Django QR Code

This is an application that provides tools for displaying QR codes on your Django site.

This application depends on the Segno QR Code generator library.

This app makes no usage of the Django models and therefore do not use any database.

Only Python >= 3.6 is supported.

Installation

Binary Package from PyPi

In order to use this app in a Django project, the simplest way is to install it from PyPi:

pip install django-qr-code

From the Source Code

In order to modify or test this app you may want to install it from the source code.

Clone the GitHub repository and then run:

pip install -r requirements.txt -r requirements-dev.txt
python manage.py collectstatic --no-input

Usage

Start by adding qr_code to your INSTALLED_APPS setting like this:

INSTALLED_APPS = (
    ...,
    'qr_code',
)

You need to load the tags provided by this app in your template with:

{% load qr_code %}

The source code on GitHub contains a simple demo app. Please check out the templates folder for an example of template, and the setting and urls files for an example of configuration and integration.

Generating Inline QR Code in your HTML (qr_from_text)

The tag qr_from_text generates an embedded svg or img tag within the HTML code produced by your template.

The following renders a tiny "hello world" QR code with a svg tag:

{% qr_from_text "Hello World!" size="T" %}

Here is a medium "hello world" QR code with an img tag:

{% qr_from_text "Hello World!" size="m" image_format="png" error_correction="L" %}

QR Code Rendering Options

The size parameter gives the size of each module of the QR code matrix. It can be either a positive integer or one of the following letters:

t or T: tiny (value: 6)
s or S: small (value: 12)
m or M: medium (value: 18)
l or L: large (value: 30)
h or H: huge (value: 48)

For PNG image format the size unit is in pixels, while the unit is 1 mm for SVG format.

Here is a "hello world" QR code using the version 12:

{% qr_from_text "Hello World!" size=8 version=12 %}

The version parameter is an integer from 1 to 40 that controls the size of the QR code matrix. Set to None to determine this automatically. The smallest, version 1, is a 21 x 21 matrix. The biggest, version 40, is 177 x 177 matrix. The size grows by 4 modules/side.

Here is a "hello world" QR code using a border of 6 modules:

{% qr_from_text "Hello World!" size=10 border=6 %}

The border parameter controls how many modules thick the border should be (the default is 4, which is the minimum according to the specs).

There are 4 error correction levels used for QR codes, with each one adding different amounts of "backup" data depending on how much damage the QR code is expected to suffer in its intended environment, and hence how much error correction may be required. The correction level can be configured with the error_correction parameter as follow:

l or L: error correction level L – up to 7% damage
m or M: error correction level M – up to 15% damage
q or Q: error correction level Q – up to 25% damage
h or H: error correction level H – up to 30% damage

Alternatively, you may use the options keyword argument with an instance of QRCodeOptions as value instead of listing every requested options. Here is a example of view:

from django.shortcuts import render
from qr_code.qrcode.utils import QRCodeOptions

def my_view(request):
    # Build context for rendering QR codes.
    context = dict(
        my_options=QRCodeOptions(size='t', border=6, error_correction='L'),
    )

    # Render the view.
    return render(request, 'my_app/my_view.html', context=context)

and an example of template for the view above:

{% qr_from_text "Hello World!" options=my_options %}

Generating URLs to QR Code Images (qr_url_from_text)

The qr_url_from_text tag generates an url to an image representing the QR code. It comes with the same options as qr_from_text to customize the image format (SVG or PNG), the size, the border, and the matrix size. It also has an additional option cache_enabled to disable caching of served image.

Here is a medium "hello world" QR code that uses an URL to serve the image in SVG format:

<img src="{% qr_url_from_text "Hello World!" %}" alt="Hello World!">

Here is a "hello world" QR code in version 10 that uses an URL to serve the image in PNG format:

<img src="{% qr_url_from_text "Hello World!" size=8 version=10 image_format='png' %}" alt="Hello World!">

The image targeted by the generated URL is served by a view provided in qr_code.urls. Therefore, you need to include the URLs provided by qr_code.urls in your app in order to make this tag work. This can be achieved with something like this:

from django.conf.urls import include
from django.urls import path

urlpatterns = [
    path('qr_code/', include('qr_code.urls', namespace="qr_code")),
]

