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sync.ts
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sync.ts
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import { consume, type ConsumerOptions, type Endpoint, produce, type Producer, type ProducerHandler } from "@ndn/endpoint";
import type { Forwarder } from "@ndn/fw";
import { Component, Interest, Name, type NameLike, nullSigner, type Signer, type Verifier } from "@ndn/packet";
import { type SyncNode, type SyncProtocol, SyncUpdate } from "@ndn/sync-api";
import { Decoder, Encoder } from "@ndn/tlv";
import { assert, randomJitter, trackEventListener } from "@ndn/util";
import type { Promisable } from "type-fest";
import { TypedEventTarget } from "typescript-event-target";
import { StateVector } from "./state-vector";
interface DebugEntry {
action: string;
own: Record<string, number>;
recv?: Record<string, number>;
state: string;
nextState?: string;
ourOlder?: number;
ourNewer?: number;
}
type EventMap = SyncProtocol.EventMap<Name> & {
debug: CustomEvent<DebugEntry>;
};
/** StateVectorSync participant. */
export class SvSync extends TypedEventTarget<EventMap> implements SyncProtocol<Name> {
public static async create({
syncPrefix,
endpoint, // eslint-disable-line etc/no-deprecated
fw = endpoint?.fw,
describe = `SvSync(${syncPrefix})`,
initialStateVector = new StateVector(),
initialize,
syncInterestLifetime = 1000,
steadyTimer = [30000, 0.1],
periodicTimeout = steadyTimer,
svs2suppression = false,
suppressionTimer = [200, 0.5],
suppressionPeriod = suppressionTimer[0],
suppressionTimeout = SvSync.suppressionExpDelay(suppressionPeriod),
signer = nullSigner,
verifier,
}: SvSync.Options): Promise<SvSync> {
if (typeof periodicTimeout === "number") {
periodicTimeout = [periodicTimeout, 0.1];
}
const sync = new SvSync(
syncPrefix,
describe,
initialStateVector,
Interest.makeModifyFunc({
canBePrefix: true,
mustBeFresh: true,
lifetime: syncInterestLifetime,
}),
{ fw, describe: `${describe}[c]`, retx: 0 },
randomJitter(periodicTimeout[1], periodicTimeout[0]),
svs2suppression ? suppressionTimeout :
randomJitter(suppressionTimer[1], suppressionTimer[0]),
svs2suppression ? suppressionPeriod : undefined,
signer,
verifier,
);
await initialize?.(sync);
sync.producer = produce(syncPrefix, sync.handleSyncInterest, {
fw,
describe: `${describe}[p]`,
routeCapture: false,
});
return sync;
}
private constructor(
public readonly syncPrefix: Name,
public readonly describe: string,
private readonly own: StateVector,
private readonly modifyInterest: Interest.ModifyFunc,
private readonly cOpts: ConsumerOptions,
private readonly steadyTimer: () => number,
private readonly suppressionTimer: () => number,
private readonly svs2suppressionPeriod: number | undefined,
private readonly signer: Signer,
private readonly verifier?: Verifier,
) {
super();
}
private readonly maybeHaveEventListener = trackEventListener(this);
private producer?: Producer;
/**
* In steady state, undefined.
* In suppression state, aggregated state vector of incoming sync Interests.
*/
private aggregated?: StateVector;
/** Sync Interest timer. */
private timer!: NodeJS.Timeout | number;
private debug(action: string, entry: Partial<DebugEntry> = {}, recv?: StateVector): void {
if (!this.maybeHaveEventListener.debug) {
return;
}
/* c8 ignore next */
this.dispatchTypedEvent("debug", new CustomEvent<DebugEntry>("debug", {
detail: {
action,
own: this.own.toJSON(),
recv: recv?.toJSON(),
state: this.aggregated ? "suppression" : "steady",
...entry,
},
}));
}
public close(): void {
clearTimeout(this.timer);
this.producer?.close();
}
public get(id: NameLike): SyncNode<Name> {
return new SvSyncNode(Name.from(id), this.nodeOp);
}
public add(id: NameLike): SyncNode<Name> {
return this.get(id);
}
/**
* Obtain a copy of own state vector.
*
* @remarks
* This may be used as {@link SvSync.Options.initialStateVector} to re-create an SvSync instance.
*/
public get currentStateVector(): StateVector {
return new StateVector(this.own);
}
/**
* Multi-purpose callback passed to {@link SvSyncNode} constructor.
