[SOLVED] Telnet connection not writing tab to a file

Issue

I have a C# WPF application that is making a Telnet connection to write some content to a file on a Linux system from a Windows system. So say I have some text like this.

Here is a bit\tof text \r\n Followed by a new line.

Here is generally how the code goes:

string ipAddress = "11.11.11.11";
int port = 66;
TelnetConnection tc = new TelnetConnection(ipAddress, port);
string s = tc.Login("root", "password", 100);
string prompt = s.TrimEnd();
if (prompt != "$" && prompt != "#"){
    throw new Exception("Connection failed");
}
tc.WriteLine("echo $'Here is a bit\tof text \r\n Followed by a new line.' >> MyFile.txt");

Here is the TelnetConnection class I use:\

enum Verbs
{
    WILL = 251,
    WONT = 252,
    DO = 253,
    DONT = 254,
    IAC = 255
}

enum Options
{
    SGA = 3
}

class TelnetConnection
{
    TcpClient tcpSocket;

    int TimeOutMs = 10;

    public TelnetConnection(string Hostname, int Port)
    {
        tcpSocket = new TcpClient(Hostname, Port);

    }

    public string Login(string Username, string Password, int LoginTimeOutMs)
    {
        int oldTimeOutMs = TimeOutMs;
        TimeOutMs = LoginTimeOutMs;
        string s = Read();
        if (!s.TrimEnd().EndsWith(":"))
            throw new Exception("Failed to connect : no login prompt");
        WriteLine(Username);

        s += Read();
        if (!s.TrimEnd().EndsWith(":"))
            throw new Exception("Failed to connect : no password prompt");
        WriteLine(Password);

        s += Read();
        TimeOutMs = oldTimeOutMs;
        return s;
    }

    public void WriteLine(string cmd)
    {
        Write(cmd + "\n");
    }

    public void Write(string cmd)
    {
        if (!tcpSocket.Connected) return;
        byte[] buf = System.Text.ASCIIEncoding.ASCII.GetBytes(cmd.Replace("\0xFF", "\0xFF\0xFF"));
        tcpSocket.GetStream().Write(buf, 0, buf.Length);
        System.Threading.Thread.Sleep(1000);
    }

    public string Read()
    {
        if (!tcpSocket.Connected) return null;
        StringBuilder sb = new StringBuilder();
        do
        {
            ParseTelnet(sb);
            System.Threading.Thread.Sleep(TimeOutMs);
        } while (tcpSocket.Available > 0);
        return sb.ToString();
    }

    public bool IsConnected
    {
        get { return tcpSocket.Connected; }
    }

    void ParseTelnet(StringBuilder sb)
    {
        while (tcpSocket.Available > 0)
        {
            int input = tcpSocket.GetStream().ReadByte();
            switch (input)
            {
                case -1:
                    break;
                case (int)Verbs.IAC:
                    // interpret as command
                    int inputverb = tcpSocket.GetStream().ReadByte();
                    if (inputverb == -1) break;
                    switch (inputverb)
                    {
                        case (int)Verbs.IAC:
                            //literal IAC = 255 escaped, so append char 255 to string
                            sb.Append(inputverb);
                            break;
                        case (int)Verbs.DO:
                        case (int)Verbs.DONT:
                        case (int)Verbs.WILL:
                        case (int)Verbs.WONT:
                            // reply to all commands with "WONT", unless it is SGA (suppres go ahead)
                            int inputoption = tcpSocket.GetStream().ReadByte();
                            if (inputoption == -1) break;
                            tcpSocket.GetStream().WriteByte((byte)Verbs.IAC);
                            if (inputoption == (int)Options.SGA)
                                tcpSocket.GetStream().WriteByte(inputverb == (int)Verbs.DO ? (byte)Verbs.WILL : (byte)Verbs.DO);
                            else
                                tcpSocket.GetStream().WriteByte(inputverb == (int)Verbs.DO ? (byte)Verbs.WONT : (byte)Verbs.DONT);
                            tcpSocket.GetStream().WriteByte((byte)inputoption);
                            break;
                        default:
                            break;
                    }
                    break;
                default:
                    sb.Append((char)input);
                    break;
            }
        }
    }
}

When I go to check the file the it is written to like this

Here is a bitof text
Followed by a new line.

So the tab character isn't even read, but the new line is for some reason. Any ideas?

Solution

The correct answer is given by @Johannes Krackowizer but the explanation is missing a detail: the 'TelnetConnection' isn't a file. What you are doing is typing to the remote computer. @Greg M also mentions this.

When you send \t in your string, you are sending a literal <tab> character. The computer at the other end is trying to finish typing a file name for you because that's what happens when you hit <tab>. If you want to get a tab back you need to send a \ and a t. The t you can just send, but the \ needs to be sent as \\ because \ is an escape character, as you know. So send:

"echo $'Here is a bit\\tof text \r\n Followed by a new line.' >> MyFile.txt"

Note the bit\\tof with two backslashes. So why does \r\n work? Because it's <Enter> and <Ctrl>+<Enter>, and the string you are typing is being typed within single quotes. When you use single quotes you can hit <Enter> and keep typing until you are done and end with the final '.

As others have mentioned, printf is generally preferred:

"printf $'Here is a bit\\tof text \r\n Followed by a new line.\n' >> MyFile.txt"

Next, in your code, the backslash should also be escaped, so you probably need to escape those characters as well:

tc.WriteLine("printf $'Here is a bit\\\\tof text \\r\\n Followed by a new line.\\n' >> MyFile.txt");

Answered By - rand'Chris

Answer Checked By - Terry (WPSolving Volunteer)