class Net::Telnet

Net::Telnet¶ ↑

Provides telnet client functionality.

This class also has, through delegation, all the methods of a socket object (by default, a TCPSocket, but can be set by the Proxy option to new()). This provides methods such as close() to end the session and sysread() to read data directly from the host, instead of via the waitfor() mechanism. Note that if you do use sysread() directly when in telnet mode, you should probably pass the output through preprocess() to extract telnet command sequences.

Overview¶ ↑

The telnet protocol allows a client to login remotely to a user account on a server and execute commands via a shell. The equivalent is done by creating a Net::Telnet class with the Host option set to your host, calling login() with your user and password, issuing one or more cmd() calls, and then calling close() to end the session. The waitfor(), print(), puts(), and write() methods, which cmd() is implemented on top of, are only needed if you are doing something more complicated.

A Net::Telnet object can also be used to connect to non-telnet services, such as SMTP or HTTP. In this case, you normally want to provide the Port option to specify the port to connect to, and set the Telnetmode option to false to prevent the client from attempting to interpret telnet command sequences. Generally, login() will not work with other protocols, and you have to handle authentication yourself.

For some protocols, it will be possible to specify the Prompt option once when you create the Telnet object and use cmd() calls; for others, you will have to specify the response sequence to look for as the Match option to every cmd() call, or call puts() and waitfor() directly; for yet others, you will have to use sysread() instead of waitfor() and parse server responses yourself.

It is worth noting that when you create a new Net::Telnet object, you can supply a proxy IO channel via the Proxy option. This can be used to attach the Telnet object to other Telnet objects, to already open sockets, or to any read-write IO object. This can be useful, for instance, for setting up a test fixture for unit testing.

Examples¶ ↑

Log in and send a command, echoing all output to stdout¶ ↑

localhost = Net::Telnet::new("Host" => "localhost",
                             "Timeout" => 10,
                             "Prompt" => /[$%#>] \z/n)
localhost.login("username", "password") { |c| print c }
localhost.cmd("command") { |c| print c }
localhost.close

Check a POP server to see if you have mail¶ ↑

pop = Net::Telnet::new("Host" => "your_destination_host_here",
                       "Port" => 110,
                       "Telnetmode" => false,
                       "Prompt" => /^\+OK/n)
pop.cmd("user " + "your_username_here") { |c| print c }
pop.cmd("pass " + "your_password_here") { |c| print c }
pop.cmd("list") { |c| print c }

References¶ ↑

There are a large number of RFCs relevant to the Telnet protocol. RFCs 854-861 define the base protocol. For a complete listing of relevant RFCs, see www.omnifarious.org/~hopper/technical/telnet-rfc.html

Attributes

sock[R]

The socket the Telnet object is using. Note that this object becomes a delegate of the Telnet object, so normally you invoke its methods directly on the Telnet object.

Public Class Methods

new(options) { |mesg| ... } click to toggle source

Creates a new Net::Telnet object.

Attempts to connect to the host (unless the Proxy option is provided: see below). If a block is provided, it is yielded status messages on the attempt to connect to the server, of the form:

Trying localhost...
Connected to localhost.

options is a hash of options. The following example lists all options and their default values.

host = Net::Telnet::new(
         "Host"       => "localhost",  # default: "localhost"
         "Port"       => 23,           # default: 23
         "Binmode"    => false,        # default: false
         "Output_log" => "output_log", # default: nil (no output)
         "Dump_log"   => "dump_log",   # default: nil (no output)
         "Prompt"     => /[$%#>] \z/n, # default: /[$%#>] \z/n
         "Telnetmode" => true,         # default: true
         "Timeout"    => 10,           # default: 10
           # if ignore timeout then set "Timeout" to false.
         "Waittime"   => 0,            # default: 0
         "Proxy"      => proxy         # default: nil
                         # proxy is Net::Telnet or IO object
       )

The options have the following meanings:

