[fix][offload] Break the fillbuffer loop when met EOF (#22722)

tiered-storage/jcloud/src/main/java/org/apache/bookkeeper/mledger/offload/jcloud/impl/BlobStoreBackedInputStreamImpl.java

@@ -107,9 +107,7 @@ private boolean refillBufferIfNeeded() throws IOException {
                     bufferOffsetEnd = endRange;
                     long bytesRead = endRange - startRange + 1;
                     int bytesToCopy = (int) bytesRead;
-                    while (bytesToCopy > 0) {
-                        bytesToCopy -= buffer.writeBytes(stream, bytesToCopy);
-                    }
+                    fillBuffer(stream, bytesToCopy);
                     cursor += buffer.readableBytes();
                 }
 
@@ -135,6 +133,20 @@ private boolean refillBufferIfNeeded() throws IOException {
         return true;
     }
 
+    void fillBuffer(InputStream is, int bytesToCopy) throws IOException {
+        while (bytesToCopy > 0) {
+            int writeBytes = buffer.writeBytes(is, bytesToCopy);
+            if (writeBytes < 0) {
+                break;
+            }
+            bytesToCopy -= writeBytes;
+        }
+    }
+
+    ByteBuf getBuffer() {
+        return buffer;
+    }
+
     @Override
     public int read() throws IOException {
         if (refillBufferIfNeeded()) {

tiered-storage/jcloud/src/test/java/org/apache/bookkeeper/mledger/offload/jcloud/impl/BlobStoreBackedInputStreamTest.java

@@ -0,0 +1,51 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.bookkeeper.mledger.offload.jcloud.impl;
+
+import static org.testng.Assert.assertEquals;
+
+import java.io.IOException;
+import java.io.InputStream;
+import org.apache.bookkeeper.mledger.offload.jcloud.BlobStoreTestBase;
+import org.testng.annotations.Test;
+
+public class BlobStoreBackedInputStreamTest extends BlobStoreTestBase {
+
+    @Test
+    public void testFillBuffer() throws Exception {
+        BlobStoreBackedInputStreamImpl bis = new BlobStoreBackedInputStreamImpl(
+            blobStore, BUCKET, "testFillBuffer", (k, md) -> {
+        }, 2048, 512);
+
+        InputStream is = new InputStream() {
+            int count = 10;
+
+            @Override
+            public int read() throws IOException {
+                if (count-- > 0) {
+                    return 1;
+                } else {
+                    return -1;
+                }
+            }
+        };
+        bis.fillBuffer(is, 20);
+        assertEquals(bis.getBuffer().readableBytes(), 10);
+    }
+}