picoweb 1.5

A very lightweight, memory-efficient async web framework for MicroPython and its uasyncio module.

picoweb
=======

picoweb is a "micro" web micro-framework (thus, "pico-framework") for
radically unbloated web applications using radically unbloated Python
implementation, MicroPython, https://github.com/pfalcon/micropython.

Features:

* Asynchronous from the start, using unbloated asyncio-like library
for MicroPython (`uasyncio <https://github.com/pfalcon/micropython-lib/tree/master/uasyncio>`_).
* Small memory usage. Initial version required about 64K of heap for
a trivial web app, and since then, it was optimized to allow run
more or less realistic web app in ~36K of heap. More optimizations
on all the levels (MicroPython and up) are planned (but may lead to
API changes).
* Has API affinity with some well-known Python web micro-framework(s),
thus it should be an easy start if you have experience with them, and
existing applications can be potentially ported, instead of requiring
complete rewrite.


Requirements and optional modules
---------------------------------

``picoweb`` depends on ``uasyncio`` for asynchronous networking
(https://github.com/pfalcon/micropython-lib/tree/master/uasyncio).

It is also indended to be used with ``utemplate``
(https://github.com/pfalcon/utemplate) for templating, but this is
a "soft" dependency - picoweb offers convenience functions to use
``utemplate`` templates, but if you don't use them or will handle
templating in your app (e.g. with a different library), it won't be
imported.

For database access, there are following options (``picoweb`` does
not depend on any of them, up to your application to choose):

* `btree <http://docs.micropython.org/en/latest/unix/library/btree.html>`_
builtin MicroPython module. This is a recommended way to do a database
storage for `picoweb`, as it allows portability across all MicroPython
targets, starting with very memory- and storage-limited baremetal systems.
* ``btreedb`` wrapper on top of ``btree`` builtin module. This may add some
overhead, but may allow to make an application portable between different
database backends (`filedb` and `uorm` below).
https://github.com/pfalcon/micropython-btreedb
* ``filedb``, for a simple database using files in a filesystem
https://github.com/pfalcon/filedb
* ``uorm``, for Sqlite3 database access (works only with MicroPython
Unix port) https://github.com/pfalcon/uorm

Last but not least, ``picoweb`` uses a standard ``logging``-compatible
logger for diagnostic output (like a connection opened, errors and debug
information). However this output is optional, and otherwise you can use
a custom logging class instead of standard ``logging`` module. Due to this,
and to not put additional dependencies burden on the small webapps for
small systems, ``logging`` module is not included in ``picoweb``'s
installation dependencies. Instead, a particular app using ``picoweb``
should depend on ``micropython-logging`` package.


Details
-------

picoweb API is roughly based on APIs of other well-known Python web
frameworks. The strongest affinity is Flask, http://flask.pocoo.org, as
arguably the most popular micro-framework. Some features are also based on
Bottle and Django. Note that this does not mean particular "compatibility"
with Flask, Bottle, or Django: most existing web frameworks are synchronous
(and threaded), while picoweb is async framework, so its architecture is
quite different. However, there is an aim to save porting efforts from
repetitive search & replace trials: for example, when methods do similar
things, they are likely named the same (but they may take slightly different
parameters, return different values, and behave slightly differently).

The biggest difference is async, non-threaded nature of picoweb. That means
that the same code may handle multiple requests at the same time, but unlike
threaded environment, there's no external context (like thread and thread
local storage) to associate with each request. Thus, there're no "global"
(or thread-local "global") request and response objects, like Flask,
Bottle, Django have. Instead, all picoweb functions explicitly pass the
current request and response objects around.

Also, picoweb, being unbloated framework, tries to avoid avoidable
abstractions. For example, HTTP at the lowest level has just read and write
endpoints of a socket. To dispatch request, picoweb needs to pre-parse
some request data from input stream, and it saves that partially (sic!)
parsed data as a "request" object, and that's what passed to application
handlers. However, there's no unavoidable need to have a "response"
abstraction - the most efficient/lightweight application may want to
just write raw HTTP status line, headers, and body to the socket. Thus,
raw write stream is passed to application handlers as the "response" object.
(But high-level convenience functions to construct an HTTP response are
provided).

Last point is questionable conveniences. For example, both Flask and Bottle
provide special objects to handle form/get parameters, with features
like "if request variable has only one value, the value is returned directly;
otherwise, list of values is returned".

.. raw:: html

<strike>

However, Python standard library
provides function parse_qs(), which always returns array of values (based
on the fact that any request variable may have more than one value). Given
2 choices, picoweb follows the interface of the standard library, instead of
providing extra wrapper class on top of it.

.. raw:: html

</strike>

Changed in 1.5: now normal single-valued fields store the value directly,
a list is used only for multi-valued fields. (Reasons: convenience, reduced
memory usage.)


API reference
-------------

The best API reference currently are examples (see below) and the ``picoweb``
source code itself. It's under 10K, so enjoy:
https://github.com/pfalcon/picoweb/blob/master/picoweb/__init__.py

Note that API is experimental and may undergo changes.


Examples
--------

* `example_webapp.py <https://github.com/pfalcon/picoweb/blob/master/example_webapp.py>`_ -
A simple webapp showing you how to generate a complete HTTP response
yourself, use ``picoweb`` convenience functions for HTTP headers generation,
and use of templates. Mapping from URLs to webapp view functions ("web
routes" or just "routes") is done Django-style, using a centralized route
list.
* `example_webapp2.py <https://github.com/pfalcon/picoweb/blob/master/example_webapp2.py>`_ -
Like above, but uses ``app.route()`` decorator for route specification,
Flask-style.
* `examples/ <https://github.com/pfalcon/picoweb/tree/master/examples>`_ -
Additional examples for various features of picoweb. See comments in each
file for additional info. To run examples in this directory, you normally
would need to have picoweb installed (i.e. available in your ``MICROPYPATH``,
which defaults to ``~/.micropython/lib/``).
* `notes-pico <https://github.com/pfalcon/notes-pico>`_ - A more realistic
example webapp, ported from the Flask original.


Running under CPython (regressed)
---------------------------------

Initial versions of picoweb could run under CPython, but later it was
further optimized for MicroPython, and ability to run under CPython
regressed. It's still on TODO to fix it, instructions below tell how
it used to work.

At least CPython 3.4.2 is required (for asyncio loop.create_task() support).
To run under CPython, uasyncio compatibility module for CPython is required
(micropython-cpython-uasyncio). This and other dependencies can be installed
using requirements-cpython.txt::

pip install -r requirements-cpython.txt