nameserv(3tcl) Name service facility nameserv(3tcl)______________________________________________________________________________NAME
nameserv - Name service facility, Client
SYNOPSIS
package require Tcl 8.4
package require nameserv ?0.4.2?
package require comm
package require logger
::nameserv::bind name data
::nameserv::release
::nameserv::search ?-async|-continuous? ?pattern?
::nameserv::protocol
::nameserv::server_protocol
::nameserv::server_features
::nameserv::cget -option
::nameserv::configure
::nameserv::configure -option
::nameserv::configure -option value...
$result destroy
$result filled
$result get name
$result names
$result size
$result getall ?pattern?
_________________________________________________________________DESCRIPTION
Please read Name service facility, introduction first.
This package provides a client for the name service facility imple‐
mented by the package nameserv::server.
This service is built in top of and for the package comm. It has noth‐
ing to do with the Internet's Domain Name System. If the reader is
looking for a package dealing with that please see Tcllib's packages
dns and resolv.
API
The package exports eight commands, as specified below:
::nameserv::bind name data
The caller of this command registers the given name as its name
in the configured name service, and additionally associates a
piece of data with it. The service does nothing with this infor‐
mation beyond storing it and delivering it as part of search
results. The meaning is entirely up to the applications using
the name service.
A generally useful choice would for example be an identifier for
a communication endpoint managed by the package comm. Anybody
retrieving the name becomes immediately able to talk to this
endpoint, i.e. the registering application.
Of further importance is that a caller can register itself under
more than one name, and each name can have its own piece of
data.
Note that the name service, and thwerefore this command, will
throw an error if the chosen name is already registered.
::nameserv::release
Invoking this command releases all names (and their data) regis‐
tered by all previous calls to ::nameserv::bind of this client.
Note that the name service will run this command implicitly when
it loses the connection to this client.
::nameserv::search ?-async|-continuous? ?pattern?
This command searches the name service for all registered names
matching the specified glob-pattern. If not specified the pat‐
tern defaults to *, matching everything. The result of the com‐
mand is a dictionary mapping the matching names to the data
associated with them at bind-time.
If either option -async or -continuous were specified the result
of this command changes and becomes the Tcl command of an object
holding the actual result. These two options are supported if
and only if the service the client is connected to supports the
protocol feature Search/Continuous.
For -async the result object is asynchronously filled with the
entries matching the pattern at the time of the search and then
not modified any more. The option -continuous extends this be‐
haviour by additionally continuously monitoring the service for
the addition and removal of entries which match the pattern, and
updating the object's contents appropriately.
Note that the caller is responsible for configuring the object
with a callback for proper notification when the current result
(or further changes) arrive.
For more information about this object see section ASYNCHRONOUS
AND CONTINUOUS SEARCHES.
::nameserv::protocol
This command returns the highest version of the name service
protocol supported by the package.
::nameserv::server_protocol
This command returns the highest version of the name service
protocol supported by the name service the client is currently
connected to.
::nameserv::server_features
This command returns a list containing the names of the features
of the name service protocol which are supported by the name
service the client is currently connected to.
::nameserv::cget -option
This command returns the currently configured value for the
specified -option. The list of supported options and their mean‐
ing can be found in section OPTIONS.
::nameserv::configure
In this form the command returns a dictionary of all supported
options, and their current values. The list of supported options
and their meaning can be found in section OPTIONS.
::nameserv::configure -option
In this form the command is an alias for "::nameserv::cget
-option]". The list of supported options and their meaning can
be found in section OPTIONS.
::nameserv::configure -option value...
In this form the command is used to configure one or more of the
supported options. At least one option has to be specified, and
each option is followed by its new value. The list of supported
options and their meaning can be found in section OPTIONS.
