/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.kafka.clients;

import org.apache.kafka.common.Cluster;
import org.apache.kafka.common.Node;
import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.errors.AuthenticationException;
import org.apache.kafka.common.errors.UnsupportedVersionException;
import org.apache.kafka.common.metrics.Sensor;
import org.apache.kafka.common.network.ChannelState;
import org.apache.kafka.common.network.NetworkReceive;
import org.apache.kafka.common.network.Selectable;
import org.apache.kafka.common.network.Send;
import org.apache.kafka.common.protocol.ApiKeys;
import org.apache.kafka.common.protocol.Errors;
import org.apache.kafka.common.protocol.CommonFields;
import org.apache.kafka.common.protocol.types.Struct;
import org.apache.kafka.common.requests.AbstractRequest;
import org.apache.kafka.common.requests.AbstractResponse;
import org.apache.kafka.common.requests.ApiVersionsRequest;
import org.apache.kafka.common.requests.ApiVersionsResponse;
import org.apache.kafka.common.requests.MetadataRequest;
import org.apache.kafka.common.requests.MetadataResponse;
import org.apache.kafka.common.requests.RequestHeader;
import org.apache.kafka.common.requests.ResponseHeader;
import org.apache.kafka.common.utils.LogContext;
import org.apache.kafka.common.utils.Time;
import org.apache.kafka.common.utils.Utils;
import org.slf4j.Logger;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.stream.Collectors;

/**
 * A network client for asynchronous request/response network i/o. This is an internal class used to implement the
 * user-facing producer and consumer clients.
 * <p>
 * This class is not thread-safe!
 */
public class NetworkClient implements KafkaClient {

    private final Logger log;

    /* the selector used to perform network i/o */
    private final Selectable selector;

    private final MetadataUpdater metadataUpdater;

    private final Random randOffset;

    /* the state of each node's connection */
    private final ClusterConnectionStates connectionStates;

    /* the set of requests currently being sent or awaiting a response */
    private final InFlightRequests inFlightRequests;

    /* the socket send buffer size in bytes */
    private final int socketSendBuffer;

    /* the socket receive size buffer in bytes */
    private final int socketReceiveBuffer;

    /* the client id used to identify this client in requests to the server */
    private final String clientId;

    /* the current correlation id to use when sending requests to servers */
    private int correlation;

    /* default timeout for individual requests to await acknowledgement from servers */
    private final int defaultRequestTimeoutMs;

    /* time in ms to wait before retrying to create connection to a server */
    private final long reconnectBackoffMs;

    private final Time time;

    /**
     * True if we should send an ApiVersionRequest when first connecting to a broker.
     */
    private final boolean discoverBrokerVersions;

    private final ApiVersions apiVersions;

    private final Map<String, ApiVersionsRequest.Builder> nodesNeedingApiVersionsFetch = new HashMap<>();

    private final List<ClientResponse> abortedSends = new LinkedList<>();

    private final Sensor throttleTimeSensor;

    public NetworkClient(Selectable selector,
                         Metadata metadata,
                         String clientId,
                         int maxInFlightRequestsPerConnection,
                         long reconnectBackoffMs,
                         long reconnectBackoffMax,
                         int socketSendBuffer,
                         int socketReceiveBuffer,
                         int defaultRequestTimeoutMs,
                         Time time,
                         boolean discoverBrokerVersions,
                         ApiVersions apiVersions,
                         LogContext logContext) {
        this(null,
             metadata,
             selector,
             clientId,
             maxInFlightRequestsPerConnection,
             reconnectBackoffMs,
             reconnectBackoffMax,
             socketSendBuffer,
             socketReceiveBuffer,
             defaultRequestTimeoutMs,
             time,
             discoverBrokerVersions,
             apiVersions,
             null,
             logContext);
    }

    public NetworkClient(Selectable selector,
            Metadata metadata,
            String clientId,
            int maxInFlightRequestsPerConnection,
            long reconnectBackoffMs,
            long reconnectBackoffMax,
            int socketSendBuffer,
            int socketReceiveBuffer,
            int defaultRequestTimeoutMs,
            Time time,
            boolean discoverBrokerVersions,
            ApiVersions apiVersions,
            Sensor throttleTimeSensor,
            LogContext logContext) {
        this(null,
             metadata,
             selector,
             clientId,
             maxInFlightRequestsPerConnection,
             reconnectBackoffMs,
             reconnectBackoffMax,
             socketSendBuffer,
             socketReceiveBuffer,
             defaultRequestTimeoutMs,
             time,
             discoverBrokerVersions,
             apiVersions,
             throttleTimeSensor,
             logContext);
    }

    public NetworkClient(Selectable selector,
                         MetadataUpdater metadataUpdater,
                         String clientId,
                         int maxInFlightRequestsPerConnection,
                         long reconnectBackoffMs,
                         long reconnectBackoffMax,
                         int socketSendBuffer,
                         int socketReceiveBuffer,
                         int defaultRequestTimeoutMs,
                         Time time,
                         boolean discoverBrokerVersions,
                         ApiVersions apiVersions,
                         LogContext logContext) {
        this(metadataUpdater,
             null,
             selector,
             clientId,
             maxInFlightRequestsPerConnection,
             reconnectBackoffMs,
             reconnectBackoffMax,
             socketSendBuffer,
             socketReceiveBuffer,
             defaultRequestTimeoutMs,
             time,
             discoverBrokerVersions,
             apiVersions,
             null,
             logContext);
    }

