Question

GOAL: I’m making a UDP socket to send and receive data.
I am testing this on my laptop, so I have a server running on the background that listens to incoming messages and echoing this back.

PROBLEM: I am seeing that the server receives one string, and when it echoes back, the client reads the string 2 times instead of ONE and adds gibberish.How to solve this?

Output from the code is: HelloHello09[btw i als get some questionsmarks that are upside down in front of the 09 and behind it, but I cannot paste it, lolz]

Code:

#define BUFLEN 5
#define PORT 12345

#import <Foundation/Foundation.h>

#define srvr_IP "127.0.0.1"

void errorSig(char *); 

int main (int argc, const char * argv[])
{
int sockSend = socket(AF_INET, SOCK_DGRAM, 0);
struct sockaddr_in si_other;

char buf[BUFLEN] = "Hello";
char bufrec[BUFLEN]; 

@autoreleasepool {

    si_other.sin_family = AF_INET; 
    si_other.sin_port = htons(PORT);
    inet_pton(AF_INET, srvr_IP, &si_other.sin_addr); 
    memset(&si_other.sin_zero, 0, sizeof(si_other.sin_zero));

    int size = sizeof(si_other); 
    sendto(sockSend, buf, BUFLEN, 0,
           (struct sockaddr *)&si_other, size);

    recvfrom(sockSend, bufrec, BUFLEN, 0, (struct sockaddr *)&si_other, (unsigned int*)&size); 
    NSString *test = [[NSString alloc]initWithUTF8String:bufrec];
    NSLog(@" data is: %@", test); 

    close(sockSend); 
    }
return 0;
}

Answer 1

I’ve just seen that you did in fact define BUFLEN as 5 (sorry I missed that when I wrote my comment above). As I suspected, you have a NULL termination issue. The length of a string in C is one more than the number of characters you want to store, to make room for the NULL terminator indicating the end of the string.

Change your BUFLEN definition to 6 and you should find it works much better.