.. historic nodename: TCP Function System

TCP Function System
================================================================================
.. index:: single: TCP function system; Command

.. index:: single: ztcp, function system based on; Command

Description
--------------------------------------------------------------------------------

A module ``zsh/net/tcp`` is provided to provide network I/O over
TCP/IP from within the shell; see its description in
:zshsectref:`The zsh/net/tcp Module <zshmodules>`.
This manual page describes a function suite based on the module.
If the module is installed, the functions are usually installed at the
same time, in which case they will be available for
autoloading in the default function search path.  In addition to the
``zsh/net/tcp`` module, the ``zsh/zselect`` module is used to implement
timeouts on read operations.  For troubleshooting tips, consult the
corresponding advice for the ``zftp`` functions described in
:manpage:`zshzftpsys`.

There are functions corresponding to the basic I/O operations open, close,
read and send, named ``tcp_open`` etc., as well as a function
``tcp_expect`` for pattern match analysis of data read as input.  The
system makes it easy to receive data from and send data to multiple named
sessions at once.  In addition, it can be linked with the shell's line
editor in such a way that input data is automatically shown at the
terminal.  Other facilities available including logging, filtering and
configurable output prompts.

To use the system where it is available, it should be enough to
``autoload -U tcp_open`` and run ``tcp_open`` as documented below to
start a session.  The ``tcp_open`` function will autoload the remaining
functions.

.. historic nodename: TCP Functions

TCP User Functions
--------------------------------------------------------------------------------

Basic I/O
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. index:: single: tcp_open; Function

``tcp_open`` [ ``-qz`` ] :var:`host port` [ :var:`sess` ]

``tcp_open`` [ ``-qz`` ] [ ``-s`` :var:`sess` | ``-l`` :var:`sess`\[``,``...] ] ... 

``tcp_open`` [ ``-qz`` ] [ ``-a`` :var:`fd` | ``-f`` :var:`fd` ] [ :var:`sess` ]
    
    Open a new session.  In the first and simplest form, open a TCP connection
    to host :var:`host` at port :var:`port`; numeric and symbolic forms are
    understood for both.
    
    If :var:`sess` is given, this becomes the name of the session which can be
    used to refer to multiple different TCP connections.  If :var:`sess` is
    not given, the function will invent a numeric name value (note this is
    :emphasis:`not` the same as the file descriptor to which the session is attached).
    It is recommended that session names not include \`funny' characters, where
    funny characters are not well-defined but certainly do not include
    alphanumerics or underscores, and certainly do include whitespace.
    
    In the second case, one or more sessions to be opened are given by name.
    A single session name is given after ``-s`` and a comma-separated list
    after ``-l``; both options may be repeated as many times as necessary.
    A failure to open any session causes ``tcp_open`` to abort.
    The host and port are read from the file ``.ztcp_sessions`` in the same
    directory as the user's zsh initialisation files, i.e. usually the home
    directory, but ``$ZDOTDIR`` if that is set.  The file consists of lines
    each giving a session name and the corresponding host and port, in that
    order (note the session name comes first, not last), separated by
    whitespace.
    
    The third form allows passive and fake TCP connections.  If the option
    ``-a`` is used, its argument is a file descriptor open for listening for
    connections.  No function front-end is provided to open such a file
    descriptor, but a call to ``ztcp -l`` :var:`port` will create one with the
    file descriptor stored in the parameter ``$REPLY``.  The listening port can
    be closed with ``ztcp -c`` :var:`fd`.  A call to ``tcp_open -a`` :var:`fd`
    will block until a remote TCP connection is made to :var:`port` on the local
    machine.  At this point, a session is created in the usual way and is
    largely indistinguishable from an active connection created with one of the
    first two forms.
    
    If the option ``-f`` is used, its argument is a file descriptor which is
    used directly as if it were a TCP session.  How well the remainder of the
    TCP function system copes with this depends on what actually underlies this
    file descriptor.  A regular file is likely to be unusable; a FIFO (pipe) of
    some sort will work better, but note that it is not a good idea for two
    different sessions to attempt to read from the same FIFO at once.
    
    If the option ``-q`` is given with any of the three forms, ``tcp_open``
    will not print informational messages, although it will in any case exit
    with an appropriate status.
    
