resources: Improve AutoEdge API and pkg breakage

I previously broke the pkg auto edges because the package list wasn't
available by the time it was called. This fixes the pkg resource so that
it gets the necessary list of packages when needed. Since this means
that a possible failure could happen, we also update the AutoEdges API
to support errors. Errors can only be generated at AutoEdge struct
creation, once the struct has been returned (right before modification
of the graph structure) there is no possibility to return any errors.

It's important to remember that the AutoEdges stuff gets called because
the Init of each resource, so make sure it doesn't depend on anything
that happens there or that gets cached as a result of Init.

This is all much nicer now and has a test too :)

resources/pkg.go

@@ -72,31 +72,12 @@ func (obj *PkgRes) Init() error {
 		return err
 	}
 
-	bus := packagekit.NewBus()
-	if bus == nil {
-		return fmt.Errorf("can't connect to PackageKit bus")
-	}
-	defer bus.Close()
-
-	result, err := obj.pkgMappingHelper(bus)
-	if err != nil {
-		return errwrap.Wrapf(err, "the pkgMappingHelper failed")
+	if obj.fileList == nil {
+		if err := obj.populateFileList(); err != nil {
+			return errwrap.Wrapf(err, "error populating file list in init")
+		}
 	}
 
-	data, ok := result[obj.Name] // lookup single package (init does just one)
-	// package doesn't exist, this is an error!
-	if !ok || !data.Found {
-		return fmt.Errorf("can't find package named '%s'", obj.Name)
-	}
-
-	packageIDs := []string{data.PackageID} // just one for now
-	filesMap, err := bus.GetFilesByPackageID(packageIDs)
-	if err != nil {
-		return errwrap.Wrapf(err, "can't run GetFilesByPackageID")
-	}
-	if files, ok := filesMap[data.PackageID]; ok {
-		obj.fileList = util.DirifyFileList(files, false)
-	}
 	return nil
 }
 
@@ -223,6 +204,39 @@ func (obj *PkgRes) pkgMappingHelper(bus *packagekit.Conn) (map[string]*packageki
 	return result, nil
 }
 
+// populateFileList fills in the fileList structure with what is in the package.
+// TODO: should this work properly if pkg has been autogrouped ?
+func (obj *PkgRes) populateFileList() error {
+
+	bus := packagekit.NewBus()
+	if bus == nil {
+		return fmt.Errorf("can't connect to PackageKit bus")
+	}
+	defer bus.Close()
+
+	result, err := obj.pkgMappingHelper(bus)
+	if err != nil {
+		return errwrap.Wrapf(err, "the pkgMappingHelper failed")
+	}
+
+	data, ok := result[obj.Name] // lookup single package (init does just one)
+	// package doesn't exist, this is an error!
+	if !ok || !data.Found {
+		return fmt.Errorf("can't find package named '%s'", obj.Name)
+	}
+
+	packageIDs := []string{data.PackageID} // just one for now
+	filesMap, err := bus.GetFilesByPackageID(packageIDs)
+	if err != nil {
+		return errwrap.Wrapf(err, "can't run GetFilesByPackageID")
+	}
+	if files, ok := filesMap[data.PackageID]; ok {
+		obj.fileList = util.DirifyFileList(files, false)
+	}
+
+	return nil
+}
+
 // CheckApply checks the resource state and applies the resource if the bool
 // input is true. It returns error info and if the state check passed or not.
 func (obj *PkgRes) CheckApply(apply bool) (checkOK bool, err error) {
@@ -419,10 +433,16 @@ func (obj *PkgResAutoEdges) Test(input []bool) bool {
 
 // AutoEdges produces an object which generates a minimal pkg file optimization
 // sequence of edges.
-func (obj *PkgRes) AutoEdges() AutoEdge {
+func (obj *PkgRes) AutoEdges() (AutoEdge, error) {
 	// in contrast with the FileRes AutoEdges() function which contains
 	// more of the mechanics, most of the AutoEdge mechanics for the PkgRes
-	// is contained in the Test() method! This design is completely okay!
+	// are contained in the Test() method! This design is completely okay!
+
+	if obj.fileList == nil {
+		if err := obj.populateFileList(); err != nil {
+			return nil, errwrap.Wrapf(err, "error populating file list for automatic edges")
+		}
+	}
 
 	// add matches for any svc resources found in pkg definition!
 	var svcUIDs []ResUID
@@ -444,7 +464,7 @@ func (obj *PkgRes) AutoEdges() AutoEdge {
 		testIsNext: false,         // start with Next() call
 		name:       obj.GetName(), // save data for PkgResAutoEdges obj
 		kind:       obj.GetKind(),
-	}
+	}, nil
 }
 
 // UIDs includes all params to make a unique identification of this object.
@@ -511,25 +531,6 @@ func (obj *PkgRes) Compare(r Res) bool {
 	return true
 }
 
-// ReturnSvcInFileList returns a list of svc names for matches like: `/usr/lib/systemd/system/*.service`.
-func ReturnSvcInFileList(fileList []string) []string {
-	result := []string{}
-	for _, x := range fileList {
-		dirname, basename := path.Split(path.Clean(x))
-		// TODO: do we also want to look for /etc/systemd/system/ ?
-		if dirname != "/usr/lib/systemd/system/" {
-			continue
-		}
-		if !strings.HasSuffix(basename, ".service") {
-			continue
-		}
-		if s := strings.TrimSuffix(basename, ".service"); !util.StrInList(s, result) {
-			result = append(result, s)
-		}
-	}
-	return result
-}
-
 // UnmarshalYAML is the custom unmarshal handler for this struct.
 // It is primarily useful for setting the defaults.
 func (obj *PkgRes) UnmarshalYAML(unmarshal func(interface{}) error) error {
@@ -549,3 +550,22 @@ func (obj *PkgRes) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	*obj = PkgRes(raw) // restore from indirection with type conversion!
 	return nil
 }
+
+// ReturnSvcInFileList returns a list of svc names for matches like: `/usr/lib/systemd/system/*.service`.
+func ReturnSvcInFileList(fileList []string) []string {
+	result := []string{}
+	for _, x := range fileList {
+		dirname, basename := path.Split(path.Clean(x))
+		// TODO: do we also want to look for /etc/systemd/system/ ?
+		if dirname != "/usr/lib/systemd/system/" {
+			continue
+		}
+		if !strings.HasSuffix(basename, ".service") {
+			continue
+		}
+		if s := strings.TrimSuffix(basename, ".service"); !util.StrInList(s, result) {
+			result = append(result, s)
+		}
+	}
+	return result
+}