Matthew Daly's Blog

I'm a web developer in Norfolk. This is my blog...

21st July 2015 9:15 pm

New Laptop

For a while now it’s been obvious that I needed a new laptop. My main workhorse for a while has been a 2008 MacBook, but I’m not really a fan of Mac OS X and it was stuck on Snow Leopard, so it was somewhat behind the times. It was also painfully slow by modern standards - regenerating this site took a couple of minutes. I had two other reasonably modern laptops, but one was too big and cumbersome, while the other was a Dell Mini, which isn’t really fast enough for a developer. When I last bought a laptop, I wasn’t even a developer, so it was long past time I got a more suitable machine.

I therefore took the plunge and ordered a new Dell XPS 13 Developer Edition, which arrived today. It’s an absolutely beautiful machine, and it’s extremely light. It’s also a lot faster than any other machine I own. The screen is exceptionally sharp, and setting it up was nice and easy.

After an hour or so with this machine, I’m already really happy with it. We’ll have to see whether I still think so after a few months using it.

4th July 2015 1:01 pm

Handling Images As Base64 Strings With Django REST Framework

I’m currently working on a Phonegap app that involves taking pictures and uploading them via a REST API. I’ve done this before, and I found at that time that the best way to do so was to fetch the image as a base-64 encoded string and push that up, rather than the image file itself. However, the last time I did so, I was using Tastypie to build the API, and I’ve since switched over to Django REST Framework as my API toolkit of choice.

It didn’t take long to find this gist giving details of how to do so, but it didn’t work as is, partly because I was using Python 3, and partly because the from_native method has gone as at Django REST Framework 3.0. It was, however, straightforward to adapt it to work. Here’s my solution:

import base64, uuid
from django.core.files.base import ContentFile
from rest_framework import serializers
# Custom image field - handles base 64 encoded images
class Base64ImageField(serializers.ImageField):
def to_internal_value(self, data):
if isinstance(data, str) and data.startswith('data:image'):
# base64 encoded image - decode
format, imgstr = data.split(';base64,') # format ~= data:image/X,
ext = format.split('/')[-1] # guess file extension
id = uuid.uuid4()
data = ContentFile(base64.b64decode(imgstr), name = id.urn[9:] + '.' + ext)
return super(Base64ImageField, self).to_internal_value(data)

This solution will handle both base 64 encoded strings and image files. Then, just use this field as normal.

17th June 2015 8:34 pm

Getting Django-behave and Celery to Work Together

I ran into a small issue today. I’m working on a Django app which uses Celery to handle certain tasks that don’t need to return a response within the context of the HTTP request. I also wanted to use django_behave for running BDD tests. The trouble is that both django_behave and Celery provide their own custom test runners that extend the default Django test runner, and so it looked like I might have to choose between the two.

However, it turned out that the Celery one was actually very simple, with only a handful of changes needing to be made to the default test runner to make it work with Celery. I was therefore able to create my own custom test runner that inherited from DjangoBehaveTestSuiteRunner and applied the changes necessary to get Celery working with it. Here is the test runner I wrote, which was saved as myproject/runner.py:

from django.conf import settings
from djcelery.contrib.test_runner import _set_eager
from django_behave.runner import DjangoBehaveTestSuiteRunner
class CeleryAndBehaveRunner(DjangoBehaveTestSuiteRunner):
def setup_test_environment(self, **kwargs):
_set_eager()
settings.BROKER_BACKEND = 'memory'
super(CeleryAndBehaveRunner, self).setup_test_environment(**kwargs)

To use it, you need to set the test runner in settings.py

TEST_RUNNER = 'myproject.runner.CeleryAndBehaveRunner'

Once that was done, my tests worked flawlessly with Celery, and the Behave tests ran as expected.

14th June 2015 9:29 pm

Setting Etags in Laravel 5

Although I’d prefer to use Python or Node.js, there are some times when circumstances dictate that I need to use PHP for a project at work. In the past, I used CodeIgniter, but that was through nothing more than inertia. For some time I’d been planning to switch to Laravel, largely because of the baked-in PHPUnit support, but events conspired against me - one big project that came along had a lot in common with an earlier one, so I forked it rather than starting over.

Recently I built a REST API for a mobile app, and I decided to use that to try out Laravel (if it had been available at the time, I’d have gone for Lumen instead). I was very pleased with the results - I was able to quickly put together the back end I wanted, with good test coverage, and the tinker command in particular was useful in debugging. The end result is fast and efficient, with query caching in place using Memcached to improve response times.

I also implemented a simple middleware to add ETags to HTTP responses and compare them on incoming requests, returning a 304 Not Modified status code if they are the same, which is given below:

<?php namespace App\Http\Middleware;
use Closure;
class ETagMiddleware {
/**
* Implement Etag support
*
* @param \Illuminate\Http\Request $request
* @param \Closure $next
* @return mixed
*/
public function handle($request, Closure $next)
{
// Get response
$response = $next($request);
// If this was a GET request...
if ($request->isMethod('get')) {
// Generate Etag
$etag = md5($response->getContent());
$requestEtag = str_replace('"', '', $request->getETags());
// Check to see if Etag has changed
if($requestEtag && $requestEtag[0] == $etag) {
$response->setNotModified();
}
// Set Etag
$response->setEtag($etag);
}
// Send response
return $response;
}
}

This is based on a solution for Laravel 4 by Nick Verwymeren, but implemented as Laravel 5 middleware, not a Laravel 4 filter. To use this with Laravel 5, save this as app/Http/Middleware/ETagMiddleware.php. Then add this to the $middleware array in app/Http/Kernel.php:

        'App\Http\Middleware\ETagMiddleware',

It’s quite simple to write this kind of middleware with Laravel, and using something like this is a no-brainer for most web apps considering the bandwidth it will likely save your users.

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About me

I'm a web and mobile app developer based in Norfolk. My skillset includes Python, PHP and Javascript, and I have extensive experience working with CodeIgniter, Laravel, Zend Framework, Django, Phonegap and React.js.