variadic command support in hiredis

[Birdy]

Hi,

Does Redis client 'hiredis' supports variadic commands (specially
variadic rpush)?
If yes, can you please tell me the usage.

Thanks,
Anurag Berdia

[Didier Spezia]

Hi,

hiredis allows you to run arbitrary commands on Redis

including the variadic ones.

redisContext *c = redisConnectUnix("/tmp/redis.sock");
...
redisReply *reply = redisCommand(c,"RPUSH key%d %s %s %s %s", key, item1, item2, item3, item4 );
...
freeReplyObject(reply);

(error handling code ommitted)

Regards,

Didier.

[Birdy]

Hi Didier,

Thanks for reply.
In the given case, how can we add N number of items at run time.
I mean in first call i want to push 3 elements, then in seconds 10 and
in third 2 and so on
How can we implement this using hiredis?

Thanks,
Anurag Berdia

[Didier Spezia]

Hi,

you could use the following function:

/* Issue a command to Redis. This function takes the

 * number of arguments, an array with arguments and an array with their

 * lengths. If the latter is set to NULL, strlen will be used to compute the

 * argument lengths.

 */

void *redisCommandArgv(redisContext *c, int argc, const char **argv, const size_t *argvlen);

Here is an example in old-school C++:

https://gist.github.com/1455082

If you plan to push a large number of items, consider splitting the operation in smaller

commands, and pipeline them using redisAppendCommandArgv (i.e. grouping 20 by 20

for instance).

Regards,

Didier.

[George Coles]

Hello again,

  I wrote some C++ code that takes matlab strings and tries to send them using redisCommandArgv. But in redisFormatCommandArg, assert(pos == totlen) fails. pos is always two greater than totlen.

This function populates the args and arg lengths:

void send( redisReply** reply, redisContext* ctx, int nprhs, int startIndex, const mxArray** prhs  ){

    

int numArgs = nprhs-startIndex;

vector<const char *> argv( numArgs );

    vector<size_t> argvlen( numArgs );

    size_t m,n;

    int argIndex = 0;

    

    mwSize index = 0;

    for ( index = startIndex; index < nprhs; index++ ){

        const mxArray* mx;

mx = prhs[index];

m = mxGetM( mx );

        n = mxGetN( mx );

        char* str;

        mxArray2Char( &str, m,n, prhs[index] );

        const char* c = str;

argv[argIndex] = c;

        argvlen[argIndex] = strlen(c);

        argIndex++;

    }

    *reply = (redisReply*)redisCommandArgv(ctx,argv.size(),&(argv[0]),&(argvlen[0]) );

}

This function is called to create a char* from each matlab string:

void mxArray2Char( char** str,  mwSize m,mwSize n, const  mxArray* mx ){

    

    *str = mxArrayToString( mx );

}

I am trying to pass the command strings "SET" "FOO" "abcdefghijklmnopqrstuvwxyz"

On Sunday, March 3, 2013 7:11:21 PM UTC-5, George Coles wrote:

I know this is old, but it is the only post on the redis forum that deals with this issue. 

I am writing a matlab interface to redis in C. I am not good at C, but I am worse at C++. I need to use redisCommandArgv, because I need to transform the args list from matlab MxArrays to char arrays, and then pass those to redisCommand. So variadic args list a la C will not work. 

I have an embarrassing question - how would you write an example that uses redisCommandArgv in C? I understand the semantics, but I am a bit confused about how to iteratively construct the char **argv. Why not just make it char* ? 

thx

George 

[George Coles]

I want to thank everyone for their help on this. I found an answer to my problem. 

I am using the hiredis-win project so that I can use redis on windows or other platforms. The author of that project neglected to touch the redisFormatCommandArgv function with his tests. On windows, as far as I can tell, the following format string does not work as intended:

pos += sprintf(cmd+pos,"$%zu\r\n",len);

This is on line 968 of hiredis.c. If you use the "%lu" format on Windows, it is fixed. I thought this would be of mild interest because while I know that WIndows is not the intended home for Redis, there many hardworking people out there who have to use it for part fo their computing life. 

I wrote my argv handling code in c++ instead of c, and it was just a matter of adapting the example code to be generic to any command not just RPUSH.

Thanks,

George