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microdot/docs/intro.rst
Miguel Grinberg 20ea305fe7 v2 (#186)
2023-12-22 20:26:07 +00:00

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Installation
------------
The installation method is different depending on the version of Python.
CPython Installation
~~~~~~~~~~~~~~~~~~~~
For use with standard Python (CPython) projects, Microdot and all of its core
extensions are installed with ``pip``::
pip install microdot
MicroPython Installation
~~~~~~~~~~~~~~~~~~~~~~~~
For MicroPython, the recommended approach is to manually copy the necessary
source files from the
`GitHub repository <https://github.com/miguelgrinberg/microdot/tree/main/src>`_
into your device, ideally after
`compiling <https://docs.micropython.org/en/latest/reference/mpyfiles.html>`_
them to *.mpy* files. These source files can also be
`frozen <https://docs.micropython.org/en/latest/develop/optimizations.html?highlight=frozen#frozen-bytecode>`_
and incorporated into a custom MicroPython firmware.
Use the following guidelines to know what files to copy:
- For a minimal setup with only the base web server functionality, copy
`microdot.py <https://github.com/miguelgrinberg/microdot/blob/main/src/microdot/microdot.py>`_
into your project.
- For a configuration that includes one or more optional extensions, create a
*microdot* directory in your device and copy the following files:
- `__init__.py <https://github.com/miguelgrinberg/microdot/blob/main/src/microdot/__init__.py>`_
- `microdot.py <https://github.com/miguelgrinberg/microdot/blob/main/src/microdot/microdot.py>`_
- any needed `extensions <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot>`_.
Getting Started
---------------
This section describes the main features of Microdot in an informal manner.
For detailed reference information, consult the :ref:`API Reference`.
If you are familiar with releases of Microdot before 2.x, review the
:ref:`Migration Guide <Migrating to Microdot 2.x from Older Releases>`.
A Simple Microdot Web Server
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The following is an example of a simple web server::
from microdot import Microdot
app = Microdot()
@app.route('/')
async def index(request):
return 'Hello, world!'
app.run()
The script imports the :class:`Microdot <microdot.Microdot>` class and creates
an application instance from it.
The application instance provides a :func:`route() <microdot.Microdot.route>`
decorator, which is used to define one or more routes, as needed by the
application.
The ``route()`` decorator takes the path portion of the URL as an
argument, and maps it to the decorated function, so that the function is called
when the client requests the URL.
When the function is called, it is passed a :class:`Request <microdot.Request>`
object as an argument, which provides access to the information passed by the
client. The value returned by the function is sent back to the client as the
response.
Microdot is an asynchronous framework that uses the ``asyncio`` package. Route
handler functions can be defined as ``async def`` or ``def`` functions, but
``async def`` functions are recommended for performance.
The :func:`run() <microdot.Microdot.run>` method starts the application's web
server on port 5000 by default. This method blocks while it waits for
connections from clients.
Running with CPython
^^^^^^^^^^^^^^^^^^^^
.. list-table::
:align: left
* - Required Microdot source files
- | `microdot.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot.py>`_
* - Required external dependencies
- | None
* - Examples
- | `hello.py <https://github.com/miguelgrinberg/microdot/blob/main/examples/hello/hello.py>`_
When using CPython, you can start the web server by running the script that
has the ``app.run()`` call at the bottom::
python main.py
After starting the script, open a web browser and navigate to
*http://localhost:5000/* to access the application at the default address for
the Microdot web server. From other computers in the same network, use the IP
address or hostname of the computer running the script instead of
``localhost``.
Running with MicroPython
^^^^^^^^^^^^^^^^^^^^^^^^
.. list-table::
:align: left
* - Required Microdot source files
- | `microdot.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot.py>`_
* - Required external dependencies
- | None
* - Examples
- | `hello.py <https://github.com/miguelgrinberg/microdot/blob/main/examples/hello/hello.py>`_
| `gpio.py <https://github.com/miguelgrinberg/microdot/blob/main/examples/gpio/gpio.py>`_
When using MicroPython, you can upload a *main.py* file containing the web
server code to your device, along with the required Microdot files, as defined
in the :ref:`MicroPython Installation` section.
MicroPython will automatically run *main.py* when the device is powered on, so
the web server will automatically start. The application can be accessed on
port 5000 at the device's IP address. As indicated above, the port can be
changed by passing the ``port`` argument to the ``run()`` method.
