Remove Headers

auth/src/main/java/io/grpc/auth/ClientAuthInterceptor.java

@@ -59,7 +59,7 @@ public class ClientAuthInterceptor implements ClientInterceptor {
 
   private final Credentials credentials;
 
-  private Metadata.Headers cached;
+  private Metadata cached;
   private Map<String, List<String>> lastMetadata;
   // TODO(louiscryan): refresh token asynchronously with this executor.
   private Executor executor;
@@ -76,9 +76,9 @@ public class ClientAuthInterceptor implements ClientInterceptor {
     // would be in WWW-Authenticate, because it does not yet have access to the header.
     return new CheckedForwardingClientCall<ReqT, RespT>(next.newCall(method, callOptions)) {
       @Override
-      protected void checkedStart(Listener<RespT> responseListener, Metadata.Headers headers)
+      protected void checkedStart(Listener<RespT> responseListener, Metadata headers)
           throws Exception {
-        Metadata.Headers cachedSaved;
+        Metadata cachedSaved;
         synchronized (ClientAuthInterceptor.this) {
           // TODO(louiscryan): This is icky but the current auth library stores the same
           // metadata map until the next refresh cycle. This will be fixed once
@@ -104,8 +104,8 @@ public class ClientAuthInterceptor implements ClientInterceptor {
     }
   }
 
-  private static final Metadata.Headers toHeaders(Map<String, List<String>> metadata) {
+  private static final Metadata toHeaders(Map<String, List<String>> metadata) {
-    Metadata.Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     if (metadata != null) {
       for (String key : metadata.keySet()) {
         Metadata.Key<String> headerKey = Metadata.Key.of(key, Metadata.ASCII_STRING_MARSHALLER);

auth/src/test/java/io/grpc/auth/ClientAuthInterceptorTests.java

@@ -31,10 +31,10 @@
 
 package io.grpc.auth;
 
-import static org.mockito.Mockito.any;
+import static org.mockito.Matchers.any;
-import static org.mockito.Mockito.isA;
+import static org.mockito.Matchers.isA;
+import static org.mockito.Matchers.same;
 import static org.mockito.Mockito.never;
-import static org.mockito.Mockito.same;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
@@ -114,7 +114,7 @@ public class ClientAuthInterceptorTests {
     when(credentials.getRequestMetadata()).thenReturn(Multimaps.asMap(values));
     ClientCall<String, Integer> interceptedCall =
         interceptor.interceptCall(descriptor, CallOptions.DEFAULT, channel);
-    Metadata.Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     interceptedCall.start(listener, headers);
     verify(call).start(listener, headers);
 
@@ -131,7 +131,7 @@ public class ClientAuthInterceptorTests {
     when(credentials.getRequestMetadata()).thenThrow(new IOException("Broken"));
     ClientCall<String, Integer> interceptedCall =
         interceptor.interceptCall(descriptor, CallOptions.DEFAULT, channel);
-    Metadata.Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     interceptedCall.start(listener, headers);
     ArgumentCaptor<Status> statusCaptor = ArgumentCaptor.forClass(Status.class);
     Mockito.verify(listener).onClose(statusCaptor.capture(), isA(Metadata.class));
@@ -142,7 +142,7 @@ public class ClientAuthInterceptorTests {
   }
 
   @Test
-  public void testWithOAuth2Credential() throws IOException {
+  public void testWithOAuth2Credential() {
     final AccessToken token = new AccessToken("allyourbase", new Date(Long.MAX_VALUE));
     final OAuth2Credentials oAuth2Credentials = new OAuth2Credentials() {
       @Override
@@ -153,7 +153,7 @@ public class ClientAuthInterceptorTests {
     interceptor = new ClientAuthInterceptor(oAuth2Credentials, Executors.newSingleThreadExecutor());
     ClientCall<String, Integer> interceptedCall =
         interceptor.interceptCall(descriptor, CallOptions.DEFAULT, channel);
-    Metadata.Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     interceptedCall.start(listener, headers);
     verify(call).start(listener, headers);
     Iterable<String> authorization = headers.getAll(AUTHORIZATION);

benchmarks/src/jmh/java/io/grpc/benchmarks/netty/AbstractBenchmark.java

@@ -242,7 +242,7 @@ public abstract class AbstractBenchmark {
                   public ServerCall.Listener<ByteBuf> startCall(
                       MethodDescriptor<ByteBuf, ByteBuf> method,
                       final ServerCall<ByteBuf> call,
-                      Metadata.Headers headers) {
+                      Metadata headers) {
                     call.request(1);
                     return new ServerCall.Listener<ByteBuf>() {
                       @Override
@@ -274,7 +274,7 @@ public abstract class AbstractBenchmark {
                   public ServerCall.Listener<ByteBuf> startCall(
                       MethodDescriptor<ByteBuf, ByteBuf> method,
                       final ServerCall<ByteBuf> call,
-                      Metadata.Headers headers) {
+                      Metadata headers) {
                     call.request(1);
                     return new ServerCall.Listener<ByteBuf>() {
                       @Override
@@ -308,7 +308,7 @@ public abstract class AbstractBenchmark {
                   public ServerCall.Listener<ByteBuf> startCall(
                       MethodDescriptor<ByteBuf, ByteBuf> method,
                       final ServerCall<ByteBuf> call,
-                      Metadata.Headers headers) {
+                      Metadata headers) {
                     call.request(1);
                     return new ServerCall.Listener<ByteBuf>() {
                       @Override

core/src/main/java/io/grpc/CallOptions.java

@@ -57,9 +57,29 @@ public final class CallOptions {
   // unnamed arguments, which is undesirable.
   private Long deadlineNanoTime;
 
+
   @Nullable
   private Compressor compressor;
 
+  @Nullable
+  private String authority;
+
+  /**
+   * Override the HTTP/2 authority the channel claims to be connecting to. <em>This is not
+   * generally safe.</em> Overriding allows advanced users to re-use a single Channel for multiple
+   * services, even if those services are hosted on different domain names. That assumes the
+   * server is virtually hosting multiple domains and is guaranteed to continue doing so. It is
+   * rare for a service provider to make such a guarantee. <em>At this time, there is no security
+   * verification of the overridden value, such as making sure the authority matches the server's
+   * TLS certificate.</em>
+   */
+  @ExperimentalApi
+  public CallOptions withAuthority(@Nullable String authority) {
+    CallOptions newOptions = new CallOptions(this);
+    newOptions.authority = authority;
+    return newOptions;
+  }
+
   /**
    * Returns a new {@code CallOptions} with the given absolute deadline in nanoseconds in the clock
    * as per {@link System#nanoTime()}.
@@ -110,6 +130,20 @@ public final class CallOptions {
     return newOptions;
   }
 
+  /**
+   * Override the HTTP/2 authority the channel claims to be connecting to. <em>This is not
+   * generally safe.</em> Overriding allows advanced users to re-use a single Channel for multiple
+   * services, even if those services are hosted on different domain names. That assumes the
+   * server is virtually hosting multiple domains and is guaranteed to continue doing so. It is
+   * rare for a service provider to make such a guarantee. <em>At this time, there is no security
+   * verification of the overridden value, such as making sure the authority matches the server's
+   * TLS certificate.</em>
+   */
+  @Nullable
+  public String getAuthority() {
+    return authority;
+  }
+
   private CallOptions() {
   }
 
@@ -119,6 +153,7 @@ public final class CallOptions {
   private CallOptions(CallOptions other) {
     deadlineNanoTime = other.deadlineNanoTime;
     compressor = other.compressor;
+    authority = other.authority;
   }
 
   @SuppressWarnings("deprecation") // guava 14.0

core/src/main/java/io/grpc/ChannelImpl.java

@@ -35,7 +35,7 @@ import static io.grpc.internal.GrpcUtil.TIMER_SERVICE;
 
 import io.grpc.ClientCallImpl.ClientTransportProvider;
 import io.grpc.MessageEncoding.Compressor;
-import io.grpc.Metadata.Headers;
+import io.grpc.Metadata;
 import io.grpc.internal.ClientStream;
 import io.grpc.internal.ClientStreamListener;
 import io.grpc.internal.ClientTransport;
@@ -393,7 +393,7 @@ public final class ChannelImpl extends Channel {
 
     @Override
     public ClientStream newStream(
-        MethodDescriptor<?, ?> method, Headers headers, ClientStreamListener listener) {
+        MethodDescriptor<?, ?> method, Metadata headers, ClientStreamListener listener) {
       listener.closed(shutdownStatus, new Metadata());
       return new ClientCallImpl.NoopClientStream();
     }

core/src/main/java/io/grpc/ClientCall.java

@@ -80,7 +80,7 @@ public abstract class ClientCall<RequestT, ResponseT> {
      *
      * @param headers containing metadata sent by the server at the start of the response.
      */
-    public abstract void onHeaders(Metadata.Headers headers);
+    public abstract void onHeaders(Metadata headers);
 
     /**
      * A response message has been received. May be called zero or more times depending on whether
@@ -123,7 +123,7 @@ public abstract class ClientCall<RequestT, ResponseT> {
    * @throws IllegalStateException if a method (including {@code start()}) on this class has been
    *                               called.
    */
-  public abstract void start(Listener<ResponseT> responseListener, Metadata.Headers headers);
+  public abstract void start(Listener<ResponseT> responseListener, Metadata headers);
 
   /**
    * Requests up to the given number of messages from the call to be delivered to

core/src/main/java/io/grpc/ClientCallImpl.java

@@ -31,6 +31,7 @@
 
 package io.grpc;
 
+import static io.grpc.internal.GrpcUtil.AUTHORITY_KEY;
 import static io.grpc.internal.GrpcUtil.MESSAGE_ENCODING_KEY;
 import static io.grpc.internal.GrpcUtil.TIMEOUT_KEY;
 import static io.grpc.internal.GrpcUtil.USER_AGENT_KEY;
@@ -94,7 +95,7 @@ final class ClientCallImpl<ReqT, RespT> extends ClientCall<ReqT, RespT> {
   }
 
   @Override
-  public void start(Listener<RespT> observer, Metadata.Headers headers) {
+  public void start(Listener<RespT> observer, Metadata headers) {
     Preconditions.checkState(stream == null, "Already started");
     Long deadlineNanoTime = callOptions.getDeadlineNanoTime();
     ClientStreamListener listener = new ClientStreamListenerImpl(observer, deadlineNanoTime);
@@ -124,6 +125,13 @@ final class ClientCallImpl<ReqT, RespT> extends ClientCall<ReqT, RespT> {
       headers.put(TIMEOUT_KEY, timeoutMicros);
     }
 
+    // Hack to propagate authority.  This should be properly pass to the transport.newStream
+    // somehow.
+    headers.removeAll(AUTHORITY_KEY);
+    if (callOptions.getAuthority() != null) {
+      headers.put(AUTHORITY_KEY, callOptions.getAuthority());
+    }
+
     // Fill out the User-Agent header.
     headers.removeAll(USER_AGENT_KEY);
     if (userAgent != null) {
@@ -241,7 +249,7 @@ final class ClientCallImpl<ReqT, RespT> extends ClientCall<ReqT, RespT> {
     }
 
     @Override
-    public void headersRead(final Metadata.Headers headers) {
+    public void headersRead(final Metadata headers) {
       callExecutor.execute(new Runnable() {
         @Override
         public void run() {

core/src/main/java/io/grpc/ClientInterceptors.java

@@ -92,7 +92,7 @@ public class ClientInterceptors {
 
   private static final ClientCall<Object, Object> NOOP_CALL = new ClientCall<Object, Object>() {
     @Override
-    public void start(Listener<Object> responseListener, Metadata.Headers headers) {}
+    public void start(Listener<Object> responseListener, Metadata headers) {}
 
