Add ability to use image previewers (#531)

* Return early on error in nav.preview

* nav.checkReg now returns a boolean instead of calling nav.preview

* Pass width, height, x, and y parameters to preview script

* Check previewer for exit code

If non-zero the preview will be assumed to have side-effects.

* Add the cleaner option

This is called upon selection changes if the previous preview was
volatile. To this end, volatilePreview was added to the nav struct

app.go

@@ -213,6 +213,8 @@ func (app *app) loop() {
 				continue
 			}
 
+			go app.nav.previewClear()
+
 			log.Print("bye!")
 
 			if err := app.writeHistory(); err != nil {
@@ -310,7 +312,10 @@ func (app *app) loop() {
 
 			app.ui.draw(app.nav)
 		case r := <-app.nav.regChan:
-			app.nav.checkReg(r)
+			if app.nav.checkReg(r) {
+				win := app.ui.wins[len(app.ui.wins)-1]
+				go app.nav.preview(r.path, win)
+			}
 
 			app.nav.regCache[r.path] = r
 
@@ -402,6 +407,7 @@ func (app *app) runShell(s string, args []string, prefix string) {
 		cmd.Stdout = os.Stdout
 		cmd.Stderr = os.Stderr
 
+		go app.nav.previewClear()
 		app.ui.pause()
 		defer app.ui.resume()
 		defer app.nav.renew()

complete.go

@@ -131,6 +131,7 @@ var (
 		"ifs",
 		"info",
 		"previewer",
+		"cleaner",
 		"promptfmt",
 		"ratios",
 		"shell",

doc.go

@@ -118,6 +118,7 @@ The following options can be used to customize the behavior of lf:
     period         int       (default 0)
     preview        bool      (default on)
     previewer      string    (default '')
+    cleaner        string    (default '')
     promptfmt      string    (default "\033[32;1m%u@%h\033[0m:\033[34;1m%w\033[0m\033[1m%f\033[0m")
     ratios         []int     (default '1:2:3')
     relativenumber bool      (default off)
@@ -591,10 +592,17 @@ Files containing the null character (U+0000) in the read portion are considered
 
 Set the path of a previewer file to filter the content of regular files for previewing.
 The file should be executable.
-Two arguments are passed to the file, first is the current file name, and second is the height of preview pane.
+Five arguments are passed to the file, first is the current file name; the second, third, fourth, and fifth are height, width, horizontal position, and vertical position of preview pane respectively.
 SIGPIPE signal is sent when enough lines are read.
+If the previewer returns a non-zero exit code, then the preview cache for the given file is disabled. This means that if the file is selected in the future, the previewer is called once again.
 Preview filtering is disabled and files are displayed as they are when the value of this option is left empty.
 
+    cleaner        string    (default '') (not called if empty)
+
+Set the path of a cleaner file. This file will be called if previewing is enabled, the previewer is set, and the previously selected file had its preview cache disabled.
+The file should be executable.
+Preview clearing is disabled when the value of this option is left empty.
+
     promptfmt      string    (default "\033[32;1m%u@%h\033[0m:\033[34;1m%w/\033[0m\033[1m%f\033[0m")
 
 Format string of the prompt shown in the top line.

docstring.go

@@ -121,6 +121,7 @@ The following options can be used to customize the behavior of lf:
     period         int       (default 0)
     preview        bool      (default on)
     previewer      string    (default '')
+    cleaner        string    (default '')
     promptfmt      string    (default "\033[32;1m%u@%h\033[0m:\033[34;1m%w\033[0m\033[1m%f\033[0m")
     ratios         []int     (default '1:2:3')
     relativenumber bool      (default off)
@@ -624,11 +625,21 @@ binary files and displayed as 'binary'.
     previewer      string    (default '') (not filtered if empty)
 
 Set the path of a previewer file to filter the content of regular files for
-previewing. The file should be executable. Two arguments are passed to the
+previewing. The file should be executable. Five arguments are passed to the
-file, first is the current file name, and second is the height of preview
+file, first is the current file name; the second, third, fourth, and fifth
-pane. SIGPIPE signal is sent when enough lines are read. Preview filtering
+are height, width, horizontal position, and vertical position of preview
-is disabled and files are displayed as they are when the value of this
+pane respectively. SIGPIPE signal is sent when enough lines are read. If the
-option is left empty.
+previewer returns a non-zero exit code, then the preview cache for the given
+file is disabled. This means that if the file is selected in the future, the
+previewer is called once again. Preview filtering is disabled and files are
+displayed as they are when the value of this option is left empty.
+
+    cleaner        string    (default '') (not called if empty)
+
+Set the path of a cleaner file. This file will be called if previewing is
+enabled, the previewer is set, and the previously selected file had its
+preview cache disabled. The file should be executable. Preview clearing is
+disabled when the value of this option is left empty.
 