.. note::
Microdot does not configure the network interface of the device in which it
is running. If your device requires a network connection to be made in
advance, for example to a Wi-Fi access point, this must be configured before
the ``run()`` method is invoked.
Web Server Configuration
^^^^^^^^^^^^^^^^^^^^^^^^
The :func:`run() <microdot.Microdot.run>` method supports a few arguments to
configure the web server.
- ``port``: The port number to listen on. Pass the desired port number in this
argument to use a port different than the default of 5000. For example::
app.run(port=6000)
- ``host``: The IP address of the network interface to listen on. By default
the server listens on all available interfaces. To listen only on the local
loopback interface, pass ``'127.0.0.1'`` as value for this argument.
- ``debug``: when set to ``True``, the server ouputs logging information to the
console. The default is ``False``.
- ``ssl``: an ``SSLContext`` instance that configures the server to use TLS
encryption, or ``None`` to disable TLS use. The default is ``None``. The
following example demonstrates how to configure the server with an SSL
certificate stored in *cert.pem* and *key.pem* files::
import ssl
# ...
sslctx = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
sslctx.load_cert_chain('cert.pem', 'key.pem')
app.run(port=4443, debug=True, ssl=sslctx)
.. note::
The ``ssl`` argument can only be used with CPython at this time, because
MicroPython's asyncio module does not currently support SSL certificates or
TLS encryption. Work on this is
`in progress <https://github.com/micropython/micropython/pull/11897>`_.
Defining Routes
~~~~~~~~~~~~~~~
The :func:`route() <microdot.Microdot.route>` decorator is used to associate an
application URL with the function that handles it. The only required argument
to the decorator is the path portion of the URL.
The following example creates a route for the root URL of the application::
@app.route('/')
async def index(request):
return 'Hello, world!'
When a client requests the root URL (for example, *http://localhost:5000/*),
Microdot will call the ``index()`` function, passing it a
:class:`Request <microdot.Request>` object. The return value of the function
is the response that is sent to the client.
Below is another example, this one with a route for a URL with two components
in its path::
@app.route('/users/active')
async def active_users(request):
return 'Active users: Susan, Joe, and Bob'
The complete URL that maps to this route is
*http://localhost:5000/users/active*.
An application can include multiple routes. Microdot uses the path portion of
the URL to determine the correct route function to call for each incoming
request.
Choosing the HTTP Method
^^^^^^^^^^^^^^^^^^^^^^^^
All the example routes shown above are associated with ``GET`` requests, which
are the default. Applications often need to define routes for other HTTP
methods, such as ``POST``, ``PUT``, ``PATCH`` and ``DELETE``. The ``route()``
decorator takes a ``methods`` optional argument, in which the application can
provide a list of HTTP methods that the route should be associated with on the
given path.
The following example defines a route that handles ``GET`` and ``POST``
requests within the same function::
@app.route('/invoices', methods=['GET', 'POST'])
async def invoices(request):
if request.method == 'GET':
return 'get invoices'
elif request.method == 'POST':
return 'create an invoice'
As an alternative to the example above, in which a single function is used to
handle multiple HTTP methods, sometimes it may be desirable to write a separate
function for each HTTP method. The above example can be implemented with two
routes as follows::
@app.route('/invoices', methods=['GET'])
async def get_invoices(request):
return 'get invoices'
@app.route('/invoices', methods=['POST'])
async def create_invoice(request):
return 'create an invoice'
Microdot provides the :func:`get() <microdot.Microdot.get>`,
:func:`post() <microdot.Microdot.post>`, :func:`put() <microdot.Microdot.put>`,
:func:`patch() <microdot.Microdot.patch>`, and
:func:`delete() <microdot.Microdot.delete>` decorators as shortcuts for the
corresponding HTTP methods. The two example routes above can be written more
concisely with them::
@app.get('/invoices')
async def get_invoices(request):
return 'get invoices'
@app.post('/invoices')
async def create_invoice(request):
return 'create an invoice'
Including Dynamic Components in the URL Path
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The examples shown above all use hardcoded URL paths. Microdot also supports
the definition of routes that have dynamic components in the path. For example,
the following route associates all URLs that have a path following the pattern
*http://localhost:5000/users/<username>* with the ``get_user()`` function::
@app.get('/users/<username>')
async def get_user(request, username):
return 'User: ' + username
As shown in the example, a path component that is enclosed in angle brackets
is considered a placeholder. Microdot accepts any values for that portion of
the URL path, and passes the value received to the function as an argument
after the request object.
