A blog about technology, protocols, security, details and fanaticism http://www.commandlinefanatic.com/index.html Friday, April 30, 2021, 10:00 -0700 Friday, April 30, 2021, 10:25 -0700 Spartan as my own designs tend to be, I do sometimes want some UI fluff like an interactive date picker. I put together a simple but functional, zero dependency, nonintrusive date picker control in plain Javascript that I've been using recently. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art097 96 Friday, April 30, 2021, 10:00 -0700 In this post, I round out this three-part series by adding support for editing/removing values, including supported subtypes. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art096 95 Wednesday, March 31, 2021, 10:00 -0700 In my last post I put together a simple web server infrastructure that could issue scans to a remote Redis server and display the results, available for paging back and forth, to a web interface. It's useful for seeing which keys are available. For starters, it's not displaying the value associated with the key. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art095 94 Wednesday, January 27, 2021, 10:00 -0700 Redis seems to grow more popular and more important every year. The redis-cli tool does a good job of routine admin tasks, but searching for keys is a big hassle on the command-line. It's come up often enough that I finally broke down and put together a simple web-based Redis browser. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art094 93 Monday, December 21, 2020, 10:00 -0700 I recently came across a problem that took longer to resolve than I would have liked. I had a box that was responsible for running a Java process and nothing else. When the Java process mysteriously died one day, I went to restart it and it failed immediately due to lack of memory. I saw that over 10,000 procmail processes were taking over the entire system. So... where did these come from and what were they doing? (And how should I get rid of them?) http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art093 92 Monday, November 30, 2020, 10:00 -0700 One of the things that makes front-end web development so complicated is that the web was really, really not designed for the sort of "desktop app" emulation that we demand of it these days. One such problem is the drag and drop interface that desktop GUI users have come to expect as standard, but which HTML struggles with. Supporting this functionality with "vanilla" Javascript is low footprint and, once you make sense of the standard event interface, not too hard to support. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art092 91 Wednesday, September 30, 2020, 10:00 -0700 Covariant and contravariant generic types seem counterintuitive at first and, since they're not as common as generics in general, are easy to overlook. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art091 90 Monday, August 31, 2020, 10:00 -0700 Computers can only represent a finite number of values for rational numbers, so there are necessarily "gaps" in between the representable ranges. Just how wide are these gaps? http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art090 89 Friday, July 31, 2020, 10:00 -0700 This installment of this series produces a working, but basic, ERD diagramming tool. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art089 88 Thursday, June 28, 2020, 10:00 -0700 Last time, I put together the beginning of a database diagram (ERD) tool that allowed for creation of tables and property/name definitions. This time, I'll expand on that a bit: first, I'll add support for deletion, and then I'll add support to move the diagrams around. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art088 87 Thursday, April 30, 2020, 10:00 -0700 One graphical tool I find myself missing on a pretty regular basis is Visio. I've long since made the switch over to OS/X, and there's really (still!) no decent equivalent in the Mac ecosystem. It occurred to me to wonder... how hard would something like this be to put together, really? http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art087 86 Tuesday, March 31, 2020, 10:00 -0700 I noticed earlier this month that one of my past posts wasn't rendering correctly - it turned out to be a surprisingly challening problem to pinpoint. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art086 85 Friday, February 28, 2020, 10:00 -0700 Gaussian elimination is a technique for solving systems of equations that lends itself well to automation. Here, I'll walk through an implementation similar to numpy's linalg.solve. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art085 84 Monday, December 30, 2019, 10:00 -0700 The most fundamental, and among the oldest, method of statistical inference is linear regression. The basic idea is to fit a set of observations to a slope and intercept and then use the implicit line to make predictions about unobserved data. Although it's considered statistically basic, it's still a useful tool for a lot of real-world cases, and at least an interesting stopping point on the way to more advanced statistical inference techniques. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art084 83 Wednesday, October 30, 2019, 10:00 -0700 So, Spark is becoming, if not has become, the de facto standard for large batch processes. Its big selling point is easy integration with the Hadoop file system and Hadoop's data types - however, I find it to be a bit opaque at times, especially when something goes wrong. Recently I was troubleshooting a parquet file and I wanted to rule out Spark itself as a culprit. It turns out to be non-trivial to do so, especially since most of the documentation I can find on reading Parquet files assumes that you want to do it from a Spark job. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art083 82 Monday, September 30, 2019, 10:00 -0700 I'm a big fan of UML as a standardized notation. I haven't been a big fan, though, of UML generation software. After having spent many years experimenting with GUI tools like Rational Rose, Visio, Gliffy and ArgoUML, I finally found a good command-line UML editor: MetaUML. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art082 81 Friday, August 30, 2019, 10:00 -0700 I'm working through the book "Mining of Massive Datasets" to catch up with some of the latest advances in data mining, and when I hit chapter 7 on clustering algorithms, I couldn't help notice how naturally these algorithms can be implemented in Python. Of course, you're supposed to do this sort of thing using scikit or at least numpy but if you're familiar with this blog, you probably know I'm going to go through it from first principles because hey, where's the fun otherwise? http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art081 80 Tuesday, July 30, 2019, 10:00 -0700 A while back, I wrote up a walkthrough of a real TLS 1.2 handshake, detailing what each byte contributed to the SSL connection establishment process. Since the latest revision of TLS, 1.3, is now almost a year old, and since it's a radical change from the TLS versions that came before it, this is probably a good time to go through the same exercise for it. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art080 79 Tuesday, June 25, 2019, 10:00 -0700 For better or for worse, modern "enterprise" Java applications are full of deeply-nested hierarchies of objects where one instance might contain a list of other objects which may themselves contain other objects, ad nauseam... debugging an unfamiliar application written in this (not very object oriented) style means familiarizing yourself with the details of this hierarchy. I finally decided to bite the bullet and write a generic, Java-only data formatting routine specifically for this purpose. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art079 78 Friday, May 31, 2019, 10:00 -0700 In this post, I'll finish my simple HTTP server by adding support for Cookies and Keep Alives. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art078 77 Tuesday, April 30, 2019, 10:00 -0700 Last time, I walked through the development of a simple HTTP server in Java. Two major missing features in that server were the lack of support for HTTP POST as well as support for HTTPS. I'll rectify both in this post. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art077 76 Thursday, March 28, 2019, 10:00 -0700 I often find myself needing a very simple HTTP server for things like mocking out external services for testing purposes. In these cases, Tomcat or even Jetty feel like overkill; I just want something that will start and stop really fast and that will allow me to manipulate any arbitrary byte of the response. I usually re-write the same little dedicated app from scratch each time, but I finally broke down this week and coded it up as a reusable component. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art076 75 Thursday, February 28, 2019, 10:00 -0700 In this installment, I'll walk through how the Angular CLI dev tools refresh your page whenever the underlying code changes. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art075 74 Tuesday, January 29, 2019, 10:00 -0700 Google's Angular is a fairly popular web application development framework As of today, the preferred solution to bootstrapping an Angular application is a command-line application generator called the Angular CLI. This is fine in the sense that it works, but it does quite a bit behind the scenes and expends a lot of effort hiding the details of what it did from you, the developer. This can be a problem because any automation, by its nature, has to make a fair number of assumptions on your behalf. If you're not aware of what those assumptions are, you can end up tripping headlong over one or more of them. In this post, I'm going to walk through the Tour of Heroes tutorial and peel back a bit of the mystery behind the "magical" commands. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art074 73 Saturday, September 30, 2018, 10:00 -0700 I recently finished reading the first three volumes of Donald Knuth's Art of Computer Programming series. I picked up the fourth one, and found that he had revamped the assembler language that he used to put together all of the examples. One interesting inclusion in the new MMIX assembler language is the MOR instruction, which I spent quite a bit of time working through. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art073 72 Friday, August 31, 2018, 10:00 -0700 I can't remember how exactly it came up, but my son asked me while we were in the car something along the lines of, "if (some number) was something else minus 20 percent, how much was the original number?" I'm sure somebody tried to teach me this at one point, but I ended up recreating a simple way to reverse percentage changes without a calculator. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art072 71 Tuesday, July 24, 2018, 10:00 -0700 Volume 4A of Donald Knuth's "The Art of Computer Programming" opens with an interesting numerical puzzle surrounding the generation of "Langford Pairs". As I was reading it, it occurred to me that generating these pairs makes for a succinct Scala exercise. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art071 70 Saturday, June 30, 2018, 10:00 -0700 I finished volume 3 of Donald Knuth's "The Art of Computer Programming" this month; I've spent the last three years working through the entire set. I found this volume to contain both the most, along with the least, relevant material for a modern developer. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art070 69 Friday, May 25, 2018, 10:00 -0700 So, this one had me beating my head against a brick wall for a few hours; maybe I can spare somebody else some pain by documenting what I discovered here. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art069 68 Monday, April 30, 2018, 10:00 -0700 The 90th academy awards came and went this month. My wife is a bit of an Oscar's fanatic, and she's managed to sweep me up in her mania. We host an Oscars-watching party every year - I tend bar and she makes snacks that are matched up to themes of nominated movies. We also print out ballots for all of the guests and let them nominate their favorites. Whoever gets the most right gets a prize; my wife has won every year for the last three, though, so we're starting to be accused of cheating (I can assure you that everything has been completely on the level). Hand-counting all of the ballots to determine the winner got to be a bit of a drag, though. Being a programmer, I was kicking around the idea of putting together a simple app to keep track of the votes - however, as it turns out, this is actually a pretty straightforward job for Excel, if you know how to take advantage of a handful of tricks. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art068 67 Friday, March 30, 2018, 10:00 -0700 Git is quite a bit different than the previous source code control systems like Subversion and CVS that it acts as a replacement for. I go through the basics of Git from the perspective of a recent Subversion convert. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art067 66 Wednesday, February 28, 2018, 10:00 -0700 When I first came across AngularJS, I found it fairly confusing - not in a, "how do I use this thing" or even a "how do I accomplish X in Angular" sort of way, but more of a "what is this thing even for? How is Angular better than... not Angular?" I wasn't trying to figure out why Angular is better than, say, React, or Boost, or jQuery, but - why is Angular better than nothing at all? What does it actually bring to the http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art066 65 Wednesday, January 31, 2018, 10:00 -0700 I found myself reviewing some of my long-forgotten calculus and I was struck immediately by how well numerical integration techniques like Simpson's rule work in a functional programming language like Python. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art065 64 Sunday, December 31, 2017, 10:00 -0700 Gradle is the new(er) kid on the Java build automation block. You probably know that Gradle was originally developed as part of the Groovy language, for automating builds of Groovy projects. However, it's becoming more and more popular for Java projects while most of the documentation remains aimed at Groovy developers, creating a bit of a mismatch and something of a learning barrier. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art064 63 Tuesday, October 31, 2017, 10:00 -0700 Almost a year ago, I posted a semi-review, semi-rumination on the first volume of Donald Knuth's classic computer science set, "The Art of Computer Programming". I enjoyed reading it thoroughly enough that there was no question in my mind at the time that I would go on to read volume 2. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art063 62 Friday, September 29, 2017, 10:00 -0700 This post rounds out my longer-than-anticipated five-part series walking through an entire modern TLS handshake. The only part of the handshake I didn't examine in my previous posts is the OCSP response, which I'll cover in this post. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art062 61 Wednesday, August 30, 2017, 10:00 -0700 In this post, I cover the SSL certificate exchange that I touched on in my previous post in much more detail. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art061 60 Thursday, July 27, 2017, 10:00 -0700 Last month, I reviewed an SSL handshake up to the key exchange portion. In this post, I'll pick up where I left off and cover the actual key exchange itself. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art060 59 Friday, June 30, 2017, 10:00 -0700 In this post, I pick up where I left off last time, walking through the client hello and server hello portions of the SSL handshake. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art059 58 Tuesday, May 30, 2017, 10:00 -0700 In this post, I capture the tcpdump output of a TCP handshake and walk through each byte of it, what each means, and what it's for. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art058 57 Tuesday, March 31, 2017, 10:00 -0700 I recently got a note from a reader of my book who asked if I wouldn't mind putting together a high-level description of the TLS handshake for a non-implementation audience. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art057 56 Tuesday, February 28, 2017, 10:00 -0700 A JWT-token is a Base64 encoded, digitally signed JSON structure. As it turns out, they're pretty easy to make sense of once you peel away the different parts. I'll do that in this post http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art056 55 Tuesday, January 31, 2017, 10:00 -0700 For a long time, I've seen other programmers write in awed, hushed tones about the multi-volume series of books written by Donald Knuth titled "The Art of Computer Programming" (TAOCP). As somebody who genuinely enjoys reading computer books, I've been meaning to settle down and read this series for a long time. I finally finished volume 1 and I must say, although it took some effort to get through, it was well worth the time I spent on it. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art055 54 Wednesday, August 31, 2016, 10:00 -0700 If you do much work with SSL or SSH, you spend a lot of time wrangling certificates and public keys. As keys age and things get shuffled around, though, you may often find yourself (as do I) trying to figure out which private keys go with which public keys. I've put together a quick reference here for anybody (including myself) who's faced with the same problem. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art054 53 Friday, July 29, 2016, 10:00 -0700 My very first post on this blog, 5 years ago, was a walk-through of the source code for a sample gunzip implementation. I've gotten quite a bit of feedback on it, mostly positive; it's still the most detailed post I've been able to put up here. Part of that write-up included bits and pieces of a gunzip session of an attached gzipped file, bit-for-bit. It occurred to me that a good companion piece would be a complete walk through of the gunzip process for the sample attachment. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art053 52 Thursday, June 30, 2016, 10:00 -0700 Last month, I presented the code for a blank guitar tablature page generator. This becomes much more interesting if it can also render tablature based on user input. I won't present a full ASCII-art tablature parser here, but sort of a middle-of-the-road utility that takes as input triplets indicating the guitar string (E,A,D,G,B or e), the fret that that string should be played on and the duration of the note. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art052 51 Tuesday, May 31, 2016, 10:00 -0700 A project I've been kicking around for a while is working out how to translate ASCII-art tablature into proper tab, along with the corresponding music notes. As it turns out, it's mostly a math exercise, but sort of an interesting one. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art051 50 Thursday, April 28, 2016, 10:00 -0700 Last month, I talked about parsing a decrypted OpenSSL-formatted RSA key into a JKS-formatted Java Keystore. The utility that I presented in last month's post, though, has one slightly annoying limitation - you must manually decrypt the private key file before you can import it this way. As it turns out, the encryption that OpenSSL uses is well documented and well standardized, and it's possible to extend my KeyImport utility to decrypt the file in memory, granted (of course) that you have the decryption key handy. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art050 49 Thursday, March 31, 2016, 10:00 -0700 OpenSSL is the de-facto standard for SSL operations, including creation and management of assymetric encryption keys. However, Java has its own format. Most of the time, you can easily convert between the two, but I've run into problems related to private keys in the past - so much so that I finally broke down and wrote a little command-line utility to deal with the conversion. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art049 48 Friday, February 26, 2016, 10:00 -0700 I have an old (early 2011) MacBook Pro that's been getting slower and slower as OS/X keeps upgrading, so I finally decided, yet again, to repurpose the hardware as a Debian host. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art048 47 Sunday, January 31, 2016, 10:00 -0700 UK Developer Mike Hadlow brought the wrath of the internet down upon him earlier this month when he suggested that not everybody can be taught to program. His post is an oblique swipe at the coding "bootcamps" that have been popping up in the last few years to address the problem of the programmer shortage that the Western world is purportedly facing. What about a college degree? Does a degree in computer science (or anything else) teach us anything useful about programming? http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art047 46 Wednesday, December 29, 2015, 10:00 -0700 Although password-based authentication is prevalent in most systems that require some sort of identity management, client certificates can be used to perform the same function with a different set of security tradeoffs. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art046 45 Monday, November 30, 2015, 16:51 -0700 I end up dealing with a lot of certificates and private keys, and since I still work primarily in Java, I necessarily end up dealing with quite a few Java Key Store files. You need them to get Tomcat up and running, you need them to do mutual SSL authentication, you need them to sign jar files... yet I always find the keytool that comes standard with Java a bit lacking. I finally got tired of repeating myself and broke down and wrote a utility to output exactly what I wanted. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art045 44 Wednesday, October 28, 2015, 15:24 -0700 The jQuery library has done a lot to improve the state of the art in Javascript development, but the way it works to separate code from presentation can make using Chrome's developer tools difficult to use when troubleshooting. There are ways to force it to work, but they vary from one jQuery version to the next. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art044 43 Tuesday, September 29, 2015, 15:24 - 0700 So, I've been running this blog for a few years now; over time I've been adding bits and pieces of dynamic functionality - not the least of which is a comment section. A little while ago, a reader pointed out that the comment section doesn't allow for formatted source code, which is something I wanted to fix. Before I did so, though, I wanted to set up a local test bed on my computer that I could verify my fixes against. The comments section (and other dynamic functionality) of my miniature content-management system is built on Perl and MySql, so to create a local instance, all I ought to need is Apache, Perl and MySql. As it turns out, Mac OS/X comes with Apache, MySql, and Perl all pre-installed... so it should be a simple matter to create a "dev" environment copy of my blog and get them all working together, right? Well, as it turned out, not quite. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art043 42 Wednesday, August 26, 2015, 15:24 - 0700 I recently found myself working with a Tomcat-based web application that required its clients to present a certificate to authenticate themselves. Being Tomcat, the whole thing was put together using Java of course; if you wanted to make a call to the server, you had to include a reference to a Java Key Store (.jks) file. One of my coworkers made a good case for using CURL for automated testing -- unfortunately, CURL doesn't understand the .jks format. Well, as it turns out, you can extract the key and certificate information from a Java Key Store for use by another client application, but the process is a bit involved, so I thought I'd document it here in case anybody else finds themselves in a similar situation. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art042 41 Thursday, July 30, 2015, 15:24 - 0700 In part 9 of my examination of the Chrome debugger tools, I'll conclude by talking about the Console tab that allows you to evaluate arbitrary Javascript expressions in the context of the page being viewed. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art041 40 Monday, June 29, 2015, 15:24 - 0700 In part 8 of my examination of the Chrome debugger tools, I'll talk about the Audits tab that can give you pointers on speeding up the client-side performance of your pages. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art040 39 Thursday, May 28, 2015, 15:24 - 0700 In part 7 of my examination of the Chrome debugger tools, I'll talk about the resources tab that shows you how your web page or application makes use of client-side storage. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art039 38 Thursday, April 30, 2015, 15:24 - 0700 In this installment of the Chrome debugger tools examination, I'll cover the Heap profiler. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art038 37 Monday, March 30, 2015, 10:25 -0700 In this installment of the Chrome debugger tools examination, I'll cover the CPU profiler. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art037 36 Saturday, February 27, 2015, 10:25 -0700 In part 4 of my multi-part series on the Chrome Debugger tools, I'll examine the first of Chrome's two profiler debugging tools, the Timeline tab. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art036 35 Saturday, January 31, 2015, 10:25 -0700 In part 3 of my multi-part series on the Chrome Debugger tools, I'll examine the workhorse of the debugger tools, and the Javascript developer's best friend, the Sources tab. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art035 34 Friday, December 31, 2014, 10:25 -0700 Welcome back to my multi-part series on the Chrome Debugger tools. Last time, I examined the first tab in the Chrome debugger tools, the Elements tab. Working left-to-right, the next tab is the Network tab, which I'll explore here. Whereas the Elements tab is useful for debugging and troubleshooting code that's not rendering properly once it has already been downloaded, the Network tab focuses on how the data that is rendered gets loaded into the browser in the first place. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art034 34 Friday, November 30, 2014, 10:25 -0700 You kids and your fancy debuggers, these days. Back in my day, we had to debug Javascript in IE 4 using nothing but alert() popups. If we got stuck in a loop, IE would idiotically keep alert()-ing us until we killed the browser manually (which, incidentally, wasn't always that easy to do). The state of the art in Javascript/client-side debugging has come a long way since those days; I hardly ever have to code alert()s any more. These days, my weapon of choice is Chrome; it comes with a built-in debugging extension that, for the most part, can do everything I need it to do. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art033 33 Tuesday, September 30, 2014, 10:25 -0700 A few weeks ago, I upgraded my laptop. Due to a bug in the latest OS/X, I wasn't able to transfer all of my files from my old computer to the new one, but since everything I do is in Subversion anyway, I didn't anticipate a major issue just reinstalling everything I needed. When it came time to install Java, I installed the latest JDK (1.8). Thinking little of it, I went back to my normal work, ran Maven, and immediately got the following error: unable to find valid certification path to requested target http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art032 32 Tuesday, August 11, 2014, 10:25 -0700 I came across this problem a few weeks ago and when I searched for a solution, I couldn't find one. As it turns out, it's a pretty straightforward algorithms application once you see how to do it; I thought it was interesting enough to share. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art031 31 Monday, June 30, 2014, 10:25 -0700 You're probably at least peripherally familiar with OpenSSL as a library that provides SSL capability to internet servers and clients. OpenSSL, however, in addition to providing a library for integration, includes a useful command line tool that can be used for effectively every aspect of SSL/PKI administration. It's a bit under-documented though; this post doesn't aim to fully document it, but I've come across some fairly useful shortcuts that I thought I'd share with you, in "cookbook" style format. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art030 30 Thursday, May 29, 2014, 10:25 -0700 So, anybody who administers a web server -- or anybody who uses a webserver administered by somebody -- has by now heard of the catastrophic "11 on a scale of 1 to 10" Heartbleed vulnerability in OpenSSL. Other than being a very cool, very memorable name that spurs even non-technical people into action, what exactly is HeartBleed? http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art029 29 Friday, April 25, 2014, 10:25 -0700 I had been using Microsoft Money to track my personal finances for years, but after the version I had was just too old to run on my computer any more, I decided to sit down and figure out how to replace it with a simple spreadsheet. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art028 28 Saturday, February 28, 2014, 10:25 -0700 The BEAST (Browser Exploit Against SSL/TLS) attack was published two years ago. Although it made quite a splash when it was first announced, it's hard to find technical details about how it works -- in particular, to determine just how worried you should be. This post describes exactly how it works and how to determine how vulnerable you are to it. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art027 27 Wednesday, January 29, 2014, 10:25 -0700 Partly by convention and partly by design, C programs are split into source files that describe the functionality of the program itself and header files that describe how to invoke that functionality from other source files. So, where does the compiler look to find these files? I was bitten by an edge case last week - it turns out there's more complexity surrounding header file searches than you may expect. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art026 26 Saturday, December 21, 2013, 10:25 -0700 svn import is a bit of a landmine. It's not obvious from the command format, nor from its (almost nonexistent) documentation exactly what shape the imported repository will actually take once it's imported - and it's difficult to impossible to rectify a mistake once you've made one, since Subversion also doesn't offer a way to preview an import or delete an Subversion import is a bit of a landmine. I've gone through and documented a couple of things that can go wrong and how to recover from them as well as how to get the right import format the first time. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art025 25 Thursday, October 24, 2013, 10:25 -0700 If you, like me, are an old-time Unix command-line fanatic now doing iOS development, you've probably wondered if you can build an iPhone app from scratch, entirely outside of XCode. After all, Mac OS/X is a *nix, and all the familiar tools -- Make, cc, ld -- are all there. So, can you build and compile completely outside of XCode? As it turns out, yes, you can, and there are actually some speed advantages to doing so. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art024 24 Wednesday, August 28, 2013, 20:45 +0000 I have a confession to make. I don't automatically reuse code. I've been met with incredulous stares when, for example, a co-worker finds out I wrote my own drag-and-drop handling for my web page rather than just drop jquery in there and be done with it. But it seems to me that those same co-workers suffer from selective memory with regards to the hidden costs of software reuse. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art023 23 Wednesday, July 31, 2013, 20:45 +0000 So hopefully I can save somebody else four hours of frustrating, hair-tearing debugging... a few days ago I had to make a minor change to one of the webapps I maintain and redeploy it. I hadn't touched it in a while, but since I'm of course using Maven for build automation, I made the change, ran mvn clean install and pushed the new .war out to my Tomcat cluster. I went to verify the change and - nothing. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art022 23 Wednesday, June 26, 2013, 20:45 +0000 One of my pet projects for a while has been a "font designer" in Javascript. I was working on a presentation that needed to show a countdown that could be rotated, sized and colored arbitrarily. Although there are probably better tools for the job, it's the sort of thing that interests me, so I've been poking at it for a while. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art021 22 Wednesday, May 29, 2013, 20:45 +0000 My entry in this year's "stupid SED tricks" is a command-line run tool for Maven-based Java projects. Maven's a great choice for managing complex dependencies, especially because of the central repository that allows you to just declare, for example, that your project uses Apache Commons HTTPClient and let Maven resolve and download it for you. But you need its help to run the finished product. Can you do it entirely using command-line tools? http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art020 21 Thursday, April 4, 2013, 20:45 +0000 I'm sure you've come across a PDF file or two in your web browsing days. Google even gives you a PDF warning to let you know that you're about to download one so that you don't potentially end up wasting your time. But did you know that PDF is actually a textual format? Did you know that you can write a valid, well-formed PDF file using nothing but a text editor? This month, I'll show you how. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art019 20 Thursday, February 22, 2013, 20:45 +0000 If you've done any sort of work with graphics, you're no doubt familiar with matrix operations - scaling, translating and rotating. In the matrix model of graphics operations, each operation is parameterized by a specific matrix, and the individual coordinates of the shapes to be manipulated are represented as column vectors. Scaling and translating are easy enough to understand, but I've never seen the rotation matrix adequately explained. Most books about linear algebra try to frame rotation matrices around the context of changes of basis of orthogonal vectors (say that five times fast!) - I'm sure that's a useful explanation to somebody, http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art018 19 Monday, December 31, 2012, 20:45 +0000 Considering how crucial date representation and computation is to so many of the sorts of commercial transactions that computers manage, you'd expect computers to be better at handling them. Contrary to reasonable expectation, though, date representation, parsing, and storage have been a thorn in the side of programmers since the dawn of computers. The standard Java JDK has quite a few routines that aim to simplify date management, but there are performance considerations and limitations to consider when using them. http://commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art017 18 Tuesday, October 27, 2012, 20:45 +0000 I've probably done a few dozen Debian installs in my life, and each one is unique. This time I had to do it with no network support at all - I'm used to not having wireless without a bit of struggle, but this time I didn't even have wired network. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art016 17 Monday, October 21, 2012, 20:45 +0000 I review Matt Neuburg's book "Programming iOS 5" http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art015 16 Tuesday, August 14, 2012 20:45 +0000 I walk through an OAuth 1.0 handshake byte-by-byte, explaining the purpose of each element and developing a simple example code library along the way. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art014 15 Monday, July 16, 2012 20:45 +0000 A single line javascript function that will display the value of any cookie set in the current domain. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art013 14 Thursday, May 23, 2012 18:31 +0000 Digital certificates are the underpinnings of the trust model that the modern internet relies on, but a lot of web users - even experienced ones - are still confused about how they work and what they defend against. This article walks through the signature verification process of a real SSL certificate. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art012 13 Thursday, April 26, 2012 18:31 +0000 Last month, I detailed how the LZW (Lempel-Ziv Welch) compression algorithm works, along with a code samle. I hinted that LZW is the compression method used by the GIF image format, but I didn't go into specifics about exactly how GIF employs it. This month, I'll modify that code slightly and incorporate it into a working GIF decoder. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art011 12 Thursday, March 29, 2012 18:31 +0000 You probably know that image files on the internet are compressed before being transmitted - there are a few competing standards such as JPG, PNG and GIF. Although the graphics formats themselves - how the individual pixels are represented - are important, the details of the algorithms behind their compression are equally important. This article examines in detail the LZW algorithm that GIF employs, along with code samples. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art010 11 Wednesday, February 15, 2012 13:08 +0000 If you want to really impress people at cocktail parties - and by impress I mean freak them out with your uncanny, weird, rainman-like borderline Asperger's-syndrome abilities - compute the day of week of any date in your head. With a little bit of memorization and some basic computational arithmetic skill, you can figure out that, for example, Jul. 4 1776 fell on a Thursday, or that your friend's birthday will fall on a Sunday three years from now. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art009 10 Tuesday, January 16, 2012 13:08 +0000 Finally finishing out my series on the GZIP algorithm I started back in April, this posting details the workings of the CRC-32 that provides integrity to gzipped archives. Starting from the concepts of polynomial division, it works up to a standards-compliant CRC32 implementation. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art008 9 Sunday, December 4, 2011 13:08 +0000 A while back, I posted an article examining the details of the GZIP compression algorithm. GZIP depends, among other things, on Huffman code compression. Although the easiest to understand (IMHO) implementation of Huffman codes and Huffman code inflation is tree-based, as detailed in my previous article, it's not very fast, nor is it very memory efficient. A better implementation is the table-based one that the open-souce gzip application uses. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art007 9 Saturday, October 29, 2011 13:08 +0000 I recently found myself in the position of having to use an SSL certificate generated using the GNU Java keytool in an Apache server. Although there are a handful of documents out there that detail how to convert a certificate generated using Sun's keytool into an Apache-friendly format, I couldn't find anything about converting a GKR-formatted certificate. After much trial and error, I managed to figure it out; I've documented it here in case anybody else runs across the same problem. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art006 8 Tuesday, October 4, 2011 14:54 +0000 I've been using Maven now for quite awhile, having migrated off of Ant in favor of it for its superior dependency management. However, although I've managed to get the hang of it now, I initially found it pretty frustrating - Maven defines a lot of default behavior implicitly, and if you don't know what's going on under the hood, Maven has a nasty tendency to surprise you. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art005 7 Monday, September 5 2011 13:54:00 +0000 The Apache server is something that I've always just taken for granted. It's always there, it always works, and I never had to worry about it. To get a real sense of how the whole thing worked, I decided to strip the configuration file down to the smallest one that would possibly work, and add features incrementally to see what each one did. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art004 6 Wed, July 18 2011 09:59:00 +0000 I've been playing around with some of the new HTML 5 features lately; the one I'm most excited about is the HTML 5 "canvas" tag that lets you draw arbitrary shapes into a web page. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art003 5 Wed, July 6 2011 09:59:00 +0000 Well, it's been a while since I updated this blog, but not for lack of trying. I've been fighting comment spamemrs non-stop since I added the comments section. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art002 5 Wed, Jun 16 2011 09:20:00 +0000 A write-up of my Master's thesis was accepted to the 4th international conference on pervasive technologies related to assistive environments - I'll share more when Dr. Athitsos gets back, since he's the one who presented it. http://www.petrae.org/program.php 4 Sat, May 7 2011 12:56:00 +0000 A presentation I recently gave at the University of Texas at Arlington. This gives a high-level overview of the material in my book, "Implemeting SSL/TLS Using Cryptography and PKI". http://www.commandlinefanatic.com/Implementing_SSL.pptx 3 Sat, May 7 2011 12:56:00 +0000 A detailed examinination of the GZIP format and the DEFLATE algorithm it depends on. http://www.commandlinefanatic.com/cgi-bin/showarticle.cgi?article=art001 2 Sat, Apr 23 2011 15:39:00 +0000