7036144: GZIPInputStream readTrailer uses faulty available() test for end-of-stream

src/java.base/share/classes/java/util/zip/GZIPInputStream.java

@@ -224,23 +224,17 @@ public void close() throws IOException {}
             (readUInt(in) != (inf.getBytesWritten() & 0xffffffffL)))
             throw new ZipException("Corrupt GZIP trailer");
 
-        // If there are more bytes available in "in" or
-        // the leftover in the "inf" is > 26 bytes:
-        // this.trailer(8) + next.header.min(10) + next.trailer(8)
         // try concatenated case
-        if (this.in.available() > 0 || n > 26) {
-            int m = 8;                  // this.trailer
-            try {
-                m += readHeader(in);    // next.header
-            } catch (IOException ze) {
-                return true;  // ignore any malformed, do nothing
-            }
-            inf.reset();
-            if (n > m)
-                inf.setInput(buf, len - n + m, n - m);
-            return false;
+        int m = 8;                  // this.trailer
+        try {
+            m += readHeader(in);    // next.header
+        } catch (IOException ze) {
+            return true;  // ignore any malformed, do nothing
         }
-        return true;
+        inf.reset();
+        if (n > m)
+            inf.setInput(buf, len - n + m, n - m);
+        return false;
     }
 
     /*

test/jdk/java/util/zip/GZIP/GZIPInputStreamAvailable.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/* @test
+ * @bug 7036144
+ * @summary Test concatenated gz streams when available() returns zero
+ * @run junit GZIPInputStreamAvailable
+ */
+
+import org.junit.jupiter.api.Test;
+
+import java.io.*;
+import java.util.*;
+import java.util.zip.*;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+public class GZIPInputStreamAvailable {
+
+    public static final int NUM_COPIES = 100;
+
+    @Test
+    public void testZeroAvailable() throws IOException {
+
+        // Create some uncompressed data and then repeat it NUM_COPIES times
+        byte[] uncompressed1 = "this is a test".getBytes("ASCII");
+        byte[] uncompressedN = repeat(uncompressed1, NUM_COPIES);
+
+        // Compress the original data and then repeat that NUM_COPIES times
+        byte[] compressed1 = deflate(uncompressed1);
+        byte[] compressedN = repeat(compressed1, NUM_COPIES);
+
+        // (a) Read back inflated data from a stream where available() is accurate and verify
+        byte[] readback1 = inflate(new ByteArrayInputStream(compressedN));
+        assertArrayEquals(uncompressedN, readback1);
+
+        // (b) Read back inflated data from a stream where available() always returns zero and verify
+        byte[] readback2 = inflate(new ZeroAvailableStream(new ByteArrayInputStream(compressedN)));
+        assertArrayEquals(uncompressedN, readback2);
+    }
+
+    public static byte[] repeat(byte[] data, int count) {
+        byte[] repeat = new byte[data.length * count];
+        int off = 0;
+        for (int i = 0; i < count; i++) {
+            System.arraycopy(data, 0, repeat, off, data.length);
+            off += data.length;
+        }
+        return repeat;
+    }
+
+    public static byte[] deflate(byte[] data) throws IOException {
+        ByteArrayOutputStream buf = new ByteArrayOutputStream();
+        try (GZIPOutputStream out = new GZIPOutputStream(buf)) {
+            out.write(data);
+        }
+        return buf.toByteArray();
+    }
+
+    public static byte[] inflate(InputStream in) throws IOException {
+        return new GZIPInputStream(in).readAllBytes();
+    }
+
+    public static class ZeroAvailableStream extends FilterInputStream {
+        public ZeroAvailableStream(InputStream in) {
+            super(in);
+        }
+        @Override
+        public int available() {
+            return 0;
+        }
+    }
+}