Native messaging

To communicate with a native Win32 app that's installed on a user's device, an extension uses an API that's similar to the other message passing APIs. The native app host sends and receives messages with extensions using standard input and standard output.

Extensions that use native messaging are installed in Microsoft Edge similar to any other extension. However, native apps aren't installed or managed by Microsoft Edge.

To acquire the extension and native app host, there are two different distribution models:

• Package your extension and the host together. When a user installs the package, both the extension and the host are installed.
• Install your extension from Microsoft Edge Add-ons, and your extension prompts users to install the host.

To create your extension to send and receive messages with native app hosts, do the following steps.

Add permissions to the extension manifest

Add the nativeMessaging permission to the manifest.json file of the extension.

This is the extension manifest file, not the native messaging host manifest file, which is covered in later sections.

{
    "name": "Native Messaging Example",
    "version": "1.0",
    "manifest_version": 3,
    "description": "Send a message to a native app.",
    "app": {
        "launch": {
            "local_path": "main.html"
        }
    },
    "icons": {
        "128": "icon-128.png"
    },
    "permissions": ["nativeMessaging"]
}

Create your native messaging host manifest file

Native apps must provide a native messaging host manifest file. A native messaging host manifest file contains the following information:

The path to the native messaging host runtime.

The method of communication with the extension.

A list of allowed extensions to which it communicates.

The browser reads and validates the native messaging host manifest. The browser doesn't install or manage the native messaging host manifest file.

The native messaging host manifest file is distinct from the Manifest V3 or V2 file that is part of the Microsoft Edge extension.

Example of a native messaging host manifest file:

{
    "name": "com.my_company.my_app",
    "description": "My App",
    "path": "C:\\Program Files\\My App\\chrome_native_messaging_host.exe",
    "type": "stdio",
    "allowed_origins": [
        "chrome-extension://knldjmfmopnpolahpmmgbagdohdnhkik/"
    ]
}

The native messaging host manifest file must be a valid JSON file that contains the following keys:

• name: Specifies the name of the native messaging host. Clients pass the string to runtime.connectNative or runtime.sendNativeMessage. The value must only contain lowercase alphanumeric characters, underscores, and dots. The value must not start or end with a dot (a period), and a dot must not be followed by another dot.
• description: Describes the app.
• path: Specifies the path to the native messaging host binary. On Windows devices, you can use relative paths to the directory that contains the native messaging host manifest file. On macOS and Linux, the path must be absolute. The host process starts with the current directory set to the directory that contains the host binary. For example (Windows), if the parameter is set to C:\App\nm_host.exe, the binary is started using the current directory (C:\App\).
• type: Specifies the type of the interface used to communicate with the native messaging host. The value instructs Microsoft Edge to use stdin and stdout to communicate with the host. The only acceptable value is stdio.
• allowed_origins: Specifies the list of extensions that have access to the native messaging host. To turn on your app to identify and communicate with an extension, in your native messaging host manifest file, set the following value: "allowed_origins": ["chrome-extension://{microsoft_catalog_extension_id}"]

Sideload

Sideload your extension to test native messaging with the host. To sideload your extension during development and retrieve microsoft_catalog_extension_id:

• Go to edge://extensions, and then turn on the Developer mode toggle button.
• Select Load unpacked, and then select your extension package to sideload.
• Click OK.
• Go to the edge://extensions page and verify that your extension is listed.
• Copy the key from microsoft_catalog_extension_id (ID) from the extension listing on the page.

When you're ready to distribute your extension to users, publish your extension at Microsoft Edge Add-ons. The extension ID of the published extension might differ from the ID that's used while sideloading your extension. If the ID changed, update allowed_origins in the native messaging host manifest file with the ID of your published extension.

Copy the native messaging host manifest file to your system

The final step involves copying the native messaging host manifest file to your computer, and making sure that this manifest file is correctly configured. To ensure your native messaging host manifest file is placed in the expected location, do the following steps. The location varies by platform.
The native messaging host manifest file may be located anywhere in the file system. The app installer must create a registry key and set the default value of the key to the full path of the native messaging host manifest file.

