This is an edited and annotated tiny_tds extconf.rb with changes needed to get tiny_tds to build as a platform-specific linux gem, statically linked with a custom build of freetds with openssl. It is intended to allow encrypted connections with MS SQL Server. Please use the tiny_tds_ports.rake Gist or else this code will not work.

tiny_tds_extconf.rb

ENV['RC_ARCHS'] = '' if RUBY_PLATFORM =~ /darwin/

# :stopdoc:

require 'mkmf'

# Shamelessly copied from nokogiri
#

# All my notes are tagged with --shannonwells.
 
# I was able to compile platform-specfic gems on OS X Mavericks, AWS-linux AMI and AWS ubuntu AMI.
# Please feel free to pm me here or on Twitter (@shannonewells) if you want help.  --shannonwells

# Commented this line out --shannonwells
#FREETDSDIR = ENV['FREETDS_DIR']

# I needed to create a platform-specific gem for heroku, which uses openssl.  That means freetds has to be built
# and statically linked, so here I just force tiny_tds to use the one it downloads.  --shannonwells
MYDIR = File.dirname(__FILE__)
FREETDSDIR = "#{MYDIR}/../../ports/x86_64-unknown-linux-gnu/freetds/0.91/"

if FREETDSDIR.nil? || FREETDSDIR.empty?
  LIBDIR     = RbConfig::CONFIG['libdir']
  INCLUDEDIR = RbConfig::CONFIG['includedir']
else
  puts "Will use #{FREETDSDIR}"
  LIBDIR = "#{FREETDSDIR}/lib"
  INCLUDEDIR = "#{FREETDSDIR}/include"
end

$CFLAGS  << " #{ENV["CFLAGS"]}"
$LDFLAGS << " #{ENV["LDFLAGS"]}"
$LIBS    << " #{ENV["LIBS"]}"

SEARCHABLE_PATHS = begin
  eop_regexp = /#{File::SEPARATOR}bin$/
  paths = ENV['PATH']
  paths = paths.gsub(File::ALT_SEPARATOR, File::SEPARATOR) if File::ALT_SEPARATOR
  paths = paths.split(File::PATH_SEPARATOR)
  bin_paths = paths.select{ |p| p =~ eop_regexp }
  bin_paths.map{ |p| p.sub(eop_regexp,'') }.compact.reject{ |p| p.empty? }.uniq
end

def searchable_paths_with_directories(*directories)
  SEARCHABLE_PATHS.map do |path|
    directories.map do |paths|
      dir = File.join path, *paths
      File.directory?(dir) ? dir : nil
    end.flatten.compact
  end.flatten.compact
end

# TRAP: lib_prefix is DEFINITELY NOT 'lib' on UNIXes.  Setting it to such will mess up your compiler options.  --shannonwells
if RbConfig::CONFIG['target_os'] =~ /mswin32|mingw32/
  lib_prefix = 'lib' unless RbConfig::CONFIG['target_os'] =~ /mingw32/
  # There's no default include/lib dir on Windows. Let's just add the Ruby ones
  # and resort on the search path specified by INCLUDE and LIB environment
  # variables
  HEADER_DIRS = [INCLUDEDIR]
  LIB_DIRS = [LIBDIR]
else
  lib_prefix = ''
  HEADER_DIRS = [
    # First search /opt/local for macports
    '/opt/local/include',
    # Then search /usr/local for people that installed from source
    '/usr/local/include',
    # Check the ruby install locations
    INCLUDEDIR,
    # Finally fall back to /usr
    '/usr/include'
  ].reject{ |dir| !File.directory?(dir) }
  LIB_DIRS = [
    # First search /opt/local for macports
    '/opt/local/lib',
    # Then search /usr/local for people that installed from source
    '/usr/local/lib',
    # Check the ruby install locations
    LIBDIR,
    # Finally fall back to /usr
    '/usr/lib',
  ].reject{ |dir| !File.directory?(dir) }
end

FREETDS_HEADER_DIRS = (searchable_paths_with_directories(['include'],['include','freetds']) + HEADER_DIRS).uniq

FREETDS_LIB_DIRS = (searchable_paths_with_directories(['lib'],['lib','freetds']) + LIB_DIRS).uniq

# lookup over searchable paths is great for native compilation, however, when
# cross compiling we need to specify our own paths.
if enable_config("lookup", true)
  dir_config('iconv',   FREETDS_HEADER_DIRS, FREETDS_LIB_DIRS)
  dir_config('freetds', FREETDS_HEADER_DIRS, FREETDS_LIB_DIRS)
# I had to add these two lines to get the find_library/find_header tests to pass.
  dir_config('sybdb', FREETDS_HEADER_DIRS, FREETDS_LIB_DIRS)
  dir_config('ct', FREETDS_HEADER_DIRS, FREETDS_LIB_DIRS)
else
  dir_config('iconv')
  dir_config('freetds')

  # remove LDFLAGS
  $LDFLAGS = ENV.fetch("LDFLAGS", "")
end

def asplode(lib)
  abort "-----\n#{lib} is missing.\n-----"
end

asplode 'libiconv' unless have_func('iconv_open', 'iconv.h') || have_library('iconv', 'iconv_open', 'iconv.h')
asplode 'freetds'  unless have_header('sybfront.h') && have_header('sybdb.h')

# I ran some test code to figure out why the original lines of this were failing.  Once I got that code working, I 
# used it here.  You must comment out the line in the ports.rake file that says "--without-odbc", because otherwise
# these entry points are not found.  Also watch out for tdsdbopen to be defined as dbopen instead (this is a configure
# option).  I saw this on OS X. You can test this by just changing tdsdbopen to dbopen, below.   --shannonwells
asplode 'freetds'  unless find_library("#{lib_prefix}ct",    'ct_bind', FREETDS_LIB_DIRS.join(File::PATH_SEPARATOR) )
asplode 'freetds'  unless find_library("#{lib_prefix}sybdb", 'tdsdbopen', FREETDS_LIB_DIRS.join(File::PATH_SEPARATOR) )

create_makefile('tiny_tds/tiny_tds')

# :startdoc: