Routing¶

Routing allows the user to specify handler functions for different URL endpoints.

A basic route looks like the following, where app is an instance of the Sanic class:

from sanic.response import json

@app.route("/")
async def test(request):
    return json({ "hello": "world" })

When the url http://server.url/ is accessed (the base url of the server), the final / is matched by the router to the handler function, test, which then returns a JSON object.

Sanic handler functions must be defined using the async def syntax, as they are asynchronous functions.

Request parameters¶

Sanic comes with a basic router that supports request parameters.

To specify a parameter, surround it with angle quotes like so: <PARAM>. Request parameters will be passed to the route handler functions as keyword arguments.

from sanic.response import text

@app.route('/tag/<tag>')
async def tag_handler(request, tag):
    return text('Tag - {}'.format(tag))

To specify a type for the parameter, add a :type after the parameter name, inside the quotes. If the parameter does not match the specified type, Sanic will throw a NotFound exception, resulting in a 404: Page not found error on the URL.

from sanic.response import text

@app.route('/number/<integer_arg:int>')
async def integer_handler(request, integer_arg):
    return text('Integer - {}'.format(integer_arg))

@app.route('/number/<number_arg:number>')
async def number_handler(request, number_arg):
    return text('Number - {}'.format(number_arg))

@app.route('/person/<name:[A-z]+>')
async def person_handler(request, name):
    return text('Person - {}'.format(name))

@app.route('/folder/<folder_id:[A-z0-9]{0,4}>')
async def folder_handler(request, folder_id):
    return text('Folder - {}'.format(folder_id))

HTTP request types¶

By default, a route defined on a URL will be available for only GET requests to that URL. However, the @app.route decorator accepts an optional parameter, methods, which allows the handler function to work with any of the HTTP methods in the list.

from sanic.response import text

@app.route('/post', methods=['POST'])
async def post_handler(request):
    return text('POST request - {}'.format(request.json))

@app.route('/get', methods=['GET'])
async def get_handler(request):
    return text('GET request - {}'.format(request.args))

There is also an optional host argument (which can be a list or a string). This restricts a route to the host or hosts provided. If there is a also a route with no host, it will be the default.

@app.route('/get', methods=['GET'], host='example.com')
async def get_handler(request):
    return text('GET request - {}'.format(request.args))

# if the host header doesn't match example.com, this route will be used
@app.route('/get', methods=['GET'])
async def get_handler(request):
    return text('GET request in default - {}'.format(request.args))

There are also shorthand method decorators:

from sanic.response import text

@app.post('/post')
async def post_handler(request):
    return text('POST request - {}'.format(request.json))

@app.get('/get')
async def get_handler(request):
    return text('GET request - {}'.format(request.args))

The `add_route` method¶

As we have seen, routes are often specified using the @app.route decorator. However, this decorator is really just a wrapper for the app.add_route method, which is used as follows:

from sanic.response import text

# Define the handler functions
async def handler1(request):
    return text('OK')

async def handler2(request, name):
    return text('Folder - {}'.format(name))

async def person_handler2(request, name):
    return text('Person - {}'.format(name))

# Add each handler function as a route
app.add_route(handler1, '/test')
app.add_route(handler2, '/folder/<name>')
app.add_route(person_handler2, '/person/<name:[A-z]>', methods=['GET'])

URL building with `url_for`¶

Sanic provides a url_for method, to generate URLs based on the handler method name. This is useful if you want to avoid hardcoding url paths into your app; instead, you can just reference the handler name. For example:

@app.route('/')
async def index(request):
    # generate a URL for the endpoint `post_handler`
    url = app.url_for('post_handler', post_id=5)
    # the URL is `/posts/5`, redirect to it
    return redirect(url)


@app.route('/posts/<post_id>')
async def post_handler(request, post_id):
    return text('Post - {}'.format(post_id))

Other things to keep in mind when using url_for:

Keyword arguments passed to url_for that are not request parameters will be included in the URL's query string. For example:

url = app.url_for('post_handler', post_id=5, arg_one='one', arg_two='two')
# /posts/5?arg_one=one&arg_two=two

Multivalue argument can be passed to url_for. For example:

url = app.url_for('post_handler', post_id=5, arg_one=['one', 'two'])
# /posts/5?arg_one=one&arg_one=two

Also some special arguments (_anchor, _external, _scheme, _method, _server) passed to url_for will have special url building (_method is not support now and will be ignored). For example:

url = app.url_for('post_handler', post_id=5, arg_one='one', _anchor='anchor')
# /posts/5?arg_one=one#anchor

url = app.url_for('post_handler', post_id=5, arg_one='one', _external=True)
# //server/posts/5?arg_one=one
# _external requires passed argument _server or SERVER_NAME in app.config or url will be same as no _external

url = app.url_for('post_handler', post_id=5, arg_one='one', _scheme='http', _external=True)
# http://server/posts/5?arg_one=one
# when specifying _scheme, _external must be True

# you can pass all special arguments one time
url = app.url_for('post_handler', post_id=5, arg_one=['one', 'two'], arg_two=2, _anchor='anchor', _scheme='http', _external=True, _server='another_server:8888')
# http://another_server:8888/posts/5?arg_one=one&arg_one=two&arg_two=2#anchor

All valid parameters must be passed to url_for to build a URL. If a parameter is not supplied, or if a parameter does not match the specified type, a URLBuildError will be thrown.

WebSocket routes¶

Routes for the WebSocket protocol can be defined with the @app.websocket decorator:

@app.websocket('/feed')
async def feed(request, ws):
    while True:
        data = 'hello!'
        print('Sending: ' + data)
        await ws.send(data)
        data = await ws.recv()
        print('Received: ' + data)

Alternatively, the app.add_websocket_route method can be used instead of the decorator:

async def feed(request, ws):
    pass

app.add_websocket_route(my_websocket_handler, '/feed')

Handlers for a WebSocket route are passed the request as first argument, and a WebSocket protocol object as second argument. The protocol object has send and recv methods to send and receive data respectively.

WebSocket support requires the websockets package by Aymeric Augustin.