The QR code images are served via a URL named qr_code:serve_qr_code_image. You can customize the path under which the images are served (i. e. the path bound to the URL named qr_code:serve_qr_code_image) with the optionnal setting SERVE_QR_CODE_IMAGE_PATH which defaults to images/serve-qr-code-image/. Note that the trailing slash is mandatory and that defining this setting to an empty string leads to using the default value. The example below will serve any QR code image from <base URL or your application>/qr-code-image/:

# In urls.py
from django.conf.urls import include
from django.urls import path

urlpatterns = [
    path('', include('qr_code.urls', namespace='qr_code')),
]

# In your settings
SERVE_QR_CODE_IMAGE_PATH = 'qr-code-image/'

Caching Served Images

A large QR code (version 40) requires 0.2 second to be generated on a powerful machine (in 2018), and probably more than half a second on a really cheap hosting.

The image served by the qr_code app can be cached to improve performances and reduce CPU usage required to generate the QR codes. In order to activate caching, you simply need to declare a cache alias with the setting QR_CODE_CACHE_ALIAS to indicate in which cache to store the generated QR codes.

For instance, you may declare an additional cache for your QR codes like this in your Django settings:

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
    },
    'qr-code': {
        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        'LOCATION': 'qr-code-cache',
        'TIMEOUT': 3600
    }
}

QR_CODE_CACHE_ALIAS = 'qr-code'

The QR_CODE_CACHE_ALIAS = 'qr-code' tells the qr_code app to use that cache for storing the generated QR codes. All QR codes will be cached with the specified TIMEOUT when a non-empty value is set to QR_CODE_CACHE_ALIAS.

If you want to activate the cache for QR codes, but skip the caching for some specific codes, you can use the keyword argument cache_enabled=False when using qr_url_from_text.

Here is a "hello world" QR code in version 20 with an error correction level Q (25% of redundant data) that uses a URL to serve the image in SVG format, and disable caching for served image:

<img src="{% qr_url_from_text "Hello World!" size=8 version=20 error_correction="Q" cache_enabled=False %}" alt="Hello World!">

Protecting Access to QR Code Images

The default settings protect the URLs that serve QR code images against external requests, and thus against possibly easy (D)DoS attacks.

Here are the available settings to manage the protection for served images:

from qr_code.qrcode import constants

QR_CODE_URL_PROTECTION = {
    constants.TOKEN_LENGTH: 30,                         # Optional random token length for URL protection. Defaults to 20.
    constants.SIGNING_KEY: 'my-secret-signing-key',     # Optional signing key for URL token. Uses SECRET_KEY if not defined.
    constants.SIGNING_SALT: 'my-signing-salt',          # Optional signing salt for URL token.
    constants.ALLOWS_EXTERNAL_REQUESTS_FOR_REGISTERED_USER: True  # Tells whether a registered user can request the QR code URLs from outside a site that uses this app. It can be a boolean value used for any user or a callable that takes a user as parameter. Defaults to False (nobody can access the URL without the signature token).
}

Signing Request URLs

By default, the application only serves QR code images for authenticated URLs (requests generated from your application and adressed to your application). The authentication uses a HMAC to sign the request query arguments. The authentication code is passed as a query argument named token which is automatically generated by qr_url_from_text. Whenever the signature is invalid, the application returns a HTTP 403 Permission denied response when processing the request for serving a QR code image.

This mechanism ensures that, by default, nobody can send external requests to your application to obtain custom QR codes for free. This is especially useful if you display QR code URLs on public pages (no user authentication).

The token query argument is not mandatory and, when a request reaches the qr_code:serve_qr_code_image URL without that token, the protection mechanism falls back to the user authentication mechanism (see chapter below).

It is possible to explicitly remove the signature token that protects a specific URL with the parameter url_signature_enabled=False. Here is a "hello world" QR code that uses a URL to serve the image in SVG format without the token query argument :

<img src="{% qr_url_from_text "Hello World!" url_signature_enabled=False %}" alt="Hello World!">

The token parameter will not be part of the query string of the generated URL, making possible to build a simpler, predictable URL. However, this will trigger the user authentication mechanism (see chapter below).

Handling User Authentication when Serving QR Code Images

If you are interested in providing the QR code images as a service, there is a setting named ALLOWS_EXTERNAL_REQUESTS_FOR_REGISTERED_USER to grant access to some controlled users. This setting tells who can bypass the url signature token (see chapter above). It can be a boolean value used for any authenticated user, or a callable that takes a user as only parameter.

