Command line interface to compress/* packages.

gocompress.go

package main

import (
	"compress/flate"
	"compress/gzip"
	"compress/lzw"
	"compress/zlib"
	"fmt"
	"io"
	"os"
	"strings"
)

type action uint8

const (
	Flate action = iota
	Gzip
	Lzw
	Zlib
)

func die(v ...interface{}) {
	fmt.Fprintln(os.Stderr, v...)
	os.Exit(1)
}

func dieusage() {
	die("gocompress TYPE FILE")
}

func parse() (a action, compress bool, in, out string) {
	if len(os.Args) != 3 {
		dieusage()
	}
	in, out = os.Args[2], os.Args[2]
	var ext string
	switch strings.ToLower(os.Args[1]) {
	case "flate":
		a, ext = Flate, ".flate"
	case "gzip":
		a, ext = Gzip, ".gz"
	case "lzw":
		a, ext = Lzw, ".lzw"
	case "zlib":
		a, ext = Zlib, ".z"
	default:
		die(os.Args[1], "is not supported")
		os.Exit(1)
	}
	if !strings.HasSuffix(in, ext) {
		compress = true
		out = in + ext
	} else {
		out = out[:len(out)-len(ext)]
	}
	return
}

func main() {
	a, compress, in, out := parse()
	r, err := os.Open(in)
	if err != nil {
		die(err)
	}
	defer r.Close()
	w, err := os.OpenFile(out, os.O_CREATE|os.O_WRONLY, 0644)
	if err != nil {
		die(err)
	}
	defer w.Close()
	switch a {
	case Flate:
		if compress {
			cw, err := flate.NewWriter(w, flate.BestCompression)
			if err != nil {
				die(err)
			}
			defer cw.Close()
			if _, err = io.Copy(cw, r); err != nil {
				die(err)
			}
		} else {
			cr := flate.NewReader(r)
			defer cr.Close()
			if _, err = io.Copy(w, cr); err != nil {
				die(err)
			}
		}
	case Gzip:
		if compress {
			cw, err := gzip.NewWriterLevel(w, gzip.BestCompression)
			if err != nil {
				die(err)
			}
			defer cw.Close()
			if _, err = io.Copy(cw, r); err != nil {
				die(err)
			}
		} else {
			cr, err := gzip.NewReader(r)
			if err != nil {
				die(err)
			}
			defer cr.Close()
			if _, err = io.Copy(w, cr); err != nil {
				die(err)
			}
		}
	case Lzw:
		if compress {
			cw := lzw.NewWriter(w, lzw.LSB, 8)
			defer cw.Close()
			if _, err = io.Copy(cw, r); err != nil {
				die(err)
			}
		} else {
			cr := lzw.NewReader(r, lzw.LSB, 8)
			defer cr.Close()
			if _, err = io.Copy(w, cr); err != nil {
				die(err)
			}
		}
	case Zlib:
		if compress {
			cw, err := zlib.NewWriterLevel(w, zlib.BestCompression)
			if err != nil {
				die(err)
			}
			defer cw.Close()
			if _, err = io.Copy(cw, r); err != nil {
				die(err)
			}
		} else {
			cr, err := zlib.NewReader(r)
			if err != nil {
				die(err)
			}
			defer cr.Close()
			if _, err = io.Copy(w, cr); err != nil {
				die(err)
			}
		}
	}
}