    private NetworkClient(MetadataUpdater metadataUpdater,
                          Metadata metadata,
                          Selectable selector,
                          String clientId,
                          int maxInFlightRequestsPerConnection,
                          long reconnectBackoffMs,
                          long reconnectBackoffMax,
                          int socketSendBuffer,
                          int socketReceiveBuffer,
                          int defaultRequestTimeoutMs,
                          Time time,
                          boolean discoverBrokerVersions,
                          ApiVersions apiVersions,
                          Sensor throttleTimeSensor,
                          LogContext logContext) {
        /* It would be better if we could pass `DefaultMetadataUpdater` from the public constructor, but it's not
         * possible because `DefaultMetadataUpdater` is an inner class and it can only be instantiated after the
         * super constructor is invoked.
         */
        if (metadataUpdater == null) {
            if (metadata == null)
                throw new IllegalArgumentException("`metadata` must not be null");
            this.metadataUpdater = new DefaultMetadataUpdater(metadata);
        } else {
            this.metadataUpdater = metadataUpdater;
        }
        this.selector = selector;
        this.clientId = clientId;
        this.inFlightRequests = new InFlightRequests(maxInFlightRequestsPerConnection);
        this.connectionStates = new ClusterConnectionStates(reconnectBackoffMs, reconnectBackoffMax);
        this.socketSendBuffer = socketSendBuffer;
        this.socketReceiveBuffer = socketReceiveBuffer;
        this.correlation = 0;
        this.randOffset = new Random();
        this.defaultRequestTimeoutMs = defaultRequestTimeoutMs;
        this.reconnectBackoffMs = reconnectBackoffMs;
        this.time = time;
        this.discoverBrokerVersions = discoverBrokerVersions;
        this.apiVersions = apiVersions;
        this.throttleTimeSensor = throttleTimeSensor;
        this.log = logContext.logger(NetworkClient.class);
    }

    /**
     * Begin connecting to the given node, return true if we are already connected and ready to send to that node.
     *
     * @param node The node to check
     * @param now The current timestamp
     * @return True if we are ready to send to the given node
     */
    @Override
    public boolean ready(Node node, long now) {
        if (node.isEmpty())
            throw new IllegalArgumentException("Cannot connect to empty node " + node);

        if (isReady(node, now))
            return true;

        if (connectionStates.canConnect(node.idString(), now))
            // if we are interested in sending to a node and we don't have a connection to it, initiate one
            initiateConnect(node, now);

        return false;
    }

    // Visible for testing
    boolean canConnect(Node node, long now) {
        return connectionStates.canConnect(node.idString(), now);
    }

    /**
     * Disconnects the connection to a particular node, if there is one.
     * Any pending ClientRequests for this connection will receive disconnections.
     *
     * @param nodeId The id of the node
     */
    @Override
    public void disconnect(String nodeId) {
        if (connectionStates.isDisconnected(nodeId))
            return;

        selector.close(nodeId);
        List<ApiKeys> requestTypes = new ArrayList<>();
        long now = time.milliseconds();
        for (InFlightRequest request : inFlightRequests.clearAll(nodeId)) {
            if (request.isInternalRequest) {
                if (request.header.apiKey() == ApiKeys.METADATA) {
                    metadataUpdater.handleDisconnection(request.destination);
                }
            } else {
                requestTypes.add(request.header.apiKey());
                abortedSends.add(new ClientResponse(request.header,
                        request.callback, request.destination, request.createdTimeMs, now,
                        true, null, null, null));
            }
        }
        connectionStates.disconnected(nodeId, now);
        if (log.isDebugEnabled()) {
            log.debug("Manually disconnected from {}. Removed requests: {}.", nodeId,
                Utils.join(requestTypes, ", "));
        }
    }

    /**
     * Closes the connection to a particular node (if there is one).
     * All requests on the connection will be cleared.  ClientRequest callbacks will not be invoked
     * for the cleared requests, nor will they be returned from poll().
     *
     * @param nodeId The id of the node
     */
    @Override
    public void close(String nodeId) {
        selector.close(nodeId);
        for (InFlightRequest request : inFlightRequests.clearAll(nodeId))
            if (request.isInternalRequest && request.header.apiKey() == ApiKeys.METADATA)
                metadataUpdater.handleDisconnection(request.destination);
        connectionStates.remove(nodeId);
    }

    /**
     * Returns the number of milliseconds to wait, based on the connection state, before attempting to send data. When
     * disconnected, this respects the reconnect backoff time. When connecting or connected, this handles slow/stalled
     * connections.
     *
     * @param node The node to check
     * @param now The current timestamp
     * @return The number of milliseconds to wait.
     */
    @Override
    public long connectionDelay(Node node, long now) {
        return connectionStates.connectionDelay(node.idString(), now);
    }

