
BEGIN = 1,
/// Data on a stream
DATA = 2,
/// Close a stream
END = 3,
/// Acknowledge a BEGIN; stream is open
CONNECTED = 4,
/// Used for flow control
SENDME = 5,
/// Extend a circuit to a new hop; deprecated
EXTEND = 6,
/// Reply to EXTEND handshake; deprecated
EXTENDED = 7,
/// Partially close a circuit
TRUNCATE = 8,
/// Circuit has been partially closed
TRUNCATED = 9,
/// Padding cell
DROP = 10,
/// Start a DNS lookup
RESOLVE = 11,
/// Reply to a DNS lookup
RESOLVED = 12,
/// Start a directory stream
BEGIN_DIR = 13,
/// Extend a circuit to a new hop
EXTEND2 = 14,
/// Reply to an EXTEND2 cell.
EXTENDED2 = 15,
/// NOTE: UDP command are reserved but only used with experimental-udp feature
/// UDP: Start of a stream
CONNECT_UDP = 16,
/// UDP: Acknowledge a CONNECT_UDP. Stream is open.
CONNECTED_UDP = 17,
/// UDP: Data on a UDP stream.
DATAGRAM = 18,
/// HS: establish an introduction point.
ESTABLISH_INTRO = 32,
/// HS: establish a rendezvous point.
ESTABLISH_RENDEZVOUS = 33,
/// HS: send introduction (client to introduction point)
INTRODUCE1 = 34,
/// HS: send introduction (introduction point to service)
INTRODUCE2 = 35,
/// HS: connect rendezvous point (service to rendezvous point)
RENDEZVOUS1 = 36,
/// HS: connect rendezvous point (rendezvous point to client)
RENDEZVOUS2 = 37,
/// HS: Response to ESTABLISH_INTRO
INTRO_ESTABLISHED = 38,
/// HS: Response to ESTABLISH_RENDEZVOUS
RENDEZVOUS_ESTABLISHED = 39,
/// HS: Response to INTRODUCE1 from introduction point to client
INTRODUCE_ACK = 40,
/// Padding: declare what kind of padding we want
PADDING_NEGOTIATE = 41,
/// Padding: reply to a PADDING_NEGOTIATE
PADDING_NEGOTIATED = 42,
}
}
/// Possible requirements on stream IDs for a relay command.
enum StreamIdReq {
/// Can only be used with a stream ID of 0
WantNone,
/// Can only be used with a stream ID that isn't 0
WantSome,
/// Can be used with any stream ID
Any,
}
impl RelayCmd {
/// Check whether this command requires a certain kind of
/// StreamId, and return a corresponding StreamIdReq.
fn expects_streamid(self) -> StreamIdReq {
match self {
RelayCmd::BEGIN
| RelayCmd::DATA
| RelayCmd::END
| RelayCmd::CONNECTED
| RelayCmd::RESOLVE
| RelayCmd::RESOLVED
| RelayCmd::BEGIN_DIR => StreamIdReq::WantSome,
#[cfg(feature = "experimental-udp")]
RelayCmd::CONNECT_UDP | RelayCmd::CONNECTED_UDP | RelayCmd::DATAGRAM => {
StreamIdReq::WantSome
}
RelayCmd::EXTEND
| RelayCmd::EXTENDED
| RelayCmd::TRUNCATE
| RelayCmd::TRUNCATED
| RelayCmd::DROP
| RelayCmd::EXTEND2
| RelayCmd::EXTENDED2
| RelayCmd::ESTABLISH_INTRO
| RelayCmd::ESTABLISH_RENDEZVOUS
| RelayCmd::INTRODUCE1
| RelayCmd::INTRODUCE2
| RelayCmd::RENDEZVOUS1
| RelayCmd::RENDEZVOUS2
| RelayCmd::INTRO_ESTABLISHED
| RelayCmd::RENDEZVOUS_ESTABLISHED
| RelayCmd::INTRODUCE_ACK => StreamIdReq::WantNone,
RelayCmd::SENDME => StreamIdReq::Any,
_ => StreamIdReq::Any,
}
}
/// Return true if this command is one that accepts the particular
/// stream ID `id`
pub fn accepts_streamid_val(self, id: Option<StreamId>) -> bool {
match self.expects_streamid() {
StreamIdReq::WantNone => id.is_none(),
StreamIdReq::WantSome => id.is_some(),
StreamIdReq::Any => true,
}
}
}
/// Identify a single stream on a circuit.
///
/// These identifiers are local to each hop on a circuit.
