Function RM_StringTruncate

src/module.cpp:2611–2640

If the string is open for writing and is of string type, resize it, padding * with zero bytes if the new length is greater than the old one. * * After this call, RM_StringDMA() must be called again to continue * DMA access with the new pointer. * * The function returns REDISMODULE_OK on success, and REDISMODULE_ERR on * error, that is, the key is not open for writing, is not a string * or

 * If the key is empty, a string key is created with the new string value
 * unless the new length value requested is zero. */
int RM_StringTruncate(RedisModuleKey *key, size_t newlen) {
    if (!(key->mode & REDISMODULE_WRITE)) return REDISMODULE_ERR;
    if (key->value && key->value->type != OBJ_STRING) return REDISMODULE_ERR;
    if (newlen > 512*1024*1024) return REDISMODULE_ERR;

    /* Empty key and new len set to 0. Just return REDISMODULE_OK without
     * doing anything. */
    if (key->value == NULL && newlen == 0) return REDISMODULE_OK;

    if (key->value == NULL) {
        /* Empty key: create it with the new size. */
        robj *o = createObject(OBJ_STRING,sdsnewlen(NULL, newlen));
        genericSetKey(key->ctx->client,key->db,key->key,o,0,0);
        key->value = o;
        decrRefCount(o);
    } else {
        /* Unshare and resize. */
        key->value = dbUnshareStringValue(key->db, key->key, key->value);
        size_t curlen = sdslen(szFromObj(key->value));
        if (newlen > curlen) {
            key->value->m_ptr = sdsgrowzero(szFromObj(key->value),newlen);
        } else if (newlen < curlen) {
            sdssubstr(szFromObj(key->value),0,newlen);
            /* If the string is too wasteful, reallocate it. */
            if (sdslen(szFromObj(key->value)) < sdsavail(szFromObj(key->value)))
                key->value->m_ptr = sdsRemoveFreeSpace(szFromObj(key->value));
        }
    }
    return REDISMODULE_OK;
}

/* --------------------------------------------------------------------------
 * ## Key API for List type