NativeMessagingHosts

• Python
• C
• C++
• QuickJS
• txiki.js
• Node.js
• Deno
• Bun
• WebAssembly/WASI
• Bash

Tested echoing new Array(209715) (1 MB in JSON format) from client to host.

Native messaging documentation

• Chrome Developers
• MDN Web Docs
• Microsoft Edge Developer documentation

Native messaging protocol (Chrome Developers)

Chrome starts each native messaging host in a separate process and communicates with it using standard input (stdin) and standard output (stdout). The same format is used to send messages in both directions; each message is serialized using JSON, UTF-8 encoded and is preceded with 32-bit message length in native byte order. The maximum size of a single message from the native messaging host is 1 MB, mainly to protect Chrome from misbehaving native applications. The maximum size of the message sent to the native messaging host is 4 GB.

Installation and usage

Installation and usage on Chrome and Chromium

1. Navigate to chrome://extensions.
2. Toggle Developer mode.
3. Click Load unpacked.
4. Select native-messaging-quickjs folder.
5. Note the generated extension ID.
6. Open, for example, nm_c_wasm.json in a text editor, set "path" to absolute path of nm_c.wasm and chrome-extension://<ID>/ using ID from 5 in "allowed_origins" array.
7. Copy the nm_c_wasm.json file to Chrome or Chromium configuration folder, e.g., Chromium on *nix ~/.config/chromium/NativeMessagingHosts; Chrome dev channel on *nix ~/.config/google-chrome-unstable/NativeMessagingHosts.
8. Make sure wasmtime for WASM host, or the single host file, e.g. when using QuickJS nm_qjs.js, are executable.
9. To test click service worker link in panel of unpacked extension which is DevTools for background.js in MV3 ServiceWorker, observe echo'ed message from Native Messaging host to client in DevTools console. To disconnect run port.disconnect().

For differences between OS and browser implementations see Chrome incompatibilities. For Firefox or Nightly usage see also Can't get response in Ubuntu #506.

Examples

• Capture system and specific audio output, stream output to browser. capture_system_audio
• Send text or SSML to local eSpeak NG speech synthesis engine, stream output to browser native-messaging-espeak-ng
• Turn local PHP server on and off from browser native-messaging-php, see also deno-server branch in native-messaging-espeak-ng
• WAT embedded in a Bash shell script nm_c_wat.sh (see usage note at 10.)
• Full duplex streaming from and to the browser over HTTP/2 with WHATWG fetch() and Streams (Deno version, Node.js version)
• nm_host.js can be run by node, deno, and bun
• nm_bash_standalone.sh does not use subshells

License

Do What the Fuck You Want to Public License WTFPLv2