feat: add X-LaunchDarkly-Instance-Id header (SDK-2356)

lib/sdk/server/contract-tests/service/src/main/java/sdktest/TestService.java

@@ -42,7 +42,8 @@ public class TestService {
     "strongly-typed",
     "tags",
     "server-side-polling",
-    "fdv1-fallback"
+    "fdv1-fallback",
+    "instance-id"
   };
 
   static final Gson gson = new GsonBuilder().serializeNulls().create();

lib/sdk/server/src/main/java/com/launchdarkly/sdk/server/ClientContextImpl.java

@@ -8,6 +8,7 @@
 import com.launchdarkly.sdk.server.subsystems.HttpConfiguration;
 import com.launchdarkly.sdk.server.subsystems.LoggingConfiguration;
 
+import java.util.UUID;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 
@@ -37,7 +38,7 @@ private ClientContextImpl(
   ) {
     super(baseContext.getSdkKey(), baseContext.getApplicationInfo(), baseContext.getHttp(),
         baseContext.getLogging(), baseContext.isOffline(), baseContext.getServiceEndpoints(),
-        baseContext.getThreadPriority(), baseContext.getWrapperInfo());
+        baseContext.getThreadPriority(), baseContext.getWrapperInfo(), baseContext.getInstanceId());
     this.sharedExecutor = sharedExecutor;
     this.diagnosticStore = diagnosticStore;
     this.dataSourceUpdateSink = null;
@@ -79,22 +80,29 @@ static ClientContextImpl fromConfig(
       LDConfig config,
       ScheduledExecutorService sharedExecutor
       ) {
+    // Generate the instance ID once and thread it through every ClientContext we build for this
+    // LDClient. Subsystems built from any of these contexts will all observe the same value.
+    String instanceId = UUID.randomUUID().toString();
+
     ClientContext minimalContext = new ClientContext(sdkKey, config.applicationInfo, null,
-        null, config.offline, config.serviceEndpoints, config.threadPriority, config.wrapperInfo);
+        null, config.offline, config.serviceEndpoints, config.threadPriority, config.wrapperInfo,
+        instanceId);
     LoggingConfiguration loggingConfig = config.logging.build(minimalContext);
-    
+
     ClientContext contextWithLogging = new ClientContext(sdkKey, config.applicationInfo, null,
-        loggingConfig, config.offline, config.serviceEndpoints, config.threadPriority, config.wrapperInfo);
+        loggingConfig, config.offline, config.serviceEndpoints, config.threadPriority,
+        config.wrapperInfo, instanceId);
     HttpConfiguration httpConfig = config.http.build(contextWithLogging);
-    
+
     if (httpConfig.getProxy() != null) {
       contextWithLogging.getBaseLogger().info("Using proxy: {} {} authentication.",
           httpConfig.getProxy(),
           httpConfig.getProxyAuthentication() == null ? "without" : "with");
     }
-
-    ClientContext contextWithHttpAndLogging = new ClientContext(sdkKey, config.applicationInfo, httpConfig,
-        loggingConfig, config.offline, config.serviceEndpoints, config.threadPriority, config.wrapperInfo);
+
+    ClientContext contextWithHttpAndLogging = new ClientContext(sdkKey, config.applicationInfo,
+        httpConfig, loggingConfig, config.offline, config.serviceEndpoints, config.threadPriority,
+        config.wrapperInfo, instanceId);
 
     // Create a diagnostic store only if diagnostics are enabled. Diagnostics are enabled as long as 1. the
     // opt-out property was not set in the config, and 2. we are using the standard event processor.

lib/sdk/server/src/main/java/com/launchdarkly/sdk/server/ComponentsImpl.java

@@ -304,6 +304,15 @@ private Result transformResult(com.launchdarkly.sdk.server.subsystems.EventSende
   }
 
   static final class HttpConfigurationBuilderImpl extends HttpConfigurationBuilder {
+    /**
+     * HTTP header used to identify this SDK instance for the purpose of estimating
+     * server-connection-minutes when polling. It contains a v4 UUID that is generated once per SDK
+     * instance and remains constant for the lifetime of the client.
+     *
+     * <p>See: sdk-specs / SCMP-server-connection-minutes-polling.
+     */
+    static final String INSTANCE_ID_HEADER = "X-LaunchDarkly-Instance-Id";
+
     @Override
     public HttpConfiguration build(ClientContext clientContext) {
       LDLogger logger = clientContext.getBaseLogger();
@@ -340,6 +349,16 @@ else if (wrapperName != null) {
         headers.put("X-LaunchDarkly-Wrapper", wrapperId);
       }
 