     @Override
     public void request(int numMessages) {}
@@ -120,7 +120,7 @@ public class ClientInterceptors {
    * A {@link io.grpc.ForwardingClientCall} that delivers exceptions from its start logic to the
    * call listener.
    *
-   * <p>{@link ClientCall#start(ClientCall.Listener, Metadata.Headers)} should not throw any
+   * <p>{@link ClientCall#start(ClientCall.Listener, Metadata)} should not throw any
    * exception other than those caused by misuse, e.g., {@link IllegalStateException}.  {@code
    * CheckedForwardingClientCall} provides {@code checkedStart()} in which throwing exceptions is
    * allowed.
@@ -140,7 +140,7 @@ public class ClientInterceptors {
      * this.delegate().start()}, as this can result in {@link ClientCall.Listener#onClose} being
      * called multiple times.
      */
-    protected abstract void checkedStart(Listener<RespT> responseListener, Metadata.Headers headers)
+    protected abstract void checkedStart(Listener<RespT> responseListener, Metadata headers)
         throws Exception;
 
     protected CheckedForwardingClientCall(ClientCall<ReqT, RespT> delegate) {
@@ -154,7 +154,7 @@ public class ClientInterceptors {
 
     @Override
     @SuppressWarnings("unchecked")
-    public final void start(Listener<RespT> responseListener, Metadata.Headers headers) {
+    public final void start(Listener<RespT> responseListener, Metadata headers) {
       try {
         checkedStart(responseListener, headers);
       } catch (Exception e) {

core/src/main/java/io/grpc/ForwardingClientCall.java

@@ -41,7 +41,7 @@ public abstract class ForwardingClientCall<ReqT, RespT> extends ClientCall<ReqT,
   protected abstract ClientCall<ReqT, RespT> delegate();
 
   @Override
-  public void start(Listener<RespT> responseListener, Metadata.Headers headers) {
+  public void start(Listener<RespT> responseListener, Metadata headers) {
     delegate().start(responseListener, headers);
   }
 

core/src/main/java/io/grpc/ForwardingClientCallListener.java

@@ -42,7 +42,7 @@ public abstract class ForwardingClientCallListener<RespT> extends ClientCall.Lis
   protected abstract ClientCall.Listener<RespT> delegate();
 
   @Override
-  public void onHeaders(Metadata.Headers headers) {
+  public void onHeaders(Metadata headers) {
     delegate().onHeaders(headers);
   }
 

core/src/main/java/io/grpc/ForwardingServerCall.java

@@ -46,7 +46,7 @@ public abstract class ForwardingServerCall<RespT> extends ServerCall<RespT> {
   }
 
   @Override
-  public void sendHeaders(Metadata.Headers headers) {
+  public void sendHeaders(Metadata headers) {
     delegate().sendHeaders(headers);
   }
 

core/src/main/java/io/grpc/Metadata.java

@@ -38,6 +38,8 @@ import com.google.common.base.Function;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Iterables;
 
+import io.grpc.internal.GrpcUtil;
+
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.LinkedHashMap;
@@ -239,6 +241,11 @@ public class Metadata {
     // One *2 for keys+values, one *2 to prevent resizing if a single key has multiple values
     List<byte[]> serialized = new ArrayList<byte[]>(store.size() * 2 * 2);
     for (Map.Entry<String, List<MetadataEntry>> keyEntry : store.entrySet()) {
+      // Intentionally skip this field on serialization.  It must be handled special by the
+      // transport.
+      if (keyEntry.getKey().equals(GrpcUtil.AUTHORITY_KEY.name())) {
+        continue;
+      }
       for (int i = 0; i < keyEntry.getValue().size(); i++) {
         MetadataEntry entry = keyEntry.getValue().get(i);
         byte[] asciiName;
@@ -297,84 +304,17 @@ public class Metadata {
 
   /**
    * Concrete instance for metadata attached to the start of a call.
-   */
-  public static class Headers extends Metadata {
-    private String path;
-    private String authority;
-
-    /**
-     * Called by the transport layer to create headers from their binary serialized values.
    *
-     * <p>This method does not copy the provided byte arrays. The byte arrays must not be mutated.
+   * @deprecated use Metadata instead.
    */
-    public Headers(byte[]... headers) {
+  @Deprecated
-      super(headers);
+  public static class Headers extends Metadata {
-    }
-
     /**
      * Called by the application layer to construct headers prior to passing them to the
      * transport for serialization.
      */
     public Headers() {
     }
-
-    /**
-     * The path for the operation.
-     */
-    public String getPath() {
-      return path;
-    }
-
-    public void setPath(String path) {
-      this.path = path;
-    }
-
-    /**
-     * The serving authority for the operation.
-     */
-    public String getAuthority() {
-      return authority;
-    }
-
-    /**
-     * Override the HTTP/2 authority the channel claims to be connecting to. <em>This is not
-     * generally safe.</em> Overriding allows advanced users to re-use a single Channel for multiple
-     * services, even if those services are hosted on different domain names. That assumes the
-     * server is virtually hosting multiple domains and is guaranteed to continue doing so. It is
-     * rare for a service provider to make such a guarantee. <em>At this time, there is no security
-     * verification of the overridden value, such as making sure the authority matches the server's
-     * TLS certificate.</em>
-     */
-    public void setAuthority(String authority) {
-      this.authority = authority;
-    }
-
-    @Override
-    public void merge(Metadata other) {
-      super.merge(other);
-      mergePathAndAuthority(other);
-    }
-
-    @Override
-    public void merge(Metadata other, Set<Key<?>> keys) {
-      super.merge(other, keys);
-      mergePathAndAuthority(other);
-    }
-
-    private void mergePathAndAuthority(Metadata other) {
-      if (other instanceof Headers) {
-        Headers otherHeaders = (Headers) other;
-        path = otherHeaders.path != null ? otherHeaders.path : path;
-        authority = otherHeaders.authority != null ? otherHeaders.authority : authority;
-      }
-    }
-
-    @Override
-    public String toString() {
-      return "Headers(path=" + path
-          + ",authority=" + authority
-          + ",metadata=" + super.toStringInternal() + ")";
-    }
   }
 
   /**

core/src/main/java/io/grpc/ServerCall.java

@@ -121,7 +121,7 @@ public abstract class ServerCall<ResponseT> {
    * @throws IllegalStateException if {@code close} has been called, a message has been sent, or
    *     headers have already been sent
    */
-  public abstract void sendHeaders(Metadata.Headers headers);
+  public abstract void sendHeaders(Metadata headers);
 
   /**
    * Send a response message. Messages are the primary form of communication associated with

core/src/main/java/io/grpc/ServerCallHandler.java

@@ -54,5 +54,5 @@ public interface ServerCallHandler<RequestT, ResponseT> {
   ServerCall.Listener<RequestT> startCall(
       MethodDescriptor<RequestT, ResponseT> method,
       ServerCall<ResponseT> call,
-      Metadata.Headers headers);
+      Metadata headers);
 }

core/src/main/java/io/grpc/ServerImpl.java

@@ -293,7 +293,7 @@ public final class ServerImpl extends Server {
 
     @Override
     public ServerStreamListener streamCreated(final ServerStream stream, final String methodName,
-        final Metadata.Headers headers) {
+        final Metadata headers) {
       final Future<?> timeout = scheduleTimeout(stream, headers);
       SerializingExecutor serializingExecutor = new SerializingExecutor(executor);
       final JumpToApplicationThreadServerStreamListener jumpListener
@@ -328,7 +328,7 @@ public final class ServerImpl extends Server {
       return jumpListener;
     }
 
-    private Future<?> scheduleTimeout(final ServerStream stream, Metadata.Headers headers) {
+    private Future<?> scheduleTimeout(final ServerStream stream, Metadata headers) {
       Long timeoutMicros = headers.get(TIMEOUT_KEY);
       if (timeoutMicros == null) {
         return DEFAULT_TIMEOUT_FUTURE;
@@ -348,7 +348,7 @@ public final class ServerImpl extends Server {
     /** Never returns {@code null}. */
     private <ReqT, RespT> ServerStreamListener startCall(ServerStream stream, String fullMethodName,
         ServerMethodDefinition<ReqT, RespT> methodDef, Future<?> timeout,
-        Metadata.Headers headers) {
+        Metadata headers) {
       // TODO(ejona86): should we update fullMethodName to have the canonical path of the method?
       final ServerCallImpl<ReqT, RespT> call = new ServerCallImpl<ReqT, RespT>(
           stream, methodDef.getMethodDescriptor());
@@ -489,7 +489,7 @@ public final class ServerImpl extends Server {
     }
 
     @Override
-    public void sendHeaders(Metadata.Headers headers) {
+    public void sendHeaders(Metadata headers) {
       Preconditions.checkState(!sendHeadersCalled, "sendHeaders has already been called");
       Preconditions.checkState(!closeCalled, "call is closed");
       Preconditions.checkState(!sendMessageCalled, "sendMessage has already been called");

core/src/main/java/io/grpc/ServerInterceptor.java

@@ -64,6 +64,6 @@ public interface ServerInterceptor {
   <RequestT, ResponseT> ServerCall.Listener<RequestT> interceptCall(
       MethodDescriptor<RequestT, ResponseT> method,
       ServerCall<ResponseT> call,
-      Metadata.Headers headers,
+      Metadata headers,
       ServerCallHandler<RequestT, ResponseT> next);
 }

core/src/main/java/io/grpc/ServerInterceptors.java

@@ -109,7 +109,7 @@ public class ServerInterceptors {
     public ServerCall.Listener<ReqT> startCall(
         MethodDescriptor<ReqT, RespT> method,
         ServerCall<RespT> call,
-        Metadata.Headers headers) {
+        Metadata headers) {
       return interceptor.interceptCall(method, call, headers, callHandler);
     }
   }

core/src/main/java/io/grpc/inprocess/InProcessTransport.java

@@ -38,6 +38,7 @@ import io.grpc.Status;
 import io.grpc.internal.ClientStream;
 import io.grpc.internal.ClientStreamListener;
 import io.grpc.internal.ClientTransport;
+import io.grpc.internal.GrpcUtil;
 import io.grpc.internal.ServerStream;
 import io.grpc.internal.ServerStreamListener;
 import io.grpc.internal.ServerTransport;
@@ -106,11 +107,12 @@ class InProcessTransport implements ServerTransport, ClientTransport {
 
   @Override
   public synchronized ClientStream newStream(MethodDescriptor<?, ?> method,
-      Metadata.Headers headers, ClientStreamListener clientStreamListener) {
+      Metadata headers, ClientStreamListener clientStreamListener) {
     if (shutdownStatus != null) {
       clientStreamListener.closed(shutdownStatus, new Metadata());
       return new NoopClientStream();
     }
+    headers.removeAll(GrpcUtil.AUTHORITY_KEY);
     InProcessStream stream = new InProcessStream();
     stream.serverStream.setListener(clientStreamListener);
     ServerStreamListener serverStreamListener = serverTransportListener.streamCreated(
@@ -265,7 +267,7 @@ class InProcessTransport implements ServerTransport, ClientTransport {
       }
 
       @Override
-      public synchronized void writeHeaders(Metadata.Headers headers) {
+      public synchronized void writeHeaders(Metadata headers) {
         if (closed) {
           return;
         }

core/src/main/java/io/grpc/internal/AbstractClientStream.java

@@ -116,7 +116,7 @@ public abstract class AbstractClientStream<IdT> extends AbstractStream<IdT>
    *
    * @param headers the parsed headers
    */
-  protected void inboundHeadersReceived(Metadata.Headers headers) {
+  protected void inboundHeadersReceived(Metadata headers) {
     if (inboundPhase() == Phase.STATUS) {
       log.log(Level.INFO, "Received headers on closed stream {0} {1}",
           new Object[]{id(), headers});

core/src/main/java/io/grpc/internal/AbstractServerStream.java

@@ -91,7 +91,7 @@ public abstract class AbstractServerStream<IdT> extends AbstractStream<IdT>
   }
 
   @Override
-  public final void writeHeaders(Metadata.Headers headers) {
+  public final void writeHeaders(Metadata headers) {
     Preconditions.checkNotNull(headers, "headers");
     outboundPhase(Phase.HEADERS);
     headersSent = true;
@@ -102,7 +102,7 @@ public abstract class AbstractServerStream<IdT> extends AbstractStream<IdT>
   @Override
   public final void writeMessage(InputStream message) {
     if (!headersSent) {
-      writeHeaders(new Metadata.Headers());
+      writeHeaders(new Metadata());
       headersSent = true;
     }
     super.writeMessage(message);
@@ -169,7 +169,7 @@ public abstract class AbstractServerStream<IdT> extends AbstractStream<IdT>
    *
    * @param headers the headers to be sent to client.
    */
-  protected abstract void internalSendHeaders(Metadata.Headers headers);
+  protected abstract void internalSendHeaders(Metadata headers);
 
