George V. Reilly's Technical Blog : General Software Development

Review: Pragmatic Version Control Using Git

george_v_reilly — Mon, 19 Oct 2009 05:44:00 GMT

Title: Pragmatic Version Control Using Git
Author: Travis Swicegood
Rating: $stars(4)
Publisher: Pragmatic Bookshelf
Copyright: 2008
ISBN: 1934356158
Pages: 179
Keywords: computers
Reading period: 10–18 October, 2009

As part of my personal conversion to Git, I read Swicegood's Git book. It's a decent introduction to Git and you learn how to do all the basic tasks as well as some more advanced topics. The examples are clear and well-paced.

I would have liked to see more about collaboration and workflow in a DVCS world, perhaps a few case studies: how is Git used in the Linux kernel development process; how a small, distributed team uses Git and GitHub; how a collocated team migrates from more traditional tools.

The book avoids discussing the lower levels of the Git object model, which is a reasonable choice for a pragmatic guide.

Recommended.

Third-Party Cookies

george_v_reilly — Sat, 17 Oct 2009 07:15:00 GMT

Over the last few weeks, I built a PHP application that overlays Approve 71 banners on profile pictures. The actual application is hosted in an iframe and lives on a server in a different domain, eq.dm, than the main server at approvereferendum71.org.

This works fine in most browsers. Then we started getting reports that it wasn't working in IE8 on Win7 RC1. The iframe content was blank.

Poking around, I found the problem with the Fiddler proxy. The landing page on eq.dm was supposed to stick some information into the PHP session, then redirect to a second page at the same site. The second page was in an endless loop, redirecting to itself. In Fiddler, I saw a different PHPSESSID cookie on each response, and no cookie in the requests.

After reading IE 8 only has access to session cookies, I told IE8 to Accept All Cookies and the iframe content appeared. That fixed it for me, but we could hardly ask people to lower their security sessions.

I created a P3P file for the second domain, using the IBM P3P Policy Editor. (KB 323752 has more background on P3P and third-party cookies.)

IE now worked at its default security level. Problem solved! Or so I thought.

A day later, we got reports of similar problems with Safari 4 on Mac OS X.

I sniffed the traffic with Wireshark. Same problem: the “third-party“ cookie wasn't being accepted by Safari.

Unfortunately, Setting cross-domain cookies in Safari indicated that there was no reasonable workaround.

We overcame the issue up playing some DNS games, which was only possible because we control both servers. The second server is now also acting as a subdomain of the first, at dev.approvereferendum71.org. We used ini_set("session.cookie_domain",".approvereferendum71.org") to scope the iframe cookies. I've tried it in a variety of Windows, Mac, and Linux browsers, and it works in all of them.

Gitting Along

george_v_reilly — Thu, 15 Oct 2009 15:24:00 GMT

In the last few weeks, I've switched over to Git for most of my version-control needs, at home and at work, after putting it on the long finger for months.

We continue to use Subversion at work, but I've recently followed Pavel and Eric's lead in using git-svn. I work locally on my own private branches and git svn dcommit and git svn rebase occasionally. I'm primarily on Windows at work, but I have a Linux box and a Mac Mini too, while at home, I have a MacBook, a Linux netbook, and a Vista desktop. I'm using msysGit, occasionally supplemented by TortoiseGit and QGit. Pavel's on a Mac and Eric's mostly on Ubuntu, so git adoption was easy for them.

When I first tried git-svn under msysGit about a year ago, it didn't work worth a damn. Git-svn works fine now, but it's slow compared to the *nix implementation. The developers say that's due to the fork() emulation of the MSys/Cygwin layer. The rest of msysGit is much faster.

For my home needs, I've had private Subversion repositories at DevjaVu.com and OpenSvn.csie.org. DevjaVu has gone out of business and OpenSvn has been unavailable too often for my liking. It was time to find some new hosting.

I've experimented with private Git repositories at GitHub and ProjectLocker. GitHub is very nice, but charges for private repositories. ProjectLocker provides free private repositories, but is comparatively clunky.

ProjectLocker lets you set up a fresh repository on their server. They tell you how to clone from that, which is great for a new repository. But they don't tell you how to hook it up to an existing local repository. Since I had some difficulty in figuring it out, here's the recipe:

git remote add origin git-foobar@freeN.projectlocker.com:foobar.git
git pull origin master
... merge, local edits and commits ...
git push origin master

I found Git, Xcode and ProjectLocker and Cygwin, SSH and ProjectLocker useful in figuring this out.

NTFS-3G: the universal filesystem

george_v_reilly — Sat, 11 Apr 2009 06:44:00 GMT

After I started running Linux and then Mac OS X, in addition to Windows, I started on a quest to find the universal filesystem. I had multiboot systems and external drives where I wanted to to be able to read and write disks under multiple operating systems.

The obvious choice is FAT32, the ubiquitous, lowest-common denominator filesystem. FAT32 is supported out-of-the-box by all major operating systems, digital cameras, and PDAs, so that's a huge advantage. FAT32 also has major shortcomings:

Maximum file size is 4GB. I have ISOs, MPEGs, and other large files exceeding this limit.
Fragmentation happens too easily.
Timestamps: accurate only to 2-second resolution. No notion of timezones or UTC.
Journaling: none. Preferred for robustness.
ACLs or Permissions. Nothing beyond R/W.

I experimented with ext3 (and its non-journaling sibling, ext2) on Windows and later on the Mac. On Windows, ext2fs works well and I used it happily for several months on a machine dualbooting XP and Ubuntu. It did not work well with Vista initially, though that seems to have been fixed since.

My experiences on the Mac were bad: ext2fsx caused some kernel panics, which was enough for me to abandon it.

There was no free solution for reading and writing Mac HFS+ disks under Linux and Windows the last time that I checked.

Both Linux and Macs natively support mounting NTFS disks read-only. The NTFS-3G project allows Linux to write to NTFS disks, and Mac NTFS-3G does likewise for Macs. I've never had a problem with NTFS-3G and it's worked flawlessly under Linux and Mac for me.

The Bowling Game

george_v_reilly — Fri, 06 Feb 2009 18:01:00 GMT

There's a flamefest going on at the moment between Robert "Uncle Bob" Martin and Joel Spolsky over the value of Test-Driven Design and the SOLID principles. I find TDD valuable and I'm reading Martin's Clean Code at present.

Poking around in the links led me to Uncle Bob's Bowling Game Kata, a Powerpoint deck demonstrating using TDD to score a bowling game.

Ron Jeffries has a very ugly OO implementation and a cleaner procedural version of the Bowling Game. Digging around in the archives of his XP Magazine turns up many other ruminations on the Bowling Game

At Atlas, I was loaned to one group that used the Bowling Game for a pair-programming interview. I found it to be a valuable exercise. It showed us whether the candidate could actually code or not and it gave us a feel for what it would be like to work with them. It gave the candidate a taste of Agile work practices like TDD and pair programming. Of course, in a real pair-programming exercise, I would have been actively making suggestions instead of holding back.

We interviewed four candidates while I was on that team. Two passed, were hired, and worked out. One failed, failed other interviews, and was eliminated. The fourth candidate was very experienced, gave great whiteboard while talking through the exercise at the beginning, and turned out to be completely horrible. He floundered badly and wrote ugly, buggy code. That eliminated him, even though he had done well on the other rounds.

#1 Technical Blog, revisited

george_v_reilly — Wed, 19 Nov 2008 08:00:05 GMT

A week ago, I said that my technical blog somehow comes up as #1 technical blog on Google.

Several people pointed out that in my screenshot, I was logged in to Google. As you can see if you click on this screenshot, I can reproduce this result even when I'm not signed in.

I'm still confounded by that ranking. My content is good, but largely unremarkable—though I'm unduly fond of A Use for Octal; my style is understated; my traffic is uncongested; and my top billing is undeserved.

But none of the technical blogs listed on that first page are of the first order, except Mark Russinovich's.

If I thought it made sense, I'd be flattered. Alas, I cannot make it so.

#1 Technical Blog

george_v_reilly — Wed, 12 Nov 2008 07:26:39 GMT

A friend whom I haven't heard from in a few years googled for technical blog this evening, and my technical blog somehow came up as the very first hit!

I have no idea how I achieved such high page rank, nor how I eclipsed Mark Russinovich.

Distributed Version Control Systems on Windows

george_v_reilly — Mon, 10 Nov 2008 08:19:23 GMT

At work, I've been experimenting with the big three Distributed Version Control Systems, Git, Mercurial, and Bazaar, on Windows over the last ten days.

Pavel and Eric have been singing the praises of Git and git-svn on their Mac and Linux boxes respectively for the last few months. Git allows them to check in small changes locally without perturbing the build. The ease of branching and merging allows them to work in more than one branch at a time at a lower cost than Subversion did. Most of our dev team continue to work in Subversion on Windows boxes. git-svn allows Pavel and Eric to easily interoperate with the Subversion server. Pavel is also a big fan of git-stash: he stacks away in-progress work and switches easily to other patches.

Although I've worked primarily in Python on Linux since the summer, I've been working on our forthcoming mobile client recently. It's ASP.NET-based, hence I'm working on Windows again. I'm in the throes of a major refactoring, extracting the mobile client out of the main webclient and hoisting other code into shared projects, while other developers continue to work on the main webclient and the mobile client.

This seemed like a perfect opportunity to bite the DVCS bullet, since I knew that branching and merging would be less painful with git-svn than with Subversion.

Getting git-svn working on Windows turned out to be a major headache. The Cygwin version of git-svn simply doesn't work for me. And msysGit doesn't currently support git-svn. (Eric has had some success with an older version of msysGit and git-svn, but I found it to be wretchedly slow.) Moreover, Git's integration with Windows is poor. There's nothing like TortoiseSVN to ease developers into using Git.

Having written off Git on Windows for now, it was time to try Bazaar (bzr), which has its own Subversion plugin, bzr-svn. The version of bzr-svn that was available for Windows the week before last was ancient, and promptly crashed. Jelmer, the developer, mailed me yesterday to say that there should be an up-to-date copy of bzr-svn in the brand new 1.9 release of Bazaar. I'll try it at work tomorrow. Windows doesn't seem like an afterthought for Bazaar; indeed, TortoiseBzr offers Explorer integration.

On to Mercurial (hg). Alas, this has the weakest integration with Subversion. There are instructions for doing it by hand (which is what I'm doing). The hgsubversion extension looks promising, but is still immature.

Even so, Mercurial is what I've ended up using for the last week. Partly because it didn't bite me. Partly because I like it best of the three. The Mercurial book takes much of the credit for that. Windows is a first-class client and TortoiseHg offers half-way decent Explorer integration.

I'm not impressed with Git as software engineering; it strikes me as an incoherent mess of C and Perl. The attitude of superiority from some Git proponents is off-putting. I watched Linus Torvalds' Google techtalk about Git on Friday; he came across as a major jerk, repeatedly calling anyone who uses Subversion an idiot. I'd still recommend watching the video: it gives good insight into the social aspects of distributed/decentralized VCSes, how very different they are from traditional centralized VCSes, and how they afford a different way of working.

Watching my compatriot Bryan O'Sullivan's Google techtalk on Mercurial this afternoon was a far more pleasant experience. He talks more about workflow and implementation.

Both Bazaar and Mercurial are written in Python and seem to be fairly well architected. Frankly, if I do have to get my hands dirty in the code (e.g., hgsubversion), I'd much rather hack in Python. I did C/C++ for fifteen years and I'm sick of unmanaged code.

Anyway, Mercurial is where I'm going for now, though I won't categorically rule out Bazaar or Git.

Preload Ajax Data as JSON

george_v_reilly — Fri, 30 May 2008 06:27:17 GMT

Preloading Ajax data as JSON has helped improve the load time and perceived performance of our family software application. Most of the pages in our web client are dynamically generated in the browser from a complex set of JavaScript and CSS, so we're always looking out for ways to make them appear more quickly.

