Simulating a broken sqlite3 server in c - c

Question

I have made an sqlite3 database that saves entries that sensors create. I am checking on leaks with valgrind, now I was wondering how to 'simulate' a broken SQL server. I am using this function:
rc = sqlite3_prepare_v2(conn, sql, -1, &res, 0);
This function works correctly, is there a way to simulate it failing? Setting rc to another value manually is an option, but doesn't make sense since a database does get created while the program thinks it doesn't.
I will add the code bellow, although I don't think this is necessary for this question.
This is the insert function that inserts a sensor into the database. This is where I want to test what happens when the prepare function fails.
void *insert_sensor(void *argument) {
storagemgr_insert_argument_t *storagemgr_insert_argument = (storagemgr_insert_argument_t *) argument;
DBCONN *conn = storagemgr_insert_argument->db_connection;
sqlite3_stmt *res = NULL;
uint16_t sensor_id_read;
double temperature_value_read;
time_t timestamp_read;
sensor_data_t data;
int buffer_working_check;
data.id = 0;
data.value = 0;
data.ts = 0;
buffer_working_check = 1;
while (connmgr_loopt_bool == 1 || buffer_working_check == 0) { //connmgr aan -> moet blijven lopen, connmgr uit maar nog data beschikbaar -> moet blijven lopen
pthread_mutex_lock(&lock);
// printf("gelockt in storagemgr\n");
buffer_working_check = sbuffer_read(shared_buffer, &data, 0, 1);
pthread_mutex_unlock(&lock);
int failed_tries = 0;
if (data.id != 0 && buffer_working_check != -1 && buffer_working_check != 1) {
res = NULL;
sensor_id_read = data.id;
temperature_value_read = data.value;
timestamp_read = data.ts;
while(failed_tries<3) {
char *sql = "INSERT INTO "TO_STRING(TABLE_NAME)" (sensor_id, sensor_value, timestamp) VALUES (#sensor_id, #sensor_value, #timestamp)";
rc = sqlite3_prepare_v2(conn, sql, -1, &res, 0);
if (rc == SQLITE_OK) {
int idx1 = sqlite3_bind_parameter_index(res, "#sensor_id");
sqlite3_bind_int(res, idx1, sensor_id_read);
int idx2 = sqlite3_bind_parameter_index(res, "#sensor_value");
sqlite3_bind_double(res, idx2, temperature_value_read);
int idx = sqlite3_bind_parameter_index(res, "#timestamp");
sqlite3_bind_int(res, idx, timestamp_read);
break;
}
else {
write_to_fifo("Insert to the SQL server failed, trying again. ", 4);
failed_tries++;
// char *err_msg = 0;
//
// fprintf(stderr, "Failed to execute statement: %s\n", sqlite3_errmsg(conn));
// sqlite3_free(err_msg);
// sqlite3_close(conn);
// return NULL;
}
sleep(2);
}
}
if (0<failed_tries && failed_tries <= 2) { //het mag =2, want als het =2 en de db faalt dan wordt het eerst geincrementeert naar 3
write_to_fifo("Connection to SQL server re-established. ", 5);
}
if(failed_tries>2) {
db_connection_failed_bool = 1;
sqlite3_close(conn);
write_to_fifo("Connection to SQL server lost. ", 6);
break;
}
if (res != NULL) {
sqlite3_step(res);
sqlite3_finalize(res);
res = NULL;
}
}
return NULL;
}

Answer 1

If you want to keep the code pure, you could always pass the insert function an invalid file path or invalid file name. If you are trying to test the recovery loop, and still want it to remain pure, you can pass the invalid file path and have the recovery loop try to build the path. SQLite won’t build a database in a folder that doesn’t exist when using sqlite3_prepare_v2.