CODEWITHSUNDEEP
gotelnet
Alexander
Alexander

Reputation: 149

How to read data from Telnet session

I'm trying to create a tool to connect to a network device by Telnet and send some commands (Expect-like with certain additional requirements) using go-telnet.

To the moment I managed to create a connection and send commands with something like this:

func main() {
    var loginBuffer = [6]byte{'r', 'o', 'o', 't', '\r', '\n'}
    var login = loginBuffer[:]

    conn, err := telnet.DialTo("10.10.10.2:23")
    if nil != err {
        fmt.Println(err)
    }
    defer conn.Close()

    conn.Write(login)
}

Using Wireshark I can see the device responding, however I cannot read any response data. Guess I'm using Read() in a wrong way, not sure.

Would appreciate a working example or an explanation of how to capture and process response data in this case.

Upvotes: 3

Views: 4480

Answers (2)

Alexander
Alexander

Reputation: 149

Thanks everyone, who spared their time to answer my question. I managed to identify the problem:

  1. Every time I created a read buffer it was too big (1024 bytes) so the program was waiting for it to fill up. Now I'm using a cycle reading to a 1 byte buffer.

  2. It seems, I also needed some criterion for the function to stop reading and proceed with sending commands.

Here is the working piece of code:

// Thin function reads from Telnet session. "expect" is a string I use as signal to stop reading
func ReaderTelnet(conn *telnet.Conn, expect string) (out string) {
    var buffer [1]byte
    recvData := buffer[:]
    var n int
    var err error

    for {
        n, err = conn.Read(recvData)
        fmt.Println("Bytes: ", n, "Data: ", recvData, string(recvData))
        if n <= 0 || err != nil || strings.Contains(out, expect) {
            break
        } else {
            out += string(recvData)
        }
    }
    return out
}

//convert a command to bytes, and send to Telnet connection followed by '\r\n' 
func SenderTelnet(conn *telnet.Conn, command string) {
    var commandBuffer []byte
    for _, char := range command {
        commandBuffer = append(commandBuffer, byte(char))
    }

    var crlfBuffer [2]byte = [2]byte{'\r', '\n'}
    crlf := crlfBuffer[:]

    fmt.Println(commandBuffer)

    conn.Write(commandBuffer)
    conn.Write(crlf)
}

func main() {
    conn, err := telnet.DialTo("10.10.10.2:23")
    if nil != err {
        fmt.Println(err)
    }

    fmt.Print(ReaderTelnet(conn, "Login"))
    SenderTelnet(conn, "root")
    fmt.Print(ReaderTelnet(conn, "Password"))
    SenderTelnet(conn, "root")
    fmt.Print(ReaderTelnet(conn, ">"))
}

Upvotes: 4

cslrnr
cslrnr

Reputation: 747

Where is your read operation from connection ? I think you need to call conn.read(buffer) to read from the connection and write it to buffer

https://godoc.org/github.com/reiver/go-telnet#Conn.Read

The examples are not helping much with hte package that you are using. May be the following example taken out of different telnet go package would be more helpful. 

https://github.com/ziutek/telnet/blob/master/examples/unix-cisco/main.go

Upvotes: 0

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