Re: Weird result of getsockopt

[CodeSun via Digitalmars-d-learn]

On Sunday, 24 May 2015 at 21:11:34 UTC, Daniel Kozak wrote:

On Sunday, 24 May 2015 at 16:51:44 UTC, CodeSun wrote:

Hello guys,

Today, I found a weird problem when I was learning to enable SO_KEEPALIVE for a specific socket. I use setsockopt to enable keepalive firstly, and then use getsockopt to show if it is enabled correctly.

My code snippet is listed below:

Dlang version:

import core.sys.posix.sys.socket;
import core.sys.posix.netinet.in_;
import std.c.stdio;

void main() {
        int sfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
        int flag = 1;
        size_t size;

setsockopt(sfd, SOL_SOCKET, SO_KEEPALIVE, &flag, cast(socklen_t)flag.sizeof);

        flag = 0;

getsockopt(sfd, SOL_SOCKET, SO_KEEPALIVE, &flag, cast(socklen_t*)&size);

        printf("%d\n", flag);
}

C version:

#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>

int main() {
        int sfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
        int flag = 1;
        size_t size;

setsockopt(sfd, SOL_SOCKET, SO_KEEPALIVE, &flag, (socklen_t)sizeof(flag));

        flag = 0;

getsockopt(sfd, SOL_SOCKET, SO_KEEPALIVE, &flag, (socklen_t*)&size);

        printf("%d\n", flag);
        return 0;
}

Dlang version always prints 0, which means keepalive is not enabled, while C version can almost display 1 all the time as expected.

So is there anything wrong inside the code? If not, whose behavior is correct?

Cause your code is wrong:

"If the size of the option value is greater than option_len, the value stored in the object pointed to by the option_value argument shall be silently truncated. Otherwise, the object pointed to by the option_len argument shall be modified to indicate the actual

       length of the value."

So because you have size set to 0 it will not work, you mast call it again and than it will probably work.

In C this work because size is not initialize which mean it could be anything

You are right, thx.