hydrogen-web/src/matrix/net/Reconnector.js

import {createEnum} from "../../utils/enum.js";
import {ObservableValue} from "../../observable/ObservableValue.js";

export const ConnectionStatus = createEnum(
    "Waiting",
    "Reconnecting",
    "Online"
);

export class Reconnector {
    constructor({retryDelay, createMeasure, onlineStatus}) {
        this._onlineStatus = onlineStatus;
        this._retryDelay = retryDelay;
        this._createTimeMeasure = createMeasure;
        // assume online, and do our thing when something fails
        this._state = new ObservableValue(ConnectionStatus.Online);
        this._isReconnecting = false;
        this._versionsResponse = null;
    }

    get lastVersionsResponse() {
        return this._versionsResponse;
    }

    get connectionStatus() {
        return this._state;
    }

    get retryIn() {
        if (this._state.get() === ConnectionStatus.Waiting) {
            return this._retryDelay.nextValue - this._stateSince.measure();
        }
        return 0;
    }

    async onRequestFailed(hsApi) {
        if (!this._isReconnecting) {  
            this._isReconnecting = true;
 
            const onlineStatusSubscription = this._onlineStatus && this._onlineStatus.subscribe(online => {
                if (online) {
                    this.tryNow();
                }
            });

            try {
                await this._reconnectLoop(hsApi);
            } catch (err) {
                // nothing is catching the error above us,
                // so just log here
                console.error(err);
            } finally {
                if (onlineStatusSubscription) {
                    // unsubscribe from this._onlineStatus
                    onlineStatusSubscription();
                }
                this._isReconnecting = false;
            }
        }
    }

    tryNow() {
        if (this._retryDelay) {
            // this will interrupt this._retryDelay.waitForRetry() in _reconnectLoop
            this._retryDelay.abort();
        }
    }

    _setState(state) {
        if (state !== this._state.get()) {
            if (state === ConnectionStatus.Waiting) {
                this._stateSince = this._createTimeMeasure();
            } else {
                this._stateSince = null;
            }
            this._state.set(state);
        }
    }
    
    async _reconnectLoop(hsApi) {
        this._versionsResponse = null;
        this._retryDelay.reset();

        while (!this._versionsResponse) {
            try {
                this._setState(ConnectionStatus.Reconnecting);
                // use 30s timeout, as a tradeoff between not giving up
                // too quickly on a slow server, and not waiting for
                // a stale connection when we just came online again
                const versionsRequest = hsApi.versions({timeout: 30000});
                this._versionsResponse = await versionsRequest.response();
                this._setState(ConnectionStatus.Online);
            } catch (err) {
                if (err.name === "ConnectionError") {
                    this._setState(ConnectionStatus.Waiting);
                    await this._retryDelay.waitForRetry();
                } else {
                    throw err;
                }
            }
        }
    }
}


import {Clock as MockClock} from "../../mocks/Clock.js";
import {ExponentialRetryDelay} from "./ExponentialRetryDelay.js";
import {ConnectionError} from "../error.js"

export function tests() {
    function createHsApiMock(remainingFailures) {
        return {
            versions() {
                return {
                    response() {
                        if (remainingFailures) {
                            remainingFailures -= 1;
                            return Promise.reject(new ConnectionError());
                        } else {
                            return Promise.resolve(42);
                        }
                    }
                };
            }
        }
    }

    return {
        "test reconnecting with 1 failure": async assert => {
            const clock = new MockClock();
            const {createMeasure} = clock;
            const onlineStatus = new ObservableValue(false);
            const retryDelay = new ExponentialRetryDelay(clock.createTimeout);
            const reconnector = new Reconnector({retryDelay, onlineStatus, createMeasure});
            const {connectionStatus} = reconnector;
            const statuses = [];
            const subscription = reconnector.connectionStatus.subscribe(s => {
                statuses.push(s);
            });
            reconnector.onRequestFailed(createHsApiMock(1));
            await connectionStatus.waitFor(s => s === ConnectionStatus.Waiting).promise;
            clock.elapse(2000);
            await connectionStatus.waitFor(s => s === ConnectionStatus.Online).promise;
            assert.deepEqual(statuses, [
                ConnectionStatus.Reconnecting,
                ConnectionStatus.Waiting,
                ConnectionStatus.Reconnecting,
                ConnectionStatus.Online
            ]);
            assert.strictEqual(reconnector.lastVersionsResponse, 42);
            subscription();
        },
        "test reconnecting with onlineStatus": async assert => {
            const clock = new MockClock();
            const {createMeasure} = clock;
            const onlineStatus = new ObservableValue(false);
            const retryDelay = new ExponentialRetryDelay(clock.createTimeout);
            const reconnector = new Reconnector({retryDelay, onlineStatus, createMeasure});
            const {connectionStatus} = reconnector;
            reconnector.onRequestFailed(createHsApiMock(1));
            await connectionStatus.waitFor(s => s === ConnectionStatus.Waiting).promise;
            onlineStatus.set(true); //skip waiting
            await connectionStatus.waitFor(s => s === ConnectionStatus.Online).promise;
            assert.equal(connectionStatus.get(), ConnectionStatus.Online);
            assert.strictEqual(reconnector.lastVersionsResponse, 42);
        },
    }
}