hydro_lang/compile/

embedded_runtime.rs

//! Runtime helpers for the embedded deployment backend.
//!
//! This module is NOT gated on the `build` feature so that the staged
//! re-exports are available at runtime in the generated code.

use std::marker::PhantomData;

use crate::live_collections::stream::{
    AtLeastOnce, ExactlyOnce, NoOrder, Ordering, Retries, TotalOrder,
};
use crate::networking::NetworkingConfig;
use crate::properties::ManualProof;

/// A channel crossing the boundary of an embedded dataflow: a network channel end, a stream
/// input, a membership stream, or an output, with its guarantees as marker types (`Ordering`
/// and `Retries`).
///
/// - For a stream input or membership stream, the guarantees are what the dataflow relies on,
///   which the host's [`Promises`] must meet.
/// - For the sending end of a network channel, they are what the dataflow sends, which the
///   host's [`Acknowledgements`] must cover, as for an output.
/// - For the receiving end of a network channel, they are what the dataflow relies on: the sent
///   stream, weakened by the channel's configuration. The host's [`Promises`] must meet them, as
///   for a stream input.
/// - For an output, they are what the dataflow provides. The host's [`Acknowledgements`] must
///   cover every way the output may be weaker than ordered and exactly-once.
///
/// Each location's generated module has a marker type implementing this for each
/// channel crossing it, named after its field: under `incoming` / `outgoing` for
/// network channel ends, `inputs` for stream inputs, `membership` for membership streams, and
/// `outputs` for outputs. Each field of the generated structs is an [`EmbeddedInputChannel`] (a stream
/// input or membership stream), a [`EmbeddedNetworkInputChannel`] (a receiving end), a [`EmbeddedNetworkOutputChannel`] (a
/// sending end), or an [`EmbeddedOutputChannel`] (an output) over its marker. The marker is inferred from
/// the field. The markers of network channel ends also implement [`EmbeddedNetworkChannel`].
pub trait EmbeddedChannel {
    /// The ordering the host must keep (for an output or the sending end of a network channel,
    /// the ordering the dataflow provides): `TotalOrder` or `NoOrder`. For a network channel,
    /// `TotalOrder` means each sender's messages in the order it sent them; for an input, that
    /// the stream's order is the order to process; for a membership stream, each member's events
    /// in the order they happened.
    type Ordering: Ordering;

    /// The retry guarantee the host must keep (for an output or the sending end of a network
    /// channel, the one the dataflow provides): `ExactlyOnce` (nothing delivered twice) or
    /// `AtLeastOnce`.
    type Retries: Retries;
}

/// What a host promises about something it supplies, each guarantee promised separately with
/// a [`manual_proof!`](crate::prelude::manual_proof) saying why it holds. An [`EmbeddedInputChannel`] or
/// [`EmbeddedNetworkInputChannel`] is built from a stream and the `Promises` that meet its marker's
/// guarantees.
pub struct Promises<O, R> {
    _promised: PhantomData<fn() -> (O, R)>,
}

impl Promises<NoOrder, AtLeastOnce> {
    /// Promises nothing: elements may arrive in any order, and any may be delivered more than
    /// once.
    pub fn new() -> Self {
        Promises {
            _promised: PhantomData,
        }
    }
}

impl Default for Promises<NoOrder, AtLeastOnce> {
    fn default() -> Self {
        Self::new()
    }
}

impl<O, R> Promises<O, R> {
    fn retag<O2, R2>(self) -> Promises<O2, R2> {
        Promises {
            _promised: PhantomData,
        }
    }
}

impl<R> Promises<NoOrder, R> {
    /// Promises the order: for a channel, each sender's messages are delivered in the order it
    /// sent them; for an input, the stream's order is the order to process; for a membership
    /// stream, each member's events arrive in the order they happened.
    pub fn total_order(self, _proof: ManualProof) -> Promises<TotalOrder, R> {
        self.retag()
    }
}

impl<O> Promises<O, AtLeastOnce> {
    /// Promises that nothing is delivered twice: a channel never duplicates a message (for
    /// example by resending it after a reconnect), and every element of an input is a distinct
    /// event.
    pub fn exactly_once(self, _proof: ManualProof) -> Promises<O, ExactlyOnce> {
        self.retag()
    }
}

