TweetFollow Us on Twitter

Feb 01 Online Volume Number: 17 (2001)
Issue Number: 2
Column Tag: MacTech Online

The New Basics: WebDAV

by Jeff Clites <online@mactech.com>

Over the last few months we have be covering a set of technologies that I've dubbed the New Basics. In brief, these are technologies that are rapidly becoming must-know items for all programmers, independent of platform, programming language, and even area of focus. Most of these technologies are new to everyone - not just to Macintosh programmers. So far, we have covered XML and POSIX threads. This month we are going to focus on a quiet revolutionary in the internet arena called WebDAV.

So What's WebDAV?

The name "WebDAV" stands for Web Distributed Authoring and Versioning (also referred to simply as "DAV"). The thumbnail sketch is that WebDAV marks the advent of the "read-write" web - where the same types of protocols which today allow us to read HTML documents over the web will also let us create and publish them.

WebDAV is an extension to the HTTP protocol, completing the set of primitive operations to allow read, write, create, copy, and delete, as well as locking, the creation and management of collections of resources (logically equivalent to directories or folders), and metadata about those resources. To put it another way, in the WebDAV world URLs get the semantics of files, so that it makes sense to save to a URL or copy a file from one URL to another. And as a true product of the times, WebDAV uses an XML-based format for its handling of metadata, allowing resources to be labeled (and searched for) by properties such as author or subject matter.

What's WebDAV Good For?

Several scenarios for usage of this type of remote or distributed authoring can be readily imagined. One common motivating example is to allow web page authors to access and edit their resources via the same URLs from which they are served, without the need to understand the mapping from a location on a server's filesystem to a location on the web. I don't actually find this example to be a particularly convincing argument for the need for a technology such as WebDAV, because I think that professional web designers need to be (and in fact are) up to the task of understanding how their resources need to be organized on a server, and more importantly commercial web sites will generally not want to perform authoring and editing directly on their live web site. (And of course, many such web sites will use application servers for much of their content, which breaks the direct URL-to-resource mapping anyway.) That said, this model could be useful for small, individual web sites, or for larger web sites with mostly static content that needs minor revisions from time-to-time. In fact, both GoLive and Dreamweaver have begun to incorporate WebDAV support into their products, allowing users to save directly to a URL.

More interesting uses present themselves as well. Once there is full support for versioning (it's actually not present in WebDAV, despite its name, and it's now a goal of the larger Delta-V effort, of which WebDAV is a part), web site authors can use this mechanism to track changes to their content, the way programmers today can use CVS to keep track of what changes were made to their code, when they were made, and by whom. (See below for more on the connection with CVS.) Even more interestingly, sites could continue to server multiple revisions of their content - for instance, a news site could correct errors in their reporting but allow readers to access the original version of a story for historical purposes, or a web page containing a current project plan for a team could allow team members to access old versions in order to track how the plan is evolving over time.

Moving away from the web arena, a mundane but potentially very welcome application is document sharing within an office. Today, despite file-sharing protocols available on every platform, and ready access to tools such as FTP, it's very common to use email to transfer documents from person to person - it's easy and it works when other methods fail, and it has no trouble crossing platform boundaries. The drawbacks are many, however: email systems often don't handle large attachments well (either rejecting them, or causing the entire mail system to bog down), recipients may have to wait through a significant delay for messages to "show up", and collaborators may end up losing changes or accidentally working on out-of-date versions of documents as they are modified and passed back and forth. Using WebDAV, authors can simply save documents to a WebDAV-enabled server and then email the URL to co-workers, if necessary. Revisions can be performed directly from this location, so at any given time there is logically only one copy of this document (the most up-to-date copy), and WebDAV's ability to impose write-locks can prevent individual contributors from accidentally overwriting each others changes if two users try to edit at the same time. And again, the ability to track and even revert changes adds an extra degree of safety, as well as an audit trail. This model should be easier to understand for most users than the transfer model of FTP, and in fact the actual transport is faster as well.

WebDAV and Software Development

So how is WebDAV important to the programmer? On the one hand, even with OS-level integration, there will still be a need for applications which are WebDAV-aware - for instance, applications which administer WebDAV servers or collections and thus need to interact with a WebDAV repository as something other than a filesystem. WebDAV may also impact programmers in another way - by changing the tool set they use to do development. There has been a high interest in using WebDAV to implement a successor to CVS. We covered CVS in this column several months back, and although it is probably the most widely used version-control system around, it does have several design-level limitations which happen to coincide with strengths of WebDAV. For one, CVS is unable to directly version directories, whereas collections are a first-class part of the WebDAV protocol. Also, CVS has only a half-hearted client-server implementation, which reflects its original design to operate only with repositories which are on the same filesystem as the user (possibly via an NFS mount), while WebDAV is inherently client-server. This can be especially important with repositories which need complicated security models to accommodate users with different access permissions.

