From: Garthy D <garthy_lmkltybr@...>
Date: 2012-01-19T09:41:05+09:00
Subject: Re: Extending/embedding Ruby


Hi Mat��j P,

I might be able to offer a few starting points. I'll just pre-warn you 
that I'm not in any way an expert on this stuff!

On 19/01/12 08:53, Mat��j P. wrote:
 > Hi! I would like to extend nfdump in Ruby, which will be probably
 > challenge for me, because I have never write any extension.
 > What is core thing is, that nfdump reads binary file with huge amount of
 > data. This reading and all other job I want to do nfdump which is in C
 > and dont have library files, so I cant use ffi or something like that.
 > Nfdump reads file header, makes a structure represents a netflow file
 > and than it reads n flow records which is represented by struct in which
 > is another struct and variables.
 > I need to get this structure to Ruby.
 > My first question is, if its possible to get struct in which is other
 > struct etc. to Ruby.

You can wrap up opaque data (eg. C structures) using Data_Wrap_Struct, 
and it back using Data_Get_Struct. You can then define a number of calls 
(using rb_define_method) to extract relevant values from your structures.

 > Second is about approach. I have some problems with embedding Ruby
 > Interpreter in C- example from Programming in Ruby fails on SegFault.

I've personally found "Programming Ruby - The Pragmatic Programmers' 
Guide", in the chapter "Extending Ruby" to be the best source of 
information on embedding Ruby. It's not easy- in fact, I've embedded Lua 
and Python and they were far easier to get working, but once I'd got it 
going, I found Ruby to be more rewarding (since I vastly prefer it over 
Lua and Python).

As for the seg fault, you might need to give a bit more info for someone 
to help you. :)

 > So
 > do you thing it is possible to write this as Ruby extension?
 > In the case of Ruby extension I didnt see in any example how to get to
 > Ruby struct which is inicialized in C. I cant inicialize it in Ruby
 > because its a lot of data and I dont know how many flows are in file.

 > I
 > cant give structs to array because of memory problem and also I need to
 > work with record as soon as its read from the file by C.
 > Your suggestion are highly welcomed. Thanks in advance.

Data_Wrap_Struct will probably solve your problem. You can create your 
object in C, and then wrap it up in a Ruby object.

I hope this helps.

Garth