blap/src/MatrixPostMessageApi.js

import Promise from "bluebird";


function defer() {
    let resolve, reject;
    let isPending = true;
    let promise = new Promise(function(...args) {
        resolve = args[0];
        reject = args[1];
    });
    return {
        resolve: function(...args) {
            if (!isPending) {
                return;
            }
            isPending = false;
            resolve(args[0]);
        },
        reject: function(...args) {
            if (!isPending) {
                return;
            }
            isPending = false;
            reject(args[0]);
        },
        isPending: function() {
            return isPending;
        },
        promise: promise,
    };
}

// NOTE: PostMessageApi only handles message events with a data payload with a
// response field
export default class PostMessageApi {
    constructor(targetWindow, timeoutMs) {
        this._window = targetWindow || window.parent; // default to parent window
        this._timeoutMs = timeoutMs || 5000; // default to 5s timer
        this._counter = 0;
        this._pending = {
            // $ID: Deferred
        };
    }

    start() {
        addEventListener('message', this.getOnMessageCallback());
    }

    stop() {
        removeEventListener('message', this.getOnMessageCallback());
    }

    // Somewhat convoluted so we can successfully capture the PostMessageApi 'this' instance.
    getOnMessageCallback() {
        if (this._onMsgCallback) {
            return this._onMsgCallback;
        }
        let self = this;
        this._onMsgCallback = function(ev) {
            // THIS IS ALL UNSAFE EXECUTION.
            // We do not verify who the sender of `ev` is!
            let payload = ev.data;
            // NOTE: Workaround for running in a mobile WebView where a
            // postMessage immediately triggers this callback even though it is
            // not the response.
            if (payload.response === undefined) {
                return;
            }
            let deferred = self._pending[payload._id];
            if (!deferred) {
                return;
            }
            if (!deferred.isPending()) {
                return;
            }
            delete self._pending[payload._id];
            deferred.resolve(payload);
        };
        return this._onMsgCallback;
    }

    exec(action, target) {
        this._counter += 1;
        target = target || "*";
        action._id = Date.now() + "-" + Math.random().toString(36) + "-" + this._counter;
        let d = defer();
        this._pending[action._id] = d;
        this._window.postMessage(action, target);

        if (this._timeoutMs > 0) {
            setTimeout(function() {
                if (!d.isPending()) {
                    return;
                }
                console.error("postMessage request timed out. Sent object: " + JSON.stringify(action));
                d.reject(new Error("Timed out"));
            }, this._timeoutMs);
        }
        return d.promise;
    }
}