Extract peer-connection tagging into a TagExtractor<InetSocketAddress>

dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/decorator/BaseDecorator.java

@@ -1,7 +1,5 @@
 package datadog.trace.bootstrap.instrumentation.decorator;
 
-import static datadog.trace.bootstrap.instrumentation.java.net.HostNameResolver.hostName;
-
 import datadog.context.Context;
 import datadog.context.ContextScope;
 import datadog.trace.api.Config;
@@ -14,8 +12,6 @@
 import datadog.trace.bootstrap.instrumentation.api.ErrorPriorities;
 import datadog.trace.bootstrap.instrumentation.api.Tags;
 import java.lang.reflect.Method;
-import java.net.Inet4Address;
-import java.net.Inet6Address;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.util.concurrent.ExecutionException;
@@ -150,10 +146,10 @@ public ContextScope onError(final ContextScope scope, final Throwable throwable)
 
   public AgentSpan onPeerConnection(
       final AgentSpan span, final InetSocketAddress remoteConnection) {
-    if (remoteConnection != null) {
-      onPeerConnection(span, remoteConnection.getAddress(), !remoteConnection.isUnresolved());
-      setPeerPort(span, remoteConnection.getPort());
-    }
+    // Invoke the extractor directly rather than via span.setTags(...): this legacy plumbing path
+    // is behavior-identical to the old inline code, and a direct call runs on test doubles too
+    // (the span-first span.setTags(...) sugar is for hand-written integration call sites).
+    PeerConnectionExtractor.INSTANCE.extract(remoteConnection, span);
     return span;
   }
 
@@ -162,17 +158,7 @@ public AgentSpan onPeerConnection(final AgentSpan span, final InetAddress remote
   }
 
   public AgentSpan onPeerConnection(AgentSpan span, InetAddress remoteAddress, boolean resolved) {
-    if (remoteAddress != null) {
-      String ip = remoteAddress.getHostAddress();
-      if (resolved && Config.get().isPeerHostNameEnabled()) {
-        span.setTag(Tags.PEER_HOSTNAME, hostName(remoteAddress, ip));
-      }
-      if (remoteAddress instanceof Inet4Address) {
-        span.setTag(Tags.PEER_HOST_IPV4, ip);
-      } else if (remoteAddress instanceof Inet6Address) {
-        span.setTag(Tags.PEER_HOST_IPV6, ip);
-      }
-    }
+    PeerConnectionExtractor.setPeerAddress(span, remoteAddress, resolved);
     return span;
   }
 

dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/decorator/PeerConnectionExtractor.java

@@ -0,0 +1,57 @@
+package datadog.trace.bootstrap.instrumentation.decorator;
+
+import static datadog.trace.bootstrap.instrumentation.java.net.HostNameResolver.hostName;
+
+import datadog.trace.api.Config;
+import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
+import datadog.trace.bootstrap.instrumentation.api.TagExtractor;
+import datadog.trace.bootstrap.instrumentation.api.Tags;
+import java.net.Inet4Address;
+import java.net.Inet6Address;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+
+/**
+ * Named singleton {@link TagExtractor} for peer-connection tags (hostname / IPv4 / IPv6 / port)
+ * from a remote {@link InetSocketAddress}.
+ *
+ * <p>Promoted from an inline lambda in {@link BaseDecorator} to a named class so it can be:
+ * referenced by name at call sites ({@code span.setTags(addr, PeerConnectionExtractor.INSTANCE)}),
+ * <em>composed</em> with other extractors (the axis the Decorator inheritance chain lacked), and
+ * given a home for the pure statics and the {@code hostName} resolver cache it consults.
+ * Non-capturing and stateless — the single {@link #INSTANCE} is effectively a static function
+ * object, so a monomorphic call site inlines it away.
+ */
+public final class PeerConnectionExtractor implements TagExtractor<InetSocketAddress> {
+  public static final PeerConnectionExtractor INSTANCE = new PeerConnectionExtractor();
+
+  private static final int UNSET_PORT = 0;
+
+  private PeerConnectionExtractor() {}
+
+  @Override
+  public void extract(final InetSocketAddress remoteConnection, final AgentSpan span) {
+    if (remoteConnection != null) {
+      setPeerAddress(span, remoteConnection.getAddress(), !remoteConnection.isUnresolved());
+      final int port = remoteConnection.getPort();
+      if (port > UNSET_PORT) {
+        span.setTag(Tags.PEER_PORT, port);
+      }
+    }
+  }
+
+  static void setPeerAddress(
+      final AgentSpan span, final InetAddress remoteAddress, final boolean resolved) {
+    if (remoteAddress != null) {
+      String ip = remoteAddress.getHostAddress();
+      if (resolved && Config.get().isPeerHostNameEnabled()) {
+        span.setTag(Tags.PEER_HOSTNAME, hostName(remoteAddress, ip));
+      }
+      if (remoteAddress instanceof Inet4Address) {
+        span.setTag(Tags.PEER_HOST_IPV4, ip);
+      } else if (remoteAddress instanceof Inet6Address) {
+        span.setTag(Tags.PEER_HOST_IPV6, ip);
+      }
+    }
+  }
+}