     promptfmt      string    (default "\033[32;1m%u@%h\033[0m:\033[34;1m%w/\033[0m\033[1m%f\033[0m")
 

eval.go

@@ -263,6 +263,8 @@ func (e *setExpr) eval(app *app, args []string) {
 		gOpts.info = toks
 	case "previewer":
 		gOpts.previewer = replaceTilde(e.val)
+	case "cleaner":
+		gOpts.cleaner = replaceTilde(e.val)
 	case "promptfmt":
 		gOpts.promptfmt = e.val
 	case "ratios":

lf.1

@@ -132,6 +132,7 @@ The following options can be used to customize the behavior of lf:
     period         int       (default 0)
     preview        bool      (default on)
     previewer      string    (default '')
+    cleaner        string    (default '')
     promptfmt      string    (default "\e033[32;1m%u@%h\e033[0m:\e033[34;1m%w\e033[0m\e033[1m%f\e033[0m")
     ratios         []int     (default '1:2:3')
     relativenumber bool      (default off)
@@ -712,7 +713,13 @@ Show previews of files and directories at the right most pane. If the file has m
     previewer      string    (default '') (not filtered if empty)
 .EE
 .PP
-Set the path of a previewer file to filter the content of regular files for previewing. The file should be executable. Two arguments are passed to the file, first is the current file name, and second is the height of preview pane. SIGPIPE signal is sent when enough lines are read. Preview filtering is disabled and files are displayed as they are when the value of this option is left empty.
+Set the path of a previewer file to filter the content of regular files for previewing. The file should be executable. Five arguments are passed to the file, first is the current file name; the second, third, fourth, and fifth are height, width, horizontal position, and vertical position of preview pane respectively. SIGPIPE signal is sent when enough lines are read. If the previewer returns a non-zero exit code, then the preview cache for the given file is disabled. This means that if the file is selected in the future, the previewer is called once again. Preview filtering is disabled and files are displayed as they are when the value of this option is left empty.
+.PP
+.EX
+    cleaner        string    (default '') (not called if empty)
+.EE
+.PP
+Set the path of a cleaner file. This file will be called if previewing is enabled, the previewer is set, and the previously selected file had its preview cache disabled. The file should be executable. Preview clearing is disabled when the value of this option is left empty.
 .PP
 .EX
     promptfmt      string    (default "\e033[32;1m%u@%h\e033[0m:\e033[34;1m%w/\e033[0m\e033[1m%f\e033[0m")

nav.go

@@ -302,6 +302,7 @@ type nav struct {
 	searchBack      bool
 	searchInd       int
 	searchPos       int
+	volatilePreview bool
 }
 
 func (nav *nav) loadDir(path string) *dir {
@@ -456,31 +457,51 @@ func (nav *nav) position() {
 	}
 }
 
-func (nav *nav) preview(path string) {
+func (nav *nav) preview(path string, win *win) {
 	reg := &reg{loadTime: time.Now(), path: path}
+	defer func() { nav.regChan <- reg }()
 
 	var reader io.Reader
 
 	if len(gOpts.previewer) != 0 {
 		exportOpts()
-		cmd := exec.Command(gOpts.previewer, path, strconv.Itoa(nav.height))
+		cmd := exec.Command(gOpts.previewer, path,
+			strconv.Itoa(win.w),
+			strconv.Itoa(win.h),
+			strconv.Itoa(win.x),
+			strconv.Itoa(win.y))
 
 		out, err := cmd.StdoutPipe()
 		if err != nil {
 			log.Printf("previewing file: %s", err)
+			return
 		}
 
 		if err := cmd.Start(); err != nil {
 			log.Printf("previewing file: %s", err)
+			out.Close()
+			return
 		}
 