   /**
    * Sends an outbound frame to the remote end point.

core/src/main/java/io/grpc/internal/ClientStreamListener.java

@@ -46,7 +46,7 @@ public interface ClientStreamListener extends StreamListener {
    *
    * @param headers the fully buffered received headers.
    */
-  void headersRead(Metadata.Headers headers);
+  void headersRead(Metadata headers);
 
   /**
    * Called when the stream is fully closed. {@link

core/src/main/java/io/grpc/internal/ClientTransport.java

@@ -67,7 +67,7 @@ public interface ClientTransport {
    */
   // TODO(nmittler): Consider also throwing for stopping.
   ClientStream newStream(MethodDescriptor<?, ?> method,
-                         Metadata.Headers headers,
+                         Metadata headers,
                          ClientStreamListener listener);
 
   /**

core/src/main/java/io/grpc/internal/GrpcUtil.java

@@ -61,6 +61,17 @@ public final class GrpcUtil {
   public static final Metadata.Key<String> MESSAGE_ENCODING_KEY =
           Metadata.Key.of(GrpcUtil.MESSAGE_ENCODING, Metadata.ASCII_STRING_MARSHALLER);
 
+  /**
+   * {@link io.grpc.Metadata.Key} for the :authority pseudo header.
+   *
+   * <p> Don't actually serialized this.
+   *
+   * <p>TODO(carl-mastrangelo): This is a hack and should exist as shortly as possible.  Remove it
+   *    once a cleaner alternative exists (passing it directly into the transport, etc.)
+   */
+  public static final Metadata.Key<String> AUTHORITY_KEY =
+          Metadata.Key.of("grpc-authority", Metadata.ASCII_STRING_MARSHALLER);
+
   /**
    * {@link io.grpc.Metadata.Key} for the Content-Type request/response header.
    */

core/src/main/java/io/grpc/internal/Http2ClientStream.java

@@ -80,7 +80,7 @@ public abstract class Http2ClientStream extends AbstractClientStream<Integer> {
    *
    * @param headers the received headers
    */
-  protected void transportHeadersReceived(Metadata.Headers headers) {
+  protected void transportHeadersReceived(Metadata headers) {
     Preconditions.checkNotNull(headers);
     if (transportError != null) {
       // Already received a transport error so just augment it.

core/src/main/java/io/grpc/internal/ServerStream.java

@@ -48,7 +48,7 @@ public interface ServerStream extends Stream {
    *
    * @param headers to send to client.
    */
-  void writeHeaders(Metadata.Headers headers);
+  void writeHeaders(Metadata headers);
 
   /**
    * Closes the stream for both reading and writing. A status code of

core/src/main/java/io/grpc/internal/ServerTransportListener.java

@@ -48,7 +48,7 @@ public interface ServerTransportListener {
    * @return a listener for events on the new stream.
    */
   ServerStreamListener streamCreated(ServerStream stream, String method,
-      Metadata.Headers headers);
+      Metadata headers);
 
   /**
    * The transport completed shutting down. All resources have been released.

core/src/test/java/io/grpc/ChannelImplTest.java

@@ -113,7 +113,7 @@ public class ChannelImplTest {
   public void immediateDeadlineExceeded() {
     ClientCall<String, Integer> call =
         channel.newCall(method, CallOptions.DEFAULT.withDeadlineNanoTime(System.nanoTime()));
-    call.start(mockCallListener, new Metadata.Headers());
+    call.start(mockCallListener, new Metadata());
     verify(mockCallListener, timeout(1000)).onClose(
         same(Status.DEADLINE_EXCEEDED), any(Metadata.class));
   }
@@ -135,7 +135,7 @@ public class ChannelImplTest {
     // Create transport and call
     ClientTransport mockTransport = mock(ClientTransport.class);
     ClientStream mockStream = mock(ClientStream.class);
-    Metadata.Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     when(mockTransportFactory.newClientTransport()).thenReturn(mockTransport);
     when(mockTransport.newStream(same(method), same(headers), any(ClientStreamListener.class)))
         .thenReturn(mockStream);
@@ -150,7 +150,7 @@ public class ChannelImplTest {
     // Second call
     ClientCall<String, Integer> call2 = channel.newCall(method, CallOptions.DEFAULT);
     ClientStream mockStream2 = mock(ClientStream.class);
-    Metadata.Headers headers2 = new Metadata.Headers();
+    Metadata headers2 = new Metadata();
     when(mockTransport.newStream(same(method), same(headers2), any(ClientStreamListener.class)))
         .thenReturn(mockStream2);
     call2.start(mockCallListener2, headers2);
@@ -169,7 +169,7 @@ public class ChannelImplTest {
 
     // Further calls should fail without going to the transport
     ClientCall<String, Integer> call3 = channel.newCall(method, CallOptions.DEFAULT);
-    call3.start(mockCallListener3, new Metadata.Headers());
+    call3.start(mockCallListener3, new Metadata());
     ArgumentCaptor<Status> statusCaptor = ArgumentCaptor.forClass(Status.class);
     verify(mockCallListener3, timeout(1000))
         .onClose(statusCaptor.capture(), any(Metadata.class));
@@ -200,7 +200,7 @@ public class ChannelImplTest {
     when(mockTransportFactory.newClientTransport()).thenReturn(mockTransport);
     doThrow(goldenStatus.asRuntimeException())
         .when(mockTransport).start(any(ClientTransport.Listener.class));
-    call.start(mockCallListener, new Metadata.Headers());
+    call.start(mockCallListener, new Metadata());
     verify(mockTransportFactory).newClientTransport();
     verify(mockTransport).start(any(ClientTransport.Listener.class));
     ArgumentCaptor<Status> statusCaptor = ArgumentCaptor.forClass(Status.class);
@@ -212,7 +212,7 @@ public class ChannelImplTest {
     call = channel.newCall(method, CallOptions.DEFAULT);
     ClientTransport mockTransport2 = mock(ClientTransport.class);
     ClientStream mockStream2 = mock(ClientStream.class);
-    Metadata.Headers headers2 = new Metadata.Headers();
+    Metadata headers2 = new Metadata();
     when(mockTransportFactory.newClientTransport()).thenReturn(mockTransport2);
     doAnswer(new Answer<Void>() {
       @Override
@@ -237,7 +237,7 @@ public class ChannelImplTest {
     call = channel.newCall(method, CallOptions.DEFAULT);
     ClientTransport mockTransport3 = mock(ClientTransport.class);
     ClientStream mockStream3 = mock(ClientStream.class);
-    Metadata.Headers headers3 = new Metadata.Headers();
+    Metadata headers3 = new Metadata();
     when(mockTransportFactory.newClientTransport()).thenReturn(mockTransport3);
     when(mockTransport3.newStream(same(method), same(headers3), any(ClientStreamListener.class)))
         .thenReturn(mockStream3);
@@ -289,7 +289,7 @@ public class ChannelImplTest {
   public void testNoDeadlockOnShutdown() {
     // Force creation of transport
     ClientCall<String, Integer> call = channel.newCall(method, CallOptions.DEFAULT);
-    call.start(mockCallListener, new Metadata.Headers());
+    call.start(mockCallListener, new Metadata());
     call.cancel();
 
     verify(mockTransport).start(transportListenerCaptor.capture());

core/src/test/java/io/grpc/ClientInterceptorsTest.java

@@ -34,11 +34,11 @@ package io.grpc;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotSame;
 import static org.junit.Assert.assertSame;
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.anyInt;
+import static org.mockito.Matchers.eq;
 import static org.mockito.Matchers.same;
-import static org.mockito.Mockito.any;
-import static org.mockito.Mockito.anyInt;
 import static org.mockito.Mockito.doAnswer;
-import static org.mockito.Mockito.eq;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
@@ -91,8 +91,7 @@ public class ClientInterceptorsTest {
     Answer<Void> checkStartCalled = new Answer<Void>() {
       @Override
       public Void answer(InvocationOnMock invocation) {
-        verify(call).start(Mockito.<ClientCall.Listener<Integer>>any(),
+        verify(call).start(Mockito.<ClientCall.Listener<Integer>>any(), Mockito.<Metadata>any());
-            Mockito.<Metadata.Headers>any());
         return null;
       }
     };
@@ -228,7 +227,7 @@ public class ClientInterceptorsTest {
         ClientCall<ReqT, RespT> call = next.newCall(method, callOptions);
         return new SimpleForwardingClientCall<ReqT, RespT>(call) {
           @Override
-          public void start(ClientCall.Listener<RespT> responseListener, Metadata.Headers headers) {
+          public void start(ClientCall.Listener<RespT> responseListener, Metadata headers) {
             headers.put(credKey, "abcd");
             super.start(responseListener, headers);
           }
@@ -240,8 +239,8 @@ public class ClientInterceptorsTest {
     ClientCall.Listener<Integer> listener = mock(ClientCall.Listener.class);
     ClientCall<String, Integer> interceptedCall = intercepted.newCall(method, CallOptions.DEFAULT);
     // start() on the intercepted call will eventually reach the call created by the real channel
-    interceptedCall.start(listener, new Metadata.Headers());
+    interceptedCall.start(listener, new Metadata());
-    ArgumentCaptor<Metadata.Headers> captor = ArgumentCaptor.forClass(Metadata.Headers.class);
+    ArgumentCaptor<Metadata> captor = ArgumentCaptor.forClass(Metadata.class);
     // The headers passed to the real channel call will contain the information inserted by the
     // interceptor.
     verify(call).start(same(listener), captor.capture());
@@ -250,7 +249,7 @@ public class ClientInterceptorsTest {
 
   @Test
   public void examineInboundHeaders() {
-    final List<Metadata.Headers> examinedHeaders = new ArrayList<Metadata.Headers>();
+    final List<Metadata> examinedHeaders = new ArrayList<Metadata>();
     ClientInterceptor interceptor = new ClientInterceptor() {
       @Override
       public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
@@ -260,10 +259,10 @@ public class ClientInterceptorsTest {
         ClientCall<ReqT, RespT> call = next.newCall(method, callOptions);
         return new SimpleForwardingClientCall<ReqT, RespT>(call) {
           @Override
-          public void start(ClientCall.Listener<RespT> responseListener, Metadata.Headers headers) {
+          public void start(ClientCall.Listener<RespT> responseListener, Metadata headers) {
             super.start(new SimpleForwardingClientCallListener<RespT>(responseListener) {
               @Override
-              public void onHeaders(Metadata.Headers headers) {
+              public void onHeaders(Metadata headers) {
                 examinedHeaders.add(headers);
                 super.onHeaders(headers);
               }
@@ -276,11 +275,11 @@ public class ClientInterceptorsTest {
     @SuppressWarnings("unchecked")
     ClientCall.Listener<Integer> listener = mock(ClientCall.Listener.class);
     ClientCall<String, Integer> interceptedCall = intercepted.newCall(method, CallOptions.DEFAULT);
-    interceptedCall.start(listener, new Metadata.Headers());
+    interceptedCall.start(listener, new Metadata());
     // Capture the underlying call listener that will receive headers from the transport.
     ArgumentCaptor<ClientCall.Listener<Integer>> captor = ArgumentCaptor.forClass(null);
-    verify(call).start(captor.capture(), Mockito.<Metadata.Headers>any());
+    verify(call).start(captor.capture(), Mockito.<Metadata>any());
-    Metadata.Headers inboundHeaders = new Metadata.Headers();
+    Metadata inboundHeaders = new Metadata();
     // Simulate that a headers arrives on the underlying call listener.
     captor.getValue().onHeaders(inboundHeaders);
     assertEquals(Arrays.asList(inboundHeaders), examinedHeaders);
@@ -303,7 +302,7 @@ public class ClientInterceptorsTest {
     assertNotSame(call, interceptedCall);
     @SuppressWarnings("unchecked")
     ClientCall.Listener<Integer> listener = mock(ClientCall.Listener.class);
-    Metadata.Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     interceptedCall.start(listener, headers);
     verify(call).start(same(listener), same(headers));
     interceptedCall.sendMessage("request");
@@ -326,8 +325,8 @@ public class ClientInterceptorsTest {
         ClientCall<ReqT, RespT> call = next.newCall(method, callOptions);
         return new CheckedForwardingClientCall<ReqT, RespT>(call) {
           @Override
-          protected void checkedStart(ClientCall.Listener<RespT> responseListener,
+          protected void checkedStart(ClientCall.Listener<RespT> responseListener, Metadata headers)
-              Metadata.Headers headers) throws Exception {
+              throws Exception {
             throw error;
             // delegate().start will not be called
           }
@@ -339,7 +338,7 @@ public class ClientInterceptorsTest {
     ClientCall.Listener<Integer> listener = mock(ClientCall.Listener.class);
     ClientCall<String, Integer> interceptedCall = intercepted.newCall(method, CallOptions.DEFAULT);
     assertNotSame(call, interceptedCall);
-    interceptedCall.start(listener, new Metadata.Headers());
+    interceptedCall.start(listener, new Metadata());
     interceptedCall.sendMessage("request");
     interceptedCall.halfClose();
     interceptedCall.request(1);

