文章目录
- 1 安装librdkafka
- 2 开启kafka相关服务
- 2.1 启动zookeeper
- 2.2 启动Kafka
- 2.3 创建topic
- 3 c语言操作kafka的范例
- 3.1 消费者
- 3.2 生产者
- 3.3 生产者和消费者的交互
- 总结
1 安装librdkafka
git clone https://github.com/edenhill/librdkafka.git cd librdkafka git checkout v1.7.0 ./configure make sudo make install sudo ldconfig
在librdkafka的examples目录下会有示例程序。比如consumer的启动需要下列参数
./consumer
.. 指定broker、group id、topic（可以订阅多个）。示例：
./consumer localhost:9092 0 test
缩略语介绍：
2 开启kafka相关服务
2.1 启动zookeeper
启动zookeeper可以通过下面的脚本来启动zookeeper服务，当然，也可以自己独立搭建zookeeper的集群来实现。这里我们直接使用kafka自带的zookeeper。
cd bin/ # 前台运行： sh zookeeper-server-start.sh ../config/zookeeper.properties # 后台运行： sh zookeeper-server-start.sh -daemon ../config/zookeeper.properties
可以通过命令lsof -i:2181 查看zookeeper是否启动成功。
$ lsof -i:2181 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME java 74930 fly 96u IPv6 734467 0t0 TCP *:2181 (LISTEN)
2.2 启动Kafka
启动kafka（kafka安装路径的bin目录下执行），默认启动端口9092。
sh kafka-server-start.sh -daemon ../config/server.properties
2.3 创建topic
sh kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic test
参数说明：
–create 是创建主题的的动作指令。
–zookeeper 指定kafka所连接的zookeeper服务地址。
–replicator-factor 指定了副本因子（即副本数量）； 表示该topic需要在不同的broker中保存几份，这里设置成1，表示在两个broker中保存两份Partitions分区数。
–partitions 指定分区个数；多通道，类似车道。
–topic 指定所要创建主题的名称，比如test。
3 c语言操作kafka的范例
3.1 消费者
在librdkafka\examples下有consumer.c文件，该文件是一个c语言操作kafka的代码范例，内容如下。
/** * Simple high-level balanced Apache Kafka consumer * using the Kafka driver from librdkafka * (https://github.com/edenhill/librdkafka) */ #include
#include #include #include /* Typical include path would be , but this program * is builtin from within the librdkafka source tree and thus differs. */ //#include #include "rdkafka.h" static volatile sig_atomic_t run = 1; /** * @brief Signal termination of program */ static void stop (int sig) { run = 0; } /** * @returns 1 if all bytes are printable, else 0. */ static int is_printable (const char *buf, size_t size) { size_t i; for (i = 0 ; i < size ; i++) if (!isprint((int)buf[i])) return 0; return 1; } int main (int argc, char **argv) { rd_kafka_t *rk; /* Consumer instance handle */ rd_kafka_conf_t *conf; /* Temporary configuration object */ rd_kafka_resp_err_t err; /* librdkafka API error code */ char errstr[512]; /* librdkafka API error reporting buffer */ const char *brokers; /* Argument: broker list */ const char *groupid; /* Argument: Consumer group id */ char **topics; /* Argument: list of topics to subscribe to */ int topic_cnt; /* Number of topics to subscribe to */ rd_kafka_topic_partition_list_t *subscription; /* Subscribed topics */ int i; /* * Argument validation */ if (argc < 4) { fprintf(stderr, "%% Usage: " "%s ..\n", argv[0]); return 1; } brokers = argv[1]; groupid = argv[2]; topics = &argv[3]; topic_cnt = argc - 3; /* * Create Kafka client configuration place-holder */ conf = rd_kafka_conf_new(); // 创建配置文件 /* Set bootstrap broker(s) as a comma-separated list of * host or host:port (default port 9092). * librdkafka will use the bootstrap brokers to acquire the full * set of brokers from the cluster. */ if (rd_kafka_conf_set(conf, "bootstrap.servers", brokers, errstr, sizeof(errstr)) != RD_KAFKA_CONF_OK) { fprintf(stderr, "%s\n", errstr); rd_kafka_conf_destroy(conf); return 1; } /* Set the consumer group id. * All consumers sharing the same group id will join the same * group, and the subscribed topic' partitions will be assigned * according to the partition.assignment.strategy * (consumer config property) to the consumers in the group. */ if (rd_kafka_conf_set(conf, "group.id", groupid, errstr, sizeof(errstr)) != RD_KAFKA_CONF_OK) { fprintf(stderr, "%s\n", errstr); rd_kafka_conf_destroy(conf); return 1; } /* If there is no previously committed offset for a partition * the auto.offset.reset strategy will be used to decide where * in the partition to start fetching messages. * By setting this to earliest the consumer will read all messages * in the partition if there was no previously committed offset. */ if (rd_kafka_conf_set(conf, "auto.offset.reset", "earliest", errstr, sizeof(errstr)) != RD_KAFKA_CONF_OK) { fprintf(stderr, "%s\n", errstr); rd_kafka_conf_destroy(conf); return 1; } /* * Create consumer instance. * * NOTE: rd_kafka_new() takes ownership of the conf object * and the application must not reference it again after * this call. */ // 创建一个kafka消费者 rk = rd_kafka_new(RD_KAFKA_CONSUMER, conf, errstr, sizeof(errstr)); if (!rk) { fprintf(stderr, "%% Failed to create new consumer: %s\n", errstr); return 1; } conf = NULL; /* Configuration object is now owned, and freed, * by the rd_kafka_t instance. */ /* Redirect all messages from per-partition queues to * the main queue so that messages can be consumed with one * call from all assigned partitions. * * The alternative is to poll the main queue (for events) * and each partition queue separately, which requires setting * up a rebalance callback and keeping track of the assignment: * but that is more complex and typically not recommended. */ rd_kafka_poll_set_consumer(rk);// poll机制，设置消费者实例到poll中 /* Convert the list of topics to a format suitable for librdkafka */ // 创建主题分区列表 subscription = rd_kafka_topic_partition_list_new(topic_cnt); for (i = 0 ; i < topic_cnt ; i++) rd_kafka_topic_partition_list_add(subscription, topics[i], /* the partition is ignored * by subscribe() */ RD_KAFKA_PARTITION_UA); /* Subscribe to the list of topics */ err = rd_kafka_subscribe(rk, subscription); if (err) { fprintf(stderr, "%% Failed to subscribe to %d topics: %s\n", subscription->cnt, rd_kafka_err2str(err)); rd_kafka_topic_partition_list_destroy(subscription); rd_kafka_destroy(rk); return 1; } fprintf(stderr, "%% Subscribed to %d topic(s), " "waiting for rebalance and messages...\n", subscription->cnt); rd_kafka_topic_partition_list_destroy(subscription); /* Signal handler for clean shutdown */ signal(SIGINT, stop); /* Subscribing to topics will trigger a group rebalance * which may take some time to finish, but there is no need * for the application to handle this idle period in a special way * since a rebalance may happen at any time. * Start polling for messages. */ while (run) { rd_kafka_message_t *rkm; rkm = rd_kafka_consumer_poll(rk, 100); if (!rkm) continue; /* Timeout: no message within 100ms, * try again. This short timeout allows * checking for `run` at frequent intervals. */ /* consumer_poll() will return either a proper message * or a consumer error (rkm->err is set). */ if (rkm->err) { /* Consumer errors are generally to be considered * informational as the consumer will automatically * try to recover from all types of errors. */ fprintf(stderr, "%% Consumer error: %s\n", rd_kafka_message_errstr(rkm)); rd_kafka_message_destroy(rkm); continue; } /* Proper message. */ printf("Message on %s [%"PRId32"] at offset %"PRId64":\n", rd_kafka_topic_name(rkm->rkt), rkm->partition, rkm->offset); /* Print the message key. */ if (rkm->key && is_printable(rkm->key, rkm->key_len)) printf(" Key: %.*s\n", (int)rkm->key_len, (const char *)rkm->key); else if (rkm->key) printf(" Key: (%d bytes)\n", (int)rkm->key_len); /* Print the message value/payload. */ if (rkm->payload && is_printable(rkm->payload, rkm->len)) printf(" Value: %.*s\n", (int)rkm->len, (const char *)rkm->payload); else if (rkm->payload) printf(" Value: (%d bytes)\n", (int)rkm->len); rd_kafka_message_destroy(rkm); } /* Close the consumer: commit final offsets and leave the group. */ fprintf(stderr, "%% Closing consumer\n"); rd_kafka_consumer_close(rk); /* Destroy the consumer */ rd_kafka_destroy(rk); return 0; } 3.2 生产者
