generator.go

// +build ignore

package main

import (
	"bytes"
	"fmt"
	"io/ioutil"
	"os"
	"strings"
)

type section struct {
	Name     string
	matchers []matcher
}
type matcher struct {
	Level, Offset, Range int
	Value                []byte
	Mask                 []byte
}

func main() {
	inp, e := ioutil.ReadFile("/usr/share/mime/magic")
	if e != nil {
		panic(e)
	}
	if !bytes.Equal([]byte("MIME-Magic\x00\n"), inp[0:12]) {
		panic("Invalid file header")
	}
	inp = inp[12:]
	out := new(bytes.Buffer)
	var s section
	ss := []section{}
	i := 0
	duplicates := map[string]bool{}
	for len(inp) > 0 {
		inp, s = pSection(inp, out)
		if duplicates[s.Name] {
			continue
		}
		duplicates[s.Name] = true
		ss = append(ss, s)
		fmt.Fprintf(out, "%#v: &sarr[%d],\n", s.Name, i)
		i++
	}

	fmt.Printf(`package mimemagic

var smap = map[string]*section{
%s}

var sarr = [...]section{
`, out.Bytes())
	for i := 0; i < len(ss); i++ {
		x := fmt.Sprintf("%#v,\n", ss[i])
		os.Stdout.WriteString(strings.Replace(x, "main.", "", -1))
	}
	os.Stdout.WriteString("}\n\n")
}

func pSection(b []byte, out *bytes.Buffer) ([]byte, section) {
	if b[0] != '[' {
		panic("Expected [")
	}
	i := bytes.IndexByte(b, ':')
	b = b[i+1:]
	j := bytes.IndexByte(b, ']')
	if b[j+1] != '\n' {
		panic("Expected newline")
	}
	name := string(b[:j])

	b = b[j+2:]
	mss := []matcher{}
	var m matcher
	for {
		b, m = pMatcher(name, b)
		mss = append(mss, m)
		if len(b) == 0 || b[0] == '[' {
			break
		}
	}

	return b, section{name, mss}
}

func pMatcher(name string, b []byte) ([]byte, matcher) {
	var lvl, soff, rang int
	var mask []byte
	lvl, b = pInt(b)
	if b[0] != '>' {
		panic("Expecting '>'")
	}
	b = b[1:]
	soff, b = pInt(b)
	if b[0] != '=' {
		panic("Expecting '='")
	}
	dlen := int(b[2]) + int(b[1])
	b = b[3:]
	value := b[0:dlen]
	b = b[dlen:]

	for {
		switch b[0] {
		case '\n':
			return b[1:], matcher{lvl, soff, rang, value, mask}
		case '&':
			mask = b[1 : 1+len(value)]
			b = b[1+len(value):]
		case '~':
			fmt.Fprintf(os.Stderr, "%s: Byte shifting not supported - using default\n", name)
			_, b = pInt(b[1:])
		case '+':
			rang, b = pInt(b[1:])
		default:
			panic("Who are you? '" + string(b[0:1]) + "'\n")
		}
	}
	panic("not reached")
}

func pInt(b []byte) (int, []byte) {
	acc := 0
	for len(b) > 0 {
		switch b[0] {
		case '1':
			acc = 1 + (acc * 10)
		case '2':
			acc = 2 + (acc * 10)
		case '3':
			acc = 3 + (acc * 10)
		case '4':
			acc = 4 + (acc * 10)
		case '5':
			acc = 5 + (acc * 10)
		case '6':
			acc = 6 + (acc * 10)
		case '7':
			acc = 7 + (acc * 10)
		case '8':
			acc = 8 + (acc * 10)
		case '9':
			acc = 9 + (acc * 10)
		case '0':
			acc = 0 + (acc * 10)
		default:
			return acc, b
		}
		b = b[1:]
	}
	return acc, b
}