core/src/test/java/io/grpc/MetadataTest.java

@@ -76,7 +76,7 @@ public class MetadataTest {
   public void testMutations() {
     Fish lance = new Fish(LANCE);
     Fish cat = new Fish("cat");
-    Metadata.Headers metadata = new Metadata.Headers();
+    Metadata metadata = new Metadata();
 
     assertEquals(null, metadata.get(KEY));
     metadata.put(KEY, lance);
@@ -107,7 +107,7 @@ public class MetadataTest {
   @Test
   public void testWriteParsed() {
     Fish lance = new Fish(LANCE);
-    Metadata.Headers metadata = new Metadata.Headers();
+    Metadata metadata = new Metadata();
     metadata.put(KEY, lance);
     // Should be able to read same instance out
     assertSame(lance, metadata.get(KEY));
@@ -127,7 +127,7 @@ public class MetadataTest {
 
   @Test
   public void testWriteRaw() {
-    Metadata.Headers raw = new Metadata.Headers(KEY.asciiName(), LANCE_BYTES);
+    Metadata raw = new Metadata(KEY.asciiName(), LANCE_BYTES);
     Fish lance = raw.get(KEY);
     assertEquals(lance, new Fish(LANCE));
     // Reading again should return the same parsed instance
@@ -136,7 +136,7 @@ public class MetadataTest {
 
   @Test
   public void testSerializeRaw() {
-    Metadata.Headers raw = new Metadata.Headers(KEY.asciiName(), LANCE_BYTES);
+    Metadata raw = new Metadata(KEY.asciiName(), LANCE_BYTES);
     byte[][] serialized = raw.serialize();
     assertArrayEquals(serialized[0], KEY.asciiName());
     assertArrayEquals(serialized[1], LANCE_BYTES);
@@ -144,8 +144,8 @@ public class MetadataTest {
 
   @Test
   public void testMergeByteConstructed() {
-    Metadata.Headers raw = new Metadata.Headers(KEY.asciiName(), LANCE_BYTES);
+    Metadata raw = new Metadata(KEY.asciiName(), LANCE_BYTES);
-    Metadata.Headers serializable = new Metadata.Headers();
+    Metadata serializable = new Metadata();
     serializable.merge(raw);
 
     byte[][] serialized = serializable.serialize();
@@ -157,11 +157,9 @@ public class MetadataTest {
   @Test
   public void headerMergeShouldCopyValues() {
     Fish lance = new Fish(LANCE);
-    Metadata.Headers h1 = new Metadata.Headers();
+    Metadata h1 = new Metadata();
 
-    Metadata.Headers h2 = new Metadata.Headers();
+    Metadata h2 = new Metadata();
-    h2.setPath("/some/path");
-    h2.setAuthority("authority");
     h2.put(KEY, lance);
 
     h1.merge(h2);
@@ -170,8 +168,6 @@ public class MetadataTest {
     assertTrue(fishes.hasNext());
     assertSame(fishes.next(), lance);
     assertFalse(fishes.hasNext());
-    assertEquals("/some/path", h1.getPath());
-    assertEquals("authority", h1.getAuthority());
   }
 
   @Test
@@ -195,13 +191,10 @@ public class MetadataTest {
 
   @Test
   public void verifyToString() {
-    Metadata.Headers h = new Metadata.Headers();
+    Metadata h = new Metadata();
-    h.setPath("/path");
-    h.setAuthority("myauthority");
     h.put(KEY, new Fish("binary"));
     h.put(Metadata.Key.of("test", Metadata.ASCII_STRING_MARSHALLER), "ascii");
-    assertEquals("Headers(path=/path,authority=myauthority,"
+    assertEquals("Metadata({test-bin=[Fish(binary)], test=[ascii]})", h.toString());
-        + "metadata={test-bin=[Fish(binary)], test=[ascii]})", h.toString());
 
     Metadata t = new Metadata();
     t.put(Metadata.Key.of("test", Metadata.ASCII_STRING_MARSHALLER), "ascii");
@@ -229,7 +222,7 @@ public class MetadataTest {
       Metadata.Key<String> keyUpperCase
           = Metadata.Key.of("IF-MODIFIED-SINCE", Metadata.ASCII_STRING_MARSHALLER);
 
-      Metadata metadata = new Metadata.Headers();
+      Metadata metadata = new Metadata();
       metadata.put(keyTitleCase, "plain string");
       assertEquals("plain string", metadata.get(keyTitleCase));
       assertEquals("plain string", metadata.get(keyLowerCase));

core/src/test/java/io/grpc/ServerImplTest.java

@@ -186,7 +186,7 @@ public class ServerImplTest {
               public ServerCall.Listener<String> startCall(
                   MethodDescriptor<String, Integer> method,
                   ServerCall<Integer> call,
-                  Metadata.Headers headers) {
+                  Metadata headers) {
                 assertEquals("Waiter/serve", method.getFullMethodName());
                 assertNotNull(call);
                 assertNotNull(headers);
@@ -198,7 +198,7 @@ public class ServerImplTest {
     ServerTransportListener transportListener
         = transportServer.registerNewServerTransport(new SimpleServerTransport());
 
-    Metadata.Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     headers.put(metadataKey, 0);
     ServerStreamListener streamListener
         = transportListener.streamCreated(stream, "Waiter/serve", headers);
@@ -254,7 +254,7 @@ public class ServerImplTest {
               public ServerCall.Listener<String> startCall(
                   MethodDescriptor<String, Integer> method,
                   ServerCall<Integer> call,
-                  Metadata.Headers headers) {
+                  Metadata headers) {
                 throw status.asRuntimeException();
               }
             }).build());
@@ -262,7 +262,7 @@ public class ServerImplTest {
         = transportServer.registerNewServerTransport(new SimpleServerTransport());
 
     ServerStreamListener streamListener
-        = transportListener.streamCreated(stream, "Waiter/serve", new Metadata.Headers());
+        = transportListener.streamCreated(stream, "Waiter/serve", new Metadata());
     assertNotNull(streamListener);
     verifyNoMoreInteractions(stream);
 

core/src/test/java/io/grpc/ServerInterceptorsTest.java

@@ -41,7 +41,7 @@ import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 import static org.mockito.Mockito.verifyZeroInteractions;
 
-import io.grpc.Metadata.Headers;
+import io.grpc.Metadata;
 import io.grpc.MethodDescriptor.Marshaller;
 import io.grpc.MethodDescriptor.MethodType;
 import io.grpc.ServerCall.Listener;
@@ -80,7 +80,7 @@ public class ServerInterceptorsTest {
           MethodDescriptor.create(
             MethodType.UNKNOWN, "basic/flow", requestMarshaller, responseMarshaller),
           handler).build();
-  private Headers headers = new Headers();
+  private Metadata headers = new Metadata();
 
   /** Set up for test. */
   @Before
@@ -88,7 +88,7 @@ public class ServerInterceptorsTest {
     MockitoAnnotations.initMocks(this);
     Mockito.when(handler.startCall(
         Mockito.<MethodDescriptor<String, Integer>>any(),
-        Mockito.<ServerCall<Integer>>any(), Mockito.<Headers>any()))
+        Mockito.<ServerCall<Integer>>any(), Mockito.<Metadata>any()))
             .thenReturn(listener);
   }
 
@@ -172,7 +172,7 @@ public class ServerInterceptorsTest {
       public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
           MethodDescriptor<ReqT, RespT> method,
           ServerCall<RespT> call,
-          Headers headers,
+          Metadata headers,
           ServerCallHandler<ReqT, RespT> next) {
         // Calling next twice is permitted, although should only rarely be useful.
         assertSame(listener, next.startCall(method, call, headers));
@@ -195,7 +195,7 @@ public class ServerInterceptorsTest {
           public ServerCall.Listener<String> startCall(
               MethodDescriptor<String, Integer> method,
               ServerCall<Integer> call,
-              Headers headers) {
+              Metadata headers) {
             order.add("handler");
             return listener;
           }
@@ -205,7 +205,7 @@ public class ServerInterceptorsTest {
           public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
               MethodDescriptor<ReqT, RespT> method,
               ServerCall<RespT> call,
-              Headers headers,
+              Metadata headers,
               ServerCallHandler<ReqT, RespT> next) {
             order.add("i1");
             return next.startCall(method, call, headers);
@@ -216,7 +216,7 @@ public class ServerInterceptorsTest {
           public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
               MethodDescriptor<ReqT, RespT> method,
               ServerCall<RespT> call,
-              Headers headers,
+              Metadata headers,
               ServerCallHandler<ReqT, RespT> next) {
             order.add("i2");
             return next.startCall(method, call, headers);
@@ -247,7 +247,7 @@ public class ServerInterceptorsTest {
         public <R1, R2> ServerCall.Listener<R1> interceptCall(
             MethodDescriptor<R1, R2> methodDescriptor,
             ServerCall<R2> call,
-            Headers headers,
+            Metadata headers,
             ServerCallHandler<R1, R2> next) {
           assertSame(method, methodDescriptor);
           assertSame(call, ServerInterceptorsTest.this.call);
@@ -287,7 +287,7 @@ public class ServerInterceptorsTest {
     public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
         MethodDescriptor<ReqT, RespT> method,
         ServerCall<RespT> call,
-        Headers headers,
+        Metadata headers,
         ServerCallHandler<ReqT, RespT> next) {
       return next.startCall(method, call, headers);
     }

core/src/test/java/io/grpc/internal/AbstractClientStreamTest.java

@@ -38,7 +38,6 @@ import static org.mockito.Mockito.verify;
 
 import io.grpc.MessageEncoding;
 import io.grpc.Metadata;
-import io.grpc.Metadata.Headers;
 import io.grpc.Status;
 import io.grpc.Status.Code;
 import io.grpc.internal.AbstractStream.Phase;
@@ -172,7 +171,7 @@ public class AbstractClientStreamTest {
   public void inboundHeadersReceived_notifiesListener() {
     AbstractClientStream<Integer> stream =
         new BaseAbstractClientStream<Integer>(allocator, mockListener);
-    Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
 
     stream.inboundHeadersReceived(headers);
     verify(mockListener).headersRead(headers);
@@ -182,7 +181,7 @@ public class AbstractClientStreamTest {
   public void inboundHeadersReceived_failsOnPhaseStatus() {
     AbstractClientStream<Integer> stream =
         new BaseAbstractClientStream<Integer>(allocator, mockListener);
-    Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     stream.inboundPhase(Phase.STATUS);
 
     thrown.expect(IllegalStateException.class);
@@ -194,7 +193,7 @@ public class AbstractClientStreamTest {
   public void inboundHeadersReceived_succeedsOnPhaseMessage() {
     AbstractClientStream<Integer> stream =
         new BaseAbstractClientStream<Integer>(allocator, mockListener);
-    Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     stream.inboundPhase(Phase.MESSAGE);
 
     stream.inboundHeadersReceived(headers);
@@ -206,7 +205,7 @@ public class AbstractClientStreamTest {
   public void inboundHeadersReceived_acceptsGzipEncoding() {
     AbstractClientStream<Integer> stream =
         new BaseAbstractClientStream<Integer>(allocator, mockListener);
-    Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     headers.put(GrpcUtil.MESSAGE_ENCODING_KEY, new MessageEncoding.Gzip().getMessageEncoding());
 
     stream.inboundHeadersReceived(headers);
@@ -217,7 +216,7 @@ public class AbstractClientStreamTest {
   public void inboundHeadersReceived_acceptsIdentityEncoding() {
     AbstractClientStream<Integer> stream =
         new BaseAbstractClientStream<Integer>(allocator, mockListener);
-    Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     headers.put(GrpcUtil.MESSAGE_ENCODING_KEY, MessageEncoding.NONE.getMessageEncoding());
 
     stream.inboundHeadersReceived(headers);
@@ -228,7 +227,7 @@ public class AbstractClientStreamTest {
   public void inboundHeadersReceived_notifiesListenerOnBadEncoding() {
     AbstractClientStream<Integer> stream =
         new BaseAbstractClientStream<Integer>(allocator, mockListener);
-    Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     headers.put(GrpcUtil.MESSAGE_ENCODING_KEY, "bad");
 
     stream.inboundHeadersReceived(headers);
@@ -275,7 +274,7 @@ public class AbstractClientStreamTest {
     public void onReady() {}
 
