Mission Data Blog
Louisville-based Web Development & Software Engineering

I think by now most sysadmin types know about rrdtool and the nice graphs it makes. I recently wanted to create some graphs by hand using PHP so I turned to the php-rrdtool extension. I found that it takes a little work to get it to compile but that could be because I’m not constantly recompiling PHP and just don’t know better. You can get this module as an rpm for fedora (php-rrdtool) but I like to compile php by hand so I couldn’t use it. I’m going to assume that you know how to compile PHP normally with whatever other items you want to include and that you have the rrdtool development libraries installed or have compiled and installed rrdtool from source.

Step 1. Get the PHP rrdtool source

Go to the contrib directory on the rrdtool distribution site:
http://people.ee.ethz.ch/~oetiker/webtools/rrdtool/pub/contrib/

There are a number of files in this directory that mention rrd. You want the one named: php_rrdtool.tgz

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A few days ago I made use of a couple Oracle built in functions and it made me happy I didn’t have to write a stored proc or some type of mini-app to do it. I needed to parse a timestamp out of a field that was put there by a java program. The timestamp was just the output of System.currentTimeInMillis() and was concatenated onto some other information.

It took a little digging to find out how to convert a epoch style timestamp but here it is:

select new_time( to_date('01011970', 'ddmmyyyy') + 1/24/60/60 * :currenttimeinmillis/1000, 'GMT', 'EDT' ) from dual

Note that I convert the output from GMT to EDT here.

Threading in java is fairly easy and now with java 1.5 some of the stuff that was harder has become even easier. A few years ago someone pointed me to a site that had some concurrency utils that where the precursor to what are now the concurrent utils in java 1.5. They are very close in functionality and if you can’t use java 1.5 the older version of the utils will work with older versions of java and give you a lot of the same functionality.

I’m going to give a quick thread pooling example using both the new and old concurrency utils. I picked the thread pooling out of both since that seems to be what I end up using the most out of all the new utilities. I may revisit this again at some point to go over the periodic executors or some of the other things I have used but just not as much.

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Techcrunch has a good review by Frank Gruber of the look and feel of mapping services. I think it is notable that ESRI’s service is not included in the review. I think it is at least as good as the mapquest service. I may have to find time to redo my review of the acuracy of each again and a more technical evaluation of each.

I recently had an opportunity to use ESRI’s ArcSDE again. It is a spatial database interface and in this instance I was using the java api. I wanted to change what used to be a query using a rectangle into a query using a circle. For some reason parts of the java api for ArcSDE require a C library or something. I gave up pretty quickly on trying to make their arc function work since the documentation wasn’t very clear on how it worked. Instead I decided to figure out how to approximate a circle with a polygon and use that instead. Here is the result of that research.

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A lot of dates that come back from XML based web services are in the ISO 8601 form. I found out recently that it isn’t straight forward to parse such a date using C functions and have the time come out in the correct timezone. It isn’t rocket science but it is a lot more convoluted than higher level languages like Java.

First of lets see an example of the ISO 8601 format:

2006-02-03T16:45:09.000Z

That breaks down into:

<date>T<time><timezone>

Where a timezone of Z is equal to UTC. I was only interested in parsing timestamps in UTC so the following only applies to that timezone.

If you want to know any more about the format check out this page.

The strptime function is a flexible way to turn a string into a struct tm given a specified format. It is like a sscanf for dates. For more information on it check here. I’m not exactly sure of the portability of this function but it seems to be fairly old now so it is probably reasonably portable.

The format used to parse the a ISO 8601 timestamp is: %FT%T%z

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I’ve been doing a little C programming lately and I have found that if you have a up to date distribution of linux there are a lot of libraries out there that make doing things you do in other languages like java easier.

As I have time I’m going to post some examples of what I have found. The first here is how to base64 encode a chunk of memory using OpenSLL.

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This has been done before with PHP (AJAX upload progress meter for PHP) etc but I needed something a little different because I wanted to upload a file and then have it loaded into a database. I looked around and found that someone had already made something that used the commons file upload package to do the upload part (AJAX Upload progress monitor for Commons-FileUpload Example). It wasn’t exactly what I was looking for but it a good start.

To understand the way this works I think it is easiest to break it down into parts:

1. A file upload extention that counts bytes as they are uploaded
2. An interface that monitors the progress of something running on the server
3. AJAX to pull the monitoring into the current screen

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Setting up ruby to work with Oracle seems to be a pain for a lot of people. Here are the steps I follow to set it up on a linux box from nothing to Active Record or DBI in 7 steps.

1. Gather the installation sources you will need. You have to be registered with oracle to get their instant client packages.
   Download the ruby oci8 drivers
   Download the oracle instant client
   You want the following packages (these examples assume the zip format):
   • Instant Client Package - Basic or Instant Client Package - Basic Lite
   • Instant Client Package - SDK
   • Instant Client Package - SQL*Plus (optional but nice to have)

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I was looking at implementing a luhn and credit card type check the other day in java and I noticed that there seems to be a lack of code for doing this in ruby. So I figured I would put something together for doing the checks in ruby.

The following function will do a luhn check for a given number (any number not just credit card numbers). The luhn algorithm is fairly simple, if you want to learn more about it check here.

def luhnCheck(ccNumber)
  ccNumber = ccNumber.gsub(/\\D/, '')
  cardLength = ccNumber.length
  parity = cardLength % 2

  sum = 0
  for i in 0...cardLength
    digit = ccNumber[i] - 48

    if i % 2 == parity
      digit = digit * 2
    end

    if digit > 9
      digit = digit - 9
    end

    sum = sum + digit
  end

  return (sum % 10) == 0
end

Before running the luhn check you may want to verify that you have a valid card type or at least one you want to accept. The following function will do that based on the current bin ranges for the differenct companies as of today (for more on this see the following: credit card number information and BIN range information). N.B. Bin ranges change from time to time so this will become dated. It should be easy enough to find the updated ranges.

def ccTypeCheck(ccNumber)
  ccNumber = ccNumber.gsub(/\\D/, '')
  case ccNumber
    when /^3[47]\\d{13}$/ then return "AMEX"
    when /^4\\d{12}(\\d{3})?$/ then return "VISA"
    when /^5\\d{15}|36\\d{14}$/ then return "MC"
    when /^6011\\d{12}|650\\d{13}$/ then return "DISC"
    when /^3(0[0-5]|8[0-1])\\d{11}$/ then return "DINERS"
    when /^(39\\d{12})|(389\\d{11})$/ then return "CB"
    when /^3\\d{15}|1800\\d{11}|2131\\d{11}$/ then return "JCB"
    else return "NA"
  end
end