From: Daniel Berger <djberg96@...>
Date: 2010-01-13T08:00:42+09:00
Subject: Re: ffi, kerberos



On Jan 12, 3:48 pm, Daniel Berger <djber...@gmail.com> wrote:
> Hi,
>
> I'm trying to wrap two function calls from kerberos, krb5_init_context
> and krb5_free_context. Here are the prototypes for both:
>
> krb5_init_context(krb5_context * context) => krb5_error_code
> krb5_free_context(krb5_context context) => void
>
> krb5_context is a struct, but unfortunately I don't know what its
> members are.
>
> From the docs:
>
>      The krb5_context structure is designed to hold all per thread
> state. All
>      global variables that are context specific are stored in this
> structure,
>      including default encryption types, credentials-cache (ticket
> file), and
>      default realms.
>
>      The internals of the structure should never be accessed directly,
> func-
>      tions exist for extracting information.
>
> All I know is that it's 8 bytes in size.
>
> I tried something like this, but it didn't work:
>
> require 'ffi'
>
> module Krb5
>   class Context
>     extend FFI::Library
>
>     class Error < StandardError; end
>
>     ffi_lib 'krb5'
>
>     attach_function :krb5_init_context, [:string], :uint
>     attach_function :krb5_free_context, [:string], :void
>
>     def initialize
>       @ctx = FFI::MemoryPointer.new(:pointer, 8)
>       ret = krb5_init_context(@ctx)
>
>       if ret > 0
>         raise Error, "krb5_init_context() failed"
>       end
>
>       if block_given?
>         begin
>           yield self
>         ensure
>           free
>         end
>       end
>     end
>
>     def free
>       krb5_free_context(@ctx)
>     end
>   end
> end
>
> k = Krb5::Context.new
> k.free
>
> I can use a plain string buffer, but then it segfaults on the 'free'
> call.
>
> Any suggestions?

Oops, here's an updated version, but it segfaults on the 'free' call:

require 'ffi'

module Krb5
  class Context
    extend FFI::Library

    class Error < StandardError; end

    ffi_lib 'krb5'

    attach_function :krb5_init_context, [:pointer], :uint
    attach_function :krb5_free_context, [:pointer], :void

    def initialize
      @ctx = FFI::MemoryPointer.new(:char, 8)
      ret = krb5_init_context(@ctx)

      if ret > 0
        raise Error, "krb5_init_context() failed"
      end

      if block_given?
        begin
          yield self
        ensure
          free
        end
      end
    end

    def free
      krb5_free_context(@ctx)
    end
  end
end

k = Krb5::Context.new
k.free