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19 Jan 2020 : The journey from ASP to PHP #
Today I made a big step forwards in improving this website. For 14 years the site has run on an MS Access and ASP backend. Yes, that's ASP, not ASP.NET, which wasn't an option when I wrote the code. There were multiple reasons for me choosing ASP, but one of them was that — given the backing of Microsoft — it looked to have better long-term prospects than the open-source underdog PHP. Now I'm in the situation where I want to move the site over to a Linux server (primarily so I can get it TLS-enabled) and so it needs to be re-written in somethig that will run properly on Linux.

In order to minimise my effort, that means re-writing it in PHP. My prediction that ultimately ASP would prevail over PHP didn't quite pan out as I expected. But that's no bad thing. I'm not a fan of PHP particularly, but I'm even less a fan of ASP.

The conversion isn't just a matter of re-writing the ASP in PHP. I also need to convert the database from MS Access to MySQML. For this I've written a simple python script that will do a complete transfer automatically. It's great because I can run it at any time to do the transfer, which is important given the site will continue to get updates (like this one) right until the switch finally happens.

Today's achievement was to finally get the site running using PHP. It's weird to see exactly the same pages popping out of completely different code running on completely different stacks. There remain a bunch of backend changes I still need to make (probably I'm no more than 20% of the way through), but this at least proves that the conversion is not only feasible, but seamlessly so.
The ASP site left, and the PHP site right

To my relief, the re-writing of the code from ASP to PHP has been surprisingly straightfoward as well. Some of the key similarities:
  1. The structuring is very similar; almost identical. Code is interwoven into HTML, executed on request in a linear way, the resulting text output is the page the requester sees.
  2. Database access is using SQL, so no big changes there.
  3. Javascript and PHP are both curly-bracket-heavy, dynamically-typed, imperative languages.
  4. ASP and PHP both include files in a similar way, which should allow the file structures to remain identical.

In fact, the structure of the two codebases is so similar that it's been practically a line-by-line conversion.
The ASP code left, and the PHP code right

There are nevertheless some important differences, some of which you can see in the screenshot above.
  1. The most obvious visual difference is that all PHP variables must be prefixd with a $ symbol, whereas javascript variable can just use pretty much any alphanumeric identifier.
  2. PHP concatenates strings using the . symbol, whereas Javascript uses the + symbol. This might seem like a minor change, but string concatenation is bread-and-butter site generation functionality, so it comes up a lot.
  3. Many Javascript types, including strings, are classes which come with their own bunch of methods. In contrast PHP seems to prefer everything to be passed as function parameters. For example: string.substring(start, end) vs. substr($string, $start, $length).
  4. PHP regex literatls are given as strings, whereas in Javascript they have their own special syntax.
  5. Javascript has this nice Date class, whereas PHP seems happier relying on integer timestamps.
  6. Variable scoping seem to be different. This caused me the biggest pain, since ASP is more liberal, meaning with PHP more effort is needed passing variables around.

In practice, none of these changes are really that bad and I was able to convert my codebase with almost no thought. It just required going through and methodically fixing each of lines in sequence. Most of it could have been automated fairly easily even.

However, as I go through converting the code I'm continually noticing both small and big ways to improve the design. Tighter SQL statements, clearer structuring, streamlining variable usage, better function structure, improved data encapsulation and so on. But in the first instance I'm sticking to this line-by-line conversion. Once it's up and running, I can think about refactoring and refining.

It feels like I'm making good progress on my plan to change the site. I was hoping to get it done by the end of January, and right now that's not looking out-of-the-question.


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