Add behavior test to ensure that ArmoredInputStream cuts away any data outside of the armor

pgpainless-core/src/test/java/org/bouncycastle/ArmoredInputStreamOverArmoredDataWithAppendedCleartextTest.java

@@ -0,0 +1,38 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.bouncycastle;
+
+import org.bouncycastle.bcpg.ArmoredInputStream;
+import org.bouncycastle.util.io.Streams;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ArmoredInputStreamOverArmoredDataWithAppendedCleartextTest {
+
+    private static final String ASCII_ARMORED_WITH_APPENDED_GARBAGE = "-----BEGIN PGP MESSAGE-----\n" +
+            "Version: PGPainless\n" +
+            "\n" +
+            "yxRiAAAAAABIZWxsbywgV29ybGQhCg==\n" +
+            "=WGju\n" +
+            "-----END PGP MESSAGE-----\n" +
+            "This is a bunch of crap that we appended.";
+    @Test
+    public void testArmoredInputStreamCutsOffAnyDataAfterTheAsciiArmor() throws IOException {
+        InputStream inputStream = new ByteArrayInputStream(ASCII_ARMORED_WITH_APPENDED_GARBAGE.getBytes(StandardCharsets.UTF_8));
+        ArmoredInputStream armorIn = new ArmoredInputStream(inputStream);
+        ByteArrayOutputStream out = new ByteArrayOutputStream();
+        Streams.pipeAll(armorIn, out);
+        armorIn.close();
+
+        assertEquals(22, out.size(), "ArmoredInputStream cuts off any appended data outside the ASCII armor.");
+    }
+}