NettyServerBuilder.java

/*
 * Copyright 2014 The gRPC Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.grpc.netty;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static io.grpc.internal.GrpcUtil.DEFAULT_MAX_MESSAGE_SIZE;
import static io.grpc.internal.GrpcUtil.DEFAULT_SERVER_KEEPALIVE_TIMEOUT_NANOS;
import static io.grpc.internal.GrpcUtil.DEFAULT_SERVER_KEEPALIVE_TIME_NANOS;
import static io.grpc.internal.GrpcUtil.SERVER_KEEPALIVE_TIME_NANOS_DISABLED;

import com.google.common.annotations.VisibleForTesting;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import io.grpc.ExperimentalApi;
import io.grpc.Internal;
import io.grpc.ServerStreamTracer;
import io.grpc.internal.AbstractServerImplBuilder;
import io.grpc.internal.FixedObjectPool;
import io.grpc.internal.GrpcUtil;
import io.grpc.internal.KeepAliveManager;
import io.grpc.internal.ObjectPool;
import io.grpc.internal.SharedResourcePool;
import io.netty.channel.ChannelFactory;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.ReflectiveChannelFactory;
import io.netty.channel.ServerChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.ssl.SslContext;
import java.io.File;
import java.io.InputStream;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.TimeUnit;
import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;
import javax.net.ssl.SSLException;

/**
 * A builder to help simplify the construction of a Netty-based GRPC server.
 */
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/1784")
@CanIgnoreReturnValue
public final class NettyServerBuilder extends AbstractServerImplBuilder<NettyServerBuilder> {

  // 1MiB
  public static final int DEFAULT_FLOW_CONTROL_WINDOW = 1024 * 1024;

  static final long MAX_CONNECTION_IDLE_NANOS_DISABLED = Long.MAX_VALUE;
  static final long MAX_CONNECTION_AGE_NANOS_DISABLED = Long.MAX_VALUE;
  static final long MAX_CONNECTION_AGE_GRACE_NANOS_INFINITE = Long.MAX_VALUE;

  private static final long MIN_KEEPALIVE_TIME_NANO = TimeUnit.MILLISECONDS.toNanos(1L);
  private static final long MIN_KEEPALIVE_TIMEOUT_NANO = TimeUnit.MICROSECONDS.toNanos(499L);
  private static final long MIN_MAX_CONNECTION_IDLE_NANO = TimeUnit.SECONDS.toNanos(1L);
  private static final long MIN_MAX_CONNECTION_AGE_NANO = TimeUnit.SECONDS.toNanos(1L);
  private static final long AS_LARGE_AS_INFINITE = TimeUnit.DAYS.toNanos(1000L);
  private static final ObjectPool<? extends EventLoopGroup> DEFAULT_BOSS_EVENT_LOOP_GROUP_POOL =
      SharedResourcePool.forResource(Utils.DEFAULT_BOSS_EVENT_LOOP_GROUP);
  private static final ObjectPool<? extends EventLoopGroup> DEFAULT_WORKER_EVENT_LOOP_GROUP_POOL =
      SharedResourcePool.forResource(Utils.DEFAULT_WORKER_EVENT_LOOP_GROUP);

  private final List<SocketAddress> listenAddresses = new ArrayList<>();

