Coding Notes

qgit

2012-01-24T10:30:00.001-08:00

Trying out qgit http://sourceforge.net/projects/qgit/

bash key bindings

2011-12-21T14:04:00.001-08:00

bind -V
bind -P

http://www.gnu.org/software/bash/manual/bashref.html#Bindable-Readline-Commands

Rails and execjs

2011-11-07T13:56:00.000-08:00


rake aborted!
Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes.

Add these 2 lines to the Gemfile in the rails 3.1 project root:


gem 'execjs'
gem 'therubyracer'

Scala self-type annotations

2011-10-25T13:38:00.000-07:00


trait A {
  this: B =>

  val x: Int

  def a() = {
    println("A.a")
    println(x)
    println(y)
    println()
  }
}

trait B {
  this: A =>

  val y: Int

  def b() = {
    println("B.b")
    println(y)
    println(x)
    println()
  }
}

object AB extends A with B {
  val x = 123
  val y = 456

  def run() = {
    a()
    b()
  }
}

AB.run()

Fixing M-x in emacs

2011-10-17T17:16:00.000-07:00

Put this in $HOME/.Xmodmap


keycode 133 = Alt_L
clear mod1
clear mod4
add mod1 = Alt_L

Scala REPL: Full Stack Trace

2011-09-30T14:49:00.001-07:00

lastException.printStackTrace

Oracle XML literals with ampersands

2011-06-14T17:51:00.000-07:00


SQL> set scan off;
SQL> select xmltype('<a>Hello&amp;World</a>') from sys.dual;

XMLTYPE('<A>HELLO&WORLD</A>')
--------------------------------------------------------------------------------
<a>Hello&World</a>

Eclipse plugins for unit testing

2011-03-08T16:17:00.000-08:00

Infinitest + MoreUnit

rspec with rails

2011-01-26T00:48:00.000-08:00

With old versions of rails, such as 2.3, we install rspec the old way:


sudo gem install rspec-rails -v 1.3.3
script/generate rspec

scaladoc via ant

2010-11-10T10:57:00.000-08:00

The scaladoc ant task documentation on the Scala site is out of date. Instead, try the command-line arguments from the man page without the hyphens.


<scaladoc destdir="doc" sourcepath="${src}"
          doctitle="Hello Browser"
          docsourceurl="http://...">
  <src path="${src}"/>
  <include name="**/*.scala"/>
  <include name="**/*.java"/>
</scaladoc>

Apply a vararg function to a list in Scala

2010-10-20T13:51:00.000-07:00

If you have a function "f" which takes a variable number of arguments, and you want to call it with the values in some list variable "values" you can do this in Lisp using the "apply" function:

(apply f values)

If you want to do this is Scala, you just call the function and cast the values to the varargs type:

val values = List(1, 2, 3)
f(values : _*)

Scala, Lift, SBT woe

2010-10-18T13:07:00.000-07:00

I'm loving Scala, but somehow sbt got into a weird state. I'd tell it to create a project using Scala 2.8.0 and it would complain that it could not download Scala 2.7.7.

Apparently it somehow got into a confused state where it was trying to find the files locally. The solution: remove the .m2 and .ivy2 directories in my home directory.


% sbt update
Project does not exist, create new project? (y/N/s) y
Name: Something
Organization: Harold
Version [1.0]:
Scala version [2.7.7]: 2.8.0
sbt version [0.7.4]:
Getting Scala 2.7.7 ...

:: problems summary ::
:::: WARNINGS
    [NOT FOUND  ] org.scala-lang#scala-compiler;2.7.7!scala-compiler.jar (3ms)

  ==== Maven2 Local: tried

    file:///Users/harold1/.m2/repository/org/scala-lang/scala-compiler/2.7.7/scala-compiler-2.7.7.jar

Apparently sbt needs to get Scala 2.7.7 first, and then it goes on to install 2.8.0.

Git: put a copy of a repository on a remote server using ssh

2010-10-08T15:00:00.000-07:00

Making a server copy of a repository using git and ssh:


ssh server
mkdir repo.git
cd repo.git
git init --bare # Must do a bare init to receive the repo
exit

git remote add server ssh://server/home/harold/repo.git
git push server master

Now you can push and pull using the remote server alias instead of the full ssh URL.

Django vs Rails

2010-02-11T15:47:00.000-08:00

Django has better documentation, but...