    If the line editor (zle) is in use, which is typically the case if the
    shell is interactive, ``tcp_open`` installs a handler inside zle which
    will check for new data at the same time as it checks for keyboard input.
    This is convenient as the shell consumes no CPU time while waiting; the
    test is performed by the operating system.  Giving the option ``-z`` to
    any of the forms of ``tcp_open`` prevents the handler from being
    installed, so data must be read explicitly.  Note, however, this is not
    necessary for executing complete sets of send and read commands from a
    function, as zle is not active at this point.  Generally speaking, the
    handler is only active when the shell is waiting for input at a command
    prompt or in the ``vared`` builtin.  The option has no effect if zle is not
    active; ``[[ -o zle]]`` will test for this.
    
    The first session to be opened becomes the current session and subsequent
    calls to ``tcp_open`` do not change it.  The current session is stored
    in the parameter ``$TCP_SESS``; see below for more detail about the
    parameters used by the system.
    
    The function ``tcp_on_open``, if defined, is called when a session
    is opened.  See the description below.
    

.. index:: single: tcp_close; Function

``tcp_close`` [ ``-qn`` ] [ ``-a`` | ``-l`` :var:`sess`\[``,``...] | :var:`sess` ... ]
    
    Close the named sessions, or the current session if none is given,
    or all open sessions if ``-a`` is given.  The options ``-l`` and ``-s`` are
    both handled for consistency with ``tcp_open``, although the latter is
    redundant.
    
    If the session being closed is the current one, ``$TCP_SESS`` is unset,
    leaving no current session, even if there are other sessions still open.
    
    If the session was opened with ``tcp_open -f``, the file descriptor is
    closed so long as it is in the range 0 to 9 accessible directly from the
    command line.  If the option ``-n`` is given, no attempt will be made to
    close file descriptors in this case.  The ``-n`` option is not used for
    genuine ``ztcp`` session; the file descriptors are always closed with the
    session.
    
    If the option ``-q`` is given, no informational messages will be printed.
    

.. index:: single: tcp_read; Function

``tcp_read`` [ ``-bdq`` ] [ ``-t`` :var:`TO` ] [ ``-T`` :var:`TO` ]

         [ ``-a`` | ``-u`` :var:`fd`\[``,``...] | ``-l`` :var:`sess`\[``,``...] | ``-s`` :var:`sess` ... ]
    
    Perform a read operation on the current session, or on a list of
    sessions if any are given with ``-u``, ``-l`` or ``-s``, or all open
    sessions if the option ``-a`` is given.  Any of the ``-u``, ``-l`` or
    ``-s`` options may be repeated or mixed together.  The ``-u`` option
    specifies a file descriptor directly (only those managed by this system
    are useful), the other two specify sessions as described for
    ``tcp_open`` above.
    
    The function checks for new data available on all the sessions listed.
    Unless the ``-b`` option is given, it will not block waiting for new data.
    Any one line of data from any of the available sessions will be read,
    stored in the parameter ``$TCP_LINE``, and displayed to standard output
    unless ``$TCP_SILENT`` contains a non-empty string.  When printed to
    standard output the string ``$TCP_PROMPT`` will be shown at the start of
    the line; the default form for this includes the name of the session being
    read.  See below for more information on these parameters.  In this mode,
    ``tcp_read`` can be called repeatedly until it returns status 2 which
    indicates all pending input from all specified sessions has been handled.
    
    With the option ``-b``, equivalent to an infinite timeout, the function
    will block until a line is available to read from one of the specified
    sessions.  However, only a single line is returned.
    
    The option ``-d`` indicates that all pending input should be drained.  In
    this case ``tcp_read`` may process multiple lines in the manner given
    above; only the last is stored in ``$TCP_LINE``, but the complete set is
    stored in the array ``$tcp_lines``.  This is cleared at the start of each
    call to ``tcp_read``.
    
    The options ``-t`` and ``-T`` specify a timeout in seconds, which may be a
    floating point number for increased accuracy.  With ``-t`` the timeout is
    applied before each line read.  With ``-T``, the timeout applies to the
    overall operation, possibly including multiple read operations if the
    option ``-d`` is present; without this option, there is no distinction
    between ``-t`` and ``-T``.
    
    The function does not print informational messages, but if the option
    ``-q`` is given, no error message is printed for a non-existent session.
    
    A return status of 2 indicates a timeout or no data to read.  Any other
    non-zero return status indicates some error condition.
    
    See ``tcp_log`` for how to control where data is sent by ``tcp_read``.
    

.. index:: single: tcp_send; Function

``tcp_send`` [ ``-cnq`` ] [ ``-s`` :var:`sess` | ``-l`` :var:`sess`\[``,``...] ] :var:`data` ...

``tcp_send`` [ ``-cnq`` ] ``-a`` :var:`data` ...
    
