lang: Initial implementation of the mgmt language

This is an initial implementation of the mgmt language. It is a
declarative (immutable) functional, reactive, domain specific
programming language. It is intended to be a language that is:

* safe
* powerful
* easy to reason about

With these properties, we hope this language, and the mgmt engine will
allow you to model the real-time systems that you'd like to automate.

This also includes a number of other associated changes. Sorry for the
large size of this patch.

gapi/helpers.go

@@ -0,0 +1,57 @@
+// Mgmt
+// Copyright (C) 2013-2018+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program 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.
+//
+// This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package gapi
+
+import (
+	"io/ioutil"
+
+	"github.com/purpleidea/mgmt/resources"
+	"github.com/purpleidea/mgmt/util"
+
+	errwrap "github.com/pkg/errors"
+)
+
+// Umask is the default to use when none has been specified.
+// TODO: apparently using 0666 is equivalent to respecting the current umask
+const Umask = 0666
+
+// CopyFileToFs copies a file from src path on the local fs to a dst path on fs.
+func CopyFileToFs(fs resources.Fs, src, dst string) error {
+	data, err := ioutil.ReadFile(src)
+	if err != nil {
+		return errwrap.Wrapf(err, "can't read from file `%s`", src)
+	}
+	if err := fs.WriteFile(dst, data, Umask); err != nil {
+		return errwrap.Wrapf(err, "can't write to file `%s`", dst)
+	}
+	return nil
+}
+
+// CopyStringToFs copies a file from src path on the local fs to a dst path on
+// fs.
+func CopyStringToFs(fs resources.Fs, str, dst string) error {
+	if err := fs.WriteFile(dst, []byte(str), Umask); err != nil {
+		return errwrap.Wrapf(err, "can't write to file `%s`", dst)
+	}
+	return nil
+}
+
+// CopyDirToFs copies a dir from src path on the local fs to a dst path on fs.
+func CopyDirToFs(fs resources.Fs, src, dst string) error {
+	return util.CopyDiskToFs(fs, src, dst, false)
+}