    // Return the remaining throttling delay in milliseconds if throttling is in progress. Return 0, otherwise.
    // This is for testing.
    public long throttleDelayMs(Node node, long now) {
        return connectionStates.throttleDelayMs(node.idString(), now);
    }

    /**
     * Return the poll delay in milliseconds based on both connection and throttle delay.
     * @param node the connection to check
     * @param now the current time in ms
     */
    @Override
    public long pollDelayMs(Node node, long now) {
        return connectionStates.pollDelayMs(node.idString(), now);
    }

    /**
     * Check if the connection of the node has failed, based on the connection state. Such connection failure are
     * usually transient and can be resumed in the next {@link #ready(org.apache.kafka.common.Node, long)} }
     * call, but there are cases where transient failures needs to be caught and re-acted upon.
     *
     * @param node the node to check
     * @return true iff the connection has failed and the node is disconnected
     */
    @Override
    public boolean connectionFailed(Node node) {
        return connectionStates.isDisconnected(node.idString());
    }

    /**
     * Check if authentication to this node has failed, based on the connection state. Authentication failures are
     * propagated without any retries.
     *
     * @param node the node to check
     * @return an AuthenticationException iff authentication has failed, null otherwise
     */
    @Override
    public AuthenticationException authenticationException(Node node) {
        return connectionStates.authenticationException(node.idString());
    }

    /**
     * Check if the node with the given id is ready to send more requests.
     *
     * @param node The node
     * @param now The current time in ms
     * @return true if the node is ready
     */
    @Override
    public boolean isReady(Node node, long now) {
        // if we need to update our metadata now declare all requests unready to make metadata requests first
        // priority
        return !metadataUpdater.isUpdateDue(now) && canSendRequest(node.idString(), now);
    }

    /**
     * Are we connected and ready and able to send more requests to the given connection?
     *
     * @param node The node
     * @param now the current timestamp
     */
    private boolean canSendRequest(String node, long now) {
        return connectionStates.isReady(node, now) && selector.isChannelReady(node) &&
            inFlightRequests.canSendMore(node);
    }

    /**
     * Queue up the given request for sending. Requests can only be sent out to ready nodes.
     * @param request The request
     * @param now The current timestamp
     */
    @Override
    public void send(ClientRequest request, long now) {
        doSend(request, false, now);
    }

    private void sendInternalMetadataRequest(MetadataRequest.Builder builder,
                                             String nodeConnectionId, long now) {
        ClientRequest clientRequest = newClientRequest(nodeConnectionId, builder, now, true);
        doSend(clientRequest, true, now);
    }

    private void doSend(ClientRequest clientRequest, boolean isInternalRequest, long now) {
        String nodeId = clientRequest.destination();
        if (!isInternalRequest) {
            // If this request came from outside the NetworkClient, validate
            // that we can send data.  If the request is internal, we trust
            // that internal code has done this validation.  Validation
            // will be slightly different for some internal requests (for
            // example, ApiVersionsRequests can be sent prior to being in
            // READY state.)
            if (!canSendRequest(nodeId, now))
                throw new IllegalStateException("Attempt to send a request to node " + nodeId + " which is not ready.");
        }
        AbstractRequest.Builder<?> builder = clientRequest.requestBuilder();
        try {
            NodeApiVersions versionInfo = apiVersions.get(nodeId);
            short version;
            // Note: if versionInfo is null, we have no server version information. This would be
            // the case when sending the initial ApiVersionRequest which fetches the version
            // information itself.  It is also the case when discoverBrokerVersions is set to false.
            if (versionInfo == null) {
                version = builder.latestAllowedVersion();
                if (discoverBrokerVersions && log.isTraceEnabled())
                    log.trace("No version information found when sending {} with correlation id {} to node {}. " +
                            "Assuming version {}.", clientRequest.apiKey(), clientRequest.correlationId(), nodeId, version);
            } else {
                version = versionInfo.latestUsableVersion(clientRequest.apiKey(), builder.oldestAllowedVersion(),
                        builder.latestAllowedVersion());
            }
            // The call to build may also throw UnsupportedVersionException, if there are essential
            // fields that cannot be represented in the chosen version.
            doSend(clientRequest, isInternalRequest, now, builder.build(version));
        } catch (UnsupportedVersionException unsupportedVersionException) {
            // If the version is not supported, skip sending the request over the wire.
            // Instead, simply add it to the local queue of aborted requests.
            log.debug("Version mismatch when attempting to send {} with correlation id {} to {}", builder,
                    clientRequest.correlationId(), clientRequest.destination(), unsupportedVersionException);
            ClientResponse clientResponse = new ClientResponse(clientRequest.makeHeader(builder.latestAllowedVersion()),
                    clientRequest.callback(), clientRequest.destination(), now, now,
                    false, unsupportedVersionException, null, null);
            abortedSends.add(clientResponse);
        }
    }

    private void doSend(ClientRequest clientRequest, boolean isInternalRequest, long now, AbstractRequest request) {
        String destination = clientRequest.destination();
        RequestHeader header = clientRequest.makeHeader(request.version());
        if (log.isDebugEnabled()) {
            int latestClientVersion = clientRequest.apiKey().latestVersion();
            if (header.apiVersion() == latestClientVersion) {
                log.trace("Sending {} {} with correlation id {} to node {}", clientRequest.apiKey(), request,
                        clientRequest.correlationId(), destination);
            } else {
                log.debug("Using older server API v{} to send {} {} with correlation id {} to node {}",
                        header.apiVersion(), clientRequest.apiKey(), request, clientRequest.correlationId(), destination);
            }
        }
        Send send = request.toSend(destination, header);
        InFlightRequest inFlightRequest = new InFlightRequest(
                clientRequest,
                header,
                isInternalRequest,
                request,
                send,
                now);
        this.inFlightRequests.add(inFlightRequest);
        selector.send(send);
    }

    /**
     * Do actual reads and writes to sockets.
     *
     * @param timeout The maximum amount of time to wait (in ms) for responses if there are none immediately,
     *                must be non-negative. The actual timeout will be the minimum of timeout, request timeout and
     *                metadata timeout
     * @param now The current time in milliseconds
     * @return The list of responses received
     */
    @Override
    public List<ClientResponse> poll(long timeout, long now) {
        if (!abortedSends.isEmpty()) {
            // If there are aborted sends because of unsupported version exceptions or disconnects,
            // handle them immediately without waiting for Selector#poll.
            List<ClientResponse> responses = new ArrayList<>();
            handleAbortedSends(responses);
            completeResponses(responses);
            return responses;
        }

        long metadataTimeout = metadataUpdater.maybeUpdate(now);
        try {
            this.selector.poll(Utils.min(timeout, metadataTimeout, defaultRequestTimeoutMs));
        } catch (IOException e) {
            log.error("Unexpected error during I/O", e);
        }

        // process completed actions
        long updatedNow = this.time.milliseconds();
        List<ClientResponse> responses = new ArrayList<>();
        handleCompletedSends(responses, updatedNow);
        handleCompletedReceives(responses, updatedNow);
        handleDisconnections(responses, updatedNow);
        handleConnections();
        handleInitiateApiVersionRequests(updatedNow);
        handleTimedOutRequests(responses, updatedNow);
        completeResponses(responses);

        return responses;
    }

    private void completeResponses(List<ClientResponse> responses) {
        for (ClientResponse response : responses) {
            try {
                response.onComplete();
            } catch (Exception e) {
                log.error("Uncaught error in request completion:", e);
            }
        }
    }

    /**
     * Get the number of in-flight requests
     */
    @Override
    public int inFlightRequestCount() {
        return this.inFlightRequests.count();
    }

    @Override
    public boolean hasInFlightRequests() {
        return !this.inFlightRequests.isEmpty();
    }

    /**
     * Get the number of in-flight requests for a given node
     */
    @Override
    public int inFlightRequestCount(String node) {
        return this.inFlightRequests.count(node);
    }

    @Override
    public boolean hasInFlightRequests(String node) {
        return !this.inFlightRequests.isEmpty(node);
    }

    @Override
    public boolean hasReadyNodes(long now) {
        return connectionStates.hasReadyNodes(now);
    }

    /**
     * Interrupt the client if it is blocked waiting on I/O.
     */
    @Override
    public void wakeup() {
        this.selector.wakeup();
    }

    /**
     * Close the network client
     */
    @Override
    public void close() {
        this.selector.close();
        this.metadataUpdater.close();
    }

    /**
     * Choose the node with the fewest outstanding requests which is at least eligible for connection. This method will
     * prefer a node with an existing connection, but will potentially choose a node for which we don't yet have a
     * connection if all existing connections are in use. This method will never choose a node for which there is no
     * existing connection and from which we have disconnected within the reconnect backoff period.
     *
     * @return The node with the fewest in-flight requests.
     */
    @Override
    public Node leastLoadedNode(long now) {
        List<Node> nodes = this.metadataUpdater.fetchNodes();
        int inflight = Integer.MAX_VALUE;
        Node found = null;

        int offset = this.randOffset.nextInt(nodes.size());
        for (int i = 0; i < nodes.size(); i++) {
            int idx = (offset + i) % nodes.size();
            Node node = nodes.get(idx);
            int currInflight = this.inFlightRequests.count(node.idString());
            if (currInflight == 0 && isReady(node, now)) {
                // if we find an established connection with no in-flight requests we can stop right away
                log.trace("Found least loaded node {} connected with no in-flight requests", node);
                return node;
            } else if (!this.connectionStates.isBlackedOut(node.idString(), now) && currInflight < inflight) {
                // otherwise if this is the best we have found so far, record that
                inflight = currInflight;
                found = node;
            } else if (log.isTraceEnabled()) {
                log.trace("Removing node {} from least loaded node selection: is-blacked-out: {}, in-flight-requests: {}",
                        node, this.connectionStates.isBlackedOut(node.idString(), now), currInflight);
            }
        }

        if (found != null)
            log.trace("Found least loaded node {}", found);
        else
            log.trace("Least loaded node selection failed to find an available node");

        return found;
    }

    public static AbstractResponse parseResponse(ByteBuffer responseBuffer, RequestHeader requestHeader) {
        Struct responseStruct = parseStructMaybeUpdateThrottleTimeMetrics(responseBuffer, requestHeader, null, 0);
        return AbstractResponse.parseResponse(requestHeader.apiKey(), responseStruct);
    }

    private static Struct parseStructMaybeUpdateThrottleTimeMetrics(ByteBuffer responseBuffer, RequestHeader requestHeader,
                                                                    Sensor throttleTimeSensor, long now) {
        ResponseHeader responseHeader = ResponseHeader.parse(responseBuffer);
        // Always expect the response version id to be the same as the request version id
        Struct responseBody = requestHeader.apiKey().parseResponse(requestHeader.apiVersion(), responseBuffer);
        correlate(requestHeader, responseHeader);
        if (throttleTimeSensor != null && responseBody.hasField(CommonFields.THROTTLE_TIME_MS))
            throttleTimeSensor.record(responseBody.get(CommonFields.THROTTLE_TIME_MS), now);
        return responseBody;
    }

    /**
     * Post process disconnection of a node
     *
     * @param responses The list of responses to update
     * @param nodeId Id of the node to be disconnected
     * @param now The current time
     */
    private void processDisconnection(List<ClientResponse> responses,
                                      String nodeId,
                                      long now,
                                      ChannelState disconnectState) {
        connectionStates.disconnected(nodeId, now);
        apiVersions.remove(nodeId);
        nodesNeedingApiVersionsFetch.remove(nodeId);
        switch (disconnectState.state()) {
            case AUTHENTICATION_FAILED:
                AuthenticationException exception = disconnectState.exception();
                connectionStates.authenticationFailed(nodeId, now, exception);
                metadataUpdater.handleAuthenticationFailure(exception);
                log.error("Connection to node {} failed authentication due to: {}", nodeId, exception.getMessage());
                break;
            case AUTHENTICATE:
                // This warning applies to older brokers which don't provide feedback on authentication failures
                log.warn("Connection to node {} terminated during authentication. This may indicate " +
                        "that authentication failed due to invalid credentials.", nodeId);
                break;
            case NOT_CONNECTED:
                log.warn("Connection to node {} could not be established. Broker may not be available.", nodeId);
                break;
            default:
                break; // Disconnections in other states are logged at debug level in Selector
        }
        for (InFlightRequest request : this.inFlightRequests.clearAll(nodeId)) {
            log.trace("Cancelled request {} {} with correlation id {} due to node {} being disconnected",
                    request.header.apiKey(), request.request, request.header.correlationId(), nodeId);
            if (!request.isInternalRequest)
                responses.add(request.disconnected(now, disconnectState.exception()));
            else if (request.header.apiKey() == ApiKeys.METADATA)
                metadataUpdater.handleDisconnection(request.destination);
        }
    }

    /**
     * Iterate over all the inflight requests and expire any requests that have exceeded the configured requestTimeout.
     * The connection to the node associated with the request will be terminated and will be treated as a disconnection.
     *
     * @param responses The list of responses to update
     * @param now The current time
     */
    private void handleTimedOutRequests(List<ClientResponse> responses, long now) {
        List<String> nodeIds = this.inFlightRequests.nodesWithTimedOutRequests(now);
        for (String nodeId : nodeIds) {
            // close connection to the node
            this.selector.close(nodeId);
            log.debug("Disconnecting from node {} due to request timeout.", nodeId);
            processDisconnection(responses, nodeId, now, ChannelState.LOCAL_CLOSE);
        }

        // we disconnected, so we should probably refresh our metadata
        if (!nodeIds.isEmpty())
            metadataUpdater.requestUpdate();
    }

    private void handleAbortedSends(List<ClientResponse> responses) {
        responses.addAll(abortedSends);
        abortedSends.clear();
    }

    /**
     * Handle any completed request send. In particular if no response is expected consider the request complete.
     *
     * @param responses The list of responses to update
     * @param now The current time
     */
    private void handleCompletedSends(List<ClientResponse> responses, long now) {
        // if no response is expected then when the send is completed, return it
        for (Send send : this.selector.completedSends()) {
            InFlightRequest request = this.inFlightRequests.lastSent(send.destination());
            if (!request.expectResponse) {
                this.inFlightRequests.completeLastSent(send.destination());
                responses.add(request.completed(null, now));
            }
        }
    }

    /**
     * If a response from a node includes a non-zero throttle delay and client-side throttling has been enabled for
     * the connection to the node, throttle the connection for the specified delay.
     *
     * @param response the response
     * @param apiVersion the API version of the response
     * @param nodeId the id of the node
     * @param now The current time
     */
    private void maybeThrottle(AbstractResponse response, short apiVersion, String nodeId, long now) {
        int throttleTimeMs = response.throttleTimeMs();
        if (throttleTimeMs > 0 && response.shouldClientThrottle(apiVersion)) {
            connectionStates.throttle(nodeId, now + throttleTimeMs);
            log.trace("Connection to node {} is throttled for {} ms until timestamp {}", nodeId, throttleTimeMs,
                      now + throttleTimeMs);
        }
    }

