Function RM_StringDMA

app/redis-6.2.6/src/module.c:2489–2509

Prepare the key associated string value for DMA access, and returns * a pointer and size (by reference), that the user can use to read or * modify the string in-place accessing it directly via pointer. * * The 'mode' is composed by bitwise OR-ing the following flags: * * REDISMODULE_READ -- Read access * REDISMODULE_WRITE -- Write access * * If the DMA is not requested for writing

 * the string, and later call StringDMA() again to get the pointer.
 */
char *RM_StringDMA(RedisModuleKey *key, size_t *len, int mode) {
    /* We need to return *some* pointer for empty keys, we just return
     * a string literal pointer, that is the advantage to be mapped into
     * a read only memory page, so the module will segfault if a write
     * attempt is performed. */
    char *emptystring = "<dma-empty-string>";
    if (key->value == NULL) {
        *len = 0;
        return emptystring;
    }

    if (key->value->type != OBJ_STRING) return NULL;

    /* For write access, and even for read access if the object is encoded,
     * we unshare the string (that has the side effect of decoding it). */
    if ((mode & REDISMODULE_WRITE) || key->value->encoding != OBJ_ENCODING_RAW)
        key->value = dbUnshareStringValue(key->db, key->key, key->value);

    *len = sdslen(key->value->ptr);
    return key->value->ptr;
}

/* 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.