  private ChannelFactory<? extends ServerChannel> channelFactory =
      Utils.DEFAULT_SERVER_CHANNEL_FACTORY;
  private final Map<ChannelOption<?>, Object> channelOptions = new HashMap<>();
  private final Map<ChannelOption<?>, Object> childChannelOptions = new HashMap<>();
  private ObjectPool<? extends EventLoopGroup> bossEventLoopGroupPool =
      DEFAULT_BOSS_EVENT_LOOP_GROUP_POOL;
  private ObjectPool<? extends EventLoopGroup> workerEventLoopGroupPool =
      DEFAULT_WORKER_EVENT_LOOP_GROUP_POOL;
  private boolean forceHeapBuffer;
  private SslContext sslContext;
  private ProtocolNegotiator protocolNegotiator;
  private int maxConcurrentCallsPerConnection = Integer.MAX_VALUE;
  private int flowControlWindow = DEFAULT_FLOW_CONTROL_WINDOW;
  private int maxMessageSize = DEFAULT_MAX_MESSAGE_SIZE;
  private int maxHeaderListSize = GrpcUtil.DEFAULT_MAX_HEADER_LIST_SIZE;
  private long keepAliveTimeInNanos = DEFAULT_SERVER_KEEPALIVE_TIME_NANOS;
  private long keepAliveTimeoutInNanos = DEFAULT_SERVER_KEEPALIVE_TIMEOUT_NANOS;
  private long maxConnectionIdleInNanos = MAX_CONNECTION_IDLE_NANOS_DISABLED;
  private long maxConnectionAgeInNanos = MAX_CONNECTION_AGE_NANOS_DISABLED;
  private long maxConnectionAgeGraceInNanos = MAX_CONNECTION_AGE_GRACE_NANOS_INFINITE;
  private boolean permitKeepAliveWithoutCalls;
  private long permitKeepAliveTimeInNanos = TimeUnit.MINUTES.toNanos(5);

  /**
   * Creates a server builder that will bind to the given port.
   *
   * @param port the port on which the server is to be bound.
   * @return the server builder.
   */
  @CheckReturnValue
  public static NettyServerBuilder forPort(int port) {
    return new NettyServerBuilder(port);
  }

  /**
   * Creates a server builder configured with the given {@link SocketAddress}.
   *
   * @param address the socket address on which the server is to be bound.
   * @return the server builder
   */
  @CheckReturnValue
  public static NettyServerBuilder forAddress(SocketAddress address) {
    return new NettyServerBuilder(address);
  }

  @CheckReturnValue
  private NettyServerBuilder(int port) {
    this.listenAddresses.add(new InetSocketAddress(port));
  }

  @CheckReturnValue
  private NettyServerBuilder(SocketAddress address) {
    this.listenAddresses.add(address);
  }

  /**
   * Adds an additional address for this server to listen on.  Callers must ensure that all socket
   * addresses are compatible with the Netty channel type, and that they don't conflict with each
   * other.
   */
  public NettyServerBuilder addListenAddress(SocketAddress listenAddress) {
    this.listenAddresses.add(checkNotNull(listenAddress, "listenAddress"));
    return this;
  }

  /**
   * Specifies the channel type to use, by default we use {@code EpollServerSocketChannel} if
   * available, otherwise using {@link NioServerSocketChannel}.
   *
   * <p>You either use this or {@link #channelFactory(io.netty.channel.ChannelFactory)} if your
   * {@link ServerChannel} implementation has no no-args constructor.
   *
   * <p>It's an optional parameter. If the user has not provided an Channel type or ChannelFactory
   * when the channel is built, the builder will use the default one which is static.
   *
   * <p>You must also provide corresponding {@link EventLoopGroup} using {@link
   * #workerEventLoopGroup(EventLoopGroup)} and {@link #bossEventLoopGroup(EventLoopGroup)}. For
   * example, {@link NioServerSocketChannel} must use {@link
   * io.netty.channel.nio.NioEventLoopGroup}, otherwise your server won't start.
   */
  public NettyServerBuilder channelType(Class<? extends ServerChannel> channelType) {
    checkNotNull(channelType, "channelType");
    return channelFactory(new ReflectiveChannelFactory<>(channelType));
  }

