% Usage: ./consumer <broker> <group.id> <topic1> <topic2>..

./consumer localhost:9092 my-group test-topic

/**
 * Simple high-level balanced Apache Kafka consumer
 * using the Kafka driver from librdkafka
 * (https://github.com/edenhill/librdkafka)
 */

#include <stdio.h>
#include <signal.h>
#include <string.h>
#include <ctype.h>


/* Typical include path would be <librdkafka/rdkafka.h>, but this program
 * is builtin from within the librdkafka source tree and thus differs. */
//#include <librdkafka/rdkafka.h>
#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 <broker> <group.id> <topic1> <topic2>..\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->err));
                        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;
}

/**
 * Simple Apache Kafka producer
 * using the Kafka driver from librdkafka
 * (https://github.com/edenhill/librdkafka)
 */

#include <stdio.h>
#include <signal.h>
#include <string.h>


/* Typical include path would be <librdkafka/rdkafka.h>, 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 <broker> <topic>\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;
}