feat: Support for tracing ID headers

src/main/java/io/qdrant/client/QdrantGrpcClient.java

@@ -1,6 +1,8 @@
 package io.qdrant.client;
 
 import io.grpc.CallCredentials;
+import io.grpc.Channel;
+import io.grpc.ClientInterceptors;
 import io.grpc.Deadline;
 import io.grpc.ManagedChannel;
 import io.grpc.ManagedChannelBuilder;
@@ -21,6 +23,7 @@ public class QdrantGrpcClient implements AutoCloseable {
   private static final Logger logger = LoggerFactory.getLogger(QdrantGrpcClient.class);
   @Nullable private final CallCredentials callCredentials;
   private final ManagedChannel channel;
+  private final Channel interceptedChannel;
   private final boolean shutdownChannelOnClose;
   @Nullable private final Duration timeout;
 
@@ -31,6 +34,8 @@ public class QdrantGrpcClient implements AutoCloseable {
       @Nullable Duration timeout) {
     this.callCredentials = callCredentials;
     this.channel = channel;
+    this.interceptedChannel =
+        ClientInterceptors.intercept(channel, RequestHeaders.newInterceptor());
     this.shutdownChannelOnClose = shutdownChannelOnClose;
     this.timeout = timeout;
   }
@@ -136,7 +141,7 @@ public ManagedChannel channel() {
    * @return a new instance of {@link QdrantFutureStub}
    */
   public QdrantGrpc.QdrantFutureStub qdrant() {
-    return QdrantGrpc.newFutureStub(channel)
+    return QdrantGrpc.newFutureStub(interceptedChannel)
         .withCallCredentials(callCredentials)
         .withDeadline(
             timeout != null ? Deadline.after(timeout.toMillis(), TimeUnit.MILLISECONDS) : null);
@@ -148,7 +153,7 @@ public QdrantGrpc.QdrantFutureStub qdrant() {
    * @return a new instance of {@link PointsFutureStub}
    */
   public PointsFutureStub points() {
-    return PointsGrpc.newFutureStub(channel)
+    return PointsGrpc.newFutureStub(interceptedChannel)
         .withCallCredentials(callCredentials)
         .withDeadline(
             timeout != null ? Deadline.after(timeout.toMillis(), TimeUnit.MILLISECONDS) : null);
@@ -160,7 +165,7 @@ public PointsFutureStub points() {
    * @return a new instance of {@link CollectionsFutureStub}
    */
   public CollectionsFutureStub collections() {
-    return CollectionsGrpc.newFutureStub(channel)
+    return CollectionsGrpc.newFutureStub(interceptedChannel)
         .withCallCredentials(callCredentials)
         .withDeadline(
             timeout != null ? Deadline.after(timeout.toMillis(), TimeUnit.MILLISECONDS) : null);
@@ -172,7 +177,7 @@ public CollectionsFutureStub collections() {
    * @return a new instance of {@link SnapshotsFutureStub}
    */
   public SnapshotsFutureStub snapshots() {
-    return SnapshotsGrpc.newFutureStub(channel)
+    return SnapshotsGrpc.newFutureStub(interceptedChannel)
         .withCallCredentials(callCredentials)
         .withDeadline(
             timeout != null ? Deadline.after(timeout.toMillis(), TimeUnit.MILLISECONDS) : null);

src/main/java/io/qdrant/client/RequestHeaders.java

@@ -0,0 +1,85 @@
+package io.qdrant.client;
+
+import io.grpc.CallOptions;
+import io.grpc.Channel;
+import io.grpc.ClientCall;
+import io.grpc.ClientInterceptor;
+import io.grpc.Context;
+import io.grpc.ForwardingClientCall;
+import io.grpc.Metadata;
+import io.grpc.MethodDescriptor;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Utilities for attaching per-request headers to gRPC calls.
+ *
+ * <pre>{@code
+ * Context ctx = RequestHeaders.withHeader(Context.current(), "x-request-id", "abc-123");
+ * ctx.run(() -> client.listCollectionsAsync());
+ * }</pre>
+ */
+public final class RequestHeaders {
+
+  static final Context.Key<Map<String, String>> HEADERS_KEY = Context.key("qdrant-request-headers");
+
+  private RequestHeaders() {}
+
+  /**
+   * Returns a new {@link Context} that carries key/value as a gRPC metadata header on every request
+   * started within that context.
+   *
+   * @param ctx the parent context
+   * @param key the header name
+   * @param value the header value
+   * @return a child context with the header attached
+   */
+  public static Context withHeader(Context ctx, String key, String value) {
+    return withHeaders(ctx, Collections.singletonMap(key, value));
+  }
+
+  /**
+   * Returns a new {@link Context} that carries all entries of headers as gRPC metadata on every
+   * request started within that context.
+   *
+   * @param ctx the parent context
+   * @param headers the headers to attach
+   * @return a child context with the headers attached
+   */
+  public static Context withHeaders(Context ctx, Map<String, String> headers) {
+    if (headers == null || headers.isEmpty()) {
+      return ctx;
+    }
+    Map<String, String> merged = new HashMap<>();
+    Map<String, String> current = HEADERS_KEY.get(ctx);
+    if (current != null) merged.putAll(current);
+    merged.putAll(headers);
+    return ctx.withValue(HEADERS_KEY, merged);
+  }
+
+  /** Returns a {@link ClientInterceptor} that injects per-request headers from the context. */
+  static ClientInterceptor newInterceptor() {
+    return new ClientInterceptor() {
+      @Override
+      public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
+          MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next) {
+        return new ForwardingClientCall.SimpleForwardingClientCall<ReqT, RespT>(
+            next.newCall(method, callOptions)) {
+          @Override
+          public void start(Listener<RespT> responseListener, Metadata headers) {
+            Map<String, String> extra = HEADERS_KEY.get();
+            if (extra != null) {
+              for (Map.Entry<String, String> entry : extra.entrySet()) {
+                headers.put(
+                    Metadata.Key.of(entry.getKey(), Metadata.ASCII_STRING_MARSHALLER),
+                    entry.getValue());
+              }
+            }
+            super.start(responseListener, headers);
+          }
+        };
+      }
+    };
+  }
+}