librdkafka的简单使用

摘要

本文是Getting Started with Apache Kafka and C/C++的中文版， kafka的hello world程序。

本文完整代码见仓库，这里只列出producer/consumer的代码

---

kafka是什么

本节来源：Kafka - 维基百科，自由的百科全书、Kafka入门简介 - 知乎

首先我们得知道什么是Kafka。

Kafka是一个分布式流处理系统，流处理系统使它可以像消息队列一样publish或者subscribe消息，分布式提供了容错性，并发处理消息的机制。

kafka有以下一些基本概念：

• Producer - 消息生产者，就是向kafka broker发消息的客户端。
• Consumer - 消息消费者，是消息的使用方，负责消费Kafka服务器上的消息。
• Topic - 主题，由用户定义并配置在Kafka服务器，用于建立Producer和Consumer之间的订阅关系。生产者发送消息到指定的Topic下，消息者从这个Topic下消费消息。
• Partition - 消息分区，一个topic可以分为多个 partition，每个partition是一个有序的队列。partition中的每条消息都会被分配一个有序的id（offset）。
• Broker - 一台kafka服务器就是一个broker。一个集群由多个broker组成。一个broker可以容纳多个topic。
• Consumer Group - 消费者分组，用于归组同类消费者。每个consumer属于一个特定的consumer group，多个消费者可以共同消费一个Topic下的消息，每个消费者消费其中的部分消息，这些消费者就组成了一个分组，拥有同一个分组名称，通常也被称为消费者集群。
• Offset - 消息在partition中的偏移量。每一条消息在partition都有唯一的偏移量，消费者可以指定偏移量来指定要消费的消息。

---

安装环境

上一节，kafka的概念看着比较简单，发布-订阅/生产-消费的模型。

为了可以调用Kafka的C/C++ API, 需要先安装环境。

# almlinux8
# dnf search kafka
# dnf install librdkafka-devel# dnf search glib
# dnf install glib2-devel# ubuntu22
# 开发库
➜ apt install librdkafka-dev  libglib2.0-dev# 安装docker环境
➜ apt install docker.io docker-compose# 本地安装 Kafka
## ref: https://docs.confluent.io/confluent-cli/current/install.html#cp
➜ wget -qO - https://packages.confluent.io/confluent-cli/deb/archive.key | sudo apt-key add
➜ add-apt-repository "deb https://packages.confluent.io/confluent-cli/deb stable main"
➜ apt install confluent-cli## 启动kafka
## usage: https://docs.confluent.io/confluent-cli/current/command-reference/local/kafka/confluent_local_kafka_start.html
## error: https://stackoverflow.com/questions/63776518/error-2-matches-found-based-on-name-network-nameofservice-default-is-ambiguo
## error:https://stackoverflow.com/questions/77985757/kafka-in-docker-using-confluent-cli-doesnt-work➜ whereis confluent
confluent: /usr/bin/confluent➜ export CONFLUENT_HOME=/usr/bin/confluent# 我执行下面命令后,没有看到Plaintext Ports信息
➜ confluent local kafka start# 停止，然后重新启动，管用了
➜ confluent local kafka stop
➜ confluent local kafka startThe local commands are intended for a single-node development environment only, NOT for production usage. See more: https://docs.confluent.io/current/cli/index.htmlPulling from confluentinc/confluent-local
Digest: sha256:ad62269bf4766820c298f7581cf872a49f46a11dbaebcccb4fd2e71049288c5b
Status: Image is up to date for confluentinc/confluent-local:7.6.0
+-----------------+-------+
| Kafka REST Port | 8082  |
| Plaintext Ports | 43465 |
+-----------------+-------+
Started Confluent Local containers "8d72d911a4".
To continue your Confluent Local experience, run `confluent local kafka topic create <topic>` and `confluent local kafka topic produce <topic>`.# Create a new topic, purchases, which you will use to produce and consume events.
➜ confluent local kafka topic create purchases
Created topic "purchases".

