Fix incorrect calculation of next buffer size in AdaptiveRecvByteBufAllocator (netty#9555)

Motivation:

Due a bug we did not always correctly calculate the next buffer size in AdaptiveRecvByteBufAllocator.

Modification:

Fix calculation and add unit test

Result:

Correct calculation is always used.

Author: brucelwl

transport/src/main/java/io/netty/channel/AdaptiveRecvByteBufAllocator.java

@@ -122,7 +122,7 @@ public int guess() {
         }
 
         private void record(int actualReadBytes) {
-            if (actualReadBytes <= SIZE_TABLE[max(0, index - INDEX_DECREMENT - 1)]) {
+            if (actualReadBytes <= SIZE_TABLE[max(0, index - INDEX_DECREMENT)]) {
                 if (decreaseNow) {
                     index = max(index - INDEX_DECREMENT, minIndex);
                     nextReceiveBufferSize = SIZE_TABLE[index];

transport/src/test/java/io/netty/channel/AdaptiveRecvByteBufAllocatorTest.java

@@ -54,6 +54,26 @@ public void rampUpBeforeReadCompleteWhenLargeDataPending() {
         allocReadExpected(handle, alloc, 8388608);
     }
 
+    @Test
+    public void memoryAllocationIntervalsTest() {
+        computingNext(512, 512);
+        computingNext(8192, 1110);
+        computingNext(8192, 1200);
+        computingNext(4096, 1300);
+        computingNext(4096, 1500);
+        computingNext(2048, 1700);
+        computingNext(2048, 1550);
+        computingNext(2048, 2000);
+        computingNext(2048, 1900);
+    }
+
+    private void computingNext(long expectedSize, int actualReadBytes) {
+        assertEquals(expectedSize, handle.guess());
+        handle.reset(config);
+        handle.lastBytesRead(actualReadBytes);
+        handle.readComplete();
+    }
+
     @Test
     public void lastPartialReadDoesNotRampDown() {
         allocReadExpected(handle, alloc, 512);