     @Override
-    public void headersRead(Headers headers) {}
+    public void headersRead(Metadata headers) {}
 
     @Override
     public void closed(Status status, Metadata trailers) {}

core/src/test/java/io/grpc/internal/TransportFrameUtilTest.java

@@ -41,8 +41,8 @@ import static org.junit.Assert.fail;
 
 import com.google.common.io.BaseEncoding;
 
+import io.grpc.Metadata;
 import io.grpc.Metadata.BinaryMarshaller;
-import io.grpc.Metadata.Headers;
 import io.grpc.Metadata.Key;
 
 import org.junit.Test;
@@ -79,7 +79,7 @@ public class TransportFrameUtilTest {
 
   @Test
   public void testToHttp2Headers() {
-    Headers headers = new Headers();
+    Metadata headers = new Metadata();
     headers.put(PLAIN_STRING, COMPLIANT_ASCII_STRING);
     headers.put(BINARY_STRING, NONCOMPLIANT_ASCII_STRING);
     headers.put(BINARY_STRING_WITHOUT_SUFFIX, NONCOMPLIANT_ASCII_STRING);
@@ -104,13 +104,13 @@ public class TransportFrameUtilTest {
 
   @Test
   public void testToAndFromHttp2Headers() {
-    Headers headers = new Headers();
+    Metadata headers = new Metadata();
     headers.put(PLAIN_STRING, COMPLIANT_ASCII_STRING);
     headers.put(BINARY_STRING, NONCOMPLIANT_ASCII_STRING);
     headers.put(BINARY_STRING_WITHOUT_SUFFIX, NONCOMPLIANT_ASCII_STRING);
     byte[][] http2Headers = TransportFrameUtil.toHttp2Headers(headers);
     byte[][] rawSerialized = TransportFrameUtil.toRawSerializedHeaders(http2Headers);
-    Headers recoveredHeaders = new Headers(rawSerialized);
+    Metadata recoveredHeaders = new Metadata(rawSerialized);
     assertEquals(COMPLIANT_ASCII_STRING, recoveredHeaders.get(PLAIN_STRING));
     assertEquals(NONCOMPLIANT_ASCII_STRING, recoveredHeaders.get(BINARY_STRING));
     assertNull(recoveredHeaders.get(BINARY_STRING_WITHOUT_SUFFIX));

examples/src/main/java/io/grpc/examples/header/HeaderClientInterceptor.java

@@ -58,12 +58,12 @@ public class HeaderClientInterceptor implements ClientInterceptor {
     return new SimpleForwardingClientCall<ReqT, RespT>(next.newCall(method, callOptions)) {
 
       @Override
-      public void start(Listener<RespT> responseListener, Metadata.Headers headers) {
+      public void start(Listener<RespT> responseListener, Metadata headers) {
         /* put custom header */
         headers.put(customHeadKey, "customRequestValue");
         super.start(new SimpleForwardingClientCallListener<RespT>(responseListener) {
           @Override
-          public void onHeaders(Metadata.Headers headers) {
+          public void onHeaders(Metadata headers) {
             /**
              * if you don't need receive header from server,
              * you can use {@link io.grpc.stub.MetadataUtils attachHeaders}

examples/src/main/java/io/grpc/examples/header/HeaderServerInterceptor.java

@@ -56,14 +56,14 @@ public class HeaderServerInterceptor implements ServerInterceptor {
   public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
       MethodDescriptor<ReqT, RespT> method,
       ServerCall<RespT> call,
-      final Metadata.Headers requestHeaders,
+      final Metadata requestHeaders,
       ServerCallHandler<ReqT, RespT> next) {
     logger.info("header received from client:" + requestHeaders.toString());
     return next.startCall(method, new SimpleForwardingServerCall<RespT>(call) {
       boolean sentHeaders = false;
 
       @Override
-      public void sendHeaders(Metadata.Headers responseHeaders) {
+      public void sendHeaders(Metadata responseHeaders) {
         responseHeaders.put(customHeadKey, "customRespondValue");
         super.sendHeaders(responseHeaders);
         sentHeaders = true;
@@ -72,7 +72,7 @@ public class HeaderServerInterceptor implements ServerInterceptor {
       @Override
       public void sendMessage(RespT message) {
         if (!sentHeaders) {
-          sendHeaders(new Metadata.Headers());
+          sendHeaders(new Metadata());
         }
         super.sendMessage(message);
       }

interop-testing/src/main/java/io/grpc/testing/integration/AbstractTransportTest.java

@@ -99,8 +99,8 @@ public abstract class AbstractTransportTest {
 
   public static final Metadata.Key<Messages.SimpleContext> METADATA_KEY =
       ProtoUtils.keyForProto(Messages.SimpleContext.getDefaultInstance());
-  private static final AtomicReference<Metadata.Headers> requestHeadersCapture =
+  private static final AtomicReference<Metadata> requestHeadersCapture =
-      new AtomicReference<Metadata.Headers>();
+      new AtomicReference<Metadata>();
   private static ScheduledExecutorService testServiceExecutor;
   private static ServerImpl server;
   private static int OPERATION_TIMEOUT = 5000;
@@ -449,7 +449,7 @@ public abstract class AbstractTransportTest {
         channel.newCall(TestServiceGrpc.METHOD_STREAMING_OUTPUT_CALL, CallOptions.DEFAULT);
     call.start(new ClientCall.Listener<StreamingOutputCallResponse>() {
       @Override
-      public void onHeaders(Metadata.Headers headers) {}
+      public void onHeaders(Metadata headers) {}
 
       @Override
       public void onMessage(final StreamingOutputCallResponse message) {
@@ -460,7 +460,7 @@ public abstract class AbstractTransportTest {
       public void onClose(Status status, Metadata trailers) {
         queue.add(status);
       }
-    }, new Metadata.Headers());
+    }, new Metadata());
     call.sendMessage(request);
     call.halfClose();
 
@@ -521,7 +521,7 @@ public abstract class AbstractTransportTest {
         TestServiceGrpc.newBlockingStub(channel);
 
     // Capture the context exchange
-    Metadata.Headers fixedHeaders = new Metadata.Headers();
+    Metadata fixedHeaders = new Metadata();
     // Send a context proto (as it's in the default extension registry)
     Messages.SimpleContext contextValue =
         Messages.SimpleContext.newBuilder().setValue("dog").build();
@@ -529,7 +529,7 @@ public abstract class AbstractTransportTest {
     stub = MetadataUtils.attachHeaders(stub, fixedHeaders);
     // .. and expect it to be echoed back in trailers
     AtomicReference<Metadata> trailersCapture = new AtomicReference<Metadata>();
-    AtomicReference<Metadata.Headers> headersCapture = new AtomicReference<Metadata.Headers>();
+    AtomicReference<Metadata> headersCapture = new AtomicReference<Metadata>();
     stub = MetadataUtils.captureMetadata(stub, headersCapture, trailersCapture);
 
     Assert.assertNotNull(stub.emptyCall(Empty.getDefaultInstance()));
@@ -544,7 +544,7 @@ public abstract class AbstractTransportTest {
     TestServiceGrpc.TestServiceStub stub = TestServiceGrpc.newStub(channel);
 
     // Capture the context exchange
-    Metadata.Headers fixedHeaders = new Metadata.Headers();
+    Metadata fixedHeaders = new Metadata();
     // Send a context proto (as it's in the default extension registry)
     Messages.SimpleContext contextValue =
         Messages.SimpleContext.newBuilder().setValue("dog").build();
@@ -552,7 +552,7 @@ public abstract class AbstractTransportTest {
     stub = MetadataUtils.attachHeaders(stub, fixedHeaders);
     // .. and expect it to be echoed back in trailers
     AtomicReference<Metadata> trailersCapture = new AtomicReference<Metadata>();
-    AtomicReference<Metadata.Headers> headersCapture = new AtomicReference<Metadata.Headers>();
+    AtomicReference<Metadata> headersCapture = new AtomicReference<Metadata>();
     stub = MetadataUtils.captureMetadata(stub, headersCapture, trailersCapture);
 
     List<Integer> responseSizes = Arrays.asList(50, 100, 150, 200);

netty/src/main/java/io/grpc/netty/NettyClientTransport.java

@@ -31,6 +31,7 @@
 
 package io.grpc.netty;
 
+import static io.grpc.internal.GrpcUtil.AUTHORITY_KEY;
 import static io.netty.channel.ChannelOption.SO_KEEPALIVE;
 
 import com.google.common.base.Preconditions;
@@ -120,7 +121,7 @@ class NettyClientTransport implements ClientTransport {
   }
 
   @Override
-  public ClientStream newStream(MethodDescriptor<?, ?> method, Metadata.Headers headers,
+  public ClientStream newStream(MethodDescriptor<?, ?> method, Metadata headers,
       ClientStreamListener listener) {
     Preconditions.checkNotNull(method, "method");
     Preconditions.checkNotNull(headers, "headers");
@@ -131,8 +132,11 @@ class NettyClientTransport implements ClientTransport {
 
     // Convert the headers into Netty HTTP/2 headers.
     AsciiString defaultPath = new AsciiString("/" + method.getFullMethodName());
+    AsciiString defaultAuthority  = new AsciiString(headers.containsKey(AUTHORITY_KEY)
+        ? headers.get(AUTHORITY_KEY) : authority);
+    headers.removeAll(AUTHORITY_KEY);
     Http2Headers http2Headers = Utils.convertClientHeaders(headers, negotiationHandler.scheme(),
-        defaultPath, authority);
+        defaultPath, defaultAuthority);
 
     ChannelFutureListener failureListener = new ChannelFutureListener() {
       @Override

netty/src/main/java/io/grpc/netty/NettyServerHandler.java

@@ -39,12 +39,11 @@ import static io.grpc.netty.Utils.TE_TRAILERS;
 
 import com.google.common.base.Preconditions;
 
-import io.grpc.Metadata.Headers;
+import io.grpc.Metadata;
 import io.grpc.Status;
 import io.grpc.internal.GrpcUtil;
 import io.grpc.internal.ServerStreamListener;
 import io.grpc.internal.ServerTransportListener;
-
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
@@ -151,7 +150,7 @@ class NettyServerHandler extends Http2ConnectionHandler {
       http2Stream.setProperty(streamKey, stream);
       String method = determineMethod(streamId, headers);
 
-      Headers metadata = Utils.convertHeaders(headers);
+      Metadata metadata = Utils.convertHeaders(headers);
       ServerStreamListener listener =
           transportListener.streamCreated(stream, method, metadata);
       stream.setListener(listener);

netty/src/main/java/io/grpc/netty/NettyServerStream.java

@@ -87,7 +87,7 @@ class NettyServerStream extends AbstractServerStream<Integer> {
   }
 
