engine: Resources package rewrite

This giant patch makes some much needed improvements to the code base.

* The engine has been rewritten and lives within engine/graph/
* All of the common interfaces and code now live in engine/
* All of the resources are in one package called engine/resources/
* The Res API can use different "traits" from engine/traits/
* The Res API has been simplified to hide many of the old internals
* The Watch & Process loops were previously inverted, but is now fixed
* The likelihood of package cycles has been reduced drastically
* And much, much more...

Unfortunately, some code had to be temporarily removed. The remote code
had to be taken out, as did the prometheus code. We hope to have these
back in new forms as soon as possible.

engine/graph/sendrecv.go

@@ -0,0 +1,118 @@
+// 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 graph
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/purpleidea/mgmt/engine"
+
+	multierr "github.com/hashicorp/go-multierror"
+	errwrap "github.com/pkg/errors"
+)
+
+// SendRecv pulls in the sent values into the receive slots. It is called by the
+// receiver and must be given as input the full resource struct to receive on.
+// It applies the loaded values to the resource.
+func (obj *Engine) SendRecv(res engine.RecvableRes) (map[string]bool, error) {
+	recv := res.Recv()
+	if obj.Debug {
+		// NOTE: this could expose private resource data like passwords
+		obj.Logf("%s: SendRecv: %+v", res, recv)
+	}
+	var updated = make(map[string]bool) // list of updated keys
+	var err error
+	for k, v := range recv {
+		updated[k] = false // default
+		v.Changed = false  // reset to the default
+
+		var st interface{} = v.Res // old style direct send/recv
+		if true {                  // new style send/recv API
+			st = v.Res.Sent()
+		}
+
+		// send
+		obj1 := reflect.Indirect(reflect.ValueOf(st))
+		type1 := obj1.Type()
+		value1 := obj1.FieldByName(v.Key)
+		kind1 := value1.Kind()
+
+		// recv
+		obj2 := reflect.Indirect(reflect.ValueOf(res)) // pass in full struct
+		type2 := obj2.Type()
+		value2 := obj2.FieldByName(k)
+		kind2 := value2.Kind()
+
+		if obj.Debug {
+			obj.Logf("Send(%s) has %v: %v", type1, kind1, value1)
+			obj.Logf("Recv(%s) has %v: %v", type2, kind2, value2)
+		}
+
+		// i think we probably want the same kind, at least for now...
+		if kind1 != kind2 {
+			e := fmt.Errorf("kind mismatch between %s: %s and %s: %s", v.Res, kind1, res, kind2)
+			err = multierr.Append(err, e) // list of errors
+			continue
+		}
+
+		// if the types don't match, we can't use send->recv
+		// FIXME: do we want to relax this for string -> *string ?
+		if e := TypeCmp(value1, value2); e != nil {
+			e := errwrap.Wrapf(e, "type mismatch between %s and %s", v.Res, res)
+			err = multierr.Append(err, e) // list of errors
+			continue
+		}
+
+		// if we can't set, then well this is pointless!
+		if !value2.CanSet() {
+			e := fmt.Errorf("can't set %s.%s", res, k)
+			err = multierr.Append(err, e) // list of errors
+			continue
+		}
+
+		// if we can't interface, we can't compare...
+		if !value1.CanInterface() || !value2.CanInterface() {
+			e := fmt.Errorf("can't interface %s.%s", res, k)
+			err = multierr.Append(err, e) // list of errors
+			continue
+		}
+
+		// if the values aren't equal, we're changing the receiver
+		if !reflect.DeepEqual(value1.Interface(), value2.Interface()) {
+			// TODO: can we catch the panics here in case they happen?
+			value2.Set(value1) // do it for all types that match
+			updated[k] = true  // we updated this key!
+			v.Changed = true   // tag this key as updated!
+			obj.Logf("SendRecv: %s.%s -> %s.%s", v.Res, v.Key, res, k)
+		}
+	}
+	return updated, err
+}
+
+// TypeCmp compares two reflect values to see if they are the same Kind. It can
+// look into a ptr Kind to see if the underlying pair of ptr's can TypeCmp too!
+func TypeCmp(a, b reflect.Value) error {
+	ta, tb := a.Type(), b.Type()
+	if ta != tb {
+		return fmt.Errorf("type mismatch: %s != %s", ta, tb)
+	}
+	// NOTE: it seems we don't need to recurse into pointers to sub check!
+
+	return nil // identical Type()'s
+}