Merge pull request #3 from brevilo/fix-2

Fix Session.decrypt()

src/main/java/io/github/brevilo/jolm/Session.java

@@ -195,15 +195,21 @@ public Message encrypt(String plainText) throws OlmException {
    */
   public String decrypt(Message message) throws OlmException {
     // get native message
+    // (add a separate message buffer as olm_decrypt_max_plaintext_length() destroys it!)
     Memory messageBuffer = Utils.toNative(message.getCipherText());
+    Memory messageBufferCopy = Utils.toNative(message.getCipherText());
 
-    // prepare output buffer and index reference
+    // determine output buffer length
     NativeSize maxPlainTextLength =
         OlmLibrary.olm_decrypt_max_plaintext_length(
-            instance, new NativeSize(message.type()), messageBuffer, new NativeSize(messageBuffer));
+            instance,
+            new NativeSize(message.type()),
+            messageBufferCopy,
+            new NativeSize(messageBufferCopy));
 
     checkOlmResult(maxPlainTextLength);
 
+    // prepare output buffer
     Memory plainTextBuffer = new Memory(maxPlainTextLength.longValue());
 
     // call olm
@@ -218,7 +224,7 @@ public String decrypt(Message message) throws OlmException {
 
     checkOlmResult(plainTextLength);
 
-    return Utils.fromNative(plainTextBuffer);
+    return Utils.fromNative(plainTextBuffer).substring(0, plainTextLength.intValue());
   }
 
   /**

src/test/java/io/github/brevilo/jolm/SessionTest.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2021 Oliver Behnke
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.github.brevilo.jolm;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import io.github.brevilo.jolm.model.Message;
+import io.github.brevilo.jolm.model.OneTimeKeys;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestInstance;
+import org.junit.jupiter.api.TestInstance.Lifecycle;
+
+@TestInstance(Lifecycle.PER_CLASS)
+class SessionTest {
+  final String message = "5-BY-5!";
+
+  Account aliceAccount;
+  Session aliceSession;
+
+  Account bobAccount;
+  Session bobSession;
+
+  String bobIdentityKey;
+  String bobOneTimeKey;
+
+  @BeforeAll
+  void setUp() throws Exception {
+    aliceAccount = new Account();
+    bobAccount = new Account();
+  }
+
+  @AfterAll
+  void tearDown() throws Exception {
+    aliceAccount.clear();
+    aliceSession.clear();
+
+    bobAccount.clear();
+    bobSession.clear();
+  }
+
+  @Test
+  void testAliceToBob() throws Exception {
+    // generate bob's identity key
+    bobIdentityKey = bobAccount.identityKeys().getCurve25519();
+
+    // generate bob's one-time key
+    bobAccount.generateOneTimeKeys(1);
+    OneTimeKeys bobOneTimeKeys = bobAccount.oneTimeKeys();
+    bobOneTimeKeys
+        .getCurve25519()
+        .forEach(
+            (id, key) -> {
+              bobOneTimeKey = key;
+            });
+
+    // create alice's outbound olm Session (to bob)
+    aliceSession = Session.createOutboundSession(aliceAccount, bobIdentityKey, bobOneTimeKey);
+
+    // encrypt message for bob
+    Message encryptedMessage = aliceSession.encrypt(message);
+
+    // create bob's inbound olm session (from alice)
+    bobSession = Session.createInboundSession(bobAccount, encryptedMessage.getCipherText());
+
+    // decrypt message from alice
+    String decryptedMessage = bobSession.decrypt(encryptedMessage);
+
+    // compare message content
+    assertEquals(decryptedMessage, message);
+
+    // remove used one-time key
+    bobAccount.removeOneTimeKeys(bobSession);
+  }
+}