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Filename : hellodict.c
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/* Hellodict -- An example of modules dictionary API
 *
 * This module implements a volatile key-value store on top of the
 * dictionary exported by the Redis modules API.
 *
 * -----------------------------------------------------------------------------
 *
 * Copyright (c) 2018-Present, Redis Ltd.
 * All rights reserved.
 *
 * Licensed under your choice of (a) the Redis Source Available License 2.0
 * (RSALv2); or (b) the Server Side Public License v1 (SSPLv1); or (c) the
 * GNU Affero General Public License v3 (AGPLv3).
 */

#include "../redismodule.h"
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>

static RedisModuleDict *Keyspace;

/* HELLODICT.SET <key> <value>
 *
 * Set the specified key to the specified value. */
int cmd_SET(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
    if (argc != 3) return RedisModule_WrongArity(ctx);
    RedisModule_DictSet(Keyspace,argv[1],argv[2]);
    /* We need to keep a reference to the value stored at the key, otherwise
     * it would be freed when this callback returns. */
    RedisModule_RetainString(NULL,argv[2]);
    return RedisModule_ReplyWithSimpleString(ctx, "OK");
}

/* HELLODICT.GET <key>
 *
 * Return the value of the specified key, or a null reply if the key
 * is not defined. */
int cmd_GET(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
    if (argc != 2) return RedisModule_WrongArity(ctx);
    RedisModuleString *val = RedisModule_DictGet(Keyspace,argv[1],NULL);
    if (val == NULL) {
        return RedisModule_ReplyWithNull(ctx);
    } else {
        return RedisModule_ReplyWithString(ctx, val);
    }
}

/* HELLODICT.KEYRANGE <startkey> <endkey> <count>
 *
 * Return a list of matching keys, lexicographically between startkey
 * and endkey. No more than 'count' items are emitted. */
int cmd_KEYRANGE(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
    if (argc != 4) return RedisModule_WrongArity(ctx);

    /* Parse the count argument. */
    long long count;
    if (RedisModule_StringToLongLong(argv[3],&count) != REDISMODULE_OK) {
        return RedisModule_ReplyWithError(ctx,"ERR invalid count");
    }

    /* Seek the iterator. */
    RedisModuleDictIter *iter = RedisModule_DictIteratorStart(
        Keyspace, ">=", argv[1]);

    /* Reply with the matching items. */
    char *key;
    size_t keylen;
    long long replylen = 0; /* Keep track of the emitted array len. */
    RedisModule_ReplyWithArray(ctx,REDISMODULE_POSTPONED_LEN);
    while((key = RedisModule_DictNextC(iter,&keylen,NULL)) != NULL) {
        if (replylen >= count) break;
        if (RedisModule_DictCompare(iter,"<=",argv[2]) == REDISMODULE_ERR)
            break;
        RedisModule_ReplyWithStringBuffer(ctx,key,keylen);
        replylen++;
    }
    RedisModule_ReplySetArrayLength(ctx,replylen);

    /* Cleanup. */
    RedisModule_DictIteratorStop(iter);
    return REDISMODULE_OK;
}

/* This function must be present on each Redis module. It is used in order to
 * register the commands into the Redis server. */
int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
    REDISMODULE_NOT_USED(argv);
    REDISMODULE_NOT_USED(argc);

    if (RedisModule_Init(ctx,"hellodict",1,REDISMODULE_APIVER_1)
        == REDISMODULE_ERR) return REDISMODULE_ERR;

    if (RedisModule_CreateCommand(ctx,"hellodict.set",
        cmd_SET,"write deny-oom",1,1,0) == REDISMODULE_ERR)
        return REDISMODULE_ERR;

    if (RedisModule_CreateCommand(ctx,"hellodict.get",
        cmd_GET,"readonly",1,1,0) == REDISMODULE_ERR)
        return REDISMODULE_ERR;

    if (RedisModule_CreateCommand(ctx,"hellodict.keyrange",
        cmd_KEYRANGE,"readonly",1,1,0) == REDISMODULE_ERR)
        return REDISMODULE_ERR;

    /* Create our global dictionary. Here we'll set our keys and values. */
    Keyspace = RedisModule_CreateDict(NULL);

    return REDISMODULE_OK;
}