feat: watch blueprint.yaml for update and auto resend

Add a file watcher that re-pushes the blueprint to the server whenever
the blueprint file is modified while Newt is running, matching the
reactive behavior of the Docker event monitor.


Former-commit-id: 025497138d

common.go

@@ -16,6 +16,7 @@ import (
 	"github.com/fosrl/newt/logger"
 	"github.com/fosrl/newt/proxy"
 	"github.com/fosrl/newt/websocket"
+	"github.com/fsnotify/fsnotify"
 	"golang.org/x/net/icmp"
 	"golang.org/x/net/ipv4"
 	"golang.zx2c4.com/wireguard/tun/netstack"
@@ -518,3 +519,61 @@ func sendBlueprint(client *websocket.Client) error {
 
 	return nil
 }
+
+func watchBlueprintFile(ctx context.Context, filePath string, send func() error) {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		logger.Error("blueprint watcher: failed to create: %v", err)
+		return
+	}
+	defer watcher.Close()
+
+	if err := watcher.Add(filePath); err != nil {
+		logger.Error("blueprint watcher: failed to watch %s: %v", filePath, err)
+		return
+	}
+
+	logger.Info("Watching blueprint file for changes: %s", filePath)
+
+	var debounce *time.Timer
+	scheduleSend := func() {
+		if debounce != nil {
+			debounce.Stop()
+		}
+		debounce = time.AfterFunc(500*time.Millisecond, func() {
+			logger.Info("Blueprint file changed, resending...")
+			if err := send(); err != nil {
+				logger.Error("blueprint watcher: resend failed: %v", err)
+			}
+		})
+	}
+
+	for {
+		select {
+		case <-ctx.Done():
+			if debounce != nil {
+				debounce.Stop()
+			}
+			return
+		case event, ok := <-watcher.Events:
+			if !ok {
+				return
+			}
+			switch {
+			case event.Has(fsnotify.Write) || event.Has(fsnotify.Create):
+				if event.Has(fsnotify.Create) {
+					_ = watcher.Add(filePath)
+				}
+				scheduleSend()
+			case event.Has(fsnotify.Remove) || event.Has(fsnotify.Rename):
+				_ = watcher.Add(filePath)
+				scheduleSend()
+			}
+		case err, ok := <-watcher.Errors:
+			if !ok {
+				return
+			}
+			logger.Error("blueprint watcher: %v", err)
+		}
+	}
+}

common_test.go

@@ -0,0 +1,146 @@
+package main
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+func TestWatchBlueprintFile_WriteTriggersSend(t *testing.T) {
+	f, err := os.CreateTemp(t.TempDir(), "blueprint-*.yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	var calls atomic.Int32
+	go watchBlueprintFile(ctx, f.Name(), func() error {
+		calls.Add(1)
+		return nil
+	})
+
+	time.Sleep(50 * time.Millisecond)
+
+	if err := os.WriteFile(f.Name(), []byte("content"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	time.Sleep(700 * time.Millisecond)
+
+	if calls.Load() != 1 {
+		t.Errorf("expected 1 send call, got %d", calls.Load())
+	}
+}
+
+func TestWatchBlueprintFile_DebounceCoalescesEvents(t *testing.T) {
+	f, err := os.CreateTemp(t.TempDir(), "blueprint-*.yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	var calls atomic.Int32
+	go watchBlueprintFile(ctx, f.Name(), func() error {
+		calls.Add(1)
+		return nil
+	})
+
+	time.Sleep(50 * time.Millisecond)
+
+	for i := 0; i < 5; i++ {
+		if err := os.WriteFile(f.Name(), []byte("change"), 0644); err != nil {
+			t.Fatal(err)
+		}
+		time.Sleep(50 * time.Millisecond)
+	}
+
+	time.Sleep(700 * time.Millisecond)
+
+	if calls.Load() != 1 {
+		t.Errorf("expected 1 send call after debounce, got %d", calls.Load())
+	}
+}
+
+func TestWatchBlueprintFile_ContextCancellationStops(t *testing.T) {
+	f, err := os.CreateTemp(t.TempDir(), "blueprint-*.yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+
+	done := make(chan struct{})
+	go func() {
+		watchBlueprintFile(ctx, f.Name(), func() error { return nil })
+		close(done)
+	}()
+
+	time.Sleep(50 * time.Millisecond)
+	cancel()
+
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Error("watchBlueprintFile did not exit after context cancellation")
+	}
+}
+
+func TestWatchBlueprintFile_AtomicWriteTriggersSend(t *testing.T) {
+	dir := t.TempDir()
+	target := filepath.Join(dir, "blueprint.yaml")
+	if err := os.WriteFile(target, []byte("initial"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	var calls atomic.Int32
+	go watchBlueprintFile(ctx, target, func() error {
+		calls.Add(1)
+		return nil
+	})
+
+	time.Sleep(50 * time.Millisecond)
+
+	tmp := filepath.Join(dir, "blueprint.yaml.tmp")
+	if err := os.WriteFile(tmp, []byte("updated"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Rename(tmp, target); err != nil {
+		t.Fatal(err)
+	}
+
+	time.Sleep(700 * time.Millisecond)
+
+	if calls.Load() < 1 {
+		t.Errorf("expected at least 1 send call after atomic write, got %d", calls.Load())
+	}
+}
+
+func TestWatchBlueprintFile_MissingFileReturnsGracefully(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	done := make(chan struct{})
+	go func() {
+		watchBlueprintFile(ctx, "/nonexistent/path/blueprint.yaml", func() error { return nil })
+		close(done)
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Error("watchBlueprintFile did not return for missing file")
+	}
+}

go.mod

@@ -41,6 +41,7 @@ require (
 	github.com/docker/go-connections v0.6.0 // indirect
 	github.com/docker/go-units v0.4.0 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/google/btree v1.1.3 // indirect

go.sum

@@ -26,6 +26,8 @@ github.com/docker/go-units v0.4.0 h1:3uh0PgVws3nIA0Q+MwDC8yjEPf9zjRfZZWXZYDct3Tw
 github.com/docker/go-units v0.4.0/go.mod h1:fgPhTUdO+D/Jk86RDLlptpiXQzgHJF7gydDDbaIK4Dk=
 github.com/felixge/httpsnoop v1.0.4 h1:NFTV2Zj1bL4mc9sqWACXbQFVBBg2W3GPvqp8/ESS2Wg=
 github.com/felixge/httpsnoop v1.0.4/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
+github.com/fsnotify/fsnotify v1.9.0 h1:2Ml+OJNzbYCTzsxtv8vKSFD9PbJjmhYF14k/jKC7S9k=
+github.com/fsnotify/fsnotify v1.9.0/go.mod h1:8jBTzvmWwFyi3Pb8djgCCO5IBqzKJ/Jwo8TRcHyHii0=
 github.com/gaissmai/bart v0.26.0 h1:xOZ57E9hJLBiQaSyeZa9wgWhGuzfGACgqp4BE77OkO0=
 github.com/gaissmai/bart v0.26.0/go.mod h1:GREWQfTLRWz/c5FTOsIw+KkscuFkIV5t8Rp7Nd1Td5c=
 github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=

main.go

@@ -1627,6 +1627,12 @@ persistent_keepalive_interval=5`, util.FixKey(privateKey.String()), util.FixKey(
 		}
 	}
 
+	if blueprintFile != "" {
+		go watchBlueprintFile(ctx, blueprintFile, func() error {
+			return sendBlueprint(client)
+		})
+	}
+
 	// Wait for context cancellation (from signal or service stop)
 	<-ctx.Done()