Issue#17: add flip() to TrackedLease (#18)

* add flip() to TrackedLease

* add currentLimit assertion to testFlip

Author: eemhu

src/main/java/com/teragrep/buf_01/buffer/lease/TrackedLease.java

@@ -58,6 +58,7 @@
  * - Provide next byte
  * - Write next byte
  * - Check if more bytes are available in current position
+ * - Flip the "buffer" aka set limit=pos and pos=0
  *
  * @collaborators
  * - Lease
@@ -72,6 +73,7 @@
  * + position(p);
  * + currentLimit();
  * + limit(l);
+ * + flip();
  * }
  *
  * TrackedLease --> Lease : provides read/write functionality and position state
@@ -85,6 +87,7 @@
  * - Provide next byte
  * - Write next byte
  * - Check if more bytes are available in current position
+ * - Flip the "buffer" aka set limit=pos and pos=0
  *
  * Collaborators:
  * - Lease
@@ -108,4 +111,6 @@ public interface TrackedLease<T> extends Lease<T> {
     public abstract long currentLimit();
 
     public abstract void limit(final long newLimit);
+
+    public abstract void flip();
 }

src/main/java/com/teragrep/buf_01/buffer/lease/TrackedMemorySegmentLease.java

@@ -225,6 +225,12 @@ public void limit(final long newLimit) {
         }
     }
 
+    @Override
+    public void flip() {
+        limit(currentPosition());
+        position(0L);
+    }
+
     @Override
     public boolean equals(final Object o) {
         if (o == null || getClass() != o.getClass()) {

src/test/java/com/teragrep/buf_01/buffer/lease/TrackedMemorySegmentLeaseTest.java

@@ -247,6 +247,30 @@ void testResettingPosition() {
         Assertions.assertEquals(0L, trackedLease.currentPosition());
     }
 
+    @Test
+    void testFlip() {
+        final OpeningPool pool = new OpeningPool(
+                new UnboundPool<>(new ArenaMemorySegmentLeaseSupplier(Arena.ofShared(), 5), new MemorySegmentLeaseStub())
+        );
+        final TrackedLease<MemorySegment> trackedLease = new TrackedMemorySegmentLease(pool.get());
+
+        // Let's read 3 bytes
+        trackedLease.next();
+        trackedLease.next();
+        trackedLease.next();
+
+        // Position should be 3, limit -1
+        Assertions.assertEquals(-1L, trackedLease.currentLimit());
+        Assertions.assertEquals(3L, trackedLease.currentPosition());
+
+        // Flip it
+        trackedLease.flip();
+
+        // Position should be 0, limit 3
+        Assertions.assertEquals(0L, trackedLease.currentPosition());
+        Assertions.assertEquals(3L, trackedLease.currentLimit());
+    }
+
     @Test
     void testEqualsContract() {
         EqualsVerifier.simple().forClass(TrackedMemorySegmentLease.class).verify();