/// A channel whose guarantees promises of ordering `O` and retries `R` meet: each guarantee the
/// channel needs is weaker than (or the same as) the one promised. It is what [`EmbeddedInputChannel::new`]
/// requires, and lets a reusable transport state once what it provides:
/// `fn source<C: SatisfiedBy<TotalOrder, ExactlyOnce>>()` serves every channel that needs at
/// most that.
pub trait SatisfiedBy<O, R>: EmbeddedChannel {}

impl<K, O, R> SatisfiedBy<O, R> for K
where
    K: EmbeddedChannel,
    K::Ordering: OrderPromisedBy<O, K>,
    K::Retries: RetriesPromisedBy<R, K>,
{
}

/// A needed order (`Self`) that the promised order `Promised` meets, for the channel end `End`.
/// Only order is promised, so a promise is needed only for `TotalOrder`.
#[diagnostic::on_unimplemented(
    message = "`{End}` relies on its elements arriving in order, but the host does not promise it",
    label = "does not promise `TotalOrder`",
    note = "add `.total_order(manual_proof!(/** why the order is kept */))` to its `Promises`"
)]
trait OrderPromisedBy<Promised, End> {}

impl<Promised: Ordering, End> OrderPromisedBy<Promised, End> for NoOrder {}
impl<End> OrderPromisedBy<TotalOrder, End> for TotalOrder {}

/// A needed retry guarantee (`Self`) that the promised one `Promised` meets, for `End`.
#[diagnostic::on_unimplemented(
    message = "`{End}` relies on each element arriving exactly once, but the host does not promise it",
    label = "does not promise `ExactlyOnce`",
    note = "add `.exactly_once(manual_proof!(/** why nothing is delivered twice */))` to its `Promises`"
)]
trait RetriesPromisedBy<Promised, End> {}

impl<Promised: Retries, End> RetriesPromisedBy<Promised, End> for AtLeastOnce {}
impl<End> RetriesPromisedBy<ExactlyOnce, End> for ExactlyOnce {}

/// A channel flowing into an embedded dataflow, as the host provides it: a `Stream` for a stream
/// input or a membership stream, for the channel `C` (its generated marker type, see
/// [`EmbeddedChannel`]). The receiving end of a network channel is a [`EmbeddedNetworkInputChannel`] instead.
///
/// An `EmbeddedInputChannel` exists only with promises that meet `C`'s guarantees:
/// [`EmbeddedInputChannel::new`] takes the [`Promises`] and checks them, so wiring a channel always
/// states its guarantees and a mismatch with the dataflow is a type error at that call. Promising
/// more than a channel needs is fine. `C` is inferred from the field the `EmbeddedInputChannel` fills.
pub struct EmbeddedInputChannel<C, S> {
    inner: S,
    _channel: PhantomData<fn() -> C>,
}

impl<C: EmbeddedChannel, S> EmbeddedInputChannel<C, S> {
    /// Wraps a host stream for channel `C`, with `promises` that must meet its guarantees.
    pub fn new<O, R>(inner: S, promises: Promises<O, R>) -> Self
    where
        C: SatisfiedBy<O, R>,
    {
        let _ = promises;
        EmbeddedInputChannel {
            inner,
            _channel: PhantomData,
        }
    }
}

impl<C, S> EmbeddedInputChannel<C, S> {
    /// The host's stream. Used by generated code.
    #[doc(hidden)]
    pub fn into_inner(self) -> S {
        self.inner
    }
}