    Send the supplied data strings to all the specified sessions in turn.  The
    underlying operation differs little from a ``print -r`` to the session's
    file descriptor, although it attempts to prevent the shell from dying owing
    to a ``SIGPIPE`` caused by an attempt to write to a defunct session.
    
    The option ``-c`` causes ``tcp_send`` to behave like ``cat``.  It reads
    lines from standard input until end of input and sends them in turn to the
    specified session(s) exactly as if they were given as :var:`data`
    arguments to individual ``tcp_send`` commands.
    
    The option ``-n`` prevents ``tcp_send`` from putting a newline at the end
    of the data strings.
    
    The remaining options all behave as for ``tcp_read``.
    
    The data arguments are not further processed once they have been passed to
    ``tcp_send``; they are simply passed down to ``print -r``.
    
    If the parameter ``$TCP_OUTPUT`` is a non-empty string and logging is
    enabled then the data sent to each session will be echoed to the log
    file(s) with ``$TCP_OUTPUT`` in front where appropriate, much
    in the manner of ``$TCP_PROMPT``.
    

Session Management
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. index:: single: tcp_alias; Function

``tcp_alias`` [ ``-q`` ] :var:`alias`\ ``=``:var:`sess` ...

``tcp_alias`` [ ``-q`` ] [ :var:`alias` ... ]

``tcp_alias`` ``-d`` [ ``-q`` ] :var:`alias` ...
    
    This function is not particularly well tested.
    
    The first form creates an alias for a session name; :var:`alias` can then be
    used to refer to the existing session :var:`sess`.  As many aliases may be
    listed as required.
    
    The second form lists any aliases specified, or all aliases if none.
    
    The third form deletes all the aliases listed.  The underlying sessions are
    not affected.
    
    The option ``-q`` suppresses an inconsistently chosen subset of error
    messages.
    

.. index:: single: tcp_log; Function

``tcp_log`` [ ``-asc`` ] [ ``-n`` | ``-N`` ] [ :var:`logfile` ]
    
    With an argument :var:`logfile`, all future input from ``tcp_read`` will be
    logged to the named file.  Unless ``-a`` (append) is given, this file will
    first be truncated or created empty.  With no arguments, show the current
    status of logging.
    
    With the option ``-s``, per-session logging is enabled.  Input from
    ``tcp_read`` is output to the file :var:`logfile`\ ``.``:var:`sess`.  As the
    session is automatically discriminated by the filename, the contents are
    raw (no ``$TCP_PROMPT``).  The option  ``-a`` applies as above.
    Per-session logging and logging of all data in one file are not mutually
    exclusive.
    
    The option ``-c`` closes all logging, both complete and per-session logs.
    
    The options ``-n`` and ``-N`` respectively turn off or restore output of
    data read by ``tcp_read`` to standard output; hence ``tcp_log -cn`` turns
    off all output by ``tcp_read``.
    
    The function is purely a convenient front end to setting the parameters
    ``$TCP_LOG``, ``$TCP_LOG_SESS``, ``$TCP_SILENT``, which are described below.
    

.. index:: single: tcp_rename; Function

``tcp_rename`` :var:`old` :var:`new`
    
    Rename session :var:`old` to session :var:`new`.  The old name becomes invalid.
    

.. index:: single: tcp_sess; Function

``tcp_sess`` [ :var:`sess` [ :var:`command` [ :var:`arg` ... ] ] ]
    
    With no arguments, list all the open sessions and associated file
    descriptors.  The current session is marked with a star.  For use in
    functions, direct access to the parameters ``$tcp_by_name``, ``$tcp_by_fd``
    and ``$TCP_SESS`` is probably more convenient; see below.
    
    With a :var:`sess` argument, set the current session to :var:`sess`.
    This is equivalent to changing ``$TCP_SESS`` directly.
    
    With additional arguments, temporarily set the current session while
    executing :var:`command` :var:`arg` ....  :var:`command` is re-evaluated
    so as to expand aliases etc., but the remaining :var:`arg`\s are passed
    through as that appear to ``tcp_sess``.  The original session is restored
    when ``tcp_sess`` exits.
    

Advanced I/O
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.. index:: single: tcp_command; Function

``tcp_command`` :var:`send-option` ... :var:`send-argument` ...
    
    This is a convenient front-end to ``tcp_send``.  All arguments are passed
    to ``tcp_send``, then the function pauses waiting for data.  While data is
    arriving at least every ``$TCP_TIMEOUT`` (default 0.3) seconds, data is
    handled and printed out according to the current settings.  Status 0 is
    always returned.
    
    This is generally only useful for interactive use, to prevent the display
    becoming fragmented by output returned from the connection.  Within a
    programme or function it is generally better to handle reading data by a
    more explicit method.
    

