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

README.md

@@ -43,7 +43,8 @@ describes the backwards incompatible changes that were made.
 The following features are planned for future releases of Microdot, both for
 MicroPython and CPython:
 
-- Support for forms encoded in `multipart/form-data` format
+- Authentication support, similar to [Flask-Login](https://github.com/maxcountryman/flask-login) for Flask (**Added in version 2.1**)
+- Support for forms encoded in `multipart/form-data` format (**Added in version 2.2**)
 - OpenAPI integration, similar to [APIFairy](https://github.com/miguelgrinberg/apifairy) for Flask
 
 In addition to the above, the following extensions are also under consideration,
@@ -52,4 +53,4 @@ but only for CPython:
 - Database integration through [SQLAlchemy](https://github.com/sqlalchemy/sqlalchemy)
 - Socket.IO support through [python-socketio](https://github.com/miguelgrinberg/python-socketio)
 
-Do you have other ideas to propose? Let's [discuss them](https://github.com/miguelgrinberg/microdot/discussions/new?category=ideas)!
+Do you have other ideas to propose? Let's [discuss them](https://github.com/:miguelgrinberg/microdot/discussions/new?category=ideas)!

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
@@ -32,6 +107,8 @@ messages respectively.
 
 Example::
 
+    from microdot.websocket import with_websocket
+
     @app.route('/echo')
     @with_websocket
     async def echo(request, ws):
@@ -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>`_,

examples/uploads/README.md

@@ -1 +1,4 @@
 This directory contains file upload examples.
+
+- `simple_uploads.py` demonstrates how to upload a single file.
+- `formdata.py` demonstrates how to process a form that includes file uploads.

examples/uploads/formdata.html

@@ -0,0 +1,17 @@
+<!doctype html>
+<html>
+  <head>
+    <title>Microdot Multipart Form-Data Example</title>
+    <meta charset="UTF-8">
+  </head>
+  <body>
+    <h1>Microdot Multipart Form-Data Example</h1>
+    <form method="POST" action="" enctype="multipart/form-data">
+      <p>Name: <input type="text" name="name" /></p>
+      <p>Age: <input type="text" name="age" /></p>
+      <p>Comments: <textarea name="comments" rows="4"></textarea></p>
+      <p>File: <input type="file" id="file" name="file" /></p>
+      <input type="submit" value="Submit" />
+    </form>
+  </body>
+</html>

examples/uploads/formdata.py

@@ -0,0 +1,26 @@
+from microdot import Microdot, send_file, Request
+from microdot.multipart import with_form_data
+
+app = Microdot()
+Request.max_content_length = 1024 * 1024  # 1MB (change as needed)
+
+
+@app.get('/')
+async def index(request):
+    return send_file('formdata.html')
+
+
+@app.post('/')
+@with_form_data
+async def upload(request):
+    print('Form fields:')
+    for field, value in request.form.items():
+        print(f'- {field}: {value}')
+    print('\nFile uploads:')
+    for field, value in request.files.items():
+        print(f'- {field}: {value.filename}, {await value.read()}')
+    return 'We have received your data!'
+
+
+if __name__ == '__main__':
+    app.run(debug=True)

examples/uploads/simple_uploads.py

@@ -6,7 +6,7 @@ Request.max_content_length = 1024 * 1024  # 1MB (change as needed)
 
 @app.get('/')
 async def index(request):
-    return send_file('index.html')
+    return send_file('simple_uploads.html')
 
 
 @app.post('/upload')

src/microdot/__init__.py

@@ -1,2 +1,2 @@
 from microdot.microdot import Microdot, Request, Response, abort, redirect, \
-    send_file, URLPattern  # noqa: F401
+    send_file, URLPattern, AsyncBytesIO, iscoroutine  # noqa: F401

src/microdot/microdot.py

@@ -371,6 +371,7 @@ class Request:
         self.sock = sock
         self._json = None
         self._form = None
+        self._files = None
         self.after_request_handlers = []
 
     @staticmethod
@@ -465,7 +466,13 @@ class Request:
     def form(self):
         """The parsed form submission body, as a
         :class:`MultiDict <microdot.MultiDict>` object, or ``None`` if the
-        request does not have a form submission."""
+        request does not have a form submission.
+
+        Forms that are URL encoded are processed by default. For multipart
+        forms to be processed, the
+        :func:`with_form_data <microdot.multipart.with_form_data>`
+        decorator must be added to the route.
+        """
         if self._form is None:
             if self.content_type is None:
                 return None
@@ -475,6 +482,17 @@ class Request:
             self._form = self._parse_urlencoded(self.body)
         return self._form
 
+    @property
+    def files(self):
+        """The files uploaded in the request as a dictionary, or ``None`` if
+        the request does not have any files.
+
+        The :func:`with_form_data <microdot.multipart.with_form_data>`
+        decorator must be added to the route that receives file uploads for
+        this property to be set.
+        """
+        return self._files
+
     def after_request(self, f):
         """Register a request-specific function to run after the request is
         handled. Request-specific after request handlers run at the very end,

