在公司业务中有场景需要实时订阅Topic，也就是当有新的Topic出现时，需要自动发现、监听、消费
诸多比较之后选择了用户群体最多的 sarama，但是遇到了一个问题，这个包并没有实现像Java的一样的正则匹配策略，不要说正则，连实时刷新机制都没有，所以需要我们自己来实现 Java 客户端 subscribe(Pattern)的通配符模式，废话不多说，直接上代码：
package main
import (
"context"
"errors"
"log"
"os"
"os/signal"
"reflect"
"sort"
"strings"
"sync"
"syscall"
"time"
"github.com/IBM/sarama"
)
// Sarama configuration options
var (
brokers = "127.0.0.1:9092"
version = "2.8.1" // Note: kafka broker version (not Sarama version)
group = "kfk_group_id"
assignor = "sticky"
)
func main() {
keepRunning := true
log.Println("Starting a new Sarama consumer")
sarama.Logger = log.New(os.Stdout, "[sarama] ", log.LstdFlags)
version, err := sarama.ParseKafkaVersion(version)
if err != nil {
log.Panicf("Error parsing Kafka version: %v", err)
}
/**
* Construct a new Sarama configuration.
* The Kafka cluster version has to be defined before the consumer/producer is initialized.
*/
config := sarama.NewConfig()
config.Version = version
config.Consumer.Offsets.Initial = sarama.OffsetOldest
switch assignor {
case "sticky":
config.Consumer.Group.Rebalance.GroupStrategies = []sarama.BalanceStrategy{sarama.NewBalanceStrategySticky()}
case "roundrobin":
config.Consumer.Group.Rebalance.GroupStrategies = []sarama.BalanceStrategy{sarama.NewBalanceStrategyRoundRobin()}
case "range":
config.Consumer.Group.Rebalance.GroupStrategies = []sarama.BalanceStrategy{sarama.NewBalanceStrategyRange()}
default:
log.Panicf("Unrecognized consumer group partition assignor: %s", assignor)
}
/**
* Set up a new Sarama consumer group
*/
consumer := Consumer{
ready: make(chan bool),
}
ctx, cancel := context.WithCancel(context.Background())
newClient, err := sarama.NewClient(strings.Split(brokers, ","), config)
consumerGroup, err := sarama.NewConsumerGroupFromClient(group, newClient)
if err != nil {
log.Fatalf("Error creating consumer group client: %v", err)
}
wg := &sync.WaitGroup{}
wg.Add(1)
// Get all the Topic
topics, err := newClient.Topics()
topics = filterTopics(topics)
go func() {
defer wg.Done()
for {
// `Consume` should be called inside an infinite loop, when a
// server-side rebalance happens, the consumer session will need to be
// recreated to get the new claims
if err := consumerGroup.Consume(ctx, topics, &consumer); err != nil {
if errors.Is(err, sarama.ErrClosedConsumerGroup) {
return
}
log.Panicf("Error from consumer: %v", err)
}
// check if context was cancelled, signaling that the consumer should stop
if ctx.Err() != nil {
log.Printf("Context err from consumer: %v", ctx.Err())
return
}
consumer.ready = make(chan bool)
}
}()
<-consumer.ready // Await till the consumer has been set up
log.Println("Sarama consumer up and running!...")