Setting the ALLOWS_EXTERNAL_REQUESTS_FOR_REGISTERED_USER option to True tells the application to serve QR code images to authenticated users only. Hence, to grant access to any authenticated user to generated images, you can use this in your settings:

from qr_code.qrcode import constants

QR_CODE_URL_PROTECTION = {
    constants.ALLOWS_EXTERNAL_REQUESTS_FOR_REGISTERED_USER: True
}

Setting the option ALLOWS_EXTERNAL_REQUESTS_FOR_REGISTERED_USER to a callable that always returns True (even for anonymous users) will allow anyone to access QR code image generation from outside your Django app. The following settings will grant access to anonymous users to generated images:

from qr_code.qrcode import constants

QR_CODE_URL_PROTECTION = {
    constants.ALLOWS_EXTERNAL_REQUESTS_FOR_REGISTERED_USER: lambda u: True
}

Please note that, if your service is available on the Internet, allowing anyone to generate any kind of QR code via your Django application - as shown above - might generate a very heavy load on your server.

QR Codes for Apps

Aside from generating a QR code from a given text, you can also generate codes for specific application purposes, that a reader can interpret as an action to take: open a mail client to send an e-mail to a given address, add a contact to your phone book, connect to a Wi-Fi, start a SMS, etc. See this documentation about what a QR code can encode.

Django QR Code proposes several utility tags to ease the generation of such codes, without having to build the appropriate text representation for each action you need. This remove the hassle of reading the specifications and handling all the required escaping for reserved chars.

Please note that some commands are common patterns, rather than formal specifications. Therefore, there is no guarantee that all QR code readers will handle them properly.

The following tags targeting apps are available:

qr_for_email and qr_url_for_email
qr_for_tel and qr_url_for_tel
qr_for_sms and qr_url_for_sms
qr_for_geolocation and qr_url_for_geolocation
qr_for_google_maps and qr_url_for_google_maps
qr_for_youtube and qr_url_for_youtube
qr_for_google_play and qr_url_for_google_play
qr_for_contact and qr_url_for_contact
qr_for_wifi and qr_url_for_wifi

You could write a view like this:

from datetime import date
from django.shortcuts import render    
from qr_code.qrcode.utils import ContactDetail, WifiConfig, Coordinates, QRCodeOptions

def application_qr_code_demo(request):
    # Use a ContactDetail instance to encapsulate the detail of the contact.
    contact_detail = ContactDetail(
        first_name='John',
        last_name='Doe',
        first_name_reading='jAAn',
        last_name_reading='dOH',
        tel='+41769998877',
        email='j.doe@company.com',
        url='http://www.company.com',
        birthday=date(year=1985, month=10, day=2),
        address='Cras des Fourches 987, 2800 Delémont, Jura, Switzerland',
        memo='Development Manager',
        org='Company Ltd',
    )

    # Use a WifiConfig instance to encapsulate the configuration of the connexion.
    wifi_config = WifiConfig(
        ssid='my-wifi',
        authentication=WifiConfig.AUTHENTICATION.WPA,
        password='wifi-password'
    )

    # Build coordinates instances.
    google_maps_coordinates = Coordinates(latitude=586000.32, longitude=250954.19)
    geolocation_coordinates = Coordinates(latitude=586000.32, longitude=250954.19, altitude=500)

    # Build context for rendering QR codes.
    context = dict(
        contact_detail=contact_detail,
        wifi_config=wifi_config,
        video_id='J9go2nj6b3M',
        google_maps_coordinates=google_maps_coordinates,
        geolocation_coordinates=geolocation_coordinates,
        options_example=QRCodeOptions(size='t', border=6, error_correction='L'),
    )

    # Render the index page.
    return render(request, 'my_app/application_qr_code_demo.html', context=context)

Then, in your template, you can render the appropriate QR codes for the given context:

<h3>Add contact '{{ contact_detail.first_name }} {{ contact_detail.last_name }}' to phone book</h3>
{% qr_for_contact contact_detail=contact_detail size='S' %}
<p>or:</p>
{% qr_for_contact contact_detail size='S' %}
<p>or:</p>
{% qr_for_contact contact_detail options=options_example %}

<h3>Configure Wi-Fi connexion to '{{ wifi_config.ssid }}'</h3>
<img src="{% qr_url_for_wifi wifi_config=wifi_config size='T' error_correction='Q' %}">
<p>or:</p>
<img src="{% qr_url_for_wifi wifi_config size='T' error_correction='Q' %}">
<p>or:</p>
<img src="{% qr_url_for_wifi wifi_config options=options_example %}">

