Hiredis waiting for message - redis

Question

I am using hiredis C library to connect to redis server. I am not able to figure out how to wait for new messages after subscribing to new message.
My code look like:
signal(SIGPIPE, SIG_IGN );
struct event_base *base = event_base_new();
redisAsyncContext *c = redisAsyncConnect("127.0.0.1", 6379);
if (c->err) {
/* Let *c leak for now... */
printf("Error: %s\n", c->errstr);
return 1;
}
redisLibeventAttach(c, base);
redisAsyncSetConnectCallback(c, connectCallback);
redisAsyncSetDisconnectCallback(c, disconnectCallback);
redisAsyncCommand(c, NULL, NULL, "SET key %b", argv[argc - 1],
strlen(argv[argc - 1]));
redisAsyncCommand(c, getCallback, (char*) "end-1", "GET key");
redisAsyncCommand(c, getCallback, (char*) "end-1", "SUBSCRIBE foo");
Now how to tell hiredis to wait for message on channel ?

Answer 1

You do not have to tell hiredis you need to wait on channel: the event loop will just wait on the Redis connection which has been previously registered.
Here is a complete example:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include "hiredis.h"
#include "async.h"
#include "adapters/libevent.h"
void subCallback(redisAsyncContext *c, void *r, void *priv) {
redisReply *reply = r;
if (reply == NULL) return;
if ( reply->type == REDIS_REPLY_ARRAY && reply->elements == 3 ) {
if ( strcmp( reply->element[0]->str, "subscribe" ) != 0 ) {
printf( "Received[%s] channel %s: %s\n",
(char*)priv,
reply->element[1]->str,
reply->element[2]->str );
}
}
}
void connectCallback(const redisAsyncContext *c, int status) {
if (status != REDIS_OK) {
printf("Error: %s\n", c->errstr);
return;
}
printf("Connected...\n");
}
void disconnectCallback(const redisAsyncContext *c, int status) {
if (status != REDIS_OK) {
printf("Error: %s\n", c->errstr);
return;
}
printf("Disconnected...\n");
}
int main (int argc, char **argv) {
signal(SIGPIPE, SIG_IGN);
struct event_base *base = event_base_new();
redisAsyncContext *c = redisAsyncConnect("127.0.0.1", 6379);
if (c->err) {
/* Let *c leak for now... */
printf("Error: %s\n", c->errstr);
return 1;
}
redisLibeventAttach(c,base);
redisAsyncSetConnectCallback(c,connectCallback);
redisAsyncSetDisconnectCallback(c,disconnectCallback);
redisAsyncCommand(c, subCallback, (char*) "sub", "SUBSCRIBE foo");
event_base_dispatch(base);
return 0;
}
You can test it by just use the following command to publish something:
redis-cli publish foo something
The event_base_dispatch function is the one which actually launches the event loop, and makes it wait on Redis subscription.

Answer 2

LibUV based solution
Redis Version: 5.0.5
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include "hiredis.h"
#include "async.h"
#include <time.h>
#include <uv.h>
#include "adapters/libevent.h"
#include "adapters/libuv.h"
void subCallback(redisAsyncContext *c, void *r, void *priv) {
redisReply *reply = r;
time_t seconds;
seconds = time(NULL);
if (reply == NULL) return;
if (reply->type == REDIS_REPLY_ARRAY && reply->elements == 3) {
if (strcmp(reply->element[0]->str, "subscribe") != 0) {
printf("[%d] Received[%s] channel %s: %s\n",
seconds,
(char *) priv,
reply->element[1]->str,
reply->element[2]->str);
}
}
}
void connectCallback(const redisAsyncContext *c, int status) {
if (status != REDIS_OK) {
printf("Error: %s\n", c->errstr);
return;
}
printf("Connected...\n");
}
void disconnectCallback(const redisAsyncContext *c, int status) {
if (status != REDIS_OK) {
printf("Error: %s\n", c->errstr);
return;
}
printf("Disconnected...\n");
}
int main(int argc, char **argv) {
signal(SIGPIPE, SIG_IGN);
uv_loop_t *loop = malloc(sizeof(uv_loop_t));
uv_loop_init(loop);
redisAsyncContext *c = redisAsyncConnect("127.0.0.1", 6379);
if (c->err) {
/* Let *c leak for now... */
printf("Error: %s\n", c->errstr);
return 1;
}
redisLibuvAttach(c, loop);
redisAsyncSetConnectCallback(c, connectCallback);
redisAsyncSetDisconnectCallback(c, disconnectCallback);
redisAsyncCommand(c, subCallback, (char *) "sub", "SUBSCRIBE test-channel");
uv_run(loop, UV_RUN_DEFAULT);
uv_loop_close(loop);
free(loop);
return 0;
}