  /**
   * Specifies the {@link ChannelFactory} to create {@link ServerChannel} instances. This method is
   * usually only used if the specific {@code ServerChannel} requires complex logic which requires
   * additional information to create the {@code ServerChannel}. Otherwise, recommend to use {@link
   * #channelType(Class)}.
   *
   * <p>It's an optional parameter. If the user has not provided an Channel type or ChannelFactory
   * when the channel is built, the builder will use the default one which is static.
   *
   * <p>You must also provide corresponding {@link EventLoopGroup} using {@link
   * #workerEventLoopGroup(EventLoopGroup)} and {@link #bossEventLoopGroup(EventLoopGroup)}. For
   * example, if the factory creates {@link NioServerSocketChannel} you must use {@link
   * io.netty.channel.nio.NioEventLoopGroup}, otherwise your server won't start.
   */
  public NettyServerBuilder channelFactory(ChannelFactory<? extends ServerChannel> channelFactory) {
    this.channelFactory = checkNotNull(channelFactory, "channelFactory");
    return this;
  }

  /**
   * Specifies a channel option. As the underlying channel as well as network implementation may
   * ignore this value applications should consider it a hint.
   *
   * @since 1.30.0
   */
  public <T> NettyServerBuilder withOption(ChannelOption<T> option, T value) {
    this.channelOptions.put(option, value);
    return this;
  }

  /**
   * Specifies a child channel option. As the underlying channel as well as network implementation
   * may ignore this value applications should consider it a hint.
   *
   * @since 1.9.0
   */
  public <T> NettyServerBuilder withChildOption(ChannelOption<T> option, T value) {
    this.childChannelOptions.put(option, value);
    return this;
  }

  /**
   * Provides the boss EventGroupLoop to the server.
   *
   * <p>It's an optional parameter. If the user has not provided one when the server is built, the
   * builder will use the default one which is static.
   *
   * <p>You must also provide corresponding {@link io.netty.channel.Channel} type using {@link
   * #channelType(Class)} and {@link #workerEventLoopGroup(EventLoopGroup)}. For example, {@link
   * NioServerSocketChannel} must use {@link io.netty.channel.nio.NioEventLoopGroup} for both boss
   * and worker {@link EventLoopGroup}, otherwise your server won't start.
   *
   * <p>The server won't take ownership of the given EventLoopGroup. It's caller's responsibility
   * to shut it down when it's desired.
   *
   * <p>Grpc uses non-daemon {@link Thread}s by default and thus a {@link io.grpc.Server} will
   * continue to run even after the main thread has terminated. However, users have to be cautious
   * when providing their own {@link EventLoopGroup}s.
   * For example, Netty's {@link EventLoopGroup}s use daemon threads by default
   * and thus an application with only daemon threads running besides the main thread will exit as
   * soon as the main thread completes.
   * A simple solution to this problem is to call {@link io.grpc.Server#awaitTermination()} to
   * keep the main thread alive until the server has terminated.
   */
  public NettyServerBuilder bossEventLoopGroup(EventLoopGroup group) {
    if (group != null) {
      return bossEventLoopGroupPool(new FixedObjectPool<>(group));
    }
    return bossEventLoopGroupPool(DEFAULT_BOSS_EVENT_LOOP_GROUP_POOL);
  }

  NettyServerBuilder bossEventLoopGroupPool(
      ObjectPool<? extends EventLoopGroup> bossEventLoopGroupPool) {
    this.bossEventLoopGroupPool = checkNotNull(bossEventLoopGroupPool, "bossEventLoopGroupPool");
    return this;
  }