/// The configuration of a network channel crossing the boundary of an embedded dataflow: the
/// transport type `Transport` of the network config the dataflow sends with (for example
/// `Tcp<FailStop>` for `TCP.fail_stop()`, or `EmbeddedTransport<ExactlyOnce, NoOrder, FailStop>`
/// for `EMBEDDED.may_reorder().never_duplicates().never_drops()`), and its serialization `Serialization` (`Bincode`, or `Embedded`
/// for an unserialized `EMBEDDED` channel).
///
/// The markers of both ends of a network channel implement it, alongside [`EmbeddedChannel`]
/// for the stream at that end. The host acknowledges the configuration exactly at each end with
/// a [`ChannelConfiguration`], so that changing the channel's network config fails the host's
/// build at both ends until it acknowledges the change.
pub trait EmbeddedNetworkChannel: EmbeddedChannel {
    /// The transport type of the channel's network config.
    type Transport;

    /// The serialization of the channel's network config.
    type Serialization;
}

/// The configuration of a network channel as the host acknowledges it: the transport `Tr` and
/// serialization `S` of its network config, which must match the channel's exactly (see
/// [`EmbeddedNetworkChannel`]). It is built from the same network config value the dataflow
/// sends with; the config's name is ignored.
pub struct ChannelConfiguration<Tr, S> {
    _acknowledged: PhantomData<fn() -> (Tr, S)>,
}

impl<Tr, S> ChannelConfiguration<Tr, S> {
    /// Acknowledges a channel configured with `config`, the same network config the dataflow
    /// sends with (for example `TCP.fail_stop().bincode()`).
    pub fn new<Name>(config: NetworkingConfig<Tr, S, Name>) -> Self {
        let _ = config;
        ChannelConfiguration {
            _acknowledged: PhantomData,
        }
    }
}

/// A network channel end whose configuration is exactly the acknowledged transport `Tr` and
/// serialization `S`. Each part is checked separately, so a mismatch names the part the host
/// acknowledges wrongly. It is what [`EmbeddedNetworkOutputChannel::new`] and [`EmbeddedNetworkInputChannel::new`] require.
pub trait ConfiguredAs<Tr, S>: EmbeddedNetworkChannel {}

impl<C, Tr, S> ConfiguredAs<Tr, S> for C
where
    C: EmbeddedNetworkChannel,
    Tr: AcknowledgesTransport<C::Transport, C>,
    S: AcknowledgesSerialization<C::Serialization, C>,
{
}

/// Checks the acknowledged transport separately, so a mismatch names it.
#[diagnostic::on_unimplemented(
    message = "the channel end `{End}` is configured with `{Declared}`, but the host acknowledges `{Self}`",
    label = "acknowledges `{Self}`",
    note = "acknowledge the same network config the dataflow sends with; the marker's docs give it"
)]
trait AcknowledgesTransport<Declared, End> {}

impl<X, End> AcknowledgesTransport<X, End> for X {}

/// Checks the acknowledged serialization separately, so a mismatch names it.
#[diagnostic::on_unimplemented(
    message = "the channel end `{End}` is serialized with `{Declared}`, but the host acknowledges `{Self}`",
    label = "acknowledges `{Self}`",
    note = "acknowledge the same network config the dataflow sends with; the marker's docs give it"
)]
trait AcknowledgesSerialization<Declared, End> {}

impl<X, End> AcknowledgesSerialization<X, End> for X {}

/// The sending end of a network channel, as the host provides it: an `FnMut` sink that hands
/// each message to the host's transport, for the channel end `C` (its generated marker type,
/// under `outgoing`).
///
/// The host agrees to both inputs of the dataflow's send: [`EmbeddedNetworkOutputChannel::new`] takes the
/// [`ChannelConfiguration`] the host acknowledges, which must match the channel's exactly, and the
/// [`Acknowledgements`] of the stream the dataflow sends, which must cover every way it may be
/// weaker than ordered and exactly-once, as for an [`EmbeddedOutputChannel`]. `C` is inferred from the
/// field the `EmbeddedNetworkOutputChannel` fills.
pub struct EmbeddedNetworkOutputChannel<C, S> {
    inner: S,
    _channel: PhantomData<fn() -> C>,
}

