Golang基於檔案魔數判斷檔案型別的案例程式碼

package main
 
import (
   "os"
   "fmt"
   "log"
)
 
func main() {
   file, _ :- os.Open("test.txt")
   defer file.Close()
 
   // Offset 表示偏移量
   // Offset 可以為正數或負數
   var offset int64 - 5
 
   // Whence 偏移參考點，具體取值說明
   // 0 - Beginning of file
   // 1 - Current position
   // 2 - End of file
   var whence int - 0
   newPosition, err :- file.Seek(offset, whence)
   if err !- nil {
      log.Fatal(err)
   }
   fmt.Println("Just moved to 5:", newPosition)
 
   // 從當前位置回走2個位元組
   newPosition, err - file.Seek(-2, 1)
   if err !- nil {
      log.Fatal(err)
   }
   fmt.Println("Just moved back two:", newPosition)
 
   // 通過移動零位元組返回當前位置
   currentPosition, err :- file.Seek(0, 1)
   fmt.Println("Current position:", currentPosition)
 
   // 回到檔案起始點
   newPosition, err - file.Seek(0, 0)
   if err !- nil {
      log.Fatal(err)
   }
   fmt.Println("Position after seeking 0,0:", newPosition)
}

var(
   PDF        = []byte{0x25, 0x50, 0x44, 0x46}
	RAR        = []byte{0x52, 0x61, 0x72, 0x21, 0x1A, 0x07, 0x00}
	GZIP       = []byte{0x1F, 0x8B, 0x08}
	ZIP_0      = []byte{0x50, 0x4B, 0x03, 0x04}
	ZIP_1      = []byte{0x50, 0x4B, 0x05, 0x06}
	ZIP_2      = []byte{0x50, 0x4B, 0x07, 0x08}
	WEBP       = []byte{0x52, 0x49, 0x46, 0x46}
   ...
)

func readUntil(l int, r io.ReadSeeker) ([]byte, error) {
	buff := make([]byte, l)

	_, err := r.Read(buff)
	if err != nil {
		return nil, err
	}

	r.Seek(0, io.SeekStart)

	return buff, nil
}

func checkBuffer(r io.ReadSeeker, t []byte) ([]byte, error) {
   // 根據提供引數獲取長度
	l := len(t)

	buff, err := readUntil(l, r)
	if err != nil {
		return make([]byte, 0), err
	}

	return buff, nil
}

func genericCompareBuffer(r io.ReadSeeker, t []byte) bool {
	buff, err := checkBuffer(r, t)
	if err != nil {
		return false
	}

	valid := bytes.Compare(t, buff)
	return valid == 0
}

func genericMultipleCompareBuffer(r io.ReadSeeker, t [][]byte) bool {
	buff, err := checkBuffer(r, t[0])
	if err != nil {
		return false
	}

	for _, v := range t {
		if bytes.Compare(v, buff) == 0 {
			return true
		}
	}

	return false
}

// IsPng function will return true if File is a valid PNG
func IsPng(r io.ReadSeeker) bool {
	return genericCompareBuffer(r, PNG)
}

// IsJpeg function will return true if File is a valid JPEG
func IsJpeg(r io.ReadSeeker) bool {
	return genericCompareBuffer(r, JPEG)
}

// IsPdf function will return true if File is a valid PDF
func IsPdf(r io.ReadSeeker) bool {
	return genericCompareBuffer(r, PDF)
}

// IsGif function will return true if File is a valid GIF
func IsGif(r io.ReadSeeker) bool {
	return genericCompareBuffer(r, GIF)
}

// IsMpg function will return true if File is a valid MPG
func IsMpg(r io.ReadSeeker) bool {
	return genericMultipleCompareBuffer(r, [][]byte{
		MPG_0,
		MPG_1,
	})
}

// IsOneOf function will validate File with multiple function
func IsOneOf(r io.ReadSeeker, functions ...function) bool {
	for _, f := range functions {
		valid := f(r)
		if valid {
			return true
		}
	}

	return false
}

package main

import (
	"fmt"
	"os"
)

func main() {
	args := os.Args

	if len(args) < 2 {
		fmt.Println("required input file")
		os.Exit(1)
	}

   // 開啟檔案
	inputFileArg := args[1]
	inFile, err := os.Open(inputFileArg)

	if err != nil {
		fmt.Println("error open input file ", err)
		os.Exit(1)
	}

   // 支援錯誤處理的關閉方式
	defer func() { 
      err := inFile.Close() 
      if err != nil {
         fmt.Println("error close input file ", err)
      }
   }()

   // 一次性判斷多種型別，如：是否為影象檔案
	valid := IsOneOf(inFile, filesig.Is3gp, filesig.IsPng, filesig.IsJpeg)
	fmt.Println(valid)

   // 當然也可以判斷單個型別
   valid = filesig.Is3gp(inFile)
	fmt.Println(valid)
}