ref: 6bb619c8db2867ddd9cd19c0aec05065f5ee0cae
dir: /man/1/listen/
.TH LISTEN 1
.SH NAME
listen, styxlisten, dial \- network connections
.SH SYNOPSIS
.B listen
[
.B -Ats
] [
.B -a
.I alg
]... [
.B -k
.I keyfile
] [
.B -i
.BI { initscript }
]
.I addr
.I command
[
.IR arg ...
]
.br
.B styxlisten
[
.B -Ats
] [
.B -a
.I alg
]... [
.B -k
.I keyfile
]
.I addr
.I command
[
.IR arg ...
]
.br
.B dial
[
.B -A
] [
.B -a
.I alg
] [
.B -k
.I keyfile
]
.I addr
.I command
[
.IR arg ...
]
.SH DESCRIPTION
.I Listen
waits for an incoming network connection on
.IR addr ,
(as accepted by
.B announce
in
.IR dial (2))
and then invokes
.IR sh (1)
to run the associated
.IR command .
If the
.B -A
option is specified, no authentication or encryption will
take place on the connection; otherwise
.I listen
will attempt to authenticate the party at the other
end of the connection, allowing any given
.I alg
to be used to encrypt and/or digest the
connection's data. If neither
.B -A
or any
.B -a
option is given, then
.I listen
will allow any algorithm allowed by the local
.IR ssl (3)
device.
If
.I keyfile
is specified, then that will be used as the server's certificate;
otherwise
.BI /usr/ user /keyring/default
will be used.
.PP
If an
.I initscript
is provided, it is executed by each listener
after announcing its network connection,
with the shell variable
.B net
set to the name of the corresponding network directory
(see
.IR dial (2)),
before listening for incoming calls.
This can be used to change, or find out the characteristics
of an announced port (for instance to find out
the actual port number that has been announced).
.PP
By default,
.I listen
backgrounds itself (after checking that the port
announcement proceeded ok); giving it the
.B -s
option causes it to run synchronously.
.PP
.I Listen
currently makes available the whole of its current name space visible to the command,
which might be undesirable, and perhaps should be optional, with a new name space
constructed for an incoming call.
The
.B -t
option declares the command to be `trusted' giving it access to
elements of the current name space such as
.B /mnt/keys
on an authentication server.
By default it has not got that access.
.PP
.I Styxlisten
is similar to
.IR listen ,
except that it multiplexes a single
.I styx
(see
.IR intro (5))
server between multiple clients.
.I Styxlisten
starts its
.I cmd
only once; it assumes it will serve styx messages
through file descriptor 0 when started. For each client that attaches to
.IR address ,
the command will see a new
.IR attach (5)
message indicating the new connection.
Unless the
.B -A
option has been given, the
.B uname
field in the attach message will be the name of the
authenticated user.
When the command exits, the process listening
on
.I address
is stopped.
.PP
.I Dial
is the complement of
.IR listen .
It tries to make a connection to
.IR addr .
If the
.B -A
option is given, no authentication or encryption will
take place; otherwise Inferno authentication and encryption
will be performed as usual, using
.I alg
if given, or a default algorithm otherwise.
.I Keyfile
is used for the certificate if given, otherwise
.BI /usr/ user /keyring/ addr\fR,\fP
if it exists, and failing that,
.BI /usr/ user /keyring/default\fR.\fP
.I Alg
is used for the encryption/digest algorithm
on the connection.
When the connection is made,
.I command
is run in the context of that connection, as described below.
.PP
For both
.I dial
and
.IR listen ,
when the command is run,
.B $user
is set to the name of the authenticated user at the other
end of the connection (if authentication
is being used), and
.B $net
is set to the
.B /net
directory corresponding to the connection.
The standard input and output of the command
is redirected to the network connection (standard
error is unaffected).
.SH EXAMPLES
Run a custom login daemon and an echo server that
logs incoming connections:
.IP
.EX
listen 'tcp!*!echo' {
echo connection from `{cat $net/remote} >[1=2]
echo user is $user >[1=2]
cat &
}
.EE
.PP
Dial up the above echo server:
.IP
.EX
dial tcp!somehost!echo {
echo made connection >[1=2]; echo hello; cat >[1=2]
}
.EE
.PP
Make the current name-space available to all:
.IP
.EX
styxlisten 'tcp!*!styx' export /
.EE
.SH SOURCE
.B /appl/cmd/dial.b
.br
.B /appl/cmd/listen.b
.SH BUGS
The way that
.I styxlisten
is implemented means that the
.B aname
from the remote
.IR mount (2)
request cannot be passed through to the
attach message seen by the command that
has been started by
.IR styxlisten .
.SH "SEE ALSO"
.IR dial (2),
.IR ssl (3),
.IR auth (6),
.IR svc (8)