+      // The instance ID originates on ClientContext (generated once when LDClient is constructed)
+      // so every subsystem built from the same context observes a consistent value for the
+      // lifetime of the SDK instance.
+      String instanceId = clientContext.getInstanceId();
+      if (instanceId != null && !instanceId.isEmpty()) {
+        headers.put(INSTANCE_ID_HEADER, instanceId);
+      }
+
+      // For consistency with other SDKs, custom headers are allowed to overwrite headers such as
+      // User-Agent and Authorization.
       if (!customHeaders.isEmpty()) {
           headers.putAll(customHeaders);
       }

lib/sdk/server/src/main/java/com/launchdarkly/sdk/server/subsystems/ClientContext.java

@@ -8,6 +8,8 @@
 import com.launchdarkly.sdk.server.interfaces.ServiceEndpoints;
 import com.launchdarkly.sdk.server.interfaces.WrapperInfo;
 
+import java.util.UUID;
+
 /**
  * Context information provided by the {@link com.launchdarkly.sdk.server.LDClient} when creating components.
  * <p>
@@ -31,11 +33,18 @@ public class ClientContext {
   private final boolean offline;
   private final ServiceEndpoints serviceEndpoints;
   private final int threadPriority;
+  private final String instanceId;
   private WrapperInfo wrapperInfo;
 
   /**
-   * Constructor that sets all properties. All should be non-null.
-   * 
+   * Constructor that sets all properties including an explicit instance ID. All should be
+   * non-null.
+   *
+   * <p>The instance ID is sent on every outbound request in the {@code X-LaunchDarkly-Instance-Id}
+   * header. It must be generated once per LDClient and remain stable for the client's lifetime.
+   * The eight-argument constructor auto-generates a v4 UUID for callers that do not need to
+   * supply their own value.
+   *
    * @param sdkKey the SDK key
    * @param applicationInfo application metadata properties from
    *   {@link Builder#applicationInfo(com.launchdarkly.sdk.server.integrations.ApplicationInfoBuilder)}
@@ -46,6 +55,7 @@ public class ClientContext {
    *   {@link Builder#serviceEndpoints(com.launchdarkly.sdk.server.integrations.ServiceEndpointsBuilder)}
    * @param threadPriority worker thread priority from {@link Builder#threadPriority(int)}
    * @param wrapperInfo wrapper configuration from {@link Builder#wrapper(com.launchdarkly.sdk.server.integrations.WrapperInfoBuilder)}
+   * @param instanceId per-LDClient identifier for the {@code X-LaunchDarkly-Instance-Id} header
    */
   public ClientContext(
       String sdkKey,
@@ -55,7 +65,8 @@ public ClientContext(
       boolean offline,
       ServiceEndpoints serviceEndpoints,
       int threadPriority,
-      WrapperInfo wrapperInfo
+      WrapperInfo wrapperInfo,
+      String instanceId
       ) {
     this.sdkKey = sdkKey;
     this.applicationInfo = applicationInfo;
@@ -65,19 +76,51 @@ public ClientContext(
     this.serviceEndpoints = serviceEndpoints;
     this.threadPriority = threadPriority;
     this.wrapperInfo = wrapperInfo;
-
+    this.instanceId = instanceId;
+
     this.baseLogger = logging == null ? LDLogger.none() :
       LDLogger.withAdapter(logging.getLogAdapter(), logging.getBaseLoggerName());
   }
-
+
+  /**
+   * Constructor that sets all properties. All should be non-null. Auto-generates a v4 UUID for
+   * the instance ID; use the nine-argument constructor if you need to thread an existing value
+   * through (for example, when copying a context for an in-flight LDClient).
+   *
+   * @param sdkKey the SDK key
+   * @param applicationInfo application metadata properties from
+   *   {@link Builder#applicationInfo(com.launchdarkly.sdk.server.integrations.ApplicationInfoBuilder)}
+   * @param http HTTP configuration properties from {@link Builder#http(ComponentConfigurer)}
+   * @param logging logging configuration properties from {@link Builder#logging(ComponentConfigurer)}
+   * @param offline true if the SDK should be entirely offline
+   * @param serviceEndpoints service endpoint URI properties from
+   *   {@link Builder#serviceEndpoints(com.launchdarkly.sdk.server.integrations.ServiceEndpointsBuilder)}
+   * @param threadPriority worker thread priority from {@link Builder#threadPriority(int)}
+   * @param wrapperInfo wrapper configuration from {@link Builder#wrapper(com.launchdarkly.sdk.server.integrations.WrapperInfoBuilder)}
+   */
+  public ClientContext(
+      String sdkKey,
+      ApplicationInfo applicationInfo,
+      HttpConfiguration http,
+      LoggingConfiguration logging,
+      boolean offline,
+      ServiceEndpoints serviceEndpoints,
+      int threadPriority,
+      WrapperInfo wrapperInfo
+      ) {
+    this(sdkKey, applicationInfo, http, logging, offline, serviceEndpoints, threadPriority,
+        wrapperInfo, UUID.randomUUID().toString());
+  }
+
   /**
    * Copy constructor.
-   * 
+   *
    * @param copyFrom the instance to copy from
    */
   protected ClientContext(ClientContext copyFrom) {
     this(copyFrom.sdkKey, copyFrom.applicationInfo, copyFrom.http, copyFrom.logging,
-        copyFrom.offline, copyFrom.serviceEndpoints, copyFrom.threadPriority, copyFrom.wrapperInfo);
+        copyFrom.offline, copyFrom.serviceEndpoints, copyFrom.threadPriority, copyFrom.wrapperInfo,
+        copyFrom.instanceId);
   }
 
