通过 Pulsar 的 WebSocket API,用户可以简单便捷地与 Pulsar 进行交互,WebSocket API 不依赖于官方客户端库。 WebSocket 支持使用 JavaGoPythonC++ 客户端中提供的所有功能来发布和订阅消息。

You can use Pulsar’s WebSocket API with any WebSocket client library. See examples for Python and Node.js below.

运行 WebSocket 服务

推荐使用单机模式的 Pulsar 进行开发,在本地开发环境中启用 WebSocket 服务。

在非单机模式下,有两种方法可以部署 WebSocket 服务:

嵌入 Pulsar Broker

在这种模式下,WebSocket 服务会使用已经在 broker 中运行的 HTTP 服务。 要启用此模式,需在安装目录下的 conf/broker.conf 文件中设置 webSocketServiceEnabled 参数。

  1. webSocketServiceEnabled=true

作为一个独立的组件

在这种模式下,WebSocket 会作为单独的服务在 Pulsar broker 上运行。 运行此模式,需在 conf/websocket.conf 文件中进行配置。 至少需要设置以下参数:

Here’s an example:

  1. configurationStoreServers=zk1:2181,zk2:2181,zk3:2181
  2. webServicePort=8080
  3. clusterName=my-cluster

启动 Broker

配置完成后,你可以使用 pulsar-daemon 命令来启动服务:

  1. $ bin/pulsar-daemon start websocket

API 手册:

Pulsar 的 WebSocket API 提供三个端点,用于生产消息消费消息阅读消息

所有通过 WebSocket API 的数据都使用 JSON 进行交互。

Producer 端

Producer 端需要在 URL 中指定租户、命名空间和 topic,例如:

  1. ws://broker-service-url:8080/ws/v2/producer/persistent/:tenant/:namespace/:topic
查询参数
Key类型是否必需说明
sendTimeoutMillislong发送超时(默认值:30秒)
batchingEnabledboolean启用批量缓存消息(默认值:false)
batchingMaxMessagesint批量消息数最大值(默认值:1000)
maxPendingMessagesint设置消息内部队列的最大值(默认值:1000)
batchingMaxPublishDelaylong批量处理消息的时间(默认:10毫秒)
messageRoutingModestring分区 producer 的消息路由模式SingleSectionRoundRobinSection
compressionTypestring压缩类型LZ4ZLIB
producerNamestringSpecify the name for the producer. Pulsar will enforce only one producer with same name can be publishing on a topic
initialSequenceIdlong设置 producer 发布消息序列 id 的标准。
hashingSchemestring在分区 topic 上发布消息时使用的哈希函数JavaStringHashMurmur3_32Hash

发布消息

  1. {
  2. "payload": "SGVsbG8gV29ybGQ=",
  3. "properties": {"key1": "value1", "key2": "value2"},
  4. "context": "1"
  5. }
Key类型是否必需说明
payloadstringBase-64 编码的负载
properties键值对应用程序定义的属性
contextstring应用程序定义的请求标识符
keystring分区 topic 中使用的分区
replicationClusters数组根据名称允许添加到集群列表的副本
响应成功示例
  1. {
  2. "result": "ok",
  3. "messageId": "CAAQAw==",
  4. "context": "1"
  5. }
响应失败示例
  1. {
  2. "result": "send-error:3",
  3. "errorMsg": "Failed to de-serialize from JSON",
  4. "context": "1"
  5. }
Key类型是否必需说明
resultstring发送成功则为 ok,否则抛出异常
messageIdstring已发布消息的 Message ID
contextstring应用程序定义的请求标识符

Consumer 端

Concumer 端要求在 URL 中指定租户、命名空间、topic 和订阅:

  1. ws://broker-service-url:8080/ws/v2/consumer/persistent/:tenant/:namespace/:topic/:subscription
查询参数
Key类型是否必需说明
ackTimeoutMillislong设置未完成消息确认的超时时间(默认值:0)
subscriptionTypestring订阅类型独占灾备共享
receiverQueueSizeintConsumer 接收队列的大小(默认:1000)
consumerNamestringConsumer 的名称
priorityLevelint指定 consumer 的优先级
maxRedeliverCountint为 consumer 指定 maxRedeliverCount(默认值:0)。 启用 Dead Letter Topic
deadLetterTopicstring为 consumer 指定 deadLetterTopic(默认值:{topic}-{subscription}-DLQ)。 启用 Dead Letter Topic
pullModebooleanEnable pull mode (default: false). See “Flow Control” below.

