dvirsky/module.md

## module.md

      
    Raw
  

              module.md
            
          
    Creating a redis Module in 15 lines of code!

A quick guide to write a very very simple "ECHO" style module to redis and load it. It's not really useful of course, but the idea is to illustrate how little boilerplate it takes.
Step 1: open your favorite editor and write/paste the following code in a file called module.c
#include "redismodule.h"
/* ECHO <string> - Echo back a string sent from the client */
int EchoCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
  if (argc < 2) return RedisModule_WrongArity(ctx);
  return RedisModule_ReplyWithString(ctx, argv[1]);
}

/* Registering the module */
int RedisModule_OnLoad(RedisModuleCtx *ctx) {
  if (RedisModule_Init(ctx, "example", 1, REDISMODULE_APIVER_1) == REDISMODULE_ERR) {
    return REDISMODULE_ERR;
  }
  if (RedisModule_CreateCommand(ctx, "example.echo", EchoCommand, "readonly", 1,1,1) == REDISMODULE_ERR) {
    return REDISMODULE_ERR;
  }
}
Step 2: Download redismodule.h to the same directory. http://bit.ly/1WpJ7gP (https://raw.githubusercontent.com/antirez/redis/unstable/src/redismodule.h)
Step 3: Compile the module:
On Linux:
$ gcc -fPIC -std=gnu99 -c -o module.o module.c
$ ld -o module.so module.o -shared -Bsymbolic -lc

On OSX:
$ gcc -dynamic -fno-common -std=gnu99 -c -o module.o module.c
$ ld -o module.so module.o -bundle -undefined dynamic_lookup -lc

And you're done!
Step 4: Download the unstable version of redis and build it in the same directory, from: http://bit.ly/1Wq1Fyc or https://codeload.github.com/antirez/redis/zip/unstable
unzip redis-unstable.zip
cd redis-unstable
make -j 4
cd ..

Step 5: Load the module from the directory it was build int:
$ ./redis-unstable/src/redis-server --loadmodule ./module.so

(If you already have redis installed and running, you'll want to add --port 9999 or another free port.
Step 6: Try it out!
$ redis-cli EXAMPLE.ECHO "hello world"

The code is available at http://bit.ly/1WpIvrH