   @Override
-  protected void internalSendHeaders(Metadata.Headers headers) {
+  protected void internalSendHeaders(Metadata headers) {
     writeQueue.enqueue(new SendResponseHeadersCommand(id(),
         Utils.convertServerHeaders(headers), false),
         true);

netty/src/main/java/io/grpc/netty/Utils.java

@@ -31,6 +31,7 @@
 
 package io.grpc.netty;
 
+import static io.grpc.internal.GrpcUtil.AUTHORITY_KEY;
 import static io.grpc.internal.GrpcUtil.CONTENT_TYPE_KEY;
 import static io.grpc.internal.GrpcUtil.USER_AGENT_KEY;
 import static io.netty.util.CharsetUtil.UTF_8;
@@ -79,16 +80,8 @@ class Utils {
   public static final Resource<EventLoopGroup> DEFAULT_WORKER_EVENT_LOOP_GROUP =
       new DefaultEventLoopGroupResource(0, "grpc-default-worker-ELG");
 
-  public static Metadata.Headers convertHeaders(Http2Headers http2Headers) {
+  public static Metadata convertHeaders(Http2Headers http2Headers) {
-    Metadata.Headers headers = new Metadata.Headers(convertHeadersToArray(http2Headers));
+    return new Metadata(convertHeadersToArray(http2Headers));
-    if (http2Headers.authority() != null) {
-      // toString() here is safe since it doesn't use the default Charset.
-      headers.setAuthority(http2Headers.authority().toString());
-    }
-    if (http2Headers.path() != null) {
-      headers.setPath(http2Headers.path().toString());
-    }
-    return headers;
   }
 
   private static byte[][] convertHeadersToArray(Http2Headers http2Headers) {
@@ -103,7 +96,7 @@ class Utils {
     return TransportFrameUtil.toRawSerializedHeaders(headerValues);
   }
 
-  public static Http2Headers convertClientHeaders(Metadata.Headers headers,
+  public static Http2Headers convertClientHeaders(Metadata headers,
       ByteString scheme,
       ByteString defaultPath,
       ByteString defaultAuthority) {
@@ -121,11 +114,8 @@ class Utils {
         .set(TE_HEADER, TE_TRAILERS);
 
     // Override the default authority and path if provided by the headers.
-    if (headers.getAuthority() != null) {
+    if (headers.containsKey(AUTHORITY_KEY)) {
-      http2Headers.authority(new ByteString(headers.getAuthority().getBytes(UTF_8)));
+      http2Headers.authority(new ByteString(headers.get(AUTHORITY_KEY).getBytes(UTF_8)));
-    }
-    if (headers.getPath() != null) {
-      http2Headers.path(new ByteString(headers.getPath().getBytes(UTF_8)));
     }
 
     // Set the User-Agent header.
@@ -135,7 +125,7 @@ class Utils {
     return http2Headers;
   }
 
-  public static Http2Headers convertServerHeaders(Metadata.Headers headers) {
+  public static Http2Headers convertServerHeaders(Metadata headers) {
     Http2Headers http2Headers = convertMetadata(headers);
     http2Headers.set(CONTENT_TYPE_HEADER, CONTENT_TYPE_GRPC);
     http2Headers.status(STATUS_OK);

netty/src/test/java/io/grpc/netty/NettyClientStreamTest.java

@@ -206,7 +206,7 @@ public class NettyClientStreamTest extends NettyStreamTestBase {
     stream().id(STREAM_ID);
     Http2Headers headers = grpcResponseHeaders();
     stream().transportHeadersReceived(headers, false);
-    verify(listener).headersRead(any(Metadata.Headers.class));
+    verify(listener).headersRead(any(Metadata.class));
   }
 
   @Test

netty/src/test/java/io/grpc/netty/NettyClientTransportTest.java

@@ -129,7 +129,7 @@ public class NettyClientTransportTest {
     // Verify that the received headers contained the User-Agent.
     assertEquals(1, serverListener.streamListeners.size());
 
-    Metadata.Headers headers = serverListener.streamListeners.get(0).headers;
+    Metadata headers = serverListener.streamListeners.get(0).headers;
     assertEquals(GrpcUtil.getGrpcUserAgent("netty", null), headers.get(USER_AGENT_KEY));
   }
 
@@ -141,13 +141,13 @@ public class NettyClientTransportTest {
 
     // Send a single RPC and wait for the response.
     String userAgent = "testUserAgent";
-    Metadata.Headers sentHeaders = new Metadata.Headers();
+    Metadata sentHeaders = new Metadata();
     sentHeaders.put(USER_AGENT_KEY, userAgent);
     new Rpc(transport, sentHeaders).halfClose().waitForResponse();
 
     // Verify that the received headers contained the User-Agent.
     assertEquals(1, serverListener.streamListeners.size());
-    Metadata.Headers receivedHeaders = serverListener.streamListeners.get(0).headers;
+    Metadata receivedHeaders = serverListener.streamListeners.get(0).headers;
     assertEquals(GrpcUtil.getGrpcUserAgent("netty", userAgent),
             receivedHeaders.get(USER_AGENT_KEY));
   }
@@ -249,10 +249,10 @@ public class NettyClientTransportTest {
     final TestClientStreamListener listener = new TestClientStreamListener();
 
     Rpc(NettyClientTransport transport) {
-      this(transport, new Metadata.Headers());
+      this(transport, new Metadata());
     }
 
-    Rpc(NettyClientTransport transport, Metadata.Headers headers) {
+    Rpc(NettyClientTransport transport, Metadata headers) {
       stream = transport.newStream(METHOD, headers, listener);
       stream.request(1);
       stream.writeMessage(new ByteArrayInputStream(MESSAGE.getBytes()));
@@ -278,7 +278,7 @@ public class NettyClientTransportTest {
     private final SettableFuture<Void> responseFuture = SettableFuture.create();
 
     @Override
-    public void headersRead(Metadata.Headers headers) {
+    public void headersRead(Metadata headers) {
     }
 
     @Override
@@ -305,9 +305,9 @@ public class NettyClientTransportTest {
   private static final class EchoServerStreamListener implements ServerStreamListener {
     final ServerStream stream;
     final String method;
-    final Metadata.Headers headers;
+    final Metadata headers;
 
-    EchoServerStreamListener(ServerStream stream, String method, Metadata.Headers headers) {
+    EchoServerStreamListener(ServerStream stream, String method, Metadata headers) {
       this.stream = stream;
       this.method = method;
       this.headers = headers;
@@ -348,7 +348,7 @@ public class NettyClientTransportTest {
 
         @Override
         public ServerStreamListener streamCreated(final ServerStream stream, String method,
-                                                  Metadata.Headers headers) {
+                                                  Metadata headers) {
           EchoServerStreamListener listener = new EchoServerStreamListener(stream, method, headers);
           streamListeners.add(listener);
           return listener;

netty/src/test/java/io/grpc/netty/NettyServerHandlerTest.java

@@ -127,7 +127,7 @@ public class NettyServerHandlerTest extends NettyHandlerTestBase {
 
     when(transportListener.streamCreated(any(ServerStream.class),
         any(String.class),
-        any(Metadata.Headers.class)))
+        any(Metadata.class)))
         .thenReturn(streamListener);
     handler = newHandler(transportListener);
     frameWriter = new DefaultHttp2FrameWriter();
@@ -358,7 +358,7 @@ public class NettyServerHandlerTest extends NettyHandlerTestBase {
         ArgumentCaptor.forClass(NettyServerStream.class);
     ArgumentCaptor<String> methodCaptor = ArgumentCaptor.forClass(String.class);
     verify(transportListener).streamCreated(streamCaptor.capture(), methodCaptor.capture(),
-        any(Metadata.Headers.class));
+        any(Metadata.class));
     stream = streamCaptor.getValue();
   }
 

netty/src/test/java/io/grpc/netty/NettyServerStreamTest.java

@@ -104,7 +104,7 @@ public class NettyServerStreamTest extends NettyStreamTestBase {
 
   @Test
   public void writeHeadersShouldSendHeaders() throws Exception {
-    Metadata.Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     stream().writeHeaders(headers);
     verify(writeQueue).enqueue(new SendResponseHeadersCommand(STREAM_ID,
         Utils.convertServerHeaders(headers), false), true);
@@ -112,7 +112,7 @@ public class NettyServerStreamTest extends NettyStreamTestBase {
 
   @Test
   public void duplicateWriteHeadersShouldFail() throws Exception {
-    Metadata.Headers headers = new Metadata.Headers();
+    Metadata headers = new Metadata();
     stream().writeHeaders(headers);
     verify(writeQueue).enqueue(new SendResponseHeadersCommand(STREAM_ID,
         Utils.convertServerHeaders(headers), false), true);

okhttp/src/main/java/io/grpc/okhttp/Headers.java

@@ -31,6 +31,7 @@
 
 package io.grpc.okhttp;
 
+import static io.grpc.internal.GrpcUtil.AUTHORITY_KEY;
 import static io.grpc.internal.GrpcUtil.CONTENT_TYPE_KEY;
 import static io.grpc.internal.GrpcUtil.USER_AGENT_KEY;
 
@@ -63,7 +64,7 @@ public class Headers {
    * creating a stream. Since this serializes the headers, this method should be called in the
    * application thread context.
    */
-  public static List<Header> createRequestHeaders(Metadata.Headers headers, String defaultPath,
+  public static List<Header> createRequestHeaders(Metadata headers, String defaultPath,
       String defaultAuthority) {
     Preconditions.checkNotNull(headers, "headers");
     Preconditions.checkNotNull(defaultPath, "defaultPath");
@@ -74,9 +75,12 @@ public class Headers {
     // Set GRPC-specific headers.
     okhttpHeaders.add(SCHEME_HEADER);
     okhttpHeaders.add(METHOD_HEADER);
-    String authority = headers.getAuthority() != null ? headers.getAuthority() : defaultAuthority;
+
+    String authority = headers.containsKey(AUTHORITY_KEY)
+        ? headers.get(AUTHORITY_KEY) : defaultAuthority;
+    headers.removeAll(AUTHORITY_KEY);
     okhttpHeaders.add(new Header(Header.TARGET_AUTHORITY, authority));
-    String path = headers.getPath() != null ? headers.getPath() : defaultPath;
+    String path = defaultPath;
     okhttpHeaders.add(new Header(Header.TARGET_PATH, path));
 
     String userAgent = GrpcUtil.getGrpcUserAgent("okhttp", headers.get(USER_AGENT_KEY));

okhttp/src/main/java/io/grpc/okhttp/OkHttpClientTransport.java

@@ -241,7 +241,7 @@ class OkHttpClientTransport implements ClientTransport {
 
   @Override
   public OkHttpClientStream newStream(MethodDescriptor<?, ?> method,
-                                      Metadata.Headers headers,
+                                      Metadata headers,
                                       ClientStreamListener listener) {
     Preconditions.checkNotNull(method, "method");
     Preconditions.checkNotNull(headers, "headers");

okhttp/src/main/java/io/grpc/okhttp/Utils.java

@@ -45,8 +45,8 @@ class Utils {
   static final int DEFAULT_WINDOW_SIZE = 65535;
   static final int CONNECTION_STREAM_ID = 0;
 