   /**
@@ -199,13 +242,24 @@ public ServiceEndpoints getServiceEndpoints() {
   /**
    * Returns the worker thread priority that is set by
    * {@link Builder#threadPriority(int)}.
-   * 
+   *
    * @return the thread priority
    */
   public int getThreadPriority() {
     return threadPriority;
   }
 
+  /**
+   * Returns the per-LDClient instance identifier sent in the {@code X-LaunchDarkly-Instance-Id}
+   * header on outbound requests. The value is generated once when the {@link ClientContext} is
+   * constructed and is stable for the client's lifetime.
+   *
+   * @return the instance ID
+   */
+  public String getInstanceId() {
+    return instanceId;
+  }
+
   /**
    * Returns the wrapper information.
    *

lib/sdk/server/src/test/java/com/launchdarkly/sdk/server/DefaultFeatureRequestorTest.java

@@ -245,6 +245,14 @@ public void ignoreEmptyFilter()  throws Exception {
   private void verifyHeaders(RequestInfo req) {
     HttpConfiguration httpConfig = clientContext(sdkKey, LDConfig.DEFAULT).getHttp();
     for (Map.Entry<String, String> kv: httpConfig.getDefaultHeaders()) {
+      // X-LaunchDarkly-Instance-Id is a per-HttpConfiguration random UUID, so the value generated
+      // here won't match the one used by the requestor in the test. We only verify that *some*
+      // instance ID header is present on the request; per-builder uniqueness is covered in
+      // HttpConfigurationBuilderTest.
+      if (kv.getKey().equals("X-LaunchDarkly-Instance-Id")) {
+        assertNotNull(req.getHeader(kv.getKey()));
+        continue;
+      }
       assertThat(req.getHeader(kv.getKey()), equalTo(kv.getValue()));
     }
   }

lib/sdk/server/src/test/java/com/launchdarkly/sdk/server/LDConfigTest.java

@@ -24,6 +24,8 @@
 import java.net.URI;
 import java.time.Duration;
 import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import static com.launchdarkly.sdk.server.TestComponents.clientContext;
@@ -198,7 +200,14 @@ public void testHttpDefaults() {
     assertEquals(defaults.getSocketTimeout(), hc.getSocketTimeout());
     assertNull(hc.getSslSocketFactory());
     assertNull(hc.getTrustManager());
-    assertEquals(ImmutableMap.copyOf(defaults.getDefaultHeaders()), ImmutableMap.copyOf(hc.getDefaultHeaders()));
+    // The X-LaunchDarkly-Instance-Id header is a fresh UUID per HttpConfiguration, so it will
+    // differ between the two configurations; compare the remaining headers and verify the
+    // instance-id header is present on both.
+    Map<String, String> defaultHeaders = new HashMap<>(ImmutableMap.copyOf(defaults.getDefaultHeaders()));
+    Map<String, String> hcHeaders = new HashMap<>(ImmutableMap.copyOf(hc.getDefaultHeaders()));
+    assertNotNull(defaultHeaders.remove("X-LaunchDarkly-Instance-Id"));
+    assertNotNull(hcHeaders.remove("X-LaunchDarkly-Instance-Id"));
+    assertEquals(defaultHeaders, hcHeaders);
   }
 
   @Test

lib/sdk/server/src/test/java/com/launchdarkly/sdk/server/StreamProcessorTest.java

@@ -208,6 +208,13 @@ public void verifyStreamRequestProperties() throws Exception {
         assertThat(req.getPath(), equalTo("/all"));
 
         for (Map.Entry<String, String> kv: httpConfig.getDefaultHeaders()) {
+          // X-LaunchDarkly-Instance-Id is a per-HttpConfiguration random UUID and the
+          // configuration here is a fresh build, distinct from the one used by the stream
+          // processor; only assert presence.
+          if (kv.getKey().equals("X-LaunchDarkly-Instance-Id")) {
+            assertNotNull(req.getHeader(kv.getKey()));
+            continue;
+          }
           assertThat(req.getHeader(kv.getKey()), equalTo(kv.getValue()));
         }
         assertThat(req.getHeader("Accept"), equalTo("text/event-stream"));