Add EncryptionBuilder.discardOutput()

Also move NullOutputStream from pgpainless-sop to pgpainless-core

pgpainless-core/src/main/kotlin/org/pgpainless/encryption_signing/EncryptionBuilder.kt

@@ -9,6 +9,7 @@ import org.pgpainless.PGPainless.Companion.getPolicy
 import org.pgpainless.algorithm.CompressionAlgorithm
 import org.pgpainless.algorithm.SymmetricKeyAlgorithm
 import org.pgpainless.algorithm.negotiation.SymmetricKeyAlgorithmNegotiator.Companion.byPopularity
+import org.pgpainless.util.NullOutputStream
 import org.slf4j.Logger
 import org.slf4j.LoggerFactory
 
@@ -19,6 +20,10 @@ class EncryptionBuilder : EncryptionBuilderInterface {
         return WithOptionsImpl(outputStream)
     }
 
+    override fun discardOutput(): EncryptionBuilderInterface.WithOptions {
+        return onOutputStream(NullOutputStream())
+    }
+
     class WithOptionsImpl(val outputStream: OutputStream) : EncryptionBuilderInterface.WithOptions {
 
         override fun withOptions(options: ProducerOptions): EncryptionStream {

pgpainless-core/src/main/kotlin/org/pgpainless/encryption_signing/EncryptionBuilderInterface.kt

@@ -8,7 +8,7 @@ import java.io.IOException
 import java.io.OutputStream
 import org.bouncycastle.openpgp.PGPException
 
-fun interface EncryptionBuilderInterface {
+interface EncryptionBuilderInterface {
 
     /**
      * Create a [EncryptionStream] wrapping an [OutputStream]. Data that is piped through the
@@ -19,6 +19,16 @@ fun interface EncryptionBuilderInterface {
      */
     fun onOutputStream(outputStream: OutputStream): WithOptions
 
+    /**
+     * Create an [EncryptionStream] that discards the data after processing it. This is useful, e.g.
+     * for generating detached signatures, where the resulting signature is retrieved from the
+     * [EncryptionResult] once the operation is finished. In this case, the plaintext data does not
+     * need to be retained.
+     *
+     * @return api handle
+     */
+    fun discardOutput(): WithOptions
+
     fun interface WithOptions {
 
         /**

pgpainless-core/src/main/kotlin/org/pgpainless/util/NullOutputStream.kt

@@ -2,7 +2,7 @@
 //
 // SPDX-License-Identifier: Apache-2.0
 
-package org.pgpainless.sop
+package org.pgpainless.util
 
 import java.io.OutputStream
 

pgpainless-sop/src/main/kotlin/org/pgpainless/sop/DetachedSignImpl.kt

@@ -53,15 +53,10 @@ class DetachedSignImpl : DetachedSign {
             }
         }
 
-        // When creating a detached signature, the output of the signing stream is actually
-        //  the unmodified plaintext data, so we can discard it.
-        //  The detached signature will later be retrieved from the metadata object instead.
-        val sink = NullOutputStream()
-
         try {
             val signingStream =
                 PGPainless.encryptAndOrSign()
-                    .onOutputStream(sink)
+                    .discardOutput()
                     .withOptions(ProducerOptions.sign(signingOptions).setAsciiArmor(armor))
 
             return object : ReadyWithResult<SigningResult>() {