.. index:: single: tcp_expect; Function

``tcp_expect`` [ ``-q`` ] [ ``-p`` :var:`var` | ``-P`` :var:`var` ] [ ``-t`` :var:`TO` | ``-T`` :var:`TO` ]

           [ ``-a`` | ``-s`` :var:`sess` | ``-l`` :var:`sess`\[``,``...] ] :var:`pattern` ...
    
    Wait for input matching any of the given :var:`pattern`\s from any of the
    specified sessions.  Input is ignored until an input line matches one of
    the given patterns; at this point status zero is returned, the matching
    line is stored in ``$TCP_LINE``, and the full set of lines read during the
    call to ``tcp_expect`` is stored in the array ``$tcp_expect_lines``.
    
    Sessions are specified in the same way as ``tcp_read``: the default is to
    use the current session, otherwise the sessions specified by ``-a``,
    ``-s``, or ``-l`` are used.
    
    Each :var:`pattern` is a standard zsh extended-globbing pattern; note that it
    needs to be quoted to avoid it being expanded immediately by filename
    generation.  It must match the full line, so to match a substring there
    must be a ``*`` at the start and end.  The line matched against includes
    the ``$TCP_PROMPT`` added by ``tcp_read``.  It is possible to include the
    globbing flags ``#b`` or ``#m`` in the patterns to make backreferences
    available in the parameters ``$MATCH``, ``$match``, etc., as described in
    the base zsh documentation on pattern matching.
    
    Unlike ``tcp_read``, the default behaviour of ``tcp_expect`` is to block
    indefinitely until the required input is found.  This can be modified by
    specifying a timeout with ``-t`` or ``-T``; these function as in
    ``tcp_read``, specifying a per-read or overall timeout, respectively, in
    seconds, as an integer or floating-point number.  As ``tcp_read``, the
    function returns status 2 if a timeout occurs.
    
    The function returns as soon as any one of the patterns given match.  If
    the caller needs to know which of the patterns matched, the option ``-p``
    :var:`var` can be used; on return, ``$var`` is set to the number of the
    pattern using ordinary zsh indexing, i.e. the first is 1, and so on.  Note
    the absence of a ``$`` in front of :var:`var`.  To avoid clashes, the
    parameter cannot begin with ``_expect``.  The index -1 is used if
    there is a timeout and 0 if there is no match.
    
    The option ``-P`` :var:`var` works similarly to ``-p``, but instead of
    numerical indexes the regular arguments must begin with a prefix
    followed by a colon: that prefix is then used as a tag to which :var:`var`
    is set when the argument matches.  The tag ``timeout`` is used if there
    is a timeout and the empty string if there is no match.  Note it is
    acceptable for different arguments to start with the same prefix if the
    matches do not need to be distinguished.
    
    The option ``-q`` is passed directly down to ``tcp_read``.
    
    As all input is done via ``tcp_read``, all the usual rules about output of
    lines read apply.  One exception is that the parameter ``$tcp_lines`` will
    only reflect the line actually matched by ``tcp_expect``; use
    ``$tcp_expect_lines`` for the full set of lines read during the function
    call.
    

.. index:: single: tcp_proxy; Function

``tcp_proxy``
    
    This is a simple-minded function to accept a TCP connection and execute a
    command with I/O redirected to the connection.  Extreme caution should be
    taken as there is no security whatsoever and this can leave your computer
    open to the world.  Ideally, it should only be used behind a firewall.
    
    The first argument is a TCP port on which the function will listen.
    
    The remaining arguments give a command and its arguments to execute with
    standard input, standard output and standard error redirected to the
    file descriptor on which the TCP session has been accepted.
    If no command is given, a new zsh is started.  This gives everyone on
    your network direct access to your account, which in many cases will be a
    bad thing.
    
    The command is run in the background, so ``tcp_proxy`` can then accept new
    connections.  It continues to accept new connections until interrupted.
    

.. index:: single: tcp_spam; Function

``tcp_spam`` [ ``-ertv`` ] [ ``-a`` | ``-s`` :var:`sess` | ``-l`` :var:`sess`\[``,``...] ] :var:`cmd` [ :var:`arg` ... ]
    
    Execute :var:`cmd` [ :var:`arg` ... ] for each session in turn.  Note this executes
    the command and arguments; it does not send the command line as data
    unless the ``-t`` (transmit) option is given.
    