注意:以上参数(pullMode 除外)适用于 WebSocket 服务的内部 consumer。 因此,即使客户端没有在 WebSocket 上消费,只要消息进入接收队列,就会受到传递设置的约束。

接收消息

Server will push messages on the WebSocket session:

  1. {
  2. "messageId": "CAAQAw==",
  3. "payload": "SGVsbG8gV29ybGQ=",
  4. "properties": {"key1": "value1", "key2": "value2"},
  5. "publishTime": "2016-08-30 16:45:57.785"
  6. }
Key类型是否必需说明
messageIdstring消息 ID
payloadstringBase-64 编码的负载
publishTimestring发布时间戳
properties键值对应用程序定义的属性
keystringProducer 设置的原始路由密钥

ACK 确认消息

Consumer needs to acknowledge the successful processing of the message to have the Pulsar broker delete it.

  1. {
  2. "messageId": "CAAQAw=="
  3. }
Key类型是否必需说明
messageIdstring处理消息的消息ID

Flow control

推送模式

默认情况下(pullMode=false),consumer 端使用 receiverQueueSize 参数设置内部接收队列的大小,并限制传递到 WebSocket 客户端的未确认消息数。 在这种模式下,如果不发送消息确认,发送到 WebSocket 客户端的消息达到 receiverQueueSize时,Pulsar WebSocket 将停止发送消息。

拉取模式

如果设置 pullModetrue,则 WebSocket 客户端需要使用 permit 命令允许 Pulsar WebSocket 服务发送更多消息。

  1. {
  2. "type": "permit",
  3. "permitMessages": 100
  4. }
Key类型是否必需说明
typestringType of command. Must be permit
permitMessagesint允许的消息数量

注意:在这种模式下,可以在不同的连接中确认消息。

Reader 端

The reader endpoint requires you to specify a tenant, namespace, and topic in the URL:

  1. ws://broker-service-url:8080/ws/v2/reader/persistent/:tenant/:namespace/:topic
查询参数
Key类型是否必需说明
readerNamestringReader name
receiverQueueSizeintConsumer 接收队列的大小(默认:1000)
messageIdint or enumMessage ID to start from, earliest or latest (default: latest)
接收消息

Server will push messages on the WebSocket session:

  1. {
  2. "messageId": "CAAQAw==",
  3. "payload": "SGVsbG8gV29ybGQ=",
  4. "properties": {"key1": "value1", "key2": "value2"},
  5. "publishTime": "2016-08-30 16:45:57.785"
  6. }
Key类型是否必需说明
messageIdstring消息 ID
payloadstringBase-64 编码的负载
publishTimestring发布时间戳
properties键值对应用程序定义的属性
keystringProducer 设置的原始路由密钥

ACK 确认消息

In WebSocket, Reader needs to acknowledge the successful processing of the message to have the Pulsar WebSocket service update the number of pending messages. If you don’t send acknowledgements, Pulsar WebSocket service will stop sending messages after reaching the pendingMessages limit.

  1. {
  2. "messageId": "CAAQAw=="
  3. }
Key类型是否必需说明
messageIdstring处理消息的消息ID

错误代码

In case of error the server will close the WebSocket session using the following error codes:

Error CodeError Message
1Failed to create producer
2Failed to subscribe
3Failed to deserialize from JSON
4Failed to serialize to JSON
5Failed to authenticate client
6Client is not authorized
7Invalid payload encoding
8Unknown error

应用程序负责在后台重新建立 WebSocket 连接。

客户端示例

Below you’ll find code examples for the Pulsar WebSocket API in Python and Node.js.

Python

This example uses the websocket-client package. You can install it using pip:

  1. $ pip install websocket-client

You can also download it from PyPI.