Routes are not limited to a single dynamic component. The following route shows
how multiple dynamic components can be included in the path::
@app.get('/users/<firstname>/<lastname>')
async def get_user(request, firstname, lastname):
return 'User: ' + firstname + ' ' + lastname
Dynamic path components are considered to be strings by default. An explicit
type can be specified as a prefix, separated from the dynamic component name by
a colon. The following route has two dynamic components declared as an integer
and a string respectively::
@app.get('/users/<int:id>/<string:username>')
async def get_user(request, id, username):
return 'User: ' + username + ' (' + str(id) + ')'
If a dynamic path component is defined as an integer, the value passed to the
route function is also an integer. If the client sends a value that is not an
integer in the corresponding section of the URL path, then the URL will not
match and the route will not be called.
A special type ``path`` can be used to capture the remainder of the path as a
single argument. The difference between an argument of type ``path`` and one of
type ``string`` is that the latter stops capturing when a ``/`` appears in the
URL.
@app.get('/tests/<path:path>')
async def get_test(request, path):
return 'Test: ' + path
For the most control, the ``re`` type allows the application to provide a
custom regular expression for the dynamic component. The next example defines
a route that only matches usernames that begin with an upper or lower case
letter, followed by a sequence of letters or numbers::
@app.get('/users/<re:[a-zA-Z][a-zA-Z0-9]*:username>')
async def get_user(request, username):
return 'User: ' + username
.. note::
Dynamic path components are passed to route functions as keyword arguments,
so the names of the function arguments must match the names declared in the
path specification.
Before and After Request Handlers
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
It is common for applications to need to perform one or more actions before a
request is handled. Examples include authenticating and/or authorizing the
client, opening a connection to a database, or checking if the requested
resource can be obtained from a cache. The
:func:`before_request() <microdot.Microdot.before_request>` decorator registers
a function to be called before the request is dispatched to the route function.
The following example registers a before-request handler that ensures that the
client is authenticated before the request is handled::
@app.before_request
async def authenticate(request):
user = authorize(request)
if not user:
return 'Unauthorized', 401
request.g.user = user
Before-request handlers receive the request object as an argument. If the
function returns a value, Microdot sends it to the client as the response, and
does not invoke the route function. This gives before-request handlers the
power to intercept a request if necessary. The example above uses this
technique to prevent an unauthorized user from accessing the requested
route.
After-request handlers registered with the
:func:`after_request() <microdot.Microdot.after_request>` decorator are called
after the route function returns a response. Their purpose is to perform any
common closing or cleanup tasks. The next example shows a combination of
before- and after-request handlers that print the time it takes for a request
to be handled::
@app.before_request
async def start_timer(request):
request.g.start_time = time.time()
@app.after_request
async def end_timer(request, response):
duration = time.time() - request.g.start_time
print(f'Request took {duration:0.2f} seconds')
After-request handlers receive the request and response objects as arguments,
and they can return a modified response object to replace the original. If
no value is returned from an after-request handler, then the original response
object is used.
The after-request handlers are only invoked for successful requests. The
:func:`after_error_request() <microdot.Microdot.after_error_request>`
decorator can be used to register a function that is called after an error
occurs. The function receives the request and the error response and is
expected to return an updated response object after performing any necessary
cleanup.
.. note::
The :ref:`request.g <The "g" Object>` object used in many of the above
examples is a special object that allows the before- and after-request
handlers, as well as the route function to share data during the life of the
request.
Error Handlers
^^^^^^^^^^^^^^
When an error occurs during the handling of a request, Microdot ensures that
the client receives an appropriate error response. Some of the common errors
automatically handled by Microdot are:
- 400 for malformed requests.
- 404 for URLs that are unknown.
- 405 for URLs that are known, but not implemented for the requested HTTP
method.
- 413 for requests that are larger than the allowed size.
- 500 when the application raises an unhandled exception.
While the above errors are fully complaint with the HTTP specification, the
application might want to provide custom responses for them. The
:func:`errorhandler() <microdot.Microdot.errorhandler>` decorator registers
functions to respond to specific error codes. The following example shows a
custom error handler for 404 errors::
@app.errorhandler(404)
async def not_found(request):
return {'error': 'resource not found'}, 404
The ``errorhandler()`` decorator has a second form, in which it takes an
exception class as an argument. Microdot will invoke the handler when an
unhandled exception that is an instance of the given class is raised. The next
example provides a custom response for division by zero errors::
@app.errorhandler(ZeroDivisionError)
async def division_by_zero(request, exception):
return {'error': 'division by zero'}, 500
When the raised exception class does not have an error handler defined, but
one or more of its parent classes do, Microdot makes an attempt to invoke the
most specific handler.
