C - Read bytes from the UDP socket buffer (Linux)

Question

I wrote the code in order to handle receiving UDP packets. The packets are all same length(120 bytes), and about 1,000 packets are coming in every second. Simply, my code is like this.

int sock = -1;
int flag = 0;
int nRead = 0;

#define LOCAL_BUFF_SIZE (8192)
char buff[LOCAL_BUFF_SIZE];

struct sockaddr_in sockAddr;

memset((void *)&sockAddr, 0x00, sizeof(struct sockaddr_in));

if((sock = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
{
    /* Print error and terminate */
}

/* Make it non-blocking */  
flag = fcntl( sock, F_GETFL, 0 );
fcntl( sock, F_SETFL, flag | O_NONBLOCK );

sockAddr.sin_family = AF_INET;
sockAddr.sin_port = htons(portNum);
sockAddr.sin_addr.s_addr = INADDR_ANY;

if(bind(sock, (struct sockaddr *)&sockAddr, sizeof (sockAddr)) < 0)
{
    /* Print error and terminate */
}

while(...)
{
    nRead = recv(sock, buff, LOCAL_BUFF_SIZE, 0);
    if(nBytes > 0)
    {
        /* Process the data */
    }
    else
    {
        /* If it's error, handle error */
    }
}

When I wrote this code, I expect that recv() function returns every bytes in the UDP socket buffer at that moment, but, it seems that it only returns one packet(120 byte) every time even though there are more bytes in the buffer. So now I encountered with packet loss. I know that there are many other ways to solve this problem, but, for now reading all existent bytes in the UDP buffer at once is the easiest way for me. So, is there any way to read all bytes in the UDP buffer at once?

Thanks in advance

Arun Kaushal Arun Kaushal · Accepted Answer · 2016-01-16T14:52:15

UDP is a message oriented protocol, therefore, you are getting single message in one recv operation. You can possible use recvmmsg() system call to receive multiple messages in a single call.

C - Read bytes from the UDP socket buffer (Linux)

1 Answers