main: Libify mgmt with a golang API

This is an initial implementation of a possible golang API. In this
particular version, the *gconfig.GraphConfig data structures are
emitted, instead of possibly building a pgraph. As long as we can
represent any local graph as the data structure, then this is fine!

Is there a way to merge the gconfig Vertex and the pgraph Vertex?

examples/lib/libmgmt1.go

@@ -0,0 +1,110 @@
+// libmgmt example
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"github.com/purpleidea/mgmt/gconfig"
+	mgmt "github.com/purpleidea/mgmt/mgmtmain"
+	"github.com/purpleidea/mgmt/resources"
+)
+
+func generateGraphConfig() *gconfig.GraphConfig {
+
+	n1, err := resources.NewNoopRes("noop1")
+	if err != nil {
+		return nil // error
+	}
+
+	gc := &gconfig.GraphConfig{
+		Graph: "libmgmt",
+		Resources: gconfig.Resources{ // must redefine anonymous struct :(
+			// in alphabetical order
+			Exec:  []*resources.ExecRes{},
+			File:  []*resources.FileRes{},
+			Msg:   []*resources.MsgRes{},
+			Noop:  []*resources.NoopRes{n1},
+			Pkg:   []*resources.PkgRes{},
+			Svc:   []*resources.SvcRes{},
+			Timer: []*resources.TimerRes{},
+			Virt:  []*resources.VirtRes{},
+		},
+		//Collector: []collectorResConfig{},
+		//Edges:     []Edge{},
+		Comment: "comment!",
+		//Hostname: "???",
+		//Remote: "???",
+	}
+	return gc
+}
+
+// Run runs an embedded mgmt server.
+func Run() error {
+
+	obj := &mgmt.Main{}
+	obj.Program = "mgmtlib" // TODO: set on compilation
+	obj.Version = "0.0.1"   // TODO: set on compilation
+	obj.TmpPrefix = true
+	obj.IdealClusterSize = -1
+	obj.ConvergedTimeout = -1
+	obj.Noop = true
+
+	obj.GAPI = generateGraphConfig // graph API function
+
+	if err := obj.Init(); err != nil {
+		return err
+	}
+
+	go func() {
+		for {
+			log.Printf("Generating new graph...")
+			obj.Switch(generateGraphConfig) // pass in function to run...
+
+			time.Sleep(15 * time.Second) // XXX: arbitrarily change graph every 30 seconds
+		}
+	}()
+
+	// install the exit signal handler
+	exit := make(chan struct{})
+	defer close(exit)
+	go func() {
+		signals := make(chan os.Signal, 1)
+		signal.Notify(signals, os.Interrupt) // catch ^C
+		//signal.Notify(signals, os.Kill) // catch signals
+		signal.Notify(signals, syscall.SIGTERM)
+
+		select {
+		case sig := <-signals: // any signal will do
+			if sig == os.Interrupt {
+				log.Println("Interrupted by ^C")
+				obj.Exit(nil)
+				return
+			}
+			log.Println("Interrupted by signal")
+			obj.Exit(fmt.Errorf("Killed by %v", sig))
+			return
+		case <-exit:
+			return
+		}
+	}()
+
+	if err := obj.Run(); err != nil {
+		return err
+	}
+	return nil
+}
+
+func main() {
+	log.Printf("Hello!")
+	if err := Run(); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+		return
+	}
+	log.Printf("Goodbye!")
+}