os: ModeType is missing os.ModeCharDevice

[somersf]

What version of Go are you using (go version)?

go1.11

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOOS="darwin"
and
GOARCH="amd64"
GOOS="linux"

What did you do?

I stat-ed a character device and analyzed the returned mode.

The os/stat_linux.go and os/stat_darwin.go implementations map a system stat value of S_IFCHR to ModeDevice | ModeCharDevice. I did not check other platforms.

However, the ModeType mask defined in os/type.go (https://golang.org/pkg/os/#FileMode) doesn't include the ModeCharDevice bit.
Masking a mode with ModeType in order to recover the type from the mode doesn't allow ModeDevice | ModeCharDevice to be recovered.

package main

import (
    "fmt"
    "os"
)

func main() {
    path := "/dev/zero"
    info, err := os.Lstat(path)
    if err != nil {
        fmt.Printf("stat failed; %v\n", err)
        return
    }
    mode := info.Mode()

    const charDev = os.ModeDevice | os.ModeCharDevice
    if mode & charDev == charDev {
        fmt.Printf("%s has character device bits set\n", path)
    }

    if mode & os.ModeType == charDev {
        fmt.Printf("%s type is character device\n", path)
    } else if mode & os.ModeType == os.ModeDevice {
        fmt.Printf("%s type is other device\n", path)
    }
}

https://play.golang.org/p/lcciw1JFCtj

What did you expect to see?

/dev/zero has character device bits set
/dev/zero type is character device

What did you see instead?

/dev/zero has character device bits set
/dev/zero type is other device

[tklauser]

FWIW, in archive/zip.fileModeToUnixMode this also leads to the character device bit not represented correctly.

os.ModeCharDevice was added by @rsc in https://golang.org/cl/5531052, but nothing indicates why it was omitted from os.ModeType. Maybe just an oversight?

[gopherbot]

Change https://golang.org/cl/135075 mentions this issue: os: add ModeCharDevice to ModeType