Host: the hostname or IP address of the host to connect to, as a String. Defaults to “localhost”.
Port: the port to connect to. Defaults to 23.
Binmode: if false (the default), newline substitution is performed. Outgoing LF is converted to CRLF, and incoming CRLF is converted to LF. If true, this substitution is not performed. This value can also be set with the binmode() method. The outgoing conversion only applies to the puts() and print() methods, not the write() method. The precise nature of the newline conversion is also affected by the telnet options SGA and BIN.
Output_log: the name of the file to write connection status messages and all received traffic to. In the case of a proper Telnet session, this will include the client input as echoed by the host; otherwise, it only includes server responses. Output is appended verbatim to this file. By default, no output log is kept.
Dump_log: as for Output_log, except that output is written in hexdump format (16 bytes per line as hex pairs, followed by their printable equivalent), with connection status messages preceded by '#', sent traffic preceded by '>', and received traffic preceded by '<'. By default, not dump log is kept.
Prompt: a regular expression matching the host's command-line prompt sequence. This is needed by the Telnet class to determine when the output from a command has finished and the host is ready to receive a new command. By default, this regular expression is /[$%#>] z/n.
Telnetmode: a boolean value, true by default. In telnet mode, traffic received from the host is parsed for special command sequences, and these sequences are escaped in outgoing traffic sent using puts() or print() (but not write()). If you are using the Net::Telnet object to connect to a non-telnet service (such as SMTP or POP), this should be set to “false” to prevent undesired data corruption. This value can also be set by the telnetmode() method.
Timeout: the number of seconds to wait before timing out both the initial attempt to connect to host (in this constructor), which raises a Net::OpenTimeout, and all attempts to read data from the host, which raises a Net::ReadTimeout (in waitfor(), cmd(), and login()). The default value is 10 seconds. You can disable the timeout by setting this value to false. In this case, the connect attempt will eventually timeout on the underlying connect(2) socket call with an Errno::ETIMEDOUT error (but generally only after a few minutes), but other attempts to read data from the host will hang indefinitely if no data is forthcoming.
Waittime: the amount of time to wait after seeing what looks like a prompt (that is, received data that matches the Prompt option regular expression) to see if more data arrives. If more data does arrive in this time, Net::Telnet assumes that what it saw was not really a prompt. This is to try to avoid false matches, but it can also lead to missing real prompts (if, for instance, a background process writes to the terminal soon after the prompt is displayed). By default, set to 0, meaning not to wait for more data.
Proxy: a proxy object to used instead of opening a direct connection to the host. Must be either another Net::Telnet object or an IO object. If it is another Net::Telnet object, this instance will use that one's socket for communication. If an IO object, it is used directly for communication. Any other kind of object will cause an error to be raised.

# File lib/net/telnet.rb, line 273
def initialize(options) # :yield: mesg
  @options = options
  @options["Host"]       = "localhost"   unless @options.has_key?("Host")
  @options["Port"]       = 23            unless @options.has_key?("Port")
  @options["Prompt"]     = /[$%#>] \z/n  unless @options.has_key?("Prompt")
  @options["Timeout"]    = 10            unless @options.has_key?("Timeout")
  @options["Waittime"]   = 0             unless @options.has_key?("Waittime")
  unless @options.has_key?("Binmode")
    @options["Binmode"]    = false
  else
    unless (true == @options["Binmode"] or false == @options["Binmode"])
      raise ArgumentError, "Binmode option must be true or false"
    end
  end

  unless @options.has_key?("Telnetmode")
    @options["Telnetmode"] = true
  else
    unless (true == @options["Telnetmode"] or false == @options["Telnetmode"])
      raise ArgumentError, "Telnetmode option must be true or false"
    end
  end

