Added Public API for Preferred/Unclean Leader Election on Topic Partitions

CHANGELOG.md

@@ -8,6 +8,7 @@ librdkafka v2.6.0 is a feature release:
    of given types.
  * Fix for permanent fetch errors when using a newer Fetch RPC version with an older
    inter broker protocol (#4806).
+ * [KIP-460](https://cwiki.apache.org/confluence/display/KAFKA/KIP-460%3A+Admin+Leader+Election+RPC) Admin Leader Election RPC (#4845)
 
 
 ## Fixes

INTRODUCTION.md

@@ -2024,7 +2024,7 @@ The [Apache Kafka Implementation Proposals (KIPs)](https://cwiki.apache.org/conf
 | KIP-436 - Start time in stats                                            | 2.3.0                       | Supported                                                                                     |
 | KIP-447 - Producer scalability for EOS                                   | 2.5.0                       | Supported                                                                                     |
 | KIP-455 - AdminAPI: Replica assignment                                   | 2.4.0 (WIP)                 | Not supported                                                                                 |
-| KIP-460 - AdminAPI: electPreferredLeader                                 | 2.4.0                       | Not supported                                                                                 |
+| KIP-460 - AdminAPI: electLeaders                                         | 2.6.0                       | Supported                                                                                     |
 | KIP-464 - AdminAPI: defaults for createTopics                            | 2.4.0                       | Supported                                                                                     |
 | KIP-467 - Per-message (sort of) error codes in ProduceResponse           | 2.4.0                       | Supported                                                                                     |
 | KIP-480 - Sticky partitioner                                             | 2.4.0                       | Supported                                                                                     |
@@ -2102,6 +2102,7 @@ release of librdkafka.
 | 36      | SaslAuthenticate              | 2          | 1              |
 | 37      | CreatePartitions              | 3          | 0              |
 | 42      | DeleteGroups                  | 2          | 1              |
+| 43      | ElectLeaders                  | 2          | 2              | 
 | 44      | IncrementalAlterConfigs       | 1          | 1              |
 | 47      | OffsetDelete                  | 0          | 0              |
 | 50      | DescribeUserScramCredentials  | 0          | 0              |

examples/.gitignore

@@ -21,4 +21,5 @@ list_consumer_group_offsets
 alter_consumer_group_offsets
 incremental_alter_configs
 user_scram
-list_offsets
+list_offsets
+elect_leaders

examples/CMakeLists.txt

@@ -62,6 +62,9 @@ target_link_libraries(describe_cluster PUBLIC rdkafka)
 add_executable(list_offsets list_offsets.c ${win32_sources})
 target_link_libraries(list_offsets PUBLIC rdkafka)
 
+add_executable(elect_leaders elect_leaders.c ${win32_sources})
+target_link_libraries(elect_leaders PUBLIC rdkafka)
+
 # The targets below has Unix include dirs and do not compile on Windows.
 if(NOT WIN32)
     add_executable(rdkafka_example rdkafka_example.c)

examples/Makefile

@@ -13,6 +13,7 @@ EXAMPLES ?= rdkafka_example rdkafka_performance rdkafka_example_cpp \
 	incremental_alter_configs \
 	user_scram \
 	list_offsets \
+	elect_leaders \
 	misc
 
 all: $(EXAMPLES)
@@ -153,6 +154,10 @@ list_offsets: ../src/librdkafka.a list_offsets.c
 	$(CC) $(CPPFLAGS) $(CFLAGS) $@.c -o $@ $(LDFLAGS) \
 		../src/librdkafka.a $(LIBS)
 
+elect_leaders: ../src/librdkafka.a elect_leaders.c
+	$(CC) $(CPPFLAGS) $(CFLAGS) $@.c -o $@ $(LDFLAGS) \
+		../src/librdkafka.a $(LIBS)
+
 misc: ../src/librdkafka.a misc.c
 	$(CC) $(CPPFLAGS) $(CFLAGS) $@.c -o $@ $(LDFLAGS) \
 		../src/librdkafka.a $(LIBS)

examples/elect_leaders.c

@@ -0,0 +1,320 @@
+/*
+ * librdkafka - Apache Kafka C library
+ *
+ * Copyright (c) 2024, Confluent Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SH THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * Example utility that shows how to use Elect Leaders (AdminAPI)
+ * to trigger preffered or unclean elections for
+ * one or more topic partitions.
+ */
+
+#include <signal.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdarg.h>
+
+#ifdef _WIN32
+#include "../win32/wingetopt.h"
+#else
+#include <getopt.h>
+#endif
+
+/* 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"
+
+const char *argv0;
+
+static rd_kafka_queue_t *queue = NULL; /** Admin result queue.
+                                        *  This is a global so we can
+                                        *  yield in stop() */
+static volatile sig_atomic_t run = 1;
+
+/**
+ * @brief Signal termination of program
+ */
+static void stop(int sig) {
+        if (!run) {
+                fprintf(stderr, "%% Forced termination\n");
+                exit(2);
+        }
+        run = 0;
+        if (queue)
+                rd_kafka_queue_yield(queue);
+}
+
+static void usage(const char *reason, ...) {
+
+        fprintf(stderr,
+                "Elect Leaders usage examples\n"
+                "\n"
+                "Usage: %s <options> <election_type> "
+                "<topic1> <partition1> ...\n"
+                "\n"
+                "Options:\n"
+                "   -b <brokers>    Bootstrap server list to connect to.\n"
+                "   -X <prop=val>   Set librdkafka configuration property.\n"
+                "                   See CONFIGURATION.md for full list.\n"
+                "   -d <dbg,..>     Enable librdkafka debugging (%s).\n"
+                "\n",
+                argv0, rd_kafka_get_debug_contexts());
+
+        if (reason) {
+                va_list ap;
+                char reasonbuf[512];
+
+                va_start(ap, reason);
+                vsnprintf(reasonbuf, sizeof(reasonbuf), reason, ap);
+                va_end(ap);
+
+                fprintf(stderr, "ERROR: %s\n", reasonbuf);
+        }
+
+        exit(reason ? 1 : 0);
+}
+
+
+#define fatal(...)                                                             \
+        do {                                                                   \
+                fprintf(stderr, "ERROR: ");                                    \
+                fprintf(stderr, __VA_ARGS__);                                  \
+                fprintf(stderr, "\n");                                         \
+                exit(2);                                                       \
+        } while (0)
+
+
+/**
+ * @brief Set config property. Exit on failure.
+ */
+static void conf_set(rd_kafka_conf_t *conf, const char *name, const char *val) {
+        char errstr[512];
+
+        if (rd_kafka_conf_set(conf, name, val, errstr, sizeof(errstr)) !=
+            RD_KAFKA_CONF_OK)
+                fatal("Failed to set %s=%s: %s", name, val, errstr);
+}
+
+static void
+print_elect_leaders_result(const rd_kafka_ElectLeaders_result_t *result) {
+        const rd_kafka_topic_partition_result_t **results;
+        size_t results_cnt;
+        size_t i;
+        const rd_kafka_ElectLeadersResult_t *res;
+
+        res = rd_kafka_ElectLeaders_result(result);
+
+        results = rd_kafka_ElectLeadersResult_partitions(res, &results_cnt);
+        printf("ElectLeaders response has %zu partition(s):\n", results_cnt);
+        for (i = 0; i < results_cnt; i++) {
+                const rd_kafka_topic_partition_t *partition =
+                    rd_kafka_topic_partition_result_partition(results[i]);
+                const rd_kafka_error_t *err =
+                    rd_kafka_topic_partition_result_error(results[i]);
+                if (rd_kafka_error_code(err)) {
+                        printf("%% ElectLeaders failed for %s [%" PRId32
+                               "] : %s\n",
+                               partition->topic, partition->partition,
+                               rd_kafka_error_string(err));
+                } else {
+                        printf("%% ElectLeaders succeeded for %s [%" PRId32
+                               "]\n",
+                               partition->topic, partition->partition);
+                }
+        }
+}
+
+/**
+ * @brief Parse an integer or fail.
+ */
+int64_t parse_int(const char *what, const char *str) {
+        char *end;
+        unsigned long n = strtoull(str, &end, 0);
+
+        if (end != str + strlen(str)) {
+                fprintf(stderr, "%% Invalid input for %s: %s: not an integer\n",
+                        what, str);
+                exit(1);
+        }
+
+        return (int64_t)n;
+}
+
+static void cmd_elect_leaders(rd_kafka_conf_t *conf, int argc, char **argv) {
