metamask-extension/ui/store/action-queue/index.ts

import pify from 'pify';
import { isManifestV3 } from '../../../shared/modules/mv3.utils';
// // A simplified pify maybe?
// function pify(apiObject) {
//   return Object.keys(apiObject).reduce((promisifiedAPI, key) => {
//     if (apiObject[key].apply) { // depending on our browser support we might use a nicer check for functions here
//       promisifiedAPI[key] = function (...args) {
//         return new Promise((resolve, reject) => {
//           return apiObject[key](
//             ...args,
//             (err, result) => {
//               if (err) {
//                 reject(err);
//               } else {
//                 resolve(result);
//               }
//             },
//           );
//         });
//       };
//     }
//     return promisifiedAPI;
//   }, {});
// }

let background:
  | ({
      connectionStream: { readable: boolean };
      DisconnectError: typeof Error;
    } & Record<string, (...args: any[]) => any>)
  | null = null;
let promisifiedBackground: Record<
  string,
  (...args: any[]) => Promise<any>
> | null = null;

interface BackgroundAction {
  actionId: number;
  request: { method: string; args: any };
  resolve: (result: any) => any;
  reject: (err: Error) => void;
}

const actionRetryQueue: BackgroundAction[] = [];

export const generateActionId = () => Date.now() + Math.random();

function failQueue() {
  actionRetryQueue.forEach(({ reject }) =>
    reject(
      Error('Background operation cancelled while waiting for connection.'),
    ),
  );
}

/**
 * Drops the entire actions queue. Rejects all actions in the queue unless silently==true
 * Does not affect the single action that is currently being processed.
 *
 * @param [silently]
 */
export function dropQueue(silently: boolean): void {
  if (!silently) {
    failQueue();
  }
  actionRetryQueue.length = 0;
}

// add action to queue
const executeActionOrAddToRetryQueue = (item: BackgroundAction): void => {
  if (actionRetryQueue.some((act) => act.actionId === item.actionId)) {
    return;
  }

  if (background?.connectionStream.readable) {
    executeAction({
      action: item,
      disconnectSideeffect: () => actionRetryQueue.push(item),
    });
  } else {
    actionRetryQueue.push(item);
  }
};

/**
 * Promise-style call to background method
 * In MV2: invokes promisifiedBackground method directly.
 * In MV3: action is added to retry queue, along with resolve handler to be executed on completion,
 * the queue is then immediately processed if background connection is available.
 * On completion (successful or error) the action is removed from the retry queue.
 *
 * @param method - name of the background method
 * @param [args] - arguments to that method, if any
 * @param [actionId] - if an action with the === same id is submitted, it'll be ignored if already in queue waiting for a retry.
 * @returns
 */
export function submitRequestToBackground<R>(
  method: string,
  args?: any[],
  actionId = generateActionId(), // current date is not guaranteed to be unique
): Promise<R> {
  if (isManifestV3) {
    return new Promise<R>((resolve, reject) => {
      executeActionOrAddToRetryQueue({
        actionId,
        request: { method, args: args ?? [] },
        resolve,
        reject,
      });
    });
  }
  return promisifiedBackground?.[method](
    ...(args ?? []),
  ) as unknown as Promise<R>;
}

type CallbackMethod<R = unknown> = (error?: unknown, result?: R) => void;

/**
 * [Deprecated] Callback-style call to background method
 * In MV2: invokes promisifiedBackground method directly.
 * In MV3: action is added to retry queue, along with resolve handler to be executed on completion,
 * the queue is then immediately processed if background connection is available.
 * On completion (successful or error) the action is removed from the retry queue.
 *
 * @deprecated Use async `submitRequestToBackground` function instead.
 * @param method - name of the background method
 * @param [args] - arguments to that method, if any
 * @param callback - Node style (error, result) callback for finishing the operation
 * @param [actionId] - if an action with the === same id is submitted, it'll be ignored if already in queue.
 */
export const callBackgroundMethod = <R>(
  method: string,
  args: any[],
  callback: CallbackMethod<R>,
  actionId = generateActionId(), // current date is not guaranteed to be unique
) => {
  if (isManifestV3) {
    const resolve = (value: R) => callback(undefined, value);
    const reject = (err: unknown) => callback(err, undefined);
    executeActionOrAddToRetryQueue({
      actionId,
      request: { method, args: args ?? [] },
      resolve,
      reject,
    });
  } else {
    background?.[method](...args, callback);
  }
};

async function executeAction({
  action,
  disconnectSideeffect,
}: {
  action: BackgroundAction;
  disconnectSideeffect: (action: BackgroundAction) => void;
}) {
  const {
    request: { method, args },
    resolve,
    reject,
  } = action;
  try {
    resolve(await promisifiedBackground?.[method](...args));
  } catch (err: any) {
    if (
      background?.DisconnectError && // necessary to not break compatibility with background stubs or non-default implementations
      err instanceof background.DisconnectError
    ) {
      disconnectSideeffect(action);
    } else {
      reject(err);
    }
  }
}

let processingQueue = false;

// Clears list of pending action in actionRetryQueue
// The results of background calls are wired up to the original promises that's been returned
// The first method on the queue gets called synchronously to make testing and reasoning about
//  a single request to an open connection easier.
async function processActionRetryQueue() {
  if (processingQueue) {
    return;
  }
  processingQueue = true;
  try {
    while (
      background?.connectionStream.readable &&
      actionRetryQueue.length > 0
    ) {
      // If background disconnects and fails the action, the next one will not be taken off the queue.
      // Retrying an action that failed because of connection loss while it was processing is not supported.
      const item = actionRetryQueue.shift();
      await executeAction({
        action: item as BackgroundAction,
        disconnectSideeffect: () =>
          actionRetryQueue.unshift(item as BackgroundAction),
      });
    }
  } catch (e) {
    // error in the queue mechanism itself, the action was malformed
    console.error(e);
  }
  processingQueue = false;
}

/**
 * Sets/replaces the background connection reference
 * Under MV3 it also triggers queue processing if the new background is connected
 *
 * @param backgroundConnection
 */
export async function _setBackgroundConnection(
  backgroundConnection: typeof background,
) {
  background = backgroundConnection;
  promisifiedBackground = pify(background as Record<string, any>);
  if (isManifestV3) {
    if (processingQueue) {
      console.warn(
        '_setBackgroundConnection called while a queue was processing and not disconnected yet',
      );
    }
    // Process all actions collected while connection stream was not available.
    processActionRetryQueue();
  }
}