prefixing with tty colors

prefixer.go

package main

import (
	"io"
	"log"
	"os"
	"os/exec"
	"os/signal"
	"syscall"

	"bufio"

	"github.com/creack/pty"
	"golang.org/x/term"
)

// https://github.com/goware/prefixer
// https://github.com/creack/pty

var prefix = []byte("prefix: ")

type Reader struct {
	reader *bufio.Reader
	unread []byte
	eof    bool
}

func (r *Reader) Read(p []byte) (n int, err error) {
	for {

		if len(r.unread) > 0 {
			m := copy(p[n:], r.unread)
			n += m
			r.unread = r.unread[m:]
			if len(r.unread) > 0 {
				return n, nil
			}
		}

		if r.eof {
			return n, io.EOF
		}

		r.unread, err = r.reader.ReadBytes('\n')

		if err == io.EOF {
			r.eof = true
		}

		if len(r.unread) == 0 {
			return n, err
		}

		r.unread = append(prefix, r.unread...)

		if err != nil {
			if err == io.EOF && len(r.unread) > 0 {

				return n, nil
			}
			return n, err
		}
	}
}

func (r *Reader) WriteTo(w io.Writer) (n int64, err error) {
	for {

		if len(r.unread) > 0 {
			m, err := w.Write(r.unread)
			n += int64(m)
			if err != nil {
				return n, err
			}
			r.unread = r.unread[m:]
			if len(r.unread) > 0 {
				return n, nil
			}
		}

		if r.eof {
			return n, io.EOF
		}

		r.unread, err = r.reader.ReadBytes('\n')

		if err == io.EOF {
			r.eof = true
		}

		if len(r.unread) == 0 {
			return n, err
		}

		r.unread = append(prefix, r.unread...)

		if err != nil {
			if err == io.EOF && len(r.unread) > 0 {

				return n, nil
			}
			return n, err
		}
	}
}

func main() {
	c := exec.Command("bat", "main.go")

	ptmx, err := pty.Start(c)
	if err != nil {
		log.Fatal(err)
	}

	defer func() { _ = ptmx.Close() }()

	ch := make(chan os.Signal, 1)
	signal.Notify(ch, syscall.SIGWINCH)
	go func() {
		for range ch {
			if err := pty.InheritSize(os.Stdin, ptmx); err != nil {
				log.Printf("error resizing pty: %s", err)
			}
		}
	}()
	ch <- syscall.SIGWINCH
	defer func() { signal.Stop(ch); close(ch) }()

	oldState, err := term.MakeRaw(int(os.Stdin.Fd()))
	if err != nil {
		panic(err)
	}
	defer func() { _ = term.Restore(int(os.Stdin.Fd()), oldState) }()

	go func() { _, _ = io.Copy(ptmx, os.Stdin) }()

	prefixReader := Reader{
		reader: bufio.NewReader(ptmx),
	}

	_, _ = io.Copy(os.Stdout, &prefixReader)
}