This form can be used only as long as the client has not con‐
tacted the name service yet. After contact has been made recon‐
figuration is not possible anymore. This means that this form of
the command is for the initalization of the client before it
use. The command forcing a contact with the name service are
bind
release
search
server_protocol
server_features
CONNECTION HANDLING
The client automatically connects to the service when one of the com‐
mands below is run for the first time, or whenever one of the commands
is run after the connection was lost, when it was lost.
bind
release
search
server_protocol
server_features
Since version 0.2 of the client it will generate an event when the con‐
nection is lost, allowing higher layers to perform additional actions.
This is done via the support package uevent. This and all other name
service related packages hereby reserve the uevent-tag nameserv. All
their events will be posted to that tag.
EVENTS
This package generates only one event, lost-connection. The detail
information provided to that event is a Tcl dictionary. The only key
contained in the dictionnary is reason, and its value will be a string
describing why the connection was lost. This string is supplied by the
underlying communication package, i.e. comm.
OPTIONS
The options supported by the client are for the specification of which
name service to contact, i.e. of the location of the name service.
They are:
-host name|ipaddress
This option specifies the host name service to contact is run‐
ning on, either by name, or by ipaddress. The initial default is
localhost, i.e. it is expected to contact a name service running
on the same host as the application using this package.
-port number
This option specifies the port the name service to contact is
listening on. It has to be a positive integer number (> 0) not
greater than 65536 (unsigned short). The initial default is the
number returned by the command ::nameserv::common::port, as pro‐
vided by the package ::nameserv::common.
ASYNCHRONOUS AND CONTINUOUS SEARCHES
Asynchronous and continuous searches are invoked by using either option
-async or -continuous as argument to the command ::nameserv::search.
Note that these two options are supported if and only if the service
the client is connected to supports the protocol feature Search/Contin‐
uous. The service provided by the package ::nameserv::server does this
since version 0.3.
For such searches the result of the search command is the Tcl command
of an object holding the actual result. The API provided by these
objects is:
Options:
-command command_prefix
This option has to be set if a user of the result object
wishes to get asynchronous notifications when the search
result or changes to it arrive.
Note that while it is possible to poll for the arrival of
the initial search result via the method filled, and for
subsequent changes by comparing the output of method
getall against a saved copy, this is not the recommended
behaviour. Setting the -command callback and processing
the notifications as they arrive is much more efficient.
The command_prefix is called with two arguments, the type
of change, and the data of the change. The type is either
add or remove, indicating new data, or deleted data,
respectively. The data of the change is always a dictio‐
nary listing the added/removed names and their associated
data.
The first change reported for a search is always the set
of matching entries at the time of the search.
Methods:
$result destroy
Destroys the object and cancels any continuous monitoring
of the service the object may have had active.
$result filled
The result is a boolean value indicating whether the
search result has already arrived (True), or not (False).
$result get name
Returns the data associated with the given name at bind-
time.
$result names
Returns a list containing all names known to the object
at the time of the invokation.
$result size
Returns an integer value specifying the size of the
result at the time of the invokation.
$result getall ?pattern?
Returns a dictionary containing the search result at the
time of the invokation, mapping the matching names to the
data associated with them at bind-time.
HISTORY
0.3.1 Fixed SF Bug 1954771.
0.3 Extended the client with the ability to perform asynchronous and
continuous searches.
0.2 Extended the client with the ability to generate events when it
loses its connection to the name service. Based on package
uevent.
0.1 Initial implementation of the client.
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain
bugs and other problems. Please report such in the category nameserv
of the Tcllib SF Trackers [http://source‐
forge.net/tracker/?group_id=12883]. Please also report any ideas for
enhancements you may have for either package and/or documentation.
SEE ALSOnameserv::common(3tcl), nameserv::server(3tcl)KEYWORDS
client, name service
CATEGORY
Networking
COPYRIGHT
Copyright (c) 2007-2008 Andreas Kupries <andreas_kupries@users.sourceforge.net>
nns 0.4.2 nameserv(3tcl)
