lang: interfaces, funcs: Port Func API to new Stream signature

This removes the `Close() error` and replaces it with a more modern
Stream API that takes a context. This removes boilerplate and makes
integration with concurrent code easier. The only downside is that there
isn't an explicit cleanup step, but only one function was even using
that and it was possible to switch it to a defer in Stream.

This also renames the functions from polyfunc to just func which we
determine by API not naming.

lang/funcs/core/example/flipflop_fact.go

@@ -18,6 +18,7 @@
 package coreexample
 
 import (
+	"context"
 	"time"
 
 	"github.com/purpleidea/mgmt/lang/funcs/facts"
@@ -38,9 +39,8 @@ func init() {
 // and is not meant for serious computing. This would be better served by a flip
 // function which you could specify an interval for.
 type FlipFlopFact struct {
-	init      *facts.Init
-	value     bool
-	closeChan chan struct{}
+	init  *facts.Init
+	value bool
 }
 
 // String returns a simple name for this fact. This is needed so this struct can
@@ -65,12 +65,11 @@ func (obj *FlipFlopFact) Info() *facts.Info {
 // Init runs some startup code for this fact.
 func (obj *FlipFlopFact) Init(init *facts.Init) error {
 	obj.init = init
-	obj.closeChan = make(chan struct{})
 	return nil
 }
 
 // Stream returns the changing values that this fact has over time.
-func (obj *FlipFlopFact) Stream() error {
+func (obj *FlipFlopFact) Stream(ctx context.Context) error {
 	defer close(obj.init.Output) // always signal when we're done
 	// TODO: don't hard code 5 sec interval
 	ticker := time.NewTicker(time.Duration(5) * time.Second)
@@ -85,7 +84,7 @@ func (obj *FlipFlopFact) Stream() error {
 			startChan = nil // disable
 		case <-ticker.C: // received the timer event
 			// pass
-		case <-obj.closeChan:
+		case <-ctx.Done():
 			return nil
 		}
 
@@ -93,16 +92,10 @@ func (obj *FlipFlopFact) Stream() error {
 		case obj.init.Output <- &types.BoolValue{ // flip
 			V: obj.value,
 		}:
-		case <-obj.closeChan:
+		case <-ctx.Done():
 			return nil
 		}
 
 		obj.value = !obj.value // flip it
 	}
 }
-
-// Close runs some shutdown code for this fact and turns off the stream.
-func (obj *FlipFlopFact) Close() error {
-	close(obj.closeChan)
-	return nil
-}

lang/funcs/core/example/vumeter_func.go

@@ -59,8 +59,6 @@ type VUMeterFunc struct {
 	peak       float64
 
 	result *string // last calculated output
-
-	closeChan chan struct{}
 }
 
 // String returns a simple name for this function. This is needed so this struct
@@ -133,12 +131,11 @@ func (obj *VUMeterFunc) Info() *interfaces.Info {
 // Init runs some startup code for this function.
 func (obj *VUMeterFunc) Init(init *interfaces.Init) error {
 	obj.init = init
-	obj.closeChan = make(chan struct{})
 	return nil
 }
 
 // Stream returns the changing values that this func has over time.
-func (obj *VUMeterFunc) Stream() error {
+func (obj *VUMeterFunc) Stream(ctx context.Context) error {
 	defer close(obj.init.Output) // the sender closes
 	ticker := newTicker()
 	defer ticker.Stop()
@@ -222,7 +219,7 @@ func (obj *VUMeterFunc) Stream() error {
 			}
 			obj.result = &result // store new result
 
-		case <-obj.closeChan:
+		case <-ctx.Done():
 			return nil
 		}
 
@@ -230,18 +227,12 @@ func (obj *VUMeterFunc) Stream() error {
 		case obj.init.Output <- &types.StrValue{
 			V: *obj.result,
 		}:
-		case <-obj.closeChan:
+		case <-ctx.Done():
 			return nil
 		}
 	}
 }
 
-// Close runs some shutdown code for this function and turns off the stream.
-func (obj *VUMeterFunc) Close() error {
-	close(obj.closeChan)
-	return nil
-}
-
 func newTicker() *time.Ticker {
 	return time.NewTicker(time.Duration(1) * time.Second)
 }