Improve backup system

This commit introduces several improvements to the backup system.

* Backups are made every 8 seconds for buffers that have been modified
  since the last backup.

* The `permbackup` option allows users to specify that backups should
  be kept permanently.

* `The backupdir` option allows users to store backups in a custom
   directory.

Fixes #1641
Fixes #1536
Ref #1539 (removes possibility of race condition for backups)

internal/buffer/backup.go

@@ -28,29 +28,53 @@ The backup was created on %s, and the file is
 
 Options: [r]ecover, [i]gnore: `
 
+var backupRequestChan chan *Buffer
+
+func backupThread() {
+	for {
+		time.Sleep(time.Second * 8)
+
+		for len(backupRequestChan) > 0 {
+			b := <-backupRequestChan
+			b.Backup()
+		}
+	}
+}
+
+func init() {
+	backupRequestChan = make(chan *Buffer, 10)
+
+	go backupThread()
+}
+
+func (b *Buffer) RequestBackup() {
+	if !b.requestedBackup {
+		select {
+		case backupRequestChan <- b:
+		default:
+			// channel is full
+		}
+		b.requestedBackup = true
+	}
+}
+
 // Backup saves the current buffer to ConfigDir/backups
-func (b *Buffer) Backup(checkTime bool) error {
+func (b *Buffer) Backup() error {
 	if !b.Settings["backup"].(bool) || b.Path == "" || b.Type != BTDefault {
 		return nil
 	}
 
-	if checkTime {
-		sub := time.Now().Sub(b.lastbackup)
-		if sub < time.Duration(backupTime)*time.Millisecond {
-			return nil
-		}
+	backupdir, err := util.ReplaceHome(b.Settings["backupdir"].(string))
+	if len(backupdir) == 0 || err != nil {
+		backupdir = filepath.Join(config.ConfigDir, "backups")
 	}
-
-	b.lastbackup = time.Now()
-
-	backupdir := filepath.Join(config.ConfigDir, "backups")
 	if _, err := os.Stat(backupdir); os.IsNotExist(err) {
 		os.Mkdir(backupdir, os.ModePerm)
 	}
 
 	name := filepath.Join(backupdir, util.EscapePath(b.AbsPath))
 
-	err := overwriteFile(name, encoding.Nop, func(file io.Writer) (e error) {
+	err = overwriteFile(name, encoding.Nop, func(file io.Writer) (e error) {
 		if len(b.lines) == 0 {
 			return
 		}
@@ -74,12 +98,14 @@ func (b *Buffer) Backup(checkTime bool) error {
 		return
 	}, false)
 
+	b.requestedBackup = false
+
 	return err
 }
 
 // RemoveBackup removes any backup file associated with this buffer
 func (b *Buffer) RemoveBackup() {
-	if !b.Settings["backup"].(bool) || b.Path == "" || b.Type != BTDefault {
+	if !b.Settings["backup"].(bool) || b.Settings["permbackup"].(bool) || b.Path == "" || b.Type != BTDefault {
 		return
 	}
 	f := filepath.Join(config.ConfigDir, "backups", util.EscapePath(b.AbsPath))
@@ -89,7 +115,7 @@ func (b *Buffer) RemoveBackup() {
 // ApplyBackup applies the corresponding backup file to this buffer (if one exists)
 // Returns true if a backup was applied
 func (b *Buffer) ApplyBackup(fsize int64) bool {
-	if b.Settings["backup"].(bool) && len(b.Path) > 0 && b.Type == BTDefault {
+	if b.Settings["backup"].(bool) && !b.Settings["permbackup"].(bool) && len(b.Path) > 0 && b.Type == BTDefault {
 		backupfile := filepath.Join(config.ConfigDir, "backups", util.EscapePath(b.AbsPath))
 		if info, err := os.Stat(backupfile); err == nil {
 			backup, err := os.Open(backupfile)

internal/buffer/buffer.go

@@ -102,9 +102,7 @@ type SharedBuffer struct {
 	diffLock          sync.RWMutex
 	diff              map[int]DiffStatus
 
-	// counts the number of edits
-	// resets every backupTime edits
-	lastbackup time.Time
+	requestedBackup bool
 
 	// ReloadDisabled allows the user to disable reloads if they
 	// are viewing a file that is constantly changing
@@ -271,6 +269,7 @@ func NewBuffer(r io.Reader, size int64, path string, startcursor Loc, btype BufT
 		}
 	}
 
+	hasBackup := false
 	if !found {
 		b.SharedBuffer = new(SharedBuffer)
 		b.Type = btype
@@ -293,7 +292,7 @@ func NewBuffer(r io.Reader, size int64, path string, startcursor Loc, btype BufT
 			b.Settings["encoding"] = "utf-8"
 		}
 
-		hasBackup := b.ApplyBackup(size)
+		hasBackup = b.ApplyBackup(size)
 
 		if !hasBackup {
 			reader := bufio.NewReader(transform.NewReader(r, enc.NewDecoder()))
@@ -356,7 +355,9 @@ func NewBuffer(r io.Reader, size int64, path string, startcursor Loc, btype BufT
 		if size > LargeFileThreshold {
 			// If the file is larger than LargeFileThreshold fastdirty needs to be on
 			b.Settings["fastdirty"] = true
-		} else {
+		} else if !hasBackup {
+			// since applying a backup does not save the applied backup to disk, we should
+			// not calculate the original hash based on the backup data
 			calcHash(b, &b.origHash)
 		}
 	}
@@ -425,7 +426,7 @@ func (b *Buffer) Insert(start Loc, text string) {
 		b.EventHandler.active = b.curCursor
 		b.EventHandler.Insert(start, text)
 
-		go b.Backup(true)
+		b.RequestBackup()
 	}
 }
 
@@ -436,7 +437,7 @@ func (b *Buffer) Remove(start, end Loc) {
 		b.EventHandler.active = b.curCursor
 		b.EventHandler.Remove(start, end)
 
-		go b.Backup(true)
+		b.RequestBackup()
 	}
 }
 

internal/config/settings.go

@@ -247,6 +247,7 @@ var defaultCommonSettings = map[string]interface{}{
 	"autoindent":     true,
 	"autosu":         false,
 	"backup":         true,
+	"backupdir":      "",
 	"basename":       false,
 	"colorcolumn":    float64(0),
 	"cursorline":     true,
@@ -261,6 +262,7 @@ var defaultCommonSettings = map[string]interface{}{
 	"keepautoindent": false,
 	"matchbrace":     true,
 	"mkparents":      false,
+	"permbackup":     false,
 	"readonly":       false,
 	"rmtrailingws":   false,
 	"ruler":          true,