NIP-55
======

Android Signer Application
--------------------------

`draft` `optional`

This NIP describes a method for 2-way communication between an Android signer and any Nostr client on Android. The Android signer is an Android Application and the client can be a web client or an Android application.

# Usage for Android applications

The Android signer uses Intents and Content Resolvers to communicate between applications.

To be able to use the Android signer in your application you should add this to your AndroidManifest.xml:

```xml
<queries>
  <intent>
    <action android:name="android.intent.action.VIEW" />
    <category android:name="android.intent.category.BROWSABLE" />
    <data android:scheme="nostrsigner" />
  </intent>
</queries>
```

Then you can use this function to check if there's a signer application installed:

```kotlin
fun isExternalSignerInstalled(context: Context): Boolean {
  val intent =
    Intent().apply {
      action = Intent.ACTION_VIEW
      data = Uri.parse("nostrsigner:")
    }
  val infos = context.packageManager.queryIntentActivities(intent, 0)
  return infos.size > 0
}
```

## Using Intents

To get the result back from the Signer Application you should use `registerForActivityResult` or `rememberLauncherForActivityResult` in Kotlin. If you are using another framework check the documentation of your framework or a third party library to get the result.

```kotlin
val launcher = rememberLauncherForActivityResult(
    contract = ActivityResultContracts.StartActivityForResult(),
    onResult = { result ->
        if (result.resultCode != Activity.RESULT_OK) {
            Toast.makeText(
                context,
                "Sign request rejected",
                Toast.LENGTH_SHORT
            ).show()
        } else {
            val signature = activityResult.data?.getStringExtra("signature")
            // Do something with signature ...
        }
    }
)
```

Create the Intent using the **nostrsigner** scheme:

```kotlin
val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$content"))
```

Set the Signer package name:

```kotlin
intent.`package` = "com.example.signer"
```

Send the Intent:

```kotlin
launcher.launch(intent)
```

### Methods

- **get_public_key**
  - params:

    ```kotlin
    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:"))
    intent.`package` = "com.example.signer"
    intent.putExtra("type", "get_public_key")
    // You can send some default permissions for the user to authorize for ever
    val permissions = listOf(
      Permission(
          type = "sign_event",
          kind = 22242
      ),
      Permission(
          type = "nip44_decrypt"
      )
    )
    intent.putExtra("permissions", permissions.toJson())
    context.startActivity(intent)
    ```
  - result:
    - If the user approved intent it will return the **npub** in the signature field

      ```kotlin
      val npub = intent.data?.getStringExtra("signature")
      // The package name of the signer application
      val packageName = intent.data?.getStringExtra("package")
      ```

- **sign_event**
  - params:

    ```kotlin
    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$eventJson"))
    intent.`package` = "com.example.signer"
    intent.putExtra("type", "sign_event")
    // To handle results when not waiting between intents
    intent.putExtra("id", event.id)
    // Send the current logged in user npub
    intent.putExtra("current_user", npub)

    context.startActivity(intent)
    ```
  - result:
    - If the user approved intent it will return the **signature**, **id** and **event** fields

      ```kotlin
      val signature = intent.data?.getStringExtra("signature")
      // The id you sent
      val id = intent.data?.getStringExtra("id")
      val signedEventJson = intent.data?.getStringExtra("event")
      ```

- **nip04_encrypt**
  - params:

    ```kotlin
    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$plaintext"))
    intent.`package` = "com.example.signer"
    intent.putExtra("type", "nip04_encrypt")
    // to control the result in your application in case you are not waiting the result before sending another intent
    intent.putExtra("id", "some_id")
    // Send the current logged in user npub
    intent.putExtra("current_user", account.keyPair.pubKey.toNpub())
    // Send the hex pubKey that will be used for encrypting the data
    intent.putExtra("pubKey", pubKey)

    context.startActivity(intent)
    ```
  - result:
    - If the user approved intent it will return the **signature** and **id** fields

      ```kotlin
      val encryptedText = intent.data?.getStringExtra("signature")
      // the id you sent
      val id = intent.data?.getStringExtra("id")
      ```

- **nip44_encrypt**
  - params:

    ```kotlin
    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$plaintext"))
    intent.`package` = "com.example.signer"
    intent.putExtra("type", "nip44_encrypt")
    // to control the result in your application in case you are not waiting the result before sending another intent
    intent.putExtra("id", "some_id")
    // Send the current logged in user npub
    intent.putExtra("current_user", account.keyPair.pubKey.toNpub())
    // Send the hex pubKey that will be used for encrypting the data
    intent.putExtra("pubKey", pubKey)

    context.startActivity(intent)
    ```
  - result:
    - If the user approved intent it will return the **signature** and **id** fields

      ```kotlin
      val encryptedText = intent.data?.getStringExtra("signature")
      // the id you sent
      val id = intent.data?.getStringExtra("id")
      ```

