Sending data to Redis in JSON format using hiredis

Question

I am completely new to Redis. I have a C application running on an Embedded Linux device which should connect to a Redis exposed locally. I am using Hiredis.

I can successfully connect to the Redis using redisConnect().

Now I need to write datapoints to the Redis in an attribute : value JSON format, for example as follows :

{
  "value" : 1000.1,
  "unit"  : "mA",
  "name"  : "Current"
}

I have been looking at example code, but don't see anything showing exactly what I am trying to achieve.

Is it ok to use the redisCommand() for this as follows? :

redisCommand(redisContext,"value %f unit %s name %s", 1000.1, "mA", "Current");

@GuyKorland Yes I did but seems overly complex for what I am trying to achieve. — Engineer999, Nov 25 '21 at 12:43

score 0 · Answer 1 · answered Jan 19 '23 at 13:29

Here is what have worked for me:

#include <stdio.h>
#include <stdlib.h>

#include <hiredis.h>

int main(void) {
    redisContext *redis_ctx = NULL;
    redisReply *reply = NULL;
    struct timeval redis_timeout = { 1, 500000 }; // 1.5 seconds
    redis_ctx = redisConnectWithTimeout("127.0.0.1", 6379, redis_timeout);
    if (redis_ctx == NULL || redis_ctx->err) {
        if (redis_ctx) {
            printf("Redis Connection error: %s\n", redis_ctx->errstr);
            redisFree(redis_ctx);
        } else {
            printf("Connection error: can't allocate redis context\n");
        }
    }
    if (redis_ctx) {
        reply = redisCommand(redis_ctx, "PUBLISH test_channel {\"attrb1\":%d,\"attrb2\":%d,\"attrb3\":%s}", 1, 2, "11");
        printf("EXTRA EXTRA: %s", reply->str);
        freeReplyObject(reply);
        redisFree(redis_ctx);
    }

    return EXIT_SUCCESS;
}

Note that the JSON part of the string, being passed to redisCommand, does not have any spaces between the fields and values.

Sending data to Redis in JSON format using hiredis

1 Answers1