Forem: Emile M.

How to send native message via Dart for Browser Extensions (Chrome, Firefox)

Emile M. — Thu, 25 Jul 2024 04:05:34 +0000

When developing an extension for multiple browsers, you may need an application (either local or cloud-based) that can manage or share state & logic across the extensions/browsers. If the local application route is your preferred choice, browsers have a protocol, called Native Messaging Protocol, to communicate with local applications via standard-in and standard-out.

This post explains how to send & receive those native messages in a compiled Dart code host application.

Context

Mozilla's Excellent Docs on Native Messaging

Introduction to Native Message Protocol specifics

Messages are sent as UTF8-encoded JSON preceded by a 32bit unsigned length in native byte order.

stdout.write() encodes the output provided to the write() function which causes issues since the native messaging protocol requires header have length of data sent in bytes.
So stdout.add() (which does not encode during output) needs to be used

data being send should be valid JSON, in order to match native messaging protocol requirements

Sample Code

import 'dart:convert';
import 'dart:io';
import 'dart:typed_data';

/// Send out JSON String native message to browser extension 
static sendNativeMessage(String data) {
  //Convert int to bytes
  Uint8List int32bytes(int value) => Uint8List(4)..buffer.asByteData().setUint32(0, value, Endian.host);

  //Convert data into utf8-encoded bytes
  final encodedData = utf8.encode(data) as Uint8List;

  //Output the encoded data's length as bytes
  stdout.add(int32bytes(encodedData.length));
  //Output the encoded data's bytes
  stdout.add(encodedData);
  stdout.flush();
}

/// Receive Native Message bytes and decode to JSON String
static String receiveNativeMessage(List<int> data) {
  //Get new mutable list from a immutable list
  final dataBytes = List.of(data);

  //Remove the length bytes from bytes list that are part of native messaing protocol spec.
  //(The first 4 hex bytes)
  dataBytes.removeRange(0, 4);

  //Decode from bytes list to JSON string
  return utf8.decode(dataBytes);
}

Fix for Remote Desktop Error code 0x207 on Mac for Ubuntu

Emile M. — Thu, 18 Jul 2024 02:52:17 +0000

If you're like me and were staring at this error popup then allow me to share what worked for me:

Prerequisite

You should've already enabled Remote Login in Ubuntu's/Gnome's settings with a username and password

It doesn't have to be a real user on device, just a username and password for RDP authentication purposes

Steps

You've likely already done this first step but if you haven't

'Add PC' in Microsoft Windows App (previously called Remote Desktop for Mac) with all changes that you'd like.
Export the config to a location of your choosing
Open the RDP config file (that you exported in the previous step) with any text editor
Edit the line that states:

use redirection server name:i:0

to

use redirection server name:i:1

Note: the last 0 has to be changed to a 1

Save file and open the RDP connection from this newly edited/saved file directly (Either by double-clicking or by dragging in the config to Microsoft Windows App)

That's it.

Hope it helped!

gRPC - Unimplemented Error 12

Emile M. — Sun, 23 Jun 2024 21:22:25 +0000

Hello, world!
Just a word of caution to all.

When you are using proto files for gRPC calls be sure that your generated proto files' versions are the same.

I had the great privilege of debugging a gRPC Error Code 12 - Unimplemented for 2 days because my client was using older proto files generated without the "package ____ " line while my server had the newer generated files WITH "package ____" on it.

(You can also get Unimplemented error if your compression and encodings are different between client and server. See here)

Turns out, that insignificant package line makes a difference to your gRPC message path and your client and your server will be talking about 2 different things (even though you think they are the same)

gRPC message path:

With package name:
/{package-name}/{rpc function}

Without package name:
/{rpc function}

Had to dig through the haystack of gRPC calls with Wireshark to even understand what was happening. (See Wireshark documentation here)

If only there had been better error messages or documentation, instead of a cryptic Unimplemented error that doesn't even show anything meaningful on a Google search. Fun!