  @telnet_option = { "SGA" => false, "BINARY" => false }

  if @options.has_key?("Output_log")
    @log = File.open(@options["Output_log"], 'a+')
    @log.sync = true
    @log.binmode
  end

  if @options.has_key?("Dump_log")
    @dumplog = File.open(@options["Dump_log"], 'a+')
    @dumplog.sync = true
    @dumplog.binmode
    def @dumplog.log_dump(dir, x)  # :nodoc:
      len = x.length
      addr = 0
      offset = 0
      while 0 < len
        if len < 16
          line = x[offset, len]
        else
          line = x[offset, 16]
        end
        hexvals = line.unpack('H*')[0]
        hexvals += ' ' * (32 - hexvals.length)
        hexvals = format("%s %s %s %s  " * 4, *hexvals.unpack('a2' * 16))
        line = line.gsub(/[\000-\037\177-\377]/n, '.')
        printf "%s 0x%5.5x: %s%s\n", dir, addr, hexvals, line
        addr += 16
        offset += 16
        len -= 16
      end
      print "\n"
    end
  end

  if @options.has_key?("Proxy")
    if @options["Proxy"].kind_of?(Net::Telnet)
      @sock = @options["Proxy"].sock
    elsif @options["Proxy"].kind_of?(IO)
      @sock = @options["Proxy"]
    else
      raise "Error: Proxy must be an instance of Net::Telnet or IO."
    end
  else
    message = "Trying " + @options["Host"] + "...\n"
    yield(message) if block_given?
    @log.write(message) if @options.has_key?("Output_log")
    @dumplog.log_dump('#', message) if @options.has_key?("Dump_log")

    begin
      if @options["Timeout"] == false
        @sock = TCPSocket.open(@options["Host"], @options["Port"])
      else
        Timeout.timeout(@options["Timeout"], Net::OpenTimeout) do
          @sock = TCPSocket.open(@options["Host"], @options["Port"])
        end
      end
    rescue Net::OpenTimeout
      raise Net::OpenTimeout, "timed out while opening a connection to the host"
    rescue
      @log.write($ERROR_INFO.to_s + "\n") if @options.has_key?("Output_log")
      @dumplog.log_dump('#', $ERROR_INFO.to_s + "\n") if @options.has_key?("Dump_log")
      raise
    end
    @sock.sync = true
    @sock.binmode

    message = "Connected to " + @options["Host"] + ".\n"
    yield(message) if block_given?
    @log.write(message) if @options.has_key?("Output_log")
    @dumplog.log_dump('#', message) if @options.has_key?("Dump_log")
  end

end

Public Instance Methods

binmode(mode = nil) click to toggle source

Turn newline conversion on (mode == false) or off (mode == true), or return the current value (mode is not specified).

# File lib/net/telnet.rb, line 405
def binmode(mode = nil)
  case mode
  when nil
    @options["Binmode"]
  when true, false
    @options["Binmode"] = mode
  else
    raise ArgumentError, "argument must be true or false"
  end
end

binmode=(mode) click to toggle source

Turn newline conversion on (false) or off (true).

# File lib/net/telnet.rb, line 417
def binmode=(mode)
  if (true == mode or false == mode)
    @options["Binmode"] = mode
  else
    raise ArgumentError, "argument must be true or false"
  end
end

close() click to toggle source

Closes the connection

# File lib/net/telnet.rb, line 757
def close
  @sock.close
end

cmd(options) { |recvdata| ... } click to toggle source

Send a command to the host.

More exactly, sends a string to the host, and reads in all received data until is sees the prompt or other matched sequence.

If a block is given, the received data will be yielded to it as it is read in. Whether a block is given or not, the received data will be return as a string. Note that the received data includes the prompt and in most cases the host's echo of our command.

options is either a String, specified the string or command to send to the host; or it is a hash of options. If a hash, the following options can be specified:

String: the command or other string to send to the host.
Match: a regular expression, the sequence to look for in the received data before returning. If not specified, the Prompt option value specified when this instance was created will be used, or, failing that, the default prompt of /[$%#>] z/n.
Timeout: the seconds to wait for data from the host before raising a Timeout error. If not specified, the Timeout option value specified when this instance was created will be used, or, failing that, the default value of 10 seconds.

The command or other string will have the newline sequence appended to it.

# File lib/net/telnet.rb, line 678
def cmd(options) # :yield: recvdata
  match    = @options["Prompt"]
  time_out = @options["Timeout"]
  fail_eof = @options["FailEOF"]

  if options.kind_of?(Hash)
    string   = options["String"]
    match    = options["Match"]   if options.has_key?("Match")
    time_out = options["Timeout"] if options.has_key?("Timeout")
    fail_eof = options["FailEOF"] if options.has_key?("FailEOF")
  else
    string = options
  end

  self.puts(string)
  if block_given?
    waitfor({"Prompt" => match, "Timeout" => time_out, "FailEOF" => fail_eof}){|c| yield c }
  else
    waitfor({"Prompt" => match, "Timeout" => time_out, "FailEOF" => fail_eof})
  end
end

The username and password can either be provided as two string arguments in that order, or as a hash with keys “Name” and “Password”.

This method looks for the strings “login” and “Password” from the host to determine when to send the username and password. If the login sequence does not follow this pattern (for instance, you are connecting to a service other than telnet), you will need to handle login yourself.

The password can be omitted, either by only provided one String argument, which will be used as the username, or by providing a has that has no “Password” key. In this case, the method will not look for the “Password:” prompt; if it is sent, it will have to be dealt with by later calls.

The method returns all data received during the login process from the host, including the echoed username but not the password (which the host should not echo). If a block is passed in, this received data is also yielded to the block as it is received.

# File lib/net/telnet.rb, line 722
def login(options, password = nil) # :yield: recvdata
  login_prompt = /[Ll]ogin[: ]*\z/n
  password_prompt = /[Pp]ass(?:word|phrase)[: ]*\z/n
  if options.kind_of?(Hash)
    username = options["Name"]
    password = options["Password"]
    login_prompt = options["LoginPrompt"] if options["LoginPrompt"]
    password_prompt = options["PasswordPrompt"] if options["PasswordPrompt"]
  else
    username = options
  end

  if block_given?
    line = waitfor(login_prompt){|c| yield c }
    if password
      line += cmd({"String" => username,
                   "Match" => password_prompt}){|c| yield c }
      line += cmd(password){|c| yield c }
    else
      line += cmd(username){|c| yield c }
    end
  else
    line = waitfor(login_prompt)
    if password
      line += cmd({"String" => username,
                   "Match" => password_prompt})
      line += cmd(password)
    else
      line += cmd(username)
    end
  end
  line
end

preprocess(string) click to toggle source

Preprocess received data from the host.

Performs newline conversion and detects telnet command sequences. Called automatically by waitfor(). You should only use this method yourself if you have read input directly using sysread() or similar, and even then only if in telnet mode.

# File lib/net/telnet.rb, line 431
def preprocess(string)
  # combine CR+NULL into CR
  string = string.gsub(/#{CR}#{NULL}/no, CR) if @options["Telnetmode"]

