novy-syndicate/src/relay.ts

import { Actor, Assertion, Entity, Handle, Ref, Turn } from './actor.js';
import { BytesLike, canonicalString, Decoder, encode, FlexMap, IdentityMap, mapPointers, underlying, Value } from 'preserves';
import {
    EncodedAttenuation,
    EntityMessage,
    IO,
    Oid,
    TurnMessage,
    WireRef,
    WireSymbol,
    _Assert,
    _Message,
    _Retract,
    _Sync,
    decodeAttenuation,
    encodeAttenuation,
    myRef,
    yourRef,
} from './protocol.js';
import { queueTask } from './task.js';
import { attenuate } from './rewrite.js';

export class SyncPeerEntity implements Entity {
    readonly relay: Relay;
    readonly peer: Ref;
    readonly handleMap = new IdentityMap<Handle, Handle>();
    e: WireSymbol | null = null;

    constructor(relay: Relay, peer: Ref) {
        this.relay = relay;
        this.peer = peer;
    }

    assert(turn: Turn, assertion: Assertion, handle: Handle): void {
        this.handleMap.set(handle, turn.assert(this.peer, assertion));
    }

    retract(turn: Turn, handle: Handle): void {
        turn.retract(this.handleMap.get(handle)!);
        this.handleMap.delete(handle);
    }

    message(turn: Turn, body: Assertion): void {
        // We get to vanish from the indexes now
        this.relay.releaseRefOut(this.e!);
        turn.message(this.peer, body);
    }

    sync(turn: Turn, peer: Ref): void {
        turn._sync(this.peer, peer);
    }
}

export class RelayEntity implements Entity {
    readonly relay: Relay;
    readonly oid: Oid;

    constructor(relay: Relay, oid: Oid) {
        this.relay = relay;
        this.oid = oid;
    }

    send(m: EntityMessage<WireRef>): void {
        this.relay.send(this.oid, m);
    }

    assert(_turn: Turn, assertion: Assertion, handle: Handle): void {
        this.send(IO.Assert(this.relay.register(assertion, handle), handle));
    }

    retract(_turn: Turn, handle: Handle): void {
        this.relay.deregister(handle);
        this.send(IO.Retract(handle));
    }

    message(_turn: Turn, body: Assertion): void {
        this.send(IO.Message(this.relay.register(body, null)));
    }

    sync(turn: Turn, peer: Ref): void {
        const peerEntity = new SyncPeerEntity(this.relay, peer);
        const exported: Array<WireSymbol> = [];
        const ior = this.relay.rewriteRefOut(turn.ref(peerEntity), false, exported);
        peerEntity.e = exported[0];
        this.send(IO.Sync(ior));
    }
}

export class Membrane {
    readonly byOid = new IdentityMap<Oid, WireSymbol>();
    readonly byRef = new IdentityMap<Ref, WireSymbol>();

    grab<Table extends "byOid" | "byRef">(table: Table,
                                          key: Parameters<Membrane[Table]['get']>[0],
                                          transient: boolean,
                                          f: () => WireSymbol): WireSymbol
    {
        let e = this[table].get(key as any);
        if (e === void 0) {
            e = f();
            this.byRef.set(e.ref, e);
            this.byOid.set(e.oid, e);
        }
        if (!transient) e.count++;
        return e;
    }

    drop(e: WireSymbol): void {
        e.count--;
        if (e.count === 0) {
            this.byOid.delete(e.oid);
            this.byRef.delete(e.ref);
        }
    }
}

export const INERT_REF: Ref = {
    relay: (() => {
        const a = new Actor();
        a.exitReason = { ok: true };
        return a;
    })(),
    target: {},
};

export type PacketWriter = (bs: Uint8Array) => void;

export interface RelayOptions {
    packetWriter: PacketWriter;
    setup(t: Turn, r: Relay): void;
    debug?: boolean;
    trustPeer?: boolean;
}