    The sessions may be selected explicitly with the standard ``-a``, ``-s`` or
    ``-l`` options, or may be chosen implicitly.  If none of the three options
    is given the rules are: first, if the array ``$tcp_spam_list`` is set, this
    is taken as the list of sessions, otherwise all sessions are taken.
    Second, any sessions given in the array ``$tcp_no_spam_list`` are removed
    from the list of sessions.
    
    Normally, any sessions added by the ``-a`` flag or when all sessions are
    chosen implicitly are spammed in alphabetic order; sessions given by the
    ``$tcp_spam_list`` array or on the command line are spammed in the order
    given.  The ``-r`` flag reverses the order however it was arrived it.
    
    The ``-v`` flag specifies that a ``$TCP_PROMPT`` will be output before each
    session.  This is output after any modification to ``TCP_SESS`` by the
    user-defined ``tcp_on_spam`` function described below.  (Obviously that
    function is able to generate its own output.)
    
    If the option ``-e`` is present, the line given as :var:`cmd` [ :var:`arg` ... ] is executed
    using ``eval``, otherwise it is executed without any further processing.
    

.. index:: single: tcp_talk; Function

``tcp_talk``
    
    This is a fairly simple-minded attempt to force input to the line editor to
    go straight to the default ``TCP_SESS``.
    
    An escape string, ``$TCP_TALK_ESCAPE``, default ``:``, is used to allow
    access to normal shell operation.  If it is on its own at the start of the
    line, or followed only by whitespace, the line editor returns to normal
    operation.  Otherwise, the string and any following whitespace are skipped
    and the remainder of the line executed as shell input without any change of
    the line editor's operating mode.
    
    The current implementation is somewhat deficient in terms of use of the
    command history.  For this reason, many users will prefer to use some form
    of alternative approach for sending data easily to the current session.
    One simple approach is to alias some special character (such as ``%``) to
    ``tcp_command --``.
    

.. index:: single: tcp_wait; Function

``tcp_wait``
    
    The sole argument is an integer or floating point number which gives the
    seconds to delay.  The shell will do nothing for that period except wait
    for input on all TCP sessions by calling ``tcp_read -a``.  This is similar
    to the interactive behaviour at the command prompt when zle handlers are
    installed.
    

\`One-shot' File Transfer
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

``tcp_point`` :var:`port`

``tcp_shoot`` :var:`host` :var:`port`
    
    This pair of functions provide a simple way to transfer a file between
    two hosts within the shell.  Note, however, that bulk data transfer is
    currently done using ``cat``.  ``tcp_point`` reads any data arriving at
    :var:`port` and sends it to standard output; ``tcp_shoot`` connects to
    :var:`port` on :var:`host` and sends its standard input.  Any unused :var:`port`
    may be used; the standard mechanism for picking a port is to think of a
    random four-digit number above 1024 until one works.
    
    To transfer a file from host ``woodcock`` to host ``springes``, on
    ``springes``:
    
    
    .. code-block:: zsh
       :class: example

        tcp_point 8091 >output_file
    
    
    and on ``woodcock``:
    
    
    .. code-block:: zsh
       :class: example

        tcp_shoot springes 8091 <input_file
    
    
    As these two functions do not require ``tcp_open`` to set up a TCP
    connection first, they may need to be autoloaded separately.
    

TCP User-defined Functions
--------------------------------------------------------------------------------

Certain functions, if defined by the user, will be called by the function
system in certain contexts.  This facility depends on the module
``zsh/parameter``, which is usually available in interactive shells as the
completion system depends on it.  None of the functions need be defined;
they simply provide convenient hooks when necessary.

Typically, these are called after the requested action has been taken, so
that the various parameters will reflect the new state.

.. index:: single: tcp_on_alias; Function

``tcp_on_alias`` :var:`alias` :var:`fd`
    
    When an alias is defined, this function will be called with two arguments:
    the name of the alias, and the file descriptor of the corresponding session.
    

.. index:: single: tcp_on_awol; Function

``tcp_on_awol`` :var:`sess` :var:`fd`
    
    If the function ``tcp_fd_handler`` is handling input from the line
    editor and detects that the file descriptor is no longer reusable,
    by default it removes it from the list of file descriptors handled
    by this method and prints a message.  If the function ``tcp_on_awol``
    is defined it is called immediately before this point.  It may
    return status 100, which indicates that the normal handling should
    still be performed; any other return status indicates that no further
    action should be taken and the ``tcp_fd_handler`` should return
    immediately with the given status.  Typically the action of ``tcp_on_awol``
    will be to close the session.
    
    The variable ``TCP_INVALIDATE_ZLE`` will be a non-empty string if it is
    necessary to invalidate the line editor display using ``zle -I`` before
    printing output from the function.
    
