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 implemented by the
package
nameserv::server.
This service is built in top of and for the package
comm. It has nothing
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
information 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)
registered 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
pattern defaults to *, matching everything. The result of the
command 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 behaviour 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 meaning
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 contacted the name
service yet. After contact has been made reconfiguration 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 commands 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 connection 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
running 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 provided 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/Continuous.
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 dictionary 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://sourceforge.net/tracker/?group_id=12883].
Please also report any ideas for enhancements you may have for either package
and/or documentation.
SEE ALSO¶
nameserv::common(3tcl), nameserv::server(3tcl)
KEYWORDS¶
client, name service
CATEGORY¶
Networking
COPYRIGHT¶
Copyright (c) 2007-2008 Andreas Kupries <andreas_kupries@users.sourceforge.net>