engine: graph, resources: Add filtered graph function

This lets a resource query the resource graph in a controlled way.

engine/graph/state.go

@@ -200,6 +200,51 @@ func (obj *State) Init() error {
 		//	return obj.Graph // we return in a func so it's fresh!
 		//},
 
+		FilteredGraph: func() (*pgraph.Graph, error) {
+			graph, err := pgraph.NewGraph("filtered")
+			if err != nil {
+				return nil, errwrap.Wrapf(err, "could not create graph")
+			}
+
+			// filter graph and build a new one...
+			adjacency := obj.Graph.Adjacency()
+			for v1 := range adjacency {
+				// check we're allowed
+				r1, ok := v1.(engine.GraphQueryableRes)
+				if !ok {
+					continue
+				}
+				// pass in information on requestor...
+				if err := r1.GraphQueryAllowed(
+					engine.GraphQueryableOptionKind(res.Kind()),
+					engine.GraphQueryableOptionName(res.Name()),
+					// TODO: add more information...
+				); err != nil {
+					continue
+				}
+				graph.AddVertex(v1)
+
+				for v2, edge := range adjacency[v1] {
+					r2, ok := v2.(engine.GraphQueryableRes)
+					if !ok {
+						continue
+					}
+					// pass in information on requestor...
+					if err := r2.GraphQueryAllowed(
+						engine.GraphQueryableOptionKind(res.Kind()),
+						engine.GraphQueryableOptionName(res.Name()),
+						// TODO: add more information...
+					); err != nil {
+						continue
+					}
+					//graph.AddVertex(v2) // redundant
+					graph.AddEdge(v1, v2, edge)
+				}
+			}
+
+			return graph, nil // we return in a func so it's fresh!
+		},
+
 		World:  obj.World,
 		VarDir: obj.varDir,
 

engine/resources.go

@@ -21,6 +21,7 @@ import (
 	"encoding/gob"
 	"fmt"
 
+	"github.com/purpleidea/mgmt/pgraph"
 	"github.com/purpleidea/mgmt/util/errwrap"
 
 	"gopkg.in/yaml.v2"
@@ -126,6 +127,14 @@ type Init struct {
 	// FIXME: it might be better to offer a safer, more limited, GraphQuery?
 	//Graph func() *pgraph.Graph // TODO: not implemented, use FilteredGraph
 
+	// FilteredGraph is a function that returns a filtered variant of the
+	// current graph. Only resource that have allowed themselves to be added
+	// into this graph will appear. If they did not consent, then those
+	// vertices and any associated edges, will not be present.
+	FilteredGraph func() (*pgraph.Graph, error)
+
+	// TODO: GraphQuery offers an interface to query the resource graph.
+
 	// World provides a connection to the outside world. This is most often
 	// used for communicating with the distributed database.
 	World World

engine/resources/resources_test.go

@@ -603,6 +603,19 @@ func TestResources2(t *testing.T) {
 			Recv: func() map[string]*engine.Send {
 				return map[string]*engine.Send{}
 			},
+
+			// Copied from state.go
+			FilteredGraph: func() (*pgraph.Graph, error) {
+				graph, err := pgraph.NewGraph("filtered")
+				if err != nil {
+					return nil, errwrap.Wrapf(err, "could not create graph")
+				}
+				// Hack: We just add ourself as allowed since
+				// we're just a one-vertex test suite...
+				graph.AddVertex(res) // hack!
+
+				return graph, nil // we return in a func so it's fresh!
+			},
 		}
 		// run Init
 		return func() error {