chore: support ETag for providers

component/resource/fetcher.go

@@ -1,9 +1,7 @@
 package resource
 
 import (
-	"bytes"
 	"context"
-	"crypto/md5"
 	"os"
 	"path/filepath"
 	"time"
@@ -29,10 +27,10 @@ type Fetcher[V any] struct {
 	name         string
 	vehicle      types.Vehicle
 	updatedAt    time.Time
-	hash         [16]byte
+	hash         types.HashType
 	parser       Parser[V]
 	interval     time.Duration
-	OnUpdate     func(V)
+	onUpdate     func(V)
 	watcher      *fswatch.Watcher
 }
 
@@ -54,92 +52,63 @@ func (f *Fetcher[V]) UpdatedAt() time.Time {
 
 func (f *Fetcher[V]) Initial() (V, error) {
 	var (
-		buf         []byte
-		err         error
-		isLocal     bool
-		forceUpdate bool
+		buf      []byte
+		contents V
+		err      error
 	)
 
 	if stat, fErr := os.Stat(f.vehicle.Path()); fErr == nil {
+		// local file exists, use it first
 		buf, err = os.ReadFile(f.vehicle.Path())
 		modTime := stat.ModTime()
-		f.updatedAt = modTime
-		isLocal = true
-		if time.Since(modTime) > f.interval {
-			forceUpdate = true
+		contents, _, err = f.loadBuf(buf, types.MakeHash(buf), false)
+		f.updatedAt = modTime // reset updatedAt to file's modTime
+
+		if err == nil {
+			err = f.startPullLoop(time.Since(modTime) > f.interval)
+			if err != nil {
+				return lo.Empty[V](), err
+			}
+			return contents, nil
 		}
-	} else {
-		buf, err = f.vehicle.Read(f.ctx)
-		f.updatedAt = time.Now()
 	}
 
+	// parse local file error, fallback to remote
+	contents, _, err = f.Update()
+
 	if err != nil {
 		return lo.Empty[V](), err
 	}
-
-	contents, err := f.parser(buf)
+	err = f.startPullLoop(false)
 	if err != nil {
-		if !isLocal {
-			return lo.Empty[V](), err
-		}
-
-		// parse local file error, fallback to remote
-		buf, err = f.vehicle.Read(f.ctx)
-		if err != nil {
-			return lo.Empty[V](), err
-		}
-
-		contents, err = f.parser(buf)
-		if err != nil {
-			return lo.Empty[V](), err
-		}
-
-		isLocal = false
+		return lo.Empty[V](), err
 	}
-
-	if f.vehicle.Type() != types.File && !isLocal {
-		if err := safeWrite(f.vehicle.Path(), buf); err != nil {
-			return lo.Empty[V](), err
-		}
-	}
-
-	f.hash = md5.Sum(buf)
-
-	// pull contents automatically
-	if f.vehicle.Type() == types.File {
-		f.watcher, err = fswatch.NewWatcher(fswatch.Options{
-			Path:     []string{f.vehicle.Path()},
-			Direct:   true,
-			Callback: f.update,
-		})
-		if err != nil {
-			return lo.Empty[V](), err
-		}
-		err = f.watcher.Start()
-		if err != nil {
-			return lo.Empty[V](), err
-		}
-	} else if f.interval > 0 {
-		go f.pullLoop(forceUpdate)
-	}
-
 	return contents, nil
 }
 
 func (f *Fetcher[V]) Update() (V, bool, error) {
-	buf, err := f.vehicle.Read(f.ctx)
+	buf, hash, err := f.vehicle.Read(f.ctx, f.hash)
 	if err != nil {
 		return lo.Empty[V](), false, err
 	}
-	return f.SideUpdate(buf)
+	return f.loadBuf(buf, hash, f.vehicle.Type() != types.File)
 }
 
 func (f *Fetcher[V]) SideUpdate(buf []byte) (V, bool, error) {
+	return f.loadBuf(buf, types.MakeHash(buf), true)
+}
+
+func (f *Fetcher[V]) loadBuf(buf []byte, hash types.HashType, updateFile bool) (V, bool, error) {
 	now := time.Now()
-	hash := md5.Sum(buf)
-	if bytes.Equal(f.hash[:], hash[:]) {
+	if f.hash.Equal(hash) {
+		if updateFile {
+			_ = os.Chtimes(f.vehicle.Path(), now, now)
+		}
 		f.updatedAt = now
-		_ = os.Chtimes(f.vehicle.Path(), now, now)
+		return lo.Empty[V](), true, nil
+	}
+
+	if buf == nil { // f.hash has been changed between f.vehicle.Read but should not happen (cause by concurrent)
 		return lo.Empty[V](), true, nil
 	}
 
@@ -148,15 +117,18 @@ func (f *Fetcher[V]) SideUpdate(buf []byte) (V, bool, error) {
 		return lo.Empty[V](), false, err
 	}
 
-	if f.vehicle.Type() != types.File {
+	if updateFile {
 		if err = safeWrite(f.vehicle.Path(), buf); err != nil {
 			return lo.Empty[V](), false, err
 		}
 	}
-
 	f.updatedAt = now
 	f.hash = hash
 
+	if f.onUpdate != nil {
+		f.onUpdate(contents)
+	}
+
 	return contents, false, nil
 }
 
@@ -176,7 +148,7 @@ func (f *Fetcher[V]) pullLoop(forceUpdate bool) {
 
 	if forceUpdate {
 		log.Warnln("[Provider] %s not updated for a long time, force refresh", f.Name())
-		f.update(f.vehicle.Path())
+		f.updateWithLog()
 	}
 
 	timer := time.NewTimer(initialInterval)
@@ -185,15 +157,40 @@ func (f *Fetcher[V]) pullLoop(forceUpdate bool) {
 		select {
 		case <-timer.C:
 			timer.Reset(f.interval)
-			f.update(f.vehicle.Path())
+			f.updateWithLog()
 		case <-f.ctx.Done():
 			return
 		}
 	}
 }
 
-func (f *Fetcher[V]) update(path string) {
-	elm, same, err := f.Update()
+func (f *Fetcher[V]) startPullLoop(forceUpdate bool) (err error) {
+	// pull contents automatically
+	if f.vehicle.Type() == types.File {
+		f.watcher, err = fswatch.NewWatcher(fswatch.Options{
+			Path:     []string{f.vehicle.Path()},
+			Direct:   true,
+			Callback: f.updateCallback,
+		})
+		if err != nil {
+			return err
+		}
+		err = f.watcher.Start()
+		if err != nil {
+			return err
+		}
+	} else if f.interval > 0 {
+		go f.pullLoop(forceUpdate)
+	}
+	return
+}
+
+func (f *Fetcher[V]) updateCallback(path string) {
+	f.updateWithLog()
+}
+
+func (f *Fetcher[V]) updateWithLog() {
+	_, same, err := f.Update()
 	if err != nil {
 		log.Errorln("[Provider] %s pull error: %s", f.Name(), err.Error())
 		return
@@ -205,9 +202,7 @@ func (f *Fetcher[V]) update(path string) {
 	}
 
 	log.Infoln("[Provider] %s's content update", f.Name())
-	if f.OnUpdate != nil {
-		f.OnUpdate(elm)
-	}
+	return
 }
 
 func safeWrite(path string, buf []byte) error {
@@ -230,7 +225,7 @@ func NewFetcher[V any](name string, interval time.Duration, vehicle types.Vehicl
 		name:      name,
 		vehicle:   vehicle,
 		parser:    parser,
-		OnUpdate:  onUpdate,
+		onUpdate:  onUpdate,
 		interval:  interval,
 	}
 }