PDFBOX-5965: combine LAST and CURRENT buffers into new LAST buffer content to avoid ArrayIndexOutOfBoundsException

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1925263 13f79535-47bb-0310-9956-ffa450edef68

Author: THausherr

io/src/main/java/org/apache/pdfbox/io/NonSeekableRandomAccessReadInputStream.java

@@ -192,7 +192,21 @@ private boolean fetch() throws IOException
         {
             // move the current data to last to support rewind operations
             // right after refilling the current buffer
-            switchBuffers(CURRENT, LAST);
+            if (bufferBytes[LAST] == BUFFER_SIZE && bufferBytes[CURRENT] > 0 && bufferBytes[CURRENT] < BUFFER_SIZE)
+            {
+                // Likely EOF, we're risking losing the previous (full) buffer and get an AIOOB
+                // Create a new LAST buffer that combines as much as possible of CURRENT and LAST into a new LAST.
+                byte[] newBuffer = new byte[BUFFER_SIZE];
+                System.arraycopy(buffers[LAST], bufferBytes[CURRENT], newBuffer, 0, BUFFER_SIZE - bufferBytes[CURRENT]);
+                System.arraycopy(buffers[CURRENT], 0, newBuffer, BUFFER_SIZE - bufferBytes[CURRENT], bufferBytes[CURRENT]);
+                switchBuffers(CURRENT, LAST);
+                buffers[LAST] = newBuffer;
+                bufferBytes[LAST] = BUFFER_SIZE;
+            }
+            else
+            {
+                switchBuffers(CURRENT, LAST);
+            }
             bufferBytes[CURRENT] = is.read(buffers[CURRENT]);
             if (bufferBytes[CURRENT] <= 0)
             {

io/src/test/java/org/apache/pdfbox/io/NonSeekableRandomAccessReadInputStreamTest.java

@@ -221,6 +221,29 @@ void testRewindException() throws IOException
         }
     }
 
+    @Test
+    void testRewindAcrossBuffers() throws IOException
+    {
+        byte[] ba = new byte[4096 + 5];
+        int rewSize = 7;
+        byte testVal = 123;
+        ba[ba.length - rewSize] = testVal;
+        ByteArrayInputStream bais = new ByteArrayInputStream(ba);
+        try (RandomAccessRead rar = new NonSeekableRandomAccessReadInputStream(bais))
+        {
+            int len = rar.read(new byte[ba.length - rewSize]);
+            assertEquals(ba.length - rewSize, len);
+            len = rar.read(new byte[rewSize]);
+            assertEquals(rewSize, len);
+            int by = rar.read();
+            assertEquals(-1, by);
+            assertTrue(rar.isEOF());
+            rar.rewind(len);
+            by = rar.read(); // went ArrayIndexOutOfBoundsException here
+            assertEquals(testVal, by);
+        }
+    }
+
     private byte[] createRandomData()
     {
         final long seed = new Random().nextLong();