    (\`AWOL' is military jargon for \`absent without leave' or some
    variation.  It has no pre-existing technical meaning known to the author.)
    

.. index:: single: tcp_on_close; Function

``tcp_on_close`` :var:`sess` :var:`fd`
    
    This is called with the name of a session being closed and the file
    descriptor which corresponded to that session.  Both will be invalid by
    the time the function is called.
    

.. index:: single: tcp_on_open; Function

``tcp_on_open`` :var:`sess` :var:`fd`
    
    This is called after a new session has been defined with the session name
    and file descriptor as arguments.  If it returns a non-zero status,
    opening the session is assumed to fail and the session is closed
    again; however, ``tcp_open`` will continue to attempt to open any
    remaining sessions given on the command line.
    

.. index:: single: tcp_on_rename; Function

``tcp_on_rename`` :var:`oldsess` :var:`fd` :var:`newsess`
    
    This is called after a session has been renamed with the three arguments
    old session name, file descriptor, new session name.
    

.. index:: single: tcp_on_spam; Function

``tcp_on_spam`` :var:`sess` :var:`command ...`
    
    This is called once for each session spammed, just :emphasis:`before` a command is
    executed for a session by ``tcp_spam``.  The arguments are the session name
    followed by the command list to be executed.  If ``tcp_spam`` was called
    with the option ``-t``, the first command will be ``tcp_send``.
    
    This function is called after ``$TCP_SESS`` is set to reflect the session
    to be spammed, but before any use of it is made.  Hence it is possible to
    alter the value of ``$TCP_SESS`` within this function.  For example, the
    session arguments to ``tcp_spam`` could include extra information to be
    stripped off and processed in ``tcp_on_spam``.
    
    If the function sets the parameter ``$REPLY`` to ``done``, the command
    line is not executed; in addition, no prompt is printed for the ``-v``
    option to ``tcp_spam``.
    

.. index:: single: tcp_on_unalias; Function

``tcp_on_unalias`` :var:`alias` :var:`fd`
    
    This is called with the name of an alias and the corresponding session's
    file descriptor after an alias has been deleted.
    

TCP Utility Functions
--------------------------------------------------------------------------------

The following functions are used by the TCP function system but will rarely
if ever need to be called directly.

.. index:: single: tcp_fd_handler; Function

``tcp_fd_handler``
    
    This is the function installed by ``tcp_open`` for handling input from
    within the line editor, if that is required.  It is in the format
    documented for the builtin ``zle -F`` in :zshsectref:`Zle Builtins <zshzle>`.
    
    While active, the function sets the parameter ``TCP_HANDLER_ACTIVE`` to 1.
    This allows shell code called internally (for example, by setting
    ``tcp_on_read``) to tell if is being called when the shell is otherwise
    idle at the editor prompt.
    

.. index:: single: tcp_output; Function

``tcp_output`` [ ``-q`` ] ``-P`` :var:`prompt` ``-F`` :var:`fd` ``-S`` :var:`sess`
    
    This function is used for both logging and handling output to standard
    output, from within ``tcp_read`` and (if ``$TCP_OUTPUT`` is set)
    ``tcp_send``.
    
    The :var:`prompt` to use is specified by ``-P``; the default is the empty
    string.  It can contain:
    
    ``%c``
        
        Expands to 1 if the session is the current session, otherwise 0.  Used
        with ternary expressions such as ``%(c.-.+)`` to
        output ``+`` for the current session and ``-`` otherwise.
        
    
    ``%f``
        
        Replaced by the session's file descriptor.
        
    
    ``%s``
        
        Replaced by the session name.
        
    
    ``%%``
        
        Replaced by a single ``%``.
        
    
    
    
    The option ``-q`` suppresses output to standard output, but not to any log
    files which are configured.
    
    The ``-S`` and ``-F`` options are used to pass in the session name and file
    descriptor for possible replacement in the prompt.
    

.. historic nodename: TCP Parameters

TCP User Parameters
--------------------------------------------------------------------------------

Parameters follow the usual convention that uppercase is used for scalars
and integers, while lowercase is used for normal and associative array.
It is always safe for user code to read these parameters.  Some parameters
may also be set; these are noted explicitly.  Others are included in this
group as they are set by the function system for the user's benefit,
i.e. setting them is typically not useful but is benign.

It is often also useful to make settable parameters local to a function.
For example, ``local TCP_SILENT=1`` specifies that data read during the
function call will not be printed to standard output, regardless of the
setting outside the function.  Likewise, ``local TCP_SESS=``:var:`sess`
sets a session for the duration of a function, and ``local
TCP_PROMPT=`` specifies that no prompt is used for input during the
function.

