{ stdenv, fetchurl, perl }:

let
  name = "openssl-1.0.1b";

  opensslCrossSystem = stdenv.lib.attrByPath [ "openssl" "system" ]
    (throw "openssl needs its platform name cross building" null)
    stdenv.cross;

  patchesCross = isCross:
    [ # Allow the location of the X509 certificate file (the CA
      # bundle) to be set through the environment variable
      # ‘OPENSSL_X509_CERT_FILE’.  This is necessary because the
      # default location ($out/ssl/cert.pem) doesn't exist, and
      # hardcoding something like /etc/ssl/cert.pem is impure and
      # cannot be overriden per-process.  For security, the
      # environment variable is ignored for setuid binaries.
      ./cert-file.patch
    ]

    ++ stdenv.lib.optionals (isCross && opensslCrossSystem == "hurd-x86")
         [ ./cert-file-path-max.patch # merge with `cert-file.patch' eventually
           ./gnu.patch                # submitted upstream
         ]

    ++ stdenv.lib.optional stdenv.isDarwin ./darwin-arch.patch
    ++ stdenv.lib.optional (stdenv.system == "x86_64-freebsd") ./freebsd-x86_64-asm.patch;
  
in

stdenv.mkDerivation {
  inherit name;

  src = fetchurl {
    urls = [
      "http://www.openssl.org/source/${name}.tar.gz"
      "http://openssl.linux-mirror.org/source/${name}.tar.gz"
    ];
    sha1 = "b6222cbbf835c27d9ad6db22262da6e4a2aca8b8";
  };

  patches = patchesCross false;

  buildNativeInputs = [ perl ];

  # On x86_64-darwin, "./config" misdetects the system as
  # "darwin-i386-cc".  So specify the system type explicitly.
  configureScript =
    if stdenv.system == "x86_64-darwin" then "./Configure darwin64-x86_64-cc" else "./config";

  configureFlags = "shared --libdir=lib";

  makeFlags = "MANDIR=$(out)/share/man";

  postInstall =
    ''
      # If we're building dynamic libraries, then don't install static
      # libraries.
      if [ -n "$(echo $out/lib/*.so)" ]; then
          rm $out/lib/*.a
      fi
    ''; # */

  crossAttrs = {
    patches = patchesCross true;

    preConfigure=''
      # It's configure does not like --build or --host
      export configureFlags="--libdir=lib --cross-compile-prefix=${stdenv.cross.config}- shared ${opensslCrossSystem}"
    '';

    postInstall = ''
      # Openssl installs readonly files, which otherwise we can't strip.
      # This could at some stdenv hash change be put out of crossAttrs, too
      chmod -R +w $out

      # Remove references to perl, to avoid depending on it at runtime
      rm $out/bin/c_rehash $out/ssl/misc/CA.pl $out/ssl/misc/tsget
    '';
    configureScript = "./Configure";
  };

  meta = {
    homepage = http://www.openssl.org/;
    description = "A cryptographic library that implements the SSL and TLS protocols";
    platforms = stdenv.lib.platforms.all;
    maintainers = [ stdenv.lib.maintainers.simons ];
    priority = 10; # resolves collision with ‘man-pages’
  };
}