(feat) Adds sliceData and getReadOnlyData methods to LogEntry, #755 (#…

…762)

jraft-core/src/main/java/com/alipay/sofa/jraft/entity/LogEntry.java

@@ -195,10 +195,35 @@ public void setOldPeers(final List<PeerId> oldPeers) {
         this.oldPeers = oldPeers;
     }
 
+    /**
+     * Returns the log data, it's not read-only, you SHOULD take care it's modification and
+     * thread-safety by yourself.
+     *
+     * @return the log data
+     */
     public ByteBuffer getData() {
         return this.data;
     }
 
+    /**
+     * Creates a new byte buffer whose content is a shared subsequence of this log entry's data
+     * buffer's content.
+     *
+     * @return The new byte buffer
+     */
+    public ByteBuffer sliceData() {
+        return this.data != null ? this.data.slice() : null;
+    }
+
+    /**
+     * Creates a new, read-only byte buffer that shares this log entry's data buffer's content.
+     *
+     * @return the new, read-only byte buffer
+     */
+    public ByteBuffer getReadOnlyData() {
+        return this.data != null ? this.data.asReadOnlyBuffer() : null;
+    }
+
     public void setData(final ByteBuffer data) {
         this.data = data;
     }

jraft-core/src/test/java/com/alipay/sofa/jraft/entity/LogEntryTest.java

@@ -17,6 +17,7 @@
 package com.alipay.sofa.jraft.entity;
 
 import java.nio.ByteBuffer;
+import java.nio.ReadOnlyBufferException;
 import java.util.Arrays;
 
 import org.junit.Assert;
@@ -28,9 +29,11 @@
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNotSame;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 public class LogEntryTest {
 
@@ -124,4 +127,37 @@ public void testChecksum() {
         assertNotEquals(c, entry.checksum());
         assertTrue(entry.isCorrupted());
     }
+
+    @Test
+    public void testSliceReadOnlyData() {
+        ByteBuffer buf = ByteBuffer.wrap("hello".getBytes());
+        LogEntry entry = new LogEntry(EnumOutter.EntryType.ENTRY_TYPE_NO_OP);
+        entry.setData(buf);
+        assertSame(buf, entry.getData());
+        final ByteBuffer slice = entry.sliceData();
+        assertNotSame(buf, slice);
+        assertEquals(5, slice.remaining());
+        assertEquals("hello", new String(slice.array()));
+        slice.position(4);
+        assertEquals(4, slice.position());
+        assertEquals(0, entry.getData().position());
+        slice.put((byte) 'a');
+        assertEquals(97, slice.get(4));
+        assertEquals("hella", new String(entry.getData().array()));
+
+        final ByteBuffer readOnly = entry.getReadOnlyData();
+        assertNotSame(buf, readOnly);
+        assertEquals(5, readOnly.remaining());
+        byte[] bs = new byte[5];
+        readOnly.get(bs);
+        assertEquals("hella", new String(bs));
+
+        try {
+            readOnly.position(4);
+            readOnly.put((byte) 1);
+            fail();
+        } catch (ReadOnlyBufferException e) {
+
+        }
+    }
 }