Mounting a Sub-Application
^^^^^^^^^^^^^^^^^^^^^^^^^^
Small Microdot applications can be written as a single source file, but this
is not the best option for applications that past a certain size. To make it
simpler to write large applications, Microdot supports the concept of
sub-applications that can be "mounted" on a larger application, possibly with
a common URL prefix applied to all of its routes. For developers familiar with
the Flask framework, this is a similar concept to Flask's blueprints.
Consider, for example, a *customers.py* sub-application that implements
operations on customers::
from microdot import Microdot
customers_app = Microdot()
@customers_app.get('/')
async def get_customers(request):
# return all customers
@customers_app.post('/')
async def new_customer(request):
# create a new customer
Similar to the above, the *orders.py* sub-application implements operations on
customer orders::
from microdot import Microdot
orders_app = Microdot()
@orders_app.get('/')
async def get_orders(request):
# return all orders
@orders_app.post('/')
async def new_order(request):
# create a new order
Now the main application, which is stored in *main.py*, can import and mount
the sub-applications to build the larger combined application::
from microdot import Microdot
from customers import customers_app
from orders import orders_app
async def create_app():
app = Microdot()
app.mount(customers_app, url_prefix='/customers')
app.mount(orders_app, url_prefix='/orders')
return app
app = create_app()
app.run()
The resulting application will have the customer endpoints available at
*/customers/* and the order endpoints available at */orders/*.
.. note::
Before-request, after-request and error handlers defined in the
sub-application are also copied over to the main application at mount time.
Once installed in the main application, these handlers will apply to the
whole application and not just the sub-application in which they were
created.
Shutting Down the Server
^^^^^^^^^^^^^^^^^^^^^^^^
Web servers are designed to run forever, and are often stopped by sending them
an interrupt signal. But having a way to gracefully stop the server is
sometimes useful, especially in testing environments. Microdot provides a
:func:`shutdown() <microdot.Microdot.shutdown>` method that can be invoked
during the handling of a route to gracefully shut down the server when that
request completes. The next example shows how to use this feature::
@app.get('/shutdown')
async def shutdown(request):
request.app.shutdown()
return 'The server is shutting down...'
The request that invokes the ``shutdown()`` method will complete, and then the
server will not accept any new requests and stop once any remaining requests
complete. At this point the ``app.run()`` call will return.
The Request Object
~~~~~~~~~~~~~~~~~~
The :class:`Request <microdot.Request>` object encapsulates all the information
passed by the client. It is passed as an argument to route handlers, as well as
to before-request, after-request and error handlers.
Request Attributes
^^^^^^^^^^^^^^^^^^
The request object provides access to the request attributes, including:
- :attr:`method <microdot.Request.method>`: The HTTP method of the request.
- :attr:`path <microdot.Request.path>`: The path of the request.
- :attr:`args <microdot.Request.args>`: The query string parameters of the
request, as a :class:`MultiDict <microdot.MultiDict>` object.
- :attr:`headers <microdot.Request.headers>`: The headers of the request, as a
dictionary.
- :attr:`cookies <microdot.Request.cookies>`: The cookies that the client sent
with the request, as a dictionary.
- :attr:`content_type <microdot.Request.content_type>`: The content type
specified by the client, or ``None`` if no content type was specified.
- :attr:`content_length <microdot.Request.content_length>`: The content
length of the request, or 0 if no content length was specified.
- :attr:`client_addr <microdot.Request.client_addr>`: The network address of
the client, as a tuple (host, port).
- :attr:`app <microdot.Request.app>`: The application instance that created the
request.
- :attr:`g <microdot.Request.g>`: The ``g`` object, where handlers can store
request-specific data to be shared among handlers. See :ref:`The "g" Object`
for details.
JSON Payloads
^^^^^^^^^^^^^
When the client sends a request that contains JSON data in the body, the
application can access the parsed JSON data using the
:attr:`json <microdot.Request.json>` attribute. The following example shows how
to use this attribute::
@app.post('/customers')
async def create_customer(request):
customer = request.json
# do something with customer
return {'success': True}
.. note::
The client must set the ``Content-Type`` header to ``application/json`` for
the ``json`` attribute of the request object to be populated.