export class Relay {
    readonly actor: Actor;
    readonly w: PacketWriter;
    readonly inboundAssertions = new IdentityMap<Handle, {
        localHandle: Handle,
        imported: Array<WireSymbol>,
    }>();
    readonly outboundAssertions = new IdentityMap<Handle, Array<WireSymbol>>();
    readonly exported = new Membrane();
    readonly imported = new Membrane();
    nextLocalOid: Oid = 0;
    pendingTurn: TurnMessage<WireRef> = [];
    debug: boolean;
    trustPeer: boolean;

    readonly decoder = new Decoder<WireRef>(void 0, {
        includeAnnotations: false,
        decodePointer: v => {
            function complain(): never {
                throw new Error(
                    `Received invalid object reference ${v.asPreservesText()} from peer`);
            }
            if (!(Array.isArray(v) && v.length >= 2 && typeof v[1] === 'number')) {
                complain();
            }
            const oid = v[1] as Oid;
            switch (v[0]) {
                case 0:
                    if (v.length > 2) complain();
                    return myRef(oid);
                case 1:
                    // TODO: check EncodedAttenuation
                    return yourRef(oid, v.slice(2) as EncodedAttenuation);
                default:
                    complain();
            }
        },
    });

    constructor(t: Turn, options: RelayOptions) {
        this.actor = t.actor;
        this.w = options.packetWriter;
        this.debug = options.debug ?? false;
        this.trustPeer = options.trustPeer ?? true;
        options.setup(t, this);
    }

    rewriteOut(assertion: Assertion, transient: boolean): [Value<WireRef>, Array<WireSymbol>]
    {
        const exported: Array<WireSymbol> = [];
        const rewritten = mapPointers(assertion, r => this.rewriteRefOut(r, transient, exported));
        return [rewritten, exported];
    }

    rewriteIn(t: Turn, a: Value<WireRef>): [Assertion, Array<WireSymbol>]
    {
        const imported: Array<WireSymbol> = [];
        const rewritten = mapPointers(a, r => this.rewriteRefIn(t, r, imported));
        return [rewritten, imported];
    }

    register(assertion: Assertion, handle: Handle | null): Value<WireRef> {
        const [rewritten, exported] = this.rewriteOut(assertion, handle === null);
        if (handle !== null) this.outboundAssertions.set(handle, exported);
        return rewritten;
    }

    deregister(handle: Handle): void {
        (this.outboundAssertions.get(handle) ?? []).forEach(e => this.releaseRefOut(e));
    }

    rewriteRefOut(r: Ref, transient: boolean, exported: Array<WireSymbol>): WireRef {
        if (r.target instanceof RelayEntity && r.target.relay === this) {
            if (r.attenuation === void 0 || r.attenuation.length === 0) {
                // No extra conditions on this reference since it was sent to us.
                return yourRef(r.target.oid, []);
            } else {
                // This reference has been attenuated since it was sent to us.
                // Do we trust the peer to enforce such attenuation on our behalf?
                if (this.trustPeer) {
                    return yourRef(r.target.oid, encodeAttenuation(r.attenuation));
                } else {
                    // fall through: treat the attenuated ref as a local ref, and re-export it.
                }
            }
        }

        const e = this.exported.grab(
            "byRef", r, transient, () => {
                if (transient) throw new Error("Cannot send transient reference");
                return { oid: this.nextLocalOid++, ref: r, count: 0 };
            });
        exported.push(e);
        return myRef(e.oid);
    }

    releaseRefOut(e: WireSymbol) {
        this.exported.drop(e);
    }

    rewriteRefIn(t: Turn, n: WireRef, imported: Array<WireSymbol>): Ref {
        switch (n.loc) {
            case 'your': {
                const r = this.lookupLocal(n.oid);
                if (n.attenuation.length === 0 || r === INERT_REF) {
                    return r;
                } else {
                    type AttenuatedRef = Ref & { __attenuations?: FlexMap<EncodedAttenuation, Ref> };
                    const ar = r as AttenuatedRef;
                    if (ar.__attenuations === void 0) {
                        ar.__attenuations = new FlexMap(canonicalString);
                    }
                    return ar.__attenuations.getOrSet(n.attenuation, () =>
                        attenuate(r, ... decodeAttenuation(n.attenuation)));
                }
            }
            case 'mine': {
                const e = this.imported.grab("byOid", n.oid, false, () =>
                    ({ oid: n.oid, ref: t.ref(new RelayEntity(this, n.oid)), count: 0 }));
                imported.push(e);
                return e.ref;
            }
        }
    }