- **nip04_decrypt**
  - params:

    ```kotlin
    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$encryptedText"))
    intent.`package` = "com.example.signer"
    intent.putExtra("type", "nip04_decrypt")
    // to control the result in your application in case you are not waiting the result before sending another intent
    intent.putExtra("id", "some_id")
    // Send the current logged in user npub
    intent.putExtra("current_user", account.keyPair.pubKey.toNpub())
    // Send the hex pubKey that will be used for decrypting the data
    intent.putExtra("pubKey", pubKey)

    context.startActivity(intent)
    ```
  - result:
    - If the user approved intent it will return the **signature** and **id** fields

      ```kotlin
      val plainText = intent.data?.getStringExtra("signature")
      // the id you sent
      val id = intent.data?.getStringExtra("id")
      ```

- **nip44_decrypt**
  - params:

    ```kotlin
    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$encryptedText"))
    intent.`package` = "com.example.signer"
    intent.putExtra("type", "nip04_decrypt")
    // to control the result in your application in case you are not waiting the result before sending another intent
    intent.putExtra("id", "some_id")
    // Send the current logged in user npub
    intent.putExtra("current_user", account.keyPair.pubKey.toNpub())
    // Send the hex pubKey that will be used for decrypting the data
    intent.putExtra("pubKey", pubKey)

    context.startActivity(intent)
    ```
  - result:
    - If the user approved intent it will return the **signature** and **id** fields

      ```kotlin
      val plainText = intent.data?.getStringExtra("signature")
      // the id you sent
      val id = intent.data?.getStringExtra("id")
      ```

- **decrypt_zap_event**
  - params:

    ```kotlin
    val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$eventJson"))
    intent.`package` = "com.example.signer"
    intent.putExtra("type", "decrypt_zap_event")
    // to control the result in your application in case you are not waiting the result before sending another intent
    intent.putExtra("id", "some_id")
    // Send the current logged in user npub
    intent.putExtra("current_user", account.keyPair.pubKey.toNpub())
    context.startActivity(intent)
    ```
  - result:
    - If the user approved intent it will return the **signature** and **id** fields

      ```kotlin
      val eventJson = intent.data?.getStringExtra("signature")
      // the id you sent
      val id = intent.data?.getStringExtra("id")
      ```

## Using Content Resolver

To get the result back from Signer Application you should use contentResolver.query in Kotlin. If you are using another framework check the documentation of your framework or a third party library to get the result.

If the user did not check the "remember my choice" option, the npub is not in Signer Application or the signer type is not recognized the `contentResolver` will return null

For the SIGN_EVENT type Signer Application returns two columns "signature" and "event". The column event is the signed event json

For the other types Signer Application returns the column "signature"

If the user chose to always reject the event, signer application will return the column "rejected" and you should not open signer application

### Methods

- **get_public_key**
  - params:

    ```kotlin
    val result = context.contentResolver.query(
        Uri.parse("content://com.example.signer.GET_PUBLIC_KEY"),
        listOf("login"),
        null,
        null,
        null
    )
    ```
  - result:
    - Will return the **npub** in the signature column

      ```kotlin
        if (result == null) return

        if (result.moveToFirst()) {
            val index = it.getColumnIndex("signature")
            if (index < 0) return
            val npub = it.getString(index)
        }
      ```

- **sign_event**
  - params:

    ```kotlin
    val result = context.contentResolver.query(
        Uri.parse("content://com.example.signer.SIGN_EVENT"),
        listOf("$eventJson", "", "${logged_in_user_npub}"),
        null,
        null,
        null
    )
    ```
  - result:
    - Will return the **signature** and the **event** columns

      ```kotlin
        if (result == null) return

        if (result.moveToFirst()) {
            val index = it.getColumnIndex("signature")
            val indexJson = it.getColumnIndex("event")
            val signature = it.getString(index)
            val eventJson = it.getString(indexJson)
        }
      ```

- **nip04_encrypt**
  - params:

    ```kotlin
    val result = context.contentResolver.query(
        Uri.parse("content://com.example.signer.NIP04_ENCRYPT"),
        listOf("$plainText", "${hex_pub_key}", "${logged_in_user_npub}"),
        null,
        null,
        null
    )
    ```
  - result:
    - Will return the **signature** column

      ```kotlin
        if (result == null) return

        if (result.moveToFirst()) {
            val index = it.getColumnIndex("signature")
            val encryptedText = it.getString(index)
        }
      ```

- **nip44_encrypt**
  - params:

    ```kotlin
    val result = context.contentResolver.query(
        Uri.parse("content://com.example.signer.NIP44_ENCRYPT"),
        listOf("$plainText", "${hex_pub_key}", "${logged_in_user_npub}"),
        null,
        null,
        null
    )
    ```
  - result:
    - Will return the **signature** column

