Problem: block repo did not serialize writes

Solution: serialize writes

block.go

@@ -25,23 +25,56 @@ import (
 )
 
 type BlockRepository interface {
-	Save(block Block) error
+	Save(id string, block Block) error
 	Load(id string) (Block, error)
 }
 
+type blockSaveMessage struct {
+	id    string
+	block Block
+}
+
 type blockRepo struct {
 	dirname string
+	saveC   chan blockSaveMessage
+	errC    chan error
 }
 
-func (br *blockRepo) Save(id string, block Block) error {
-	f, err := os.OpenFile(filepath.Join(br.dirname, BlocksDirectory, id), os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
-	defer f.Close()
+func saveBlock(dirname, id string, block Block) error {
+	f, err := os.OpenFile(filepath.Join(dirname, BlocksDirectory, id), os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
 	if err != nil {
 		return err
 	}
+	defer f.Close()
 	enc := json.NewEncoder(f)
 	enc.SetIndent("", "  ")
-	return enc.Encode(&block)
+	err = enc.Encode(&block)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func NewBlockRepo(dirname string) BlockRepository {
+	saveC := make(chan blockSaveMessage, 1)
+	errC := make(chan error)
+	go func() {
+		for msg := range saveC {
+			err := saveBlock(dirname, msg.id, msg.block)
+			errC <- err
+		}
+	}()
+	return &blockRepo{
+		dirname: dirname,
+		saveC:   saveC,
+		errC:    errC,
+	}
+}
+
+func (br *blockRepo) Save(id string, block Block) error {
+	br.saveC <- blockSaveMessage{id, block}
+	err := <-br.errC
+	return err
 }
 
 func (br *blockRepo) Load(id string) (Block, error) {

main.go

@@ -1064,6 +1064,7 @@ func main() {
 	}
 
 	mp = NewFilePages(dataDir, searchIndex)
+	repo := NewBlockRepo("data")
 
 	http.Handle("/auth/", &authHandler{})
 	http.HandleFunc("/api/block/view", wrapAuth(func(w http.ResponseWriter, r *http.Request) {
@@ -1081,7 +1082,6 @@ func main() {
 
 		id := r.URL.Query().Get("id")
 
-		repo := blockRepo{dirname: "data"}
 		block, err := repo.Load(id)
 		if err != nil {
 			http.Error(w, err.Error(), 500)
@@ -1165,7 +1165,6 @@ func main() {
 			http.Error(w, "missing id", 400)
 			return
 		}
-		repo := blockRepo{dirname: "data"}
 		block, err := repo.Load(id)
 		block.Text = r.Form.Get("text")
 		err = repo.Save(id, block)
@@ -1196,9 +1195,6 @@ func main() {
 			http.Error(w, "missing id", 400)
 			return
 		}
-		repo := blockRepo{
-			dirname: "data",
-		}
 		newBlock := Block{
 			Text:     r.Form.Get("text"),
 			Children: []string{},