Readers familiar with CVS may at first think that WebDAV is a complete mismatch, given that the latter uses locking extensively while the former allows multiple users to modify resources concurrently. (In fact, this is one of the strengths of CVS, as version control systems with a lock-based model can actually inhibit the development process. Note that, however, the locking-based model may be more appropriate in an office environment, where users tend to work with binary files which are difficult to compare and merge, such as images or Microsoft Office files.) It should be straightforward, however, to use WebDAV as merely a transport protocol for CVS, without modifying the semantics of CVS. (In fact, WebDAV's locking would find a use during the checkout and commit processes, where CVS does in fact use locking to prevent corruption which could occur if a given file were simultaneously being checked out by one user and checked in by another.) Another point of significant difference is that editing under the CVS model occurs via local working copies, whereas WebDAV editing logically occurs directly on the server. Here again there is potential for an interesting synergy, if WebDAV's model is not taken too literally. One approach would be to maintain the CVS concept of editing via working copies (a "sandbox"), but to leave these copies actually on a remote WebDAV server. By mounting the remote sandbox as a filesystem, the user would retain the experience of a local copy, but with a few optimizations. For instance, checkout and merge speeds could be increased by delaying the creation of actual copies of files until the developer modifies them (copy-on-write semantics), so that files the developer doesn't actually modify are never physically copied. Also, since the "checked out" files are still accessed via WebDAV, it should be possible to continue to version them, allowing the developer to track (and revert) changes that take place in between commits to the main repository. Builds could also occur remotely, on the server machine, with the generated object files also under version control, if desired, giving a team of developers a consistent build environment. (Server-resident files would also allow for a consistent backup policy, and a consistent set of tools for examining differences between versions.)

Most of this, of course, is still at the "what if" stage, but it's pretty clear that WebDAV has a lot to offer to the developer community, both as a new technology to be used in creative applications, and as a tool to improve the development process itself.

Mac OS X v. Windows 2000

Judging from the beta version of Mac OS X, as well as a few other public comments, Apple's new operating system will support mounting remote WebDAV servers - in other words, allowing users to access them as though they were local disk drives. The bad new is that Microsoft's Windows 2000 has beaten us to the punch, but the good news is that they've taken the wrong approach. Windows 2000 (or possible IE, as it is hard to tell where one ends and the other begins) has a feature called Web Folders, which allows applications to access WebDAV servers, but only if the applications are specifically written to do so - it treats the WebDAV server more like a database than a filesystem. The obvious downside of this is that most existing applications won't be able to take advantage of this feature, and it shifts the burden onto developers to make their applications "Web Folder aware". With Mac OS X's approach, any application will be able to join the party - to them, a WebDAV server will be just another volume.

Apache v. IIS

Given that WebDAV is an extension to HTTP (although it will be natural to apply it in contexts which are very different that what we traditionally think of as "the web"), WebDAV servers are usually traditional web servers. In particular, both Apache and Microsoft's Internet Information Server (IIS) support WebDAV, with Apache's support coming via the mod_dav module. It's interesting to look at the different approaches the two servers take to access permissions. IIS controls access to WebDAV resources via local file permissions, so that resources accessed via WebDAV have exactly the same restrictions as they have when accessed directly via the server's filesystem. Apache, on the other hand, "owns" all of the files it servers via WebDAV, so that access by way of the WebDAV protocol is controlled by Apache's permissions system, but direct access to these files on the server is not permitted. The IIS approach has the advantage that files may be accessed through several different protocols while maintaining a consistent access policy (this is a theme of Windows 2000 and its Active Directory permissions system), and Apache's approach has the advantage of permitting "WebDAV users" which are not otherwise known to the local system, and possibly imposing a more sophisticated security model than is implemented in the local file system. Different applications may naturally favor one approach over the other, and given the inherent flexibility of Apache it is likely that it will eventually support the "local permissions" model as well.

WebDAV Resources

The main resource on the web for information on WebDAV is, of course, the WebDAV home page. There you will find all the expected information: news, links to relevant standards and working groups, links to an FAQ, and listings of products currently supporting WebDAV. WebTechniques magazine has a very good overview article by Jim Whitehead, chair of the IETF WebDAV Working Group. It makes a strong case for the synergy of WebDAV and CVS, and has an interesting sidebar on the details of Microsoft's approach to WebDAV in their Office 2000 suite. And while we're on the subject of Microsoft, they also have an interview with Jim Whitehead, which gives a further high-level overview. If you are interested in the version-control angle, you might also want to take a look at Subversion, an open-source effort to provide a CVS alternative, and it does, in fact, use WebDAV for its transport.