go refreshTopics(newClient, consumerGroup, topics)
sigusr1 := make(chan os.Signal, 1)
signal.Notify(sigusr1, syscall.SIGUSR1)
sigterm := make(chan os.Signal, 1)
signal.Notify(sigterm, syscall.SIGINT, syscall.SIGTERM)
for keepRunning {
select {
case <-ctx.Done():
log.Println("terminating: context cancelled")
keepRunning = false
case <-sigterm:
log.Println("terminating: via signal")
keepRunning = false
case <-sigusr1:
}
}
cancel()
wg.Wait()
if err = consumerGroup.Close(); err != nil {
log.Panicf("Error closing client: %v", err)
}
}
func EqualSlices(s1, s2 []string) bool {
if len(s1) != len(s2) {
return false
}
m1 := make(map[string]struct{})
m2 := make(map[string]struct{})
for _, v := range s1 {
m1[v] = struct{}{}
}
for _, v := range s2 {
m2[v] = struct{}{}
}
return reflect.DeepEqual(m1, m2)
}
func filterTopics(topics []string) []string {
filteredTopics := make([]string, 0)
for _, topic := range topics {
if topic != "__consumer_offsets" {
filteredTopics = append(filteredTopics, topic)
}
}
return filteredTopics
}
func refreshTopics(client sarama.Client, prevConsumerGroup sarama.ConsumerGroup, topicsOld []string) {
ticker := time.NewTicker(5 * time.Second)
for {
<-ticker.C
if err := client.RefreshMetadata(); err != nil {
log.Printf("Error refreshing metadata: %v", err)
continue
}
topics, err := client.Topics()
if err != nil {
log.Printf("Error refreshing topics: %v", err)
continue
}
filteredTopics := filterTopics(topics) // filter "__consumer_offsets"
sort.Strings(filteredTopics)
log.Printf("All Topics: %v", filteredTopics)
if !EqualSlices(filteredTopics, topicsOld) {
topicsOld = filteredTopics
if prevConsumerGroup != nil {
err := prevConsumerGroup.Close()
if err != nil {
log.Printf("Error closing prev consumer group: %v", err)
}
}
newConsumer := Consumer{
ready: make(chan bool),
}
newConsumerGroup, err := sarama.NewConsumerGroupFromClient(group, client)
if err != nil {
log.Printf("Error creating new consumer group: %v", err)
return
}
defer func(newConsumerGroup sarama.ConsumerGroup) {
err := newConsumerGroup.Close()
if err != nil {
log.Printf("Error closing new consumer group: %v", err)
}
}(newConsumerGroup)
go func() {
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
wg := &sync.WaitGroup{}
wg.Add(1)
// start Consume
go func() {
defer wg.Done()
if err := newConsumerGroup.Consume(ctx, filteredTopics, &newConsumer); err != nil {
log.Printf("Error from consumer: %v", err)
}
}()
wg.Wait()
}()
}
}
}
// Consumer represents a Sarama consumer group consumer
type Consumer struct {
ready chan bool
}
// Setup is run at the beginning of a new session, before ConsumeClaim
func (consumer *Consumer) Setup(sarama.ConsumerGroupSession) error {
// Mark the consumer as ready
close(consumer.ready)
return nil
}
// Cleanup is run at the end of a session, once all ConsumeClaim goroutines have exited
func (consumer *Consumer) Cleanup(sarama.ConsumerGroupSession) error {
return nil
}
// ConsumeClaim must start a consumer loop of ConsumerGroupClaim's Messages().
// Once the Messages() channel is closed, the Handler must finish its processing
// loop and exit.
func (consumer *Consumer) ConsumeClaim(session sarama.ConsumerGroupSession, claim sarama.ConsumerGroupClaim) error {
// NOTE:
// Do not move the code below to a goroutine.
// The `ConsumeClaim` itself is called within a goroutine, see:
// https://github.com/IBM/sarama/blob/main/consumer_group.go#L27-L29
for {
select {
case message, ok := <-claim.Messages():
if !ok {
log.Printf("message channel was closed")
return nil
}
log.Printf("Message claimed: value = %s, timestamp = %v, topic = %s", string(message.Value), message.Timestamp, message.Topic)
session.MarkMessage(message, "")
// Should return when `session.Context()` is done.
// If not, will raise `ErrRebalanceInProgress` or `read tcp :: i/o timeout` when kafka rebalance. see:
// https://github.com/IBM/sarama/issues/1192
case <-session.Context().Done():
return nil
}
}
}
代码很简单，相信大家都能看懂我是在做什么了，其实就是增加了一个 refreshTopics 来刷新Topic，当检测到新的Topic的时候关掉之前的消费者组、创建新的组、订阅新的主题
注意：此处有一个大坑！当新的Topic加入的时候，refreshTopics 监测到新的消息进行消费，这里如果不进行配置，则只会消费订阅之后的消息，你不要忘记啊，能触发订阅新的主题的条件是有了一条新的消息，那这条触发订阅的消息去哪了呢？首先肯定不会被原消费者组消费，因为他们还没订阅，其次，新启动的消费这组虽然订阅了新的Topic，但是因为你没有配置，它默认没有消费记录的新的Topic会从消息的最后的位置进行消费（有消费记录的Topic从未消费的位置开始消费），所以，根本就不会消费到那条消息！那怎么办呢？你只需要在启动的时候增加一个配置即可：
config.Consumer.Offsets.Initial = sarama.OffsetOldest问题解决，撒花···