rfc1184.txt

来自「RFC 的详细文档！」· 文本 代码 · 共 1,291 行 · 第 1/4 页

      The sender of this command REQUESTS that the list of octet
      triplets be used to set the local character to be used to send to
      perform the specified function.

      There are four levels that a function may be set to.
      SLC_NOSUPPORT is the lowest, SLC_CANTCHANGE is the next higher
      level, SLC_VALUE is above that, and SLC_DEFAULT is the highest
      level.

      If the SLC_LEVELBITS in the second octet are equal to SLC_DEFAULT,



Telnet Working Group                                            [Page 6]

RFC 1184                 Telnet Linemode Option             October 1990


      then this particular function should use the system default on the
      other side of the connection.

      If the SLC_LEVELBITS in the second octet are equal to SLC_VALUE,
      then this function is supported, and the current value is
      specified by the third octet.

      If the SLC_LEVELBITS in the second octet are equal to
      SLC_CANTCHANGE, then this is a function that is supported, but the
      value for this function, specified in the third octet, cannot be
      changed.

      If the SLC_LEVELBITS in the second octet are equal to
      SLC_NOSUPPORT, then this particular function is not supported and
      should be disabled by the other side.

      If this is a response to a previous request to change a special
      character, and we are agreeing to the change, then the SLC_ACK bit
      must be set in the second octet.

      If the SLC_FLUSHIN bit is set in the second octet, then whenever
      this function is sent, a Telnet "sync" should be sent at the same
      time to flush the input stream.

      If the SLC_FLUSHOUT bit is set in the second octet, then whenever
      this function is sent, output data should be flushed.

      Only the client may send an octet triplet with the first octet
      equal to zero.  In this case, the SLC_LEVELBITS may only be set to
      SLC_DEFAULT or SLC_VALUE, and the third octet does not matter.
      When the server receives 0 SLC_DEFAULT 0, it should switch to its
      system default special character settings, and send all those
      special characters to the client.  When the server receives 0
      SLC_VALUE 0, it should just send its current special character
      settings.  Note that if the server does not support some of the
      editing functions, they should be sent as XXX SLC_DEFAULT 0,
      rather than as XXX SLC_NOSUPPORT 0, so that the client may choose
      to use its own values for those functions, rather than have to
      disable those functions even if it supports them.

      If any of the octets in the list of octet triplets is equal to
      IAC, it must be sent as a double IAC.

   When a connection is established, it is the responsibility of the
   client to either request the remote default values for the special
   characters, or to send across what all the special characters should
   be set to.




Telnet Working Group                                            [Page 7]

RFC 1184                 Telnet Linemode Option             October 1990


   The function values can be put into two groups, functions that are to
   be translated to their Telnet equivalents before being sent across
   the Telnet connection, and functions that are to be recognized and
   processed locally.

   First, we have those characters that are to be mapped into their
   Telnet equivalents:

      SLC_SYNCH Synch.  See RFC 854, "TELNET PROTOCOL SPECIFICATION",
                for a complete description.

      SLC_BRK   Break.  See RFC 854, "TELNET PROTOCOL SPECIFICATION",
                for a complete description.

      SLC_IP    Interrupt Process.  See RFC 854, "TELNET PROTOCOL
                SPECIFICATION", for a complete description.

      SLC_AO    Abort Output.  See RFC 854, "TELNET PROTOCOL
                SPECIFICATION", for a complete description.

      SLC_AYT   Are You There.  See RFC 854, "TELNET PROTOCOL
                SPECIFICATION", for a complete description.

      SLC_EOR   End of Record.  See RFC 885, "TELNET END OF RECORD
                OPTION" for a complete description.

      SLC_ABORT Abort.  See section 2.5 for a complete description.

      SLC_EOF   End of File.  See section 2.5 for a complete
                description.

      SLC_SUSP  Suspend.  See section 2.5 for a complete description.

   Next, we have the locally interpreted functions.

      SLC_EC    Erase Character.  This is the character that is typed to
                erase one character from the input stream.  See RFC 854,
                "TELNET PROTOCOL SPECIFICATION", for a complete
                description.

      SLC_EL    Erase Line.  This is the character that is typed to
                erase the entire contents of the current line of input.
                See RFC 854, "TELNET PROTOCOL SPECIFICATION", for a
                complete description.

      SLC_EW    Erase Word.  This is the character that is typed to
                erase one word from the input stream.




Telnet Working Group                                            [Page 8]

RFC 1184                 Telnet Linemode Option             October 1990


      SLC_RP    Reprint Line.  This is the character that is typed to
                cause the current line of input to be reprinted, leaving
                the cursor at the end of the line.

      SLC_LNEXT Literal Next.  This is the character that is typed to
                indicate that the next character is to be taken
                literally, no character processing should be done with
                it, and if it is a special character that would normally
                get mapped into a Telnet option, that mapping should
                not be done.

      SLC_XON   Start Output.  This is the character that is sent to
                resume output to the users terminal.

      SLC_XOFF  Stop Output.  This is the character that is sent to stop
                output to the users terminal.

      SLC_FORW1 Forwarding character.  This is a character that should
                cause all data currently being buffered, and this
                character, to be sent immediately.

      SLC_FORW2 Forwarding character.  This is another character that is
                to be treated in the same manner as SLC_FORW1.

