TweetFollow Us on Twitter

Network Services Location Tech

Volume Number: 14 (1998)
Issue Number: 7
Column Tag: Emerging Technologies

Network Services Location Technology

by by the Apple Network Services Location Project Team
Edited by Peter N Lewis

How the NSL Technology Can Benefit Your Application

Introduction

When Apple introduced the Chooser and AppleTalk, they allowed users unprecedented ease-of-use in browsing for network services such as printers and file servers. With the introduction of the Network Services Location (NSL) Technology, Apple is bringing that same ease-of-use to the Internet. With NSL users have the ability to browse through Internet services such as FTP and HTTP via TCP/IP in the same way they have traditionally browsed for AppleTalk services using the Chooser. By adopting this technology, applications can provide a more intuitive and convenient method for users to access network services.

The NSL Technology is composed of a Manager and a set of plug-ins that gather data via particular network protocols (such as DNS). The NSL Manager provides a single API across any number of resource discovery protocols, and by developing additional plug-ins, new methods for resource discovery can be added with no additional work on the part of the application developer. In this article we will present the NSL technology and show you, the developer, how to incorporate it into your next project.

What is NSL?

The Network Services Location Manager provides a protocol-independent way for applications to discover available network services with minimal network traffic. The NSL Manager provides:

  • AppleTalk-like ease-of-use for the dynamic discovery of traditional and non-traditional network services.
  • Support for accepted and proposed industry standards, including Domain Name Service (DNS) and Service Location Protocol (SLP). SLP is an emerging standard (see RFC 2165) for registering and finding Internet services dynamically.
  • A flexible, expandable architecture that can be easily leveraged by client and server applications.

A variety of applications can benefit from NSL technology. Calls to the NSL Manager can make these applications more intuitive and easier to use. For example:

  • Instead of requiring the user to type a URL to locate a web server, a browser application that calls the NSL Manager could have an "Open Location" command that polls a network for HTTP servers and returns a list of URLs in the browser window from which a particular URL can be selected.
  • Collaboration software, such as a video conferencing server could register itself as an available service on the corporate Intranet. The users of client video conferencing software could then search the Intranet for available conferences and join a particular conference without having to remember a cryptic URL or IP address.

Using NSL

The NSL Manager acts as an intermediary between the providers of network services and applications that want information about those services. Service applications register themselves with the NSL Manager and which then acts through NSL plug-ins to perform the actual searches. The NSL Manager can pass requests from applications to any plug-in that implements the NSL Manager API.

An NSL plug-in is an extension that makes itself available to the NSL Manager when the NSL Manager is initialized, but resides in memory only when it is responding to an application's lookup request. The Extensions Manager can be used to enable and disable individual NSL plug-ins. When the NSL Manager is initialized, each NSL plug-in provides the following information to the NSL Manager:

  • The types of services the plug-in can search for, such as HTTP and FTP.
  • The protocol the plug-in uses to conduct searches, such as DNS.

The NSL Manager will be available on all PowerPC-based computers that run the Mac OS release code-named Allegro or later. The first release will be accompanied by two NSL plug-ins: DNS and SLP. Additional NSL plug-ins may also become available from Apple Computer or third-party developers.

Figure 1 illustrates the relationship between applications, the NSL Manager, and NSL plug-ins.

Figure 1. The relationship between the NSL Manager, NSL plug-ins, and Applications.

To search for network services, an application opens a session with the NSL Manager using NSLOpenNavigationAPI:

	status = NSLOpenNavigationAPI( &gOurClientRef );

Then it must prepare three data values that are used as parameters to the NSLStartServicesLookup function:

  • A request parameter block that describes the services you want to look for.
  • A lookup request that describes how you want results to be returned to you.
  • A neighborhood that describes the virtual "geographic" scope of the search.

Creating the Request Parameter Block

To create a request parameter block, your application first makes a service list that specifies the services to be searched for using NSLMakeNewServicesList and then pass the service list and any attributes to NSLMakeRequestPB. For example, to search for HTTP and FTP services, you would do something like this:

serviceList = NSLMakeNewServicesList( "http,ftp" );
iErr.theErr = NSLMakeRequestPB( serviceList, "",&newDataPtr);

In the call to NSLMakeRequestPB, your application can use the attribute parameter to specify a string that is to be used to narrow the scope of the search. For example, if the attribute parameter is "Web Sharing," the search results will include only those Personal Web Sharing HTTP services that have registered with "Web Sharing" as an attribute.

