Re: Fwd: freeport(1)
Hi
Thanks for the contribution. Given the simplicity of this tool,
together with the inherent race condition, and the availability of a
shell script that offers similar functionality suggested by Alex Colomar
in a reply, my preference is that it is not worth the maintenance burden
to introduce a tool like this into GNU InetUtils. I think the best
approach is to publish your work as a separate project, and if
eventually there is significant use of it on Unix platforms, we can
always reconsider and include a variant of it in GNU InetUtils.
/Simon
Alejandro Colomar writes:
> Hi,
>
> Bernd recommended me to consider inetutils for this program (see the
> forwarded mail), since net-tools is deprecated.
>
> Yes, it has a race condition by the nature of the port being free at
> the time the program prints it, but the kernel will not reuse it
> unless all other ports have been used first (AFAIK), so the chances
> are quite low, and also the program for which we will use it is just
> some introductory tutorial, and not something critical.
>
> Options for selecting the interface, and also to select a port range,
> could be implemented easily, and seem useful to me. (Thanks, Bernd,
> for your recommendations and small review.)
>
> Would you be interested in adding this tool to inetutils? I would
> help maintain it.
>
> Cheers,
>
> Alex
>
>
> Forwarded Message
>
> [resent from a subscribed address; again, since it didn't work...]
> [D'oh, I hadn't confirmed subscription; sorry Mike for spamming you :/]
>
> Hi,
>
> As a side effect of doing some work for NGINX Unit, I developed the
> following program, which I think might be useful for the general
> public and not only for us. Would you want to pick the program for
> the net-tools project? I'd be able to help maintain it. Also, since
> I'm also the maintainer of the Linux man-pages, you can expect that
> I'll provide a manual page for the program.
>
> The program is as simple as it gets. A draft for the manual page would be:
>
>
> NAME
> freeport - get a random unused port number
>
> SYNOPSIS
> freeport
>
> DESCRIPTION
> This program prints an available IPv4 port and exits.
>
> The port is chosen at random from the ephemeral ports range
> (see ip(7)).
>
> EXIT STATUS
> 0Success
> 1Error
>
> On error, a message is printed on standard error.
>
>
> And the source code is:
>
>
> $ cat freeport.c
> /*
> * SPDX-License-Identifier: GPL-2.0-or-later
> * Copyright 2022 NGINX, Inc.
> * Copyright 2022 F5, Inc.
> *
> * Author: Alejandro Colomar
> */
>
>
> #include
> #include
> #include
> #include
> #include
> #include
>
>
> int32_t get_free_port(void);
>
>
> int
> main(void)
> {
> int32_t port;
>
> port = get_free_port();
> if (port == -1)
> exit(EXIT_FAILURE);
>
> printf("%d\n", port);
> exit(EXIT_SUCCESS);
> }
>
>
> int32_t
> get_free_port(void)
> {
> int sfd;
> int32_t port;
> socklen_t len;
> struct sockaddr_in addr;
>
> sfd = socket(PF_INET, SOCK_STREAM, 0);
> if (sfd == -1) {
> perror("socket()");
> return -1;
> }
>
> bzero(, sizeof(addr));
> addr.sin_family = AF_INET;
> addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
> addr.sin_port = htons(0); // random port
>
> len = sizeof(addr);
> if (bind(sfd, (struct sockaddr *) , len)) {
> perror("bind()");
> goto fail;
> }
>
> if (getsockname(sfd, (struct sockaddr *) , )) {
> perror("getsockname()");
> goto fail;
> }
>
> port = ntohs(addr.sin_port);
>
> fail:
> close(sfd);
> return port;
> }
>
>
> Would you be interested in this program?
> It was written on Linux, and I'm not sure about its portability
> (didn't check), so one of the things to check for adding it to
> net-tools would be that.
>
>
> Cheers,
> Alex
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Description: PGP signature
Re: Fwd: freeport(1)
On 10/2/22 00:22, Alejandro Colomar wrote:
[...]
NAME
freeport - get a random unused port number
SYNOPSIS
freeport
DESCRIPTION
This program prints an available IPv4 port and exits.
The port is chosen at random from the ephemeral ports range
(see ip(7)).
EXIT STATUS
0 Success
1 Error
On error, a message is printed on standard error.
