Nick Moore's Blog http:/// I’m a freelance Software Consultant, mostly working with Open Source technologies and web services. A lot of my work these days is in business analysis: working out what the problem actually is, as opposed to what it seems to be. I prefer to code in Python , but also work in Perl, C/C#/Objective-C, SQL and (for my sins) JavaScript . [...] http:///art/_about.html art/_about.htmlThu, 01 Mar 2012 22:10:42 HTML5 apps can use Cache Manifests to configure the browser's Application Cache, allowing faster startup of HTML5 apps and also offline operation. There is a problem, however. The behaviour of cache manifests can make development a smidge tricky . This is because the browser will only check if the contents of the Application Cache have changed if the Cache Manifest has changed. You can manually edit this file every time, but you'd probably rather not. [...] http:///art/html5/taming-cache-manifest-caching.html art/html5/taming-cache-manifest-caching.htmlThu, 16 Feb 2012 15:49:29 An odd little one: I was compiling some older code on gcc 4.6 / Ubuntu 11.10 and it failed to make, with the traditional error: undefined reference to `sqrt' My Makefile was trying to do something like this: gcc -c -o eg.o eg.c gcc -lm -o eg eg.o ... [...] http:///art/etc/gcc-linker-libs.html art/etc/gcc-linker-libs.htmlThu, 16 Feb 2012 09:49:54 As seen on a popular "deals" website: Ad for ID Shield Block Stamp Sure, this is going to obscure some of your information for a human viewer, but stamping soluble ink over fused laser toner is never going to prevent a determined reader. And unlike "tiresome shredding", where the fragments are mixed, the documents are still whole and an attacker can easily select which documents to recover ... http:///art/security/id-stamp.html art/security/id-stamp.htmlWed, 15 Feb 2012 12:10:05 data URLs ( RFC2397 ) allow you to embed small images and such right into your HTML or CSS and thus avoid the overhead of an HTTP request just for one tiny 16x16 icon. I think these are a more elegant solution for small icons than CSS Sprites , because they localize the icons right there in the stylesheet. There are lots of "online tools" out there, but the process is actually trivial: a data URL is just a base64 encoding of the file with a label and a mime-type tacked on the front. [...] http:///art/etc/make-data-url.html art/etc/make-data-url.htmlMon, 01 Aug 2011 07:24:00 These pages are static HTML generated by a bundle of scripts and hacks which I call "blogart", pronounced to rhyme with Boggart . Well, the thing is, I used to host this domain on wordpress.com , and while they were actually pretty good, I found the whole experience of trying to write something sensible into that itty-bitty in-browser editor incredibly frustrating, to the point where if I had anything sensible to write I generally didn't. [...] http:///art/blogart/ art/blogart/index.htmlMon, 01 Aug 2011 07:24:00 Consider these two regex substitutions: s/fi?b/i/ s/fii(i*)b/f$1bfi$1b/ (For those unfamiliar with Perlish regexes : that first one says “replace the string fb or fib with the string i ”. The second one says “replace a string fiiXb with fXbfiXb , where X is zero or more i s.”) We can repeatedly apply these rules to a string until the string stops changing. [...] http:///art/Languages/regex.html subst1Wed, 22 Jun 2011 06:33:26 More Trickiness With SSH is my only blog post which has ever received useful comments, so I'd hate to lose them while converting files. Hopefully these comments aren't too mangled in transit. Thanks to the original authors: Here is a script that automates the whole process, eliminating the need to touch config files. I wrote it today impulsed by the amazingness felt when i knew you could do L2 tunnels with ssh %P. [...] http:///art/etc/ssh_tricks/comments.html art/etc/ssh_tricks/comments.htmlSun, 15 May 2011 23:34:06 Guy Steele’s recent talk [VID] [PDF] [PAPER] on “Organizing Functional Code for Parallel Execution” came up a while ago on reddit and I found it very interesting. I haven’t had a lot to do with functional programming in my career, but I’m kind of perpetually hovering on the fringes of learning more and I find myself attracted to the functional way within imperative languages such as Perl and Python. [...] http:///art/Languages/parallel.html art/Languages/parallel.htmlSun, 15 May 2011 09:03:36 There have been a lot of very interesting articles posted recently about the cause and effects of the April 2011 AWS outages. This article is an attempt to tie some of them together. According to Amazon, the outage was caused by: [... H] igh error rates and latencies for EBS calls to these APIs across the entire US East Region. [...] http:///art/aws/ art/aws/index.htmlWed, 04 May 2011 12:15:45 Netscape shipped the first Javascript interpreter in 1995 and its position in the web browser has made it almost universal. But imagine, for the sake of the argument, if Python had got there first. The timing would have been close, with Python 1.2 out in 1995 too. And there's a lot of similarity between the languages: dynamic typing, first-class functions, eval() (and somewhat bizarre treatment of whitespace) ... [...] http:///art/python/browser/ art/python/browser/index.htmlSun, 01 May 2011 00:07:16 Virtual Localization is a technique for Mesh Network routing. It tries to make it easy to route packets across the mesh by assigning each node a “Virtual Location”, which can then be used for Greedy Forwarding. It is a fully distributed algorithm … no one node holds the whole map of the network, the map is spread