NativeMessagingProxy

This is a simple proxy that sends messages received and sent by both parties through a proxy, allowing meddling ability for debugging and reverse-engineering.

So far only HTTP proxy and SOCKS5 proxies are supported.

Features

Sends messages through a proxy
Supports injection of messages

Usage

Open the manifest and look for path. In Linux and macOS, manifests can be found in NativeMessagingHosts directory under Chrome/Chromium configs directory (in Linux: /home/USER/.config/chromium/NativeMessagingHosts).
Copy its value and write the config file in your config directory. (default in Linux: /home/USER/.config/nmproxy.cfg):

command: '/home/USER/.bin/myextension_host'
proxy: socks5://127.0.0.1:1080/
log: /home/USER/nmproxy.log

Now change the path in manifest to point to NativeMessagingProxy.
Start a mitmproxy instance on the address that you specified in the config.
Run Chrome/Chromium.

Valid values

command: full path to single executable without args.
proxy: proxy URI with these protocols: socks5, socks5h, http, https. for example: socks5://127.0.0.1:1080
log: file path and stderr.

Custom Config Path

You may specify custom configuration file path through NMPROXY_CONFIG environment variable.

Credits

Code from miku's gist has been used to enable usage of HTTP(S) proxies.

License

MIT