-		defer cmd.Wait()
+		defer func() {
+			if err := cmd.Wait(); err != nil {
+				if e, ok := err.(*exec.ExitError); ok {
+					if e.ExitCode() != 0 {
+						nav.volatilePreview = true
+						reg.volatile = true
+					}
+				} else {
+					log.Printf("loading file: %s", err)
+				}
+			}
+		}()
 		defer out.Close()
 		reader = out
 	} else {
 		f, err := os.Open(path)
 		if err != nil {
 			log.Printf("opening file: %s", err)
+			return
 		}
 
 		defer f.Close()
@@ -489,11 +510,10 @@ func (nav *nav) preview(path string) {
 
 	buf := bufio.NewScanner(reader)
 
-	for i := 0; i < nav.height && buf.Scan(); i++ {
+	for i := 0; i < win.h && buf.Scan(); i++ {
 		for _, r := range buf.Text() {
 			if r == 0 {
 				reg.lines = []string{"\033[7mbinary\033[0m"}
-				nav.regChan <- reg
 				return
 			}
 		}
@@ -503,28 +523,39 @@ func (nav *nav) preview(path string) {
 	if buf.Err() != nil {
 		log.Printf("loading file: %s", buf.Err())
 	}
-
-	nav.regChan <- reg
 }
 
-func (nav *nav) loadReg(path string) *reg {
+func (nav *nav) previewClear() {
+	if len(gOpts.cleaner) != 0 && nav.volatilePreview {
+		nav.volatilePreview = false
+
+		cmd := exec.Command(gOpts.cleaner)
+		if err := cmd.Run(); err != nil {
+			log.Printf("cleaning preview: %s", err)
+		}
+	}
+}
+
+func (nav *nav) loadReg(path string, win *win) *reg {
 	r, ok := nav.regCache[path]
-	if !ok {
+	if !ok || r.volatile {
-		r := &reg{loading: true, loadTime: time.Now(), path: path}
+		r := &reg{loading: true, loadTime: time.Now(), path: path, volatile: true}
 		nav.regCache[path] = r
-		go nav.preview(path)
+		go nav.preview(path, win)
 		return r
 	}
 
-	nav.checkReg(r)
+	if nav.checkReg(r) {
+		go nav.preview(path, win)
+	}
 
 	return r
 }
 
-func (nav *nav) checkReg(reg *reg) {
+func (nav *nav) checkReg(reg *reg) bool {
 	s, err := os.Stat(reg.path)
 	if err != nil {
-		return
+		return false
 	}
 
 	now := time.Now()
@@ -532,13 +563,15 @@ func (nav *nav) checkReg(reg *reg) {
 	// XXX: Linux builtin exFAT drivers are able to predict modifications in the future
 	// https://bugs.launchpad.net/ubuntu/+source/ubuntu-meta/+bug/1872504
 	if s.ModTime().After(now) {
-		return
+		return false
 	}
 
 	if s.ModTime().After(reg.loadTime) {
 		reg.loadTime = now
-		go nav.preview(reg.path)
+		return true
 	}
+
+	return false
 }
 
 func (nav *nav) sort() {

opts.go

@@ -51,6 +51,7 @@ var gOpts struct {
 	filesep        string
 	ifs            string
 	previewer      string
+	cleaner        string
 	promptfmt      string
 	shell          string
 	timefmt        string
@@ -89,6 +90,7 @@ func init() {
 	gOpts.filesep = "\n"
 	gOpts.ifs = ""
 	gOpts.previewer = ""
+	gOpts.cleaner = ""
 	gOpts.promptfmt = "\033[32;1m%u@%h\033[0m:\033[34;1m%w\033[0m\033[1m%f\033[0m"
 	gOpts.shell = gDefaultShell
 	gOpts.timefmt = time.ANSIC

ui.go

@@ -609,6 +609,7 @@ func (ui *ui) echoerrf(format string, a ...interface{}) {
 
 type reg struct {
 	loading  bool
+	volatile bool
 	loadTime time.Time
 	path     string
 	lines    []string
@@ -624,10 +625,12 @@ func (ui *ui) loadFile(nav *nav) {
 		return
 	}
 
+	go nav.previewClear()
 	if curr.IsDir() {
 		ui.dirPrev = nav.loadDir(curr.path)
 	} else if curr.Mode().IsRegular() {
-		ui.regPrev = nav.loadReg(curr.path)
+		win := ui.wins[len(ui.wins)-1]
+		ui.regPrev = nav.loadReg(curr.path, win)
 	}
 }