can't read data from the tun device

[akalio ja]

func openTun(ch chan int, timer *time.Timer) {

    fd, err := unix.Open("/dev/net/tun", unix.O_RDWR|unix.O_NONBLOCK, 0)

    if err != nil {

        panic(err)

    }

    defer unix.Close(fd)

    var ifr struct {

        name  [16]byte

        flags uint16

        _     [22]byte

    }

    copy(ifr.name[:], "tun0")

    ifr.flags = unix.IFF_TUN | unix.IFF_NO_PI

    _, _, errno := unix.Syscall(unix.SYS_IOCTL, uintptr(fd), unix.TUNSETIFF, uintptr(unsafe.Pointer(&ifr)))

    if errno != 0 {

        log.Println("err to syscall:", errno)

        return

    }

    ch <- fd

    bytes := []byte("hell can you recv?")

    fmt.Println(unix.Write(fd, bytes))

    ticker := time.NewTicker(time.Second * 10)

    for {

        select {

        case <-ticker.C:

            fmt.Println(unix.Write(fd, bytes))

        case <-timer.C:

            return

        }

    }

}

func readFd(fd int) {

    ticker := time.NewTicker(time.Second * 10)

    buffer := make([]byte, 1024)

    for {

        <-ticker.C

        n, err := unix.Read(fd, buffer)

        if err != nil {

            if err == unix.EAGAIN {

                log.Println("No data available at the moment")

            } else {

                log.Println("Error reading from file descriptor:", err)

                return

            }

        } else {

            log.Println("reading from file descriptor:", string(buffer[:n]))

        }

    }

}

func main() {

    fdchannel, done := make(chan int, 1), time.NewTimer(time.Minute)

    go openTun(fdchannel, done)

    fd := <-fdchannel

    log.Println("opened fd", fd)

    go readFd(fd)

    <- done.C

}

[Ian Lance Taylor]

What version of Go are you using?

Ian

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[akalio ja]

GO111MODULE=""

GOARCH="amd64"

GOBIN=""

GOCACHE="/root/.cache/go-build"

GOENV="/root/.config/go/env"

GOEXE=""

GOEXPERIMENT=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="linux"

GOINSECURE=""

GOMODCACHE="/root/go/pkg/mod"

GONOPROXY=""

GONOSUMDB=""

GOOS="linux"

GOPATH="/root/go"

GOPRIVATE=""

GOPROXY="https://proxy.golang.org,direct"

GOROOT="/usr/local/go"

GOSUMDB="sum.golang.org"

GOTMPDIR=""

GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"

GOVCS=""

GOVERSION="go1.20.3"

GCCGO="gccgo"

GOAMD64="v1"

AR="ar"

CC="gcc"

CXX="g++"

CGO_ENABLED="1"

GOMOD="/root/projs/tmp/go.mod"

GOWORK=""

CGO_CFLAGS="-O2 -g"

CGO_CPPFLAGS=""

CGO_CXXFLAGS="-O2 -g"

CGO_FFLAGS="-O2 -g"

CGO_LDFLAGS="-O2 -g"

PKG_CONFIG="pkg-config"

GOGCCFLAGS="-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3940382547=/tmp/go-build -gno-record-gcc-switches"

this my env

[Ian Lance Taylor]

On Thu, Jun 15, 2023 at 10:41 PM akalio ja <jaak...@gmail.com> wrote:
>
> GOVERSION="go1.20.3"

Thanks. You didn't say what the exact problem was, but I would guess
that you are running into the problem described at
https://go.dev/issue/59545. That problem should be fixed in the
upcoming 1.21 release.

Ian

> To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/5f004bba-963d-4f3e-b5bb-e15ee43c0d2fn%40googlegroups.com.