How can I get the local machine's netmask programmatically?

ruby-talk
1

I'm working on a Rails app that needs to restrict certain privileged
operations/requests to only those requests that originate from within
the local subnet.

How can I find out the machine's netmask programmatically?

Thanks,

Wolf

2

Hi,

what operating system? windows/linux(distribution?)/osx?
how many network adapters are in the machine?

on windows use `ipconfig /all` and parse output or WMI through Win32OLE
on unix `/sbin/ifconfig -a`

If there are more adapters, you have to choose the right one (or allow
all local nets).

J.

···

On 6/13/07, wolfram <wolframarnold@gmail.com> wrote:

I'm working on a Rails app that needs to restrict certain privileged
operations/requests to only those requests that originate from within
the local subnet.

How can I find out the machine's netmask programmatically?

3

what operating system? windows/linux(distribution?)/osx?
how many network adapters are in the machine?

Linux.

on windows use `ipconfig /all` and parse output or WMI through Win32OLE
on unix `/sbin/ifconfig -a`

I know about the system commands. Is there a library/API to get these
programmatically without having to parse output from a sytem command?

Thanks,
W.

4

Create a socket and pull it from the socket structure.

···

On Thu, 2007-06-14 at 07:45 +0900, wolfram wrote:

> what operating system? windows/linux(distribution?)/osx?
> how many network adapters are in the machine?

Linux.

> on windows use `ipconfig /all` and parse output or WMI through Win32OLE
> on unix `/sbin/ifconfig -a`

I know about the system commands. Is there a library/API to get these
programmatically without having to parse output from a sytem command?

Thanks,
W.

5

see if this works....???

rthompso@shienar ~ $ cat getnetmask.rb
require 'rubygems'
require "inline"

class NetMask
  inline do |builder|
    builder.include '<sys/types.h>'
    builder.include '<sys/socket.h>'
    builder.include '<sys/ioctl.h>'
    builder.include '<netinet/in.h>'
    builder.include '<net/if.h>'
    builder.c "

    char * nmask() {
        int fd;
        struct ifreq ifr;

        fd = socket(AF_INET, SOCK_DGRAM, 0);
        ifr.ifr_addr.sa_family = AF_INET;
        strncpy(ifr.ifr_name, \"eth0\", IFNAMSIZ-1);
        ioctl(fd, SIOCGIFNETMASK, &ifr);
        close(fd);

        return (char *)inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr);
  }"
  end
end

nm = NetMask.new()
nmaa = nm.nmask()
puts nmaa

rthompso@shienar ~ $ ruby getnetmask.rb
255.255.255.0

···

On Thu, 2007-06-14 at 08:30 +0900, Reid Thompson wrote:

On Thu, 2007-06-14 at 07:45 +0900, wolfram wrote:
> > what operating system? windows/linux(distribution?)/osx?
> > how many network adapters are in the machine?
>
> Linux.
>
> > on windows use `ipconfig /all` and parse output or WMI through Win32OLE
> > on unix `/sbin/ifconfig -a`
>
> I know about the system commands. Is there a library/API to get these
> programmatically without having to parse output from a sytem command?
>
> Thanks,
> W.
>
Create a socket and pull it from the socket structure.

6

I spent quite a bit of time last night trying to figure this out to no
avail.

Reid, how long did it take you to come up with this? Could anyone
without C experience figured this out?

···

On Jun 13, 9:18 pm, Reid Thompson <Reid.Thomp...@ateb.com> wrote:

On Thu, 2007-06-14 at 08:30 +0900, Reid Thompson wrote:
> On Thu, 2007-06-14 at 07:45 +0900, wolfram wrote:
> > > what operating system? windows/linux(distribution?)/osx?
> > > how many network adapters are in the machine?

> > Linux.

> > > on windows use `ipconfig /all` and parse output or WMI through Win32OLE
> > > on unix `/sbin/ifconfig -a`

> > I know about the system commands. Is there a library/API to get these
> > programmatically without having to parse output from a sytem command?

> > Thanks,
> > W.

> Create a socket and pull it from the socket structure.

see if this works....???

rthompso@shienar ~ $ cat getnetmask.rb
require 'rubygems'
require "inline"

class NetMask
  inline do |builder|
    builder.include '<sys/types.h>'
    builder.include '<sys/socket.h>'
    builder.include '<sys/ioctl.h>'
    builder.include '<netinet/in.h>'
    builder.include '<net/if.h>'
    builder.c "

    char * nmask() {
        int fd;
        struct ifreq ifr;

        fd = socket(AF_INET, SOCK_DGRAM, 0);
        ifr.ifr_addr.sa_family = AF_INET;
        strncpy(ifr.ifr_name, \"eth0\", IFNAMSIZ-1);
        ioctl(fd, SIOCGIFNETMASK, &ifr);
        close(fd);

        return (char *)inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr);
  }"
  end
end

nm = NetMask.new()
nmaa = nm.nmask()
puts nmaa

rthompso@shienar ~ $ ruby getnetmask.rb
255.255.255.0

7

1) I was previously aware of RubyInline -- so didn't have to
'find/research' it

2) I knew that getting the info in C code was doable
3) I googled for examples of getting socket info
4) it took me about 15 minutes probably

4a) I think a non-C programmer could have figured it out in time
I basically copied the C RubyInline example ( the factorial one )
and pasted in the socket code.

