{
  lib,
  stdenv,
  fetchurl,
  fetchpatch2,
  zlib,
  lzo,
  libtasn1,
  nettle,
  pkg-config,
  lzip,
  perl,
  gmp,
  autoconf,
  automake,
  libidn2,
  libiconv,
  texinfo,
  unbound,
  dns-root-data,
  gettext,
  util-linux,
  cxxBindings ? !stdenv.hostPlatform.isStatic, # tries to link libstdc++.so
  tpmSupport ? false,
  trousers,
  which,
  nettools,
  libunistring,
  withP11-kit ? !stdenv.hostPlatform.isStatic,
  p11-kit,
  Security, # darwin Security.framework
# certificate compression - only zlib now, more possible: zstd, brotli

# for passthru.tests
# , curlWithGnuTls
# , emacs
# , ffmpeg
# , haskellPackages
# , knot-resolver
# , ngtcp2-gnutls
# , ocamlPackages
# , pkgsStatic
# , python3Packages
# , qemu
# , rsyslog
# , openconnect
# , samba
}:

let

  # XXX: Gnulib's `test-select' fails on FreeBSD:
  # https://hydra.nixos.org/build/2962084/nixlog/1/raw .
  doCheck = !stdenv.isFreeBSD && !stdenv.isDarwin && stdenv.buildPlatform == stdenv.hostPlatform;

  inherit (stdenv.hostPlatform) isDarwin;
in

stdenv.mkDerivation rec {
  pname = "gnutls";
  version = "3.8.4";

  src = fetchurl {
    url = "mirror://gnupg/gnutls/v${lib.versions.majorMinor version}/gnutls-${version}.tar.xz";
    hash = "sha256-K+pOFUeU8/ABgPoqXFH+iwBax6Mc1YvUTN+n8268Ops=";
  };

  outputs =
    [
      "bin"
      "dev"
      "out"
    ]
    ++ lib.optionals (!stdenv.hostPlatform.isMinGW) [
      "man"
      "devdoc"
    ];

  # Not normally useful docs.
  outputInfo = "devdoc";
  outputDoc = "devdoc";

  patches = [
    ./nix-ssl-cert-file.patch
    # Revert https://gitlab.com/gnutls/gnutls/-/merge_requests/1800
    # dlopen isn't as easy in NixPkgs, as noticed in tests broken by this.
    # Without getting the libs into RPATH they won't be found.
    (fetchpatch2 {
      name = "revert-dlopen-compression.patch";
      url = "https://gitlab.com/gnutls/gnutls/-/commit/8584908d6b679cd4e7676de437117a793e18347c.diff";
      revert = true;
      hash = "sha256-r/+Gmwqy0Yc1LHL/PdPLXlErUBC5JxquLzCBAN3LuRM=";
    })
  ];

  # Skip some tests:
  #  - pkg-config: building against the result won't work before installing (3.5.11)
  #  - fastopen: no idea; it broke between 3.6.2 and 3.6.3 (3437fdde6 in particular)
  #  - trust-store: default trust store path (/etc/ssl/...) is missing in sandbox (3.5.11)
  #  - psk-file: no idea; it broke between 3.6.3 and 3.6.4
  # Change p11-kit test to use pkg-config to find p11-kit
  postPatch =
    ''
      sed '2iexit 77' -i tests/{pkgconfig,fastopen}.sh
      sed '/^void doit(void)/,/^{/ s/{/{ exit(77);/' -i tests/{trust-store,psk-file}.c
      sed 's:/usr/lib64/pkcs11/ /usr/lib/pkcs11/ /usr/lib/x86_64-linux-gnu/pkcs11/:`pkg-config --variable=p11_module_path p11-kit-1`:' -i tests/p11-kit-trust.sh
    ''
    + lib.optionalString stdenv.hostPlatform.isMusl ''
      # See https://gitlab.com/gnutls/gnutls/-/issues/945
         sed '2iecho "certtool tests skipped in musl build"\nexit 0' -i tests/cert-tests/certtool.sh
    ''
    + lib.optionalString stdenv.hostPlatform.isStatic ''
      # Adapted from https://gitlab.com/gnutls/gnutls/-/commit/d214cd4570fb1559a20e941bb7ceac7df52e96d3
      # Can be removed with 3.8.5+.
      sed -i lib/nettle/backport/rsa-sign-tr.c -e \
        '/^#include <nettle\/rsa\.h>/i\
      #define nettle_rsa_compute_root_tr _gnutls_nettle_backport_rsa_compute_root_tr'
    '';