在librdkafka\examples下有producer.c文件，该文件是一个c语言操作kafka的代码范例，内容如下。
/** * Simple Apache Kafka producer * using the Kafka driver from librdkafka * (https://github.com/edenhill/librdkafka) */ #include
#include #include /* Typical include path would be , but this program * is builtin from within the librdkafka source tree and thus differs. */ #include "rdkafka.h" static volatile sig_atomic_t run = 1; /** * @brief Signal termination of program */ static void stop (int sig) { run = 0; fclose(stdin); /* abort fgets() */ } /** * @brief Message delivery report callback. * * This callback is called exactly once per message, indicating if * the message was succesfully delivered * (rkmessage->err == RD_KAFKA_RESP_ERR_NO_ERROR) or permanently * failed delivery (rkmessage->err != RD_KAFKA_RESP_ERR_NO_ERROR). * * The callback is triggered from rd_kafka_poll() and executes on * the application's thread. */ static void dr_msg_cb (rd_kafka_t *rk, const rd_kafka_message_t *rkmessage, void *opaque) { if (rkmessage->err) fprintf(stderr, "%% Message delivery failed: %s\n", rd_kafka_err2str(rkmessage->err)); else fprintf(stderr, "%% Message delivered (%zd bytes, " "partition %"PRId32")\n", rkmessage->len, rkmessage->partition); /* The rkmessage is destroyed automatically by librdkafka */ } int main (int argc, char **argv) { rd_kafka_t *rk; /* Producer instance handle */ rd_kafka_conf_t *conf; /* Temporary configuration object */ char errstr[512]; /* librdkafka API error reporting buffer */ char buf[512]; /* Message value temporary buffer */ const char *brokers; /* Argument: broker list */ const char *topic; /* Argument: topic to produce to */ /* * Argument validation */ if (argc != 3) { fprintf(stderr, "%% Usage: %s \n", argv[0]); return 1; } brokers = argv[1]; topic = argv[2]; /* * Create Kafka client configuration place-holder */ conf = rd_kafka_conf_new(); /* Set bootstrap broker(s) as a comma-separated list of * host or host:port (default port 9092). * librdkafka will use the bootstrap brokers to acquire the full * set of brokers from the cluster. */ if (rd_kafka_conf_set(conf, "bootstrap.servers", brokers, errstr, sizeof(errstr)) != RD_KAFKA_CONF_OK) { fprintf(stderr, "%s\n", errstr); return 1; } /* Set the delivery report callback. * This callback will be called once per message to inform * the application if delivery succeeded or failed. * See dr_msg_cb() above. * The callback is only triggered from rd_kafka_poll() and * rd_kafka_flush(). */ rd_kafka_conf_set_dr_msg_cb(conf, dr_msg_cb); /* * Create producer instance. * * NOTE: rd_kafka_new() takes ownership of the conf object * and the application must not reference it again after * this call. */ rk = rd_kafka_new(RD_KAFKA_PRODUCER, conf, errstr, sizeof(errstr)); if (!rk) { fprintf(stderr, "%% Failed to create new producer: %s\n", errstr); return 1; } /* Signal handler for clean shutdown */ signal(SIGINT, stop); fprintf(stderr, "%% Type some text and hit enter to produce message\n" "%% Or just hit enter to only serve delivery reports\n" "%% Press Ctrl-C or Ctrl-D to exit\n"); while (run && fgets(buf, sizeof(buf), stdin)) { size_t len = strlen(buf); rd_kafka_resp_err_t err; if (buf[len-1] == '\n') /* Remove newline */ buf[--len] = '\0'; if (len == 0) { /* Empty line: only serve delivery reports */ rd_kafka_poll(rk, 0/*non-blocking */); continue; } /* * Send/Produce message. * This is an asynchronous call, on success it will only * enqueue the message on the internal producer queue. * The actual delivery attempts to the broker are handled * by background threads. * The previously registered delivery report callback * (dr_msg_cb) is used to signal back to the application * when the message has been delivered (or failed). */ retry: err = rd_kafka_producev( /* Producer handle */ rk, /* Topic name */ RD_KAFKA_V_TOPIC(topic), /* Make a copy of the payload. */ RD_KAFKA_V_MSGFLAGS(RD_KAFKA_MSG_F_COPY), /* Message value and length */ RD_KAFKA_V_VALUE(buf, len), /* Per-Message opaque, provided in * delivery report callback as * msg_opaque. */ RD_KAFKA_V_OPAQUE(NULL), /* End sentinel */ RD_KAFKA_V_END); if (err) { /* * Failed to *enqueue* message for producing. */ fprintf(stderr, "%% Failed to produce to topic %s: %s\n", topic, rd_kafka_err2str(err)); if (err == RD_KAFKA_RESP_ERR__QUEUE_FULL) { /* If the internal queue is full, wait for * messages to be delivered and then retry. * The internal queue represents both * messages to be sent and messages that have * been sent or failed, awaiting their * delivery report callback to be called. * * The internal queue is limited by the * configuration property * queue.buffering.max.messages */ rd_kafka_poll(rk, 1000/*block for max 1000ms*/); goto retry; } } else { fprintf(stderr, "%% Enqueued message (%zd bytes) " "for topic %s\n", len, topic); } /* A producer application should continually serve * the delivery report queue by calling rd_kafka_poll() * at frequent intervals. * Either put the poll call in your main loop, or in a * dedicated thread, or call it after every * rd_kafka_produce() call. * Just make sure that rd_kafka_poll() is still called * during periods where you are not producing any messages * to make sure previously produced messages have their * delivery report callback served (and any other callbacks * you register). */ rd_kafka_poll(rk, 0/*non-blocking*/); } /* Wait for final messages to be delivered or fail. * rd_kafka_flush() is an abstraction over rd_kafka_poll() which * waits for all messages to be delivered. */ fprintf(stderr, "%% Flushing final messages..\n"); rd_kafka_flush(rk, 10*1000 /* wait for max 10 seconds */); /* If the output queue is still not empty there is an issue * with producing messages to the clusters. */ if (rd_kafka_outq_len(rk) > 0) fprintf(stderr, "%% %d message(s) were not delivered\n", rd_kafka_outq_len(rk)); /* Destroy the producer instance */ rd_kafka_destroy(rk); return 0; } 3.3 生产者和消费者的交互
（1）启动消费者。
./consumer localhost:9092 0 test
显示：
% Subscribed to 1 topic(s), waiting for rebalance and messages...
（2）启动生产者。
./producer localhost:9092 test
显示：
% Type some text and hit enter to produce message % Or just hit enter to only serve delivery reports % Press Ctrl-C or Ctrl-D to exit
（3）通信过程。
生产者发送hello：
$ ./producer localhost:9092 test % Type some text and hit enter to produce message % Or just hit enter to only serve delivery reports % Press Ctrl-C or Ctrl-D to exit hello consumer % Enqueued message (14 bytes) for topic test
消费者接收：
$ ./consumer localhost:9092 0 test % Subscribed to 1 topic(s), waiting for rebalance and messages... Message on test [0] at offset 4: Value: hello consumer
总结
- 一个分区只能被一个消费者读取。如果一个topic只有一个分区，多个消费者读取时只有一个消费者能读到数据；单个分区开启多个消费者去读取数据是没有意义的。