Windows OpenFile标志

Question

I am trying to write a program that reads a file while allowing other applications to access it. I’ve learned that in Windows you need to pass syscall.FILESHARE_READ/WRITE flags to prevent file locking. However, introducing these flags restricts me from reading the file in the first place, with the error — read ‘file’: Access is denied. This is my code:

os.OpenFile(path, syscall.O_RDONLY | syscall.FILE_SHARE_WRITE | syscall.FILE_SHARE_READ, 0444)

Am I using the correct flags? Is this functionality allowed on Windows?

Here's an example Go program Building with this command - GOOS=windows GOARCH=amd64 go build -v -o testRead.exe

package main

import (
    "fmt"
    "os"
    "time"
    "bufio"
    "syscall"
)

func main() {

if len(os.Args) != 2 {
    fmt.Println("Specify file!")
    return
}

path := os.Args[1]
f, err := os.OpenFile(path, syscall.O_RDONLY|syscall.FILE_SHARE_WRITE | syscall.FILE_SHARE_READ, 0444)
//f, err := os.Open(path)
if err != nil {
    fmt.Println("Can't open file")
    fmt.Println(err)
    return
}
defer f.Close()

reader := bufio.NewReader(f)
line, _, err := reader.ReadLine()
if (err != nil) {
    fmt.Println(err)
}
fmt.Println(line)


// Keeps the program alive
t1 := time.Now().Local().Add(time.Second * time.Duration(3))
for {
    if time.Now().After(t1) {
        fmt.Println("Still Alive!")
        t1 = time.Now().Local().Add(time.Second * time.Duration(3))
    }
}
} 

I've observed that reading works fine with os.Open and os.OpenFile(path, syscall.O_RDONLY, 0444).

Answer 1

The XY problem is asking about your attempted solution rather than your actual problem: The XY Problem.

---

If we open the file with

f, err := os.OpenFile(path, syscall.O_RDONLY, 0444)

your program runs with no errors.

On Windows, the program uses CreateFile with

DesiredAccess = GENERIC_READ
ShareMode = FILE_SHARE_READ | FILE_SHARE_WRITE

---

For some unknown reason, you are using arbitrary os.OpenFile flag bit smashing on Windows.

f, err := os.OpenFile(path, syscall.O_RDONLY|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_READ, 0444)

where

const (
    O_RDONLY   = 0x00000
    O_WRONLY   = 0x00001
    O_RDWR     = 0x00002

    FILE_SHARE_READ     = 0x00000001
    FILE_SHARE_WRITE    = 0x00000002
)

Smashing the os.OpenFile flag mode bits with unrelated file share bits, you have

flag = syscall.O_RDONLY|syscall.FILE_SHARE_WRITE|syscall.FILE_SHARE_READ

or

flag = O_RDONLY|O_WRONLY|O_RDWR

The results are undefined.

On Windows, an error is reported: read test.file: Access is denied..

On Linux, an error is detected: read test.file: bad file descriptor.