azon_seeker/webext-bridge/src/content-script.ts

import { createEndpointRuntime } from './internal/endpoint-runtime';
import { usePostMessaging } from './internal/post-message';
import { createStreamWirings } from './internal/stream';
import { createPersistentPort } from './internal/persistent-port';
import type { InternalMessage } from './types';

const win = usePostMessaging('content-script');
const port = createPersistentPort();
const endpointRuntime = createEndpointRuntime('content-script', (message) => {
  if (message.destination.context === 'window') win.postMessage(message);
  else port.postMessage(message);
});

win.onMessage((message: InternalMessage) => {
  endpointRuntime.handleMessage(
    Object.assign({}, message, {
      origin: {
        // a message event inside `content-script` means a script inside `window` dispatched it to be forwarded
        // so we're making sure that the origin is not tampered (i.e script is not masquerading it's true identity)
        context: 'window',
        tabId: null,
      },
    }),
  );
});

port.onMessage(endpointRuntime.handleMessage);

port.onFailure((message) => {
  if (message.origin.context === 'window') {
    win.postMessage({
      type: 'error',
      transactionID: message.transactionId,
    });

    return;
  }

  endpointRuntime.endTransaction(message.transactionId);
});

export function allowWindowMessaging(nsps: string): void {
  win.setNamespace(nsps);
  win.enable();
}

export const { sendMessage, onMessage } = endpointRuntime;
export const { openStream, onOpenStreamChannel } = createStreamWirings(endpointRuntime);