feat: initial commit

internal/agent/controller/persistence/controller.go

@@ -0,0 +1,218 @@
+package persistence
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"forge.cadoles.com/Cadoles/emissary/internal/agent"
+	"forge.cadoles.com/Cadoles/emissary/internal/spec"
+	"github.com/pkg/errors"
+	"gitlab.com/wpetit/goweb/logger"
+)
+
+type Controller struct {
+	trackedSpecRevisions map[spec.Name]int
+	filename             string
+	loaded               bool
+}
+
+// Name implements node.Controller.
+func (c *Controller) Name() string {
+	return "persistence-controller"
+}
+
+// Reconcile implements node.Controller.
+func (c *Controller) Reconcile(ctx context.Context, state *agent.State) error {
+	specs := state.Specs()
+	changed := c.specChanged(state.Specs())
+
+	switch {
+	// If first cycle, load state from file system
+	case !c.loaded:
+		logger.Info(ctx, "first cycle, loading state", logger.F("stateFile", c.filename))
+
+		if err := c.loadState(ctx, state); err != nil {
+			if errors.Is(err, os.ErrNotExist) {
+				logger.Info(ctx, "state file not found", logger.F("stateFile", c.filename))
+
+				c.loaded = true
+
+				return nil
+			}
+
+			return errors.WithStack(err)
+		}
+
+		c.trackSpecsRevisions(specs)
+
+		c.loaded = true
+
+		return nil
+
+		// If specs did not change, return
+	case !changed:
+		logger.Info(ctx, "no changes detected, doing nothing")
+
+		return nil
+
+	// If specs has changed, save it
+	case changed:
+		logger.Info(ctx, "saving state", logger.F("stateFile", c.filename))
+
+		if err := c.writeState(ctx, state); err != nil {
+			return errors.WithStack(err)
+		}
+
+		c.trackSpecsRevisions(specs)
+	}
+
+	return nil
+}
+
+func (c *Controller) specChanged(specs agent.Specs) bool {
+	if len(specs) != len(c.trackedSpecRevisions) {
+		return true
+	}
+
+	for name, spec := range specs {
+		trackedRevision, exists := c.trackedSpecRevisions[name]
+		if !exists {
+			return true
+		}
+
+		if trackedRevision != spec.SpecRevision() {
+			return true
+		}
+	}
+
+	for trackedSpecName, trackedRevision := range c.trackedSpecRevisions {
+		spec, exists := specs[trackedSpecName]
+		if !exists {
+			return true
+		}
+
+		if trackedRevision != spec.SpecRevision() {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (c *Controller) trackSpecsRevisions(specs agent.Specs) {
+	c.trackedSpecRevisions = make(map[spec.Name]int)
+
+	for name, spec := range specs {
+		c.trackedSpecRevisions[name] = spec.SpecRevision()
+	}
+}
+
+func (c *Controller) loadState(ctx context.Context, state *agent.State) error {
+	data, err := ioutil.ReadFile(c.filename)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	if err := json.Unmarshal(data, state); err != nil {
+		return errors.WithStack(err)
+	}
+
+	return nil
+}
+
+func (c *Controller) writeState(ctx context.Context, state *agent.State) error {
+	dir, file := filepath.Split(c.filename)
+	if dir == "" {
+		dir = "."
+	}
+
+	f, err := ioutil.TempFile(dir, file)
+	if err != nil {
+		return errors.Errorf("cannot create temp file: %v", err)
+	}
+
+	defer func() {
+		if err == nil {
+			return
+		}
+
+		if err := os.Remove(f.Name()); err != nil {
+			if errors.Is(err, os.ErrNotExist) {
+				return
+			}
+
+			logger.Error(ctx, "could not remove temporary file", logger.E(errors.WithStack(err)))
+		}
+	}()
+
+	defer func() {
+		if err := f.Close(); err != nil {
+			if errors.Is(err, os.ErrClosed) {
+				return
+			}
+
+			logger.Error(ctx, "could not close temporary file", logger.E(errors.WithStack(err)))
+		}
+	}()
+
+	data, err := json.Marshal(state)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+
+	name := f.Name()
+	if err := ioutil.WriteFile(name, data, os.ModePerm); err != nil {
+		return errors.Errorf("cannot write data to temporary file %q: %v", name, err)
+	}
+
+	if err := f.Sync(); err != nil {
+		return errors.Errorf("can't flush temporary file %q: %v", name, err)
+	}
+
+	if err := f.Close(); err != nil {
+		return errors.Errorf("can't close temporary file %q: %v", name, err)
+	}
+
+	// get the file mode from the original file and use that for the replacement
+	// file, too.
+	destInfo, err := os.Stat(c.filename)
+
+	switch {
+	case os.IsNotExist(err):
+		// Do nothing
+
+	case err != nil:
+		return errors.WithStack(err)
+
+	default:
+		sourceInfo, err := os.Stat(name)
+		if err != nil {
+			return errors.WithStack(err)
+		}
+
+		if sourceInfo.Mode() != destInfo.Mode() {
+			if err := os.Chmod(name, destInfo.Mode()); err != nil {
+				return fmt.Errorf("can't set filemode on temporary file %q: %v", name, err)
+			}
+		}
+	}
+
+	if err := os.Rename(name, c.filename); err != nil {
+		return fmt.Errorf("cannot replace %q with temporary file %q: %v", c.filename, name, err)
+	}
+
+	return nil
+}
+
+func NewController(filename string) *Controller {
+	return &Controller{
+		filename:             filename,
+		trackedSpecRevisions: make(map[spec.Name]int),
+	}
+}
+
+var _ agent.Controller = &Controller{}