add external pager support via ES_JSON_PAGER (#65)

README.md

@@ -23,6 +23,8 @@ Features:
 - Shell completion support (bash, zsh and fish). Put this into your
   rc: `source <(esctl completion bash)`.
 - Cluster settings can be viewed and modified.
+- Comprehensive cluster status.
+- Cluster reroute support.
 - Search: you can search indices using full text or by fields, select
   logical condition (OR, AND), use PIT, limit datetime (ES date math
   can be used), etc. It is however not yet possible to create
@@ -47,7 +49,9 @@ Features:
   elasticsearch API.  You can  run API calls  on the  current selected
   cluster w/o the hassle to specify the whole url, credentials etc. It
   has line  editing and history  support. If `jq` is  installed output
-  JSON will be syntax highlighted.
+  JSON will  be syntax  highlighted. A simple  internal pager  will be
+  used if output exceeds the terminal height. You can tweak this using
+  the `$ES_JSON_PAGER` environment variable (I'd recommend [fx](https://fx.wtf/)).
 - Doc support. You can put, delete and show docs for an index. Very
   handy if you want to play with it. Just create a new index:
   `esctl index create foo` and then insert docs into it for search

cmd/api.go

@@ -83,6 +83,16 @@ func ApiRepl(conf *cfg.Config) *cli.Command {
 		Aliases: []string{"shell"},
 		Usage:   "interactive API repl",
 
+		Flags: []cli.Flag{
+			&cli.StringFlag{
+				Name:        "pager",
+				Usage:       "external viewer program (default:internal)",
+				Destination: &conf.Pager,
+				Aliases:     []string{"p"},
+				Sources:     cli.EnvVars("PAGER", "ES_JSON_PAGER"),
+			},
+		},
+
 		Action: func(ctx context.Context, cmd *cli.Command) error {
 			return es.ApiRepl(conf)
 		},

pkg/cfg/config.go

@@ -106,6 +106,8 @@ type Config struct {
 
 	FromNode, ToNode             string // cluster reroute move: -f + -t
 	AllowPrimary, AcceptDataLoss bool   // cluster reroute cancel: -p,-a
+
+	Pager string // api repl: -p || PAGER
 }
 
 func NewConfig() *Config {

pkg/cfg/term.go

@@ -36,3 +36,14 @@ func GetTermWidth() int {
 
 	return 80
 }
+
+func GetTermHeight() int {
+	if term.IsTerminal(int(os.Stdout.Fd())) {
+		_, height, err := term.GetSize(int(os.Stdout.Fd()))
+		if err == nil {
+			return height
+		}
+	}
+
+	return 25
+}

pkg/es/api.go

@@ -141,14 +141,50 @@ func ApiRepl(conf *cfg.Config) error {
 			fmt.Printf("failed to call API: %s\n", esErrorString(err))
 		}
 
-		if err := prettyfiJson(conf, raw); err != nil {
-			fmt.Println(err)
-		}
+		pageJsonOutput(conf, raw)
 	}
 
 	return nil
 }
 
+func pageJsonOutput(conf *cfg.Config, raw []byte) {
+	tmpconf := &cfg.Config{HaveJQ: conf.HaveJQ}
+
+	if conf.Pager != "" {
+		tmpconf.HaveJQ = false
+	}
+
+	output, err := prettyfiJson(tmpconf, raw)
+	if err != nil {
+		fmt.Println(err)
+	}
+
+	lines := len(strings.Split(output, "\n"))
+	height := cfg.GetTermHeight()
+
+	if lines > height {
+		if conf.Pager != "" {
+			cmd := strings.Split(conf.Pager, " ")
+			pager := exec.Command(cmd[0], cmd[1:]...)
+
+			var buf bytes.Buffer
+			buf.WriteString(output)
+
+			pager.Stdout = os.Stdout
+			pager.Stdin = &buf
+			pager.Stderr = os.Stderr
+
+			err := pager.Run()
+
+			if err != nil {
+				fmt.Printf("failed to execute pager '%s': %s", conf.Pager, err)
+			}
+		} else {
+			printer.Pager("json output", output)
+		}
+	}
+}
+
 func encodeAuth(username, password string) string {
 	return base64.StdEncoding.EncodeToString([]byte(username + ":" + password))
 }
@@ -197,7 +233,7 @@ func CallAPI(conf *cfg.Config, verb, path, data string) ([]byte, error) {
 	return body, nil
 }
 
-func prettyfiJson(conf *cfg.Config, raw []byte) error {
+func prettyfiJson(conf *cfg.Config, raw []byte) (string, error) {
 	if conf.HaveJQ {
 		cmd := exec.CommandContext(context.Background(), "jq", "-C")
 		cmd.Stdin = bytes.NewReader(raw)
@@ -207,23 +243,18 @@ func prettyfiJson(conf *cfg.Config, raw []byte) error {
 
 		err := cmd.Run()
 		if err != nil {
-			return err
+			return "", err
 		}
 
-		fmt.Println(out.String())
-
-		return nil
+		return out.String(), nil
 	}
-
 	var pretty bytes.Buffer
 	err := json.Indent(&pretty, raw, "", "\t")
 	if err != nil {
-		return fmt.Errorf("json parse error: %s", err)
+		return "", fmt.Errorf("json parse error: %s", err)
 	}
 
-	fmt.Println(pretty.String())
-
-	return nil
+	return pretty.String(), nil
 }
 
 // interactively  read  arbitrary  JSON  data  from  STDIN,  which  is

pkg/es/index_template_settings.go

@@ -39,9 +39,11 @@ func getIndexTemplateSettings(conf *cfg.Config, tplname string, table *printer.T
 	}
 
 	if conf.Debug {
-		if err := prettyfiJson(conf, raw); err != nil {
+		output, err := prettyfiJson(conf, raw)
+		if err != nil {
 			return err
 		}
+		fmt.Println(output)
 	}
 
 	if len(data.IndexTemplates) == 0 {