package termstatus import ( "bufio" "bytes" "context" "fmt" "io" "os" "strings" "golang.org/x/crypto/ssh/terminal" "golang.org/x/text/width" ) // Terminal is used to write messages and display status lines which can be // updated. When the output is redirected to a file, the status lines are not // printed. type Terminal struct { wr *bufio.Writer fd uintptr errWriter io.Writer buf *bytes.Buffer msg chan message status chan status canUpdateStatus bool // will be closed when the goroutine which runs Run() terminates, so it'll // yield a default value immediately closed chan struct{} clearCurrentLine func(io.Writer, uintptr) moveCursorUp func(io.Writer, uintptr, int) } type message struct { line string err bool } type status struct { lines []string } type fder interface { Fd() uintptr } // New returns a new Terminal for wr. A goroutine is started to update the // terminal. It is terminated when ctx is cancelled. When wr is redirected to // a file (e.g. via shell output redirection) or is just an io.Writer (not the // open *os.File for stdout), no status lines are printed. The status lines and // normal output (via Print/Printf) are written to wr, error messages are // written to errWriter. If disableStatus is set to true, no status messages // are printed even if the terminal supports it. func New(wr io.Writer, errWriter io.Writer, disableStatus bool) *Terminal { t := &Terminal{ wr: bufio.NewWriter(wr), errWriter: errWriter, buf: bytes.NewBuffer(nil), msg: make(chan message), status: make(chan status), closed: make(chan struct{}), } if disableStatus { return t } if d, ok := wr.(fder); ok && canUpdateStatus(d.Fd()) { // only use the fancy status code when we're running on a real terminal. t.canUpdateStatus = true t.fd = d.Fd() t.clearCurrentLine = clearCurrentLine(wr, t.fd) t.moveCursorUp = moveCursorUp(wr, t.fd) } return t } // Run updates the screen. It should be run in a separate goroutine. When // ctx is cancelled, the status lines are cleanly removed. func (t *Terminal) Run(ctx context.Context) { defer close(t.closed) if t.canUpdateStatus { t.run(ctx) return } t.runWithoutStatus(ctx) } // run listens on the channels and updates the terminal screen. func (t *Terminal) run(ctx context.Context) { var status []string for { select { case <-ctx.Done(): if IsProcessBackground(t.fd) { // ignore all messages, do nothing, we are in the background process group continue } t.undoStatus(len(status)) return case msg := <-t.msg: if IsProcessBackground(t.fd) { // ignore all messages, do nothing, we are in the background process group continue } t.clearCurrentLine(t.wr, t.fd) var dst io.Writer if msg.err { dst = t.errWriter // assume t.wr and t.errWriter are different, so we need to // flush clearing the current line err := t.wr.Flush() if err != nil { fmt.Fprintf(os.Stderr, "flush failed: %v\n", err) } } else { dst = t.wr } if _, err := io.WriteString(dst, msg.line); err != nil { fmt.Fprintf(os.Stderr, "write failed: %v\n", err) continue } t.writeStatus(status) if err := t.wr.Flush(); err != nil { fmt.Fprintf(os.Stderr, "flush failed: %v\n", err) } case stat := <-t.status: if IsProcessBackground(t.fd) { // ignore all messages, do nothing, we are in the background process group continue } status = status[:0] status = append(status, stat.lines...) t.writeStatus(status) } } } func (t *Terminal) writeStatus(status []string) { for _, line := range status { t.clearCurrentLine(t.wr, t.fd) _, err := t.wr.WriteString(line) if err != nil { fmt.Fprintf(os.Stderr, "write failed: %v\n", err) } // flush is needed so that the current line is updated err = t.wr.Flush() if err != nil { fmt.Fprintf(os.Stderr, "flush failed: %v\n", err) } } if len(status) > 0 { t.moveCursorUp(t.wr, t.fd, len(status)-1) } err := t.wr.Flush() if err != nil { fmt.Fprintf(os.Stderr, "flush failed: %v\n", err) } } // runWithoutStatus listens on the channels and just prints out the messages, // without status lines. func (t *Terminal) runWithoutStatus(ctx context.Context) { for { select { case <-ctx.Done(): return case msg := <-t.msg: var flush func() error var dst io.Writer if msg.err { dst = t.errWriter } else { dst = t.wr flush = t.wr.Flush } if _, err := io.WriteString(dst, msg.line); err != nil { fmt.Fprintf(os.Stderr, "write failed: %v\n", err) } if flush == nil { continue } if err := flush(); err != nil { fmt.Fprintf(os.Stderr, "flush failed: %v\n", err) } case <-t.status: // discard status lines } } } func (t *Terminal) undoStatus(lines int) { for i := 0; i < lines; i++ { t.clearCurrentLine(t.wr, t.fd) _, err := t.wr.WriteRune('\n') if err != nil { fmt.Fprintf(os.Stderr, "write failed: %v\n", err) } // flush is needed so that the current line is updated err = t.wr.Flush() if err != nil { fmt.Fprintf(os.Stderr, "flush failed: %v\n", err) } } t.moveCursorUp(t.wr, t.fd, lines) err := t.wr.Flush() if err != nil { fmt.Fprintf(os.Stderr, "flush failed: %v\n", err) } } func (t *Terminal) print(line string, isErr bool) { // make sure the line ends with a line break if line[len(line)-1] != '\n' { line += "\n" } select { case t.msg <- message{line: line, err: isErr}: case <-t.closed: } } // Print writes a line to the terminal. func (t *Terminal) Print(line string) { t.print(line, false) } // Printf uses fmt.Sprintf to write a line to the terminal. func (t *Terminal) Printf(msg string, args ...interface{}) { s := fmt.Sprintf(msg, args...) t.Print(s) } // Error writes an error to the terminal. func (t *Terminal) Error(line string) { t.print(line, true) } // Errorf uses fmt.Sprintf to write an error line to the terminal. func (t *Terminal) Errorf(msg string, args ...interface{}) { s := fmt.Sprintf(msg, args...) t.Error(s) } // Truncate s to fit in width (number of terminal cells) w. // If w is negative, returns the empty string. func truncate(s string, w int) string { if len(s) < w { // Since the display width of a character is at most 2 // and all of ASCII (single byte per rune) has width 1, // no character takes more bytes to encode than its width. return s } for i, r := range s { // Determine width of the rune. This cannot be determined without // knowing the terminal font, so let's just be careful and treat // all ambigous characters as full-width, i.e., two cells. wr := 2 switch width.LookupRune(r).Kind() { case width.Neutral, width.EastAsianNarrow: wr = 1 } w -= wr if w < 0 { return s[:i] } } return s } // SetStatus updates the status lines. func (t *Terminal) SetStatus(lines []string) { if len(lines) == 0 { return } width, _, err := terminal.GetSize(int(t.fd)) if err != nil || width <= 0 { // use 80 columns by default width = 80 } // make sure that all lines have a line break and are not too long for i, line := range lines { line = strings.TrimRight(line, "\n") line = truncate(line, width-2) + "\n" lines[i] = line } // make sure the last line does not have a line break last := len(lines) - 1 lines[last] = strings.TrimRight(lines[last], "\n") select { case t.status <- status{lines: lines}: case <-t.closed: } }