I like that Rails isn't monolithic, the way Django is. With Rails I can use gem to install just ActiveRecord and use that in random scripts to save objects in a database. To use Django, I need to install the whole platform and set some environment variables before I can do that.

The Rails approach would be good for a class: you can introduce ActiveRecord alone and cover it thoroughly before discussing anything about server-side web application architecture.

If you come from the top-down school of thought, ActiveRecord should probably be learned before file I/O or SQL. It's higher-level and easier to use, and newbies should probably start by coding to ActiveRecord rather than trying to manage their own CSV or XML data files (or worse, custom packed binary data structures). And with SQLite, you don't need to know about database servers - it's just a file.

Ruby's yield is unusual

2009-11-20T16:11:00.000-08:00

yield in Ruby calls an implicit block parameter keeping the current function on the stack

curl : allow cached

2009-11-04T15:18:00.000-08:00

Was just testing curl to see the performance difference of mod_disk_cache, but curl inserts Pragma: no-cache by default. The solution:

curl -H Pragma: -v ...

jUnit execution via ant

2009-10-30T00:18:00.001-07:00

Run in server mode for finer grained multithreading:

<jvmarg value="-server"/>

Make sure the assert keyword throws on failure:

<assertions><enable/></assertions>

ThreadLocal and Tomcat

2009-10-29T12:56:00.001-07:00

Since Tomcat doesn't kill and restart the worker threads when a webapp is redeployed (ouch - that'd hurt), ThreadLocals leak because they're tied to the Class object (in turn tied to the WebappClassLoader).

So you need to avoid ThreadLocal or use a ServletContextListener to null out ThreadLocals on redeploy to avoid a memory leak. Yuck.

ANTLR for Unicode support

2009-10-08T17:23:00.001-07:00

options {
 charVocabulary = '\u0000'..'\uFFFE';
}

Eclipse bookmarks

2009-09-10T13:49:00.001-07:00

http://etc.to/eclipse_bookmarks_plugin<br class="khtml-block-placeholder">

Beginner's tools

2009-09-03T13:52:00.001-07:00

IDE: Eclipse, vim, emacs<br>

Build tool: make, ant/rake/etc.

Version control: SVN, git

Network capture: Wireshark, tcpdump

In-browser developer tools: Firebug, Safari, Yslow

Database: sqlite, MySQL, Derby

OSGi implementation: Equinox

2009-06-09T16:35:00.001-07:00

http://www.eclipse.org/equinox/documents/quickstart.php

rlwrap

2009-05-19T15:56:00.001-07:00

use rlwrap to add readline support to anything.

fink install rlwrap

pid listening on port

2009-05-19T12:27:00.001-07:00

lsof -i :8080

htaccess to set Content-Type

2009-04-24T14:29:00.001-07:00

AddType 'application/xml; charset=UTF-8' xhtml

httpd.conf on OS X

2009-04-20T20:24:00.001-07:00

/private/etc/apache2/httpd.conf

Eclipse JDOM Detail Formatter

2009-04-20T13:11:00.001-07:00

java.io.ByteArrayOutputStream os =

new java.io.ByteArrayOutputStream();

org.jdom.output.XMLOutputter outputter =

new org.jdom.output.XMLOutputter(

org.jdom.output.Format.getPrettyFormat());

outputter.output(content, os);

return new String(os.toByteArray());

Have Eclipse auto-transfer files via ssh/scp

2009-03-18T13:46:00.000-07:00

Eclipse includes the optional Ant library and its dependancies for making scp transfers. So add an Ant builder and send files after a manual build. Sample build.xml:

<project name="jschtest" default="test" basedir=".">
<target name="test">
<scp localfile="build.xml"
todir="userid@host:from-ant"
keyfile="/home/userid/.ssh/id_dsa"
passphrase=""/>
</target>
</project>

Sybase setuser

2009-01-07T10:27:00.001-08:00

Like su!