---

librdkafka的简单使用

confluenceinc/librdkafka是Apache Kafka协议的 C 库实现 ，提供生产者、消费者和管理客户端。

下面运行的程序来自：Apache Kafka and C/C++ - Getting Started Tutorial

代码中kafka的API可以查询：librdkafka: librdkafka documentation

代码中使用了glib库，日常开发我不会使用这个库，因为感觉比较冷，它的API可查询：GLib – 2.0: Automatic Cleanup

---

生产者

总体逻辑：

• 从配置文件中加载配置
• 创建生产者
• 生产者发送消息

#include <glib.h>
#include <librdkafka/rdkafka.h>#include "common.c"#define ARR_SIZE(arr) ( sizeof((arr)) / sizeof((arr[0])) )/* Optional per-message delivery callback (triggered by poll() or flush())* when a message has been successfully delivered or permanently* failed delivery (after retries).*/
static void dr_msg_cb (rd_kafka_t *kafka_handle,const rd_kafka_message_t *rkmessage,void *opaque) {if (rkmessage->err) {g_error("Message delivery failed: %s", rd_kafka_err2str(rkmessage->err));}
}int main (int argc, char **argv) {rd_kafka_t *producer;rd_kafka_conf_t *conf;char errstr[512];// Parse the command line.if (argc != 2) {g_error("Usage: %s <config.ini>", argv[0]);return 1;}// Parse the configuration.// See https://github.com/edenhill/librdkafka/blob/master/CONFIGURATION.mdconst char *config_file = argv[1];g_autoptr(GError) error = NULL;g_autoptr(GKeyFile) key_file = g_key_file_new();if (!g_key_file_load_from_file (key_file, config_file, G_KEY_FILE_NONE, &error)) {g_error ("Error loading config file: %s", error->message);return 1;}// Load the relevant configuration sections.conf = rd_kafka_conf_new();load_config_group(conf, key_file, "default");// Install a delivery-error callback.rd_kafka_conf_set_dr_msg_cb(conf, dr_msg_cb);// Create the Producer instance.producer = rd_kafka_new(RD_KAFKA_PRODUCER, conf, errstr, sizeof(errstr));if (!producer) {g_error("Failed to create new producer: %s", errstr);return 1;}// Configuration object is now owned, and freed, by the rd_kafka_t instance.conf = NULL;// Produce data by selecting random values from these lists.int message_count = 10;const char *topic = "purchases";const char *user_ids[6] = {"eabara", "jsmith", "sgarcia", "jbernard", "htanaka", "awalther"};const char *products[5] = {"book", "alarm clock", "t-shirts", "gift card", "batteries"};for (int i = 0; i < message_count; i++) {const char *key =  user_ids[random() % ARR_SIZE(user_ids)];const char *value =  products[random() % ARR_SIZE(products)];size_t key_len = strlen(key);size_t value_len = strlen(value);rd_kafka_resp_err_t err;err = rd_kafka_producev(producer,RD_KAFKA_V_TOPIC(topic),RD_KAFKA_V_MSGFLAGS(RD_KAFKA_MSG_F_COPY),RD_KAFKA_V_KEY((void*)key, key_len),RD_KAFKA_V_VALUE((void*)value, value_len),RD_KAFKA_V_OPAQUE(NULL),RD_KAFKA_V_END);if (err) {g_error("Failed to produce to topic %s: %s", topic, rd_kafka_err2str(err));return 1;} else {g_message("Produced event to topic %s: key = %12s value = %12s", topic, key, value);}rd_kafka_poll(producer, 0);}// Block until the messages are all sent.g_message("Flushing final messages..");rd_kafka_flush(producer, 10 * 1000);if (rd_kafka_outq_len(producer) > 0) {g_error("%d message(s) were not delivered", rd_kafka_outq_len(producer));}g_message("%d events were produced to topic %s.", message_count, topic);rd_kafka_destroy(producer);return 0;
}

---

消费者

总体逻辑：

• 从配置文件中加载配置
• 创建消费者
• 订阅topic
• 轮询消费者的消息

#include <glib.h>
#include <librdkafka/rdkafka.h>#include "common.c"static volatile sig_atomic_t run = 1;/*** @brief Signal termination of program*/
static void stop(int sig) { run = 0; }int main(int argc, char **argv) {rd_kafka_t *consumer;rd_kafka_conf_t *conf;rd_kafka_resp_err_t err;char errstr[512];// Parse the command line.if (argc != 2) {g_error("Usage: %s <config.ini>", argv[0]);return 1;}// Parse the configuration.// See https://github.com/edenhill/librdkafka/blob/master/CONFIGURATION.mdconst char *config_file = argv[1];g_autoptr(GError) error = NULL;g_autoptr(GKeyFile) key_file = g_key_file_new();if (!g_key_file_load_from_file(key_file, config_file, G_KEY_FILE_NONE,&error)) {g_error("Error loading config file: %s", error->message);return 1;}// Load the relevant configuration sections.conf = rd_kafka_conf_new();load_config_group(conf, key_file, "default");load_config_group(conf, key_file, "consumer");// Create the Consumer instance.consumer = rd_kafka_new(RD_KAFKA_CONSUMER, conf, errstr, sizeof(errstr));if (!consumer) {g_error("Failed to create new consumer: %s", errstr);return 1;}rd_kafka_poll_set_consumer(consumer);// Configuration object is now owned, and freed, by the rd_kafka_t instance.conf = NULL;// Convert the list of topics to a format suitable for librdkafka.const char *topic = "purchases";rd_kafka_topic_partition_list_t *subscription =rd_kafka_topic_partition_list_new(1);rd_kafka_topic_partition_list_add(subscription, topic, RD_KAFKA_PARTITION_UA);// Subscribe to the list of topics.err = rd_kafka_subscribe(consumer, subscription);if (err) {g_error("Failed to subscribe to %d topics: %s", subscription->cnt,rd_kafka_err2str(err));rd_kafka_topic_partition_list_destroy(subscription);rd_kafka_destroy(consumer);return 1;}rd_kafka_topic_partition_list_destroy(subscription);// Install a signal handler for clean shutdown.signal(SIGINT, stop);// Start polling for messages.while (run) {rd_kafka_message_t *consumer_message;consumer_message = rd_kafka_consumer_poll(consumer, 500);if (!consumer_message) {g_message("Waiting...");continue;}if (consumer_message->err) {if (consumer_message->err == RD_KAFKA_RESP_ERR__PARTITION_EOF) {/* We can ignore this error - it just means we've read* everything and are waiting for more data.*/} else {g_message("Consumer error: %s",rd_kafka_message_errstr(consumer_message));return 1;}} else {g_message("Consumed event from topic %s: key = %.*s value = %s",rd_kafka_topic_name(consumer_message->rkt),(int)consumer_message->key_len, (char *)consumer_message->key,(char *)consumer_message->payload);}// Free the message when we're done.rd_kafka_message_destroy(consumer_message);}// Close the consumer: commit final offsets and leave the group.g_message("Closing consumer");rd_kafka_consumer_close(consumer);// Destroy the consumer.rd_kafka_destroy(consumer);return 0;
}