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


#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

On 6/13/07, wolfram removed_email_address@domain.invalid 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?

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.


#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

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

Thanks,
W.

Create a socket and pull it from the socket structure.


#5

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?


#6

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

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

On Fri, 2007-06-15 at 01:48 +0900, removed_email_address@domain.invalid wrote:

how many network adapters are in the machine?
W.
inline do |builder|

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

rthompso@shienar ~ $ ruby getnetmask.rb
255.255.255.0

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


#8

On Fri, 2007-06-15 at 01:48 +0900, removed_email_address@domain.invalid wrote:

require ‘rubygems’

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

  1. 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: ).