fix universal profiling in java8 again (#4394)

* fix universal profiling java 8 compatibility again

* remove another potential issue

* update changelog

Author: SylvainJuge

CHANGELOG.next-release.md

@@ -10,6 +10,8 @@ This file contains all changes which are not released yet.
 # Fixes
 <!--FIXES-START-->
 
+* fix universal profiling integration compatibility with java8 - [#4394](https://github.com/elastic/apm-agent-java/pull/4394)
+
 <!--FIXES-END-->
 # Features and enhancements
 <!--ENHANCEMENTS-START-->

apm-agent-core/src/main/java/co/elastic/apm/agent/universalprofiling/ProfilerSharedMemoryWriter.java

@@ -48,8 +48,7 @@ public class ProfilerSharedMemoryWriter {
     static ByteBuffer generateProcessCorrelationStorage(String serviceName, @Nullable String environment, String socketFilePath) {
         ByteBuffer buffer = ByteBuffer.allocateDirect(4096);
         buffer.order(ByteOrder.nativeOrder());
-        //To make it java 8 compatible regardless of how it's compiled, need to explicitly use Buffer.position(int)
-        ((Buffer) buffer).position(0);
+        setBufferPosition(buffer, 0);
 
         buffer.putChar((char) 1); // layout-minor-version
         writeUtf8Str(buffer, serviceName);
@@ -64,6 +63,19 @@ private static void writeUtf8Str(ByteBuffer buffer, String str) {
         buffer.put(utf8);
     }
 
+    /**
+     * Set {@link ByteBuffer} position in a way that is compatible with Java8.
+     *
+     * @param buffer byte buffer
+     * @param position new position to set
+     */
+    private static void setBufferPosition(ByteBuffer buffer, int position) {
+        //To make it java 8 compatible regardless of how it's compiled, need to explicitly use Buffer.position(int)
+        // a covariant return type override was introduced in ByteBuffer.position(int) in Java 9 which makes it break
+        // binary compatibility with Java 8.
+        ((Buffer) buffer).position(position);
+    }
+
     /**
      * This method ensures that all writes which happened prior to this method call are not moved
      * after the method call due to reordering.
@@ -96,11 +108,11 @@ static void updateThreadCorrelationStorage(@Nullable AbstractSpanImpl<?> newSpan
                     TransactionImpl tx = newSpan.getParentTransaction();
                     tls.put(TLS_TRACE_PRESENT_OFFSET, (byte) 1);
                     tls.put(TLS_TRACE_FLAGS_OFFSET, newSpan.getTraceContext().getFlags());
-                    tls.position(TLS_TRACE_ID_OFFSET);
+                    setBufferPosition(tls, TLS_TRACE_ID_OFFSET);
                     newSpan.getTraceContext().getTraceId().writeToBuffer(tls);
-                    tls.position(TLS_SPAN_ID_OFFSET);
+                    setBufferPosition(tls,TLS_SPAN_ID_OFFSET);
                     newSpan.getTraceContext().getId().writeToBuffer(tls);
-                    tls.position(TLS_LOCAL_ROOT_SPAN_ID_OFFSET);
+                    setBufferPosition(tls, TLS_LOCAL_ROOT_SPAN_ID_OFFSET);
                     tx.getTraceContext().getId().writeToBuffer(tls);
                 } else {
                     tls.put(TLS_TRACE_PRESENT_OFFSET, (byte) 0);

apm-agent-plugin-sdk/src/main/java/co/elastic/apm/agent/sdk/internal/util/IOUtils.java

@@ -285,7 +285,7 @@ public static byte[] copyToByteArray(List<ByteBuffer> buffers) {
         int off = 0;
         for (ByteBuffer buff : buffers) {
             int len = buff.position();
-            buff.position(0);
+            ((Buffer) buff).position(0);
             buff.get(data, off, len);
             off += len;
         }