Kotlin conversion: MissingPublicKeyCallback

pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/MissingPublicKeyCallback.kt

@@ -0,0 +1,28 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.decryption_verification
+
+import org.bouncycastle.openpgp.PGPPublicKeyRing
+
+fun interface MissingPublicKeyCallback {
+
+    /**
+     * This method gets called if we encounter a signature made by a key which was not provided for signature verification.
+     * If you cannot provide the requested key, it is safe to return null here.
+     * PGPainless will then continue verification with the next signature.
+     *
+     * Note: The key-id might belong to a subkey, so be aware that when looking up the [PGPPublicKeyRing],
+     * you may not only search for the key-id on the key rings primary key!
+     *
+     * It would be super cool to provide the OpenPgp fingerprint here, but unfortunately one-pass-signatures
+     * only contain the key id.
+     *
+     * @param keyId ID of the missing signing (sub)key
+     * @return keyring containing the key or null
+     *
+     * @see <a href="https://datatracker.ietf.org/doc/html/rfc4880#section-5.4">RFC</a>
+     */
+    fun onMissingPublicKeyEncountered(keyId: Long): PGPPublicKeyRing?
+}