<h3>Watch YouTube video '{{ video_id }}'</h3>
{% qr_for_youtube video_id image_format='png' size='T' %}
<p>or:</p>
{% qr_for_youtube video_id options=options_example %}

<h3>Open map at location: ({{ geolocation_coordinates }})</h3>
<img src="{% qr_url_for_geolocation coordinates=geolocation_coordinates %}">
<p>or:</p>
<img src="{% qr_url_for_geolocation latitude=geolocation_coordinates.latitude longitude=geolocation_coordinates.longitude altitude=geolocation_coordinates.altitude %}">
<p>or:</p>
<img src="{% qr_url_for_geolocation latitude=geolocation_coordinates.latitude longitude=geolocation_coordinates.longitude altitude=geolocation_coordinates.altitude options=options_example %}">

<h3>Open Google Maps App at location: ({{ google_maps_coordinates }})</h3>
{% qr_for_google_maps coordinates=google_maps_coordinates %}
<p>or:</p>
{% qr_for_google_maps latitude=google_maps_coordinates.latitude longitude=google_maps_coordinates.longitude %}
<p>or:</p>
{% qr_for_google_maps latitude=google_maps_coordinates.latitude longitude=google_maps_coordinates.longitude options=options_example %}

Please check-out the demo application to see more examples.

Notes

Image Formats

The SVG is the default image format. It is a vector image format so it can be scaled up and down without quality loss. However, it has two drawbacks. The size is not given in pixel, which can be problematic if the design of your website relies on a fixed width (in pixels). The format is less compact than PNG and results in a larger HTML content. Note that a base64 PNG is less compressible than a SVG tag, so it might not matter that much of you use HTML compression on your web server.

SVG has broad support now, and it will work properly on any modern web browser.

qr_from_text vs qr_url_from_text

The tag qr_url_from_text has several advantages over qr_from_text, despite the fact that it requires a bit more of writing:

the generated HTML code does not contain heavy inline image data (lighter and cleaner content)
the generated images can be cached (served with a separate HTML request)
the HTML tag used to render the QR code is always an <img> tag, which may simplify CSS handling
the HTML tag embedding the image is not generated for you, which allows for customization of attributes (height, width, alt)
the page can be loaded asynchronously, which improves responsiveness
you can provide links to QR codes instead of displaying them, which is not possible with qr_from_text

One disadvantage of qr_url_from_text is that it increases the number of requests to the server: one request to serve the page containing the URL and another to request the image.

Be aware that serving image files (which are generated on the fly) from a URL can be abused and lead to (D)DoS attack pretty easily, for instance by requesting very large QR codes from outside your application. This is the reason why the associated setting ALLOWS_EXTERNAL_REQUESTS_FOR_REGISTERED_USER in QR_CODE_URL_PROTECTION defaults to completely forbid external access to the API. Be careful when opening external access.

QR Codes Caching

Caching QR codes reduces CPU usage, but the usage of qr_url_from_text (which caching depends on) increases the number of requests to the server (one request to serve the page containing the URL and another to request the image).

Moreover, be aware that the largest QR codes, in version 40 with a border of 4 modules and rendered in SVG format, have a size of ~800 KB. Be sure that your cache options are reasonable and can be supported by your server(s), especially for in-memory caching.

Note that even without caching the generated QR codes, the app will return a HTTP 304 Not Modified status code whenever the same QR code is requested again. The URL named qr_code:serve_qr_code_image adds the ETag and Last-Modified headers to the response if the headers aren't already set, enabling HTTP 304 Not Modified response upon following requests.

Demo Application

If you want to try this app, you may want to use the demo application shipped alongside the source code.

Get the source code from GitHub, follow the installation instructions above, and run the runserver command of Django:

python manage.py runserver

The demo application should be running at http://127.0.0.1:8000/qr-code-demo/.

If you have Docker Compose installed, you can simply run the following from a terminal (this will save you the burden of setting up a proper python environment):

cd scripts
./run-demo-app.sh

The demo application should be running at http://127.0.0.1:8910/qr-code-demo/.

Testing

Get the source code from GitHub, follow the installation instructions above, and run the test command of Django:

python manage.py test

This will run the test suite with the locally installed version of Python and Django.