Get buffer from recvfrom - c

Question

I'm trying to write tic-tack-toe game communicates through UDP.
For now I have code:
int recv_txt(int sock, struct sockaddr_in *incoming_addr)
{
char bud[MAX_LENGTH];
unsigned int incoming_add_len;
incoming_add_len = sizeof(*incoming_addr);
if(recvfrom(sock, &buf, MAX_LENGTH, 0 (struct sockaddr*)incoming_addr, &incoming_addr_len) < 0)
{
return 0;
}
printf("received %s", buf);
return 1;
}
int main(int argv, char **argc)
{
/** some code to create socket etc */
struct sockaddr_in incoming_addr;
for(;;)
{
recv_txt(sock, &incoming_addr);
//here I would like to create new thread, which will process the buffer from recv_txt and send response;
}
}
and now I need to get buffer from recv_txt, put it inside structure like this:
struct M_s
{
struct sockaddr_in address;
char[MAX_LENGTH] buffer;
}
and pass it to new thread. But I can't get the buffer from recv_txt. Im pretty new in C and for now i can't work with pointers very well.
Thanks for any advice.
EDIT
I tried solution provided by Frankie_c, but I have problem with printf now.
When I try in main:
LP_ARGS_STRUCT args = recv_txt(sock)
printf("data from: %s", inet_ntoa(args->address.sin_adrr))
i don't get any print to console or get error message.
EDIT2 - full code
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <pthread.h>
#define SRV_PORT 23456
#define MAX_TXT_LENGTH 1000
#define MAX_ROOMS 1
int sock;
typedef struct args_s
{
struct sockaddr_in address;
char buffer[MAX_TXT_LENGTH];
} ARGS_STRUCT, *LP_ARGS_STRUCT;
//typedef struct args_s args;
LP_ARGS_STRUCT recv_txt(int sock)
{
LP_ARGS_STRUCT args = malloc(sizeof(ARGS_STRUCT));
//memory error
if(!args)
{
return 1;
}
unsigned int incoming_addr_len = sizeof(args->address);
//incoming_addr_len = sizeof(*incoming_addr);
if (recvfrom(sock, &args->buffer, MAX_TXT_LENGTH, 0,
(struct sockaddr*)&args->address, &incoming_addr_len) < 0)
{
free(args);
return NULL;
}
printf("received: %s %s\n", args->buffer, inet_ntoa(args->address.sin_addr));
return 1;
}
int main(int argv, char **argc)
{
int i = 0;
int optval;
struct sockaddr_in addr, incoming_addr;
char buffer[MAX_TXT_LENGTH];
/* create socket */
sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (sock < 0)
{
err("socket()");
}
/* set reusable flag */
optval = 1;
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval));
/* prepare inet address */
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(SRV_PORT);
addr.sin_addr.s_addr = htonl(INADDR_ANY); /* listen on all interfaces */
if (bind(sock, (struct sockaddr*)&addr, sizeof(addr)) < 0)
{
err("bind");
}
for(;;)
{
LP_ARGS_STRUCT args = recv_txt(sock);
if(!args) continue;
printf("%s\n", args->buffer);
}
return 0;
}
and after receiving a packet I get:
received: Hello 192.168.56.1
Segmentation fault (code dumped)
Process returned 139 (0x8B)

Answer 1

For the original question try this:
typedef struct M_s
{
struct sockaddr_in address;
char[MAX_LENGTH] buffer;
} M_STRUCT, *LP_M_STRUCT; //Create a typedef for struct
//Modify your function to return a structure pointer and having just socket as par...
LP_M_STRUCT recv_txt(int sock)
{
LP_M_STRUCT pMs = malloc(sizeof(M_STRUCT));
if (!pMs)
{
//Handle memory error here!
return NULL;
}
unsigned int incoming_add_len = sizeof(pMs->incoming_addr);
if (recvfrom(sock, &pMs->buffer, MAX_LENGTH, 0, (struct sockaddr *)&pMs->incoming_addr, &incoming_addr_len) < 0)
{
free(pMs); //Release memory
return NULL; //Return nothing...
}
//If we are here we were successfull.
//The structure pMs holds all data we need... so give it to caller...
printf("From %s received %s", inet_ntoa(pMs->address.sin_addr), pMs->buffer);
return pMs;
}
int main(int argv, char **argc)
{
/** some code to create socket etc */
for (;;)
{
LP_M_STRUCT pMs = recv_txt(sock);
if (!pMs) //Check if we get a sign of life on UDP...
continue; //No continue to wait for ...
//We print values again to check that it is ok...
printf("From %s received %s", inet_ntoa(pMs->address.sin_addr), pMs->buffer);
//here create new thread to process the buffer from recv_txt and send response;
//The new thread code have to release structure memory when done!!!
}
}
EDIT: Your problem is that you don't return the allocated structure when successfull and don't return NULL when fail. See:
LP_ARGS_STRUCT recv_txt(int sock)
{
LP_ARGS_STRUCT args = malloc(sizeof(ARGS_STRUCT));
//memory error
if(!args)
{
//return 1; !!!WRONG!!!
return NULL;
}
unsigned int incoming_addr_len = sizeof(args->address);
//incoming_addr_len = sizeof(*incoming_addr);
if (recvfrom(sock, &args->buffer, MAX_TXT_LENGTH, 0,
(struct sockaddr*)&args->address, &incoming_addr_len) < 0)
{
free(args);
return NULL;
}
printf("received: %s %s\n", args->buffer, inet_ntoa(args->address.sin_addr));
//return 1; WRONG! You have to return the allocated struct
return args;
}