    /**
     * Handle any completed receives and update the response list with the responses received.
     *
     * @param responses The list of responses to update
     * @param now The current time
     */
    private void handleCompletedReceives(List<ClientResponse> responses, long now) {
        for (NetworkReceive receive : this.selector.completedReceives()) {
            String source = receive.source();
            InFlightRequest req = inFlightRequests.completeNext(source);
            Struct responseStruct = parseStructMaybeUpdateThrottleTimeMetrics(receive.payload(), req.header,
                throttleTimeSensor, now);
            if (log.isTraceEnabled()) {
                log.trace("Completed receive from node {} for {} with correlation id {}, received {}", req.destination,
                    req.header.apiKey(), req.header.correlationId(), responseStruct);
            }
            // If the received response includes a throttle delay, throttle the connection.
            AbstractResponse body = AbstractResponse.parseResponse(req.header.apiKey(), responseStruct);
            maybeThrottle(body, req.header.apiVersion(), req.destination, now);
            if (req.isInternalRequest && body instanceof MetadataResponse)
                metadataUpdater.handleCompletedMetadataResponse(req.header, now, (MetadataResponse) body);
            else if (req.isInternalRequest && body instanceof ApiVersionsResponse)
                handleApiVersionsResponse(responses, req, now, (ApiVersionsResponse) body);
            else
                responses.add(req.completed(body, now));
        }
    }

    private void handleApiVersionsResponse(List<ClientResponse> responses,
                                           InFlightRequest req, long now, ApiVersionsResponse apiVersionsResponse) {
        final String node = req.destination;
        if (apiVersionsResponse.error() != Errors.NONE) {
            if (req.request.version() == 0 || apiVersionsResponse.error() != Errors.UNSUPPORTED_VERSION) {
                log.warn("Received error {} from node {} when making an ApiVersionsRequest with correlation id {}. Disconnecting.",
                        apiVersionsResponse.error(), node, req.header.correlationId());
                this.selector.close(node);
                processDisconnection(responses, node, now, ChannelState.LOCAL_CLOSE);
            } else {
                nodesNeedingApiVersionsFetch.put(node, new ApiVersionsRequest.Builder((short) 0));
            }
            return;
        }
        NodeApiVersions nodeVersionInfo = new NodeApiVersions(apiVersionsResponse.apiVersions());
        apiVersions.update(node, nodeVersionInfo);
        this.connectionStates.ready(node);
        log.debug("Recorded API versions for node {}: {}", node, nodeVersionInfo);
    }

    /**
     * Handle any disconnected connections
     *
     * @param responses The list of responses that completed with the disconnection
     * @param now The current time
     */
    private void handleDisconnections(List<ClientResponse> responses, long now) {
        for (Map.Entry<String, ChannelState> entry : this.selector.disconnected().entrySet()) {
            String node = entry.getKey();
            log.debug("Node {} disconnected.", node);
            processDisconnection(responses, node, now, entry.getValue());
        }
        // we got a disconnect so we should probably refresh our metadata and see if that broker is dead
        if (this.selector.disconnected().size() > 0)
            metadataUpdater.requestUpdate();
    }

    /**
     * Record any newly completed connections
     */
    private void handleConnections() {
        for (String node : this.selector.connected()) {
            // We are now connected.  Node that we might not still be able to send requests. For instance,
            // if SSL is enabled, the SSL handshake happens after the connection is established.
            // Therefore, it is still necessary to check isChannelReady before attempting to send on this
            // connection.
            if (discoverBrokerVersions) {
                this.connectionStates.checkingApiVersions(node);
                nodesNeedingApiVersionsFetch.put(node, new ApiVersionsRequest.Builder());
                log.debug("Completed connection to node {}. Fetching API versions.", node);
            } else {
                this.connectionStates.ready(node);
                log.debug("Completed connection to node {}. Ready.", node);
            }
        }
    }

    private void handleInitiateApiVersionRequests(long now) {
        Iterator<Map.Entry<String, ApiVersionsRequest.Builder>> iter = nodesNeedingApiVersionsFetch.entrySet().iterator();
        while (iter.hasNext()) {
            Map.Entry<String, ApiVersionsRequest.Builder> entry = iter.next();
            String node = entry.getKey();
            if (selector.isChannelReady(node) && inFlightRequests.canSendMore(node)) {
                log.debug("Initiating API versions fetch from node {}.", node);
                ApiVersionsRequest.Builder apiVersionRequestBuilder = entry.getValue();
                ClientRequest clientRequest = newClientRequest(node, apiVersionRequestBuilder, now, true);
                doSend(clientRequest, true, now);
                iter.remove();
            }
        }
    }

    /**
     * Validate that the response corresponds to the request we expect or else explode
     */
    private static void correlate(RequestHeader requestHeader, ResponseHeader responseHeader) {
        if (requestHeader.correlationId() != responseHeader.correlationId())
            throw new IllegalStateException("Correlation id for response (" + responseHeader.correlationId()
                    + ") does not match request (" + requestHeader.correlationId() + "), request header: " + requestHeader);
    }

    /**
     * Initiate a connection to the given node
     */
    private void initiateConnect(Node node, long now) {
        String nodeConnectionId = node.idString();
        try {
            log.debug("Initiating connection to node {}", node);
            this.connectionStates.connecting(nodeConnectionId, now);
            selector.connect(nodeConnectionId,
                             new InetSocketAddress(node.host(), node.port()),
                             this.socketSendBuffer,
                             this.socketReceiveBuffer);
        } catch (IOException e) {
            /* attempt failed, we'll try again after the backoff */
            connectionStates.disconnected(nodeConnectionId, now);
            /* maybe the problem is our metadata, update it */
            metadataUpdater.requestUpdate();
            log.warn("Error connecting to node {}", node, e);
        }
    }

    class DefaultMetadataUpdater implements MetadataUpdater {

        /* the current cluster metadata */
        private final Metadata metadata;

        /* true iff there is a metadata request that has been sent and for which we have not yet received a response */
        private boolean metadataFetchInProgress;

        DefaultMetadataUpdater(Metadata metadata) {
            this.metadata = metadata;
            this.metadataFetchInProgress = false;
        }

        @Override
        public List<Node> fetchNodes() {
            return metadata.fetch().nodes();
        }

        @Override
        public boolean isUpdateDue(long now) {
            return !this.metadataFetchInProgress && this.metadata.timeToNextUpdate(now) == 0;
        }

        @Override
        public long maybeUpdate(long now) {
            // should we update our metadata?
            long timeToNextMetadataUpdate = metadata.timeToNextUpdate(now);
            long waitForMetadataFetch = this.metadataFetchInProgress ? defaultRequestTimeoutMs : 0;

            long metadataTimeout = Math.max(timeToNextMetadataUpdate, waitForMetadataFetch);

            if (metadataTimeout > 0) {
                return metadataTimeout;
            }

            // Beware that the behavior of this method and the computation of timeouts for poll() are
            // highly dependent on the behavior of leastLoadedNode.
            Node node = leastLoadedNode(now);
            if (node == null) {
                log.debug("Give up sending metadata request since no node is available");
                return reconnectBackoffMs;
            }

            return maybeUpdate(now, node);
        }

        @Override
        public void handleDisconnection(String destination) {
            Cluster cluster = metadata.fetch();
            // 'processDisconnection' generates warnings for misconfigured bootstrap server configuration
            // resulting in 'Connection Refused' and misconfigured security resulting in authentication failures.
            // The warning below handles the case where connection to a broker was established, but was disconnected
            // before metadata could be obtained.
            if (cluster.isBootstrapConfigured()) {
                int nodeId = Integer.parseInt(destination);
                Node node = cluster.nodeById(nodeId);
                if (node != null)
                    log.warn("Bootstrap broker {} disconnected", node);
            }

            metadataFetchInProgress = false;
        }

        @Override
        public void handleAuthenticationFailure(AuthenticationException exception) {
            metadataFetchInProgress = false;
            if (metadata.updateRequested())
                metadata.failedUpdate(time.milliseconds(), exception);
        }

        @Override
        public void handleCompletedMetadataResponse(RequestHeader requestHeader, long now, MetadataResponse response) {
            this.metadataFetchInProgress = false;
            Cluster cluster = response.cluster();

            // If any partition has leader with missing listeners, log a few for diagnosing broker configuration
            // issues. This could be a transient issue if listeners were added dynamically to brokers.
            List<TopicPartition> missingListenerPartitions = response.topicMetadata().stream().flatMap(topicMetadata ->
                topicMetadata.partitionMetadata().stream()
                    .filter(partitionMetadata -> partitionMetadata.error() == Errors.LISTENER_NOT_FOUND)
                    .map(partitionMetadata -> new TopicPartition(topicMetadata.topic(), partitionMetadata.partition())))
                .collect(Collectors.toList());
            if (!missingListenerPartitions.isEmpty()) {
                int count = missingListenerPartitions.size();
                log.warn("{} partitions have leader brokers without a matching listener, including {}",
                        count, missingListenerPartitions.subList(0, Math.min(10, count)));
            }

            // check if any topics metadata failed to get updated
            Map<String, Errors> errors = response.errors();
            if (!errors.isEmpty())
                log.warn("Error while fetching metadata with correlation id {} : {}", requestHeader.correlationId(), errors);

            // don't update the cluster if there are no valid nodes...the topic we want may still be in the process of being
            // created which means we will get errors and no nodes until it exists
            if (cluster.nodes().size() > 0) {
                this.metadata.update(cluster, response.unavailableTopics(), now);
            } else {
                log.trace("Ignoring empty metadata response with correlation id {}.", requestHeader.correlationId());
                this.metadata.failedUpdate(now, null);
            }
        }

        @Override
        public void requestUpdate() {
            this.metadata.requestUpdate();
        }

        @Override
        public void close() {
            this.metadata.close();
        }

        /**
         * Return true if there's at least one connection establishment is currently underway
         */
        private boolean isAnyNodeConnecting() {
            for (Node node : fetchNodes()) {
                if (connectionStates.isConnecting(node.idString())) {
                    return true;
                }
            }
            return false;
        }

        /**
         * Add a metadata request to the list of sends if we can make one
         */
        private long maybeUpdate(long now, Node node) {
            String nodeConnectionId = node.idString();

            if (canSendRequest(nodeConnectionId, now)) {
                this.metadataFetchInProgress = true;
                MetadataRequest.Builder metadataRequest;
                if (metadata.needMetadataForAllTopics())
                    metadataRequest = MetadataRequest.Builder.allTopics();
                else
                    metadataRequest = new MetadataRequest.Builder(new ArrayList<>(metadata.topics()),
                            metadata.allowAutoTopicCreation());


                log.debug("Sending metadata request {} to node {}", metadataRequest, node);
                sendInternalMetadataRequest(metadataRequest, nodeConnectionId, now);
                return defaultRequestTimeoutMs;
            }

            // If there's any connection establishment underway, wait until it completes. This prevents
            // the client from unnecessarily connecting to additional nodes while a previous connection
            // attempt has not been completed.
            if (isAnyNodeConnecting()) {
                // Strictly the timeout we should return here is "connect timeout", but as we don't
                // have such application level configuration, using reconnect backoff instead.
                return reconnectBackoffMs;
            }

            if (connectionStates.canConnect(nodeConnectionId, now)) {
                // we don't have a connection to this node right now, make one
                log.debug("Initialize connection to node {} for sending metadata request", node);
                initiateConnect(node, now);
                return reconnectBackoffMs;
            }

            // connected, but can't send more OR connecting
            // In either case, we just need to wait for a network event to let us know the selected
            // connection might be usable again.
            return Long.MAX_VALUE;
        }

    }

    @Override
    public ClientRequest newClientRequest(String nodeId,
                                          AbstractRequest.Builder<?> requestBuilder,
                                          long createdTimeMs,
                                          boolean expectResponse) {
        return newClientRequest(nodeId, requestBuilder, createdTimeMs, expectResponse, defaultRequestTimeoutMs, null);
    }

    @Override
    public ClientRequest newClientRequest(String nodeId,
                                          AbstractRequest.Builder<?> requestBuilder,
                                          long createdTimeMs,
                                          boolean expectResponse,
                                          int requestTimeoutMs,
                                          RequestCompletionHandler callback) {
        return new ClientRequest(nodeId, requestBuilder, correlation++, clientId, createdTimeMs, expectResponse,
                defaultRequestTimeoutMs, callback);
    }

    public boolean discoverBrokerVersions() {
        return discoverBrokerVersions;
    }

    static class InFlightRequest {
        final RequestHeader header;
        final String destination;
        final RequestCompletionHandler callback;
        final boolean expectResponse;
        final AbstractRequest request;
        final boolean isInternalRequest; // used to flag requests which are initiated internally by NetworkClient
        final Send send;
        final long sendTimeMs;
        final long createdTimeMs;
        final long requestTimeoutMs;

        public InFlightRequest(ClientRequest clientRequest,
                               RequestHeader header,
                               boolean isInternalRequest,
                               AbstractRequest request,
                               Send send,
                               long sendTimeMs) {
            this(header,
                 clientRequest.requestTimeoutMs(),
                 clientRequest.createdTimeMs(),
                 clientRequest.destination(),
                 clientRequest.callback(),
                 clientRequest.expectResponse(),
                 isInternalRequest,
                 request,
                 send,
                 sendTimeMs);
        }

        public InFlightRequest(RequestHeader header,
                               int requestTimeoutMs,
                               long createdTimeMs,
                               String destination,
                               RequestCompletionHandler callback,
                               boolean expectResponse,
                               boolean isInternalRequest,
                               AbstractRequest request,
                               Send send,
                               long sendTimeMs) {
            this.header = header;
            this.requestTimeoutMs = requestTimeoutMs;
            this.createdTimeMs = createdTimeMs;
            this.destination = destination;
            this.callback = callback;
            this.expectResponse = expectResponse;
            this.isInternalRequest = isInternalRequest;
            this.request = request;
            this.send = send;
            this.sendTimeMs = sendTimeMs;
        }

        public ClientResponse completed(AbstractResponse response, long timeMs) {
            return new ClientResponse(header, callback, destination, createdTimeMs, timeMs,
                    false, null, null, response);
        }

        public ClientResponse disconnected(long timeMs, AuthenticationException authenticationException) {
            return new ClientResponse(header, callback, destination, createdTimeMs, timeMs,
                    true, null, authenticationException, null);
        }

        @Override
        public String toString() {
            return "InFlightRequest(header=" + header +
                    ", destination=" + destination +
                    ", expectResponse=" + expectResponse +
                    ", createdTimeMs=" + createdTimeMs +
                    ", sendTimeMs=" + sendTimeMs +
                    ", isInternalRequest=" + isInternalRequest +
                    ", request=" + request +
                    ", callback=" + callback +
                    ", send=" + send + ")";
        }
    }

}