/// This can't be zero; if you need something that can be zero in the protocol,
/// use `Option<StreamId>`.
#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
pub struct StreamId(NonZeroU16);
impl From<NonZeroU16> for StreamId {
fn from(id: NonZeroU16) -> Self {
Self(id)
}
}
impl From<StreamId> for NonZeroU16 {
fn from(id: StreamId) -> NonZeroU16 {
id.0
}
}
impl From<StreamId> for u16 {
fn from(id: StreamId) -> u16 {
id.0.get()
}
}
impl std::fmt::Display for StreamId {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error> {
self.0.fmt(f)
}
}
impl StreamId {
/// Creates a `StreamId` for non-zero `stream_id`.
///
/// Returns `None` when `stream_id` is zero. Messages with a zero/None stream ID
/// apply to the circuit as a whole instead of a particular stream.
pub fn new(stream_id: u16) -> Option<Self> {
NonZeroU16::new(stream_id).map(Self)
}
/// Convenience function to convert to a `u16`; `None` is mapped to 0.
pub fn get_or_zero(stream_id: Option<Self>) -> u16 {
match stream_id {
Some(stream_id) => stream_id.0.get(),
None => 0,
}
}
}
/// Specifies which encoding version of RelayCell to use.
#[non_exhaustive]
#[derive(Copy, Clone, Debug)]
pub enum RelayCellFormat {
/// This is the "legacy" pre-prop340 format. No packing or fragmentation.
V0,
}
/// Specifies a relay cell format and associated types.
pub trait RelayCellFormatTrait {
/// Which format this object is for.
const FORMAT: RelayCellFormat;
/// A `RelayCellFields` type for this format.
type FIELDS: RelayCellFields;
// TODO: Consider making a trait for the decoder as well and adding the
// corresponding associated type here.
}
/// Format type corresponding to `RelayCellFormat::V0`.
#[non_exhaustive]
pub struct RelayCellFormatV0;
impl RelayCellFormatTrait for RelayCellFormatV0 {
const FORMAT: RelayCellFormat = RelayCellFormat::V0;
type FIELDS = RelayCellFieldsV0;
}
/// Specifies field layout for a particular relay cell format.
pub trait RelayCellFields {
/// The range containing the `recognized` field, within a relay cell's body.
const RECOGNIZED_RANGE: std::ops::Range<usize>;
/// The range containing the `digest` field, within a relay cell's body.
const DIGEST_RANGE: std::ops::Range<usize>;
/// A static array of zeroes of the same size as this format uses for the
/// digest field. e.g. this enables updating a comparison-digest in one
/// hash-update method call, instead of having to loop over `DIGEST_RANGE`.
const EMPTY_DIGEST: &'static [u8];
}
/// Specifies fields for `RelayCellFormat::V0`.
#[non_exhaustive]
pub struct RelayCellFieldsV0;
impl RelayCellFields for RelayCellFieldsV0 {
const RECOGNIZED_RANGE: std::ops::Range<usize> = 1..3;
const DIGEST_RANGE: std::ops::Range<usize> = 5..9;
const EMPTY_DIGEST: &'static [u8] = &[0, 0, 0, 0];
}
/// Internal decoder state.
#[derive(Clone, Debug)]
enum RelayCellDecoderInternal {
/// Internal state for `RelayCellFormat::V0`
V0,
}
/// Decodes a stream of relay cell bodies into `UnparsedRelayMsg`s.
#[derive(Clone, Debug)]
pub struct RelayCellDecoder {
/// Internal representation.
internal: RelayCellDecoderInternal,
}
impl RelayCellDecoder {
/// Returns a new `Decoder`, handling a stream of relay cells
/// of the given `version`.
pub fn new(version: RelayCellFormat) -> Self {
match version {
RelayCellFormat::V0 => Self {
internal: RelayCellDecoderInternal::V0,
},
}
}
/// Parse a RELAY or RELAY_EARLY cell body.
///
/// Requires that the cryptographic checks on the message have already been
/// performed
pub fn decode(&mut self, cell: BoxedCellBody) -> Result<RelayCellDecoderResult> {
match &self.internal {
RelayCellDecoderInternal::V0 => Ok(RelayCellDecoderResult {
msgs: smallvec![UnparsedRelayMsg {
internal: UnparsedRelayMsgInternal::V0(cell)
}],
incomplete: None,
}),
}
}
/// Returns the `IncompleteRelayMsgInfo` describing the partial
/// (fragmented) relay message at the end of the so-far-processed relay cell
/// stream.
pub fn incomplete_info(&self) -> Option<IncompleteRelayMsgInfo> {
match &self.internal {
// V0 doesn't support fragmentation, so there is never a pending fragment.
