Usage for Android applications

Amber uses Intents and Content Resolvers to communicate between applications.

To be able to use Amber in your application you should add the following in your AndroidManifest.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 an external signer installed:

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 Amber 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.

Create the Intent using the nostrsigner scheme:

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

Set the Amber package name

intent.`package` = "com.greenart7c3.nostrsigner"

Methods

get_public_key

params:

val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:"))
intent.`package` = "com.greenart7c3.nostrsigner"

// You can send some default permissions for the user authorize for ever
val permissions = listOf(
  Permission(
      "sign_event",
      22242
  ),
  Permission(
      "nip04_encrypt"
  ),
  Permission(
      "nip04_decrypt"
  ),
  Permission(
      "nip44_encrypt"
  ),
  Permission(
      "nip44_decrypt"
  ),
  Permission(
      "decrypt_zap_event"
  ),
)
intent.putExtra("permissions", permissions.toJson())

intent.putExtra("type", "get_public_key")
context.startActivity(intent)

result:

If the user approved intent it will return the npub in the signature field

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

sign_event

params:

val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$eventJson"))
intent.`package` = "com.greenart7c3.nostrsigner"
intent.putExtra("type", "sign_event")
// to control the result in your application in case you are not waiting the result before sending another intent
intent.putExtra("id", event.id)
// Send the current logged in user npub
intent.putExtra("current_user", account.keyPair.pubKey.toNpub())

// If you are sending multiple intents without awaiting you can add some intent flags to sign all events without opening multiple screens
intent.addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP or Intent.FLAG_ACTIVITY_CLEAR_TOP)

context.startActivity(intent)

result:

If the user approved intent it will return the signature, id and event fields

// if you used the flags (Intent.FLAG_ACTIVITY_SINGLE_TOP or Intent.FLAG_ACTIVITY_CLEAR_TOP) when sending the intent and there's more than 1 event amber will return an array with the results
[
  {"package":null,"signature":"event_signature","id":"event_id"},
  {"package":null,"signature":"event_signature","id":"event_id"},
  {"package":null,"signature":"event_signature","id":"event_id"}
]

// if you sent only 1 event or did not used the flags (Intent.FLAG_ACTIVITY_SINGLE_TOP or Intent.FLAG_ACTIVITY_CLEAR_TOP) Amber will return the fields signature, id and event
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:

val intent = Intent(Intent.ACTION_VIEW, Uri.parse("nostrsigner:$plaintext"))
intent.`package` = "com.greenart7c3.nostrsigner"
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: