Apache Pulsar 源码走读（二）二进制协议

pulsar 使用protocolBuf 作为二进制协议编写的工具

文件位置

本文主要说明其中几个主要的RPC 的作用。
并大致说一下这个几个RPC会被使用的位置。具体每个字段的含义会在后续的文章中说明。（因为目前代码还是在逐步熟悉过程中）

这里可能是由于历史的原因，
最开始定义的消息都不是严格一个Request对应一个Response的。
所以看代码有的时候会感觉非常困惑。

大致的消息类型（截止2.7版本）

message BaseCommand {
    enum Type {
        CONNECT     = 2;
        CONNECTED   = 3;

        // consumer 注册
        SUBSCRIBE   = 4;

        // producer 注册
        PRODUCER    = 5;

        // 向topic写入消息
        SEND        = 6;
        // 写入的response
        SEND_RECEIPT= 7;
        // 写入异常的response
        SEND_ERROR  = 8;

        // 发message 给consumer
        MESSAGE     = 9;
        // 确认某个消息是否成功消费
        ACK         = 10;
        // consumer 请求消息
        FLOW        = 11;

        UNSUBSCRIBE = 12;

        // 通用的一个成功的response
        SUCCESS     = 13;
        // 通用的一个异常的response
        ERROR       = 14;

        CLOSE_PRODUCER = 15;
        CLOSE_CONSUMER = 16;

        // Producer 的 response
        PRODUCER_SUCCESS = 17;

        // 网络层keepAlive 用的
        PING = 18;
        PONG = 19;

        // 
        REDELIVER_UNACKNOWLEDGED_MESSAGES = 20;

        PARTITIONED_METADATA           = 21;
        PARTITIONED_METADATA_RESPONSE  = 22;

        LOOKUP           = 23;
        LOOKUP_RESPONSE  = 24;

        CONSUMER_STATS        = 25;
        CONSUMER_STATS_RESPONSE    = 26;


        // 
        REACHED_END_OF_TOPIC = 27;

        SEEK = 28;

        GET_LAST_MESSAGE_ID = 29;
        GET_LAST_MESSAGE_ID_RESPONSE = 30;

        // 
        ACTIVE_CONSUMER_CHANGE = 31;


        GET_TOPICS_OF_NAMESPACE             = 32;
        GET_TOPICS_OF_NAMESPACE_RESPONSE     = 33;

        GET_SCHEMA = 34;
        GET_SCHEMA_RESPONSE = 35;

        AUTH_CHALLENGE = 36;
        AUTH_RESPONSE = 37;

        ACK_RESPONSE = 38;

        GET_OR_CREATE_SCHEMA = 39;
        GET_OR_CREATE_SCHEMA_RESPONSE = 40;

        // transaction related
        // 事务相关的比较容易理解，下面先忽略了 50 - 61 

    }

    // .....
}

CommandConnect

这里是客户端与server连接的channel一连上就会发送一个CONNECT 请求
这里会有一些鉴权和协议版本上报的信息。
沟通客户端版本之后，服务端就知道客户端支持哪些特性，会做一些兼容处理
相当于kafka 里面的ApiVersionRequest

// org.apache.pulsar.client.impl.ClientCnx

public void channelActive(ChannelHandlerContext ctx) throws Exception {
        super.channelActive(ctx);
        this.timeoutTask = this.eventLoopGroup.scheduleAtFixedRate(() -> checkRequestTimeout(), operationTimeoutMs,
                operationTimeoutMs, TimeUnit.MILLISECONDS);

        if (proxyToTargetBrokerAddress == null) {
            if (log.isDebugEnabled()) {
                log.debug("{} Connected to broker", ctx.channel());
            }
        } else {
            log.info("{} Connected through proxy to target broker at {}", ctx.channel(), proxyToTargetBrokerAddress);
        }
        // Send CONNECT command
        ctx.writeAndFlush(newConnectCommand())
                .addListener(future -> {
                    if (future.isSuccess()) {
                        if (log.isDebugEnabled()) {
                            log.debug("Complete: {}", future.isSuccess());
                        }
                        state = State.SentConnectFrame;
                    } else {
                        log.warn("Error during handshake", future.cause());
                        ctx.close();
                    }
                });
    }

CommandConnected

这里实际上是CommandConnect 的response ，但是换了名字
（很容易对不上号）

// org.apache.pulsar.broker.service.ServerCnx
protected void handleConnect(CommandConnect connect) {
        checkArgument(state == State.Start);

        if (log.isDebugEnabled()) {
            log.debug("Received CONNECT from {}, auth enabled: {}:"
                    + " has original principal = {}, original principal = {}",
                remoteAddress,
                service.isAuthenticationEnabled(),
                connect.hasOriginalPrincipal(),
                connect.getOriginalPrincipal());
        }

        String clientVersion = connect.getClientVersion();
        int clientProtocolVersion = connect.getProtocolVersion();
        features = new FeatureFlags();
        if (connect.hasFeatureFlags()) {
            features.copyFrom(connect.getFeatureFlags());
        }

        if (!service.isAuthenticationEnabled()) {
            completeConnect(clientProtocolVersion, clientVersion);
            return;
        }

      // ......
}

CommandSubscribe

这个RPC是consumer用来在服务端注册的。

具体调用的位置是，在ConsumerImpl构造函数的最后一行会请求服务端和客户端进行连接，如果拿到了一个Connection，会调用这个连接成功的回调connectionOpened 如果是consumer的话就会发送这个请求，来注册consumer相关的信息。

如果和上面的CommandConnect请求联动起来，这个请求是在CommandConnect 之后发送的。

// org.apache.pulsar.client.impl.ConsumerImpl
@Override
    public void connectionOpened(final ClientCnx cnx) {
        // ... 上面做了一大堆的准备参数先忽略

        // 构建一个subscription
        ByteBuf request = Commands.newSubscribe(topic,
                subscription,
                consumerId,
                requestId,
                getSubType(),
                priorityLevel,
                consumerName,
                isDurable,
                startMessageIdData,
                metadata,
                readCompacted,
                conf.isReplicateSubscriptionState(),
                InitialPosition.valueOf(subscriptionInitialPosition.getValue()),
                startMessageRollbackDuration,
                schemaInfo,
                createTopicIfDoesNotExist,
                conf.getKeySharedPolicy());

}

proto定义说明（见注释）

message CommandSubscribe {
    // 这里对应subscription的4种类型
    enum SubType {
        Exclusive = 0;
        Shared    = 1;
        Failover  = 2;
        Key_Shared = 3;
    }
   
    // topic 名字
    required string topic        = 1;
   // subscription 名字
    required string subscription = 2;
   // subscription 类型
    required SubType subType     = 3;
   // 这个是用来标记这个网络连接上的consumer标识
    required uint64 consumer_id  = 4;
   // 网络层的请求标识
    required uint64 request_id   = 5;
   // consumer 名字
    optional string consumer_name = 6;
   // consumer 的优先级，优先级高的consumer 容易先收到请求
    optional int32 priority_level = 7;

   // 这个subsciption是否是持久化的

    // Signal wether the subscription should be backed by a
    // durable cursor or not
    optional bool durable = 8 [default = true];

    // If specified, the subscription will position the cursor
    // markd-delete position  on the particular message id and
    // will send messages from that point
    optional MessageIdData start_message_id = 9;


    // 加了一些consumer 的自定义tag Map
    /// Add optional metadata key=value to this consumer
    repeated KeyValue metadata = 10;

    optional bool read_compacted = 11;

    optional Schema schema = 12;

   // 初始化位置从哪里开始，最新还是最旧
    enum InitialPosition {
        Latest   = 0;
        Earliest = 1;
    }
    // Signal whether the subscription will initialize on latest
    // or not -- earliest
    optional InitialPosition initialPosition = 13 [default = Latest];


    // geo-replication 相关，先忽略
    // Mark the subscription as "replicated". Pulsar will make sure
    // to periodically sync the state of replicated subscriptions
    // across different clusters (when using geo-replication).
    optional bool replicate_subscription_state = 14;

    // If true, the subscribe operation will cause a topic to be
    // created if it does not exist already (and if topic auto-creation
    // is allowed by broker.
    // If false, the subscribe operation will fail if the topic
    // does not exist.
    optional bool force_topic_creation = 15 [default = true];

    // 这个是按照时间重置消费进度的时候
    // If specified, the subscription will reset cursor's position back
    // to specified seconds and  will send messages from that point
    optional uint64 start_message_rollback_duration_sec = 16 [default = 0];

    // key_Share 模式使用的，暂时不看
    optional KeySharedMeta keySharedMeta = 17;
}

CommandProducer

这个RPC 和 consumer相对应的，是producer在服务端注册用的，调用位置也是相同的org.apache.pulsar.client.impl.ProducerImpl.connectionOpened 里面。

/// Create a new Producer on a topic, assigning the given producer_id,
/// all messages sent with this producer_id will be persisted on the topic
message CommandProducer {
    // topic 
    required string topic         = 1;
    required uint64 producer_id   = 2;

    // 网络层的请求编号
    required uint64 request_id    = 3;

    /// If a producer name is specified, the name will be used,
    /// otherwise the broker will generate a unique name
    optional string producer_name = 4;

    // 是否是加密的写入
    optional bool encrypted       = 5 [default = false];


    // 元数据 Map
    /// Add optional metadata key=value to this producer
    repeated KeyValue metadata    = 6;

    optional Schema schema = 7;


    // 这里应该叫producer_epoch
    // If producer reconnect to broker, the epoch of this producer will +1
    optional uint64 epoch = 8 [default = 0];

    // Indicate the name of the producer is generated or user provided
    // Use default true here is in order to be forward compatible with the client
    optional bool user_provided_producer_name = 9 [default = true];


    // 这里是写入的3种方式

    // Require that this producers will be the only producer allowed on the topic
    optional ProducerAccessMode producer_access_mode = 10 [default = Shared];

    // Topic epoch is used to fence off producers that reconnects after a new
    // exclusive producer has already taken over. This id is assigned by the
    // broker on the CommandProducerSuccess. The first time, the client will
    // leave it empty and then it will always carry the same epoch number on
    // the subsequent reconnections.
    optional uint64 topic_epoch = 11;
}

enum ProducerAccessMode {
    Shared           = 0; // By default multiple producers can publish on a topic
    Exclusive        = 1; // Require exclusive access for producer. Fail immediately if there's already a producer connected.
    WaitForExclusive = 2; // Producer creation is pending until it can acquire exclusive access
}

CommandProducerSuccess

这个是作为CommandProduce 请求的成功response

/// Response from CommandProducer
message CommandProducerSuccess {
    // 网络层id
    required uint64 request_id    = 1;
    // producer 名字
    required string producer_name = 2;

    // The last sequence id that was stored by this producer in the previous session
    // This will only be meaningful if deduplication has been enabled.
    optional int64  last_sequence_id = 3 [default = -1];
    optional bytes schema_version = 4;

    // The topic epoch assigned by the broker. This field will only be set if we
    // were requiring exclusive access when creating the producer.
    optional uint64 topic_epoch = 5;


    // 这个应该和上面ProducerAccessMode 相关，后面有机会来介绍这个吧
    // If producer is not "ready", the client will avoid to timeout the request
    // for creating the producer. Instead it will wait indefinitely until it gets 
    // a subsequent  `CommandProducerSuccess` with `producer_ready==true`.
    optional bool producer_ready = 6 [default = true];
}

CommandSend

这个是producer 用来发送消息到服务端用的RPC
可以通过org.apache.pulsar.client.impl.ProducerImpl.sendAsync 这个方法一路追到这个调用的位置，一般消息经过batch，加密，分块等逻辑处理之后，会将消息序列化成这个请求。

具体序列化的格式是下面这个
BaseCommand就是CommandSend

// org.apache.pulsar.common.protocol.Commands
private static ByteBufPair serializeCommandSendWithSize(BaseCommand cmd, ChecksumType checksumType,
            MessageMetadata msgMetadata, ByteBuf payload) {
        // / Wire format
        // [TOTAL_SIZE] [CMD_SIZE][CMD] [MAGIC_NUMBER][CHECKSUM] [METADATA_SIZE][METADATA] [PAYLOAD]

这里面的protocol格式实际只包含了上面的 [CMD] 部分

message CommandSend {
    required uint64 producer_id = 1;
    required uint64 sequence_id = 2;
    optional int32 num_messages = 3 [default = 1];
    optional uint64 txnid_least_bits = 4 [default = 0];
    optional uint64 txnid_most_bits = 5 [default = 0];

    /// Add highest sequence id to support batch message with external sequence id
    optional uint64 highest_sequence_id = 6 [default = 0];
    optional bool is_chunk     =7 [default = false];
}

CommandSendReceipt

这个是服务端成功处理完消息持久化之后成功的response

message CommandSendReceipt {
    required uint64 producer_id = 1;
    // 这个是用来保证顺序的
    required uint64 sequence_id = 2;
    optional MessageIdData message_id = 3;
    // 这个应该是用来去重的
    optional uint64 highest_sequence_id = 4 [default = 0];
}

// 这个是返回的写入成功的消息id，这个结构会在其他位置复用
message MessageIdData {
    required uint64 ledgerId = 1;
    required uint64 entryId  = 2;
    optional int32 partition = 3 [default = -1];
    // 这里是
    optional int32 batch_index = 4 [default = -1];
    repeated int64 ack_set = 5;
    optional int32 batch_size = 6;
}

CommandSendError

这个是CommandSend 异常的response

message CommandSendError {
    required uint64 producer_id = 1;
    required uint64 sequence_id = 2;
    required ServerError error  = 3;
    required string message     = 4;
}

CommandFlow

这个是用来告知服务端我这个consumer当前可以接受消息的数目
服务端会记录一个subscription里面每个consumer当前可以接受消息的数目
分配消息给哪个consumer的时候会按照这个数目来确定consumer当前能否接受消息。

目前了解到的位置是在connectionOpened的这个方法成功处理Subscription 注册之后会发送一个CommandFlow 请求，来让服务端推送消息。
不过可以想到，如果consumer队列是空闲的状态下都会发送这个消息。

message CommandFlow {
    required uint64 consumer_id       = 1;

    // Max number of messages to prefetch, in addition
    // of any number previously specified
    required uint32 messagePermits     = 2;
}

CommandMessage

这里实际上可能是服务端推消息给consumer，服务端会主动发送这个请求给consumer。（这个逻辑在服务端的 subscription 里的 dispatcher里面）

具体的调用位置在 org.apache.pulsar.broker.service.Consumer#sendMessages
这个方法在往上看一层的话都是org.apache.pulsar.broker.service.Dispatcher 这个类调用的。

这里和上面写入的格式一样这里的Command 实际上是一个RPC的header后面会加上消息的payload。

//  Wire format
// [TOTAL_SIZE] [CMD_SIZE][CMD] [MAGIC_NUMBER][CHECKSUM] [METADATA_SIZE][METADATA] [PAYLOAD]
//
// metadataAndPayload contains from magic-number to the payload included

message CommandMessage {
    required uint64 consumer_id       = 1;
    // 这里是消息的id
    required MessageIdData message_id = 2;
    // 这个消息重发了多少次
    optional uint32 redelivery_count  = 3 [default = 0];
    // 这个消息里面哪些已经被ack了
    repeated int64 ack_set = 4;
}

CommandAck

这个用来ack成功消费的消息，可以单独ack一条消息，
也可以累积确认（类似kafka）。
这里为了减少RPC的频率，在客户端做了一个batch ack 的优化。
服务端的对应处理一般会更新ManagedCursor里面保存的数据，将这个ack的结果持久化。

message CommandAck {
    
    // ack 类型，是累积确认还是单独确认
    enum AckType {
        Individual = 0;
        Cumulative = 1;
    }

    required uint64 consumer_id       = 1;
    required AckType ack_type         = 2;

    // 这里类型是repeated类型的可以把ack做batch

    // In case of individual acks, the client can pass a list of message ids
    repeated MessageIdData message_id = 3;

    // Acks can contain a flag to indicate the consumer
    // received an invalid message that got discarded
    // before being passed on to the application.
    enum ValidationError {
        UncompressedSizeCorruption = 0;
        DecompressionError = 1;
        ChecksumMismatch = 2;
        BatchDeSerializeError = 3;
        DecryptionError = 4;
    }

    // 一些异常情况可能也会ack这个消息，这里会记录一些信息
    optional ValidationError validation_error = 4;


    repeated KeyLongValue properties = 5;

    optional uint64 txnid_least_bits = 6 [default = 0];
    optional uint64 txnid_most_bits = 7 [default = 0];

    // 网络层请求id
    optional uint64 request_id = 8;
}

CommandRedeliverUnacknowledgedMessages

这个是consumer告诉服务端哪些消息需要重新被投递的RPC

message CommandRedeliverUnacknowledgedMessages {
    required uint64 consumer_id = 1;
    repeated MessageIdData message_ids = 2;
}

CommandSuccess & CommandError

这个其实是一个公用的response，如果请求没有特殊需要返回的字段的话，几乎可以被所有的请求使用。
这里不像Kafka 每个request和response 都带着一个ApiKey不会严格一一对应。

message CommandSuccess {
    required uint64 request_id = 1;
    optional Schema schema = 2;
}
message CommandError {
    required uint64 request_id  = 1;
    required ServerError error = 2;
    required string message    = 3;
}

CommandPing & CommandPong

这2个都是空的，主要作用是用来维护tcp连接应用层的keepAlive
org.apache.pulsar.common.protocol.PulsarHandler#handleKeepAliveTimeout

// Commands to probe the state of connection.
// When either client or broker doesn't receive commands for certain
// amount of time, they will send a Ping probe.
message CommandPing {
}
message CommandPong {
}