Creating the Lookup Request

To create a synchronous lookup request, your application calls NSLPrepareRequest like this:

iErr = NSLPrepareRequest( NULL, NULL, gOurClientRef, &ourRequestRef, buffer, bufLen, &ourAsyncInfo );

To create an asynchronous lookup request, your application calls NSLPrepareRequest like this:

iErr = NSLPrepareRequest( notifierPtr, NULL, gOurClientRef, &ourRequestRef,buffer, bufLen, &ourAsyncInfo );

When you call NSLPrepareRequest, you can specify NULL as the value for the notifier parameter (the first parameter in the first call above), if you want to wait for search results to be returned (synchronous mode). If instead, you want the NSL Manager to call your notification routine when search results are ready to be returned (asynchronous mode), specify a pointer to your notification routine. In the second call above notifierPtr is a procedure pointer to the client's asynchronous notifier.

The other parameters to the NSLPrepareRequest function are:

  • contextPtr, which you can use to specify contextual information about this lookup.
  • theClient, which is a value that your application received when it opened a with the NSL Manager.
  • ref, which on output is a pointer to the search request that NSLPrepareRequest will create.
  • bufPtr, which is a pointer to the buffer in which search results are to be placed.
  • bufLen, which is the length of bufPtr.
  • infoPtr, which is a structure that contains values, such as a maximum search time and the interval at which NSL Manager is to return search results, that control how the search will be conducted. Your application can change the default values before it starts the search.

Creating the Neighborhood

To define the virtual "geographic" boundary of the search, your application calls NSLMakeNewNeighborhood. You can explicitly specify which a neighborhood, for example apple.com. In the following example, the application creates a neighborhood whose boundary is apple.com.

neighborhood = NSLMakeNewNeighborhood("apple.com", NULL );

Or, you can use the default neighborhood:

neighborhood = NSLMakeNewNeighborhood( "", NULL );

Starting the Lookup

Once your application has created the request parameter block, the lookup request, and the neighborhood, it calls NSLStartServicesLookup to start the search:

iErr = NSLStartServicesLookup( ourRequestRef, neighborhood, newDataPtr, ourAsyncInfo );

The parameters to the NSLStartServices function are:

  • ref, which is the search request created when your application called NSLPrepareRequest.
  • neighborhood, which is the neighborhood value created earlier by calling NSLMakeNewNeighborhood.
  • requestData, which is the request parameter block created by calling NSLMakeRequestPB.
  • asyncInfo, which is the structure that contains values that control the way the NSL Manager returns search results, obtained by previously calling NSLPrepareRequest.

Continuing the Lookup

If the NSLStartServicesLookup was called synchronously, NSLStartServicesLookup returns after having placed the first lookup results in the results buffer field of asyncInfo. If NSLStartServicesLookup was called asynchronously, the NSL Manager places the first lookup results in the results buffer and calls your application's notification routine. Your application copies the results and calls NSLContinueLookup, which continues the lookup and returns more lookup results in the results buffer. Your application continues to call NSLContinueLookup until all of the results have been returned.

Conclusion

This article has provided a brief overview of NSL. For more detailed information on the NSL technology, API and sample User Interface recommendations, please refer to the Network Services Location Manager Developer's Kit Documentation located in the July issue of the Mac OS SDK CD distributed by Apple Computer, Inc.


The authors of this article are members of the Network Services Location Project Team at Apple Computer, Inc.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

The best scanner app on mobile
People always say that the best camera is the one you have with you. Well, the same is true with scanners, and your phone can be a pretty great tool for scanning receipts and other documents while you're on the go. [Read more] | Read more »
MARVEL Avengers Academy guide - How to g...
MARVEL Avengers Academy lets you build your own superhero school and fill it with heroes from the Marvel universe. It can be a little slow going to get your school's attendance up though, so we've gathered together somesome tips to help you do this... | Read more »
Shadow Blade: Reload guide - How to hack...
Shadow Blade: Reload is the kind of action-platformer that would have happily sucked up hours of your time on a console a few years back.Now, you can take it with you wherever you go, and its mobile conversion is not too shabby at all. To help you... | Read more »
Tomb of the Mask guide - How to increase...
Tomb of the Mask is a great endless arcade game from Happymagenta in which quick reflexes and a persistent attitude can go a long way toward earning a top score. Check out these tips to see if you can give yourself an edge on the leaderboards. [... | Read more »
Smooth Operator! (Games)
Smooth Operator! 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Smooth Operator is a weird, weird two-player kissing game. Squeeze in for 2 player fun on a single iPad, creating awkward... | Read more »
Sinless: Remastered (Games)
Sinless: Remastered 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: | Read more »
_PRISM Guide - How to solve those puzzle...
_PRISM is a rather delightful puzzle game that’s been tailor made for touch screens. While part of the fun is figuring things out as you go along, we thought we’d offer you a helping hand at getting in the right mindset. Don’t worry about messing... | Read more »
Fractal Space (Games)
Fractal Space 1.3.1 Device: iOS Universal Category: Games Price: $.99, Version: 1.3.1 (iTunes) Description: Live the memorable experience of Fractal Space, a unique first person adventure & puzzle game by Haze Games! Will you... | Read more »
Set off on an adventure through the Cand...
Like match three puzzlers? If so, Jelly Blast, the innovative iOS and Android game which launched last year, is worth a look. Jelly Blast sees you head off on an epic adventure through the Candy Kingdom with your friends Lily, Mr. Hare, and Mr.... | Read more »
Ellipsis - Touch. Explore. Survive. (...
Ellipsis - Touch. Explore. Survive. 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