JS debug in Safari

2009-01-07T09:51:00.001-08:00

http://blog.jagregory.com/2006/05/15/javascript-console-in-safari/

DB2 on Mac OS X

2009-01-03T22:19:00.001-08:00

IBM DB2 Express-C is now available for Mac OS X, but you have to increase the shmmax/shmall kernel parameters. You can try interactively like so (these values of 256MB and 100MB worked for me where 200 and 100 saw db2start fail):

sudo sysctl -w kern.sysv.shmmax=268435456

sudo sysctl -w kern.sysv.shmall=131072000

then you add it to (probably creating) /etc/sysctl.conf to survive reboots.

wireshark http method filter

2008-12-19T12:18:00.001-08:00

http.request.method == "GET"

Sun's HttpClient and Tomcat's WebappClassLoader leak

2008-12-19T11:25:00.001-08:00

Running Tomcat servlets that use the JDK's built-in HTTP client (think URL.openConnection("http://...")), it seems to leak memory when the context / webapp is redeployed. Looking closer with jmap and Eclipse MAT, it seems like the keep-alive functionality in the JDK is to blame.

sun.net.www.http.HttpClient has a static KeepAliveCache member, which keeps a Thread object around (not running by the time I get to it). That Thread's context class loader is my Tomcat WebappClassLoader, so that can't get GCed. Not sure why, but this seems to cause every redeploy to leak a WebappClassLoader and eventually I get the dreaded OOM PermGen.

If I use a different HTTP client and dramatically disable Sun's by setting HttpClient.kac = null, then on redeploy, the WebappClassLoader is GCed and the classes are unloaded (freeing the PermGen space) *most* of the time.

Tomcat sessions

2008-12-15T13:47:00.001-08:00

<session-config>
<session-timeout>
60 
</session-timeout>
</session-config>

goes in web.xml, at the bottom of the web-app.

Enable jconsole

2008-12-15T13:02:00.001-08:00

-Dcom.sun.management.jmxremote

Java array copying

2008-12-10T15:58:00.001-08:00

System.arraycopy should've been added to Arrays ... sigh.

DTD to Relax NG compact

2008-12-10T15:57:00.001-08:00

fink install trang
trang -I dtd -O rnc file.dtd file.rnc
# Yay!

Syntactic Macros

2008-12-09T12:35:00.001-08:00

Java's generics and assert show how helpful Common Lisp's features are - you could add them yourself.

A co-worker gave up on Java's assert because it is too awkward to enable, opting to use throw new AssertionError instead. But if syntactic macros were available, we could fix assert ourselves.

At the same time, C shows how to do it badly: text manipulation instead of parse tree transforms.

Inheritance, Delegates, AOP

2008-12-09T12:21:00.001-08:00

Heavy delegate pattern in the Objective-C Cocoa libraries provides a better alternative to inheritance in many scenarios. For example, delegates can provide a way to add a mix-in feature to a class without multiple inheritance (logging, security check, caching, proxying, and on and on). Simple inheritance doesn't work if you want a way to cleanly add a mix-in to various subclasses of an interface/ABC where, as with factories. Every time I do this, though, it feels like I'm writing the code that an AOP tool should be generating for me.

Emacs Relax NG validation

2008-11-12T13:41:00.001-08:00

nxml-mode uses rnc files to validate and complete contents. To see which grammar is being used for the current buffer, C-c C-s C-w (rng-what-schema).

XPath 2 has "let"

2008-11-12T11:40:00.000-08:00

XPath 2 actually has the functional programming favorite "let" hidden in the "for" syntax. "for" iterates across a sequence, but in XPath, a single value is also a sequence allowing you to use it for "let", e.g.


for $name in 'Bob' return $name

Tomcat and symlinks

2008-10-15T10:45:00.000-07:00

Couldn't figure out why my servlets weren't getting hit - set a breakpoint in doGet and everything. Turns out that Tomcat ignores symlinks to be more secure unless you put allowLinking="true" in your context XML config file.

OpenVPN 192.168.45.1 problem solved

2008-10-15T10:42:00.000-07:00

After building openvpn for OS X using these great instructions, it seemed to start up fine. Everything for the VPN'd IP addresses was routed to 192.168.45.1 ... but there was nothing there! Turns out, if the server wants LZO compression, you have to use it too. So after rebuilding with the LZO library and turning on lzo in the config file, it works. Yay.

Apache docs

2008-09-30T15:49:00.000-07:00

For JDOM and Log4j I haven't been happy with the docs I find, but the source has helped immensely.

No chunking XML-RPC

2008-09-18T13:35:00.000-07:00

Apparently XML-RPC doesn't support chunked transfers (http://www.xmlrpc.com/spec).