The gotcha's would probably have been
    a)figuring out to use the builder.include, described in the C++
example, to get the header files included
    b)getting rid of a warning message due to the original C code not
casting to (char *) the return value of inet_ntoa()

5) Ruby's various socket classes probably provide access to the same
info - but I couldn't find out how to get at it ( like you, I spent
waaaay more time trying to find a pure ruby way of getting the info than
coding the example ) i.e. Ruby's Socket class has a getsockname which
returns the struct sockaddr packed into a string -- It may have all the
info needed, but I'm not familiar enough with unpacking a sockaddr
structure to try to figure it out ( or unpacking anything in Ruby for
that matter :slight_smile: ).

···

On Fri, 2007-06-15 at 01:48 +0900, list.rb@gmail.com wrote:

I spent quite a bit of time last night trying to figure this out to no
avail.

Reid, how long did it take you to come up with this? Could anyone
without C experience figured this out?

>
> see if this works....???
>
> rthompso@shienar ~ $ cat getnetmask.rb
> require 'rubygems'
> require "inline"
>
> class NetMask
> inline do |builder|
> builder.include '<sys/types.h>'
> builder.include '<sys/socket.h>'
> builder.include '<sys/ioctl.h>'
> builder.include '<netinet/in.h>'
> builder.include '<net/if.h>'
> builder.c "
>
> char * nmask() {
> int fd;
> struct ifreq ifr;
>
> fd = socket(AF_INET, SOCK_DGRAM, 0);
> ifr.ifr_addr.sa_family = AF_INET;
> strncpy(ifr.ifr_name, \"eth0\", IFNAMSIZ-1);
> ioctl(fd, SIOCGIFNETMASK, &ifr);
> close(fd);
>
> return (char *)inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr);
> }"
> end
> end
>
> nm = NetMask.new()
> nmaa = nm.nmask()
> puts nmaa
>
> rthompso@shienar ~ $ ruby getnetmask.rb
> 255.255.255.0

8

http://www.hashcode.eti.br/?p=46 makes an interesting read also

···

On Fri, 2007-06-15 at 01:48 +0900, list.rb@gmail.com wrote:

I spent quite a bit of time last night trying to figure this out to no
avail.

Reid, how long did it take you to come up with this? Could anyone
without C experience figured this out?

On Jun 13, 9:18 pm, Reid Thompson <Reid.Thomp...@ateb.com> wrote:
> On Thu, 2007-06-14 at 08:30 +0900, Reid Thompson wrote:
> > On Thu, 2007-06-14 at 07:45 +0900, wolfram wrote:
> > > > what operating system? windows/linux(distribution?)/osx?
> > > > how many network adapters are in the machine?
>
> > > Linux.
>
> > > > on windows use `ipconfig /all` and parse output or WMI through Win32OLE
> > > > on unix `/sbin/ifconfig -a`
>
> > > I know about the system commands. Is there a library/API to get these
> > > programmatically without having to parse output from a sytem command?
>
> > > Thanks,
> > > W.
>
> > Create a socket and pull it from the socket structure.
>
> see if this works....???
>
> rthompso@shienar ~ $ cat getnetmask.rb
> require 'rubygems'
> require "inline"
>
> class NetMask
> inline do |builder|
> builder.include '<sys/types.h>'
> builder.include '<sys/socket.h>'
> builder.include '<sys/ioctl.h>'
> builder.include '<netinet/in.h>'
> builder.include '<net/if.h>'
> builder.c "
>
> char * nmask() {
> int fd;
> struct ifreq ifr;
>
> fd = socket(AF_INET, SOCK_DGRAM, 0);
> ifr.ifr_addr.sa_family = AF_INET;
> strncpy(ifr.ifr_name, \"eth0\", IFNAMSIZ-1);
> ioctl(fd, SIOCGIFNETMASK, &ifr);
> close(fd);
>
> return (char *)inet_ntoa(((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr);
> }"
> end
> end
>
> nm = NetMask.new()
> nmaa = nm.nmask()
> puts nmaa
>
> rthompso@shienar ~ $ ruby getnetmask.rb
> 255.255.255.0