Native messaging in safari web extension

I am trying to send information about the current page to my native app.

I have nativeMessaging listed as a permission in the manifest.json. When the user clicks a button in the popup.html, popup.js sends a message to content, which sends a message to the background service, which should send a message to the extension. I can see that everything up to the native message is working, but nothing happens at that point.

popup.js

//handle response/error

function notifyContentPage(e) {  
  browser.tabs.query({active: true, currentWindow: true}, function(tabs) {
    if (tabs.length == 0) {
      console.log("could not send mesage to current tab");
    } else {
      console.log("Popup sending get html message");
      const sendingToContent = browser.tabs.sendMessage(tabs[0].id, {type: "get html"});
      sendingToContent.then(handleResponse, handleError);
    }
  });
}

document.getElementById("parse").addEventListener("click", notifyContentPage);

content.js

browser.runtime.onMessage.addListener((request, sender, sendResponse) => {
  if (!sender.tab && request.type == "get html") {
    
    console.log("Content sending save parsed message");
    browser.runtime.sendMessage({ type: "save parsed" }, function(response) {
        console.log(`Content received save parsed response: ${response}`);
    })
  }
  sendResponse("ok");
});

background.js

browser.runtime.onMessage.addListener((request, sender, sendResponse) => {
  
  if (request.type = "save parsed") {
    browser.runtime.sendNativeMessage("application.id", {message: request}, function(response) {
      sendResponse(`Received native message response ${response[0]}`);
    });
  } else {
    sendResponse(`Received unknown request ${request.type}`);
    return true;
  }
});

SafariWebExtensionHandler

import SafariServices
import os.log

let SFExtensionMessageKey = "message"

class SafariWebExtensionHandler: NSObject, NSExtensionRequestHandling {

    func beginRequest(with context: NSExtensionContext) {
      os_log("started processing request")
        let item = context.inputItems[0] as! NSExtensionItem
        let message = item.userInfo?[SFExtensionMessageKey]
        os_log(.default, "Received message from browser.runtime.sendNativeMessage: %@", message as! CVarArg)

        let response = NSExtensionItem()
        response.userInfo = [ SFExtensionMessageKey: [ "Response to": message ] ]

        context.completeRequest(returningItems: [response], completionHandler: nil)
    }

}

manifest.json

{
    "manifest_version": 3,
    "default_locale": "en",

    "name": "__MSG_extension_name__",
    "description": "__MSG_extension_description__",
    "version": "1.0",

    "icons": {
        "48": "images/icon-48.png",
        "96": "images/icon-96.png",
        "128": "images/icon-128.png",
        "256": "images/icon-256.png",
        "512": "images/icon-512.png"
    },

    "background": {
      "service_worker": "background.js"
    },

    "content_scripts": [{
        "js": [ "content.js" ],
        "matches": [ "<all_urls>" ]
    }],

    "action": {
        "default_popup": "popup.html",
        "default_icon": {
            "16": "images/toolbar-icon-16.png",
            "19": "images/toolbar-icon-19.png",
            "32": "images/toolbar-icon-32.png",
            "38": "images/toolbar-icon-38.png",
            "48": "images/toolbar-icon-48.png",
            "72": "images/toolbar-icon-72.png"
        }
    },

    "permissions": [
        "<all_urls>",
        "nativeMessaging",
        "activeTab"
    ]
}

I think I found the answer based on this article by Ben Dodson.

It looks I had a typo in the call the sendNativeMessage, and his article mentions

> One important item to note here is that you must return true when you are responding to a message from the content otherwise the connection is closed instantly (i.e. it will not wait for the native app to respond).

browser.runtime.onMessage.addListener((request, sender, sendResponse) => {
  
  if (request.type = "save parsed") {
    browser.runtime.sendNativeMessage("application.id", **request**, function(response) {
      sendResponse(`Received native message response ${response[0]}`);
    });
    **return true;**
  } else {
    sendResponse(`Received unknown request ${request.type}`);
    **return true;**
  }
});