URLEncoded Form Data
^^^^^^^^^^^^^^^^^^^^
The request object also supports standard HTML form submissions through the
:attr:`form <microdot.Request.form>` attribute, which presents the form data
as a :class:`MultiDict <microdot.MultiDict>` object. Example::
@app.route('/', methods=['GET', 'POST'])
async def index(req):
name = 'Unknown'
if req.method == 'POST':
name = req.form.get('name')
return f'Hello {name}'
.. note::
Form submissions are only parsed when the ``Content-Type`` header is set by
the client to ``application/x-www-form-urlencoded``. Form submissions using
the ``multipart/form-data`` content type are currently not supported.
Accessing the Raw Request Body
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
For cases in which neither JSON nor form data is expected, the
:attr:`body <microdot.Request.body>` request attribute returns the entire body
of the request as a byte sequence.
If the expected body is too large to fit safely in memory, the application can
use the :attr:`stream <microdot.Request.stream>` request attribute to read the
body contents as a file-like object. The
:attr:`max_body_length <microdot.Request.max_body_length>` attribute of the
request object defines the size at which bodies are streamed instead of loaded
into memory.
Cookies
^^^^^^^
Cookies that are sent by the client are made available through the
:attr:`cookies <microdot.Request.cookies>` attribute of the request object in
dictionary form.
The "g" Object
^^^^^^^^^^^^^^
Sometimes applications need to store data during the lifetime of a request, so
that it can be shared between the before- and after-request handlers, the
route function and any error handlers. The request object provides the
:attr:`g <microdot.Request.g>` attribute for that purpose.
In the following example, a before request handler authorizes the client and
stores the username so that the route function can use it::
@app.before_request
async def authorize(request):
username = authenticate_user(request)
if not username:
return 'Unauthorized', 401
request.g.username = username
@app.get('/')
async def index(request):
return f'Hello, {request.g.username}!'
Request-Specific After-Request Handlers
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Sometimes applications need to perform operations on the response object
before it is sent to the client, for example to set or remove a cookie. A good
option to use for this is to define a request-specific after-request handler
using the :func:`after_request <microdot.Microdot.after_request>` decorator.
Request-specific after-request handlers are called by Microdot after the route
function returns and all the application-wide after-request handlers have been
called.
The next example shows how a cookie can be updated using a request-specific
after-request handler defined inside a route function::
@app.post('/logout')
async def logout(request):
@request.after_request
def reset_session(request, response):
response.set_cookie('session', '', http_only=True)
return response
return 'Logged out'
Request Limits
^^^^^^^^^^^^^^
To help prevent malicious attacks, Microdot provides some configuration options
to limit the amount of information that is accepted:
- :attr:`max_content_length <microdot.Request.max_content_length>`: The
maximum size accepted for the request body, in bytes. When a client sends a
request that is larger than this, the server will respond with a 413 error.
The default is 16KB.
- :attr:`max_body_length <microdot.Request.max_body_length>`: The maximum
size that is loaded in the :attr:`body <microdot.Request.body>` attribute, in
bytes. Requests that have a body that is larger than this size but smaller
than the size set for ``max_content_length`` can only be accessed through the
:attr:`stream <microdot.Request.stream>` attribute. The default is also 16KB.
- :attr:`max_readline <microdot.Request.max_readline>`: The maximum allowed
size for a request line, in bytes. The default is 2KB.
The following example configures the application to accept requests with
payloads up to 1MB in size, but prevents requests that are larger than 8KB from
being loaded into memory::
from microdot import Request
Request.max_content_length = 1024 * 1024
Request.max_body_length = 8 * 1024
Responses
~~~~~~~~~
The value or values that are returned from the route function are used by
Microdot to build the response that is sent to the client. The following
sections describe the different types of responses that are supported.
The Three Parts of a Response
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Route functions can return one, two or three values. The first or only value is
always returned to the client in the response body::
@app.get('/')
async def index(request):
return 'Hello, World!'
In the above example, Microdot issues a standard 200 status code response, and
inserts default headers.
The application can provide its own status code as a second value returned from
the route to override the 200 default. The example below returns a 202 status
code::
@app.get('/')
async def index(request):
return 'Hello, World!', 202
The application can also return a third value, a dictionary with additional
headers that are added to, or replace the default ones included by Microdot.
The next example returns an HTML response, instead of a default text response::
@app.get('/')
async def index(request):
return '<h1>Hello, World!</h1>', 202, {'Content-Type': 'text/html'}
If the application needs to return custom headers, but does not need to change
the default status code, then it can return two values, omitting the status
code::
@app.get('/')
async def index(request):
return '<h1>Hello, World!</h1>', {'Content-Type': 'text/html'}
The application can also return a :class:`Response <microdot.Response>` object
containing all the details of the response as a single value.
