\section{\module{telnetlib} ---
         Telnet client}

\declaremodule{standard}{telnetlib}
\modulesynopsis{Telnet client class.}
\sectionauthor{Skip Montanaro}{skip@mojam.com}

The \module{telnetlib} module provides a \class{Telnet} class that
implements the Telnet protocol.  See \rfc{854} for details about the
protocol.


\begin{classdesc}{Telnet}{\optional{host\optional{, port}}}
\class{Telnet} represents a connection to a telnet server. The
instance is initially not connected; the \method{open()} method must
be used to establish a connection.  Alternatively, the host name and
optional port number can be passed to the constructor, too.

Do not reopen an already connected instance.

This class has many \method{read_*()} methods.  Note that some of them 
raise \exception{EOFError} when the end of the connection is read,
because they can return an empty string for other reasons.  See the
individual descriptions below.
\end{classdesc}


\begin{seealso}
  \seerfc{854}{Telnet Protocol Specification}{
          Definition of the Telnet protocol.}
\end{seealso}



\subsection{Telnet Objects \label{telnet-objects}}

\class{Telnet} instances have the following methods:


\begin{methoddesc}{read_until}{expected\optional{, timeout}}
Read until a given string is encountered or until timeout.

When no match is found, return whatever is available instead,
possibly the empty string.  Raise \exception{EOFError} if the connection
is closed and no cooked data is available.
\end{methoddesc}

\begin{methoddesc}{read_all}{}
Read all data until \EOF{}; block until connection closed.
\end{methoddesc}

\begin{methoddesc}{read_some}{}
Read at least one byte of cooked data unless \EOF{} is hit.
Return \code{''} if \EOF{} is hit.  Block if no data is immediately
available.
\end{methoddesc}

\begin{methoddesc}{read_very_eager}{}
Read everything that can be without blocking in I/O (eager).

Raise \exception{EOFError} if connection closed and no cooked data
available.  Return \code{''} if no cooked data available otherwise.
Do not block unless in the midst of an IAC sequence.
\end{methoddesc}

\begin{methoddesc}{read_eager}{}
Read readily available data.

Raise \exception{EOFError} if connection closed and no cooked data
available.  Return \code{''} if no cooked data available otherwise.
Do not block unless in the midst of an IAC sequence.
\end{methoddesc}

\begin{methoddesc}{read_lazy}{}
Process and return data already in the queues (lazy).

Raise \exception{EOFError} if connection closed and no data available.
Return \code{''} if no cooked data available otherwise.  Do not block
unless in the midst of an IAC sequence.
\end{methoddesc}

\begin{methoddesc}{read_very_lazy}{}
Return any data available in the cooked queue (very lazy).

Raise \exception{EOFError} if connection closed and no data available.
Return \code{''} if no cooked data available otherwise.  This method
never blocks.
\end{methoddesc}

\begin{methoddesc}{open}{host\optional{, port}}
Connect to a host.
The optional second argument is the port number, which
defaults to the standard telnet port (23).

Do not try to reopen an already connected instance.
\end{methoddesc}

\begin{methoddesc}{msg}{msg\optional{, *args}}
Print a debug message when the debug level is \code{>} 0.
If extra arguments are present, they are substituted in the
message using the standard string formatting operator.
\end{methoddesc}

\begin{methoddesc}{set_debuglevel}{debuglevel}
Set the debug level.  The higher the value of \var{debuglevel}, the
more debug output you get (on \code{sys.stdout}).
\end{methoddesc}

\begin{methoddesc}{close}{}
Close the connection.
\end{methoddesc}

\begin{methoddesc}{get_socket}{}
Return the socket object used internally.
\end{methoddesc}

\begin{methoddesc}{fileno}{}
Return the file descriptor of the socket object used internally.
\end{methoddesc}

\begin{methoddesc}{write}{buffer}
Write a string to the socket, doubling any IAC characters.
This can block if the connection is blocked.  May raise
\exception{socket.error} if the connection is closed.
\end{methoddesc}

\begin{methoddesc}{interact}{}
Interaction function, emulates a very dumb telnet client.
\end{methoddesc}

\begin{methoddesc}{mt_interact}{}
Multithreaded version of \method{interact()}.
\end{methoddesc}

\begin{methoddesc}{expect}{list\optional{, timeout}}
Read until one from a list of a regular expressions matches.

The first argument is a list of regular expressions, either
compiled (\class{re.RegexObject} instances) or uncompiled (strings).
The optional second argument is a timeout, in seconds; the default
is to block indefinately.

Return a tuple of three items: the index in the list of the
first regular expression that matches; the match object
returned; and the text read up till and including the match.

If end of file is found and no text was read, raise
\exception{EOFError}.  Otherwise, when nothing matches, return
\code{(-1, None, \var{text})} where \var{text} is the text received so
far (may be the empty string if a timeout happened).

If a regular expression ends with a greedy match (e.g. \regexp{.*})
or if more than one expression can match the same input, the
results are undeterministic, and may depend on the I/O timing.
\end{methoddesc}


\subsection{Telnet Example \label{telnet-example}}
\sectionauthor{Peter Funk}{pf@artcom-gmbh.de}

A simple example illustrating typical use:

\begin{verbatim}
import getpass
import sys
import telnetlib

HOST = "localhost"
user = raw_input("Enter your remote account: ")
password = getpass.getpass()

tn = telnetlib.Telnet(HOST)

tn.read_until("login: ")
tn.write(user + "\n")
if password:
    tn.read_until("Password: ")
    tn.write(password + "\n")

tn.write("ls\n")
tn.write("exit\n")

print tn.read_all()
\end{verbatim}