nns_protocol - Man Page
Name service facility, client/server protocol
Synopsis
Bind name data
Release
Search pattern
ProtocolVersion
ProtocolFeatures
Search/Continuous/Start tag pattern
Search/Continuous/Stop tag
Search/Continuous/Change tag add|remove response
Description
The packages nameserv::server, nameserv, and nameserv::common provide a simple unprotected name service facility for use in small trusted environments.
Please read Name service facility, introduction first.
This document contains the specification of the network protocol which is used by client and server to talk to each other, enabling implementations of the same protocol in other languages.
Nano Name Service Protocol Version 1
This protocol defines the basic set of messages to be supported by a name service, also called the Core feature.
Basic Layer
The basic communication between client and server is done using the remote-execution protocol specified by the Tcl package comm. The relevant document specifying its on-the-wire protocol can be found in comm_wire.
All the scripts exchanged via this protocol are single commands in list form and thus can be interpreted as plain messages instead of as Tcl commands. The commands/messages specified in the next section are the only commands understood by the server-side. Command and variable substitutions are not allowed within the messages, i.e. arguments have to be literal values.
The protocol is synchronous. I.e. for each message sent a response is expected, and has to be generated. All messages are sent by the client. The server does not sent messages, only responses to messages.
Message Layer
- Bind name data
The client sends this message when it registers itself at the service with a name and some associated data. The server has to send an error response if the name is already in use. Otherwise the response has to be an empty string.
The server has to accept multiple names for the same client.
- Release
The client sends this message to unregister all names it is known under at the service. The response has to be an empty string, always.
- Search pattern
The client sends this message to search the service for names matching the glob-pattern. The response has to be a dictionary containing the matching names as keys, and mapping them to the data associated with it at Bind-time.
- ProtocolVersion
The client sends this message to query the service for the highest version of the name service protocol it supports. The response has to be a positive integer number.
Servers supporting only Nano Name Service Protocol Version 1 have to return 1.
- ProtocolFeatures
The client sends this message to query the service for the features of the name service protocol it supports. The response has to be a list containing feature names.
Servers supporting only Nano Name Service Protocol Version 1 have to return {Core}.
Nano Name Service Protocol Extension: Continuous Search
This protocol defines an extended set of messages to be supported by a name service, also called the Search/Continuous feature. This feature defines additional messages between client and server, and is otherwise identical to version 1 of the protocol. See the last section for the details of our foundation.
A service supporting this feature has to put the feature name Search/Continuous into the list of features returned by the message ProtocolFeatures.
For this extension the protocol is asynchronous. No direct response is expected for any of the messages in the extension. Furthermore the server will start sending messages on its own, instead of only responses to messages, and the client has to be able to handle these notifications.
- Search/Continuous/Start tag pattern
The client sends this message to start searching the service for names matching the glob-pattern. In contrast to the regular Search request this one asks the server to continuously monitor the database for the addition and removal of matching entries and to notify the client of all such changes. The particular search is identified by the tag.
No direct response is expected, rather the clients expect to be notified of changes via explicit Search/Continuous/Result messages generated by the service.
It is further expected that the tag information is passed unchanged to the Search/Continuous/Result messages. This tagging of the results enables clients to start multiple searches and distinguish between the different results.
- Search/Continuous/Stop tag
The client sends this message to stop the continuous search identified by the tag.
- Search/Continuous/Change tag add|remove response
This message is sent by the service to clients with active continuous searches to transfer found changes. The first such message for a new continuous search has to contains the current set of matching entries.
To ensure this a service has to generate an add-message with an empty response if there were no matching entries at the time.
The response has to be a dictionary containing the matching names as keys, and mapping them to the data associated with it at Bind-time. The argument coming before the response tells the client whether the names in the response were added or removed from the service.
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 output 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
comm_wire(n), nameserv(n), nameserv::server(n)
Keywords
comm, name service, protocol
Category
Networking
Copyright
Copyright (c) 2007-2008 Andreas Kupries <andreas_kupries@users.sourceforge.net>