across all nodes with each node having a small map of its immediate surroundings. [...] http:///art/virtloc/ art/virtloc/index.htmlSat, 30 Apr 2011 17:30:12 So the VRML rendering thing isn’t panning out so well. “Making the simple things simple by making the difficult things impossible”. We’re talking, here, about a language which has a clock, but no way to display the time. You can display strings on billboards, and the billboards even point at the camera most of the time. But you can’t cast the float time to a displayable string, without calling out to Javascript anyway, and I never could get that to work the same way twice. [...] http:///art/virtloc/vrml.html art/virtloc/vrml.htmlSat, 30 Apr 2011 17:24:43 I saw an article on reddit about SSH trickery . SSH is a very subversive protocol, able to work around many kinds of unwise security policies. Here’s a couple more useful things to know. [...] http:///art/etc/ssh_tricks/ art/etc/ssh_tricks/index.htmlFri, 29 Apr 2011 16:53:09 N. Moore. “RFC 4429: Optimistic Duplicate Address Detection”, IETF Proposed Standard, April 2006. N. Moore, JH. Choi, B. Pentland, “Edge Handovers for Mobile IPv6”, IETF Internet Draft draft-moore-mobopts-edge-handovers-01.txt, July 2004. N. Moore, JH. Choi, B. Pentland, “Tunnel Buffering for Mobile IPv6”, IETF Internet Draft draft-moore-mobopts-tunnel-buffering-00.txt, July 2004. N. Moore, Y. A. Şekercioğlu and Gregory K. Egan. [...] http:///art/_pubs.html art/_pubs.htmlFri, 29 Apr 2011 00:18:16 TortoiseCVS and TortoiseSVN are nifty tools for using CVS and Subversion from Windows . From time to time I have to deal with The Beast Of Redmond in its various forms, and this makes it a lot easier ... Throughout, this example will refer to repohost , meaning the machine you’ve got the repository on. [...] http:///art/etc/tortoise_svn.html art/etc/tortoise_svn.htmlThu, 28 Apr 2011 22:05:19 I find myself writing some C# code while still thinking in Python. One thing in particular caught me out … it seems, at first, that C# doesn’t have first class classes. This is annoying, because I’d started writing some device driver classes where each class is a type of device, and instances represent the individual devices themselves. [...] http:///art/csharp/firstclassclasses/ art/csharp/firstclassclasses/index.htmlThu, 28 Apr 2011 19:03:12 So I’m playing around with Google AppEngine (still!) trying to put together some kind of sensible use for it. AppEngine is neat-O, but it is also quite limited in what it can and can’t do. [...] http:///art/python/multiple_inequalities/ art/python/multiple_inequalities/index.htmlThu, 28 Apr 2011 17:52:20 wget 1.10.2 seems to silently fail to use an SSL client certificate unless you specify both –certificate and –private-key: wget --certificate=$PEMFILE --private-key=$PEMFILE Even though both things are in the same .PEM file. It does read and check the PEM file if you specify only the former, it just doesn’t use it. I mention this only as a humble gift to the panopticon: may you spend less time gnashing your teeth than I just have as a result ... [...] http:///art/etc/wget_certificate_private_key.html art/etc/wget_certificate_private_key.htmlThu, 28 Apr 2011 17:41:38 Ever since I started working on Internet Stuff, I've been wrestling with crazy Template Languages. This article is an attempt to compare some of the more common template languages out there. I've consolidated this from a series of blog articles I wrote back in 2009. As a result, some of it may be a little disjointed and/or outdated. Like most of its ilk, TT2 doesn’t want to interpret its template language from within the already interpreted Perl … that’d be silly. [...] http:///art/templates/fugit/ art/templates/fugit/index.htmlThu, 28 Apr 2011 17:41:38 Just a quick note for anyone trying to do FreeTDS through a tunnel or a firewall pinhole or whatever: If you specify an Instance name, FreeTDS goes and probes UDP 1434 to determine the port number for that instance, even if you also explicitly specify the TCP port number you want it to use. [...] http:///art/etc/FreeTDS/ art/etc/FreeTDS/index.htmlThu, 28 Apr 2011 17:41:38 I stumbled across this problem because I was reading a protocol document for a device connected by RS-232. The document described what bytes to put in a text file, and how to use Hyperterminal’s “send text file” to send them. That all worked great. But as soon as I tried to get it working in C#, nothing nada zip. Unfortunately, “Line Feed” (ASCII LF, 0x0A) was one of those bytes. This problem is mostly suffered by people trying to use Hyperterminal to send files to, eg: a microcontroller. [...] http:///art/etc/hyperterminal_eats_ascii_lf_0x0a/ art/etc/hyperterminal_eats_ascii_lf_0x0a/index.htmlThu, 28 Apr 2011 17:41:38 [...] http:///art/python/syntax_error_keyword_argument_repeated/ art/python/syntax_error_keyword_argument_repeated/index.htmlThu, 28 Apr 2011 17:41:38 Well, I’ve decided to declare 2011 the year of finally getting my ergonomics sorted out, and to that end I went and splashed out on a Kinesis Freestyle split keyboard , and an Apple Magic Trackpad . More on the keyboard later, this post is all about the Magic Trackpad. [...] http:///art/apple/magic_trackpad.html art/apple/magic_trackpad.htmlThu, 28 Apr 2011 17:41:38 Finally got this to work properly. The biggest trap is that when it restores / upgrades / whatever, it changes its USB ID, so don’t filter just on what it is when its working, or it will get stuck in recovery mode. [...] http:///art/apple/itunes-virtualbox.html art/apple/itunes-virtualbox.htmlThu, 28 Apr 2011 17:41:38