RelayCellDecoderInternal::V0 => None,
}
}
}
/// Result of calling `RelayCellDecoder::decode`.
#[derive(Debug)]
pub struct RelayCellDecoderResult {
/// Complete messages obtained by decoding the cell. i.e. messages
/// that were completely contained within the cell, or for which the cell
/// contained the final fragment.
msgs: SmallVec<[UnparsedRelayMsg; 1]>,
/// Description of the partial message at the end of the cell, if any.
incomplete: Option<IncompleteRelayMsgInfo>,
}
impl RelayCellDecoderResult {
/// Returns a non-empty iterator over commands in relay messages that the
/// cell producing this result contained *any* part of. i.e. this includes
/// the command of "head", "middle", and/or "tail" message fragments that
/// were in the cell.
pub fn cmds(&self) -> impl Iterator<Item = RelayCmd> + '_ {
let complete_msg_cmds = self.msgs.iter().map(|m| m.cmd());
let partial_msg_cmd = self.incomplete.as_ref().map(|c| c.cmd());
complete_msg_cmds.chain(partial_msg_cmd)
}
/// Converts `self` to an iterator over the complete messages, and metadata
/// about the trailing incomplete message (as for `Self::incomplete_info`),
/// if any.
pub fn into_parts(
self,
) -> (
impl Iterator<Item = UnparsedRelayMsg>,
Option<IncompleteRelayMsgInfo>,
) {
(self.msgs.into_iter(), self.incomplete)
}
/// Returns the `IncompleteRelayMsgInfo` describing the incomplete
/// relay message that this cell contained a fragment of, if any.
///
/// Note that:
/// * This does not describe a fragment that includes the end of the relay
/// message, since the message is then complete.
/// * This *does* include a fragment that continues, but does not complete,
/// a message started in an earlier relay cell.
/// * There is at most one such incomplete relay message, since no current
/// relay cell format supports starting a new message before completing the
/// previous one.
pub fn incomplete_info(&self) -> Option<IncompleteRelayMsgInfo> {
self.incomplete.clone()
}
}
/// Information about a relay message for which we don't yet have the complete body.
#[derive(Clone, Debug)]
pub struct IncompleteRelayMsgInfo {
/// The message's command.
cmd: RelayCmd,
/// The message's stream ID, if any.
stream_id: Option<StreamId>,
/// The total number of bytes in the body of the message.
total_msg_len: usize,
/// The number of bytes of the body of the message that we've decoded so
/// far.
num_bytes_present: usize,
}
impl IncompleteRelayMsgInfo {
/// Returns the message's command.
pub fn cmd(&self) -> RelayCmd {
self.cmd
}
/// Returns the message's `StreamId`, if any.
pub fn stream_id(&self) -> Option<StreamId> {
self.stream_id
}
/// Returns the total size of the complete message body.
pub fn total_msg_len(&self) -> usize {
self.total_msg_len
}
/// Returns the number of bytes of the message body that we have so far.
pub fn num_bytes_present(&self) -> usize {
self.num_bytes_present
}
/// Returns the number of bytes of the message body that we still need.
pub fn num_bytes_missing(&self) -> usize {
self.total_msg_len - self.num_bytes_present
}
}
/// Internal representation of an `UnparsedRelayMsg`.
#[derive(Clone, Debug)]
enum UnparsedRelayMsgInternal {
/// For `RelayCellFormat::V0` we can avoid copying data around by just
/// storing the original cell body here.
// NOTE: we could also have a separate command and stream ID field here, but
// we expect to be working with a TON of these, so we will be mildly
// over-optimized and just peek into the body.
//
// It *is* a bit ugly to have to encode so much knowledge about the format in
// different functions here, but that information shouldn't leak out of this module.
V0(BoxedCellBody),
}
/// An enveloped relay message that has not yet been fully parsed, but where we
/// have access to the command and stream ID, for dispatching purposes.
#[derive(Clone, Debug)]
pub struct UnparsedRelayMsg {
/// The internal representation.
internal: UnparsedRelayMsgInternal,
}
/// Position of the stream ID within the cell body.
const STREAM_ID_OFFSET: usize = 3;
impl UnparsedRelayMsg {
/// Wrap a BoxedCellBody as an UnparsedRelayMsg.
///
/// Fails if the body doesn't correspond to exactly one relay message, but
/// doesn't parse the message itself.