Python producer

Here’s an example Python producer that sends a simple message to a Pulsar topic:

  1. import websocket, base64, json
  2. TOPIC = 'ws://localhost:8080/ws/v2/producer/persistent/public/default/my-topic'
  3. ws = websocket.create_connection(TOPIC)
  4. # Send one message as JSON
  5. ws.send(json.dumps({
  6. 'payload' : base64.b64encode('Hello World'),
  7. 'properties': {
  8. 'key1' : 'value1',
  9. 'key2' : 'value2'
  10. },
  11. 'context' : 5
  12. }))
  13. response = json.loads(ws.recv())
  14. if response['result'] == 'ok':
  15. print 'Message published successfully'
  16. else:
  17. print 'Failed to publish message:', response
  18. ws.close()

Python consumer

Here’s an example Python consumer that listens on a Pulsar topic and prints the message ID whenever a message arrives:

  1. import websocket, base64, json
  2. TOPIC = 'ws://localhost:8080/ws/v2/consumer/persistent/public/default/my-topic/my-sub'
  3. ws = websocket.create_connection(TOPIC)
  4. while True:
  5. msg = json.loads(ws.recv())
  6. if not msg: break
  7. print "Received: {} - payload: {}".format(msg, base64.b64decode(msg['payload']))
  8. # Acknowledge successful processing
  9. ws.send(json.dumps({'messageId' : msg['messageId']}))
  10. ws.close()

Python reader

Here’s an example Python reader that listens on a Pulsar topic and prints the message ID whenever a message arrives:

  1. import websocket, base64, json
  2. TOPIC = 'ws://localhost:8080/ws/v2/reader/persistent/public/default/my-topic'
  3. ws = websocket.create_connection(TOPIC)
  4. while True:
  5. msg = json.loads(ws.recv())
  6. if not msg: break
  7. print "Received: {} - payload: {}".format(msg, base64.b64decode(msg['payload']))
  8. # Acknowledge successful processing
  9. ws.send(json.dumps({'messageId' : msg['messageId']}))
  10. ws.close()

Node.js

This example uses the ws package. You can install it using npm:

  1. $ npm install ws

Node.js producer

Here’s an example Node.js producer that sends a simple message to a Pulsar topic:

  1. var WebSocket = require('ws'),
  2. topic = "ws://localhost:8080/ws/v2/producer/persistent/public/default/my-topic",
  3. ws = new WebSocket(topic);
  4. var message = {
  5. "payload" : new Buffer("Hello World").toString('base64'),
  6. "properties": {
  7. "key1" : "value1",
  8. "key2" : "value2"
  9. },
  10. "context" : "1"
  11. };
  12. ws.on('open', function() {
  13. // Send one message
  14. ws.send(JSON.stringify(message));
  15. });
  16. ws.on('message', function(message) {
  17. console.log('received ack: %s', message);
  18. });
  19. Text
  20. XPath: /pre[20]/code

Node.js consumer

Here’s an example Node.js consumer that listens on the same topic used by the producer above:

  1. var WebSocket = require('ws'),
  2. topic = "ws://localhost:8080/ws/v2/consumer/persistent/public/default/my-topic/my-sub",
  3. ws = new WebSocket(topic);
  4. ws.on('message', function(message) {
  5. var receiveMsg = JSON.parse(message);
  6. console.log('Received: %s - payload: %s', message, new Buffer(receiveMsg.payload, 'base64').toString());
  7. var ackMsg = {"messageId" : receiveMsg.messageId};
  8. ws.send(JSON.stringify(ackMsg));
  9. });

NodeJS reader

  1. var WebSocket = require('ws'),
  2. topic = "ws://localhost:8080/ws/v2/reader/persistent/public/default/my-topic",
  3. ws = new WebSocket(topic);
  4. ws.on('message', function(message) {
  5. var receiveMsg = JSON.parse(message);
  6. console.log('Received: %s - payload: %s', message, new Buffer(receiveMsg.payload, 'base64').toString());
  7. var ackMsg = {"messageId" : receiveMsg.messageId};
  8. ws.send(JSON.stringify(ackMsg));
  9. });