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Date: Fri, 14 Sep 2001 12:23:57 -0700
From: Jos Backus <josb@cncdsl.com>
To: freebsd-net@freebsd.org
Subject: How does getsockname() work?
Message-ID: <20010914122357.A49323@lizzy.bugworks.com>
Reply-To: Jos Backus <josb@cncdsl.com>
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--PEIAKu/WMn1b1Hv9
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I am seeing the following difference between FreeBSD and Solaris when using
the attached program, which uses getsockname().
I am using the following command to test this program:

    snmpwalk -p 1234 <host> public

<host> being either goldenbytes or taiko.

On FreeBSD 4 I see:

goldenbytes:~/udp% ./udp &
[1] 64015
goldenbytes:~/udp% received on 0.0.0.0:0
received 37 bytes from 157.57.212.23:1446
received on 0.0.0.0:0
received 37 bytes from 157.57.212.23:1446
received on 0.0.0.0:0
received 37 bytes from 157.57.212.23:1446
received on 0.0.0.0:0
received 37 bytes from 157.57.212.23:1446

On Solaris 7 I see:

taiko:~/udp% ./udp &
[1] 21129
taiko:~/udp% received on 0.0.0.0:1234
received 37 bytes from 157.57.212.23:1448
received on 0.0.0.0:1234
received 37 bytes from 157.57.212.23:1448
received on 0.0.0.0:1234
received 37 bytes from 157.57.212.23:1448
received on 0.0.0.0:1234
received 37 bytes from 157.57.212.23:1448

The 0.0.0.0 is caused by using INADDR_ANY as the binding address; what I don't
understand is why Solaris shows the portnumber whereas FreeBSD doesn't. Surely
I am doing something wrong, but what?

Thanks,
-- 
Jos Backus                 _/  _/_/_/        Santa Clara, CA
                          _/  _/   _/
                         _/  _/_/_/             
                    _/  _/  _/    _/
josb@cncdsl.com     _/_/   _/_/_/            use Std::Disclaimer;

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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define PDU_SIZE 1500

struct sock {
	int             fport;
	int             fsockfd;
	long            sockbuflen;
};

static int
init_sock(ctx)
	struct sock    *ctx;
{
	struct sockaddr_in local_address;

	bzero(&local_address, sizeof local_address);
	local_address.sin_family = AF_INET;
	local_address.sin_addr.s_addr = htonl(INADDR_ANY);
	local_address.sin_port = htons(ctx->fport);

	if ((ctx->fsockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
		fprintf(stderr, "socket(): %s\n", strerror(errno));
		exit(1);
	}
	if (bind(ctx->fsockfd,
	     (struct sockaddr *)&local_address, sizeof local_address) < 0) {
		fprintf(stderr, "bind(): %s\n", strerror(errno));
		exit(1);
	}
}

static int
receive(ctx)
	struct sock    *ctx;
{
	unsigned char   fpdu[PDU_SIZE];
	struct sockaddr_in remote_address;
	struct sockaddr_in local_address;
	int             i, len, n, local_len;

	while (1) {
		len = sizeof remote_address;
		if ((n = recvfrom(ctx->fsockfd, (char *)fpdu,
				  sizeof(fpdu), 0,
			 (struct sockaddr *)&remote_address, &len)) == -1) {
			fprintf(stderr, "recvfrom(): %s\n", strerror(errno));
			exit(1);
		}
		if (getsockname(ctx->fsockfd, (struct sockaddr *)&local_address,
					                &local_len) == -1) {
			fprintf(stderr, "getsockname(): %s\n", strerror(errno));
			exit(1);
		}
		if              (n > PDU_SIZE) {
			fprintf(stderr, "Warning: %d excess bytes discarded\n",
				n - PDU_SIZE);
			n = PDU_SIZE;
		}
		if (len != sizeof remote_address) {
			fprintf(stderr, "recvfrom() return address length %d - expected %d\n",
				len, sizeof remote_address);
			exit(1);
		}
		fprintf(stderr, "received on %s:%d\n",
			inet_ntoa(local_address.sin_addr),
			(int)ntohs(local_address.sin_port));
		fprintf(stderr, "received %d bytes from %s:%d\n",
			n,
			inet_ntoa(remote_address.sin_addr),
			(int)ntohs(remote_address.sin_port));
	}
}

int
main(int ac, char *av[])
{
	struct sock s;

	s.fport = 1234;
	s.sockbuflen = 65536;

	init_sock(&s);

	receive(&s);
}

--PEIAKu/WMn1b1Hv9--

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