For Mac-OS-X-specific coverage, start with an article on the O'Reilly Network, which gives an overview of the WebDAV support in Mac OS X Public Beta. Also of interested is a note on one of the WebDAV mailing lists, simply entitled "Another Dav client", unofficially announcing the Mac's forthcoming support for the protocol at the filesystem level. Also of interest is Goliath, a WebDAV-based web site management tool for the Macintosh. (It's a Carbon application, so it runs under both Mac OS 9 and Mac OS X.) Goliath shows off WebDAV's ability to manage locking, including supplying information about which user currently holds the lock on a given resource. For even more fun, check out an article on MacNN which steps through the (very easy) process of activating WebDAV support in Apache as it ships with Mac OS X Public Beta, allowing your machine to act as a WebDAV server. (Note that this is, of course, not necessary for you to act as a WebDAV client.)

For a more developer-centric view of things, start with WebDAV in 2 Minutes, and if you plan on implementing a WebDAV client or server, you'll want to look at the specification itself, RFC 2518, as well as related specifications, and keep up with the IETF Working Groups on WebDAV and Delta-V. For an introduction to the use of XML in WebDAV, check out Communicating XML Data Over the Web with WebDAV on Microsoft's developer site.

WebDAV promises some exciting developments for collaboration, and just for simple remote access to files. It remains to be seen how WebDAV will stack up against established protocols such as NFS (Sun's Network File System) for distributed filesystems, but I look forward to seeing where it is going to take us.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Final Cut Pro X 10.4 - Professional vide...
Final Cut Pro X is a professional video editing solution. Completely redesigned from the ground up, Final Cut Pro adds extraordinary speed, quality, and flexibility to every part of the post-... Read more
Motion 5.4 - Create and customize Final...
Motion is designed for video editors, Motion 5 lets you customize Final Cut Pro titles, transitions, and effects. Or create your own dazzling animations in 2D or 3D space, with real-time feedback as... Read more
Logic Pro X 10.3.3 - Music creation and...
Logic Pro X is the most advanced version of Logic ever. Sophisticated new tools for professional songwriting, editing, and mixing are built around a modern interface that's designed to get creative... Read more
Compressor 4.4 - Adds power and flexibil...
Compressor adds power and flexibility to Final Cut Pro X export. Customize output settings, work faster with distributed encoding, and tap into a comprehensive set of delivery features. Features... Read more
Drive Genius 5.1.0 - $99.00
Drive Genius features a comprehensive Malware Scan. Automate your malware protection. Protect your investment from any threat. The Malware Scan is part of the automated DrivePulse utility. DrivePulse... Read more
Microsoft Office 2016 15.41 - Popular pr...
Microsoft Office 2016 - Unmistakably Office, designed for Mac. The new versions of Word, Excel, PowerPoint, Outlook and OneNote provide the best of both worlds for Mac users - the familiar Office... Read more
iExplorer 4.1.13 - View and transfer fil...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
Civilization VI 1.0.6 - Next iteration o...
Sid Meier’s Civilization VI is the next entry in the popular Civilization franchise. Originally created by legendary game designer Sid Meier, Civilization is a strategy game in which you attempt to... Read more
Data Rescue 5.0.3 - Powerful hard drive...
Data Rescue’s new and improved features let you scan, search, and recover your files faster than ever before. We have modernized the file-preview capabilities, added new files types to the recovery... Read more
Civilization VI 1.0.6 - Next iteration o...
Sid Meier’s Civilization VI is the next entry in the popular Civilization franchise. Originally created by legendary game designer Sid Meier, Civilization is a strategy game in which you attempt to... Read more

