On Tuesday, April 28, 2020 at 1:42:15 AM UTC-7, Liam wrote:
>
>
>
> On Tuesday, April 28, 2020 at 12:05:00 AM UTC-7, Liam wrote:
>>
>>
>>
>> On Monday, April 27, 2020 at 10:00:52 PM UTC-7, Ian Lance Taylor wrote:
>>>
>>> On Mon, Apr 27, 2020 at 6:59 PM Liam <[email protected]> wrote:
>>> >
>>> > On Monday, April 27, 2020 at 5:56:52 PM UTC-7, Ian Lance Taylor wrote:
>>> >>
>>> >> On Mon, Apr 27, 2020 at 5:10 PM Liam <[email protected]> wrote:
>>> >> >
>>> >> > On Monday, April 27, 2020 at 4:22:41 PM UTC-7, Ian Lance Taylor
>>> wrote:
>>> >> >>
>>> >> >> On Sun, Apr 26, 2020 at 4:55 PM Liam <[email protected]> wrote:
>>> >> >> >
>>> >> >> > During an io.Copy() where the Writer is a TCPConn and the Reader
>>> is a 200K disk file, my code may concurrently Write() on the same TCPConn.
>>> >> >> >
>>> >> >> > I see the result of the Write() inserted into the result of the
>>> io.Copy(). I had the impression that was impossible, but I must be
>>> mistaken, as the sendfile(2) docs read:
>>> >> >> >
>>> >> >> > Note that a successful call to sendfile() may write fewer bytes
>>> than requested; the caller should be prepared to retry the call if there
>>> were unsent bytes.
>>> >> >> >
>>> >> >> > Could someone confirm that one must indeed synchronize
>>> concurrent use of tcpConn.Write() and io.Copy(tcpConn, file)?
>>> >> >>
>>> >> >> Synchronization should not be required. internal/poll.Sendfile
>>> >> >> acquires a write lock on dstFD, which is the TCP socket. That
>>> should
>>> >> >> ensure that the contents of an ordinary Write (which also acquires
>>> a
>>> >> >> write lock) should not interleave with the sendfile data.
>>> >> >>
>>> >> >> That said, if the sendfile system call cannot be used for whatever
>>> >> >> reason, the net package will fall back on doing ordinary Read and
>>> >> >> Write calls. And those Write calls can be interleaved with other
>>> >> >> Write calls done by a different goroutine. I think that is
>>> probably
>>> >> >> permitted, in that io.Copy doesn't promise to not interleave with
>>> >> >> simultaneous Write calls on the destination.
>>> >> >>
>>> >> >> So in the general case you should indeed use your own locking to
>>> avoid
>>> >> >> interleaving between io.Copy and a concurrent Write.
>>> >> >
>>> >> >
>>> >> > Thanks for the details. Where could I add a Println() to reveal why
>>> it doesn't call poll.Sendfile()?
>>> >> >
>>> >> > I expect this system to use sendfile(2). The file is a normal file
>>> on a local partition (running on a Digital Ocean Droplet).
>>> >> >
>>> >> >
>>> >> > /etc/fstab has:
>>> >> > UUID=[omitted] / ext4 defaults 1 1
>>> >> >
>>> >> >
>>> >> > $ df -h
>>> >> > Filesystem Size Used Avail Use% Mounted on
>>> >> > devtmpfs 981M 0 981M 0% /dev
>>> >> > tmpfs 996M 0 996M 0% /dev/shm
>>> >> > tmpfs 996M 436K 995M 1% /run
>>> >> > tmpfs 996M 0 996M 0% /sys/fs/cgroup
>>> >> > /dev/vda1 59G 5.7G 51G 11% /
>>> >> > tmpfs 200M 0 200M 0% /run/user/0
>>>
>>
>> Well this is a surprise... Added some println()s
>>
>> // my network setup
>> aCfgTcp := net.ListenConfig{KeepAlive: -1}
>> aListener, err := aCfgTcp.Listen(nil, iConf.Listen.Net,
>> iConf.Listen.Laddr)
>> if err != nil { return err }
>> aCert, err := tls.LoadX509KeyPair(iConf.Listen.CertPath,
>> iConf.Listen.KeyPath)
>> if err != nil { return err }
>> aCfgTls := tls.Config{Certificates: []tls.Certificate{aCert}}
>> aListener = tls.NewListener(aListener, &aCfgTls)
>>
>
> I left out my accept loop:
> var aConn net.Conn
> for {
> aConn, err = aListener.Accept()
> ...
>
Adding these to the Accept() loop shows that I see a tls.Conn but not a
net.TCPConn:
if _, ok := aConn.(*net.TCPConn); ok { fmt.Println(".. have tcpconn") }
if _, ok := aConn.(*tls.Conn); ok { fmt.Println(".. have tlsconn") }
Why doesn't tls.Conn either implement ReadFrom() or provide a way to obtain
the underlying TCPConn?
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