core: add Metadata.discardAll()

Metadata.removeAll creates an iterator for looking through removed
values even if the call doens't use it.  This change adds a similar
method which doesn't create garbage.

This change makes it easier in the future to alter the internals
of Metadata where it may be expensive to return removed values.

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

@@ -271,6 +271,16 @@ public final class Metadata {
     return new ValueIterable<T>(key, values);
   }
 
+  /**
+   * Remove all values for the given key without returning them.  This is a minor performance
+   * optimization if you do not need the previous values.
+   */
+  @ExperimentalApi
+  public <T> void discardAll(Key<T> key) {
+    List<MetadataEntry> removed = store.remove(key.name());
+    storeCount -= removed != null ? removed.size() : 0;
+  }
+
   /**
    * Serialize all the metadata entries.
    *

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

@@ -145,8 +145,8 @@ public abstract class AbstractServerStream extends AbstractStream2
   }
 
   private void addStatusToTrailers(Metadata trailers, Status status) {
-    trailers.removeAll(Status.CODE_KEY);
+    trailers.discardAll(Status.CODE_KEY);
-    trailers.removeAll(Status.MESSAGE_KEY);
+    trailers.discardAll(Status.MESSAGE_KEY);
     trailers.put(Status.CODE_KEY, status);
     if (status.getDescription() != null) {
       trailers.put(Status.MESSAGE_KEY, status.getDescription());

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

@@ -140,12 +140,12 @@ final class ClientCallImpl<ReqT, RespT> extends ClientCall<ReqT, RespT>
   @VisibleForTesting
   static void prepareHeaders(Metadata headers, DecompressorRegistry decompressorRegistry,
       Compressor compressor) {
-    headers.removeAll(MESSAGE_ENCODING_KEY);
+    headers.discardAll(MESSAGE_ENCODING_KEY);
     if (compressor != Codec.Identity.NONE) {
       headers.put(MESSAGE_ENCODING_KEY, compressor.getMessageEncoding());
     }
 
-    headers.removeAll(MESSAGE_ACCEPT_ENCODING_KEY);
+    headers.discardAll(MESSAGE_ACCEPT_ENCODING_KEY);
     String advertisedEncodings = decompressorRegistry.getRawAdvertisedMessageEncodings();
     if (!advertisedEncodings.isEmpty()) {
       headers.put(MESSAGE_ACCEPT_ENCODING_KEY, advertisedEncodings);
@@ -251,7 +251,7 @@ final class ClientCallImpl<ReqT, RespT> extends ClientCall<ReqT, RespT>
    */
   private static void updateTimeoutHeaders(@Nullable Deadline effectiveDeadline,
       @Nullable Deadline callDeadline, @Nullable Deadline outerCallDeadline, Metadata headers) {
-    headers.removeAll(TIMEOUT_KEY);
+    headers.discardAll(TIMEOUT_KEY);
 
     if (effectiveDeadline == null) {
       return;

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

@@ -238,8 +238,8 @@ public abstract class Http2ClientStream extends AbstractClientStream<Integer> {
    * the application layer.
    */
   private static void stripTransportDetails(Metadata metadata) {
-    metadata.removeAll(HTTP2_STATUS);
+    metadata.discardAll(HTTP2_STATUS);
-    metadata.removeAll(Status.CODE_KEY);
+    metadata.discardAll(Status.CODE_KEY);
-    metadata.removeAll(Status.MESSAGE_KEY);
+    metadata.discardAll(Status.MESSAGE_KEY);
   }
 }

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

@@ -104,7 +104,7 @@ final class ServerCallImpl<ReqT, RespT> extends ServerCall<ReqT, RespT> {
     checkState(!sendHeadersCalled, "sendHeaders has already been called");
     checkState(!closeCalled, "call is closed");
 
-    headers.removeAll(MESSAGE_ENCODING_KEY);
+    headers.discardAll(MESSAGE_ENCODING_KEY);
     if (compressor == null) {
       compressor = Codec.Identity.NONE;
     } else {
@@ -125,7 +125,7 @@ final class ServerCallImpl<ReqT, RespT> extends ServerCall<ReqT, RespT> {
 
     stream.setCompressor(compressor);
 
-    headers.removeAll(MESSAGE_ACCEPT_ENCODING_KEY);
+    headers.discardAll(MESSAGE_ACCEPT_ENCODING_KEY);
     String advertisedEncodings = decompressorRegistry.getRawAdvertisedMessageEncodings();
     if (!advertisedEncodings.isEmpty()) {
       headers.put(MESSAGE_ACCEPT_ENCODING_KEY, advertisedEncodings);

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

@@ -114,6 +114,17 @@ public class MetadataTest {
     assertEquals(null, metadata.get(KEY));
   }
 
+  @Test
+  public void discardAll() {
+    Fish lance = new Fish(LANCE);
+    Metadata metadata = new Metadata();
+
+    metadata.put(KEY, lance);
+    metadata.discardAll(KEY);
+    assertEquals(null, metadata.getAll(KEY));
+    assertEquals(null, metadata.get(KEY));
+  }
+
   @Test
   public void testGetAllNoRemove() {
     Fish lance = new Fish(LANCE);

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

@@ -105,7 +105,7 @@ abstract class NettyClientStream extends Http2ClientStream implements StreamIdHo
       defaultPath = new AsciiString("/" + method.getFullMethodName());
       methodDescriptorAccessor.setRawMethodName(method, defaultPath);
     }
-    headers.removeAll(GrpcUtil.USER_AGENT_KEY);
+    headers.discardAll(GrpcUtil.USER_AGENT_KEY);
     Http2Headers http2Headers
         = Utils.convertClientHeaders(headers, scheme, defaultPath, authority, userAgent);
     headers = null;

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

@@ -139,7 +139,7 @@ class OkHttpClientStream extends Http2ClientStream {
   public void start(ClientStreamListener listener) {
     super.start(listener);
     String defaultPath = "/" + method.getFullMethodName();
-    headers.removeAll(GrpcUtil.USER_AGENT_KEY);
+    headers.discardAll(GrpcUtil.USER_AGENT_KEY);
     List<Header> requestHeaders =
         Headers.createRequestHeaders(headers, defaultPath, authority, userAgent);
     headers = null;