Latest Forum Discussions

See All

The 5 best Star Wars games on iOS
The time has almost come.Star Wars: The Last Jedifinally hits theaters in the cinematic event that might be bigger than Christmas. To celebrate, we're taking a look at the best--and only the best--Star Warsmobile games to date. [Read more] | Read more »
Life Is Strange (Games)
Life Is Strange 1.1 Device: iOS Universal Category: Games Price: $2.99, Version: 1.1 (iTunes) Description: Life Is Strange is a five part episodic game that sets out to revolutionize story-based choice and consequence games by... | Read more »
Oddworld: New 'n' Tasty (Game...
Oddworld: New 'n' Tasty 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: ** PLEASE NOTE: Requires 3.6GB free space to install. Runs at variable resolutions based on device capabilities.... | Read more »
Gorogoa (Games)
Gorogoa 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Gorogoa is an elegant evolution of the puzzle genre, told through a beautifully hand-drawn story designed and illustrated by Jason... | Read more »
Why Guns of Boom will be big for mobile...
Earlier this week, Game Insight, the minds that brought you Guns of Boom, revealed plans for an esports mode in the popular FPS title, with big implications for the game's future. Guns of Boom has been quite popular for some time now, so it's... | Read more »
Rules of Survival guide - how to boost y...
It's not easy surviving in the "every-man-for-himself" world of Rules of Survival. You'll be facing off against many other players who might be more skilled than you, or are luckier than you. There are a lot of factors weighing against you. With... | Read more »
FEZ Pocket Edition (Games)
FEZ Pocket Edition 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »
Amazing Katamari Damacy guide - beginner...
Amazing Katamari Damacy brings the bizarro world of the original games to mobile and shifts them into an endless format that's just as addictive as the PlayStation entries. Your goal is still to roll as much random stuff as you possibly can, though... | Read more »
Portal Knights guide - crafting tips and...
In Portal Knights, you're only as strong as the items you have at your disposal. This sandbox adventure is all about crafting and building up the next big thing. Whether you're an avid explorer or collector, crafting will likely play a large part... | Read more »
The best deals on the App Store this wee...
A new week means new discounts on the App Store. This week's deals run the gamut of action-adventure titles, puzzle games, and one of the best narrative adventure series out there. If you're looking to fill out your mobile gaming library on a... | Read more »

Price Scanner via MacPrices.net

Beats Holiday sale at B&H, headphones and...
B&H Photo has Beats by Dr. Dre headphones, earphones, and speakers on sale for up to $80 off MSRP as part of their Holiday sale. Expedited shipping is free, and B&H charges sales tax to NY... Read more
Holiday sale: Apple resellers offer 2017 15″...
MacMall has 15″ MacBook Pros on sale for $220-$300 off MSRP, each including free shipping: – 15″ 2.8GHz MacBook Pro Space Gray (MPTR2LL/A): $2179, $220 off MSRP – 15″ 2.8GHz MacBook Pro Silver (... Read more
Holiday sale: Apple resellers offer 13″ MacBo...
B&H Photo has 13″ MacBook Pros on sale for up to $150 off MSRP. Shipping is free, and B&H charges sales tax for NY & NJ residents only: – 13-inch 2.3GHz/128GB Space Gray MacBook Pro (... Read more
Apple Watch Series 2, Certified Refurbished,...
Apple has Certified Refurbished Apple Watch Nike+ Series 2s, 42mm Space Gray Aluminum Case with Anthracite/Black Nike Sport Bands, available for $249 (38mm) or $279 (42mm). The 38mm model was out of... Read more
Apple offers Certified Refurbished 2016 12″ R...
Apple has Certified Refurbished 2016 12″ Retina MacBooks available starting at $949. Apple will include a standard one-year warranty with each MacBook, and shipping is free. The following... Read more
B&H drops price on 13″ 256GB MacBook Air...
B&H has the 13″ 1.8GHz/256GB Apple MacBook Air (MQD42LL/A) now on sale for $1079 including free shipping plus NY & NJ sales tax only. Their price is $120 off MSRP, and it’s the lowest price... Read more
Holiday sale: 9″ iPads starting at $299, take...
MacMall has 9″ WiFi iPads on sale for $30 off including free shipping: – 9″ 32GB WiFi iPad: $299 – 9″ 128GB WiFi iPad: $399 Read more
Green Monday deal: 15″ 2.8GHz MacBook Pro on...
B&H Photo has the 15″ 2.8GHz Space Gray MacBook Pro on sale for $250 off MSRP for today only as part of their Green Monday/Holiday sale. Shipping is free, and B&H charges sales tax for NY... Read more
Green Monday sale: B&H offers 12″ Apple i...
B&H Photo has 12″ iPad Pros on sale for up to $150 off MSRP as part of their Green Monday/Holiday sale. Shipping is free, and B&H charges sales tax in NY & NJ only: – 12″ 64GB WiFi iPad... Read more
Holiday deal: 21″ and 27″ Apple iMacs on sale...
MacMall has 2017 21″ and 27″ Apple iMacs on sale for up to $200 off MSRP. Shipping is free: – 21″ 2.3GHz iMac: $999 $100 off MSRP – 21″ 3.0GHz iMac: $1199 $100 off MSRP – 21″ 3.4GHz iMac: $1379 $120... Read more

Jobs Board

*Apple* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 113124408 Waterford, CT, Connecticut, United States Posted: 17-Oct-2017 Weekly Hours: 40.00 **Job Summary** Are you Read more
QA Automation Engineer, *Apple* Pay - Apple...
# QA Automation Engineer, Apple Pay Job Number: 113202642 Santa Clara Valley, California, United States Posted: 11-Dec-2017 Weekly Hours: 40.00 **Job Summary** At Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.