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/sendrecv.go

@@ -0,0 +1,67 @@
+// 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 engine
+
+// SendableRes is the interface a resource must implement to support sending
+// named parameters. You must specify to the engine what kind of values (and
+// with their types) you will be sending. This is used for static type checking.
+// Formerly, you had to make sure not to overwrite omitted parameters, otherwise
+// it will be as if you've now declared a fixed state for that param. For that
+// example, if a parameter `Foo string` had the zero value to mean that it was
+// undefined, and you learned that the value is actually `up`, then sending on
+// that param would cause that state to be managed, when it was previously not.
+// This new interface actually provides a different namespace for sending keys.
+type SendableRes interface {
+	Res // implement everything in Res but add the additional requirements
+
+	// Sends returns a struct containing the defaults of the type we send.
+	Sends() interface{}
+
+	// Send is used in CheckApply to send the desired data. It returns an
+	// error if the data is malformed or doesn't type check.
+	Send(st interface{}) error
+
+	// Sent returns the most recently sent data. This is used by the engine.
+	Sent() interface{}
+}
+
+// RecvableRes is the interface a resource must implement to support receiving
+// on public parameters. The resource only has to include the correct trait for
+// this interface to be fulfilled, as no additional methods need to be added. To
+// get information about received changes, you can use the Recv method from the
+// input API that comes in via Init.
+type RecvableRes interface {
+	Res
+
+	// SetRecv stores the map of sendable data which should arrive here. It
+	// is called by the GAPI when building the resource.
+	SetRecv(recv map[string]*Send)
+
+	// Recv is used by the resource to get information on changes. This data
+	// can be used to invalidate caches, restart watches, or it can be
+	// ignored entirely.
+	Recv() map[string]*Send
+}
+
+// Send points to a value that a resource will send.
+type Send struct {
+	Res SendableRes // a handle to the resource which is sending a value
+	Key string      // the key in the resource that we're sending
+
+	Changed bool // set to true if this key was updated, read only!
+}