  /**
   * Provides the worker EventGroupLoop to the server.
   *
   * <p>It's an optional parameter. If the user has not provided one when the server is built, the
   * builder will create one.
   *
   * <p>You must also provide corresponding {@link io.netty.channel.Channel} type using {@link
   * #channelType(Class)} and {@link #bossEventLoopGroup(EventLoopGroup)}. For example, {@link
   * NioServerSocketChannel} must use {@link io.netty.channel.nio.NioEventLoopGroup} for both boss
   * and worker {@link EventLoopGroup}, otherwise your server won't start.
   *
   * <p>The server won't take ownership of the given EventLoopGroup. It's caller's responsibility
   * to shut it down when it's desired.
   *
   * <p>Grpc uses non-daemon {@link Thread}s by default and thus a {@link io.grpc.Server} will
   * continue to run even after the main thread has terminated. However, users have to be cautious
   * when providing their own {@link EventLoopGroup}s.
   * For example, Netty's {@link EventLoopGroup}s use daemon threads by default
   * and thus an application with only daemon threads running besides the main thread will exit as
   * soon as the main thread completes.
   * A simple solution to this problem is to call {@link io.grpc.Server#awaitTermination()} to
   * keep the main thread alive until the server has terminated.
   */
  public NettyServerBuilder workerEventLoopGroup(EventLoopGroup group) {
    if (group != null) {
      return workerEventLoopGroupPool(new FixedObjectPool<>(group));
    }
    return workerEventLoopGroupPool(DEFAULT_WORKER_EVENT_LOOP_GROUP_POOL);
  }

  NettyServerBuilder workerEventLoopGroupPool(
      ObjectPool<? extends EventLoopGroup> workerEventLoopGroupPool) {
    this.workerEventLoopGroupPool =
        checkNotNull(workerEventLoopGroupPool, "workerEventLoopGroupPool");
    return this;
  }

  /**
   * Force using heap buffer when custom allocator is enabled.
   */
  void setForceHeapBuffer(boolean value) {
    forceHeapBuffer = value;
  }

  /**
   * Sets the TLS context to use for encryption. Providing a context enables encryption. It must
   * have been configured with {@link GrpcSslContexts}, but options could have been overridden.
   */
  public NettyServerBuilder sslContext(SslContext sslContext) {
    if (sslContext != null) {
      checkArgument(sslContext.isServer(),
          "Client SSL context can not be used for server");
      GrpcSslContexts.ensureAlpnAndH2Enabled(sslContext.applicationProtocolNegotiator());
    }
    this.sslContext = sslContext;
    return this;
  }

  /**
   * Sets the {@link ProtocolNegotiator} to be used. If non-{@code null}, overrides the value
   * specified in {@link #sslContext(SslContext)}.
   *
   * <p>Default: {@code null}.
   */
  @Internal
  public final NettyServerBuilder protocolNegotiator(
          @Nullable ProtocolNegotiator protocolNegotiator) {
    this.protocolNegotiator = protocolNegotiator;
    return this;
  }

  @Override
  protected void setTracingEnabled(boolean value) {
    super.setTracingEnabled(value);
  }

  @Override
  protected void setStatsEnabled(boolean value) {
    super.setStatsEnabled(value);
  }

  @Override
  protected void setStatsRecordStartedRpcs(boolean value) {
    super.setStatsRecordStartedRpcs(value);
  }

  @Override
  protected void setStatsRecordRealTimeMetrics(boolean value) {
    super.setStatsRecordRealTimeMetrics(value);
  }

  /**
   * The maximum number of concurrent calls permitted for each incoming connection. Defaults to no
   * limit.
   */
  public NettyServerBuilder maxConcurrentCallsPerConnection(int maxCalls) {
    checkArgument(maxCalls > 0, "max must be positive: %s", maxCalls);
    this.maxConcurrentCallsPerConnection = maxCalls;
    return this;
  }

  /**
   * Sets the HTTP/2 flow control window. If not called, the default value
   * is {@link #DEFAULT_FLOW_CONTROL_WINDOW}).
   */
  public NettyServerBuilder flowControlWindow(int flowControlWindow) {
    checkArgument(flowControlWindow > 0, "flowControlWindow must be positive: %s",
        flowControlWindow);
    this.flowControlWindow = flowControlWindow;
    return this;
  }

  /**
   * Sets the maximum message size allowed to be received on the server. If not called,
   * defaults to 4 MiB. The default provides protection to services who haven't considered the
   * possibility of receiving large messages while trying to be large enough to not be hit in normal
   * usage.
   *
   * @deprecated Call {@link #maxInboundMessageSize} instead. This method will be removed in a
   *     future release.
   */
  @Deprecated
  public NettyServerBuilder maxMessageSize(int maxMessageSize) {
    return maxInboundMessageSize(maxMessageSize);
  }