More at the Cozi Tech Blog.

Sharing Dotfiles between Windows and *nix

george_v_reilly — Wed, 14 May 2008 06:28:00 GMT

Tomas Restrepo wrote a post about sharing dotfiles between Windows and Ubuntu, specifically about sharing .vimrc (Linux) and _vimrc (Windows) and the .vim (Linux) and vimfiles (Windows) directories.

I have a different solution. On Windows, my C:\AutoExec.bat includes:

set HOME=C:\gvr
set VIM=C:\Vim
set VIMDIR=%VIM%\vim71
set EDITOR=%VIMDIR%\gvim.exe
set PATH=%PATH%;C:\Win32app;C:\GnuWin32\bin;C:\UnxUtils;C:\SysInternals;C:\Python25\Scripts

%HOME% (C:\gvr) contains _vimrc, vimfiles, and other stuff accumulated over many years. This directory is stored in a personal Subversion repository at DevjaVu. All my Vim files are stored with Unix LF endings, not Windows CR-LFs, so that they'll work on my Mac OS X and Linux boxen. I play some games with if has("win32") and if has('gui_macvim') to ensure that my _vimrc works cross-platform.

On my *nix boxes, the gvr folder lives under my home directory at ~/gvr, and ~/.vimrc and ~/.vim are symlinks:

$ ln -s ~/gvr/_vimrc ~/.vimrc
$ ln -s ~/gvr/vimfiles/ ~/.vim

In addition, the dotfiles that I keep in SVN are stored locally in ~/gvr/dotfiles without a leading period in their names, which makes them easy to see:

$ ln -s ~/gvr/dotfiles/bashrc ~/.bashrc

This arrangement works well for me.

Multiple Firefox Profiles: Run Firefox 2 and 3 Side-By-Side, and More

george_v_reilly — Wed, 02 Apr 2008 17:35:13 GMT

I find it useful to have multiple Firefox profiles for developing and testing. A clean profile for testing allows you to replicate most users' environments, who don't install extensions. Running a development profile in a separate profile lets you restart the browser without messing with your default environment. You can also run Firefox 2 and Firefox 3 side-by-side in separate profiles.

More at the Cozi Tech Blog.

Debugging JavaScript in IE from Visual Web Developer 2008 Express Edition

george_v_reilly — Wed, 19 Mar 2008 20:34:22 GMT

It's not at all obvious how to use Visual Web Developer 2008 Express Edition to debug JavaScript in Internet Explorer. So I wrote it up at the Cozi Tech Blog.

Daylight Savings Time and JavaScript

george_v_reilly — Thu, 13 Mar 2008 20:58:27 GMT

The JavaScript engines in Firefox 2 (Windows) and IE6 can't handle the new Daylight Savings Time rules in the U.S. The Date() function returns a value that is off by an hour if the system time is between the second Sunday of March and the first Sunday of April.

More at the Cozi Tech Blog.

Update 2008/03/14: Mea culpa. This is not a widespread problem. It is caused by the presence of set TZ=PST8PDT in my C:\AutoExec.bat. Per KB932590, the existence of the TZ environment variable will cause the CRT to use the old DST rules. (I can't remember why I set TZ several years ago. It's part of the accumulated mess of files that I bring everywhere with me.)

Transparent PNGs can Deadlock IE6

george_v_reilly — Mon, 10 Mar 2008 21:47:32 GMT

Over at Cozi, we've started a new technical blog. I just put my first post up, describing a nasty problem we had late last year.

Here's the summary:

Internet Explorer 6 does not support transparency in PNG images. The best-known solution is to use the DirectX AlphaImageLoader CSS filter. It's less well known that using AlphaImageLoader sometimes leads to a deadlock in IE6. There are two workarounds. Either wait until after the image has been downloaded to apply the filter to the image's style, or use the little-known transparent PNG8 format instead of the filter.

More here.