How to get terminal dimensions from a terminal request

[h3x4d3c1m4l]

Hi all,

For my photobooth project, I'm currently working on a control server in which I'd like in incorporate a SSH server for management and status purposes. I'm currently stuck in getting the terminal dimensions from the pty-req package.

My channel request handler looks as follows:

server.ChannelRequest += (channel, e) =>
{
    if (channel is SshChannel sshChannel)
    {
        if (e.RequestType == ChannelRequestTypes.Terminal)
        {
            // TODO: Find the terminal dimensions
            // I expected e.Request to be of type [TerminalRequestMessage] instead of type [ChannelRequestMessage]
            // which contains the fields I need.
            
            // Accept PTY allocation
            e.IsAuthorized = true;
        }
    }
}

I would have expected to get an object of type TerminalRequestMessage with the following fields (from RFC 4254):

      byte      SSH_MSG_CHANNEL_REQUEST
      uint32    recipient channel
      string    "pty-req"
      boolean   want_reply
      string    TERM environment variable value (e.g., vt100)
      uint32    terminal width, characters (e.g., 80)
      uint32    terminal height, rows (e.g., 24)
      uint32    terminal width, pixels (e.g., 640)
      uint32    terminal height, pixels (e.g., 480)
      string    encoded terminal modes

(From: https://www.rfc-editor.org/rfc/rfc4254#section-6.2)

[Bip901]

ChannelRequestMessage is the base type of all channel requests. You can parse it into any other request type:

TerminalRequestMessage terminalRequestMessage = e.Request.ConvertTo<TerminalRequestMessage>();

Behind the scenes, this just calls the OnRead method of TerminalRequestMessage, which looks like:

        Term = reader.ReadString(Encoding.ASCII);
        Columns = reader.ReadUInt32();
        Rows = reader.ReadUInt32();
        PixelWidth = reader.ReadUInt32();
        PixelHeight = reader.ReadUInt32();

This design means you can easily define your own custom message types.