.. index:: single: tcp_expect_lines; Variable

``tcp_expect_lines``
    
    Array.  The set of lines read during the last call to ``tcp_expect``,
    including the last (``$TCP_LINE``).
    

.. index:: single: tcp_filter; Variable

``tcp_filter``
    
    Array. May be set directly.  A set of extended globbing patterns which,
    if matched in ``tcp_output``, will cause the line not to be printed to
    standard output.  The patterns should be defined as described for the
    arguments to ``tcp_expect``.  Output of line to log files is not affected.
    

.. index:: single: TCP_HANDLER_ACTIVE; Variable

``TCP_HANDLER_ACTIVE``
    
    Scalar.  Set to 1 within ``tcp_fd_handler`` to indicate to functions
    called recursively that they have been called during an editor session.
    Otherwise unset.
    

.. index:: single: TCP_LINE; Variable

``TCP_LINE``
    
    The last line read by ``tcp_read``, and hence also ``tcp_expect``.
    

.. index:: single: TCP_LINE_FD; Variable

``TCP_LINE_FD``
    
    The file descriptor from which ``$TCP_LINE`` was read.
    ``${tcp_by_fd[$TCP_LINE_FD]}`` will give the corresponding session name.
    

.. index:: single: tcp_lines; Variable

``tcp_lines``
    
    Array. The set of lines read during the last call to ``tcp_read``,
    including the last (``$TCP_LINE``).
    

.. index:: single: TCP_LOG; Variable

``TCP_LOG``
    
    May be set directly, although it is also controlled by ``tcp_log``.
    The name of a file to which output from all sessions will be sent.
    The output is proceeded by the usual ``$TCP_PROMPT``.  If it is not an
    absolute path name, it will follow the user's current directory.
    

.. index:: single: TCP_LOG_SESS; Function

``TCP_LOG_SESS``
    
    May be set directly, although it is also controlled by ``tcp_log``.
    The prefix for a set of files to which output from each session separately
    will be sent; the full filename is ``${TCP_LOG_SESS}.``:var:`sess`.
    Output to each file is raw; no prompt is added.  If it is not an absolute
    path name, it will follow the user's current directory.
    

.. index:: single: tcp_no_spam_list; Variable

``tcp_no_spam_list``
    
    Array.  May be set directly.  See ``tcp_spam`` for how this is used.
    

.. index:: single: TCP_OUTPUT; Variable

``TCP_OUTPUT``
    
    May be set directly.  If a non-empty string, any data sent to a session by
    ``tcp_send`` will be logged.  This parameter gives the prompt to be used
    in a file specified by ``$TCP_LOG`` but not in a file generated from
    ``$TCP_LOG_SESS``.  The prompt string has the same format as
    ``TCP_PROMPT`` and the same rules for its use apply.
    

.. index:: single: TCP_PROMPT; Variable

``TCP_PROMPT``
    
    May be set directly.  Used as the prefix for data read by ``tcp_read``
    which is printed to standard output or to the log file given by
    ``$TCP_LOG``, if any.  Any ``%s``, ``%f`` or ``%%`` occurring in the
    string will be replaced by the name of the session, the session's
    underlying file descriptor, or a single ``%``, respectively.  The
    expression ``%c`` expands to 1 if the session being read is the current
    session, else 0; this is most useful in ternary expressions such as
    ``%(c.-.+)`` which outputs ``+`` if the session is
    the current one, else ``-``.
    
    If the prompt starts with ``%P``, this is stripped and the complete
    result of the previous stage is passed through standard prompt ``%``-style
    formatting before being output.
    

.. index:: single: TCP_READ_DEBUG; Variable

``TCP_READ_DEBUG``
    
    May be set directly.  If this has non-zero length, ``tcp_read`` will give
    some limited diagnostics about data being read.
    

.. index:: single: TCP_SECONDS_START; Variable

``TCP_SECONDS_START``
    
    This value is created and initialised to zero by tcp_open.
    
    The functions ``tcp_read`` and ``tcp_expect`` use the shell's
    ``SECONDS`` parameter for their own timing purposes.  If that parameter
    is not of floating point type on entry to one of the functions, it will
    create a local parameter ``SECONDS`` which is floating point and set the
    parameter ``TCP_SECONDS_START`` to the previous value of ``$SECONDS``.
    If the parameter is already floating point, it is used without a local
    copy being created and ``TCP_SECONDS_START`` is not set.  As the global
    value is zero, the shell elapsed time is guaranteed to be the sum of
    ``$SECONDS`` and ``$TCP_SECONDS_START``.
    