cb Hardcase – Handmade and Premium Protective...
Baden-Baden, Germany based company cb innovations has introduced the new cb Hardcase for iPhone. Featuring fine Italian Premium leather that makes for a unique look and feel, the cb Hardcase... Read more
Sale! B&H Photo offers 12-inch Retina Mac...
B&H Photo has 12″ Retina MacBooks on sale for $300 off MSRP for a limited time. Shipping is free, and B&H charges NY tax only: - 12″ 1.1GHz Gray Retina MacBook: $999 $300 off MSRP - 12″ 1.... Read more
App Annie Reveals Future of the App Economy:...
App Annie, a San Francisco based mobile app data and insights platform, has launched its first comprehensive app economy forecast. This new offering will provide brands, agencies, investors and app... Read more
Apple restocks Certified Refurbished Mac mini...
Apple has restocked Certified Refurbished 2014 Mac minis, with models available starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: - 1.4GHz Mac mini: $419 $... Read more
What iPad Pro Still Needs To Make It Truly Pr...
I love my iPad Air 2. So much that I’m grudgingly willing to put up with its compromises and limitations as a production tool in order to take advantage of its virtues. However, since a computer for... Read more
21-inch 3.1GHz 4K on sale for $1399, $100 off...
B&H Photo has the 21″ 3.1GHz 4K iMac on sale $1399 for a limited time. Shipping is free, and B&H charges NY sales tax only. Their price is $100 off MSRP: - 21″ 3.1GHz 4K iMac (MK452LL/A): $... Read more
Apple price trackers, updated continuously
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: - 15″... Read more
Save up to $240 with Apple Certified Refurbis...
Apple is now offering Certified Refurbished 12″ Retina MacBooks for up to $240 off the cost of new models. Apple will include a standard one-year warranty with each MacBook, and shipping is free. The... Read more
Apple refurbished 13-inch Retina MacBook Pros...
Apple has Certified Refurbished 13″ Retina MacBook Pros available for up to $270 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free: - 13″ 2.7GHz... Read more
Apple refurbished Time Capsules available for...
Apple has certified refurbished Time Capsules available for $120 off MSRP. Apple’s one-year warranty is included with each Time Capsule, and shipping is free: - 2TB Time Capsule: $179, $120 off - 3TB... Read more

Jobs Board

*Apple* Reporter - Business Insider, Inc. (U...
Business Insider is looking for a reporter to cover Apple , the biggest and arguably most important company in tech. As our primary Apple reporter, you will: * Read more
Infrastructure Engineer - *Apple* /Mac - Rem...
…part of a team Requires proven problem solving skills Preferred Additional: Apple Certified System Administrator (ACSA) Apple Certified Technical Coordinator (ACTC) Read more
Lead Engineer *Apple* OSX & Hardware -...
Lead Engineer Apple OSX & Hardware **Job ID:** 3125919 **Full/Part\-Time:** Full\-time **Regular/Temporary:** Regular **Listed:** 2016\-02\-10 **Location:** Cary, Read more
*Apple* Mobile Master - Best Buy (United Sta...
Job Title Apple Mobile Master **Brand** Best Buy **Job Description** **What does a Best Buy Apple Mobile Master do?** At Best Buy, our mission is to leverage the Read more
Infrastructure Engineer - *Apple* /Mac - Rem...
…part of a team Requires proven problem solving skills Preferred Additional: Apple Certified System Administrator (ACSA) Apple Certified Technical Coordinator (ACTC) Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.