crossedstreams.com

If you’re going to fiddle with networkaddress.cache.ttl, do it before you touch the network.

I was using the java.net.InetAddress class to resolve IP addresses from DNS names the other day.

I wanted to test my code by manipulating my local system’s ‘hosts’ file, to quickly simulate moving IP addresses around behind a DNS name, so I also set disabled caching the resolved addresses from one call to the next by programmatically setting the networkaddress.cache.ttl Security property to ‘0′. According to the javadocs,

The value [assigned to networkaddress.cache.ttl] is specified as as integer to indicate the number of seconds to cache the successful lookup.

which is true, and everything was peachy – my hosts file changes were immediately picked up.

At first.

I continued to build my code and all of a sudden, the caching came back and the changes I was making in my hosts file were ignored.

By backtracking my changes, I worked out that the breaking change happened when I executed a network call which involved name resolution BEFORE I disabled the cache.

I moved the setting of the property to happen before I touched the network et voila – everything peachy again.

This (feature|problem|bug) is documented in a couple of places when you know what you’re looking for, like here.

And here’s a simple code demo of it in action:

public static void main(String[] args) throws Exception {
  String name = "google.com";

  //lookup(name);

  Security.setProperty("networkaddress.cache.ttl", "0");
  while (true) {
    lookup("google.com");
    Thread.sleep(1000);
  }

  public static void lookup(String name) throws Exception {
    System.out.println(name + ":" + InetAddress.getByName(name).getHostAddress());
  }
}

Running the sample above as-is:
google.com:74.125.127.100
google.com:74.125.67.100
google.com:74.125.127.100
google.com:74.125.67.100
google.com:74.125.127.100

But uncomment the first call to lookup(), and
google.com:74.125.45.100
google.com:74.125.45.100
google.com:74.125.45.100
google.com:74.125.45.100
google.com:74.125.45.100

Cheers,

Paul Brabban Development, Java

I found a new email client called K-9 Mail the other day, following a little Googling – and it’s great.

My HTC Magic came with an email client installed. It ticked all the style boxes, but over the past couple of months I’ve learned that it ticks none of the usability boxes.

It has trouble keeping synchronized with my email accounts.
There’s no easy access to next or previous emails.
There’s no one-touch delete.

Yuk.
So, I had a look around and found a couple of endorsements of K-9 Mail, and I looked it up in the Market.

Compared to the pre-installed client, it’s the mutt’s nuts – a much more pleasant experience – so if you’re struggling with email on Android, give it a whirl.

Cheers,

Paul Brabban Development android, email, HTC Magic, K-9

I’ve been having some problems with my feeds, in that the news items were getting truncated after only a few words with [...]

I’ve sorted this out today, but either my upgrade or my faffing with the feeds has reset the feed on my reader, so that the posts I’d already read appeared as unread again.

Not sure why that happened, and sorrysorrysorry if it’s caused anyone any inconvenience.

Sorry!

Paul Brabban Development feed, wordpress