Add article section "Writing the chrome_native_messaging_host.exe app"

microsoft-edge/extensions-chromium/developer-guide/native-messaging.md

@@ -1,16 +1,16 @@
 ---
 title: Native messaging
-description: To communicate with a native Win32 app that's installed on a user's device, an extension uses the message-passing APIs.  The native app host sends and receives messages with extensions using standard input and standard output.
+description: To communicate with a native Win32 app that's installed on a user's device, an extension uses message-passing APIs.  The native app host sends and receives messages with extensions using standard input and standard output.
 author: MSEdgeTeam
 ms.author: msedgedevrel
 ms.topic: conceptual
 ms.service: microsoft-edge
 ms.subservice: extensions
-ms.date: 03/31/2021
+ms.date: 01/09/2024
 ---
 # Native messaging
 
-To communicate with a native Win32 app that's installed on a user's device, an extension uses the message-passing APIs.  The native app host sends and receives messages with extensions using standard input and standard output.
+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](https://developer.chrome.com/docs/extensions/develop/concepts/messaging) 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.
 
@@ -24,7 +24,7 @@ To create your extension to send and receive messages with native app hosts, do
 
 
 <!-- ====================================================================== -->
-## Step 1 - Add permissions to the extension manifest
+## Step 1: Add permissions to the extension manifest
 
 Add the `nativeMessaging` permission to the **manifest.json** file of the extension.
 
@@ -77,7 +77,7 @@ The following is an example **manifest.json** file:
 
 
 <!-- ====================================================================== -->
-## Step 2 - Create your native messaging host manifest file
+## Step 2: 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:
 
@@ -111,7 +111,7 @@ The native messaging host manifest file must be a valid JSON file that contains
 
 | Key | Details |
 | --- | --- |
-| `name` | Specifies the name of the native messaging host.  Clients pass the string to `runtime.connectNative` or `runtime.sendNativeMessage`.<br/>  The value must only contain lowercase alphanumeric characters, underscores, and dots.<br/> The value must not start or end with a dot, and a dot must not be followed by another dot. |
+| `name` | Specifies the name of the native messaging host.  Clients pass the string to `runtime.connectNative` or `runtime.sendNativeMessage`.<br/>  The value must only contain lowercase alphanumeric characters, underscores, and dots.<br/> 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.<br/> On Windows devices, you can use relative paths to the directory that contains the native messaging host manifest file.<br/>  On macOS and Linux, the path must be absolute.<br/>  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`. |
@@ -133,7 +133,7 @@ When you're ready to distribute your extension to users, publish your extension
 
 
 <!-- ====================================================================== -->
-## Step 3 - Copy the native messaging host manifest file to your system
+## Step 3: 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.
 
@@ -197,23 +197,23 @@ HKEY_LOCAL_MACHINE\SOFTWARE\Google\Chrome\NativeMessagingHosts\
 
 #### WOW6432Node registry node
 
-The `HKEY_CURRENT_USER\SOFTWARE\WOW6432Node` registry node is not searched on 64-bit machines, due to the way registry works on them. For more information, see [Registry Keys Affected by Windows Installations That Include Windows on Windows (WOW) Support For Multiple Processor Architectures](/windows/win32/winprog64/shared-registry-keys).
+The `HKEY_CURRENT_USER\SOFTWARE\WOW6432Node` registry node is not searched on 64-bit machines, due to the way the registry works on them. For more information, see [Registry Keys Affected by Windows Installations That Include Windows on Windows (WOW) Support For Multiple Processor Architectures](/windows/win32/winprog64/shared-registry-keys).
 
 #### Extension IDs required for both stores
 
-If you have extensions on the Microsoft Edge Add-ons and the Chrome Webstore, you must add the extension IDs corresponding to both the stores in the `allowed_origins` of the native messaging host manifest file.  This is required because only the native messaging host manifest file that corresponds to the first registry location found is read.
+If you have extensions on the Microsoft Edge Add-ons and the Chrome Web Store, you must add the extension IDs corresponding to both the stores in the `allowed_origins` of the native messaging host manifest file.  This is required because only the native messaging host manifest file that corresponds to the first registry location found is read.
 
 ##### [macOS](#tab/macos/)
 
 To store the native messaging host manifest file:
 
-*  System-wide native messaging hosts, which are available to all users, are stored in a fixed location.  For example, the native messaging host manifest file must be stored in following location:
+*  System-wide native messaging hosts, which are available to all users, are stored in a fixed location.  For example, the native messaging host manifest file must be stored in the following location:
 
    ```bash
    /Library/Microsoft/Edge/NativeMessagingHosts/com.my_company.my_app.json
    ```
 
-*  User-specific native messaging hosts, which are available to the current user only, are located in the `NativeMessagingHosts` subdirectory in the user profile directory.  For example, the native messaging host manifest file must be stored in following location:
+*  User-specific native messaging hosts, which are available to the current user only, are located in the `NativeMessagingHosts` subdirectory in the [user data directory](https://chromium.googlesource.com/chromium/src/+/HEAD/docs/user_data_dir.md).  For example, the native messaging host manifest file must be stored in the following location:
 
    ```bash
    ~/Library/Application Support/Microsoft Edge {Channel_Name}/NativeMessagingHosts/com.my_company.my_app.json
@@ -237,13 +237,131 @@ To store the native messaging host manifest file:
    /etc/opt/edge/native-messaging-hosts
    ```
 
