1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
|
/*
* librdkafka - Apache Kafka C library
*
* Copyright (c) 2019, Magnus Edenhill
* 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 SHALL 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.
*/
/**
* 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();
/* 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.
*/
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);
/* Convert the list of topics to a format suitable for librdkafka */
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
" (leader epoch %" PRId32 "):\n",
rd_kafka_topic_name(rkm->rkt), rkm->partition,
rkm->offset, rd_kafka_message_leader_epoch(rkm));
/* 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;
}
|
