tweak onComplete logic, fix bug in unit tests

Author: kessplas

src/main/java/software/amazon/encryption/s3/internal/CipherSubscriber.java

@@ -129,10 +129,10 @@ public void onError(Throwable t) {
     public void onComplete() {
         // In rare cases, e.g. when the last part of a low-level MPU has 0 length,
         // onComplete will be called before onNext is called once.
-        // tagLength should only be added on Encrypt
-        if (contentRead.get() + (isEncrypt ? tagLength : 0) >= contentLength) {
-            finalBytes();
-        }
+        // So, call finalBytes here just in case there's any unsent data left.
+        // Most likely, finalBytes has already been called by the last onNext,
+        // but finalBytes guards against multiple invocations so it's safe to call again.
+        finalBytes();
         wrappedSubscriber.onComplete();
     }
 

src/test/java/software/amazon/encryption/s3/internal/CipherSubscriberTest.java

@@ -185,7 +185,7 @@ public void testSubscriberBehaviorOneChunk() {
         // we reject 0-ized IVs, so just do something
         iv[0] = 1;
         SimpleSubscriber wrappedSubscriber = new SimpleSubscriber();
-        CipherSubscriber subscriber = new CipherSubscriber(wrappedSubscriber, (long) plaintext.getBytes(StandardCharsets.UTF_8).length, materials, iv);
+        CipherSubscriber subscriber = new CipherSubscriber(wrappedSubscriber, materials.getCiphertextLength(), materials, iv);
 
         // Act
         TestPublisher<ByteBuffer> publisher = new TestPublisher<>();
@@ -239,7 +239,7 @@ public void testSubscriberBehaviorTagLengthLastChunk() {
         // we reject 0-ized IVs, so just do something non-zero
         iv[0] = 1;
         SimpleSubscriber wrappedSubscriber = new SimpleSubscriber();
-        CipherSubscriber subscriber = new CipherSubscriber(wrappedSubscriber, (long) plaintext.getBytes(StandardCharsets.UTF_8).length, materials, iv);
+        CipherSubscriber subscriber = new CipherSubscriber(wrappedSubscriber, materials.getCiphertextLength(), materials, iv);
 
         // Setup Publisher
         TestPublisher<ByteBuffer> publisher = new TestPublisher<>();