-*  User-specific native messaging hosts, which are available to the current user only, are located in the `NativeMessagingHosts` subdirectory in the user profile directory.  The native messaging host manifest file must be stored in the following location:
+*  User-specific native messaging hosts, which are available to the current user only, are located in the `NativeMessagingHosts` subdirectory in the [user data directory](https://chromium.googlesource.com/chromium/src/+/HEAD/docs/user_data_dir.md).  The native messaging host manifest file must be stored in the following location:
 
    ```bash
    ~/.config/microsoft-edge/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](#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=<decimal handle value>`.  This lets the native messaging host create native UI windows that are correctly parented.  Note that this value will be 0 if the calling context is a service worker.
+
+When a messaging port is created by using [`runtime.connectNative`](https://developer.chrome.com/docs/extensions/reference/runtime/#method-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`](https://developer.chrome.com/docs/extensions/reference/api/runtime#method-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`](https://developer.chrome.com/docs/extensions/reference/api/runtime#method-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`](https://developer.chrome.com/docs/extensions/reference/runtime/#method-connectNative) is used instead of [`runtime.connect`](https://developer.chrome.com/docs/extensions/reference/runtime/#method-connect), and [`runtime.sendNativeMessage`](https://developer.chrome.com/docs/extensions/reference/api/runtime#method-sendNativeMessage) is used instead of [`runtime.sendMessage`](https://developer.chrome.com/docs/extensions/reference/runtime/#method-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](#step-1-add-permissions-to-the-extension-manifest), above.<!-- or [Declare permissions](https://developer.chrome.com/docs/extensions/mv3/declare_permissions) -->
+
+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`](https://developer.chrome.com/docs/extensions/reference/runtime/#type-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:
+
+```js
+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`](https://developer.chrome.com/docs/extensions/reference/api/runtime#method-sendNativeMessage) to send a message to the native application without creating a port; for example:
+
+```js
+chrome.runtime.sendNativeMessage(
+  'com.my_company.my_application',
+  {text: 'Hello'},
+  function (response) {
+    console.log('Received ' + response);
+  }
+);
+```
+
+
+<!-- ====================================================================== -->
+## Debugging native messaging
+
+When certain native messaging failures occur, output is written to the error log of Microsoft Edge.  This includes when the native messaging host fails to start, writes to `stderr` or violates the communication protocol.  On
+Linux and macOS, this log can easily be accessed by starting Microsoft Edge from the command line and watching its output in the terminal.  On Windows, use `--enable-logging` as explained at [How to enable logging](https://www.chromium.org/for-testers/enable-logging).
+
+Here are some common errors and tips for solving them:
+
+
+<!-- ------------------------------ -->
+**Failed to start native messaging host.**
+
+Check whether you have sufficient permissions to execute the native messaging host file.
+
+
+<!-- ------------------------------ -->
+**Invalid native messaging host name specified.**
+
+Check whether the name contains invalid characters.  Only lowercase alphanumeric characters, underscores, and dots (periods) are allowed.  A name cannot start or end with a dot, and a dot cannot be followed by another dot.
+
+
+<!-- ------------------------------ -->
+**Native host has exited.**
+
+The pipe to the native messaging host was broken before the message was read by Microsoft Edge.  This is most likely initiated from your native messaging host.
+
+
+<!-- ------------------------------ -->
+**Specified native messaging host not found.**
+
+Check the following:
+
+* Is the name spelled correctly in the extension and in the manifest file?
+
+* Is the manifest in the right directory and with the correct name? See [native messaging host location](#step-3-copy-the-native-messaging-host-manifest-file-to-your-system) for the expected formats.
+
+* Is the manifest file in the correct format?  In particular, is the JSON valid and well-formed, and do the values match the definition of a _native messaging host manifest_, per [Step 2: Create your native messaging host manifest file](#step-2-create-your-native-messaging-host-manifest-file) above?
+
+* Does the file specified in `path` exist? On Windows, paths may be relative, but on macOS and Linux, the paths must be absolute.
+
+
+<!-- ------------------------------ -->
+**Native messaging host _host name_ is not registered. (Windows-only)**
+
+The native messaging host was not found in the Windows registry.  Double-check using `regedit` whether the key was really created and matches the required format as documented at [native messaging host location](#step-3-copy-the-native-messaging-host-manifest-file-to-your-system).
+
+
+<!-- ------------------------------ -->
+**Access to the specified native messaging host is forbidden.**
+
+Is the extension's origin listed in `allowed_origins`?
+
+
+<!-- ------------------------------ -->
+**Error when communicating with the native messaging host.**
+
+This indicates an incorrect implementation of the communication protocol in the native messaging host.
+
+* Make sure that all output in `stdout` adheres to the [native messaging protocol](#native-messaging-protocol).  If you want to print some data for debugging purposes, write to `stderr`.
+
+* Make sure that the 32-bit message length is in the platform's native integer format (little-endian or big-endian).
+
+* The message length must not exceed 1024\*1024.
+
+* The message size must be equal to the number of bytes in the message.  This may differ from the "length" of a string, because characters may be represented by multiple bytes.
+
+* **Windows-only:** Make sure that the program's I/O mode is set to `O_BINARY`.  By default, the I/O mode is `O_TEXT`, which corrupts the message format as line breaks (`\n` = `0A`) are replaced with Windows-style line endings (`\r\n` = `0D 0A`).  The I/O mode can be set by using [`__setmode`](/cpp/c-runtime-library/reference/setmode).
 
 
 <!-- ====================================================================== -->