COMMENT(!MOD!zsh/net/tcp
Manipulation of TCP sockets
!MOD!)
The tt(zsh/net/tcp) module makes available one builtin command:

startitem()
findex(ztcp)
cindex(TCP)
cindex(sockets, TCP)
item(tt(ztcp) [ tt(-acflLtv) ] [ tt(-d) var(fd) ] [ var(args) ])(
tt(ztcp) is implemented as a builtin to allow full use of shell
command line editing, file I/O, and job control mechanisms.

If tt(ztcp) is run with no options, it will output
the contents of its session table.

If it is run with only the option tt(-L), it will output the contents of
the session table in a format suitable for automatic parsing.  The option
is ignored if given with a command to open or close a session.  The output
consists of a set of lines, one per session, each containing the following
elements separated by spaces:

startitem()
item(File descriptor)(
The file descriptor in use for the connection.  For normal inbound (tt(I))
and outbound (tt(O)) connections this may be read and written by the usual
shell mechanisms.  However, it should only be close with `tt(ztcp -c)'.
)
item(Connection type)(
A letter indicating how the session was created:

startitem()
item(tt(Z))(
A session created with the tt(zftp) command.
)
item(tt(L))(
A connection opened for listening with `tt(ztcp -l)'.
)
item(tt(I))(
An inbound connection accepted with `tt(ztcp -a)'.
)
item(tt(O))(
An outbound connection created with `tt(ztcp) var(host) var(...)'.
)
enditem()

)
item(The local host)(
This is usually set to an all-zero IP address as the address of the
localhost is irrelevant.
)
item(The local port)(
This is likely to be zero unless the connection is for listening.
)
item(The remote host)(
This is the fully qualified domain name of the peer, if available, else an
IP address.  It is an all-zero IP address for a session opened for
listening.
)
item(The remote port)(
This is zero for a connection opened for listening.
)
enditem()
)
enditem()

subsect(Outbound Connections)
cindex(sockets, outbound TCP)

startitem()
item(tt(ztcp) [ tt(-v) ] [ tt(-d) var(fd) ] var(host) [ var(port) ])(
Open a new TCP connection to var(host).  If the var(port) is
omitted, it will default to port 23.  The connection will
be added to the session table and the shell parameter
tt(REPLY) will be set to the file descriptor associated
with that connection.

If tt(-d) is specified, its argument will be taken as the target file
descriptor for the connection.

In order to elicit more verbose output, use tt(-v).
)
enditem()

subsect(Inbound Connections)
cindex(sockets, inbound TCP)

startitem()
item(tt(ztcp) tt(-l) [ tt(-v) ] [ tt(-d) var(fd) ] var(port))(
tt(ztcp -l) will open a socket listening on TCP
var(port).  The socket will be added to the
session table and the shell parameter tt(REPLY)
will be set to the file descriptor associated
with that listener.

If tt(-d) is specified, its argument will be taken as the target file
descriptor for the connection.

In order to elicit more verbose output, use tt(-v).
)
item(tt(ztcp) tt(-a) [ tt(-tv) ] [ tt(-d) var(targetfd) ] var(listenfd))(
tt(ztcp -a) will accept an incoming connection
to the port associated with var(listenfd).
The connection will be added to the session
table and the shell parameter tt(REPLY) will
be set to the file descriptor associated with
the inbound connection.

If tt(-d) is specified, its argument
will be taken as the target file descriptor for the
connection.

If tt(-t) is specified, tt(ztcp) will return
if no incoming connection is pending.  Otherwise
it will wait for one.

In order to elicit more verbose output, use tt(-v).
)
enditem()

subsect(Closing Connections)
cindex(sockets, closing TCP)

startitem()
xitem(tt(ztcp) tt(-cf) [ tt(-v) ] [ var(fd) ])
item(tt(ztcp) tt(-c) [ tt(-v) ] [ var(fd) ])(
tt(ztcp -c) will close the socket associated
with var(fd).  The socket will be removed from the
session table.  If var(fd) is not specified,
tt(ztcp) will close everything in the session table.

Normally, sockets registered by zftp (see
ifzman(\
zmanref(zshmodules)
)\
ifnzman(\
noderef(The zsh/zftp Module)
)) cannot be closed this way.  In order
to force such a socket closed, use tt(-f).

In order to elicit more verbose output, use tt(-v).
)
enditem()

subsect(Example)
cindex(TCP, example)
Here is how to create a TCP connection between two instances of zsh.  We
need to pick an unassigned port; here we use the randomly chosen 5123.

On tt(host1),
example(zmodload zsh/net/tcp
ztcp -l 5123
listenfd=$REPLY
ztcp -a $listenfd
fd=$REPLY)
The second from last command blocks until there is an incoming connection.

Now create a connection from tt(host2) (which may, of course, be the same
machine):
example(zmodload zsh/net/tcp
ztcp host1 5123
fd=$REPLY)

Now on each host, tt($fd) contains a file descriptor for talking to the
other.  For example, on tt(host1):
example(print This is a message >&$fd)
and on tt(host2):
example(read -r line <&$fd; print -r - $line)
prints `tt(This is a message)'.

To tidy up, on tt(host1):
example(ztcp -c $listenfd
ztcp -c $fd)
and on tt(host2)
example(ztcp -c $fd)