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

[wolfram]

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

 

[Jano Svitok]

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.

 

[wolfram]

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.

 

[Reid Thompson]

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.

 

[Reid Thompson]

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

 

[list.rb]

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?

 

[Reid Thompson]

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?

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 ).

 

[Reid Thompson]

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?

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