element-web/src/WidgetMessaging.js

/*
Copyright 2017 New Vector Ltd

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

/*
Listens for incoming postMessage requests from embedded widgets. The following API is exposed:
{
    api: "widget",
    action: "content_loaded",
    widgetId: $WIDGET_ID,
    data: {}
    // additional request fields
}

The complete request object is returned to the caller with an additional "response" key like so:
{
    api: "widget",
    action: "content_loaded",
    widgetId: $WIDGET_ID,
    data: {},
    // additional request fields
    response: { ... }
}

The "api" field is required to use this API, and must be set to "widget" in all requests.

The "action" determines the format of the request and response. All actions can return an error response.

Additional data can be sent as additional, abritrary fields. However, typically the data object should be used.

A success response is an object with zero or more keys.

An error response is a "response" object which consists of a sole "error" key to indicate an error.
They look like:
{
    error: {
        message: "Unable to invite user into room.",
        _error: <Original Error Object>
    }
}
The "message" key should be a human-friendly string.

INBOUND ACTIONS
===============
** All actions must include an "api" field with value of "widget".**
All actions can return an error response instead of the response outlined below.

content_loaded
--------------
Indicates that widget contet has fully loaded

Request:
 - widgetId is the unique ID of the widget instance in riot / matrix state.
 - No additional fields.
Response:
{
    success: "true"
}
Example:
{
    api: "widget",
    action: "content_loaded",
    widgetId: $WIDGET_ID
}


api_version
-----------
Get the current version of the widget postMessage API

Request:
 - No additional fields.
Response:
{
    api_version: "0.0.1"
}
Example:
{
    api: "widget",
    action: "api_version",
}

supported_api_versions
----------------------
Get versions of the widget postMessage API that are currently supported

Request:
 - No additional fields.
Response:
{
    api: "widget"
    supported_versions: ["0.0.1"]
}
Example:
{
    api: "widget",
    action: "supported_api_versions",
}


OUTBOUND ACTIONS
================

In addition to listening for inbound requests, the API can be used to initiate
actions in the widget iframe, and request data from the widget instance.

Outbound actions use the "widget_client" API key / name, which must be included
on all requests.

{
    api: "widget_client",
    action: "screenshot",
    widgetId: $WIDGET_ID,
    data: {}
    // additional request fields
}


screenshot
----------

Request a screenshot from the widget (if supported).
This can currently only be supported by widgets that have access to all of their DOM tree.
For example, widgets that nest further levels of iframes can not support this.

The screenshot is returned as a Blob object.

Request:
 - No additional fields.
Response:
{
    screenshot: {<Blob>data...}
}
Example:
{
    api: "widget_client",
    action: "screenshot",
    widgetId: $WIDGET_ID
}

*/

import URL from 'url';
import dis from './dispatcher';
import MatrixPostMessageApi from './MatrixPostMessageApi';
import Promise from 'bluebird';

const WIDGET_API_VERSION = '0.0.1'; // Current API version
const SUPPORTED_WIDGET_API_VERSIONS = [
    '0.0.1',
];

if (!global.mxWidgetMessagingListenerCount) {
    global.mxWidgetMessagingListenerCount = 0;
}
if (!global.mxWidgetMessagingMessageEndpoints) {
    global.mxWidgetMessagingMessageEndpoints = [];
}

export default class WidgetMessaging extends MatrixPostMessageApi {
    constructor(targetWindow) {
        super(targetWindow);
    }

    exec(action) {
        return super.exec(action).then((data) => {
            // check for errors and reject if found
            if (data.response === undefined) { // null is valid
                throw new Error("Missing 'response' field");
            }
            if (data.response && data.response.error) {
                const err = data.response.error;
                const msg = String(err.message ? err.message : "An error was returned");
                if (err._error) {
                    console.error(err._error);
                }
                // Potential XSS attack if 'msg' is not appropriately sanitized,
                // as it is untrusted input by our parent window (which we assume is Riot).
                // We can't aggressively sanitize [A-z0-9] since it might be a translation.
                throw new Error(msg);
            }
            // return the response field for the request
            return data.response;
        });
    }

    /**
     * Register widget message event listeners
     */
    startListening() {
        this.start();
        if (global.mxWidgetMessagingListenerCount === 0) {
            window.addEventListener("message", () => this.onMessage, false);
        }
        global.mxWidgetMessagingListenerCount += 1;
    }

    /**
     * De-register widget message event listeners
     */
    stopListening() {
        this.stop();
        global.mxWidgetMessagingListenerCount -= 1;
        if (global.mxWidgetMessagingListenerCount === 0) {
            window.removeEventListener("message", () => this.onMessage);
        }
        if (global.mxWidgetMessagingListenerCount < 0) {
            // Make an error so we get a stack trace
            const e = new Error(
                "WidgetMessaging: mismatched startListening / stopListening detected." +
                " Negative count",
            );
            console.error(e);
        }
    }

    /**
     * Register a widget endpoint for trusted postMessage communication
     * @param {string} widgetId    Unique widget identifier
     * @param {string} endpointUrl Widget wurl origin (protocol + (optional port) + host)
     */
    addEndpoint(widgetId, endpointUrl) {
        const u = URL.parse(endpointUrl);
        if (!u || !u.protocol || !u.host) {
            console.warn("Invalid origin:", endpointUrl);
            return;
        }

        const origin = u.protocol + '//' + u.host;
        const endpoint = new WidgetMessageEndpoint(widgetId, origin);
        if (global.mxWidgetMessagingMessageEndpoints) {
            if (global.mxWidgetMessagingMessageEndpoints.some(function(ep) {
                return (ep.widgetId === widgetId && ep.endpointUrl === endpointUrl);
            })) {
                // Message endpoint already registered
                console.warn("Endpoint already registered");
                return;
            }
            global.mxWidgetMessagingMessageEndpoints.push(endpoint);
        }
    }

