static bool s_is_valid_topic()

in source/mqtt.c [18:78]

• 40 lines of code
• 14 McCabe index (conditional complexity)

static bool s_is_valid_topic(const struct aws_byte_cursor *topic, bool is_filter) {

    /* [MQTT-4.7.3-1] Check existance and length */
    if (!topic->ptr || !topic->len) {
        return false;
    }

    /* [MQTT-4.7.3-2] Check for the null character */
    if (memchr(topic->ptr, 0, topic->len)) {
        return false;
    }

    /* [MQTT-4.7.3-3] Topic must not be too long */
    if (topic->len > 65535) {
        return false;
    }

    bool saw_hash = false;

    struct aws_byte_cursor topic_part;
    AWS_ZERO_STRUCT(topic_part);
    while (aws_byte_cursor_next_split(topic, '/', &topic_part)) {

        if (saw_hash) {
            /* [MQTT-4.7.1-2] If last part was a '#' and there's still another part, it's an invalid topic */
            return false;
        }

        if (topic_part.len == 0) {
            /* 0 length parts are fine */
            continue;
        }

        /* Check single level wildcard */
        if (memchr(topic_part.ptr, '+', topic_part.len)) {
            if (!is_filter) {
                /* [MQTT-4.7.1-3] + only allowed on filters */
                return false;
            }
            if (topic_part.len > 1) {
                /* topic part must be 1 character long */
                return false;
            }
        }

        /* Check multi level wildcard */
        if (memchr(topic_part.ptr, '#', topic_part.len)) {
            if (!is_filter) {
                /* [MQTT-4.7.1-2] # only allowed on filters */
                return false;
            }
            if (topic_part.len > 1) {
                /* topic part must be 1 character long */
                return false;
            }
            saw_hash = true;
        }
    }

    return true;
}