    send(remoteOid: Oid, m: EntityMessage<WireRef>): void {
        if (this.pendingTurn.length === 0) {
            queueTask(() => {
                if (this.debug) console.log('OUT', this.pendingTurn.asPreservesText());
                this.w(underlying(encode<WireRef>(this.pendingTurn, {
                    canonical: true,
                    encodePointer: n => {
                        switch (n.loc) {
                            case 'mine': return [0, n.oid];
                            case 'your': return [1, n.oid, ... n.attenuation];
                        }
                    },
                })));
                this.pendingTurn = [];
            });
        }
        this.pendingTurn.push([remoteOid, m]);
    }

    lookupLocal(localOid: Oid): Ref {
        return this.exported.byOid.get(localOid)?.ref ?? INERT_REF;
    }

    accept(bs: BytesLike): void {
        Turn.for(this.actor, t => {
            this.decoder.write(bs);
            while (true) {
                const wireTurn = this.decoder.try_next() as (TurnMessage<WireRef> | undefined);
                if (wireTurn === void 0) break;
                // TODO: deep check that wireTurn really is a TurnMessage
                if (this.debug) console.log('IN', wireTurn.asPreservesText());
                wireTurn.forEach(v => {
                    const [localOid, m] = v;
                    this.handle(t, this.lookupLocal(localOid), m);
                });
            }
        });
    }

    handle(t: Turn, r: Ref, m: EntityMessage<WireRef>) {
        switch (m.label) {
            case _Assert: {
                const [a, imported] = this.rewriteIn(t, IO.Assert._.assertion(m));
                this.inboundAssertions.set(IO.Assert._.handle(m), {
                    localHandle: t.assert(r, a),
                    imported,
                });
                break;
            }
            case _Retract: {
                const remoteHandle = IO.Retract._.handle(m);
                const h = this.inboundAssertions.get(remoteHandle);
                if (h === void 0) throw new Error(`Peer retracted invalid handle ${remoteHandle}`);
                this.inboundAssertions.delete(remoteHandle);
                h.imported.forEach(e => this.imported.drop(e));
                t.retract(h.localHandle);
                break;
            }
            case _Message: {
                const [a, imported] = this.rewriteIn(t, IO.Message._.body(m));
                if (imported.length > 0) throw new Error("Cannot receive transient reference");
                t.message(r, a);
                break;
            }
            case _Sync: {
                const imported: Array<WireSymbol> = [];
                const k = this.rewriteRefIn(t, IO.Sync._.peer(m), imported);
                t.sync(r).then(t => {
                    t.message(k, true);
                    imported.forEach(e => this.imported.drop(e));
                });
                break;
            }
        }
    }
}

export interface RelayActorOptions extends RelayOptions {
    initialOid?: Oid;
    initialRef?: Ref;
    nextLocalOid?: Oid;
}

export function spawnRelay(t: Turn, options: RelayActorOptions): Promise<Ref | null> {
    return new Promise(resolve => {
        t.spawn(t => {
            const relay = new Relay(t, options);
            if (options.initialRef !== void 0) {
                relay.rewriteRefOut(options.initialRef, false, []);
            }
            if (options.initialOid !== void 0) {
                resolve(relay.rewriteRefIn(t, myRef(options.initialOid), []));
            } else {
                resolve(null);
            }
            if (options.nextLocalOid !== void 0) {
                relay.nextLocalOid = (options.nextLocalOid === 0) ? 1 : options.nextLocalOid;
            }
        });
    });
}