    /**
     * De-register a widget endpoint from trusted communication sources
     * @param  {string} widgetId Unique widget identifier
     * @param  {string} endpointUrl Widget wurl origin (protocol + (optional port) + host)
     * @return {boolean} True if endpoint was successfully removed
     */
    removeEndpoint(widgetId, endpointUrl) {
        const u = URL.parse(endpointUrl);
        if (!u || !u.protocol || !u.host) {
            console.warn("Invalid origin");
            return;
        }

        const origin = u.protocol + '//' + u.host;
        if (global.mxWidgetMessagingMessageEndpoints && global.mxWidgetMessagingMessageEndpoints.length > 0) {
            const length = global.mxWidgetMessagingMessageEndpoints.length;
            global.mxWidgetMessagingMessageEndpoints = global.mxWidgetMessagingMessageEndpoints.
                filter(function(endpoint) {
                return (endpoint.widgetId != widgetId || endpoint.endpointUrl != origin);
            });
            return (length > global.mxWidgetMessagingMessageEndpoints.length);
        }
        return false;
    }


    /**
     * Handle widget postMessage events
     * @param  {Event} event Event to handle
     * @return {undefined}
     */
    onMessage(event) {
        if (!event.origin) { // Handle chrome
            event.origin = event.originalEvent.origin;
        }

        // Event origin is empty string if undefined
        if (
            event.origin.length === 0 ||
            !this.trustedEndpoint(event.origin) ||
            event.data.api !== "widget" ||
            !event.data.widgetId
        ) {
            return; // don't log this - debugging APIs like to spam postMessage which floods the log otherwise
        }

        const action = event.data.action;
        const widgetId = event.data.widgetId;
        if (action === 'content_loaded') {
            dis.dispatch({
                action: 'widget_content_loaded',
                widgetId: widgetId,
            });
            this.sendResponse(event, {success: true});
        } else if (action === 'supported_api_versions') {
            this.sendResponse(event, {
                api: "widget",
                supported_versions: SUPPORTED_WIDGET_API_VERSIONS,
            });
        } else if (action === 'api_version') {
            this.sendResponse(event, {
                api: "widget",
                version: WIDGET_API_VERSION,
            });
        } else {
            console.warn("Widget postMessage event unhandled");
            this.sendError(event, {message: "The postMessage was unhandled"});
        }
    }

    /**
     * Check if message origin is registered as trusted
     * @param  {string} origin PostMessage origin to check
     * @return {boolean}       True if trusted
     */
    trustedEndpoint(origin) {
        if (!origin) {
            return false;
        }

        return global.mxWidgetMessagingMessageEndpoints.some((endpoint) => {
            return endpoint.endpointUrl === origin;
        });
    }

    /**
     * Send a postmessage response to a postMessage request
     * @param  {Event} event  The original postMessage request event
     * @param  {Object} res   Response data
     */
    sendResponse(event, res) {
        const data = JSON.parse(JSON.stringify(event.data));
        data.response = res;
        event.source.postMessage(data, event.origin);
    }

    /**
     * Send an error response to a postMessage request
     * @param  {Event} event        The original postMessage request event
     * @param  {string} msg         Error message
     * @param  {Error} nestedError  Nested error event (optional)
     */
    sendError(event, msg, nestedError) {
        console.error("Action:" + event.data.action + " failed with message: " + msg);
        const data = JSON.parse(JSON.stringify(event.data));
        data.response = {
            error: {
                message: msg,
            },
        };
        if (nestedError) {
            data.response.error._error = nestedError;
        }
        event.source.postMessage(data, event.origin);
    }

    /**
     * Request a screenshot from a widget
     * @return {Promise} To be resolved when screenshot has been generated
     */
    getScreenshot() {
        return new Promise((resolve, reject) => {
            this.exec({
                api: "widget_client",
                action: "screenshot",
            }).then(function(response) {
                // console.warn("got screenshot", response.screenshot);
                resolve(response.screenshot);
            }).catch((error) => {
                reject(Error("Failed to get screenshot: " + error.message));
            });
        });
    }

    getCapabilities() {
        return new Promise((resolve, reject) => {
            this.exec({
                api: "widget_client",
                action: "capabilities",
            }).then(function(response) {
                // console.warn("got capabilities", response.capabilities);
                resolve(response.capabilities);
            }).catch((error) => {
                reject(Error("Failed to get capabilities: " + error.message));
            });
        });
    }
}


/**
 * Represents mapping of widget instance to URLs for trusted postMessage communication.
 */
class WidgetMessageEndpoint {
    /**
     * Mapping of widget instance to URL for trusted postMessage communication.
     * @param  {string} widgetId    Unique widget identifier
     * @param  {string} endpointUrl Widget wurl origin.
     */
    constructor(widgetId, endpointUrl) {
        if (!widgetId) {
            throw new Error("No widgetId specified in widgetMessageEndpoint constructor");
        }
        if (!endpointUrl) {
            throw new Error("No endpoint specified in widgetMessageEndpoint constructor");
        }
        this.widgetId = widgetId;
        this.endpointUrl = endpointUrl;
    }
}