package main

import (
	"bytes"
	"encoding/hex"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"
)

var picMap map[string]string

func init() {
	picMap = make(map[string]string)
	picMap["ffd8ffe0"] = "jpg"
	picMap["ffd8ffe1"] = "jpg"
	picMap["ffd8ffe8"] = "jpg"
	picMap["89504e47"] = "png"
}

func main() {
	file,err := os.Open("pic/type/test.jpeg")
	if err != nil {
		log.Fatal(err.Error())
	}
	defer file.Close()
	result := judgeType(file)
	fmt.Println("判断结果: ",result)
}

func judgeType(file *os.File) bool {
	buf := make([]byte, 20)
	n, _ := file.Read(buf)

	fileCode := bytesToHexString(buf[:n])
	for k,_ := range picMap {
		if strings.HasPrefix(fileCode, k) {
			return true
		}
	}
	return false
}

func bytesToHexString(src []byte) string {
	res := bytes.Buffer{}
	if src == nil || len(src) <= 0 {
		return ""
	}
	temp := make([]byte, 0)
	i, length := 100, len(src)
	if length < i {
		i = length
	}
	for j := 0; j < i; j++ {
		sub := src[j] & 0xFF
		hv := hex.EncodeToString(append(temp, sub))
		if len(hv) < 2 {
			res.WriteString(strconv.FormatInt(int64(0), 10))
		}
		res.WriteString(hv)
	}
	return res.String()
}