///
/// Non-test code should generally use `RelayCellDecoder` instead.
// Ideally we'd make this `#[cfg(test)]`, but then we wouldn't be able
// to use it in integration tests.
// https://github.com/rust-lang/rust/issues/84629
pub fn from_singleton_body(version: RelayCellFormat, body: BoxedCellBody) -> Result<Self> {
let mut decoder = RelayCellDecoder::new(version);
let res = decoder.decode(body)?;
let (mut msgs, incomplete) = res.into_parts();
let Some(msg) = msgs.next() else {
// There was no complete message in the cell.
return Err(Error::Truncated);
};
if incomplete.is_some() {
// There was an incomplete message at the end of the cell.
return Err(Error::ExtraneousBytes);
}
if msgs.next().is_some() {
// There was more than one message in the cell.
return Err(Error::ExtraneousBytes);
}
Ok(msg)
}
/// Return the command for this cell.
pub fn cmd(&self) -> RelayCmd {
match &self.internal {
UnparsedRelayMsgInternal::V0(body) => {
/// Position of the command within the cell body.
const CMD_OFFSET: usize = 0;
body[CMD_OFFSET].into()
}
}
}
/// Return the stream ID for the stream that this msg corresponds to, if any.
pub fn stream_id(&self) -> Option<StreamId> {
match &self.internal {
UnparsedRelayMsgInternal::V0(body) => StreamId::new(u16::from_be_bytes(
body[STREAM_ID_OFFSET..STREAM_ID_OFFSET + 2]
.try_into()
.expect("two-byte slice was not two bytes long!?"),
)),
}
}
/// Decode this unparsed cell into a given cell type.
pub fn decode<M: RelayMsg>(self) -> Result<RelayMsgOuter<M>> {
match self.internal {
UnparsedRelayMsgInternal::V0(body) => {
let mut reader = Reader::from_slice(body.as_ref());
RelayMsgOuter::decode_v0_from_reader(&mut reader)
}
}
}
}
/// A decoded and parsed relay message of unrestricted type,
/// with an accompanying optional Stream ID.
pub type AnyRelayMsgOuter = RelayMsgOuter<msg::AnyRelayMsg>;
/// A deprecated name for AnyRelayMsgOuter.
#[deprecated(note = "Use AnyRelayMsgOuter instead.")]
pub type AnyRelayCell = AnyRelayMsgOuter;
/// Trait implemented by anything that can serve as a relay message.
///
/// Typically, this will be [`RelayMsg`] (to represent an unrestricted relay
/// message), or a restricted subset of `RelayMsg`.
pub trait RelayMsg {
/// Return the stream command associated with this message.
fn cmd(&self) -> RelayCmd;
/// Encode the body of this message, not including command or length
fn encode_onto<W: tor_bytes::Writer + ?Sized>(self, w: &mut W) -> tor_bytes::EncodeResult<()>;
/// Extract the body of a message with command `cmd` from reader `r`.
fn decode_from_reader(cmd: RelayCmd, r: &mut Reader<'_>) -> Result<Self>
where
Self: Sized;
}
/// A decoded and parsed relay message, along with an optional Stream ID.
///
/// This type represents a message that can be sent along a
/// circuit, along with the ID for an associated stream that the
/// message is meant for.
///
/// NOTE: This name is a placeholder; we intend to replace it once we have
/// standardized our vocabulary in this area.
#[derive(Debug)]
pub struct RelayMsgOuter<M> {
/// The stream ID for the stream that this cell corresponds to.
streamid: Option<StreamId>,
/// The relay message for this cell.
msg: M,
}
/// A deprecated name for RelayMsgOuter.
#[deprecated(note = "Use RelayMsgOuter instead.")]
pub type RelayCell<M> = RelayMsgOuter<M>;
impl<M: RelayMsg> RelayMsgOuter<M> {
/// Construct a new relay cell.
pub fn new(streamid: Option<StreamId>, msg: M) -> Self {
RelayMsgOuter { streamid, msg }
}
/// Consume this cell and return its components.
pub fn into_streamid_and_msg(self) -> (Option<StreamId>, M) {
(self.streamid, self.msg)
}
/// Return the command for this cell.
pub fn cmd(&self) -> RelayCmd {
self.msg.cmd()
}
/// Return the stream ID for the stream that this cell corresponds to.
pub fn stream_id(&self) -> Option<StreamId> {
self.streamid
}
/// Return the underlying message for this cell.
pub fn msg(&self) -> &M {
&self.msg
}
/// Consume this cell and return the underlying message.