+        rd_kafka_t *rk;
+        char errstr[512];
+        rd_kafka_AdminOptions_t *options;
+        rd_kafka_event_t *event                     = NULL;
+        rd_kafka_topic_partition_list_t *partitions = NULL;
+        rd_kafka_ElectionType_t election_type;
+        rd_kafka_ElectLeaders_t *elect_leaders;
+        int i;
+        int retval = 0;
+
+        if ((argc - 1) % 2 != 0) {
+                usage("Invalid number of arguments");
+        }
+
+        election_type = parse_int("election_type", argv[0]);
+
+        argc--;
+        argv++;
+        if (argc > 0) {
+                partitions = rd_kafka_topic_partition_list_new(argc / 2);
+                for (i = 0; i < argc; i += 2) {
+                        rd_kafka_topic_partition_list_add(
+                            partitions, argv[i],
+                            parse_int("partition", argv[i + 1]));
+                }
+        }
+
+        elect_leaders = rd_kafka_ElectLeaders_new(election_type, partitions);
+
+        if (partitions) {
+                rd_kafka_topic_partition_list_destroy(partitions);
+        }
+
+        /*
+         * Create consumer 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_CONSUMER, conf, errstr, sizeof(errstr));
+        if (!rk)
+                fatal("Failed to create new consumer: %s", errstr);
+
+        /*
+         * Elect Leaders
+         */
+        queue = rd_kafka_queue_new(rk);
+
+        /* Signal handler for clean shutdown */
+        signal(SIGINT, stop);
+
+
+        options = rd_kafka_AdminOptions_new(rk, RD_KAFKA_ADMIN_OP_ELECTLEADERS);
+
+        if (rd_kafka_AdminOptions_set_request_timeout(
+                options, 30 * 1000 /* 30s */, errstr, sizeof(errstr))) {
+                fprintf(stderr, "%% Failed to set timeout: %s\n", errstr);
+                goto exit;
+        }
+
+        if (rd_kafka_AdminOptions_set_operation_timeout(
+                options, 30 * 1000 /* 30s */, errstr, sizeof(errstr))) {
+                fprintf(stderr, "%% Failed to set operation timeout: %s\n",
+                        errstr);
+                goto exit;
+        }
+
+        rd_kafka_ElectLeaders(rk, elect_leaders, options, queue);
+
+        rd_kafka_ElectLeaders_destroy(elect_leaders);
+        rd_kafka_AdminOptions_destroy(options);
+
+        /* Wait for results */
+        event = rd_kafka_queue_poll(queue, -1 /* indefinitely but limited by
+                                               * the request timeout set
+                                               * above  */);
+
+        if (!event) {
+                /* User hit Ctrl-C,
+                 * see yield call in stop() signal handler */
+                fprintf(stderr, "%% Cancelled by user\n");
+
+        } else if (rd_kafka_event_error(event)) {
+                rd_kafka_resp_err_t err = rd_kafka_event_error(event);
+                /* ElectLeaders request failed */
+                fprintf(stderr, "%% ElectLeaders failed[%" PRId32 "]: %s\n",
+                        err, rd_kafka_event_error_string(event));
+                retval = 1;
+                goto exit;
+        } else {
+                /* ElectLeaders request succeeded */
+                const rd_kafka_ElectLeaders_result_t *result;
+                result = rd_kafka_event_ElectLeaders_result(event);
+                print_elect_leaders_result(result);
+        }
+
+
+exit:
+        if (event)
+                rd_kafka_event_destroy(event);
+
+        rd_kafka_queue_destroy(queue);
+        /* Destroy the client instance */
+        rd_kafka_destroy(rk);
+
+        exit(retval);
+}
+
+
+int main(int argc, char **argv) {
+        rd_kafka_conf_t *conf; /**< Client configuration object */
+        int opt;
+        argv0 = argv[0];
+
+        /*
+         * Create Kafka client configuration place-holder
+         */
+        conf = rd_kafka_conf_new();
+
+        /*
+         * Parse common options
+         */
+        while ((opt = getopt(argc, argv, "b:X:d:")) != -1) {
+                switch (opt) {
+                case 'b':
+                        conf_set(conf, "bootstrap.servers", optarg);
+                        break;
+
+                case 'X': {
+                        char *name = optarg, *val;
+
+                        if (!(val = strchr(name, '=')))
+                                fatal("-X expects a name=value argument");
+
+                        *val = '\0';
+                        val++;
+
+                        conf_set(conf, name, val);
+                        break;
+                }
+
+                case 'd':
+                        conf_set(conf, "debug", optarg);
+                        break;
+
+                default:
+                        usage("Unknown option %c", (char)opt);
+                }
+        }
+
+        cmd_elect_leaders(conf, argc - optind, &argv[optind]);
+
+        return 0;
+}