C - alternative using snprintf to prepare MySQL statements? - mysql

Question

I've been tearing my hair out for a while on this one. The C code is called from a bash script, which loops through a command's output in a while loop and passes variables to the C script as args. It goes through a list and partitions data properly. I've been using the C MySQL api, and up until now everything has been relatively straight forward. It tries to run a SELECT(EXISTS) command to dictate whether to input a new row, or update an existing one.
I have typed the command into MySQL terminal and it works perfectly. I have even printf'd it and copied the command directly into the terminal. It works....
So why then, am I getting Syntax errors? I've tried escaping fields and input using backticks, single quotes and double quotes and I'm still getting this dumbounding error. I thought maybe it was something to do with the null space? But I'm at my witts end. Here's the code, any advice would be greatly appreciated :)
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <mysql/mysql.h>
const int MAXLEN = 100;
/* Compile with:
gcc db.connect.c `mysql_config --libs` -O1
for the best results
*/
/* Function definitions for later */
void finish_with_error(MYSQL *con);
int send_query(MYSQL *con, char query[MAXLEN]);
/* If any SQL commands fail, return an error message */
void finish_with_error(MYSQL *con)
{
fprintf(stderr, "%s\n", mysql_error(con));
mysql_close(con);
exit(1);
}
/* Helper function to send queries to MySQL database */
int send_query(MYSQL *con, char query[MAXLEN])
{
if (mysql_query(con, query)) {
finish_with_error(con);
}
return 0;
}
int main(int argc, char ** argv)
{
// Establish MySQL API connection, if not- fail with err
MYSQL *con = mysql_init(NULL);
if (con == NULL) {
finish_with_error(con);
}
// Connection string.
if (mysql_real_connect(con, "localhost", "user", "password",
NULL, 0, NULL, 0) == NULL){
finish_with_error(con);
}
if (argv[1] == NULL){
printf("No query passed, terminating script \n");
return 1;
}
if (argv[1] != NULL) {
if( strcmp( argv[1], "--help" ) == 0 ) {
printf("This program was created to interact with MySQL, by checking and updating live network stats\n");
printf("It has 2 parameters, an IP address to look in the database for and a value to update a field by, \
if that IP address is found. ");
printf("If the value is not found, the program will insert a new row.");
return 1;
}
// Works out how much memory to allocate to buffer for snprintf
// Originally cmd_len was 65- as this was the amount of bits needed by the address string.
// This was changed to MAXLEN to prevent SEGFAULTS and give the function breathing room.
size_t cmd_len = MAXLEN;
size_t param_len = sizeof(argv[2]);
size_t q_len = cmd_len + param_len;
// Allocates that memory to a buffer, referenced as query
char *query = malloc(sizeof(char) * q_len);
snprintf(query, q_len, "SELECT EXISTS(SELECT * FROM `analytics`.`live` WHERE `foreign_addr` = `%s`)", argv[1]);
printf("%s\n", query);
send_query(con, query);
free(query);
// Used to store the result of the MySQL select commands
MYSQL_RES *result = mysql_store_result(con);
if (result == NULL) {
finish_with_error(con);
}
// num_fields stores the number of fields, i and x are counters, answer is 1 or 0
int num_fields = mysql_num_fields(result);
int i = 0;
// Loops through each row in the answer statement.
// There will only be one row in the answer, which will be 1 or 0
// Basically, if the IP is found.
MYSQL_ROW row;
while ((row = mysql_fetch_row(result))){
for (i=0; i<num_fields; i++) {
// If the IP isn't in the table
if(!atoi(row[i]))
send_query(con, argv[1]);
// If the IP is already in the table
if(atoi(row[i])) {
snprintf(query, q_len, "UPDATE analytics.live SET count=count+1 WHERE foreign_addr = '%s'", argv[1]);
printf("%s\n", query);
free(query);
snprintf(query, q_len, "UPDATE analytics.live SET dat_sent = dat_sent + %s", argv[2]);
printf("%s\n", query);
free(query);
}
}
}
mysql_close(con);
return 1;
}
mysql_close(con);
return 0;
}