And the source code is:
$ cat freeport.c
/*
* SPDX-License-Identifier: GPL-2.0-or-later
* Copyright 2022 NGINX, Inc.
* Copyright 2022 F5, Inc.
*
* Author: Alejandro Colomar
*/
#include
#include
#include
#include
#include
#include
int32_t get_free_port(void);
int
main(void)
{
int32_t port;
port = get_free_port();
if (port == -1)
exit(EXIT_FAILURE);
printf("%d\n", port);
exit(EXIT_SUCCESS);
}
int32_t
get_free_port(void)
{
int sfd;
int32_t port;
socklen_t len;
struct sockaddr_in addr;
sfd = socket(PF_INET, SOCK_STREAM, 0);
if (sfd == -1) {
perror("socket()");
return -1;
}
bzero(, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
addr.sin_port = htons(0); // random port
len = sizeof(addr);
if (bind(sfd, (struct sockaddr *) , len)) {
perror("bind()");
goto fail;
}
if (getsockname(sfd, (struct sockaddr *) , )) {
perror("getsockname()");
goto fail;
}
port = ntohs(addr.sin_port);
fail:
close(sfd);
return port;
}
And here's a sh(1) implementation:
$ cat freeport
#!/bin/sh
nc -l localhost 0 &
lsof -i \
| grep $! \
| awk '{print $9}' \
| cut -d':' -f2;
kill $!;
Cheers,
Alex
--
Fwd: freeport(1)
Hi,
Bernd recommended me to consider inetutils for this program (see the
forwarded mail), since net-tools is deprecated.
Yes, it has a race condition by the nature of the port being free at the
time the program prints it, but the kernel will not reuse it unless all
other ports have been used first (AFAIK), so the chances are quite low,
and also the program for which we will use it is just some introductory
tutorial, and not something critical.
Options for selecting the interface, and also to select a port range,
could be implemented easily, and seem useful to me. (Thanks, Bernd, for
your recommendations and small review.)
Would you be interested in adding this tool to inetutils? I would help
maintain it.
Cheers,
Alex
Forwarded Message
[resent from a subscribed address; again, since it didn't work...]
[D'oh, I hadn't confirmed subscription; sorry Mike for spamming you :/]
Hi,
As a side effect of doing some work for NGINX Unit, I developed the
following program, which I think might be useful for the general public
and not only for us. Would you want to pick the program for the
net-tools project? I'd be able to help maintain it. Also, since I'm
also the maintainer of the Linux man-pages, you can expect that I'll
provide a manual page for the program.
The program is as simple as it gets. A draft for the manual page would be:
NAME
freeport - get a random unused port number
SYNOPSIS
freeport
DESCRIPTION
This program prints an available IPv4 port and exits.
The port is chosen at random from the ephemeral ports range
(see ip(7)).
EXIT STATUS
0Success
1Error
On error, a message is printed on standard error.
And the source code is:
$ cat freeport.c
/*
* SPDX-License-Identifier: GPL-2.0-or-later
* Copyright 2022 NGINX, Inc.
* Copyright 2022 F5, Inc.
*
* Author: Alejandro Colomar
*/
#include
#include
#include
#include
#include
#include
int32_t get_free_port(void);
int
main(void)
{
int32_t port;
port = get_free_port();
if (port == -1)
exit(EXIT_FAILURE);
printf("%d\n", port);
exit(EXIT_SUCCESS);
}
int32_t
get_free_port(void)
{
int sfd;
int32_t port;
socklen_t len;
struct sockaddr_in addr;
sfd = socket(PF_INET, SOCK_STREAM, 0);
if (sfd == -1) {
perror("socket()");
return -1;
}
bzero(, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
addr.sin_port = htons(0); // random port
len = sizeof(addr);
if (bind(sfd, (struct sockaddr *) , len)) {
perror("bind()");
goto fail;
}
if (getsockname(sfd, (struct sockaddr *) , )) {
perror("getsockname()");
goto fail;
}
port = ntohs(addr.sin_port);
fail:
close(sfd);
return port;
}
Would you be interested in this program?
It was written on Linux, and I'm not sure about its portability (didn't
check), so one of the things to check for adding it to net-tools would
be that.
Cheers,
Alex
--