pub fn into_msg(self) -> M {
self.msg
}
/// Consume this relay message and encode it as a 509-byte padded cell
/// body.
pub fn encode<R: Rng + CryptoRng>(self, rng: &mut R) -> crate::Result<BoxedCellBody> {
/// We skip this much space before adding any random padding to the
/// end of the cell
const MIN_SPACE_BEFORE_PADDING: usize = 4;
let (mut body, enc_len) = self.encode_to_cell()?;
debug_assert!(enc_len <= CELL_DATA_LEN);
if enc_len < CELL_DATA_LEN - MIN_SPACE_BEFORE_PADDING {
rng.fill_bytes(&mut body[enc_len + MIN_SPACE_BEFORE_PADDING..]);
}
Ok(body)
}
/// Consume a relay cell and return its contents, encoded for use
/// in a RELAY or RELAY_EARLY cell.
fn encode_to_cell(self) -> EncodeResult<(BoxedCellBody, usize)> {
// NOTE: This implementation is a bit optimized, since it happens to
// literally every relay cell that we produce.
// TODO -NM: Add a specialized implementation for making a DATA cell from
// a body?
/// Wrap a BoxedCellBody and implement AsMut<[u8]>
struct BodyWrapper(BoxedCellBody);
impl AsMut<[u8]> for BodyWrapper {
fn as_mut(&mut self) -> &mut [u8] {
self.0.as_mut()
}
}
/// The position of the length field within a relay cell.
const LEN_POS: usize = 9;
/// The position of the body a relay cell.
const BODY_POS: usize = 11;
let body = BodyWrapper(Box::new([0_u8; 509]));
let mut w = crate::slicewriter::SliceWriter::new(body);
w.write_u8(self.msg.cmd().into());
w.write_u16(0); // "Recognized"
debug_assert_eq!(
w.offset().expect("Overflowed a cell with just the header!"),
STREAM_ID_OFFSET
);
w.write_u16(StreamId::get_or_zero(self.streamid));
w.write_u32(0); // Digest
// (It would be simpler to use NestedWriter at this point, but it uses an internal Vec that we are trying to avoid.)
debug_assert_eq!(
w.offset().expect("Overflowed a cell with just the header!"),
LEN_POS
);
w.write_u16(0); // Length.
debug_assert_eq!(
w.offset().expect("Overflowed a cell with just the header!"),
BODY_POS
);
self.msg.encode_onto(&mut w)?; // body
let (mut body, written) = w.try_unwrap().map_err(|_| {
EncodeError::Bug(internal!(
"Encoding of relay message was too long to fit into a cell!"
))
})?;
let payload_len = written - BODY_POS;
debug_assert!(payload_len < std::u16::MAX as usize);
*(<&mut [u8; 2]>::try_from(&mut body.0[LEN_POS..LEN_POS + 2])
.expect("Two-byte slice was not two bytes long!?")) =
(payload_len as u16).to_be_bytes();
Ok((body.0, written))
}
/// Parse a RELAY or RELAY_EARLY cell body into a RelayMsgOuter.
/// Requires that the cryptographic checks on the message have already been
/// performed
///
/// Fails if the cell doesn't contain exactly one message.
///
/// Non-test code should generally use `RelayCellDecoder` instead.
// Ideally we'd make this `#[cfg(test)]`, but then we wouldn't be able
// to use it in integration tests.
// https://github.com/rust-lang/rust/issues/84629
#[allow(clippy::needless_pass_by_value)] // TODO this will go away soon.
pub fn decode_singleton(version: RelayCellFormat, body: BoxedCellBody) -> Result<Self> {
let unparsed_msg = UnparsedRelayMsg::from_singleton_body(version, body)?;
unparsed_msg.decode()
}
/// Parse a `RelayCellFormat::V0` RELAY or RELAY_EARLY cell body into a
/// RelayMsgOuter from a reader.
///
/// Requires that the cryptographic checks on the message have already been
/// performed
fn decode_v0_from_reader(r: &mut Reader<'_>) -> Result<Self> {
let cmd = r.take_u8()?.into();
r.advance(2)?; // "recognized"
let streamid = StreamId::new(r.take_u16()?);
r.advance(4)?; // digest
let len = r.take_u16()? as usize;
if r.remaining() < len {
return Err(Error::InvalidMessage(
"Insufficient data in relay cell".into(),
));
}
r.truncate(len);
let msg = M::decode_from_reader(cmd, r)?;
Ok(Self { streamid, msg })
}
}