ctl: pd-ctl cmd will work well in char device mode (#4479)

* pd-ctl cmd will work well in crontab && close 4478

Signed-off-by: bufferflies <1045931706@qq.com>

* add unit test && close #4478

Signed-off-by: bufferflies <1045931706@qq.com>

* string nil and add return

Signed-off-by: bufferflies <1045931706@qq.com>

Co-authored-by: Ti Chi Robot <ti-community-prow-bot@tidb.io>

tools/pd-ctl/main.go

@@ -16,10 +16,8 @@ package main
 
 import (
 	"fmt"
-	"io"
 	"os"
 	"os/signal"
-	"strings"
 	"syscall"
 
 	"github.com/tikv/pd/tools/pd-ctl/pdctl"
@@ -49,16 +47,15 @@ func main() {
 		}
 	}()
 
-	var input []string
+	var inputs []string
 	stat, _ := os.Stdin.Stat()
 	if (stat.Mode() & os.ModeCharDevice) == 0 {
-		b, err := io.ReadAll(os.Stdin)
+		in, err := pdctl.ReadStdin(os.Stdin)
 		if err != nil {
 			fmt.Println(err)
 			return
 		}
-		input = strings.Split(strings.TrimSpace(string(b)), " ")
+		inputs = in
 	}
-
-	pdctl.MainStart(append(os.Args[1:], input...))
+	pdctl.MainStart(append(os.Args[1:], inputs...))
 }

tools/pd-ctl/pdctl/ctl.go

@@ -198,3 +198,15 @@ func genCompleter(cmd *cobra.Command) []readline.PrefixCompleterInterface {
 	}
 	return pc
 }
+
+// ReadStdin convert stdin to string array
+func ReadStdin(r io.Reader) (input []string, err error) {
+	b, err := io.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+	if s := strings.TrimSpace(string(b)); len(s) > 0 {
+		input = strings.Split(s, " ")
+	}
+	return input, nil
+}

tools/pd-ctl/pdctl/ctl_test.go

@@ -15,6 +15,8 @@
 package pdctl
 
 import (
+	"io"
+	"strings"
 	"testing"
 
 	"github.com/spf13/cobra"
@@ -68,3 +70,30 @@ func TestGenCompleter(t *testing.T) {
 		}
 	}
 }
+
+func TestReadStdin(t *testing.T) {
+	s := []struct {
+		in      io.Reader
+		targets []string
+	}{{
+		in:      strings.NewReader(""),
+		targets: []string{},
+	}, {
+		in:      strings.NewReader("a b c"),
+		targets: []string{"a", "b", "c"},
+	}}
+	for _, v := range s {
+		in, err := ReadStdin(v.in)
+		if err != nil {
+			t.Errorf("ReadStdin err:%v", err)
+		}
+		if len(v.targets) != len(in) {
+			t.Errorf("ReadStdin =  %v, want %s, nil", in, v.targets)
+		}
+		for i, target := range v.targets {
+			if target != in[i] {
+				t.Errorf("ReadStdin = %v, want %s, nil", in, v.targets)
+			}
+		}
+	}
+}