fix: fix Synapse 3.0 instrumentation bugs and harden span propagation

Three deterministic bugs fixed:

1. Key mismatch in PassthruInstrumentation: PR #9422 renamed the context
   key constant but forgot to update the hardcoded string literal in
   SynapsePassthruInstrumentation, breaking parent span propagation
   across the passthru mechanism.

2. http.url test assertion: QueryObfuscator recombines http.url with the
   query string after obfuscation. The test expected path-only but the
   actual value correctly includes the query string.

3. Missing peer.service in V1 client spans: SynapseClientDecorator
   returns relative URIs (no host), so peer.hostname was never set.
   Added peer hostname/IP/port extraction from NHttpClientConnection.

Additionally, hardened the passthru span propagation to read the server
span directly from the source connection context rather than relying
solely on activeSpan(). SourceHandler.requestReceived() dispatches to a
worker thread pool, and while java-concurrent instrumentation normally
handles context propagation across ThreadPoolExecutor, the connection-
based lookup is more robust.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bm1549

dd-java-agent/instrumentation/synapse-3.0/src/main/java/datadog/trace/instrumentation/synapse3/SynapseClientInstrumentation.java

@@ -22,8 +22,10 @@
 import datadog.trace.agent.tooling.InstrumenterModule;
 import datadog.trace.agent.tooling.annotation.AppliesOn;
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
+import datadog.trace.bootstrap.instrumentation.api.Tags;
 import net.bytebuddy.asm.Advice;
 import org.apache.axis2.context.MessageContext;
+import org.apache.http.HttpInetConnection;
 import org.apache.http.HttpResponse;
 import org.apache.http.nio.NHttpClientConnection;
 import org.apache.synapse.transport.passthru.TargetContext;
@@ -107,6 +109,19 @@ public static void requestSubmitted(
       // populate span using details from the submitted HttpRequest (resolved URI, etc.)
       AgentSpan span = spanFromContext(scope.context());
       DECORATE.onRequest(span, TargetContext.getRequest(connection).getRequest());
+
+      // set peer hostname from the connection since request URIs are relative paths
+      if (connection instanceof HttpInetConnection) {
+        java.net.InetAddress remoteAddress = ((HttpInetConnection) connection).getRemoteAddress();
+        if (remoteAddress != null) {
+          span.setTag(Tags.PEER_HOSTNAME, remoteAddress.getHostName());
+          span.setTag(Tags.PEER_HOST_IPV4, remoteAddress.getHostAddress());
+          int remotePort = ((HttpInetConnection) connection).getRemotePort();
+          if (remotePort > 0) {
+            span.setTag(Tags.PEER_PORT, remotePort);
+          }
+        }
+      }
       scope.close();
     }
   }

dd-java-agent/instrumentation/synapse-3.0/src/main/java/datadog/trace/instrumentation/synapse3/SynapsePassthruInstrumentation.java

@@ -2,10 +2,13 @@
 
 import static datadog.trace.agent.tooling.bytebuddy.matcher.NameMatchers.named;
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activeSpan;
+import static datadog.trace.bootstrap.instrumentation.api.Java8BytecodeBridge.spanFromContext;
+import static datadog.trace.instrumentation.synapse3.SynapseClientDecorator.SYNAPSE_CONTEXT_KEY;
 import static net.bytebuddy.matcher.ElementMatchers.isMethod;
 import static net.bytebuddy.matcher.ElementMatchers.takesArgument;
 
 import com.google.auto.service.AutoService;
+import datadog.context.Context;
 import datadog.trace.agent.tooling.Instrumenter;
 import datadog.trace.agent.tooling.InstrumenterModule;
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
@@ -14,6 +17,7 @@
 import java.util.Map;
 import net.bytebuddy.asm.Advice;
 import org.apache.axis2.context.MessageContext;
+import org.apache.http.nio.NHttpServerConnection;
 
 /** Helps propagate parent spans over 'passthru' mechanism to synapse-client instrumentation. */
 @AutoService(InstrumenterModule.class)
@@ -53,10 +57,26 @@ public static void submit(@Advice.Argument(0) final MessageContext message) {
         }
       }
 
-      // use message context to propagate active spans across Synapse's 'passthru' mechanism
-      AgentSpan span = activeSpan();
+      // Propagate the server span to the client via the message context.
+      // Prefer reading the span directly from the source connection's context (where
+      // SynapseServerInstrumentation stored it) over activeSpan(). SourceHandler dispatches
+      // request processing to a worker thread pool, and while java-concurrent instrumentation
+      // normally propagates context across ThreadPoolExecutor, the connection-based lookup is
+      // more robust as it doesn't depend on automatic context propagation.
+      AgentSpan span = null;
+      Object sourceConn = message.getProperty("pass-through.Source-Connection");
+      if (sourceConn instanceof NHttpServerConnection) {
+        Object ctx =
+            ((NHttpServerConnection) sourceConn).getContext().getAttribute(SYNAPSE_CONTEXT_KEY);
+        if (ctx instanceof Context) {
+          span = spanFromContext((Context) ctx);
+        }
+      }
+      if (null == span) {
+        span = activeSpan();
+      }
       if (null != span) {
-        message.setNonReplicableProperty("dd.trace.synapse.span", span);
+        message.setNonReplicableProperty(SYNAPSE_CONTEXT_KEY, span);
       }
     }
   }

dd-java-agent/instrumentation/synapse-3.0/src/test/groovy/datadog/trace/instrumentation/synapse3/SynapseTest.groovy

@@ -247,7 +247,7 @@ abstract class SynapseTest extends VersionedNamingTestBase {
         "$Tags.SPAN_KIND" Tags.SPAN_KIND_SERVER
         "$Tags.PEER_HOST_IPV4" "127.0.0.1"
         "$Tags.PEER_PORT" Integer
-        "$Tags.HTTP_URL" "/services/SimpleStockQuoteService"
+        "$Tags.HTTP_URL" query ? "/services/SimpleStockQuoteService?${query}" : "/services/SimpleStockQuoteService"
         "$DDTags.HTTP_QUERY" query
         "$Tags.HTTP_METHOD" method
         "$Tags.HTTP_STATUS" statusCode
@@ -302,6 +302,9 @@ abstract class SynapseTest extends VersionedNamingTestBase {
       tags {
         "$Tags.COMPONENT" "synapse-client"
         "$Tags.SPAN_KIND" Tags.SPAN_KIND_CLIENT
+        "$Tags.PEER_HOSTNAME" String
+        "$Tags.PEER_HOST_IPV4" "127.0.0.1"
+        "$Tags.PEER_PORT" Integer
         "$Tags.HTTP_URL" "/services/SimpleStockQuoteService"
         "$Tags.HTTP_METHOD" method
         "$Tags.HTTP_STATUS" statusCode
@@ -311,7 +314,6 @@ abstract class SynapseTest extends VersionedNamingTestBase {
   }
 }
 
-@Flaky("Occasionally times out when receiving traces")
 class SynapseV0ForkedTest extends SynapseTest implements TestingGenericHttpNamingConventions.ClientV0 {
 
 
@@ -321,7 +323,6 @@ class SynapseV0ForkedTest extends SynapseTest implements TestingGenericHttpNamin
   }
 }
 
-@Flaky("Occasionally times out when receiving traces")
 class SynapseV1ForkedTest extends SynapseTest implements TestingGenericHttpNamingConventions.ClientV1 {
 
   @Override