Patch the idn gem for ruby 1.9

gistfile1.sh

# Retreive the patch file and name it idn.patch
...

# Download the archive from ruby forge of Ruby IDN
$ wget http://rubyforge.org/frs/download.php/8555/idn-0.0.2.tar.gz

# Extract the archive 
$ tar -zxvf idn-0.0.2.tar.gz
x idn-0.0.2/
x idn-0.0.2/README
x idn-0.0.2/CHANGES
x idn-0.0.2/LICENSE
x idn-0.0.2/NOTICE
x idn-0.0.2/Rakefile
x idn-0.0.2/ext/
x idn-0.0.2/ext/idn.c
x idn-0.0.2/ext/idna.c
x idn-0.0.2/ext/punycode.c
x idn-0.0.2/ext/stringprep.c
x idn-0.0.2/ext/idn.h
x idn-0.0.2/ext/extconf.rb
x idn-0.0.2/test/
x idn-0.0.2/test/tc_Idna.rb
x idn-0.0.2/test/tc_Punycode.rb
x idn-0.0.2/test/tc_Stringprep.rb
x idn-0.0.2/test/ts_IDN.rb

$ cd idn-0.0.2

# Patch the freshly downloaded library with the Miklos porting tips
$ patch -p1 -i ../idn.patch
patching file ext/idna.c
patching file ext/punycode.c
patching file ext/stringprep.c

# install it with the help of Rake
$ rake install

ruby1.9_idn_002.patch

diff -crB idn-0.0.2/ext/idna.c idn-0.0.2.patched/ext/idna.c
*** idn-0.0.2/ext/idna.c	2005-09-26 02:23:45.000000000 +0200
--- idn-0.0.2.patched/ext/idna.c	2010-09-04 14:38:37.000000000 +0200
***************
*** 85,91 ****
      flags = 0x0000;
    }
  
!   rc = idna_to_ascii_8z(RSTRING(str)->ptr, &buf, flags);
  
    if (rc != IDNA_SUCCESS) {
      xfree(buf);
--- 85,91 ----
      flags = 0x0000;
    }
  
!   rc = idna_to_ascii_8z(RSTRING_PTR(str), &buf, flags);
  
    if (rc != IDNA_SUCCESS) {
      xfree(buf);
***************
*** 125,131 ****
      flags = 0x0000;
    }
  
!   rc = idna_to_unicode_8z8z(RSTRING(str)->ptr, &buf, flags);
  
    if (rc != IDNA_SUCCESS) {
      xfree(buf);
--- 125,131 ----
      flags = 0x0000;
    }
  
!   rc = idna_to_unicode_8z8z(RSTRING_PTR(str), &buf, flags);
  
    if (rc != IDNA_SUCCESS) {
      xfree(buf);
diff -crB idn-0.0.2/ext/punycode.c idn-0.0.2.patched/ext/punycode.c
*** idn-0.0.2/ext/punycode.c	2005-09-26 02:23:45.000000000 +0200
--- idn-0.0.2.patched/ext/punycode.c	2010-09-04 14:12:04.000000000 +0200
***************
*** 66,72 ****
    VALUE retv;
  
    str = rb_check_convert_type(str, T_STRING, "String", "to_s");
!   ustr = stringprep_utf8_to_ucs4(RSTRING(str)->ptr, RSTRING(str)->len, &len);
  
    while (1) {
      buf = realloc(buf, buflen);
--- 66,72 ----
    VALUE retv;
  
    str = rb_check_convert_type(str, T_STRING, "String", "to_s");
!   ustr = stringprep_utf8_to_ucs4(RSTRING_PTR(str), RSTRING_LEN(str), &len);
  
    while (1) {
      buf = realloc(buf, buflen);
***************
*** 116,122 ****
  
    str = rb_check_convert_type(str, T_STRING, "String", "to_s");
  
!   len = RSTRING(str)->len;
    ustr = malloc(len * sizeof(punycode_uint));
  
    if (ustr == NULL) {
--- 116,122 ----
  
    str = rb_check_convert_type(str, T_STRING, "String", "to_s");
  
!   len = RSTRING_LEN(str);
    ustr = malloc(len * sizeof(punycode_uint));
  
    if (ustr == NULL) {
***************
*** 124,130 ****
      return Qnil;
    }
  
!   rc = punycode_decode(RSTRING(str)->len, RSTRING(str)->ptr,
                         &len, ustr, NULL);
  
    if (rc != PUNYCODE_SUCCESS) {
--- 124,130 ----
      return Qnil;
    }
  
!   rc = punycode_decode(RSTRING_LEN(str), RSTRING_PTR(str),
                         &len, ustr, NULL);
  
    if (rc != PUNYCODE_SUCCESS) {
diff -crB idn-0.0.2/ext/stringprep.c idn-0.0.2.patched/ext/stringprep.c
*** idn-0.0.2/ext/stringprep.c	2006-02-11 16:46:43.000000000 +0100
--- idn-0.0.2.patched/ext/stringprep.c	2010-09-04 14:16:37.000000000 +0200
***************
*** 64,70 ****
    VALUE retv;
  
    str = rb_check_convert_type(str, T_STRING, "String", "to_s");
!   rc = stringprep_profile(RSTRING(str)->ptr, &buf, profile, 0);
  
    if (rc != STRINGPREP_OK) {
      rb_raise(eStringprepError, "%s (%d)", stringprep_strerror(rc), rc);
--- 64,70 ----
    VALUE retv;
  
    str = rb_check_convert_type(str, T_STRING, "String", "to_s");
!   rc = stringprep_profile(RSTRING_PTR(str), &buf, profile, 0);
  
    if (rc != STRINGPREP_OK) {
      rb_raise(eStringprepError, "%s (%d)", stringprep_strerror(rc), rc);
***************
*** 135,141 ****
  static VALUE with_profile(VALUE self, VALUE str, VALUE profile)
  {
    profile = rb_check_convert_type(profile, T_STRING, "String", "to_s");
!   return stringprep_internal(str, RSTRING(profile)->ptr);
  }
  
  /*
--- 135,141 ----
  static VALUE with_profile(VALUE self, VALUE str, VALUE profile)
  {
    profile = rb_check_convert_type(profile, T_STRING, "String", "to_s");
!   return stringprep_internal(str, RSTRING_PTR(profile));
  }
  
  /*
***************
*** 153,159 ****
    VALUE retv;
  
    str = rb_check_convert_type(str, T_STRING, "String", "to_s");
!   buf = stringprep_utf8_nfkc_normalize(RSTRING(str)->ptr, RSTRING(str)->len);
  
    retv = rb_str_new2(buf);
    xfree(buf);
--- 153,159 ----
    VALUE retv;
  
    str = rb_check_convert_type(str, T_STRING, "String", "to_s");
!   buf = stringprep_utf8_nfkc_normalize(RSTRING_PTR(str), RSTRING_LEN(str));
  
    retv = rb_str_new2(buf);
    xfree(buf);

This patch fix the problem of compiling the IDN for Ruby, under Ruby 1.9, following the tips published on the Miklós Fazekas' blog (http://boga.wordpress.com/2008/04/15/ruby-19-porting-notes/)