File: plain.go
   1 /*
   2 The MIT License (MIT)
   3 
   4 Copyright © 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 To compile a smaller-sized command-line app, you can use the `go` command as
  27 follows:
  28 
  29 go build -ldflags "-s -w" -trimpath plain.go
  30 */
  31 
  32 package main
  33 
  34 import (
  35     "bufio"
  36     "errors"
  37     "io"
  38     "os"
  39 )
  40 
  41 // Note: the code is avoiding using the fmt package to save hundreds of
  42 // kilobytes on the resulting executable, which is a noticeable difference.
  43 
  44 const info = `
  45 plain [options...] [file...]
  46 
  47 
  48 Turn potentially ANSI-styled plain-text into actual plain-text.
  49 
  50 Input is assumed to be UTF-8, and all CRLF byte-pairs are turned into line
  51 feeds.
  52 
  53 All (optional) leading options start with either single or double-dash:
  54 
  55     -h          show this help message
  56     -help       show this help message
  57 `
  58 
  59 // errNoMoreOutput is a dummy error whose message is ignored, and which
  60 // causes the app to quit immediately and successfully
  61 var errNoMoreOutput = errors.New(`no more output`)
  62 
  63 func main() {
  64     args := os.Args[1:]
  65 
  66     if len(args) > 0 {
  67         switch args[0] {
  68         case `-h`, `--h`, `-help`, `--help`:
  69             os.Stdout.WriteString(info[1:])
  70             return
  71 
  72         case `--`:
  73             args = args[1:]
  74         }
  75     }
  76 
  77     liveLines := true
  78     if _, err := os.Stdout.Seek(0, io.SeekCurrent); err == nil {
  79         liveLines = false
  80     }
  81 
  82     if err := run(os.Stdout, args, liveLines); isActualError(err) {
  83         os.Stderr.WriteString(err.Error())
  84         os.Stderr.WriteString("\n")
  85         os.Exit(1)
  86     }
  87 }
  88 
  89 func run(w io.Writer, args []string, live bool) error {
  90     bw := bufio.NewWriter(w)
  91     defer bw.Flush()
  92 
  93     if len(args) == 0 {
  94         return plain(bw, os.Stdin, live)
  95     }
  96 
  97     for _, name := range args {
  98         if err := handleFile(bw, name, live); err != nil {
  99             return err
 100         }
 101     }
 102     return nil
 103 }
 104 
 105 func handleFile(w *bufio.Writer, name string, live bool) error {
 106     if name == `` || name == `-` {
 107         return plain(w, os.Stdin, live)
 108     }
 109 
 110     f, err := os.Open(name)
 111     if err != nil {
 112         return errors.New(`can't read from file named "` + name + `"`)
 113     }
 114     defer f.Close()
 115 
 116     return plain(w, f, live)
 117 }
 118 
 119 // isActualError is to figure out whether not to ignore an error, and thus
 120 // show it as an error message
 121 func isActualError(err error) bool {
 122     return err != nil && err != errNoMoreOutput
 123 }
 124 
 125 // indexEscapeSequence finds the first ANSI-style escape-sequence, which is
 126 // the multi-byte sequences starting with ESC[; the result is a pair of slice
 127 // indices which can be independently negative when either the start/end of
 128 // a sequence isn't found; given their fairly-common use, even the hyperlink
 129 // ESC]8 sequences are supported
 130 func indexEscapeSequence(s []byte) (int, int) {
 131     var prev byte
 132 
 133     for i, b := range s {
 134         if prev == '\x1b' && b == '[' {
 135             j := indexLetter(s[i+1:])
 136             if j < 0 {
 137                 return i, -1
 138             }
 139             return i - 1, i + 1 + j + 1
 140         }
 141 
 142         if prev == '\x1b' && b == ']' && i+1 < len(s) && s[i+1] == '8' {
 143             j := indexPair(s[i+1:], '\x1b', '\\')
 144             if j < 0 {
 145                 return i, -1
 146             }
 147             return i - 1, i + 1 + j + 2
 148         }
 149 
 150         prev = b
 151     }
 152 
 153     return -1, -1
 154 }
 155 
 156 func indexLetter(s []byte) int {
 157     for i, b := range s {
 158         upper := b &^ 32
 159         if 'A' <= upper && upper <= 'Z' {
 160             return i
 161         }
 162     }
 163 
 164     return -1
 165 }
 166 
 167 func indexPair(s []byte, x byte, y byte) int {
 168     var prev byte
 169 
 170     for i, b := range s {
 171         if prev == x && b == y {
 172             return i
 173         }
 174         prev = b
 175     }
 176 
 177     return -1
 178 }
 179 
 180 func plain(w *bufio.Writer, r io.Reader, live bool) error {
 181     const gb = 1024 * 1024 * 1024
 182     sc := bufio.NewScanner(r)
 183     sc.Buffer(nil, 8*gb)
 184 
 185     for sc.Scan() {
 186         for line := sc.Bytes(); len(line) > 0; {
 187             i, j := indexEscapeSequence(line)
 188             if i < 0 {
 189                 w.Write(line)
 190                 break
 191             }
 192             if j < 0 {
 193                 j = len(line)
 194             }
 195 
 196             if i > 0 {
 197                 w.Write(line[:i])
 198             }
 199 
 200             line = line[j:]
 201         }
 202 
 203         if w.WriteByte('\n') != nil {
 204             return errNoMoreOutput
 205         }
 206 
 207         if !live {
 208             continue
 209         }
 210 
 211         if err := w.Flush(); err != nil {
 212             return errNoMoreOutput
 213         }
 214     }
 215 
 216     return sc.Err()
 217 }