add a lookup for workers

events/registry/registry.go

@@ -28,6 +28,7 @@ var (
 
 	ErrRegistryUninitialized         = errors.New("controller registry uninitialized")
 	ErrRegistryPreviouslyInitialized = errors.New("controller registry previously initialized")
+	ErrBadRegistryData               = errors.New("bad registry data")
 )
 
 func InitializeActiveControllerRegistry(njs *events.NatsJetstream) error {
@@ -91,3 +92,21 @@ func DeregisterController(id ControllerID) error {
 	}
 	return registry.Delete(id.String())
 }
+
+func LastContact(id ControllerID) (time.Time, error) {
+	var zt time.Time
+	if registry == nil {
+		return zt, ErrRegistryUninitialized
+	}
+	entry, err := registry.Get(id.String())
+	if err != nil {
+		return zt, err // this can either be a communication error or nats.ErrKeyNotFound
+	}
+	// if we have an entry the controller was alive in the last TTL period
+	var ar activityRecord
+	err = json.Unmarshal(entry.Value(), &ar)
+	if err != nil {
+		return zt, ErrBadRegistryData // consumers should *probably* treat this as a success?
+	}
+	return ar.LastActive, nil
+}

events/registry/registry_test.go

@@ -4,6 +4,7 @@ package registry
 import (
 	"testing"
 
+	"github.com/nats-io/nats.go"
 	"github.com/stretchr/testify/require"
 
 	"go.hollow.sh/toolbox/events"
@@ -24,6 +25,9 @@ func TestAppLifecycle(t *testing.T) {
 	err = DeregisterController(id)
 	require.Error(t, err)
 	require.Equal(t, ErrRegistryUninitialized, err)
+	_, err = LastContact(id)
+	require.Error(t, err)
+	require.Equal(t, ErrRegistryUninitialized, err)
 
 	//OK, now let's get serious
 	srv := kvTest.StartJetStreamServer(t)
@@ -43,6 +47,11 @@ func TestAppLifecycle(t *testing.T) {
 	require.NoError(t, err)
 	err = ControllerCheckin(id)
 	require.NoError(t, err)
+	_, err = LastContact(id)
+	require.NoError(t, err)
 	err = DeregisterController(id)
 	require.NoError(t, err)
+	_, err = LastContact(id)
+	require.Error(t, err)
+	require.ErrorIs(t, err, nats.ErrKeyNotFound)
 }

events/registry/types.go

@@ -1,12 +1,19 @@
+// nolint: wsl // it's useless
 package registry
 
 import (
+	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"github.com/google/uuid"
 )
 
+var (
+	ErrBadFormat = errors.New("bad worker id format")
+)
+
 type ControllerID interface {
 	fmt.Stringer
 	updateVersion(uint64)
@@ -23,6 +30,21 @@ func (id *workerUUID) String() string {
 	return id.appName + "/" + id.uuid.String()
 }
 
+func ControllerIDFromString(s string) (ControllerID, error) {
+	name, uuidStr, found := strings.Cut(s, "/")
+	if !found {
+		return nil, fmt.Errorf("%w: missing delimiter", ErrBadFormat)
+	}
+	uuid, err := uuid.Parse(uuidStr)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %s", ErrBadFormat, err.Error())
+	}
+	return &workerUUID{
+		appName: name,
+		uuid:    uuid,
+	}, nil
+}
+
 func (id *workerUUID) updateVersion(rev uint64) {
 	id.kvVersion = rev
 }

events/registry/types_test.go

@@ -1,8 +1,10 @@
+//nolint:all // it's a test
 package registry
 
 import (
 	"testing"
 
+	"github.com/google/uuid"
 	"github.com/stretchr/testify/require"
 )
 
@@ -14,4 +16,17 @@ func TestWorkerID(t *testing.T) {
 	id2 := GetID("myAppName")
 	require.NotNil(t, id2)
 	require.NotEqual(t, id.String(), id2.String())
+
+	idStr := id.String()
+
+	reconstituted, err := ControllerIDFromString(idStr)
+	require.NoError(t, err)
+	require.Equal(t, id.(*workerUUID).appName, reconstituted.(*workerUUID).appName)
+	require.Equal(t, id.(*workerUUID).uuid, reconstituted.(*workerUUID).uuid)
+
+	_, err = ControllerIDFromString(uuid.New().String())
+	require.ErrorIs(t, err, ErrBadFormat, "no slash in name")
+
+	_, err = ControllerIDFromString("app-name/bogus")
+	require.ErrorIs(t, err, ErrBadFormat, "bogus uuid")
 }