x/crypto/ssh: Session.Run returns error EOF

[QijingLi]

Please answer these questions before submitting your issue. Thanks!

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

go1.10 darwin/amd64

Does this issue reproduce with the latest release?

yes

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

darwin and amd64

What did you do?

I'm trying to run command on the device through ssh. I got same error with closed issue.
#16194

I tried changing WantReply to false. it didn't work.
please see the last comment.

What did you expect to see?

no error

What did you see instead?

error

[ianlancetaylor]

Please tell us exactly what you did: what program did you run, what was the complete output? Thanks.

[QijingLi]

this is the code i run against some device which implements SSH server.

	var sshConfig ssh.Config
	sshConfig.SetDefaults()
	sshConfig.Ciphers = append(sshConfig.Ciphers, "aes128-cbc", "aes256-cbc", "3des-cbc")
	fmt.Println("cipers:", sshConfig.Ciphers)
	config := &ssh.ClientConfig{
		Config: sshConfig,
		User:   login.Username,
		Auth: []ssh.AuthMethod{
			ssh.Password(login.Password),
		},
		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
		Timeout:         timeout,
	}
	if client, err = ssh.Dial("tcp", "192.168.0.10:22", config); err != nil {
		err = errors.New("unable to connect: " + err.Error())
		return
	}
	defer client.Close()
	if session, err = client.NewSession(); err != nil {
		err = errors.New("unable to open session" + err.Error())
		return
	}
	defer session.Close()

	// start to run command show macs
	var streamOut io.Reader
	if streamOut, err = session.StdoutPipe(); err != nil {
		err = errors.New("unable to make stdpipe connected: " + err.Error())
		return
	}
	if err = session.Run("show mac addresses"); err != nil {
		err = errors.New("unable to run the command:"+ err.Error())
		return
	}

The program returns the following:

unable to run the command: EOF.

After I enabled debugMux variable

018/10/10 14:19:17 send global(1): ssh.channelOpenMsg{ChanType:"session", PeersID:0x1, PeersWindow:0x200000, MaxPacketSize:0x8000, TypeSpecificData:[]uint8(nil)}
2018/10/10 14:19:17 decoding(1): 91 &ssh.channelOpenConfirmMsg{PeersID:0x1, MyID:0x1, MyWindow:0x1000, MaxPacketSize:0x1000, TypeSpecificData:[]uint8{}} - 17 bytes
2018/10/10 14:19:17 send(1): ssh.channelRequestMsg{PeersID:0x1, Request:"exec", WantReply:true, RequestSpecificData:[]uint8{0x0, 0x0, 0x0, 0x10, 0x73, 0x68, 0x6f, 0x77, 0x20, 0x63, 0x61, 0x62, 0x6c, 0x65, 0x20, 0x6d, 0x6f, 0x64, 0x65, 0x6d}}
2018/10/10 14:19:17 decoding(1): data packet - 28 bytes
2018/10/10 14:19:17 decoding(1): data packet - 264 bytes
2018/10/10 14:19:17 decoding(1): data packet - 173 bytes
2018/10/10 14:19:17 decoding(1): data packet - 120 bytes
2018/10/10 14:19:17 decoding(1): data packet - 120 bytes
2018/10/10 14:19:17 decoding(1): data packet - 129 bytes
2018/10/10 14:19:17 decoding(1): data packet - 129 bytes

after changed WantReply to false in Start function in session.go

2018/10/10 14:34:27 send global(1): ssh.channelOpenMsg{ChanType:"session", PeersID:0x1, PeersWindow:0x200000, MaxPacketSize:0x8000, TypeSpecificData:[]uint8(nil)}
2018/10/10 14:34:27 decoding(1): 91 &ssh.channelOpenConfirmMsg{PeersID:0x1, MyID:0x1, MyWindow:0x1000, MaxPacketSize:0x1000, TypeSpecificData:[]uint8{}} - 17 bytes
2018/10/10 14:34:27 send(1): ssh.channelRequestMsg{PeersID:0x1, Request:"exec", WantReply:false, RequestSpecificData:[]uint8{0x0, 0x0, 0x0, 0x10, 0x73, 0x68, 0x6f, 0x77, 0x20, 0x63, 0x61, 0x62, 0x6c, 0x65, 0x20, 0x6d, 0x6f, 0x64, 0x65, 0x6d}}
2018/10/10 14:34:27 send(1): ssh.channelEOFMsg{PeersID:0x1}
2018/10/10 14:34:27 decoding(1): 96 &ssh.channelEOFMsg{PeersID:0x1} - 5 bytes
2018/10/10 14:34:27 decoding(1): 97 &ssh.channelCloseMsg{PeersID:0x1} - 5 bytes
2018/10/10 14:34:27 send(1): ssh.channelCloseMsg{PeersID:0x1}
2018/10/10 14:34:27 send(1): ssh.channelCloseMsg{PeersID:0x1}
2018/10/10 14:34:27 loop exit read tcp 10.172.58.120:61108->192.168.0.10:22: use of closed network connection
{"level":"error","time":"2018-10-10T14:34:27.445-0700","message":"failed to fetch the MACs","error":"unable to run the command: wait: remote command exited without exit status or exit signal"}

[QijingLi]

here is comment from @hanwen
Our library is waiting for the exit-status or exit-signal message, which isn't coming. According to RFC 4254, those are optional, so we should probably do something intelligent in case the remote end doesn't send a status message. --

I have a question here. if the server doesn't send message when the command finishes, how the ssh client knows when it finish?

[hanwen]

The first trace looks OK; data is going over the wire.

Why did you change wantReply? That would likely cause the remote end to error out.

[QijingLi]

on the first trace, it ended up with returning EOF. The ssh client didn't get any data.
After reading this issue #16194, it looks exactly same.
the reason cause returning EOF is the server side didn't send the message when it's done the work,
but client want a reply. So I tried to change wantReply.

[hanwen]

the debugMux output looks completely different.

[QijingLi]

@hanwen got it working. thanks for your reply!
In my case, EOF actually is the sign of the server side finish the work.