Support for multipart/form-data requests (#287)

docs/api.rst

@@ -14,6 +14,12 @@ Core API
    :members:
 
 
+Multipart Forms
+---------------
+
+.. automodule:: microdot.multipart
+   :members:
+
 WebSocket
 ---------
 

docs/extensions.rst

@@ -5,8 +5,82 @@ Microdot is a highly extensible web application framework. The extensions
 described in this section are maintained as part of the Microdot project in
 the same source code repository.
 
+Multipart Forms
+~~~~~~~~~~~~~~~
+
+.. list-table::
+   :align: left
+
+   * - Compatibility
+     - | CPython & MicroPython
+
+   * - Required Microdot source files
+     -  | `multipart.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/multipart.py>`_
+        | `helpers.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/helpers.py>`_
+
+   * - Required external dependencies
+     - | None
+
+   * - Examples
+     - | `formdata.py <https://github.com/miguelgrinberg/microdot/blob/main/examples/uploads/formdata.py>`_
+
+The multipart extension handles multipart forms, including those that have file
+uploads.
+
+The :func:`with_form_data <microdot.multipart.with_form_data>` decorator
+provides the simplest way to work with these forms. With this decorator added
+to the route, whenever the client sends a multipart request the
+:attr:`request.form <microdot.Request.form>` and
+:attr:`request.files <microdot.Request.files>` properties are populated with
+the submitted data. For form fields the field values are always strings. For
+files, they are instances of the
+:class:`FileUpload <microdot.multipart.FileUpload>` class.
+
+Example::
+
+    from microdot.multipart import with_form_data
+
+    @app.post('/upload')
+    @with_form_data
+    async def upload(request):
+        print('form fields:', request.form)
+        print('files:', request.files)
+
+One disadvantage of the ``@with_form_data`` decorator is that it has to copy
+any uploaded files to memory or temporary disk files, depending on their size.
+The :attr:`FileUpload.max_memory_size <microdot.multipart.FileUpload.max_memory_size>`
+attribute can be used to control the cutoff size above which a file upload
+is transferred to a temporary file.
+
+A more performant alternative to the ``@with_form_data`` decorator is the
+:class:`FormDataIter <microdot.multipart.FormDataIter>` class, which iterates
+over the form fields sequentially, giving the application the option to parse
+the form fields on the fly and decide what to copy and what to discard. When
+using ``FormDataIter`` the ``request.form`` and ``request.files`` attributes
+are not used.
+
+Example::
+
+
+    from microdot.multipart import FormDataIter
+
+    @app.post('/upload')
+    async def upload(request):
+        async for name, value in FormDataIter(request):
+            print(name, value)
+
+For fields that contain an uploaded file, the ``value`` returned by the
+iterator is the same ``FileUpload`` instance. The application can choose to
+save the file with the :meth:`save() <microdot.multipart.FileUpload.save>`
+method, or read it with the :meth:`read() <microdot.multipart.FileUpload.read>`
+method, optionally passing a size to read it in chunks. The
+:meth:`copy() <microdot.multipart.FileUpload.copy>` method is also available to
+apply the copying logic used by the ``@with_form_data`` decorator, which is
+inefficient but allows the file to be set aside to be processed later, after
+the remaining form fields.
+
 WebSocket
-~~~~~~~~-
+~~~~~~~~~
 
 .. list-table::
    :align: left
@@ -16,6 +90,7 @@ WebSocket
 
    * - Required Microdot source files
      -  | `websocket.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/websocket.py>`_
+        | `helpers.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/helpers.py>`_
 
    * - Required external dependencies
      - | None
@@ -32,12 +107,14 @@ messages respectively.
 
 Example::
 
-        @app.route('/echo')
-        @with_websocket
-        async def echo(request, ws):
-            while True:
-                message = await ws.receive()
-                await ws.send(message)
+    from microdot.websocket import with_websocket
+
+    @app.route('/echo')
+    @with_websocket
+    async def echo(request, ws):
+        while True:
+            message = await ws.receive()
+            await ws.send(message)
 
 Server-Sent Events
 ~~~~~~~~~~~~~~~~~~
@@ -50,6 +127,7 @@ Server-Sent Events
 
    * - Required Microdot source files
      -  | `sse.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/sse.py>`_
+        | `helpers.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/helpers.py>`_
 
    * - Required external dependencies
      - | None
@@ -65,6 +143,8 @@ asynchronous method to send an event to the client.
 
 Example::
 
+    from microdot.sse import with_sse
+
     @app.route('/events')
     @with_sse
     async def events(request, sse):
@@ -213,6 +293,7 @@ Secure User Sessions
 
    * - Required Microdot source files
      - | `session.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/session.py>`_
+       | `helpers.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/helpers.py>`_
 
    * - Required external dependencies
      - | CPython: `PyJWT <https://pyjwt.readthedocs.io/>`_
@@ -369,6 +450,7 @@ User Logins
    * - Required Microdot source files
      - | `login.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/auth.py>`_
        | `session.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/session.py>`_
+       | `helpers.py <https://github.com/miguelgrinberg/microdot/tree/main/src/microdot/helpers.py>`_
    * - Required external dependencies
      - | CPython: `PyJWT <https://pyjwt.readthedocs.io/>`_
        | MicroPython: `jwt.py <https://github.com/micropython/micropython-lib/blob/master/python-ecosys/pyjwt/jwt.py>`_,