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.

resources/interfaces.go

@@ -0,0 +1,89 @@
+// 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 resources
+
+import (
+	"os"
+
+	"github.com/purpleidea/mgmt/etcd/scheduler"
+
+	"github.com/spf13/afero"
+)
+
+// World is an interface to the rest of the different graph state. It allows
+// the GAPI to store state and exchange information throughout the cluster. It
+// is the interface each machine uses to communicate with the rest of the world.
+type World interface { // TODO: is there a better name for this interface?
+	ResWatch() chan error
+	ResExport([]Res) error
+	// FIXME: should this method take a "filter" data struct instead of many args?
+	ResCollect(hostnameFilter, kindFilter []string) ([]Res, error)
+
+	StrWatch(namespace string) chan error
+	StrIsNotExist(error) bool
+	StrGet(namespace string) (string, error)
+	StrSet(namespace, value string) error
+	StrDel(namespace string) error
+
+	// XXX: add the exchange primitives in here directly?
+	StrMapWatch(namespace string) chan error
+	StrMapGet(namespace string) (map[string]string, error)
+	StrMapSet(namespace, value string) error
+	StrMapDel(namespace string) error
+
+	Scheduler(namespace string, opts ...scheduler.Option) (*scheduler.Result, error)
+
+	Fs(uri string) (Fs, error)
+}
+
+// from the ioutil package:
+// NopCloser(r io.Reader) io.ReadCloser // not implemented here
+// ReadAll(r io.Reader) ([]byte, error)
+// ReadDir(dirname string) ([]os.FileInfo, error)
+// ReadFile(filename string) ([]byte, error)
+// TempDir(dir, prefix string) (name string, err error)
+// TempFile(dir, prefix string) (f *os.File, err error) // slightly different here
+// WriteFile(filename string, data []byte, perm os.FileMode) error
+
+// Fs is an interface that represents this file system API that we support.
+// TODO: this should be in the gapi package or elsewhere.
+type Fs interface {
+	//fmt.Stringer // TODO: add this method?
+	afero.Fs     // TODO: why doesn't this interface exist in the os pkg?
+	URI() string // returns the URI for this file system
+
+	//DirExists(path string) (bool, error)
+	//Exists(path string) (bool, error)
+	//FileContainsAnyBytes(filename string, subslices [][]byte) (bool, error)
+	//FileContainsBytes(filename string, subslice []byte) (bool, error)
+	//FullBaseFsPath(basePathFs *BasePathFs, relativePath string) string
+	//GetTempDir(subPath string) string
+	//IsDir(path string) (bool, error)
+	//IsEmpty(path string) (bool, error)
+	//NeuterAccents(s string) string
+	//ReadAll(r io.Reader) ([]byte, error) // not needed
+	ReadDir(dirname string) ([]os.FileInfo, error)
+	ReadFile(filename string) ([]byte, error)
+	//SafeWriteReader(path string, r io.Reader) (err error)
+	TempDir(dir, prefix string) (name string, err error)
+	TempFile(dir, prefix string) (f afero.File, err error) // slightly different from upstream
+	//UnicodeSanitize(s string) string
+	//Walk(root string, walkFn filepath.WalkFunc) error
+	WriteFile(filename string, data []byte, perm os.FileMode) error
+	//WriteReader(path string, r io.Reader) (err error)
+}