impl<C: EmbeddedNetworkChannel, S> EmbeddedNetworkOutputChannel<C, S> {
    /// Wraps a host sink for the channel end `C`, with the acknowledgements of its
    /// configuration (`channel`) and of the stream sent on it (`acknowledgements`).
    pub fn new<Tr, Ser, O, R>(
        inner: S,
        channel: ChannelConfiguration<Tr, Ser>,
        acknowledgements: Acknowledgements<O, R>,
    ) -> Self
    where
        C: ConfiguredAs<Tr, Ser> + AcknowledgedBy<O, R>,
    {
        let _ = (channel, acknowledgements);
        EmbeddedNetworkOutputChannel {
            inner,
            _channel: PhantomData,
        }
    }
}

impl<C, S> EmbeddedNetworkOutputChannel<C, S> {
    /// The host's sink. Used by generated code.
    #[doc(hidden)]
    pub fn into_inner(self) -> S {
        self.inner
    }
}

/// The receiving end of a network channel, as the host provides it: a `Stream` of the messages
/// its transport delivers, for the channel end `C` (its generated marker type, under
/// `incoming`).
///
/// The host agrees to the channel's configuration and to the stream it delivers:
/// [`EmbeddedNetworkInputChannel::new`] takes the [`ChannelConfiguration`] the host acknowledges,
/// which must match exactly, and the [`Promises`] of the stream it delivers, which must meet what
/// the dataflow relies on, as for an [`EmbeddedInputChannel`]. That stream is the sent stream weakened by
/// the channel's configuration (a channel that may reorder delivers a `NoOrder` stream), so it
/// may be weaker than what the sending end acknowledges. `C` is inferred from the field the
/// `EmbeddedNetworkInputChannel` fills.
pub struct EmbeddedNetworkInputChannel<C, S> {
    inner: S,
    _channel: PhantomData<fn() -> C>,
}

impl<C: EmbeddedNetworkChannel, S> EmbeddedNetworkInputChannel<C, S> {
    /// Wraps a host stream for the channel end `C`, with the acknowledgement of its
    /// configuration (`channel`) and the promises of the stream it delivers (`promises`).
    pub fn new<Tr, Ser, O, R>(
        inner: S,
        channel: ChannelConfiguration<Tr, Ser>,
        promises: Promises<O, R>,
    ) -> Self
    where
        C: ConfiguredAs<Tr, Ser> + SatisfiedBy<O, R>,
    {
        let _ = (channel, promises);
        EmbeddedNetworkInputChannel {
            inner,
            _channel: PhantomData,
        }
    }
}

impl<C, S> EmbeddedNetworkInputChannel<C, S> {
    /// The host's stream. Used by generated code.
    #[doc(hidden)]
    pub fn into_inner(self) -> S {
        self.inner
    }
}

/// What a host acknowledges about a stream the dataflow provides (an output, or the stream sent
/// on a network channel): each way it may be weaker than ordered and exactly-once. The stream's
/// type already says what it may do, so an acknowledgement needs no justification: calling it is
/// the host's agreement, and a stream that becomes weaker fails the host's build until the host
/// acknowledges the change. An
/// [`EmbeddedOutputChannel`] or [`EmbeddedNetworkOutputChannel`] is built from a sink and the `Acknowledgements` that
/// cover what its marker's stream may do.
pub struct Acknowledgements<O, R> {
    _acknowledged: PhantomData<fn() -> (O, R)>,
}

impl Acknowledgements<TotalOrder, ExactlyOnce> {
    /// Acknowledges nothing: the sink relies on receiving elements in the dataflow's order, each
    /// exactly once.
    pub fn new() -> Self {
        Acknowledgements {
            _acknowledged: PhantomData,
        }
    }
}

impl Default for Acknowledgements<TotalOrder, ExactlyOnce> {
    fn default() -> Self {
        Self::new()
    }
}

impl<O, R> Acknowledgements<O, R> {
    fn retag<O2, R2>(self) -> Acknowledgements<O2, R2> {
        Acknowledgements {
            _acknowledged: PhantomData,
        }
    }
}

impl<R> Acknowledgements<TotalOrder, R> {
    /// Acknowledges that elements may arrive in any order.
    pub fn no_order(self) -> Acknowledgements<NoOrder, R> {
        self.retag()
    }
}

impl<O> Acknowledgements<O, ExactlyOnce> {
    /// Acknowledges that an element may arrive more than once.
    pub fn at_least_once(self) -> Acknowledgements<O, AtLeastOnce> {
        self.retag()
    }
}

/// An output whose guarantees acknowledgements of ordering `O` and retries `R` cover: each
/// acknowledged guarantee is weaker than (or the same as) the one the output provides. It is
/// what [`EmbeddedOutputChannel::new`]
/// requires.
pub trait AcknowledgedBy<O, R>: EmbeddedChannel {}

impl<K, O, R> AcknowledgedBy<O, R> for K
where
    K: EmbeddedChannel,
    K::Ordering: OrderAcknowledgedBy<O, K>,
    K::Retries: RetriesAcknowledgedBy<R, K>,
{
}

/// A provided order (`Self`) that the acknowledged order `Acknowledged` covers, for `End`.
/// Only a weaker order is acknowledged, so an acknowledgement is needed only for `NoOrder`.
#[diagnostic::on_unimplemented(
    message = "`{End}` may deliver its elements in any order, which the host must acknowledge",
    label = "does not acknowledge `NoOrder`",
    note = "add `.no_order()` to its `Acknowledgements`"
)]
trait OrderAcknowledgedBy<Acknowledged, End> {}

impl<Acknowledged: Ordering, End> OrderAcknowledgedBy<Acknowledged, End> for TotalOrder {}
impl<End> OrderAcknowledgedBy<NoOrder, End> for NoOrder {}

/// A provided retry guarantee (`Self`) that the acknowledged one `Acknowledged` covers, for `End`.
#[diagnostic::on_unimplemented(
    message = "`{End}` may deliver an element more than once, which the host must acknowledge",
    label = "does not acknowledge `AtLeastOnce`",
    note = "add `.at_least_once()` to its `Acknowledgements`"
)]
trait RetriesAcknowledgedBy<Acknowledged, End> {}

impl<Acknowledged: Retries, End> RetriesAcknowledgedBy<Acknowledged, End> for ExactlyOnce {}
impl<End> RetriesAcknowledgedBy<AtLeastOnce, End> for AtLeastOnce {}

/// An output of an embedded dataflow, as the host provides it: an `FnMut` sink for the channel
/// `M` (its generated marker type, under `outputs`), whose [`EmbeddedChannel`] guarantees are
/// what the dataflow's output stream provides.
///
/// An `EmbeddedOutputChannel` exists only with acknowledgements that cover what the output may do:
/// [`EmbeddedOutputChannel::new`] takes the [`Acknowledgements`] and checks them, so a sink cannot
/// silently receive elements out of order or more than once. Acknowledging more than an output
/// may do is fine. `M` is inferred from the field the `EmbeddedOutputChannel` fills.
pub struct EmbeddedOutputChannel<M, S> {
    inner: S,
    _output: PhantomData<fn() -> M>,
}

impl<M: EmbeddedChannel, S> EmbeddedOutputChannel<M, S> {
    /// Wraps a host sink for output `M`, with `acknowledgements` that cover what `M` may do.
    pub fn new<O, R>(inner: S, acknowledgements: Acknowledgements<O, R>) -> Self
    where
        M: AcknowledgedBy<O, R>,
    {
        let _ = acknowledgements;
        EmbeddedOutputChannel {
            inner,
            _output: PhantomData,
        }
    }
}

impl<M, S> EmbeddedOutputChannel<M, S> {
    /// The host's sink. Used by generated code.
    #[doc(hidden)]
    pub fn into_inner(self) -> S {
        self.inner
    }
}