  # combine EOL into "\n"
  string = string.gsub(/#{EOL}/no, "\n") unless @options["Binmode"]

  # remove NULL
  string = string.gsub(/#{NULL}/no, '') unless @options["Binmode"]

  string.gsub(/#{IAC}(
               [#{IAC}#{AO}#{AYT}#{DM}#{IP}#{NOP}]|
               [#{DO}#{DONT}#{WILL}#{WONT}]
                 [#{OPT_BINARY}-#{OPT_NEW_ENVIRON}#{OPT_EXOPL}]|
               #{SB}[^#{IAC}]*#{IAC}#{SE}
             )/xno) do
    if    IAC == $1  # handle escaped IAC characters
      IAC
    elsif AYT == $1  # respond to "IAC AYT" (are you there)
      self.write("nobody here but us pigeons" + EOL)
      ''
    elsif DO[0] == $1[0]  # respond to "IAC DO x"
      if OPT_BINARY[0] == $1[1]
        @telnet_option["BINARY"] = true
        self.write(IAC + WILL + OPT_BINARY)
      else
        self.write(IAC + WONT + $1[1..1])
      end
      ''
    elsif DONT[0] == $1[0]  # respond to "IAC DON'T x" with "IAC WON'T x"
      self.write(IAC + WONT + $1[1..1])
      ''
    elsif WILL[0] == $1[0]  # respond to "IAC WILL x"
      if    OPT_BINARY[0] == $1[1]
        self.write(IAC + DO + OPT_BINARY)
      elsif OPT_ECHO[0] == $1[1]
        self.write(IAC + DO + OPT_ECHO)
      elsif OPT_SGA[0]  == $1[1]
        @telnet_option["SGA"] = true
        self.write(IAC + DO + OPT_SGA)
      else
        self.write(IAC + DONT + $1[1..1])
      end
      ''
    elsif WONT[0] == $1[0]  # respond to "IAC WON'T x"
      if    OPT_ECHO[0] == $1[1]
        self.write(IAC + DONT + OPT_ECHO)
      elsif OPT_SGA[0]  == $1[1]
        @telnet_option["SGA"] = false
        self.write(IAC + DONT + OPT_SGA)
      else
        self.write(IAC + DONT + $1[1..1])
      end
      ''
    else
      ''
    end
  end
end

print(string) click to toggle source

Sends a string to the host.

This does not automatically append a newline to the string. Embedded newlines may be converted and telnet command sequences escaped depending upon the values of telnetmode, binmode, and telnet options set by the host.

# File lib/net/telnet.rb, line 625
def print(string)
  string = string.gsub(/#{IAC}/no, IAC + IAC) if @options["Telnetmode"]

  if @options["Binmode"]
    self.write(string)
  else
    if @telnet_option["BINARY"] and @telnet_option["SGA"]
      # IAC WILL SGA IAC DO BIN send EOL --> CR
      self.write(string.gsub(/\n/n, CR))
    elsif @telnet_option["SGA"]
      # IAC WILL SGA send EOL --> CR+NULL
      self.write(string.gsub(/\n/n, CR + NULL))
    else
      # NONE send EOL --> CR+LF
      self.write(string.gsub(/\n/n, EOL))
    end
  end
end

puts(string) click to toggle source

Sends a string to the host.

Same as print(), but appends a newline to the string.

# File lib/net/telnet.rb, line 647
def puts(string)
  self.print(string + "\n")
end

telnetmode(mode = nil) click to toggle source

Set telnet command interpretation on (mode == true) or off (mode == false), or return the current value (mode not provided). It should be on for true telnet sessions, off if using Net::Telnet to connect to a non-telnet service such as SMTP.

# File lib/net/telnet.rb, line 381
def telnetmode(mode = nil)
  case mode
  when nil
    @options["Telnetmode"]
  when true, false
    @options["Telnetmode"] = mode
  else
    raise ArgumentError, "argument must be true or false, or missing"
  end
end

telnetmode=(mode) click to toggle source

Turn telnet command interpretation on (true) or off (false). It should be on for true telnet sessions, off if using Net::Telnet to connect to a non-telnet service such as SMTP.

# File lib/net/telnet.rb, line 395
def telnetmode=(mode)
  if (true == mode or false == mode)
    @options["Telnetmode"] = mode
  else
    raise ArgumentError, "argument must be true or false"
  end
end

waitfor(options) { |recvdata| ... } click to toggle source

Read data from the host until a certain sequence is matched.