  /** {@inheritDoc} */
  @Override
  public NettyServerBuilder maxInboundMessageSize(int bytes) {
    checkArgument(bytes >= 0, "bytes must be non-negative: %s", bytes);
    this.maxMessageSize = bytes;
    return this;
  }

  /**
   * Sets the maximum size of header list allowed to be received. This is cumulative size of the
   * headers with some overhead, as defined for
   * <a href="http://httpwg.org/specs/rfc7540.html#rfc.section.6.5.2">
   * HTTP/2's SETTINGS_MAX_HEADER_LIST_SIZE</a>. The default is 8 KiB.
   *
   * @deprecated Use {@link #maxInboundMetadataSize} instead
   */
  @Deprecated
  public NettyServerBuilder maxHeaderListSize(int maxHeaderListSize) {
    return maxInboundMetadataSize(maxHeaderListSize);
  }

  /**
   * Sets the maximum size of metadata allowed to be received. This is cumulative size of the
   * entries with some overhead, as defined for
   * <a href="http://httpwg.org/specs/rfc7540.html#rfc.section.6.5.2">
   * HTTP/2's SETTINGS_MAX_HEADER_LIST_SIZE</a>. The default is 8 KiB.
   *
   * @param bytes the maximum size of received metadata
   * @return this
   * @throws IllegalArgumentException if bytes is non-positive
   * @since 1.17.0
   */
  @Override
  public NettyServerBuilder maxInboundMetadataSize(int bytes) {
    checkArgument(bytes > 0, "maxInboundMetadataSize must be positive: %s", bytes);
    this.maxHeaderListSize = bytes;
    return this;
  }

  /**
   * Sets a custom keepalive time, the delay time for sending next keepalive ping. An unreasonably
   * small value might be increased, and {@code Long.MAX_VALUE} nano seconds or an unreasonably
   * large value will disable keepalive.
   *
   * @since 1.3.0
   */
  public NettyServerBuilder keepAliveTime(long keepAliveTime, TimeUnit timeUnit) {
    checkArgument(keepAliveTime > 0L, "keepalive time must be positive：%s", keepAliveTime);
    keepAliveTimeInNanos = timeUnit.toNanos(keepAliveTime);
    keepAliveTimeInNanos = KeepAliveManager.clampKeepAliveTimeInNanos(keepAliveTimeInNanos);
    if (keepAliveTimeInNanos >= AS_LARGE_AS_INFINITE) {
      // Bump keepalive time to infinite. This disables keep alive.
      keepAliveTimeInNanos = SERVER_KEEPALIVE_TIME_NANOS_DISABLED;
    }
    if (keepAliveTimeInNanos < MIN_KEEPALIVE_TIME_NANO) {
      // Bump keepalive time.
      keepAliveTimeInNanos = MIN_KEEPALIVE_TIME_NANO;
    }
    return this;
  }

  /**
   * Sets a custom keepalive timeout, the timeout for keepalive ping requests. An unreasonably small
   * value might be increased.
   *
   * @since 1.3.0
   */
  public NettyServerBuilder keepAliveTimeout(long keepAliveTimeout, TimeUnit timeUnit) {
    checkArgument(keepAliveTimeout > 0L, "keepalive timeout must be positive: %s",
        keepAliveTimeout);
    keepAliveTimeoutInNanos = timeUnit.toNanos(keepAliveTimeout);
    keepAliveTimeoutInNanos =
        KeepAliveManager.clampKeepAliveTimeoutInNanos(keepAliveTimeoutInNanos);
    if (keepAliveTimeoutInNanos < MIN_KEEPALIVE_TIMEOUT_NANO) {
      // Bump keepalive timeout.
      keepAliveTimeoutInNanos = MIN_KEEPALIVE_TIMEOUT_NANO;
    }
    return this;
  }

  /**
   * Sets a custom max connection idle time, connection being idle for longer than which will be
   * gracefully terminated. Idleness duration is defined since the most recent time the number of
   * outstanding RPCs became zero or the connection establishment. An unreasonably small value might
   * be increased. {@code Long.MAX_VALUE} nano seconds or an unreasonably large value will disable
   * max connection idle.
   *
   * @since 1.4.0
   */
  public NettyServerBuilder maxConnectionIdle(long maxConnectionIdle, TimeUnit timeUnit) {
    checkArgument(maxConnectionIdle > 0L, "max connection idle must be positive: %s",
        maxConnectionIdle);
    maxConnectionIdleInNanos = timeUnit.toNanos(maxConnectionIdle);
    if (maxConnectionIdleInNanos >= AS_LARGE_AS_INFINITE) {
      maxConnectionIdleInNanos = MAX_CONNECTION_IDLE_NANOS_DISABLED;
    }
    if (maxConnectionIdleInNanos < MIN_MAX_CONNECTION_IDLE_NANO) {
      maxConnectionIdleInNanos = MIN_MAX_CONNECTION_IDLE_NANO;
    }
    return this;
  }

  /**
   * Sets a custom max connection age, connection lasting longer than which will be gracefully
   * terminated. An unreasonably small value might be increased.  A random jitter of +/-10% will be
   * added to it. {@code Long.MAX_VALUE} nano seconds or an unreasonably large value will disable
   * max connection age.
   *
   * @since 1.3.0
   */
  public NettyServerBuilder maxConnectionAge(long maxConnectionAge, TimeUnit timeUnit) {
    checkArgument(maxConnectionAge > 0L, "max connection age must be positive: %s",
        maxConnectionAge);
    maxConnectionAgeInNanos = timeUnit.toNanos(maxConnectionAge);
    if (maxConnectionAgeInNanos >= AS_LARGE_AS_INFINITE) {
      maxConnectionAgeInNanos = MAX_CONNECTION_AGE_NANOS_DISABLED;
    }
    if (maxConnectionAgeInNanos < MIN_MAX_CONNECTION_AGE_NANO) {
      maxConnectionAgeInNanos = MIN_MAX_CONNECTION_AGE_NANO;
    }
    return this;
  }

  /**
   * Sets a custom grace time for the graceful connection termination. Once the max connection age
   * is reached, RPCs have the grace time to complete. RPCs that do not complete in time will be
   * cancelled, allowing the connection to terminate. {@code Long.MAX_VALUE} nano seconds or an
   * unreasonably large value are considered infinite.
   *
   * @see #maxConnectionAge(long, TimeUnit)
   * @since 1.3.0
   */
  public NettyServerBuilder maxConnectionAgeGrace(long maxConnectionAgeGrace, TimeUnit timeUnit) {
    checkArgument(maxConnectionAgeGrace >= 0L, "max connection age grace must be non-negative: %s",
        maxConnectionAgeGrace);
    maxConnectionAgeGraceInNanos = timeUnit.toNanos(maxConnectionAgeGrace);
    if (maxConnectionAgeGraceInNanos >= AS_LARGE_AS_INFINITE) {
      maxConnectionAgeGraceInNanos = MAX_CONNECTION_AGE_GRACE_NANOS_INFINITE;
    }
    return this;
  }

  /**
   * Specify the most aggressive keep-alive time clients are permitted to configure. The server will
   * try to detect clients exceeding this rate and when detected will forcefully close the
   * connection. The default is 5 minutes.
   *
   * <p>Even though a default is defined that allows some keep-alives, clients must not use
   * keep-alive without approval from the service owner. Otherwise, they may experience failures in
   * the future if the service becomes more restrictive. When unthrottled, keep-alives can cause a
   * significant amount of traffic and CPU usage, so clients and servers should be conservative in
   * what they use and accept.
   *
   * @see #permitKeepAliveWithoutCalls(boolean)
   * @since 1.3.0
   */
  public NettyServerBuilder permitKeepAliveTime(long keepAliveTime, TimeUnit timeUnit) {
    checkArgument(keepAliveTime >= 0, "permit keepalive time must be non-negative: %s",
        keepAliveTime);
    permitKeepAliveTimeInNanos = timeUnit.toNanos(keepAliveTime);
    return this;
  }