-  public static Metadata.Headers convertHeaders(List<Header> http2Headers) {
+  public static Metadata convertHeaders(List<Header> http2Headers) {
-    return new Metadata.Headers(convertHeadersToArray(http2Headers));
+    return new Metadata(convertHeadersToArray(http2Headers));
   }
 
   public static Metadata convertTrailers(List<Header> http2Headers) {

okhttp/src/test/java/io/grpc/okhttp/OkHttpClientTransportTest.java

@@ -196,8 +196,8 @@ public class OkHttpClientTransportTest {
     initTransport();
     MockStreamListener listener1 = new MockStreamListener();
     MockStreamListener listener2 = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener1).request(1);
+    clientTransport.newStream(method, new Metadata(), listener1).request(1);
-    clientTransport.newStream(method, new Metadata.Headers(), listener2).request(1);
+    clientTransport.newStream(method, new Metadata(), listener2).request(1);
     assertEquals(2, activeStreamCount());
     assertContainStream(3);
     assertContainStream(5);
@@ -219,7 +219,7 @@ public class OkHttpClientTransportTest {
     final int numMessages = 10;
     final String message = "Hello Client";
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener).request(numMessages);
+    clientTransport.newStream(method, new Metadata(), listener).request(numMessages);
     assertContainStream(3);
     frameHandler().headers(false, false, 3, 0, grpcResponseHeaders(), HeadersMode.HTTP_20_HEADERS);
     assertNotNull(listener.headers);
@@ -263,7 +263,7 @@ public class OkHttpClientTransportTest {
   public void invalidInboundHeadersCancelStream() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener).request(1);
+    clientTransport.newStream(method, new Metadata(), listener).request(1);
     assertContainStream(3);
     // Empty headers block without correct content type or status
     frameHandler().headers(false, false, 3, 0, new ArrayList<Header>(),
@@ -281,7 +281,7 @@ public class OkHttpClientTransportTest {
   public void readStatus() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener);
+    clientTransport.newStream(method, new Metadata(), listener);
     assertContainStream(3);
     frameHandler().headers(true, true, 3, 0, grpcResponseTrailers(), HeadersMode.HTTP_20_HEADERS);
     listener.waitUntilStreamClosed();
@@ -292,7 +292,7 @@ public class OkHttpClientTransportTest {
   public void receiveReset() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener);
+    clientTransport.newStream(method, new Metadata(), listener);
     assertContainStream(3);
     frameHandler().rstStream(3, ErrorCode.PROTOCOL_ERROR);
     listener.waitUntilStreamClosed();
@@ -303,7 +303,7 @@ public class OkHttpClientTransportTest {
   public void cancelStream() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener);
+    clientTransport.newStream(method, new Metadata(), listener);
     getStream(3).cancel(Status.CANCELLED);
     verify(frameWriter, timeout(TIME_OUT_MS)).rstStream(eq(3), eq(ErrorCode.CANCEL));
     listener.waitUntilStreamClosed();
@@ -315,7 +315,7 @@ public class OkHttpClientTransportTest {
   public void headersShouldAddDefaultUserAgent() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener);
+    clientTransport.newStream(method, new Metadata(), listener);
     Header userAgentHeader = new Header(GrpcUtil.USER_AGENT_KEY.name(),
             GrpcUtil.getGrpcUserAgent("okhttp", null));
     List<Header> expectedHeaders = Arrays.asList(SCHEME_HEADER, METHOD_HEADER,
@@ -332,7 +332,7 @@ public class OkHttpClientTransportTest {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
     String userAgent = "fakeUserAgent";
-    Metadata.Headers metadata = new Metadata.Headers();
+    Metadata metadata = new Metadata();
     metadata.put(GrpcUtil.USER_AGENT_KEY, userAgent);
     clientTransport.newStream(method, metadata, listener);
     List<Header> expectedHeaders = Arrays.asList(SCHEME_HEADER, METHOD_HEADER,
@@ -350,7 +350,7 @@ public class OkHttpClientTransportTest {
   public void cancelStreamForDeadlineExceeded() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener);
+    clientTransport.newStream(method, new Metadata(), listener);
     getStream(3).cancel(Status.DEADLINE_EXCEEDED);
     verify(frameWriter, timeout(TIME_OUT_MS)).rstStream(eq(3), eq(ErrorCode.CANCEL));
     listener.waitUntilStreamClosed();
@@ -362,7 +362,7 @@ public class OkHttpClientTransportTest {
     final String message = "Hello Server";
     MockStreamListener listener = new MockStreamListener();
     OkHttpClientStream stream =
-        clientTransport.newStream(method, new Metadata.Headers(), listener);
+        clientTransport.newStream(method, new Metadata(), listener);
     InputStream input = new ByteArrayInputStream(message.getBytes(UTF_8));
     assertEquals(12, input.available());
     stream.writeMessage(input);
@@ -380,8 +380,8 @@ public class OkHttpClientTransportTest {
     initTransport();
     MockStreamListener listener1 = new MockStreamListener();
     MockStreamListener listener2 = new MockStreamListener();
-    clientTransport.newStream(method,new Metadata.Headers(), listener1).request(2);
+    clientTransport.newStream(method,new Metadata(), listener1).request(2);
-    clientTransport.newStream(method,new Metadata.Headers(), listener2).request(2);
+    clientTransport.newStream(method,new Metadata(), listener2).request(2);
     assertEquals(2, activeStreamCount());
     OkHttpClientStream stream1 = getStream(3);
     OkHttpClientStream stream2 = getStream(5);
@@ -438,7 +438,7 @@ public class OkHttpClientTransportTest {
   public void windowUpdateWithInboundFlowControl() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener).request(1);
+    clientTransport.newStream(method, new Metadata(), listener).request(1);
 
     int messageLength = Utils.DEFAULT_WINDOW_SIZE / 2 + 1;
     byte[] fakeMessage = new byte[messageLength];
@@ -462,7 +462,7 @@ public class OkHttpClientTransportTest {
   public void outboundFlowControl() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata.Headers(), listener);
+    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata(), listener);
 
     // The first message should be sent out.
     int messageLength = Utils.DEFAULT_WINDOW_SIZE / 2 + 1;
@@ -496,7 +496,7 @@ public class OkHttpClientTransportTest {
   public void outboundFlowControlWithInitialWindowSizeChange() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata.Headers(), listener);
+    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata(), listener);
     int messageLength = 20;
     setInitialWindowSize(HEADER_LENGTH + 10);
     InputStream input = new ByteArrayInputStream(new byte[messageLength]);
@@ -541,9 +541,9 @@ public class OkHttpClientTransportTest {
     MockStreamListener listener1 = new MockStreamListener();
     MockStreamListener listener2 = new MockStreamListener();
     OkHttpClientStream stream1
-        = clientTransport.newStream(method, new Metadata.Headers(), listener1);
+        = clientTransport.newStream(method, new Metadata(), listener1);
     OkHttpClientStream stream2
-        = clientTransport.newStream(method, new Metadata.Headers(), listener2);
+        = clientTransport.newStream(method, new Metadata(), listener2);
     assertEquals(2, activeStreamCount());
     clientTransport.shutdown();
     verify(frameWriter, timeout(TIME_OUT_MS)).goAway(eq(0), eq(ErrorCode.NO_ERROR), (byte[]) any());
@@ -567,8 +567,8 @@ public class OkHttpClientTransportTest {
     // start 2 streams.
     MockStreamListener listener1 = new MockStreamListener();
     MockStreamListener listener2 = new MockStreamListener();
-    clientTransport.newStream(method,new Metadata.Headers(), listener1).request(1);
+    clientTransport.newStream(method,new Metadata(), listener1).request(1);
-    clientTransport.newStream(method,new Metadata.Headers(), listener2).request(1);
+    clientTransport.newStream(method,new Metadata(), listener2).request(1);
     assertEquals(2, activeStreamCount());
 
     // Receive goAway, max good id is 3.
@@ -620,7 +620,7 @@ public class OkHttpClientTransportTest {
     initTransport(startId);
 
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener).request(1);
+    clientTransport.newStream(method, new Metadata(), listener).request(1);
 
     // New stream should be failed.
     assertNewStreamFail();
@@ -653,11 +653,11 @@ public class OkHttpClientTransportTest {
     final MockStreamListener listener1 = new MockStreamListener();
     final MockStreamListener listener2 = new MockStreamListener();
     OkHttpClientStream stream1
-        = clientTransport.newStream(method, new Metadata.Headers(), listener1);
+        = clientTransport.newStream(method, new Metadata(), listener1);
 
     // The second stream should be pending.
     OkHttpClientStream stream2 =
-        clientTransport.newStream(method, new Metadata.Headers(), listener2);
+        clientTransport.newStream(method, new Metadata(), listener2);
     String sentMessage = "hello";
     InputStream input = new ByteArrayInputStream(sentMessage.getBytes(UTF_8));
     assertEquals(5, input.available());
@@ -690,7 +690,7 @@ public class OkHttpClientTransportTest {
     setMaxConcurrentStreams(0);
     MockStreamListener listener = new MockStreamListener();
     OkHttpClientStream stream
-        = clientTransport.newStream(method, new Metadata.Headers(), listener);
+        = clientTransport.newStream(method, new Metadata(), listener);
     waitForStreamPending(1);
     stream.sendCancel(Status.CANCELLED);
     // The second cancel should be an no-op.
@@ -706,9 +706,9 @@ public class OkHttpClientTransportTest {
     setMaxConcurrentStreams(1);
     final MockStreamListener listener1 = new MockStreamListener();
     final MockStreamListener listener2 = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener1);
+    clientTransport.newStream(method, new Metadata(), listener1);
     // The second stream should be pending.
-    clientTransport.newStream(method, new Metadata.Headers(), listener2);
+    clientTransport.newStream(method, new Metadata(), listener2);
 
     waitForStreamPending(1);
     assertEquals(1, activeStreamCount());
@@ -731,7 +731,7 @@ public class OkHttpClientTransportTest {
     setMaxConcurrentStreams(0);
     final MockStreamListener listener = new MockStreamListener();
     // The second stream should be pending.
-    clientTransport.newStream(method, new Metadata.Headers(), listener);
+    clientTransport.newStream(method, new Metadata(), listener);
     waitForStreamPending(1);
 
     clientTransport.shutdown();
@@ -752,11 +752,11 @@ public class OkHttpClientTransportTest {
     final MockStreamListener listener3 = new MockStreamListener();
 
     OkHttpClientStream stream1 =
-        clientTransport.newStream(method, new Metadata.Headers(), listener1);
+        clientTransport.newStream(method, new Metadata(), listener1);
 
     // The second and third stream should be pending.
-    clientTransport.newStream(method, new Metadata.Headers(), listener2);
+    clientTransport.newStream(method, new Metadata(), listener2);
-    clientTransport.newStream(method, new Metadata.Headers(), listener3);
+    clientTransport.newStream(method, new Metadata(), listener3);
 
     waitForStreamPending(2);
     assertEquals(1, activeStreamCount());
@@ -777,7 +777,7 @@ public class OkHttpClientTransportTest {
   public void receivingWindowExceeded() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener).request(1);
+    clientTransport.newStream(method, new Metadata(), listener).request(1);
 
     frameHandler().headers(false, false, 3, 0, grpcResponseHeaders(), HeadersMode.HTTP_20_HEADERS);
 
@@ -821,7 +821,7 @@ public class OkHttpClientTransportTest {
   private void shouldHeadersBeFlushed(boolean shouldBeFlushed) throws Exception {
     initTransport();
     OkHttpClientStream stream = clientTransport.newStream(
-        method, new Metadata.Headers(), new MockStreamListener());
+        method, new Metadata(), new MockStreamListener());
     verify(frameWriter, timeout(TIME_OUT_MS)).synStream(
         eq(false), eq(false), eq(3), eq(0), Matchers.anyListOf(Header.class));
     if (shouldBeFlushed) {
@@ -836,7 +836,7 @@ public class OkHttpClientTransportTest {
   public void receiveDataWithoutHeader() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method,new Metadata.Headers(), listener).request(1);
+    clientTransport.newStream(method,new Metadata(), listener).request(1);
     Buffer buffer = createMessageFrame(new byte[1]);
     frameHandler().data(false, 3, buffer, (int) buffer.size());
 
@@ -854,7 +854,7 @@ public class OkHttpClientTransportTest {
   public void receiveDataWithoutHeaderAndTrailer() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener).request(1);
+    clientTransport.newStream(method, new Metadata(), listener).request(1);
     Buffer buffer = createMessageFrame(new byte[1]);
     frameHandler().data(false, 3, buffer, (int) buffer.size());
 
@@ -872,7 +872,7 @@ public class OkHttpClientTransportTest {
   public void receiveLongEnoughDataWithoutHeaderAndTrailer() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener).request(1);
+    clientTransport.newStream(method, new Metadata(), listener).request(1);
     Buffer buffer = createMessageFrame(new byte[1000]);
     frameHandler().data(false, 3, buffer, (int) buffer.size());
 
@@ -889,7 +889,7 @@ public class OkHttpClientTransportTest {
   public void receiveDataForUnknownStreamUpdateConnectionWindow() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata.Headers(), listener);
+    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata(), listener);
     stream.cancel(Status.CANCELLED);
 
