daemon: Add "builtin:download" derivation builder.

This ensures that 1) the derivation doesn't change when Guix changes;
2) the derivation closure doesn't contain Guix and its dependencies; 3)
we don't have to rely on ugly chroot hacks.

Adapted from Nix commit 0a2bee307b20411f5b0dda0c662b1f9bb9e0e131.

* nix/libstore/build.cc (DerivationGoal::runChild): Add special case for
'isBuiltin(drv)'.  Disable chroot when 'isBuiltin(drv)'.
* nix/libstore/builtins.cc, nix/libstore/builtins.hh,
nix/scripts/download.in, guix/scripts/perform-download.scm: New files.
* guix/ui.scm (show-guix-help)[internal?]: Add 'perform-download'.
* nix/local.mk (libstore_a_SOURCES): Add builtins.cc.
(libstore_headers): Add builtins.hh.
(nodist_pkglibexec_SCRIPTS): Add 'scripts/download'.
* config-daemon.ac: Emit 'scripts/download'.
* Makefile.am (MODULES): Add 'guix/scripts/perform-download.scm'.
* tests/derivations.scm ("unknown built-in builder")
("'download' built-in builder")
("'download' built-in builder, invalid hash")
("'download' built-in builder, not found")
("'download' built-in builder, not fixed-output"): New tests.

Co-authored-by: Eelco Dolstra <eelco.dolstra@logicblox.com>

1 files changed, 69 insertions, 0 deletions

diff --git a/nix/libstore/builtins.cc b/nix/libstore/builtins.cc
new file mode 100644
index 0000000000..605e44079a
--- /dev/null
+++ b/nix/libstore/builtins.cc
@@ -0,0 +1,69 @@
+/* GNU Guix --- Functional package management for GNU
+   Copyright (C) 2016 Ludovic Courtès <ludo@gnu.org>
+
+   This file is part of GNU Guix.
+
+   GNU Guix is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or (at
+   your option) any later version.
+
+   GNU Guix is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <builtins.hh>
+#include <util.hh>
+#include <globals.hh>
+
+#include <unistd.h>
+
+namespace nix {
+
+static void builtinDownload(const Derivation &drv,
+			    const std::string &drvPath)
+{
+    /* Invoke 'guix perform-download'.  */
+    Strings args;
+    args.push_back("perform-download");
+    args.push_back(drvPath);
+
+    /* Close all other file descriptors. */
+    closeMostFDs(set<int>());
+
+    const char *const argv[] = { "download", drvPath.c_str(), NULL };
+
+    /* XXX: Hack our way to use the 'download' script from 'LIBEXECDIR/guix'
+       or just 'LIBEXECDIR', depending on whether we're running uninstalled or
+       not.  */
+    const string subdir = getenv("GUIX_UNINSTALLED") != NULL
+	? "" : "/guix";
+
+    const string program = settings.nixLibexecDir + subdir + "/download";
+    execv(program.c_str(), (char *const *) argv);
+
+    throw SysError(format("failed to run download program '%1%'") % program);
+}
+
+static const std::map<std::string, derivationBuilder> builtins =
+{
+    { "download", builtinDownload }
+};
+
+derivationBuilder lookupBuiltinBuilder(const std::string & name)
+{
+    if (name.substr(0, 8) == "builtin:")
+    {
+	auto realName = name.substr(8);
+	auto builder = builtins.find(realName);
+	return builder == builtins.end() ? NULL : builder->second;
+    }
+    else
+	return NULL;
+}
+
+}