nns_intro(3tcl) Name service facility nns_intro(3tcl)
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NAME
nns_intro - Name service facility, introduction
DESCRIPTION
nns (short for nano nameservice) is a facility built for the package
comm, adding a simple name service to it. It is also built on top of
comm, using it for the exchange of messages between the client and
server parts.
This name service facility has nothing to do with the Internet's Domain
Name System, otherwise known as DNS. If the reader is looking for a
package dealing with that please see either of the packages dns and re-
solv, both found in Tcllib too.
Tcllib provides 2 applications and 4 packages which are working to-
gether and provide access to the facility at different levels.
APPLICATIONS
The application nnsd provides a simple name server which can be run by
anybody anywhere on their system, as they see fit. It is also an exam-
ple on the use of the server-side package nameserv::server.
Complementing this server is the nns client application. A possible,
but no very sensible use would be to enter name/port bindings into a
server from a shell script. Not sensible, as shell scripts normally do
not provide a comm-based service.
The only case for this to make some sense would be in a shell script
wrapped around a Tcl script FOO which is using comm, to register the
listening port used by FOO. However even there it would much more sen-
sible to extend FOO to use the nameservice directly. And in regard on
how to that nns can be used as both example and template. Beyond that
it may also be useful to perform nameservice queries from shell
scripts.
The third application, nnslog is a stripped down form of the nns client
application. It is reduced to perform a continuous search for all
changes and logs all received events to stdout.
Both clients use the nameserv::auto package to automatically hande the
loss and restoration of the connection to the server.
PACKAGES
The two main packages implementing the service are nameserv and name-
serv::server, i.e. client and server. The latter has not much of an
API, just enough to start, stop, and configure it. See the application
nnsd on how to use it.
The basic client, in package nameserv, provides the main API to manipu-
late and query the service. An example of its use is the application
nns.
The second client package, nameserv::auto is API compatible to the ba-
sic client, but provides the additional functionality that it will au-
tomatically restore data like bound names when the connection to the
name service was lost and then reestablished. I.e. it automatically de-
tects the loss of the server and re-enters the data when the server
comes back.
The package nameserv::common is of no interest to users. It is an in-
ternal package containing code and definitions common to the packages
nameserv and nameserv::server.
All packages use the uevent package for the reporting of special cir-
cumstances via events, and reserve the uevent-tag nameserv for their
exclusive use. All their events will be posted to that tag.
INTERNALS
The document Name service facility, client/server protocol specifies
the protocol used by the packages nameserv and nameserv::server to talk
to each other. It is of no interest to users of either the packages or
applications.
Developers wishing to modify and/or extend or to just understand the
internals of the nameservice facility however are strongly advised to
read it.
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 Trackers [http://core.tcl.tk/tcllib/reportlist]. Please
also report any ideas for enhancements you may have for either package
and/or documentation.
When proposing code changes, please provide unified diffs, i.e the out-
put of diff -u.
Note further that attachments are strongly preferred over inlined
patches. Attachments can be made by going to the Edit form of the
ticket immediately after its creation, and then using the left-most
button in the secondary navigation bar.
SEE ALSO
nameserv(3tcl), nameserv::auto(3tcl), nameserv::common(3tcl), name-
serv::protocol(3tcl), nameserv::server(3tcl), nnsd(3tcl), nss(3tcl)
KEYWORDS
client, name service, server
CATEGORY
Networking
COPYRIGHT
Copyright (c) 2008 Andreas Kupries <andreas_kupries@users.sourceforge.net>
tcllib 1.0 nns_intro(3tcl)