Man1 - zshtcpsys.1

zshtcpsys - zsh tcp system

A module zsh/net/tcp is provided to provide network I/O over TCP/IP from within the shell; see its description in /zshmodules/(1). 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 /zshzftpsys/(1).

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.

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.

tcp_send [ -cnq ] [ -s sess | -l sess[*,*…] ] data …

tcp_send [ -cnq ] -a 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 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.

input matching any of the given /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 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 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. 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 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 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.

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.

(no term)

tcp_spam [ -ertv ] [ -a | -s sess | -l sess[*,*…] ] cmd [ arg … ] :: Execute `/cmd/ [ 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 `/cmd/ [ arg … ]’ is executed using eval, otherwise it is executed without any further processing.

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 –*’.

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.

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.

tcp_on_alias alias 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.

tcp_on_awol sess 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.)

tcp_on_close sess 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.

tcp_on_open sess 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.

tcp_on_rename oldsess fd newsess

This is called after a session has been renamed with the three arguments old session name, file descriptor, new session name.

tcp_on_spam sess command …

This is called once for each session spammed, just 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.

tcp_on_unalias alias fd

This is called with the name of an alias and the corresponding session’s file descriptor after an alias has been deleted.

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

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 /zshzle/(1) .

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.

tcp_output [ -q ] -P prompt -F fd -S 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 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.

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=*/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.

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

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.

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.

TCP_LINE

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

TCP_LINE_FD

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

tcp_lines

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

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.

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}.*/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.

tcp_no_spam_list

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

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.

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.

TCP_READ_DEBUG

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

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.

TCP_SESS

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

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.

tcp_spam_list

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

TCP_TALK_ESCAPE

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

TCP_TIMEOUT

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

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

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.

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

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.

tcp_by_fd

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

tcp_by_name

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

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):

    tcp_proxy 7337 dc

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

    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):

    tcp_command 2 4 + p

To close the session:

    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.

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

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.