    This can be avoided by setting ``SECONDS`` globally to a floating point
    value using ``typeset -F SECONDS``; then the TCP functions will never
    make a local copy and never set ``TCP_SECONDS_START`` to a non-zero value.
    

.. index:: single: TCP_SESS; Variable

``TCP_SESS``
    
    May be set directly.  The current session; must refer to one of the
    sessions established by ``tcp_open``.
    

.. index:: single: TCP_SILENT; Variable

``TCP_SILENT``
    
    May be set directly, although it is also controlled by ``tcp_log``.
    If of non-zero length, data read by ``tcp_read`` will not be written to
    standard output, though may still be written to a log file.
    

.. index:: single: tcp_spam_list; Variable

``tcp_spam_list``
    
    Array.  May be set directly.  See the description of the function
    ``tcp_spam`` for how this is used.
    

.. index:: single: TCP_TALK_ESCAPE; Variable

``TCP_TALK_ESCAPE``
    
    May be set directly.  See the description of the function ``tcp_talk`` for
    how this is used.
    

.. index:: single: TCP_TIMEOUT; Variable

``TCP_TIMEOUT``
    
    May be set directly.  Currently this is only used by the function
    ``tcp_command``, see above.
    

TCP User-defined Parameters
--------------------------------------------------------------------------------

The following parameters are not set by the function system, but have
a special effect if set by the user.

.. index:: single: tcp_on_read; Variable

``tcp_on_read``
    
    This should be an associative array; if it is not, the behaviour is
    undefined.  Each key is the name of a shell function or other command,
    and the corresponding value is a shell pattern (using ``EXTENDED_GLOB``).
    Every line read from a TCP session directly or indirectly using
    ``tcp_read`` (which includes lines read by ``tcp_expect``) is compared
    against the pattern.  If the line matches, the command given in the key is
    called with two arguments: the name of the session from which the line was
    read, and the line itself.
    
    If any function called to handle a line returns a non-zero status, the
    line is not output.  Thus a ``tcp_on_read`` handler containing only
    the instruction ``return 1`` can be used to suppress output of
    particular lines (see, however, ``tcp_filter`` above).  However, the line
    is still stored in ``TCP_LINE`` and ``tcp_lines``; this occurs after all
    ``tcp_on_read`` processing.
    

TCP Utility Parameters
--------------------------------------------------------------------------------

These parameters are controlled by the function system; they may be read
directly, but should not usually be set by user code.

.. index:: single: tcp_aliases; Function

``tcp_aliases``
    
    Associative array.  The keys are the names of sessions established with
    ``tcp_open``; each value is a space-separated list of aliases which refer
    to that session.
    

.. index:: single: tcp_by_fd; Function

``tcp_by_fd``
    
    Associative array.  The keys are session file descriptors; each
    value is the name of that session.
    

.. index:: single: tcp_by_name; Function

``tcp_by_name``
    
    Associative array.  The keys are the names of sessions; each value is the
    file descriptor associated with that session.
    

.. historic nodename: TCP Examples

TCP Examples
--------------------------------------------------------------------------------

Here is a trivial example using a remote calculator.

To create a calculator server on port 7337 (see the ``dc`` manual page for
quite how infuriating the underlying command is):

.. code-block:: zsh
   :class: example

    tcp_proxy 7337 dc

To connect to this from the same host with a session also named ``dc``:

.. code-block:: zsh
   :class: example

    tcp_open localhost 7337 dc

To send a command to the remote session and wait a short while for output
(assuming ``dc`` is the current session):

.. code-block:: zsh
   :class: example

    tcp_command 2 4 + p

To close the session:

.. code-block:: zsh
   :class: example

    tcp_close

The ``tcp_proxy`` needs to be killed to be stopped.  Note this will not
usually kill any connections which have already been accepted, and also
that the port is not immediately available for reuse.

The following chunk of code puts a list of sessions into an xterm header,
with the current session followed by a star.

.. code-block:: zsh
   :class: example

    print -n "\033]2;TCP:" ${(k)tcp_by_name:/$TCP_SESS/$TCP_SESS\*} "\a"

.. historic nodename: TCP Bugs

TCP Bugs
--------------------------------------------------------------------------------

The function ``tcp_read`` uses the shell's normal ``read`` builtin.  As
this reads a complete line at once, data arriving without a terminating
newline can cause the function to block indefinitely.

Though the function suite works well for interactive use and for data
arriving in small amounts, the performance when large amounts of data are
being exchanged is likely to be extremely poor.
