/share?msg=foo endpoint using forward message dialog (#29874)

* basic implementation of an /share?msg=foo endpoint

* SharePayload

* add sharing html & md while we're at it

* remove whitespace from imports to appease linter

* lint

* Add unit test

* More tests

* Test for showScreen

* Use one of the typed strings

* Test nasty tags stripped out

* Add playwright test

* Fix flake

by not relying on the name being synced as soon as we load

---------

Co-authored-by: David Baker <dbkr@users.noreply.github.com>

src/components/structures/MatrixChat.tsx

@@ -13,7 +13,8 @@ import {
     EventType,
     HttpApiEvent,
     type MatrixClient,
-    type MatrixEvent,
+    MatrixEvent,
+    MsgType,
     type RoomType,
     SyncState,
     type SyncStateData,
@@ -24,9 +25,9 @@ import { logger } from "matrix-js-sdk/src/logger";
 import { throttle } from "lodash";
 import { CryptoEvent, type KeyBackupInfo } from "matrix-js-sdk/src/crypto-api";
 import { TooltipProvider } from "@vector-im/compound-web";
-
 // what-input helps improve keyboard accessibility
 import "what-input";
+import sanitizeHtml from "sanitize-html";
 
 import PosthogTrackers from "../../PosthogTrackers";
 import { DecryptionFailureTracker } from "../../DecryptionFailureTracker";
@@ -50,6 +51,7 @@ import ThemeController from "../../settings/controllers/ThemeController";
 import { startAnyRegistrationFlow } from "../../Registration";
 import ResizeNotifier from "../../utils/ResizeNotifier";
 import AutoDiscoveryUtils from "../../utils/AutoDiscoveryUtils";
+import { makeRoomPermalink } from "../../utils/permalinks/Permalinks";
 import ThemeWatcher, { ThemeWatcherEvent } from "../../settings/watchers/ThemeWatcher";
 import { FontWatcher } from "../../settings/watchers/FontWatcher";
 import { storeRoomAliasInCache } from "../../RoomAliasCache";
@@ -94,7 +96,6 @@ import VerificationRequestToast from "../views/toasts/VerificationRequestToast";
 import PerformanceMonitor, { PerformanceEntryNames } from "../../performance";
 import UIStore, { UI_EVENTS } from "../../stores/UIStore";
 import SoftLogout from "./auth/SoftLogout";
-import { makeRoomPermalink } from "../../utils/permalinks/Permalinks";
 import { copyPlaintext } from "../../utils/strings";
 import { PosthogAnalytics } from "../../PosthogAnalytics";
 import { initSentry } from "../../sentry";
@@ -124,7 +125,7 @@ import { viewUserDeviceSettings } from "../../actions/handlers/viewUserDeviceSet
 import GenericToast from "../views/toasts/GenericToast";
 import RovingSpotlightDialog from "../views/dialogs/spotlight/SpotlightDialog";
 import { findDMForUser } from "../../utils/dm/findDMForUser";
-import { Linkify } from "../../HtmlUtils";
+import { getHtmlText, Linkify } from "../../HtmlUtils";
 import { NotificationLevel } from "../../stores/notifications/NotificationLevel";
 import { type UserTab } from "../views/dialogs/UserTab";
 import { shouldSkipSetupEncryption } from "../../utils/crypto/shouldSkipSetupEncryption";
@@ -136,6 +137,10 @@ import { LoginSplashView } from "./auth/LoginSplashView";
 import { cleanUpDraftsIfRequired } from "../../DraftCleaner";
 import { InitialCryptoSetupStore } from "../../stores/InitialCryptoSetupStore";
 import { setTheme } from "../../theme";
+import { type OpenForwardDialogPayload } from "../../dispatcher/payloads/OpenForwardDialogPayload";
+import { ShareFormat, type SharePayload } from "../../dispatcher/payloads/SharePayload";
+import Markdown from "../../Markdown";
+import { sanitizeHtmlParams } from "../../Linkify";
 