     Buffer buffer = createMessageFrame(
@@ -913,7 +913,7 @@ public class OkHttpClientTransportTest {
   public void receiveWindowUpdateForUnknownStream() throws Exception {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
-    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata.Headers(), listener);
+    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata(), listener);
     stream.cancel(Status.CANCELLED);
     // This should be ignored.
     frameHandler().windowUpdate(3, 73);
@@ -931,7 +931,7 @@ public class OkHttpClientTransportTest {
     initTransport();
     MockStreamListener listener = new MockStreamListener();
     OkHttpClientStream stream = clientTransport.newStream(
-        method, new Metadata.Headers(), listener);
+        method, new Metadata(), listener);
     assertTrue(stream.isReady());
     assertTrue(listener.isOnReadyCalled());
     stream.cancel(Status.CANCELLED);
@@ -946,7 +946,7 @@ public class OkHttpClientTransportTest {
     setInitialWindowSize(0);
     MockStreamListener listener = new MockStreamListener();
     OkHttpClientStream stream = clientTransport.newStream(
-        method, new Metadata.Headers(), listener);
+        method, new Metadata(), listener);
     assertTrue(stream.isReady());
     // Be notified at the beginning.
     assertTrue(listener.isOnReadyCalled());
@@ -1084,7 +1084,7 @@ public class OkHttpClientTransportTest {
     initTransportAndDelayConnected();
     final String message = "Hello Server";
     MockStreamListener listener = new MockStreamListener();
-    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata.Headers(), listener);
+    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata(), listener);
     InputStream input = new ByteArrayInputStream(message.getBytes(UTF_8));
     stream.writeMessage(input);
     stream.flush();
@@ -1107,7 +1107,7 @@ public class OkHttpClientTransportTest {
     initTransportAndDelayConnected();
     final String message = "Hello Server";
     MockStreamListener listener = new MockStreamListener();
-    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata.Headers(), listener);
+    OkHttpClientStream stream = clientTransport.newStream(method, new Metadata(), listener);
     InputStream input = new ByteArrayInputStream(message.getBytes(UTF_8));
     stream.writeMessage(input);
     stream.flush();
@@ -1122,7 +1122,7 @@ public class OkHttpClientTransportTest {
   public void shutdownDuringConnecting() throws Exception {
     initTransportAndDelayConnected();
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener);
+    clientTransport.newStream(method, new Metadata(), listener);
 
     clientTransport.shutdown();
     allowTransportConnected();
@@ -1162,7 +1162,7 @@ public class OkHttpClientTransportTest {
 
   private void assertNewStreamFail() throws Exception {
     MockStreamListener listener = new MockStreamListener();
-    clientTransport.newStream(method, new Metadata.Headers(), listener);
+    clientTransport.newStream(method, new Metadata(), listener);
     listener.waitUntilStreamClosed();
     assertFalse(listener.status.isOk());
   }
@@ -1261,7 +1261,7 @@ public class OkHttpClientTransportTest {
 
   private static class MockStreamListener implements ClientStreamListener {
     Status status;
-    Metadata.Headers headers;
+    Metadata headers;
     Metadata trailers;
     CountDownLatch closed = new CountDownLatch(1);
     ArrayList<String> messages = new ArrayList<String>();
@@ -1271,7 +1271,7 @@ public class OkHttpClientTransportTest {
     }
 
     @Override
-    public void headersRead(Metadata.Headers headers) {
+    public void headersRead(Metadata headers) {
       this.headers = headers;
     }
 

stub/src/main/java/io/grpc/stub/ClientCalls.java

@@ -188,7 +188,7 @@ public class ClientCalls {
 
   private static <ReqT, RespT> void startCall(ClientCall<ReqT, RespT> call,
       ClientCall.Listener<RespT> responseListener, boolean streamingResponse) {
-    call.start(responseListener, new Metadata.Headers());
+    call.start(responseListener, new Metadata());
     if (streamingResponse) {
       call.request(1);
     } else {
@@ -237,7 +237,7 @@ public class ClientCalls {
     }
 
     @Override
-    public void onHeaders(Metadata.Headers headers) {
+    public void onHeaders(Metadata headers) {
     }
 
     @Override
@@ -278,7 +278,7 @@ public class ClientCalls {
     }
 
     @Override
-    public void onHeaders(Metadata.Headers headers) {
+    public void onHeaders(Metadata headers) {
     }
 
     @Override
@@ -393,7 +393,7 @@ public class ClientCalls {
       private boolean done = false;
 
       @Override
-      public void onHeaders(Metadata.Headers headers) {
+      public void onHeaders(Metadata headers) {
       }
 
       @Override

stub/src/main/java/io/grpc/stub/MetadataUtils.java

@@ -58,7 +58,7 @@ public class MetadataUtils {
   @SuppressWarnings({"unchecked", "rawtypes"})
   public static <T extends AbstractStub> T attachHeaders(
       T stub,
-      final Metadata.Headers extraHeaders) {
+      final Metadata extraHeaders) {
     return (T) stub.withInterceptors(newAttachHeadersInterceptor(extraHeaders));
   }
 
@@ -68,7 +68,7 @@ public class MetadataUtils {
    * @param extraHeaders the headers to be passed by each call that is processed by the returned
    *                     interceptor
    */
-  public static ClientInterceptor newAttachHeadersInterceptor(final Metadata.Headers extraHeaders) {
+  public static ClientInterceptor newAttachHeadersInterceptor(final Metadata extraHeaders) {
     return new ClientInterceptor() {
       @Override
       public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
@@ -77,7 +77,7 @@ public class MetadataUtils {
           Channel next) {
         return new SimpleForwardingClientCall<ReqT, RespT>(next.newCall(method, callOptions)) {
           @Override
-          public void start(Listener<RespT> responseListener, Metadata.Headers headers) {
+          public void start(Listener<RespT> responseListener, Metadata headers) {
             headers.merge(extraHeaders);
             super.start(responseListener, headers);
           }
@@ -97,7 +97,7 @@ public class MetadataUtils {
   @SuppressWarnings({"unchecked", "rawtypes"})
   public static <T extends AbstractStub> T captureMetadata(
       T stub,
-      AtomicReference<Metadata.Headers> headersCapture,
+      AtomicReference<Metadata> headersCapture,
       AtomicReference<Metadata> trailersCapture) {
     return (T) stub.withInterceptors(
         newCaptureMetadataInterceptor(headersCapture, trailersCapture));
@@ -111,7 +111,7 @@ public class MetadataUtils {
    * @return an implementation of the channel with captures installed.
    */
   public static ClientInterceptor newCaptureMetadataInterceptor(
-      final AtomicReference<Metadata.Headers> headersCapture,
+      final AtomicReference<Metadata> headersCapture,
       final AtomicReference<Metadata> trailersCapture) {
     return new ClientInterceptor() {
       @Override
@@ -121,12 +121,12 @@ public class MetadataUtils {
           Channel next) {
         return new SimpleForwardingClientCall<ReqT, RespT>(next.newCall(method, callOptions)) {
           @Override
-          public void start(Listener<RespT> responseListener, Metadata.Headers headers) {
+          public void start(Listener<RespT> responseListener, Metadata headers) {
             headersCapture.set(null);
             trailersCapture.set(null);
             super.start(new SimpleForwardingClientCallListener<RespT>(responseListener) {
               @Override
-              public void onHeaders(Metadata.Headers headers) {
+              public void onHeaders(Metadata headers) {
                 headersCapture.set(headers);
                 super.onHeaders(headers);
               }

stub/src/main/java/io/grpc/stub/ServerCalls.java

@@ -125,7 +125,7 @@ public class ServerCalls {
       public ServerCall.Listener<ReqT> startCall(
           MethodDescriptor<ReqT, RespT> methodDescriptor,
           final ServerCall<RespT> call,
-          Metadata.Headers headers) {
+          Metadata headers) {
         final ResponseObserver<RespT> responseObserver = new ResponseObserver<RespT>(call);
         // We expect only 1 request, but we ask for 2 requests here so that if a misbehaving client
         // sends more than 1 requests, we will catch it in onMessage() and emit INVALID_ARGUMENT.
@@ -177,7 +177,7 @@ public class ServerCalls {
       public ServerCall.Listener<ReqT> startCall(
           MethodDescriptor<ReqT, RespT> methodDescriptor,
           final ServerCall<RespT> call,
-          Metadata.Headers headers) {
+          Metadata headers) {
         call.request(1);
         final ResponseObserver<RespT> responseObserver = new ResponseObserver<RespT>(call);
         final StreamObserver<ReqT> requestObserver = method.invoke(responseObserver);

stub/src/test/java/io/grpc/stub/ClientCallsTest.java

@@ -69,7 +69,7 @@ public class ClientCallsTest {
     Integer req = 2;
     ListenableFuture<String> future = ClientCalls.futureUnaryCall(call, req);
     ArgumentCaptor<ClientCall.Listener<String>> listenerCaptor = ArgumentCaptor.forClass(null);
-    verify(call).start(listenerCaptor.capture(), any(Metadata.Headers.class));
+    verify(call).start(listenerCaptor.capture(), any(Metadata.class));
     ClientCall.Listener<String> listener = listenerCaptor.getValue();
     verify(call).sendMessage(req);
     verify(call).halfClose();
@@ -82,7 +82,7 @@ public class ClientCallsTest {
     Integer req = 2;
     ListenableFuture<String> future = ClientCalls.futureUnaryCall(call, req);
     ArgumentCaptor<ClientCall.Listener<String>> listenerCaptor = ArgumentCaptor.forClass(null);
-    verify(call).start(listenerCaptor.capture(), any(Metadata.Headers.class));
+    verify(call).start(listenerCaptor.capture(), any(Metadata.class));
     ClientCall.Listener<String> listener = listenerCaptor.getValue();
     listener.onClose(Status.INVALID_ARGUMENT, new Metadata());
     try {
@@ -98,7 +98,7 @@ public class ClientCallsTest {
     Integer req = 2;
     ListenableFuture<String> future = ClientCalls.futureUnaryCall(call, req);
     ArgumentCaptor<ClientCall.Listener<String>> listenerCaptor = ArgumentCaptor.forClass(null);
-    verify(call).start(listenerCaptor.capture(), any(Metadata.Headers.class));
+    verify(call).start(listenerCaptor.capture(), any(Metadata.class));
     ClientCall.Listener<String> listener = listenerCaptor.getValue();
     future.cancel(true);
     verify(call).cancel();

testing/src/main/java/io/grpc/testing/TestUtils.java

@@ -84,14 +84,14 @@ public class TestUtils {
       public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
           MethodDescriptor<ReqT, RespT> method,
           ServerCall<RespT> call,
-          final Metadata.Headers requestHeaders,
+          final Metadata requestHeaders,
           ServerCallHandler<ReqT, RespT> next) {
         return next.startCall(method,
             new SimpleForwardingServerCall<RespT>(call) {
               boolean sentHeaders;
 
               @Override
-              public void sendHeaders(Metadata.Headers responseHeaders) {
+              public void sendHeaders(Metadata responseHeaders) {
                 responseHeaders.merge(requestHeaders, keySet);
                 super.sendHeaders(responseHeaders);
                 sentHeaders = true;
@@ -100,7 +100,7 @@ public class TestUtils {
               @Override
               public void sendMessage(RespT message) {
                 if (!sentHeaders) {
-                  sendHeaders(new Metadata.Headers());
+                  sendHeaders(new Metadata());
                 }
                 super.sendMessage(message);
               }
@@ -121,13 +121,13 @@ public class TestUtils {
    * {@link #echoRequestHeadersInterceptor}.
    */
   public static ServerInterceptor recordRequestHeadersInterceptor(
-      final AtomicReference<Metadata.Headers> headersCapture) {
+      final AtomicReference<Metadata> headersCapture) {
     return new ServerInterceptor() {
       @Override
       public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
           MethodDescriptor<ReqT, RespT> method,
           ServerCall<RespT> call,
-          Metadata.Headers requestHeaders,
+          Metadata requestHeaders,
           ServerCallHandler<ReqT, RespT> next) {
         headersCapture.set(requestHeaders);
         return next.startCall(method, call, requestHeaders);