ROZeroConf

From RemObjects Wiki

(Redirected from ZeroConf)
Jump to:navigation, search

This is a RemObjects SDK Features topic
Feel free to add your notes to this topic below.


ROZeroConf is an infrastructure for service discovery that is being added to RemObjects SDK. It first shipped in the Summer 2009 releases, for all three editions of RemObjects SDK.

ROZeroConf is based on open standards and also know under the names of DNS-SD (DNS Service Discovery) and Bonjour, and is available on all supported platforms, including Windows, Linux and Mac Xcode.

Contents

Basic Functionality

ROZeroConf provides two major features:

How ZeroConf Works

In ZeroConf, service providers (concrete instances of a service) are discovered based on two identifiers: a service type and a service name.

As the name indicates, the service type is used to uniquely identify the specific type of service, with the idea that services of the same type can be interacted with in the same manner. In RemObjects SDK terminology, this would mean that a service type represents a specific service interface (or possibly group of interfaces) you have defined in your RODL.

All service type names follow the schema _name._tcp., and some predefined (non-RO) types would include _http._tcp. for HTTP or _ipp._tcp. for network printers. RemObjects SDK extends this to _name_rosdk._tcp. for all services registered through it's ZeroConf support, to make them easier to distinguish, and avoid name conflicts.

The service name is used to identify the individual instance of a service that is running somewhere on the network. In most cases (and by default), this will be the host name of the computer running the server, but it is possible (and depending on the use case might be sensible) to override this from code, so your application can give administrators the option to choose a name.

The basic idea is that a client application would be capable to talk to any service of a given service type, and distinguish between different available choices, using the service name.

For example, you might be deploying three servers offering access to a certain service you are providing, running on servers server1 and server2. Clients could browse for the well-known service type on the network. If these services are advertised through ZeroConf with a custom-defined _MyCoSampleService_rosdk._tcp. service type, client applications could then browse for this type and automatically discover both server1 and server2. Whats more, as new servers go online, or existing servers are shut down, clients will automatically learn about the changes and can adapt, for example my connecting to a new server.

Requirements

Because ZeroConf allows seamless discovery of not just RemObjects SDK servers but also other services, it uses a central service running on each machine that coordinates the publication and discovery of services across the network. This service is available by default on Mac OS X (as Bonjour) and most newer Linux distributions (as Avahi), but needs to be installed manually on Windows machines.

One (and the preferred) option is Bonjour for Windows, which is available and distributable free of charge from Apple at [1]. Apple's Bonjour implementation is based on open source DNS-SD implementations, and if you do not wish to deploy Bonjour, you can build your own version from the source available at [2]. Bonjour for Windows might already be installed on many systems, for example as part of a network printer installation, or iTunes.

Another option is the ROZeroConf Hub application that ships with RemObjects SDK. This application is freely deployable and can be run standalone or as Windows background service, and can take over the same role as Bonjour for Windows for RemObjects SDK ROzeroConf applications.

Applications written with ROZeroConf can seamlessly detect whether Bonjour or the ROZeroConf Hub is running, and leverage the available option. They will also recover gracefully - but of course not publish themselves - if no ZeroConf services are available.

Making Your Services Discoverable

Allowing your services to be discovered requires only two very small changes to your server application.

.NET
In your .NET servers, the following changes are necessary:

This is all that's needed, and after you rebuild and run your service, it will be discoverable on the local network, provided Bonjour or ROZeroConf Hub are installed. (As you will see below, a bit central configuration is needed to allow global discovery outside the LAN).

Delphi
In your Delphi servers, the following changes are necessary: 

 RegisterForZeroConf(fClassFactory, 'YourServiceTypeName' );

Note that because services are published for a specific host and port, you can only publish one server channel, even if your server might be making its services available thru several channels at the same time. We suggest to use your preferred or most optimal channel for discovery. Also note that if the service type you specify does not adhere to the naming scheme described above, RemObjects SDK will automatically pre-pend an underscore and append _rosdk._tcp. as needed, so you do not need to worry about this and can provide a "simple" name.

Discovering Available Services

.NET
In your .NET clients, the following changes are necessary: 

private void ZeroConfBrowser_ServiceAdded(object sender, ZeroConfBrowseResultArgs args)
{
  ZeroConfService service = args.Record;
  if (service.TryResolve())
    //Some actions here to handle information about newly appeared service
    LogMessage(String.Format("Added service: {0} at port {1}", args.Record.Name, args.Record.Port));
}

private void ZeroConfBrowser_ServiceRemoved(object sender, ZeroConfBrowseResultArgs args)
{
  ZeroConfService service = args.Record;
  //Some actions here to handle information about disappeared service
  LogMessage(String.Format("Service has gone down: {0} (at host {1}:{2})", service.HostTarget, service.HostTarget, service.Port));
}

Delphi
In your Delphi clients, the following changes are necessary: 

procedure TClientForm.ROZeroConfBrowserServiceAdded(
  Sender: TROZeroConfBrowser; aRecord: TROZeroConfService);
var
    host: string
begin
  if  aRecord.TryResolve  then  begin
//Some actions here to handle information about newly appeared service
    host := StringReplace(aRecord.HostTarget, LOCAL_SUFFIX, '', [rfIgnoreCase]);
    LogMessage(Format('Service resolved. Host name: %s Port number: %d', [host, aRecord.Port]));
  end;
end;

procedure TClientForm.ROZeroConfBrowserServiceRemoved(
  Sender: TROZeroConfBrowser; aRecord: TROZeroConfService);
begin
  //Some actionshere to handle information about disappeared service
  LogMessage(Format('Service has gone down: %s (at host %s:%d)',
                            [aRecord.ServiceName,
                             aRecord.HostTarget,
                             aRecord.Port]));
end;
Note that there are BonjourDiscovery sample where you can look at ZeroConf in action (shipped with both RemObjects SDK for Delphi and RemObjects SDK for .NET)


Xcode (TODO: write)

Preparing for Global Registration and Discovery

(TODO: write)

Using RemObjects ZeroConf Test Nameserver

If you cannot set up your own DNS server but want to test global discovery beyond the LAN, you can use the test server we have have set up by specifying the test.zeroconf.remobjects.com domain name and using password (TODO: give password).

Please be aware that this server does not scale for production use, and is accessible by all customers. Make sure your services registered here (as well as those you deploy for production, come to think of it) employ proper authentication, to avoid unauthorized access. Do not use this server for production use.


External Links


See Also


Ro-48.png

Product: RemObjects SDK
Available Editions: RemObjects SDK for .NET, Delphi and Xcode

Glossary — Architecture — Articles — Features — Library — Samples

Retrieved from "http://wiki.remobjects.com/wiki/ROZeroConf"
Navigation
products
hubs
special
Toolbox