engine: resources: http: Recurse on Init and Watch

Make this resource handle sub-resources more powerfully.

engine/resources/http.go

@@ -32,6 +32,7 @@ import (
 
 	"github.com/purpleidea/mgmt/engine"
 	"github.com/purpleidea/mgmt/engine/traits"
+	"github.com/purpleidea/mgmt/pgraph"
 	"github.com/purpleidea/mgmt/util/errwrap"
 
 	securefilepath "github.com/cyphar/filepath-securejoin"
@@ -121,6 +122,7 @@ type HTTPServerRes struct {
 
 	// TODO: should we allow adding a list of one-of files directly here?
 
+	eventsChanMap map[engine.Res]chan error
 	interruptChan chan struct{}
 
 	conn     net.Listener
@@ -216,9 +218,62 @@ func (obj *HTTPServerRes) Init(init *engine.Init) error {
 
 	// NOTE: If we don't Init anything that's autogrouped, then it won't
 	// even get an Init call on it.
+
+	obj.eventsChanMap = make(map[engine.Res]chan error)
+
 	// TODO: should we do this in the engine? Do we want to decide it here?
 	for _, res := range obj.GetGroup() { // grouped elements
-		if err := res.Init(init); err != nil {
+		// NOTE: We build a new init, but it's not complete. We only add
+		// what we're planning to use, and we ignore the rest for now...
+		r := res // bind the variable!
+
+		obj.eventsChanMap[r] = make(chan error)
+		event := func() {
+			select {
+			case obj.eventsChanMap[r] <- nil:
+				// send!
+			}
+			// We don't do this here (why?) we instead read from the
+			// above channel and then send on multiplexedChan to the
+			// main loop, where it runs the obj.init.Event function.
+			//obj.init.Event() // notify engine of an event (this can block)
+		}
+
+		newInit := &engine.Init{
+			Program:  obj.init.Program,
+			Version:  obj.init.Version,
+			Hostname: obj.init.Hostname,
+
+			// Watch:
+			Running: event,
+			Event:   event,
+
+			// CheckApply:
+			Refresh: func() bool {
+				innerRes, ok := r.(engine.RefreshableRes)
+				if !ok {
+					panic("res does not support the Refreshable trait")
+				}
+				return innerRes.Refresh()
+			},
+			Send: engine.GenerateSendFunc(r),
+			Recv: engine.GenerateRecvFunc(r), // unused
+
+			FilteredGraph: func() (*pgraph.Graph, error) {
+				panic("FilteredGraph for HTTP not implemented")
+			},
+
+			Local: obj.init.Local,
+			World: obj.init.World,
+			//VarDir: obj.init.VarDir, // TODO: wrap this
+
+			Debug: obj.init.Debug,
+			Logf: func(format string, v ...interface{}) {
+				obj.init.Logf(r.String()+": "+format, v...)
+			},
+		}
+
+		if err := res.Init(newInit); err != nil {
 			return errwrap.Wrapf(err, "autogrouped Init failed")
 		}
 	}
@@ -268,14 +323,60 @@ func (obj *HTTPServerRes) Watch(ctx context.Context) error {
 		//MaxHeaderBytes: 1 << 20, XXX: should we add a param for this?
 	}
 
+	multiplexedChan := make(chan error)
+	defer close(multiplexedChan) // closes after everyone below us is finished
+
+	wg := &sync.WaitGroup{}
+	defer wg.Wait()
+
+	for _, r := range obj.GetGroup() { // grouped elements
+		res := r // optional in newer golang
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			defer close(obj.eventsChanMap[res]) // where Watch sends events
+			if err := res.Watch(ctx); err != nil {
+				select {
+				case multiplexedChan <- err:
+				case <-ctx.Done():
+				}
+			}
+		}()
+		// wait for Watch first Running() call or immediate error...
+		select {
+		case <-obj.eventsChanMap[res]: // triggers on start or on err...
+		}
+
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for {
+				var ok bool
+				var err error
+				select {
+				// receive
+				case err, ok = <-obj.eventsChanMap[res]:
+					if !ok {
+						return
+					}
+				}
+
+				// send (multiplex)
+				select {
+				case multiplexedChan <- err:
+				case <-ctx.Done():
+					return
+				}
+			}
+		}()
+	}
+	// we block until all the children are started first...
+
 	obj.init.Running() // when started, notify engine that we're running
 
 	var closeError error
 	closeSignal := make(chan struct{})
 
-	wg := &sync.WaitGroup{}
-	defer wg.Wait()
-
 	shutdownChan := make(chan struct{}) // server shutdown finished signal
 	wg.Add(1)
 	go func() {
@@ -336,6 +437,16 @@ func (obj *HTTPServerRes) Watch(ctx context.Context) error {
 			startupChan = nil
 			send = true
 
+		case err, ok := <-multiplexedChan:
+			if !ok { // shouldn't happen
+				multiplexedChan = nil
+				continue
+			}
+			if err != nil {
+				return err
+			}
+			send = true
+
 		case <-closeSignal: // something shut us down early
 			return closeError