      ```kotlin
        if (result == null) return

        if (result.moveToFirst()) {
            val index = it.getColumnIndex("signature")
            val encryptedText = it.getString(index)
        }
      ```

- **nip04_decrypt**
  - params:

    ```kotlin
    val result = context.contentResolver.query(
        Uri.parse("content://com.example.signer.NIP04_DECRYPT"),
        listOf("$encryptedText", "${hex_pub_key}", "${logged_in_user_npub}"),
        null,
        null,
        null
    )
    ```
  - result:
    - Will return the **signature** column

      ```kotlin
        if (result == null) return

        if (result.moveToFirst()) {
            val index = it.getColumnIndex("signature")
            val encryptedText = it.getString(index)
        }
      ```

- **nip44_decrypt**
  - params:

    ```kotlin
    val result = context.contentResolver.query(
        Uri.parse("content://com.example.signer.NIP44_DECRYPT"),
        listOf("$encryptedText", "${hex_pub_key}", "${logged_in_user_npub}"),
        null,
        null,
        null
    )
    ```
  - result:
    - Will return the **signature** column

      ```kotlin
        if (result == null) return

        if (result.moveToFirst()) {
            val index = it.getColumnIndex("signature")
            val encryptedText = it.getString(index)
        }
      ```

- **decrypt_zap_event**
  - params:

    ```kotlin
    val result = context.contentResolver.query(
        Uri.parse("content://com.example.signer.DECRYPT_ZAP_EVENT"),
        listOf("$eventJson", "", "${logged_in_user_npub}"),
        null,
        null,
        null
    )
    ```
  - result:
    - Will return the **signature** column

      ```kotlin
        if (result == null) return

        if (result.moveToFirst()) {
            val index = it.getColumnIndex("signature")
            val eventJson = it.getString(index)
        }
      ```

# Usage for Web Applications

Since web applications can't receive a result from the intent, you should add a modal to paste the signature or the event json or create a callback url.

If you send the callback url parameter, Signer Application will send the result to the url.

If you don't send a callback url, Signer Application will copy the result to the clipboard.

You can configure the `returnType` to be **signature** or **event**.

Android intents and browser urls have limitations, so if you are using the `returnType` of **event** consider using the parameter **compressionType=gzip** that will return "Signer1" + Base64 gzip encoded event json

## Methods

- **get_public_key**
  - params:

    ```js
    window.href = `nostrsigner:?compressionType=none&returnType=signature&type=get_public_key&callbackUrl=https://example.com/?event=`;
    ```

- **sign_event**
  - params:

    ```js
    window.href = `nostrsigner:${eventJson}?compressionType=none&returnType=signature&type=sign_event&callbackUrl=https://example.com/?event=`;
    ```

- **nip04_encrypt**
  - params:

    ```js
    window.href = `nostrsigner:${plainText}?pubKey=${hex_pub_key}&compressionType=none&returnType=signature&type=nip04_encrypt&callbackUrl=https://example.com/?event=`;
    ```

- **nip44_encrypt**
  - params:

    ```js
    window.href = `nostrsigner:${plainText}?pubKey=${hex_pub_key}&compressionType=none&returnType=signature&type=nip44_encrypt&callbackUrl=https://example.com/?event=`;
    ```

- **nip04_decrypt**
  - params:

    ```js
    window.href = `nostrsigner:${encryptedText}?pubKey=${hex_pub_key}&compressionType=none&returnType=signature&type=nip04_decrypt&callbackUrl=https://example.com/?event=`;
    ```

- **nip44_decrypt**
  - params:

    ```js
    window.href = `nostrsigner:${encryptedText}?pubKey=${hex_pub_key}&compressionType=none&returnType=signature&type=nip44_decrypt&callbackUrl=https://example.com/?event=`;
    ```

- **decrypt_zap_event**
  - params:

    ```js
    window.href = `nostrsigner:${eventJson}?compressionType=none&returnType=signature&type=decrypt_zap_event&callbackUrl=https://example.com/?event=`;
    ```

## Example

```js
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <h1>Test</h1>

    <script>
        window.onload = function() {
            var url = new URL(window.location.href);
            var params = url.searchParams;
            if (params) {
                var param1 = params.get("event");
                if (param1) alert(param1)
            }
            let json = {
                kind: 1,
                content: "test"
            }
            let encodedJson = encodeURIComponent(JSON.stringify(json))
            var newAnchor = document.createElement("a");
            newAnchor.href = `nostrsigner:${encodedJson}?compressionType=none&returnType=signature&type=sign_event&callbackUrl=https://example.com/?event=`;
            newAnchor.textContent = "Open External Signer";
            document.body.appendChild(newAnchor)
        }
    </script>
</body>
</html>
```