JSON Responses
^^^^^^^^^^^^^^
If the application needs to return a response with JSON formatted data, it can
return a dictionary or a list as the first value, and Microdot will
automatically format the response as JSON.
Example::
@app.get('/')
async def index(request):
return {'hello': 'world'}
.. note::
A ``Content-Type`` header set to ``application/json`` is automatically added
to the response.
Redirects
^^^^^^^^^
The :func:`redirect <microdot.Response.redirect>` function is a helper that
creates redirect responses::
from microdot import redirect
@app.get('/')
async def index(request):
return redirect('/about')
File Responses
^^^^^^^^^^^^^^
The :func:`send_file <microdot.Response.send_file>` function builds a response
object for a file::
from microdot import send_file
@app.get('/')
async def index(request):
return send_file('/static/index.html')
A suggested caching duration can be returned to the client in the ``max_age``
argument::
from microdot import send_file
@app.get('/')
async def image(request):
return send_file('/static/image.jpg', max_age=3600) # in seconds
.. note::
Unlike other web frameworks, Microdot does not automatically configure a
route to serve static files. The following is an example route that can be
added to the application to serve static files from a *static* directory in
the project::
@app.route('/static/<path:path>')
async def static(request, path):
if '..' in path:
# directory traversal is not allowed
return 'Not found', 404
return send_file('static/' + path, max_age=86400)
Streaming Responses
^^^^^^^^^^^^^^^^^^^
Instead of providing a response as a single value, an application can opt to
return a response that is generated in chunks, by returning a Python generator.
The example below returns all the numbers in the fibonacci sequence below 100::
@app.get('/fibonacci')
async def fibonacci(request):
async def generate_fibonacci():
a, b = 0, 1
while a < 100:
yield str(a) + '\n'
a, b = b, a + b
return generate_fibonacci()
.. note::
Under CPython, the generator function can be a ``def`` or ``async def``
function, as well as a class-based generator.
Under MicroPython, asynchronous generator functions are not supported, so
only ``def`` generator functions can be used. Asynchronous class-based
generators are supported.
Changing the Default Response Content Type
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Microdot uses a ``text/plain`` content type by default for responses that do
not explicitly include the ``Content-Type`` header. The application can change
this default by setting the desired content type in the
:attr:`default_content_type <microdot.Response.default_content_type>` attribute
of the :class:`Response <microdot.Response>` class.
The example that follows configures the application to use ``text/html`` as
default content type::
from microdot import Response
Response.default_content_type = 'text/html'
Setting Cookies
^^^^^^^^^^^^^^^
Many web applications rely on cookies to maintain client state between
requests. Cookies can be set with the ``Set-Cookie`` header in the response,
but since this is such a common practice, Microdot provides the
:func:`set_cookie() <microdot.Response.set_cookie>` method in the response
object to add a properly formatted cookie header to the response.
Given that route functions do not normally work directly with the response
object, the recommended way to set a cookie is to do it in a
:ref:`request-specific after-request handler <Request-Specific After-Request Handlers>`.
Example::
@app.get('/')
async def index(request):
@request.after_request
async def set_cookie(request, response):
response.set_cookie('name', 'value')
return response
return 'Hello, World!'
Another option is to create a response object directly in the route function::
@app.get('/')
async def index(request):
response = Response('Hello, World!')
response.set_cookie('name', 'value')
return response
.. note::
Standard cookies do not offer sufficient privacy and security controls, so
never store sensitive information in them unless you are adding additional
protection mechanisms such as encryption or cryptographic signing. The
:ref:`session <Maintaining Secure User Sessions>` extension implements signed
cookies that prevent tampering by malicious actors.
Concurrency
~~~~~~~~~~~
Microdot implements concurrency through the ``asyncio`` package. Applications
must ensure their handlers do not block, as this will prevent other concurrent
requests from being handled.
When running under CPython, ``async def`` handler functions run as native
asyncio tasks, while ``def`` handler functions are executed in a
`thread executor <https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.loop.run_in_executor>`_
to prevent them from blocking the asynchronous loop.
Under MicroPython the situation is different. Most microcontroller boards
implementing MicroPython do not have threading support or executors, so ``def``
handler functions in this platform can only run in the main and only thread.
These functions will block the asynchronous loop when they take too long to
complete so ``async def`` handlers properly written to allow other handlers to
run in parallel should be preferred.
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