If a block is given, the received data will be yielded as it is read in (not necessarily all in one go), or nil if EOF occurs before any data is received. Whether a block is given or not, all data read will be returned in a single string, or again nil if EOF occurs before any data is received. Note that received data includes the matched sequence we were looking for.

options can be either a regular expression or a hash of options. If a regular expression, this specifies the data to wait for. If a hash, this can specify the following options:

Match: a regular expression, specifying the data to wait for.
Prompt: as for Match; used only if Match is not specified.
String: as for Match, except a string that will be converted into a regular expression. Used only if Match and Prompt are not specified.
Timeout: the number of seconds to wait for data from the host before raising a Timeout::Error. If set to false, no timeout will occur. If not specified, the Timeout option value specified when this instance was created will be used, or, failing that, the default value of 10 seconds.
Waittime: the number of seconds to wait after matching against the input data to see if more data arrives. If more data arrives within this time, we will judge ourselves not to have matched successfully, and will continue trying to match. If not specified, the Waittime option value specified when this instance was created will be used, or, failing that, the default value of 0 seconds, which means not to wait for more input.
FailEOF: if true, when the remote end closes the connection then an EOFError will be raised. Otherwise, defaults to the old behaviour that the function will return whatever data has been received already, or nil if nothing was received.

# File lib/net/telnet.rb, line 528
def waitfor(options) # :yield: recvdata
  time_out = @options["Timeout"]
  waittime = @options["Waittime"]
  fail_eof = @options["FailEOF"]

  if options.kind_of?(Hash)
    prompt   = if options.has_key?("Match")
                 options["Match"]
               elsif options.has_key?("Prompt")
                 options["Prompt"]
               elsif options.has_key?("String")
                 Regexp.new( Regexp.quote(options["String"]) )
               end
    time_out = options["Timeout"]  if options.has_key?("Timeout")
    waittime = options["Waittime"] if options.has_key?("Waittime")
    fail_eof = options["FailEOF"]  if options.has_key?("FailEOF")
  else
    prompt = options
  end

  if time_out == false
    time_out = nil
  end

  line = ''
  buf = ''
  rest = ''
  until(prompt === line and not IO::select([@sock], nil, nil, waittime))
    unless IO::select([@sock], nil, nil, time_out)
      raise Net::ReadTimeout, "timed out while waiting for more data"
    end
    begin
      c = @sock.readpartial(1024 * 1024)
      @dumplog.log_dump('<', c) if @options.has_key?("Dump_log")
      if @options["Telnetmode"]
        c = rest + c
        if Integer(c.rindex(/#{IAC}#{SE}/no) || 0) <
           Integer(c.rindex(/#{IAC}#{SB}/no) || 0)
          buf = preprocess(c[0 ... c.rindex(/#{IAC}#{SB}/no)])
          rest = c[c.rindex(/#{IAC}#{SB}/no) .. -1]
        elsif pt = c.rindex(/#{IAC}[^#{IAC}#{AO}#{AYT}#{DM}#{IP}#{NOP}]?\z/no) ||
                   c.rindex(/\r\z/no)
          buf = preprocess(c[0 ... pt])
          rest = c[pt .. -1]
        else
          buf = preprocess(c)
          rest = ''
        end
     else
       # Not Telnetmode.
       #
       # We cannot use preprocess() on this data, because that
       # method makes some Telnetmode-specific assumptions.
       buf = rest + c
       rest = ''
       unless @options["Binmode"]
         if pt = buf.rindex(/\r\z/no)
           buf = buf[0 ... pt]
           rest = buf[pt .. -1]
         end
         buf.gsub!(/#{EOL}/no, "\n")
       end
      end
      @log.print(buf) if @options.has_key?("Output_log")
      line += buf
      yield buf if block_given?
    rescue EOFError # End of file reached
      raise if fail_eof
      if line == ''
        line = nil
        yield nil if block_given?
      end
      break
    end
  end
  line
end

write(string) click to toggle source

Write string to the host.

Does not perform any conversions on string. Will log string to the dumplog, if the Dump_log option is set.

# File lib/net/telnet.rb, line 610
def write(string)
  length = string.length
  while 0 < length
    IO::select(nil, [@sock])
    @dumplog.log_dump('>', string[-length..-1]) if @options.has_key?("Dump_log")
    length -= @sock.syswrite(string[-length..-1])
  end
end