Extract text from x pos binary file

问题

I am trying to read a binary file to grab string from different positions; read {IP,login,pwd} my idea is to find the first ip and read the data after that because the length between is the same like this :

Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
00000060  5F 00 00 00 00 11 E0 BB 5F 00 00 00 00 01 34 31  _.....à»_.....40
00000070  2E 31 39 31 2E 39 37 2E 36 32 00 00 00 00 00 00  .091.17.02......
00000080  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000090  00 00 73 75 70 70 6F 72 74 00 00 00 00 00 00 00  ..support.......
000000A0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000000B0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000000C0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000000D0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000000E0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000000F0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000100  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000110  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000120  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000130  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000140  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000150  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000160  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000170  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000180  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000190  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000001A0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000001B0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000001C0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000001D0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000001E0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
000001F0  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000200  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000210  00 00 00 00 31 71 61 7A 40 57 53 58 00 00 00 00  ....1qaz@WSX....
00000220  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
00000230  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................

My Go code

import (
    "io"
    "log"
    "os"
)
func main() {
    file, err := os.Open("data")
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()
    o2, err := file.Seek(110, io.SeekCurrent) <---- find first occurrence 
    byteSlice := make([]byte, 32)

    bytesRead, err := file.Read(byteSlice)
    if err != nil {
        log.Fatal(err)
    }
    
    log.Printf("IP: %s\n", byteSlice)
    
}

how to find all occurrences { ip, login, pwd } after finding ip, with my code I can just find the first one (ip) 32bits.

回答1:

One approach would be to iterate the file. Essentially you could reimplement the strings program. It would be similar to using bufio#Scanner.Scan, but you would need to iterate on null bytes instead of newlines. You can use bufio#Scanner.Split, and Go even offers some premade functions.

However the premade functions are ScanBytes, ScanLines, ScanRunes and ScanWords, none of which really help in this case. I took a look at ScanLines, but it returns empty lines too. And we definitely dont want thousands of returns on repeat null bytes. So best chance is with ScanWords. I tossed out the Unicode stuff as we are dealing with binary data. Then I basically changed isSpace to "is null byte". Here is the result:

package main

func ScanNull(y []byte, b bool) (int, []byte, error) {
   n1 := 0
   for n1 < len(y) {
      if y[n1] != '\x00' {
         break
      }
      n1++
   }
   for n2 := n1; n2 < len(y); n2++ {
      if y[n2] == '\x00' {
         return n2 + 1, y[n1:n2], nil
      }
   }
   if b && len(y) > n1 {
      return len(y), y[n1:], nil
   }
   return n1, nil, nil
}

and in use:

package main

import (
   "bufio"
   "strings"
)

func main() {
   const input = "March\x00April\x00May\x00\x00June"
   scanner := bufio.NewScanner(strings.NewReader(input))
   scanner.Split(ScanNull)
   for scanner.Scan() {
      println(scanner.Text())
   }
}

回答2:

Thank you for help,

I use file.Seek(x,0) like this code:

file, err := os.Open("data.bin")
check(err)
defer file.Close()

o1, err := file.Seek(110, 0)  <--- first position
check(err)
_ip := make([]byte, 15)
ipRead, err := file.Read(_ip)
clean_ip := strings.ReplaceAll(string(_ip[:]), " ", " ")

o2, err := file.Seek(21, io.SeekCurrent)
check(err)
_user := make([]byte, 15)
userRead, err := file.Read(_user)
clean_user := strings.ReplaceAll(string(_user[:]), " ", " ")

o3, err := file.Seek(532, 0)  <---- Second position
check(err)
_pwd := make([]byte, 20)
pwdRead, err := file.Read(_pwd)
clean_pwd := strings.ReplaceAll(string(_pwd[:]), " ", " ")

Its working but not clean

来源：https://stackoverflow.com/questions/65112561/extract-text-from-x-pos-binary-file

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