  preConfigure = "patchShebangs .";
  configureFlags =
    lib.optionals withP11-kit [
      "--with-default-trust-store-file=/etc/ssl/certs/ca-certificates.crt"
      "--with-default-trust-store-pkcs11=pkcs11:"
    ]
    ++ [
      "--disable-dependency-tracking"
      "--enable-fast-install"
      "--with-unbound-root-key-file=${dns-root-data}/root.key"
      (lib.withFeature withP11-kit "p11-kit")
      (lib.enableFeature cxxBindings "cxx")
    ]
    ++ lib.optionals (stdenv.hostPlatform.isMinGW) [ "--disable-doc" ];

  enableParallelBuilding = true;

  hardeningDisable = [ "trivialautovarinit" ];

  buildInputs = [
    lzo
    lzip
    libtasn1
    libidn2
    zlib
    gmp
    libunistring
    unbound
    gettext
    libiconv
  ] ++ lib.optional (withP11-kit) p11-kit ++ lib.optional (tpmSupport && stdenv.isLinux) trousers;

  nativeBuildInputs =
    [
      perl
      pkg-config
      texinfo
    ]
    ++ [
      autoconf
      automake
    ]
    ++ lib.optionals doCheck [
      which
      nettools
      util-linux
    ];

  propagatedBuildInputs =
    [ nettle ]
    # Builds dynamically linking against gnutls seem to need the framework now.
    ++ lib.optional isDarwin Security;

  inherit doCheck;
  # stdenv's `NIX_SSL_CERT_FILE=/no-cert-file.crt` breaks tests.
  # Also empty files won't work, and we want to avoid potentially impure /etc/
  preCheck = "NIX_SSL_CERT_FILE=${./dummy.crt}";

  # Fixup broken libtool and pkg-config files
  preFixup =
    lib.optionalString (!isDarwin) ''
      sed ${lib.optionalString tpmSupport "-e 's,-ltspi,-L${trousers}/lib -ltspi,'"} \
          -e 's,-lz,-L${zlib.out}/lib -lz,' \
          -e 's,-L${gmp.dev}/lib,-L${gmp.out}/lib,' \
          -e 's,-lgmp,-L${gmp.out}/lib -lgmp,' \
          -i $out/lib/*.la "$dev/lib/pkgconfig/gnutls.pc"
    ''
    + ''
      # It seems only useful for static linking but basically noone does that.
      substituteInPlace "$out/lib/libgnutls.la" \
        --replace "-lunistring" ""
    '';

  # passthru.tests = {
  #   inherit ngtcp2-gnutls curlWithGnuTls ffmpeg emacs qemu knot-resolver samba openconnect;
  #   inherit (ocamlPackages) ocamlnet;
  #   haskell-gnutls = haskellPackages.gnutls;
  #   python3-gnutls = python3Packages.python3-gnutls;
  #   rsyslog = rsyslog.override { withGnutls = true; };
  #   static = pkgsStatic.gnutls;
  # };

  meta = with lib; {
    description = "The GNU Transport Layer Security Library";

    longDescription = ''
      GnuTLS is a project that aims to develop a library which
      provides a secure layer, over a reliable transport
      layer. Currently the GnuTLS library implements the proposed standards by
      the IETF's TLS working group.

      Quoting from the TLS protocol specification:

      "The TLS protocol provides communications privacy over the
      Internet. The protocol allows client/server applications to
      communicate in a way that is designed to prevent eavesdropping,
      tampering, or message forgery."
    '';

    homepage = "https://gnutls.org/";
    license = licenses.lgpl21Plus;
    maintainers = with maintainers; [ vcunat ];
    platforms = platforms.all;
  };
}