File: plain.go
   1 /*
   2 The MIT License (MIT)
   3 
   4 Copyright © 2020-2025 pacman64
   5 
   6 Permission is hereby granted, free of charge, to any person obtaining a copy of
   7 this software and associated documentation files (the “Software”), to deal
   8 in the Software without restriction, including without limitation the rights to
   9 use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
  10 of the Software, and to permit persons to whom the Software is furnished to do
  11 so, subject to the following conditions:
  12 
  13 The above copyright notice and this permission notice shall be included in all
  14 copies or substantial portions of the Software.
  15 
  16 THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22 SOFTWARE.
  23 */
  24 
  25 /*
  26 Single-file source-code for plain.
  27 
  28 To compile a smaller-sized command-line app, you can use the `go` command as
  29 follows:
  30 
  31 go build -ldflags "-s -w" -trimpath plain.go
  32 */
  33 
  34 package main
  35 
  36 import (
  37     "bufio"
  38     "errors"
  39     "io"
  40     "os"
  41 )
  42 
  43 // Note: the code is avoiding using the fmt package to save hundreds of
  44 // kilobytes on the resulting executable, which is a noticeable difference.
  45 
  46 const info = `
  47 plain [options...] [file...]
  48 
  49 
  50 Turn potentially ANSI-styled plain-text into actual plain-text.
  51 
  52 Input is assumed to be UTF-8, and all CRLF byte-pairs are turned into line
  53 feeds.
  54 
  55 All (optional) leading options start with either single or double-dash:
  56 
  57     -h          show this help message
  58     -help       show this help message
  59 `
  60 
  61 const errorStyle = "\x1b[31m"
  62 
  63 // errNoMoreOutput is a dummy error whose message is ignored, and which
  64 // causes the app to quit immediately and successfully
  65 var errNoMoreOutput = errors.New(`no more output`)
  66 
  67 func main() {
  68     if len(os.Args) > 1 {
  69         switch os.Args[1] {
  70         case `-h`, `--h`, `-help`, `--help`:
  71             os.Stderr.WriteString(info[1:])
  72             return
  73         }
  74     }
  75 
  76     if err := run(os.Stdout, os.Args[1:]); isActualError(err) {
  77         os.Stderr.WriteString(errorStyle)
  78         os.Stderr.WriteString(err.Error())
  79         os.Stderr.WriteString("\x1b[0m\n")
  80         os.Exit(1)
  81     }
  82 }
  83 
  84 func run(w io.Writer, args []string) error {
  85     bw := bufio.NewWriter(w)
  86     defer bw.Flush()
  87 
  88     if len(args) == 0 {
  89         return plain(bw, os.Stdin)
  90     }
  91 
  92     for _, name := range args {
  93         if err := handleFile(bw, name); err != nil {
  94             return err
  95         }
  96     }
  97     return nil
  98 }
  99 
 100 func handleFile(w *bufio.Writer, name string) error {
 101     if name == `` || name == `-` {
 102         return plain(w, os.Stdin)
 103     }
 104 
 105     f, err := os.Open(name)
 106     if err != nil {
 107         return errors.New(`can't read from file named "` + name + `"`)
 108     }
 109     defer f.Close()
 110 
 111     return plain(w, f)
 112 }
 113 
 114 // isActualError is to figure out whether not to ignore an error, and thus
 115 // show it as an error message
 116 func isActualError(err error) bool {
 117     return err != nil && err != io.EOF && err != errNoMoreOutput
 118 }
 119 
 120 // indexEscapeSequence finds the first ANSI-style escape-sequence, which is
 121 // either the alert/bell byte, or the multi-byte sequences starting either
 122 // with ESC[ or ESC]; either returned index can be negative
 123 func indexEscapeSequence(s []byte) (int, int) {
 124     var prev byte
 125 
 126     for i, b := range s {
 127         if b == '\a' {
 128             return i, i + 1
 129         }
 130 
 131         if prev == '\x1b' && b == '[' {
 132             j := indexLetter(s[i+1:])
 133             if j < 0 {
 134                 return i, -1
 135             }
 136             return i - 1, i + 1 + j + 1
 137         }
 138 
 139         // if prev == '\x1b' && b == ']' {
 140         //  j := bytes.IndexByte(s[i+1:], ':')
 141         //  if j < 0 {
 142         //      return i, -1
 143         //  }
 144         //  return i - 1, i + 1 + j + 1
 145         // }
 146 
 147         // if prev == '\x1b' && b == '\\' {
 148         //  return i - 1, i + 1
 149         // }
 150 
 151         prev = b
 152     }
 153 
 154     return -1, -1
 155 }
 156 
 157 func indexLetter(s []byte) int {
 158     for i, b := range s {
 159         if 'A' <= b && b <= 'Z' {
 160             return i
 161         }
 162         if 'a' <= b && b <= 'z' {
 163             return i
 164         }
 165     }
 166 
 167     return -1
 168 }
 169 
 170 func plain(w *bufio.Writer, r io.Reader) error {
 171     const gb = 1024 * 1024 * 1024
 172     sc := bufio.NewScanner(r)
 173     sc.Buffer(nil, 8*gb)
 174 
 175     for sc.Scan() {
 176         line := sc.Bytes()
 177 
 178         for len(line) > 0 {
 179             i, j := indexEscapeSequence(line)
 180             if i < 0 {
 181                 w.Write(line)
 182                 break
 183             }
 184 
 185             w.Write(line[:i])
 186 
 187             if j < 0 {
 188                 break
 189             }
 190             line = line[j:]
 191         }
 192 
 193         w.WriteByte('\n')
 194         if err := w.Flush(); err != nil {
 195             // a write error may be the consequence of stdout being closed,
 196             // perhaps by another app along a pipe
 197             return errNoMoreOutput
 198         }
 199     }
 200 
 201     return sc.Err()
 202 }