[erlang-questions] How to add a option for inet:getopts

Serge Aleynikov <>
Fri Jan 19 14:29:51 CET 2007


Kenneth,

Thanks for sharing this preliminary info.  As a caveat, it looks to me 
that this option would require to run erl with root privileges (that 
from the security point of view is not a good thing).  There's actually 
a work around on Linux for this using 'cap_net_raw' capability, where 
you can start the process as root, set the capability and switch to 
effective user.  This would allow to retain access to a raw socket and 
not to be root.

If interested I can provide a sample code.

Regards,

Serge

Kenneth Lundin wrote:
> Hi,
> 
> We have preliminary planned to implement a new option called "raw" as
> an  extension to the
> inet:getopts(Socket,Options)
> and
> inet:setopts(Socket,Options)
> and all other places where socket options are handled.
> 
> The new "raw" option would look something like this:
> {{raw,Level,OptionCode},OptionValue}
> 
> Both OptionCode and OptionValue is positive integers assumed to be 
> mapped on
> UINT32 in C. Thus the use is limited to OptionValues that fits in an 
> UINT32.
> Of course the inet_driver will be updated to support this as well.
> 
> With this new raw option it should be possible to use various non 
> standard and
> non supported socket options directly from Erlang code.
> Thus the example
> 
> 'getsockopt(fd,SOL_IP,SO_ORIGINAL_DST,&server,&slen)'.
> 
> could be implemented something like this:
> 
> -define(SOL_IP,10).  % the value 10 is only an example
> -define(SO_ORIGINAL_DST,47). % the value 47 is only an example
> %% The user has to find the right values from the C header files.
> ....
> inet:getopts(Socket,[{raw,$SOL_IP,$SO_ORIGINAL_DST}])
> 
> which should return
> 
> [{{raw,$SOL_IP,$SO_ORIGINAL_DST},OptionValue}]
> 
> Note that this is preliminary ideas which may be adjusted when we 
> implement it.
> 
> /Regards Kenneth (Erlang responsible at Ericsson)
> 
> On 1/19/07, Serge Aleynikov <> wrote:
>> The only way to get this socket option accessible from Erlang is to add
>> support for it in the network driver (inet_drv.c).
>>
>> Serge
>>
>> William Gan wrote:
>> > Hello,
>> >
>> > I am preparing to implement a transparent proxy by erlang, and I 
>> need an
>> > equivalent call for
>> > 'getsockopt(fd,SOL_IP,SO_ORIGINAL_DST,&server,&slen)'.
>> >
>> > Can anyone give me some advice how to add such a call in erlang?
>> >
>> > William Gan



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