  /**
   * Sets whether to allow clients to send keep-alive HTTP/2 PINGs even if there are no outstanding
   * RPCs on the connection. Defaults to {@code false}.
   *
   * @see #permitKeepAliveTime(long, TimeUnit)
   * @since 1.3.0
   */
  public NettyServerBuilder permitKeepAliveWithoutCalls(boolean permit) {
    permitKeepAliveWithoutCalls = permit;
    return this;
  }

  @Override
  @CheckReturnValue
  protected List<NettyServer> buildTransportServers(
      List<? extends ServerStreamTracer.Factory> streamTracerFactories) {
    assertEventLoopsAndChannelType();

    ProtocolNegotiator negotiator = protocolNegotiator;
    if (negotiator == null) {
      negotiator = sslContext != null
          ? ProtocolNegotiators.serverTls(sslContext, this.getExecutorPool())
          : ProtocolNegotiators.serverPlaintext();
    }

    List<NettyServer> transportServers = new ArrayList<>(listenAddresses.size());
    for (SocketAddress listenAddress : listenAddresses) {
      NettyServer transportServer = new NettyServer(
          listenAddress, channelFactory, channelOptions, childChannelOptions,
          bossEventLoopGroupPool, workerEventLoopGroupPool, forceHeapBuffer, negotiator,
          streamTracerFactories, getTransportTracerFactory(), maxConcurrentCallsPerConnection,
          flowControlWindow, maxMessageSize, maxHeaderListSize, keepAliveTimeInNanos,
          keepAliveTimeoutInNanos, maxConnectionIdleInNanos, maxConnectionAgeInNanos,
          maxConnectionAgeGraceInNanos, permitKeepAliveWithoutCalls, permitKeepAliveTimeInNanos,
          getChannelz());
      transportServers.add(transportServer);
    }
    return Collections.unmodifiableList(transportServers);
  }

  @VisibleForTesting
  void assertEventLoopsAndChannelType() {
    boolean allProvided = channelFactory != Utils.DEFAULT_SERVER_CHANNEL_FACTORY
        && bossEventLoopGroupPool != DEFAULT_BOSS_EVENT_LOOP_GROUP_POOL
        && workerEventLoopGroupPool != DEFAULT_WORKER_EVENT_LOOP_GROUP_POOL;
    boolean nonProvided = channelFactory == Utils.DEFAULT_SERVER_CHANNEL_FACTORY
        && bossEventLoopGroupPool == DEFAULT_BOSS_EVENT_LOOP_GROUP_POOL
        && workerEventLoopGroupPool == DEFAULT_WORKER_EVENT_LOOP_GROUP_POOL;
    checkState(
        allProvided || nonProvided,
        "All of BossEventLoopGroup, WorkerEventLoopGroup and ChannelType should be provided or "
            + "neither should be");
  }

  @Override
  public NettyServerBuilder useTransportSecurity(File certChain, File privateKey) {
    try {
      sslContext = GrpcSslContexts.forServer(certChain, privateKey).build();
    } catch (SSLException e) {
      // This should likely be some other, easier to catch exception.
      throw new RuntimeException(e);
    }
    return this;
  }

  @Override
  public NettyServerBuilder useTransportSecurity(InputStream certChain, InputStream privateKey) {
    try {
      sslContext = GrpcSslContexts.forServer(certChain, privateKey).build();
    } catch (SSLException e) {
      // This should likely be some other, easier to catch exception.
      throw new RuntimeException(e);
    }
    return this;
  }
}