Toby's Log page 90

Testing the Monty Hall problem

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I have always had trouble understanding and even believing the proposition of the Monty Hall problem. It feels like it is proposing that the probability of past events affect the probability of future events, like suggesting that a coin landing on heads will be more likely to land on tails the next time. Rather, it’s about the information provided by the circumstances. I still don’t intuitively understand it, but at least I have now verified for myself that the proposed probability approximates outcomes. I have created a PHP simulation of the game and script to iterate it numerous times.

The code allows testing other numbers of doors and number of doors for the host to reveal. Increasing the numbers shows increasing odds. Even if Monty opens less than all but the remaining door (obviously requires more than three total doors), it still increases odds by switching.

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ASCII art source code signature for my site

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Sometimes I see sites with ASCII art hidden in comments in their source code. I’ve long admired the retro computer nerdiness of ASCII art. At times, I’ve wanted to add some to my site, but have been reluctant because of the extra bites it would add to page weight, the difficulty in making it look good, the lack of a subject I felt worth it, and the problems they can have with differing fonts and display widths. However, after adding an easter egg recently, I was more receptive to the idea when reminded about it by the source code of archive.org.

I spent some time this past weekend trying various different ASCII versions of my name. Some examples:

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Konami easter egg

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What web developer’s site is complete without an easter egg? Until today, mine didn’t have one, but I had long wanted something. Since I was struggling to make forward progress on what I had actually wanted to work on this weekend, and had just been reminded of the Konami Code, I decided it was finally time to add one. I had seen a friend do a key sequence easter egg on a site he built a while back, which had put the idea in my head. The Konami Code sequence has been used on several websites already (Digg and Vogue are two examples I could get to work), so why not mine?

A simple Konami Code script:

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Symfony AppCache and ‘X-Reverse-Proxy-TTL’, a hack

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Symfony’s HttpCache reverse proxy is a simple way to get caching of pages with Symfony. It is simple to set up, easy to work with, and easy to clear. I started using it recently on my own site.

A simple app/console cache:clear will clear the entire cache. Otherwise, following the HTTP-oriented spirit of the framework, invalidation is based entirely on HTTP headers. In this way, it works the same as proxy / gateway caches. It only caches responses with public Cache-Control headers. It is age based, using the Cache-Control s-maxage or maxage values or Expires headers (following that order of precedence). It then considers the cached items fresh until they are stored for longer than those headers specify they can be stored. The cached version is served, bypassing the router / controller, as long as the cache is fresh.

This is all nice, but using long max-ages for those headers means that caches outside of my control can cache pages for long periods of time. cache:clear won’t help when a page changes. One possible option would be to have shorter and safer max-ages as Cache-Control headers and use something else for HTTPCache.

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404 with autofilling form

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Inspired by a tweet by @simevidas about a 404 page search form, I decided to finally replace Symfony’s default 404 page on my site. The tweet was about an example site’s 404 pages that take pieces from the URL path to populate a search field. Upon seeing it, I immediately thought how easy it would be to implement a simple version of that.

I had been thinking of customizing my 404 for a while, but stopped trying because Twig doesn’t seem to know about bundle paths in the error pages, preventing me from extending the “base” template in my bundle. I still didn’t find a solution for this, so the 404 page has an unstyled look, but I wanted to capture the search form idea while it was on my mind.

Looking into 404 best practices, I found three things that I wanted on mine: branding, guidance / next steps for the user, and small size / low power.

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Websites in Multiple File Formats

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Since I saw Symfony’s _format routing parameter, which is used to effectively set the file type of the response, I’ve thought it would be cool to have every page on a website support more than just ‘html’ response types by adding a .{_format} to the end of the URL and make a template version for each. Users would be able to consume the same information in different formats depending on their needs. ‘txt’, for example, would basically have just the content that would go in the “ element, in pure text format, providing a fallback or simplified view that can be read even by curl users. ‘json’ or ‘xml’ formats might provide the content and meta data about it in a machine consumable format. You could even go all out with an ‘mp3’ format where you read the page content.

Yesterday, I took my first step toward this idea on my site by implementing my homepage in the ‘txt’ format. This was very simple since my content is already being composed in markdown, a visually pleasing structure for text content.

Obviously, adding more pages and formats will add development time. This probably wouldn’t be useful enough to be worth it for a normal site, but for my own site, I get to play with whatever cool ideas I want.

Symfony AppCache: built in reverse HTTP proxy

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I finally set up my site to work with Symfony’s built in HTTP reverse proxy. Took a little bit of time since I had to fix a couple minor bugs in how things are set up with my symfony-initial and Symfony Standard Edition Bundle and then made a mistake in testing whether or not it was working that made me think it wasn’t when it was.

One useful way to test if it’s working is to set the ‘debug’ option of AppCache to true (turn this back off for production). This will set an X-Symfony-Cache header that will provide info on the cache behaviour. You can see these headers on the shell by running curl -I your.url. If it says ‘fresh’ as part of the header value, that means it was served from the cache. If it shows the header at all, that means AppCache is being used.

For the cache to work, the response must be public and have something set to control how the cache becomes stale. See Symfony’s docs on caching for more details. Since my content rarely changes at the moment, I went with the Cache-Control header with max-age. A cool thing about using Symfony’s reverse proxy is that the entire cache will be cleared when clearing Symfony’s cache like normal. This means that if you make a mistake and must remove it from the cache, there is a quick and easy way.

Toby Now

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My roommate has been out of town this week for work. It’s been me and the dogs. I got to work from home a couple days so I could feed them. Normally when I work from “home”, I actually work from the library, because my roommate doesn’t like me working from home. The dogs have been mostly good, though as usual they can be a bit demanding for attention.

Bought myself a few things earlier this week. Got my first ever electric razor (Phillips-Norelco PQ208). I’ve only used it once, but it seems like it’s going to speed up my shaving experience and make it more likely for me to do. Also, since I usually let my blades get rather dull before buying new ones, it will be less painful. It’s just a travel one, so it cost around as much as a 5 pack of blades for my former razor, the Mach 3.

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House fire down the street

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To continue with my fire theme (see Van fire), I was awoken around 0500 to the sound of some yelling and then some fire trucks. I couldn’t see any fire or smoke from my bedroom window, but could see the trucks and firefighters and neighbors outside. I could hear some talking and at one point chopping and breaking glass. There were so many fire trucks with flashing lights that a red glow came through the curtain, reminding me of a certain Seinfeld episode. They took up like half the block parked along the street. One firetruck parked right in front of our house. They were there for a couple hours probably and kept me awake for at least that long (I often have trouble falling asleep). The event got a brief blurb and video on the channel 5 website.

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