Small improvement to onion request memory use

app/src/main/java/org/session/libsession/snode/OnionRequestEncryption.kt

@@ -5,6 +5,7 @@ import org.session.libsession.utilities.AESGCM
 import org.session.libsession.utilities.AESGCM.EncryptionResult
 import org.session.libsignal.utilities.JsonUtil
 import org.session.libsignal.utilities.toHexString
+import java.io.ByteArrayOutputStream
 import java.nio.Buffer
 import java.nio.ByteBuffer
 import java.nio.ByteOrder
@@ -14,16 +15,15 @@ object OnionRequestEncryption {
     internal fun encode(ciphertext: ByteArray, json: Map<*, *>): ByteArray {
         // The encoding of V2 onion requests looks like: | 4 bytes: size N of ciphertext | N bytes: ciphertext | json as utf8 |
         val jsonAsData = JsonUtil.toJson(json).toByteArray()
-        val ciphertextSize = ciphertext.size
-        val buffer = ByteBuffer.allocate(Int.SIZE_BYTES)
-        buffer.order(ByteOrder.LITTLE_ENDIAN)
-        buffer.putInt(ciphertextSize)
-        val ciphertextSizeAsData = ByteArray(buffer.capacity())
-        // Casting here avoids an issue where this gets compiled down to incorrect byte code. See
-        // https://github.com/eclipse/jetty.project/issues/3244 for more info
-        (buffer as Buffer).position(0)
-        buffer.get(ciphertextSizeAsData)
-        return ciphertextSizeAsData + ciphertext + jsonAsData
+        val output = ByteArray(4 + ciphertext.size + jsonAsData.size)
+
+        ByteBuffer.wrap(output).apply {
+            order(ByteOrder.LITTLE_ENDIAN).putInt(ciphertext.size)
+            put(ciphertext)
+            put(jsonAsData)
+        }
+
+        return output
     }
 
     /**

app/src/main/java/org/session/libsession/utilities/AESGCM.kt

@@ -9,6 +9,7 @@ import org.session.libsignal.utilities.ByteArraySlice.Companion.view
 import org.session.libsignal.utilities.ByteUtil
 import org.session.libsignal.utilities.Hex
 import org.session.libsignal.utilities.Util
+import java.nio.ByteBuffer
 import javax.crypto.Cipher
 import javax.crypto.Mac
 import javax.crypto.spec.GCMParameterSpec
@@ -57,10 +58,19 @@ internal object AESGCM {
      */
     fun encrypt(plaintext: ByteArraySlice, symmetricKey: ByteArray): ByteArray {
         val iv = Util.getSecretBytes(ivSize)
-        synchronized(CIPHER_LOCK) {
+
+        return synchronized(CIPHER_LOCK) {
             val cipher = Cipher.getInstance("AES/GCM/NoPadding")
             cipher.init(Cipher.ENCRYPT_MODE, SecretKeySpec(symmetricKey, "AES"), GCMParameterSpec(gcmTagSize, iv))
-            return ByteUtil.combine(iv, cipher.doFinal(plaintext.data, plaintext.offset, plaintext.len))
+
+            val output = ByteArray(ivSize + cipher.getOutputSize(plaintext.len))
+
+            ByteBuffer.wrap(output).also { buffer ->
+                buffer.put(iv)
+                cipher.doFinal(ByteBuffer.wrap(plaintext.data, plaintext.offset, plaintext.len), buffer)
+            }
+
+            output
         }
     }
 

app/src/main/java/org/session/libsignal/crypto/ecc/DjbECPublicKey.java

@@ -10,6 +10,8 @@
 import java.math.BigInteger;
 import java.util.Arrays;
 
+import kotlin.collections.ArraysKt;
+
 public class DjbECPublicKey implements ECPublicKey {
 
   private final byte[] publicKey;
@@ -21,7 +23,7 @@ public DjbECPublicKey(byte[] publicKey) {
   @Override
   public byte[] serialize() {
     byte[] type = {Curve.DJB_TYPE};
-    return ByteUtil.combine(type, publicKey);
+    return ArraysKt.plus(type, publicKey);
   }
 
   @Override

app/src/main/java/org/session/libsignal/utilities/ByteUtil.java

@@ -5,28 +5,10 @@
  */
 package org.session.libsignal.utilities;
 
-import org.session.libsignal.utilities.Hex;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
 import java.text.ParseException;
 
 public class ByteUtil {
 
-  public static byte[] combine(byte[]... elements) {
-    try {
-      ByteArrayOutputStream baos = new ByteArrayOutputStream();
-
-      for (byte[] element : elements) {
-        baos.write(element);
-      }
-
-      return baos.toByteArray();
-    } catch (IOException e) {
-      throw new AssertionError(e);
-    }
-  }
-
   public static byte[][] split(byte[] input, int firstLength, int secondLength) {
     byte[][] parts = new byte[2][];