plugin: Add pager to info command

cmd/plugin/rpaasv2/cmd/info.go

@@ -411,10 +411,22 @@ func runInfo(c *cli.Context) error {
 		return writeInfoOnJSONFormat(c.App.Writer, infoPayload)
 	}
 
-	err = instanceInfoTemplate.Execute(c.App.Writer, infoPayload)
+	writer := newPagerWriter(c.App.Writer)
+
+	err = instanceInfoTemplate.Execute(writer, infoPayload)
 	if err != nil {
 		return err
 	}
 
+	if pw, ok := writer.(*pagerWriter); ok {
+		if pw.pagerPipe != nil {
+			pw.pagerPipe.Close()
+		}
+		err = pw.Wait()
+		if err != nil {
+			return err
+		}
+	}
+
 	return nil
 }

cmd/plugin/rpaasv2/cmd/pager.go

@@ -0,0 +1,92 @@
+// Copyright 2020 tsuru authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+package cmd
+
+import (
+	"bytes"
+	"io"
+	"os/exec"
+	"strings"
+	"syscall"
+
+	"golang.org/x/crypto/ssh/terminal"
+)
+
+type descriptable interface {
+	Fd() uintptr
+}
+
+func newPagerWriter(baseWriter io.Writer) io.Writer {
+	pager, found := syscall.Getenv("TSURU_PAGER")
+	if found && pager == "" {
+		return baseWriter
+	}
+
+	outputDesc, ok := baseWriter.(descriptable)
+	if !ok {
+		return baseWriter
+	}
+	terminalFd := int(outputDesc.Fd())
+	if !terminal.IsTerminal(terminalFd) {
+		return baseWriter
+	}
+
+	if pager == "" {
+		pager = "less -RFXE"
+	}
+	return &pagerWriter{baseWriter: baseWriter, pager: pager}
+}
+
+type pagerWriter struct {
+	baseWriter io.Writer
+	pagerPipe  io.WriteCloser
+	cmd        *exec.Cmd
+	pager      string
+	buf        bytes.Buffer
+	erroed     bool
+}
+
+func (w *pagerWriter) Write(data []byte) (int, error) {
+	if w.pagerPipe != nil {
+		return w.pagerPipe.Write(data)
+	}
+	if w.erroed {
+		return w.baseWriter.Write(data)
+	}
+	w.buf.Write(data)
+	if w.cmd == nil {
+		var err error
+		pagerParts := strings.Split(w.pager, " ")
+		w.cmd = exec.Command(pagerParts[0], pagerParts[1:]...)
+		w.cmd.Stdout = w.baseWriter
+		w.pagerPipe, err = w.cmd.StdinPipe()
+		if err != nil {
+			w.erroed = true
+		}
+		err = w.cmd.Start()
+		if err != nil {
+			w.pagerPipe = nil
+			w.erroed = true
+		}
+	}
+	w.flush()
+	return len(data), nil
+}
+
+func (w *pagerWriter) Wait() error {
+	if w.cmd == nil {
+		return nil
+	}
+
+	return w.cmd.Wait()
+}
+
+func (w *pagerWriter) flush() {
+	if w.pagerPipe != nil {
+		w.pagerPipe.Write(w.buf.Bytes())
+	} else {
+		w.baseWriter.Write(w.buf.Bytes())
+	}
+	w.buf.Reset()
+}

go.mod

@@ -37,6 +37,7 @@ require (
 	github.com/willf/bitset v1.1.11
 	go.uber.org/multierr v1.6.0 // indirect
 	go.uber.org/zap v1.16.0 // indirect
+	golang.org/x/crypto v0.0.0-20200820211705-5c72a883971a
 	golang.org/x/net v0.0.0-20200822124328-c89045814202
 	k8s.io/api v0.19.2
 	k8s.io/apimachinery v0.19.2