micropython-phew 0.0.3

A small webserver and templating library specifically designed for MicroPython on the Pico W.

phew! the Pico (or Python) HTTP Endpoint Wrangler

:warning: Heads up! This is a very new project and should be considered, at best, alpha stage.

A small webserver and templating library specifically designed for MicroPython on the Pico W. It aims to provide a complete toolkit for easily creating high quality web based interfaces for your projects.

phew! is ideal for creating web based provisioning interfaces for connected projects using the Raspberry Pi Pico W.

• What phew! does
• Basic example
• Function reference
  • server module
    • add_route
    • set_catchall
    • run
  • Types
    • Request type
    • Response type
      • Shorthand
  • Templates
    • render_template
    • Template expressions
      • Variables
      • Conditional display
      • Includes
  • dns module
    • run_catchall

What phew! does:

• a basic web server
• optimised for speed (at import and during execution)
• minimal use of memory
• parameterised routing rules /greet/<name>
• templating engine that allows inline python expressions {{name.lower()}}
• GET, POST request methods
• query string decoding and parsing
• catchall handler for unrouted requests
• multipart/form-data, x-www-form-urlencoded, and JSON POST bodies
• string, byte, or generator based responses
• connect_to_wifi convenience method

Where possible phew! tries to minimise the amount of code and setup that you, the developer, has to do in favour of picking sane defaults and hiding away bits of minutiae that rarely needs to be tweaked.

Basic example

An example web server that returns a random number between 1 and 100 (or optionally the range specified by the callee) when requested:

from phew import server, connect_to_wifi

connect_to_wifi("<ssid>", "<password>")

@server.route("/random", methods=["GET"])
def random_number(request):
  import random
  min = int(request.query.get("min", 0))
  max = int(request.query.get("max", 100))
  return str(random.randint(min, max))

@server.catchall()
def catchall(request):
  return "Not found", 404

server.run()

phew is designed specifically with performance and minimal resource use in mind. Generally this means it will prioritise doing as little work as possible including assuming the correctness of incoming requests.

---

Function reference

server module

The server module provides all functionality for running a web server with route handlers.

add_route

server.add_route(path, handler, methods=["GET"])

Adds a new route into the routing table. When an incoming request is received the server checks each route to find the most specific one that matches the request based on the path and method. If a route is found then the handler function is called with a request parameter that contains details about the request.

def my_handler(request):
  return "I got it!", 200

server.add_route("/testpath", my_handler, methods=["GET"])

Or, alternatively, using a decorator:

@server.route("/testpath", methods=["GET"])
def my_handler(request):
  return "I got it!", 200

set_catchall

server.set_catchall(handler)

Provide a catchall method for requests that didn't match a route.

def my_catchall(request):
  return "No matching route", 404

server.set_catchall(my_catchall)

Or, alternatively, using a decorator:

@server.set_catchall()
def my_catchall(request):
  return "No matching route", 404

run

server.run(host="0.0.0.0", port=80)

Starts up the web server and begins handling incoming requests.

server.run()

Types

Request

The Request object contains all of the information that was parsed out of the incoming request including form data, query string parameters, HTTP method, path, and more.

Handler functions provided to add_route and set_catchall will recieve a Request object as their first parameter.

member	example	type	description
protocol	"HTTP/1.1"	string	protocol version
method	"GET" or "POST"	string	HTTP method used for this request
uri	"/path/to/page?parameter=foo"	string	full URI of the request
path	"/path/to/page"	string	just the path part of the URI
query_string	"parameter=foo"	string	just the query string part of the URI
form	{"foo": "bar", "name": "geoff"}	dict	POST body parsed as multipart/form-data
data	[{"name": "jenny"}, {"name": "geoff"}]	any	POST body parsed as JSON
query	{"parameter": "foo"}	dict	result of parsing the query string

At the time your route handler is being called the request has been fully parsed and you can access any properties that are relevant to the request (e.g. the form dictionary for a multipart/form-data request) any irrelevant properties will be set to None.

@server.add_route("/login", ["POST"])
def login_form(request):
  username = request.form.get("username", None)
  password = request.form.get("password", None)

  # check the user credentials with your own code
  # for example: 
  # 
  # logged_in = authenticate_user(username, password)

  if not logged_in:
    return "Username or password not recognised", 401

  return "Logged in!", 200

Response

The Response object encapsulates all of the attributes of your programs response to an incoming request. This include the status code of the result (e.g. 200 OK!) , the data to return, and any associated headers.

Handler functions can create and return a Response object explicitly or use a couple of shorthand forms to avoid writing the boilerplate needed.

member	example	type	description
status	200	int	HTTP status code
headers	{"Content-Type": "text/html"}	dict	dictionary of headers to return
body	"this is the response body"	string or generator	the content to be returned

@server.add_route("/greeting/<name>", ["GET"])
def user_details(request):
  return Response(f"Hello, {name}", status=200, {"Content-Type": "text/html"})

Shorthand

As shorthand instead of returning a Response object the handle may also return a tuple with between one and three values:

• body - either a string or generator method
• status code - defaults to 200 if not provided
• headers - defaults to {"Content-Type": "text/html"} if not provided

For example:

@server.add_route("/greeting/<name>", ["GET"])
def user_details(request, name):
  return f"Hello, {name}", 200

Templates

A web server isn't much use without something to serve. While it's straightforward to serve the contents of a file or some generated JSON things get more complicated when we want to present a dynamically generated web page to the user.

phew! provides a templating engine which allows you to write normal HTML with fragments of Python code embedded to output variable values, parse input, or dynamically load assets.

render_template

render_template(template, param1="foo", param2="bar", ...):

The render_template method takes a path to a template file on the filesystem and a list of named paramaters which will be passed into the template when parsing.

The method is a generator which yields the parsing result in chunks, minimising the amount of memory used to hold the results as they can be streamed directly out rather than having to build the entire result as a string first.

Generally you will call render_template to create the body of a Response in one of your handler methods.

Template expressions

Templates are not much use if you can't inject dynamic data into them. With phew! you can embed Python expressions with {{<expression here>}} which will be evaluated during parsing.

Variables

In the simplest form you can embed a simple value by just enclosing it in double curly braces. It's also possible to perform more complicated transformations using any built in Python method.

  <div id="name">{{name}}</div>

  <div id="name">{{name.upper()}}</div>
  
  <div id="name">{{"/".join(name.split(" "))}}</div>

Conditional display

If you want to show a value only if some other condition is met then you can use the (slightly clunky) Python tenary operator.

<div>
  You won
  {{"1st" if prize == 1 else ""}}
  {{"2nd" if prize == 2 else ""}}
  {{"3rd" if prize == 3 else ""}}
  prize!
</div>

or

<div>
  You won
  {{["1st", "2nd", "3rd"][prize]}}
  prize!
</div>

While a bit unweildy this methods works. An alternative would be to select the appropriate value in your handler and simply pass it into the template as a parameter however that would mean having some of your copy embedded into your Python code rather than all of it in one place in the template file.

Includes

You can include another template by calling render_template() again within your outer template.

include.html

Hello there {{name}}!

main.html

<!DOCTYPE html>
<body>
  {{render_template("include.html", name=name)}}
</body>

:warning: Note: you need to explicitly pass through template parameters into the included template - they are not available by default.

dns module

To make implementing device provisioning interfaces (via captive portal) simple phew! provides a catchall DNS server.

If you put the Pico W into access point mode and then run the catchall DNS server it will route all DNS requests back to the local device so that they can be handled.

run_catchall

dns.run_catchall(ip_address)

Pass in the IP address of your device once in access point mode.