Cleaner handling of cli error messages

Author: rs

data/http.go

@@ -40,6 +40,7 @@ func (h httpSource) run(url string, interval time.Duration) {
 		case <-t.C:
 			h.fetch(url)
 		case <-h.done:
+			close(h.c)
 			return
 		}
 	}

main.go

@@ -40,7 +40,6 @@ func main() {
 	} else {
 		dp = data.FromStdin(*steps)
 	}
-	defer dp.Close()
 	dash := graph.Dash{
 		Specs: specs,
 		Data:  dp,
@@ -58,11 +57,13 @@ func main() {
 		c := make(chan os.Signal, 2)
 		signal.Notify(c, os.Interrupt, syscall.SIGTERM)
 		i := 0
-		prepare(*rows)
-		defer cleanup(*rows)
 		for {
 			select {
 			case <-t.C:
+				if i == 0 {
+					prepare(*rows)
+					defer cleanup(*rows)
+				}
 				i++
 				if i%120 == 0 {
 					// Clear scrollback to avoid iTerm from eating all the memory.
@@ -72,11 +73,13 @@ func main() {
 				render(dash, *rows)
 				osc.CursorRestorePosition()
 			case <-exit:
-				render(dash, *rows)
+				if i == 0 {
+					render(dash, *rows)
+				}
 				return
 			case <-c:
-				cleanup(*rows)
-				os.Exit(0)
+				dp.Close()
+				signal.Stop(c)
 			}
 		}
 	}()
@@ -94,11 +97,10 @@ func fatal(a ...interface{}) {
 func prepare(rows int) {
 	osc.HideCursor()
 	if rows == 0 {
-		size, err := osc.Size()
-		if err != nil {
+		var err error
+		if rows, err = osc.Rows(); err != nil {
 			fatal("Cannot get window size: ", err)
 		}
-		rows = size.Row
 	}
 	print(strings.Repeat("\n", rows))
 	osc.CursorMove(osc.Up, rows)
@@ -107,8 +109,7 @@ func prepare(rows int) {
 func cleanup(rows int) {
 	osc.ShowCursor()
 	if rows == 0 {
-		size, _ := osc.Size()
-		rows = size.Row
+		rows, _ = osc.Rows()
 	}
 	osc.CursorMove(osc.Down, rows)
 	print("\n")

osc/iterm2.go

@@ -3,6 +3,7 @@ package osc
 import (
 	"bytes"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -15,6 +16,9 @@ import (
 var ecsi = "\033]"
 var st = "\007"
 
+var cellSizeOnce sync.Once
+var cellWidth, cellHeight float64
+
 func init() {
 	if os.Getenv("TERM") == "screen" {
 		ecsi = "\033Ptmux;\033" + ecsi
@@ -35,26 +39,38 @@ type TermSize struct {
 	Height int
 }
 
-// Size gathers sizing information of the current session's controling terminal.
-func Size() (size TermSize, err error) {
-	size.Col, size.Row, err = terminal.GetSize(1)
-	if err != nil {
-		return
-	}
+func initCellSize() {
 	s, err := terminal.MakeRaw(1)
 	if err != nil {
 		return
 	}
 	defer terminal.Restore(1, s)
-	var cellWidth, cellHeight float64
 	fmt.Fprint(os.Stdout, ecsi+"1337;ReportCellSize"+st)
 	fileSetReadDeadline(os.Stdout, time.Now().Add(time.Second))
 	defer fileSetReadDeadline(os.Stdout, time.Time{})
-	_, err = fmt.Fscanf(os.Stdout, "\033]1337;ReportCellSize=%f;%f\033\\", &cellHeight, &cellWidth)
+	fmt.Fscanf(os.Stdout, "\033]1337;ReportCellSize=%f;%f\033\\", &cellHeight, &cellWidth)
+}
+
+// Size gathers sizing information of the current session's controling terminal.
+func Size() (size TermSize, err error) {
+	size.Col, size.Row, err = terminal.GetSize(1)
+	if err != nil {
+		return
+	}
+	cellSizeOnce.Do(initCellSize)
+	if cellWidth+cellHeight == 0 {
+		err = errors.New("cannot get iTerm2 cell size")
+	}
 	size.Width, size.Height = size.Col*int(cellWidth), size.Row*int(cellHeight)
 	return
 }
 
+// Rows returns the number of rows for the controling terminal.
+func Rows() (rows int, err error) {
+	_, rows, err = terminal.GetSize(1)
+	return
+}
+
 // ImageWriter is a writer that write into iTerm2 terminal the PNG data written
 // to it.
 type ImageWriter struct {