 // legacy export
 export { default as Views } from "../../Views";
@@ -780,6 +785,9 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             case Action.ViewHomePage:
                 this.viewHome(payload.justRegistered);
                 break;
+            case Action.Share:
+                this.viewShare(payload.format, payload.msg);
+                break;
             case Action.ViewStartChatOrReuse:
                 this.chatCreateOrReuse(payload.user_id);
                 break;
@@ -1115,6 +1123,58 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         });
     }
 
+    private viewShare(format: ShareFormat, msg: string): void {
+        // Wait for the first sync so we can present possible rooms to share into
+        this.firstSyncPromise.promise.then(() => {
+            this.notifyNewScreen("share");
+            let rawEvent;
+            switch (format) {
+                case ShareFormat.Html: {
+                    rawEvent = {
+                        type: "m.room.message",
+                        content: {
+                            msgtype: MsgType.Text,
+                            body: getHtmlText(msg),
+                            format: "org.matrix.custom.html",
+                            formatted_body: sanitizeHtml(msg, sanitizeHtmlParams),
+                        },
+                        origin_server_ts: Date.now(),
+                    };
+                    break;
+                }
+                case ShareFormat.Markdown: {
+                    const html = new Markdown(msg).toHTML({ externalLinks: true });
+                    rawEvent = {
+                        type: "m.room.message",
+                        content: {
+                            msgtype: MsgType.Text,
+                            body: msg,
+                            format: "org.matrix.custom.html",
+                            formatted_body: html,
+                        },
+                        origin_server_ts: Date.now(),
+                    };
+                    break;
+                }
+                default:
+                    rawEvent = {
+                        type: "m.room.message",
+                        content: {
+                            msgtype: MsgType.Text,
+                            body: msg,
+                        },
+                        origin_server_ts: Date.now(),
+                    };
+            }
+            const event = new MatrixEvent(rawEvent);
+            dis.dispatch<OpenForwardDialogPayload>({
+                action: Action.OpenForwardDialog,
+                event: event,
+                permalinkCreator: null,
+            });
+        });
+    }
+
     private async createRoom(defaultPublic = false, defaultName?: string, type?: RoomType): Promise<void> {
         const modal = Modal.createDialog(CreateRoomDialog, {
             type,
@@ -1742,6 +1802,20 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
             dis.dispatch({
                 action: Action.CreateChat,
             });
+        } else if (screen === "share") {
+            if (params && params["msg"] !== undefined) {
+                dis.dispatch<SharePayload>({
+                    action: Action.Share,
+                    msg: params["msg"],
+                    format: params["format"],
+                });
+            }
+            // if we weren't already coming at this from an existing screen
+            // and we're logged in, then explicitly default to home.
+            // if we're not logged in, then the login flow will do the right thing.
+            if (!this.state.currentRoomId && !this.state.currentUserId) {
+                this.viewHome();
+            }
         } else if (screen === "settings") {
             dis.fire(Action.ViewUserSettings);
         } else if (screen === "welcome") {

src/dispatcher/actions.ts

@@ -26,6 +26,11 @@ export enum Action {
      */
     ViewUser = "view_user",
 
+    /**
+     * Share a text message by forwarding it to a room selected by the user
+     */
+    Share = "share",
+
     /**
      * Open the user settings. No additional payload information required.
      * Optionally can include an OpenToTabPayload.

src/dispatcher/payloads/SharePayload.ts

@@ -0,0 +1,29 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+import { type ActionPayload } from "../payloads";
+import { type Action } from "../actions";
+
+export enum ShareFormat {
+    Text = "text",
+    Html = "html",
+    Markdown = "md",
+}
+
+export interface SharePayload extends ActionPayload {
+    action: Action.Share;
+
+    /**
+     * The format of message to be shared (optional)
+     */
+    format: ShareFormat;
+
+    /**
+     * The message to be shared.
+     */
+    msg: string;
+}