# Custom Protocol Scheme association

Custom Protocols feature allows you to associate specific custom protocol with your app so that when users open links with this protocol,
your app is launched to handle them. This can be particularly useful to connect your desktop app with your web app.
In this guide, we'll walk through the steps to implement custom protocols in Wails app.

## Set Up Custom Protocol Schemes Association:

To set up custom protocol, you need to modify your application's wails.json file.
In "info" section add a "protocols" section specifying the protocols your app should be associated with.

For example:

```json
{
  "info": {
    "protocols": [
      {
        "scheme": "myapp",
        "description": "My App Protocol",
        "role": "Editor"
      }
    ]
  }
}
```

| Property    | Description                                                                           |
| :---------- | :------------------------------------------------------------------------------------ |
| scheme      | Custom Protocol scheme. e.g. myapp                                                    |
| description | Windows-only. The description.                                                        |
| role        | macOS-only. The app’s role with respect to the type. Corresponds to CFBundleTypeRole. |

## Platform Specifics:

### macOS

When you open custom protocol with your app, the system will launch your app and call the `OnUrlOpen` function in your Wails app. Example:

```go title="main.go"
func main() {
	// Create application with options
	err := wails.Run(&options.App{
		Title:  "wails-open-file",
		Width:  1024,
		Height: 768,
		AssetServer: &assetserver.Options{
			Assets: assets,
		},
		BackgroundColour: &options.RGBA{R: 27, G: 38, B: 54, A: 1},
		Mac: &mac.Options{
			OnUrlOpen: func(url string) { println(url) },
		},
		Bind: []interface{}{
			app,
		},
	})

	if err != nil {
		println("Error:", err.Error())
	}
}
```

### Windows

On Windows Custom Protocol Schemes is supported only with NSIS installer. During installation, the installer will create a
registry entry for your schemes. When you open url with your app, new instance of app is launched and url is passed
as argument to your app. To handle this you should parse command line arguments in your app. Example:

```go title="main.go"
func main() {
	argsWithoutProg := os.Args[1:]

	if len(argsWithoutProg) != 0 {
    println("launchArgs", argsWithoutProg)
  }
}
```

You also can enable single instance lock for your app. In this case, when you open url with your app, new instance of app is not launched
and arguments are passed to already running instance. Check single instance lock guide for details. Example:

```go title="main.go"
func main() {
	// Create application with options
	err := wails.Run(&options.App{
		Title:  "wails-open-file",
		Width:  1024,
		Height: 768,
		AssetServer: &assetserver.Options{
			Assets: assets,
		},
		BackgroundColour: &options.RGBA{R: 27, G: 38, B: 54, A: 1},
		SingleInstanceLock: &options.SingleInstanceLock{
			UniqueId:               "e3984e08-28dc-4e3d-b70a-45e961589cdc",
			OnSecondInstanceLaunch: app.onSecondInstanceLaunch,
		},
		Bind: []interface{}{
			app,
		},
	})
}
```

### Linux

Currently, Wails doesn't support bundling for Linux. So, you need to create file associations manually.
For example if you distribute your app as a .deb package, you can create file associations by adding required files in you bundle.
You can use [nfpm](https://nfpm.goreleaser.com/) to create .deb package for your app.

1. Create a .desktop file for your app and specify file associations there (note that `%u` is important in Exec). Example:

```ini
[Desktop Entry]
Categories=Office
Exec=/usr/bin/wails-open-file %u
Icon=wails-open-file.png
Name=wails-open-file
Terminal=false
Type=Application
MimeType=x-scheme-handler/myapp;
```

2. Prepare postInstall/postRemove scripts for your package. Example:

```sh
# reload desktop database to load app in list of available
update-desktop-database /usr/share/applications
```

3. Configure nfpm to use your scripts and files. Example:

```yaml
name: "wails-open-file"
arch: "arm64"
platform: "linux"
version: "1.0.0"
section: "default"
priority: "extra"
maintainer: "FooBarCorp <FooBarCorp@gmail.com>"
description: "Sample Package"
vendor: "FooBarCorp"
homepage: "http://example.com"
license: "MIT"
contents:
- src: ../bin/wails-open-file
  dst: /usr/bin/wails-open-file
- src: ./main.desktop
  dst: /usr/share/applications/wails-open-file.desktop
- src: ../appicon.svg
  dst: /usr/share/icons/hicolor/scalable/apps/wails-open-file.svg
# copy icons to Yaru theme as well. For some reason Ubuntu didn't pick up fileicons from hicolor theme
- src: ../appicon.svg
  dst: /usr/share/icons/Yaru/scalable/apps/wails-open-file.svg
scripts:
  postinstall: ./postInstall.sh
  postremove: ./postRemove.sh
```

6. Build your .deb package using nfpm:

```sh
nfpm pkg --packager deb --target .
```

7. Now when your package is installed, your app will be associated with custom protocol scheme. When you open url with your app,
   new instance of app is launched and file path is passed as argument to your app.
   To handle this you should parse command line arguments in your app. Example:

```go title="main.go"
func main() {
	argsWithoutProg := os.Args[1:]

	if len(argsWithoutProg) != 0 {
    println("launchArgs", argsWithoutProg)
  }
}
```

You also can enable single instance lock for your app. In this case, when you open url with your app, new instance of app is not launched
and arguments are passed to already running instance. Check single instance lock guide for details. Example:

```go title="main.go"
func main() {
	// Create application with options
	err := wails.Run(&options.App{
		Title:  "wails-open-file",
		Width:  1024,
		Height: 768,
		AssetServer: &assetserver.Options{
			Assets: assets,
		},
		BackgroundColour: &options.RGBA{R: 27, G: 38, B: 54, A: 1},
		SingleInstanceLock: &options.SingleInstanceLock{
			UniqueId:               "e3984e08-28dc-4e3d-b70a-45e961589cdc",
			OnSecondInstanceLaunch: app.onSecondInstanceLaunch,
		},
		Bind: []interface{}{
			app,
		},
	})
}
```
