okhttp:Use a locally specified value instead of Segment.SIZE in okhttp (grpc#11899)

Switched to using 8192 which is the current value of Segment.SIZE and just have a test check that they are equal.  

The reason for doing this is that Segment.SIZE is Kotlin internal so shouldn't be used outside of its module.

Author: larry-safran

okhttp/src/main/java/io/grpc/okhttp/OkHttpWritableBufferAllocator.java

@@ -19,7 +19,6 @@
 import io.grpc.internal.WritableBuffer;
 import io.grpc.internal.WritableBufferAllocator;
 import okio.Buffer;
-import okio.Segment;
 
 /**
  * The default allocator for {@link OkHttpWritableBuffer}s used by the OkHttp transport. OkHttp
@@ -30,6 +29,7 @@ class OkHttpWritableBufferAllocator implements WritableBufferAllocator {
 
   // Set the maximum buffer size to 1MB
   private static final int MAX_BUFFER = 1024 * 1024;
+  public static final int SEGMENT_SIZE_COPY = 8192; // Should equal Segment.SIZE
 
   /**
    * Construct a new instance.
@@ -45,7 +45,7 @@ class OkHttpWritableBufferAllocator implements WritableBufferAllocator {
   public WritableBuffer allocate(int capacityHint) {
     // okio buffer uses fixed size Segments, round capacityHint up
     capacityHint = Math.min(MAX_BUFFER,
-        (capacityHint + Segment.SIZE - 1) / Segment.SIZE * Segment.SIZE);
+        (capacityHint + SEGMENT_SIZE_COPY - 1) / SEGMENT_SIZE_COPY * SEGMENT_SIZE_COPY);
     return new OkHttpWritableBuffer(new Buffer(), capacityHint);
   }
 }

okhttp/src/test/java/io/grpc/okhttp/OkHttpWritableBufferAllocatorTest.java

@@ -16,6 +16,7 @@
 
 package io.grpc.okhttp;
 
+import static io.grpc.okhttp.OkHttpWritableBufferAllocator.SEGMENT_SIZE_COPY;
 import static org.junit.Assert.assertEquals;
 
 import io.grpc.internal.WritableBuffer;
@@ -39,11 +40,12 @@ protected WritableBufferAllocator allocator() {
     return allocator;
   }
 
+  @SuppressWarnings("KotlinInternal")
   @Test
   public void testCapacity() {
     WritableBuffer buffer = allocator().allocate(4096);
     assertEquals(0, buffer.readableBytes());
-    assertEquals(Segment.SIZE, buffer.writableBytes());
+    assertEquals(SEGMENT_SIZE_COPY, buffer.writableBytes());
   }
 
   @Test
@@ -55,8 +57,14 @@ public void testInitialCapacityHasMaximum() {
 
   @Test
   public void testIsExactBelowMaxCapacity() {
-    WritableBuffer buffer = allocator().allocate(Segment.SIZE + 1);
+    WritableBuffer buffer = allocator().allocate(SEGMENT_SIZE_COPY + 1);
     assertEquals(0, buffer.readableBytes());
-    assertEquals(Segment.SIZE * 2, buffer.writableBytes());
+    assertEquals(SEGMENT_SIZE_COPY * 2, buffer.writableBytes());
+  }
+
+  @SuppressWarnings("KotlinInternal")
+  @Test
+  public void testSegmentSizeMatchesKotlin() {
+    assertEquals(Segment.SIZE, SEGMENT_SIZE_COPY);
   }
 }