The following locations are examples of registry keys:

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Edge\NativeMessagingHosts\com.my_company.my_app
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Edge\NativeMessagingHosts\com.my_company.my_app

To add a registry key to the directory with the manifest key run a command in the command prompt:

REG ADD "HKCU\Software\Microsoft\Edge\NativeMessagingHosts\com.my_company.my_app" /ve /t REG_SZ /d "C:\path\to\nmh-manifest.json" /f

Microsoft Edge queries the HKEY_CURRENT_USER root key, followed by HKEY_LOCAL_MACHINE. In both of the keys, the 32-bit registry is searched first, and then the 64-bit registry is searched to identify native messaging hosts. The registry key specifies the location of the native messaging host manifest file.

If the registry entries for Microsoft Edge don't have the location of the native messaging host manifest file, the Chromium and Chrome registry locations are used as fallback options.

If Microsoft Edge finds the registry key at any of the previously listed locations, it doesn't query the locations that are listed in the following code snippet.

The search order for the registry locations is:

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Edge\NativeMessagingHosts\
HKEY_CURRENT_USER\SOFTWARE\Chromium\NativeMessagingHosts\
HKEY_CURRENT_USER\SOFTWARE\Google\Chrome\NativeMessagingHosts\

HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Edge\NativeMessagingHosts\
HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Chromium\NativeMessagingHosts\
HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Google\Chrome\NativeMessagingHosts\

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Edge\NativeMessagingHosts\
HKEY_LOCAL_MACHINE\SOFTWARE\Chromium\NativeMessagingHosts\
HKEY_LOCAL_MACHINE\SOFTWARE\Google\Chrome\NativeMessagingHosts\

Native messaging protocol

Microsoft Edge 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 Microsoft Edge from misbehaving native applications. The maximum size of the message sent to the native messaging host is 4 GB.

The first argument to the native messaging host is the origin of the caller, usually chrome-extension://[ID of allowed extension]. This allows native messaging hosts to identify the source of the message when multiple extensions are specified in the allowed_origins key in the native messaging host manifest; see Step 2: Create your native messaging host manifest file, above.

On Windows, the native messaging host is also passed a command line argument with a handle to the calling Microsoft Edge native window: --parent-window=. This lets the native messaging host create native UI windows that are correctly parented. This value will be 0 if the calling context is a service worker.

When a messaging port is created by using runtime.connectNative, Microsoft Edge starts a native messaging host process and keeps it running until the port is destroyed. On the other hand, when a message is sent by using runtime.sendNativeMessage, without creating a messaging port, Microsoft Edge starts a new native messaging host process for each message. In that case, the first message that's generated by the host process is handled as a response to the original request, and Microsoft Edge will pass it to the response callback specified when runtime.sendNativeMessage is called. All other messages generated by the native messaging host in that case are ignored.

Connecting to a native application

Sending and receiving messages to and from a native application is very similar to cross-extension messaging. The main difference is that runtime.connectNative is used instead of runtime.connect, and runtime.sendNativeMessage is used instead of runtime.sendMessage.

To use these methods, the nativeMessaging permission must be declared in your extensions's manifest file; see Step 1: Add permissions to the extension manifest, above.

These methods are not available inside content scripts, only inside your extension's pages and service worker. If you want to communicate from a content script to the native application, send the message to your service worker to pass it along to the native application.

The following example creates a runtime.Port object that's connected to native messaging host com.my_company.my_application, starts listening for messages from that port and sends one outgoing message:

var port = chrome.runtime.connectNative('com.my_company.my_application');
port.onMessage.addListener(function (msg) {
  console.log('Received' + msg);
});
port.onDisconnect.addListener(function () {
  console.log('Disconnected');
});
port.postMessage({text: 'Hello, my_application'});
Use runtime.sendNativeMessage to send a message to the native application without creating a port; for example:

chrome.runtime.sendNativeMessage(
  'com.my_company.my_application',
  {text: 'Hello'},
  function (response) {
    console.log('Received ' + response);
  }
);

Ref: https://learn.microsoft.com/en-us/microsoft-edge/extensions/developer-guide/native-messaging