*
* @remarks
* - `nodeOp(id)`: get seqNum
* - `nodeOp(id, n)`: set seqNum, return new seqNum
* - `nodeOp(id, 0)`: delete node during initialization
*/
private readonly nodeOp = (id: Name, n: number | undefined): number => {
if (n !== undefined) { // setSeqNum requested
if (!this.producer) { // decrement/remove permitted during initialization
this.own.set(id, n);
} else if (n > this.own.get(id)) { // increment only after initialization
this.own.set(id, n);
this.debug("publish");
this.resetTimer(true);
}
}
return this.own.get(id);
};
private readonly handleSyncInterest: ProducerHandler = async (interest) => {
await this.verifier?.verify(interest);
const vComp = interest.name.at(this.syncPrefix.length);
assert(vComp.type === StateVector.Type, "name component is not a StateVector");
const recv = new Decoder(vComp.value).decode(StateVector);
const ourOlder = this.own.listOlderThan(recv);
const ourNewer = recv.listOlderThan(this.own);
this.debug("recv", {
nextState: (!this.aggregated && ourNewer.length > 0) ? "suppression" : undefined,
ourOlder: ourOlder.length,
ourNewer: ourNewer.length,
}, recv);
this.own.mergeFrom(recv);
for (const { id, loSeqNum, hiSeqNum } of ourOlder) {
this.dispatchTypedEvent("update", new SyncUpdate(this.get(id), loSeqNum, hiSeqNum));
}
if (this.aggregated) { // in suppression state
this.aggregated.mergeFrom(recv);
return undefined;
}
// in steady state
if (this.shouldEnterSuppression(ourNewer)) {
// entering suppression state
this.aggregated = recv;
}
this.resetTimer();
return undefined;
};
private shouldEnterSuppression(ourNewer: readonly StateVector.DiffEntry[]): boolean {
if (this.svs2suppressionPeriod === undefined) {
return ourNewer.length > 0;
}
const ignoreUpdatedAfter = Date.now() - this.svs2suppressionPeriod;
return ourNewer.some(({ id }) => this.own.getEntry(id).lastUpdate <= ignoreUpdatedAfter);
}
private resetTimer(immediate = false): void {
clearTimeout(this.timer);
const delay = immediate ? 0 : this.aggregated ? this.suppressionTimer() : this.steadyTimer();
this.timer = setTimeout(this.handleTimer, delay);
}
private readonly handleTimer = () => {
if (this.aggregated) { // in suppression state, exiting to steady state
const ourNewer = this.aggregated.listOlderThan(this.own);
this.debug("timer", {
nextState: "steady",
ourNewer: ourNewer.length,
});
if (ourNewer.length > 0) {
void this.sendSyncInterest();
}
this.aggregated = undefined;
} else { // in steady state
this.debug("timer");
void this.sendSyncInterest();
}
this.resetTimer();
};
private async sendSyncInterest(): Promise<void> {
this.debug("send");
const interest = new Interest();
interest.name = this.syncPrefix.append(new Component(StateVector.Type, Encoder.encode(this.own)));
this.modifyInterest(interest);
await this.signer.sign(interest);
try {
await consume(interest, this.cOpts);
} catch {
// not expecting a reply, so that a timeout will happen and it shall be ignored
}
}
}
export namespace SvSync {
/**
* Timer settings.
* @deprecated No longer supported.
*/
export type Timer = [ms: number, jitter: number];
/** {@link SvSync.create} options. */
export interface Options {
/** Sync group prefix. */
syncPrefix: Name;
/**
* Endpoint for communication.
* @deprecated Specify `.fw`.
*/
endpoint?: Endpoint;
/**
* Use the specified logical forwarder.
* @defaultValue `Forwarder.getDefault()`
*/
fw?: Forwarder;
/** Description for debugging purpose. */
describe?: string;
/**
* Initial state vector.
* @defaultValue empty state vector
*/
initialStateVector?: StateVector;
/**
* Application initialization function.
*
* @remarks
* During initialization, it's possible to remove SyncNode or decrease seqNum.
* Calling `sync.close()` has no effect.
*
* Sync protocol starts running after the returned Promise is resolved.
*/
initialize?: (sync: SvSync) => Promisable<void>;
/**
* Sync Interest lifetime in milliseconds.
* @defaultValue 1000
*/
syncInterestLifetime?: number;
/**
* Sync Interest timer in steady state (SVS v1).
* @defaultValue `[30000ms, ±10%]`
* @remarks
* - median: median interval in milliseconds.
* - jitter: ± percentage, in [0.0, 1.0) range.
*/
steadyTimer?: [median: number, jitter: number];
/**
* Sync Interest timer in steady state (SVS v2).
* @defaultValue `[30000ms, ±10%]`
* @remarks
* If specified as tuple,
* - median: median interval in milliseconds.
* - jitter: ± percentage, in [0.0, 1.0) range.
*
* If specified as number, it's interpreted as median.
*
* SVS v1 `steadyTimer` and SVS v2 `periodicTimeout` are equivalent.
* If both are specified, this option takes precedence.
* @experimental
*/
periodicTimeout?: number | [median: number, jitter: number];
/**
* Use SVS v2 suppression timer and suppression logic.
* @defaultValue false
* @experimental
*/
svs2suppression?: boolean;
/**
* Sync Interest timer in suppression state (SVS v1).
* @defaultValue `[200ms, ±50%]`
* @remarks
* - median: median interval in milliseconds.
* - jitter: ± percentage, in [0.0, 1.0) range.
*
* This option takes effect only if `.svs2suppression` is false.
*/
suppressionTimer?: [median: number, jitter: number];
/**
* Sync Interest timer in suppression state, maximum value (SVS v2).
* @defaultValue `200ms`
* @experimental
*/
suppressionPeriod?: number;
/**
* Sync Interest timer in suppression state, value generator (SVS v2).
* @defaultValue `SvSync.suppressionExpDelay(suppressionPeriod)`
* @remarks
* The maximum value returned by the generator function should be `suppressionPeriod`.
*
* This option takes effect only if `.svs2suppression` is true.
* @experimental
*/
suppressionTimeout?: () => number;
/**
* Sync Interest signer.
* @defaultValue nullSigner
*/
signer?: Signer;
/**
* Sync Interest verifier.
* @defaultValue no verification
*/
verifier?: Verifier;
}
/**
* SVS v2 suppression timeout exponential decay function.
* @param c - Constant factor.
* @param f - Decay factor.
* @returns Function to generate suppression timeout values.
* @experimental
*/
export function suppressionExpDelay(c: number, f = 10): () => number {
const cf = c / f;
return () => {
const v = Math.random() * c;
return -c * Math.expm1((v - c) / cf);
};
}
}
class SvSyncNode implements SyncNode<Name> {
constructor(
public readonly id: Name,
private readonly op: (id: Name, n: number | undefined) => number,
) {}
public get seqNum(): number {
return this.op(this.id, undefined);
}
public set seqNum(n: number) {
this.op(this.id, n);
}
public remove(): void {
this.op(this.id, 0);
}
}