      SLC_MCL   Move cursor one character left.  When visual editing is
                supported, this is the character that, when typed, will
                move the cursor one character to the left in the
                display.

      SLC_MCR   Move cursor one character right.  When visual editing is
                supported, this is the character that, when typed, will
                move the cursor one character to the right in the
                display.

      SLC_MCWL  Move cursor one word left.  When visual editing is
                supported, this is the character that, when typed, will
                move the cursor one word to the left in the display.

      SLC_MCWR  Move cursor one word right.  When visual editing is
                supported, this is the character that, when typed, will
                move the cursor one word to the right in the display.

      SLC_MCBOL Move cursor to the begining of the line.  When visual
                editing is supported, this is the character that, when
                typed, will move the cursor to the begining of the line
                that is being edited.

      SLC_MCEOL Move cursor to the end of the line.  When visual editing



Telnet Working Group                                            [Page 9]

RFC 1184                 Telnet Linemode Option             October 1990


                is supported, this is the character that, when typed,
                will move the cursor to the end of the line that is
                being edited.

      SLC_INSRT Enter insert mode.  When visual editing is supported,
                after this character is typed, all normal characters
                that are subsequently typed will be inserted into the
                display.

      SLC_OVER  Enter overstrike mode.  When visual editing is
                supported, after this character is typed, all normal
                charactersthat are subsequently typed will overwrite
                any characters in the current display.  If the
                SLC_INSRT and SLC_OVER variables are set to the same
                value, then that value is to act as a toggle between
                overstrike and insert mode.

      SLC_ECR   Erase character to the right.  When visual editing is
                supported, this is the character that, when typed, will
                erase one character to the right of the cursor.

      SLC_EWR   Erase word to the right.  When visual editing is
                supported, this is the character that, when typed,
                will erase one word to the right of the cursor.

      SLC_EBOL  Erase to the begining of the line.  When visual editing
                is supported, this is the character that, when typed,
                will erase all the characters to the left of the cursor.

      SLC_EEOL  Erase to the end of the line.  When visual editing is
                supported, this is the character that, when typed, will
                erase all characters to the right of the cursor.

   For SLC_EEOL, SLC_EWR, and SLC_ECR, if a system has a cursor that is
   not diplayed between characters, but is positioned over a character,
   that character is assumed to be to the right of the cursor.  Thus,
   the SLC_ECR will erase the character that is under the current cursor
   position.

2.5 New control characters

   IAC ABORT

      Abort.  Similar to "IAC IP", but means only to abort or terminate
      the process to which the NVT is connected.  (The Telnet spec says
      IP may "suspend, interrupt, abort or terminate" the process.) If a
      system does not have two methods of interrupting a process, then
      ABORT and IP should have the same effect.



Telnet Working Group                                           [Page 10]

RFC 1184                 Telnet Linemode Option             October 1990


   IAC SUSP

      Suspend the execution of the current process attached to the NVT
      in such a way that another process will take over control of the
      NVT, and the suspended process can be resumed at a later time. If
      the receiving system does not support this functionality, it
      should be ignored.

   IAC EOF

      End Of File.  The recipient should notify the process connected to
      the NVT that an end of file has been reached.  This is intended
      for systems that support the ability for the user to type in an
      EOF character at the keyboard.

3.  Default Specification

   The default specification for this option is

      WONT LINEMODE

      DONT LINEMODE

   meaning there will not be any subnegotiation of the mode of the
   connection.

   If WILL LINEMODE is negotiated, the defaults are:

      IAC SB LINEMODE MODE 0 IAC SE
      IAC SB LINEMODE WONT FORWARDMASK IAC SE

   If DO LINEMODE is negotiated, the defaults are:

      IAC SB LINEMODE MODE 0 IAC SE
      IAC SB LINEMODE DONT FORWARDMASK IAC SE

   Character values for SLC default to SLC_NOSUPPORT.

4.  Motivation

   With increasing Telnet usage, it has become apparent that the ability
   to do command line processing on the local machine and send completed
   lines to the remote machine is a feature necessary in several
   environments.  First, in the case of a connection over long delay
   equipment, it is very frustrating to the user to have the echoing of
   his data take several seconds.  Second, some supercomputers, due to
   their nature, are not good at handling and processing single
   character input.  For these machines, it is better to have the front



Telnet Working Group                                           [Page 11]

RFC 1184                 Telnet Linemode Option             October 1990


   end computer do the character processing, and leave the
   supercomputer's cycles available for doing vectorized number
   crunching.

   There have been attempts to make local line editing work within the
   existing Telnet specs.  Indeed, the 4.3 BSD tape includes a version
   of Telnet that attempts to do this through recognition of the state
   of the ECHO and SUPRESS-GO-AHEAD options; other implementations do
   this recognition purely through the ECHO option.

   There are problems with both of these methods.  Using just the ECHO
   provides no mechanism to have ECHO to the user turned off, and leave
   local character processing on, for example, when a user is typing a
   password.

   The usage of the SUPRESS-GO-AHEAD comes from reading into RFC 858,
   where it states:

      "In many TELNET implementations it will be desirable to couple the
      SUPRESS-GO-AHEAD option to the echo option so that when the echo
      option is in effect, the SUPPRESS-GO-AHEAD option is in effect
      simultaneously: both of these options will normally have to be in
      effect simultaneously to effect what it commonly understood to be
      character at a time echoing by the remote computer."