src/microdot/multipart.py

@@ -0,0 +1,291 @@
+import os
+from random import choice
+from microdot import abort, iscoroutine, AsyncBytesIO
+from microdot.helpers import wraps
+
+
+class FormDataIter:
+    """Asynchronous iterator that parses a ``multipart/form-data`` body and
+    returns form fields and files as they are parsed.
+
+    :param request: the request object to parse.
+
+    Example usage::
+
+        from microdot.multipart import FormDataIter
+
+        @app.post('/upload')
+        async def upload(request):
+            async for name, value in FormDataIter(request):
+                print(name, value)
+
+    The iterator returns no values when the request has a content type other
+    than ``multipart/form-data``. For a file field, the returned value is of
+    type :class:`FileUpload`, which supports the
+    :meth:`read() <FileUpload.read>` and :meth:`save() <FileUpload.save>`
+    methods. Values for regular fields are provided as strings.
+
+    The request body is read efficiently in chunks of size
+    :attr:`buffer_size <FormDataIter.buffer_size>`. On iterations in which a
+    file field is encountered, the file must be consumed before moving on to
+    the next iteration, as the internal stream stored in ``FileUpload``
+    instances is invalidated at the end of the iteration.
+    """
+    #: The size of the buffer used to read chunks of the request body.
+    buffer_size = 256
+
+    def __init__(self, request):
+        self.request = request
+        self.buffer = None
+        try:
+            mimetype, boundary = request.content_type.rsplit('; boundary=', 1)
+        except ValueError:
+            return  # not a multipart request
+        if mimetype.split(';', 1)[0] == \
+                'multipart/form-data':  # pragma: no branch
+            self.boundary = b'--' + boundary.encode()
+            self.extra_size = len(boundary) + 4
+            self.buffer = b''
+
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        if self.buffer is None:
+            raise StopAsyncIteration
+
+        # make sure we have consumed the previous entry
+        while await self._read_buffer(self.buffer_size) != b'':
+            pass
+
+        # make sure we are at a boundary
+        s = self.buffer.split(self.boundary, 1)
+        if len(s) != 2 or s[0] != b'':
+            abort(400)  # pragma: no cover
+        self.buffer = s[1]
+        if self.buffer[:2] == b'--':
+            # we have reached the end
+            raise StopAsyncIteration
+        elif self.buffer[:2] != b'\r\n':
+            abort(400)  # pragma: no cover
+        self.buffer = self.buffer[2:]
+
+        # parse the headers of this part
+        name = ''
+        filename = None
+        content_type = None
+        while True:
+            await self._fill_buffer()
+            lines = self.buffer.split(b'\r\n', 1)
+            if len(lines) != 2:
+                abort(400)  # pragma: no cover
+            line, self.buffer = lines
+            if line == b'':
+                # we reached the end of the headers
+                break
+            header, value = line.decode().split(':', 1)
+            header = header.lower()
+            value = value.strip()
+            if header == 'content-disposition':
+                parts = value.split(';')
+                if len(parts) < 2 or parts[0] != 'form-data':
+                    abort(400)  # pragma: no cover
+                for part in parts[1:]:
+                    part = part.strip()
+                    if part.startswith('name="'):
+                        name = part[6:-1]
+                    elif part.startswith('filename="'):  # pragma: no branch
+                        filename = part[10:-1]
+            elif header == 'content-type':  # pragma: no branch
+                content_type = value
+
+        if filename is None:
+            # this is a regular form field, so we read the value
+            value = b''
+            while True:
+                v = await self._read_buffer(self.buffer_size)
+                value += v
+                if len(v) < self.buffer_size:  # pragma: no branch
+                    break
+            return name, value.decode()
+        return name, FileUpload(filename, content_type, self._read_buffer)
+
+    async def _fill_buffer(self):
+        self.buffer += await self.request.stream.read(
+            self.buffer_size + self.extra_size - len(self.buffer))
+
+    async def _read_buffer(self, n=-1):
+        data = b''
+        while n == -1 or len(data) < n:
+            await self._fill_buffer()
+            s = self.buffer.split(self.boundary, 1)
+            data += s[0][:n] if n != -1 else s[0]
+            self.buffer = s[0][n:] if n != -1 else b''
+            if len(s) == 2:  # pragma: no branch
+                # the end of this part is in the buffer
+                if len(self.buffer) < 2:
+                    # we have read all the way to the end of this part
+                    data = data[:-(2 - len(self.buffer))]  # remove last "\r\n"
+                self.buffer += self.boundary + s[1]
+                return data
+        return data
+
+
+class FileUpload:
+    """Class that represents an uploaded file.
+
+    :param filename: the name of the uploaded file.
+    :param content_type: the content type of the uploaded file.
+    :param read: a coroutine that reads from the uploaded file's stream.
+
+    An uploaded file can be read from the stream using the :meth:`read()`
+    method or saved to a file using the :meth:`save()` method.
+
+    Instances of this class do not normally need to be created directly.
+    """
+    #: The size at which the file is copied to a temporary file.
+    max_memory_size = 1024
+
+    def __init__(self, filename, content_type, read):
+        self.filename = filename
+        self.content_type = content_type
+        self._read = read
+        self._close = None
+
+    async def read(self, n=-1):
+        """Read up to ``n`` bytes from the uploaded file's stream.
+
+        :param n: the maximum number of bytes to read. If ``n`` is -1 or not
+                  given, the entire file is read.
+        """
+        return await self._read(n)
+
+    async def save(self, path_or_file):
+        """Save the uploaded file to the given path or file object.
+
+        :param path_or_file: the path to save the file to, or a file object
+                             to which the file is to be written.
+
+        The file is read and written in chunks of size
+        :attr:`FormDataIter.buffer_size`.
+        """
+        if isinstance(path_or_file, str):
+            f = open(path_or_file, 'wb')
+        else:
+            f = path_or_file
+        while True:
+            data = await self.read(FormDataIter.buffer_size)
+            if not data:
+                break
+            f.write(data)
+        if f != path_or_file:
+            f.close()
+
+    async def copy(self, max_memory_size=None):
+        """Copy the uploaded file to a temporary file, to allow the parsing of
+        the multipart form to continue.
+
+        :param max_memory_size: the maximum size of the file to keep in memory.
+                                If not given, then the class attribute of the
+                                same name is used.
+        """
+        max_memory_size = max_memory_size or FileUpload.max_memory_size
+        buffer = await self.read(max_memory_size)
+        if len(buffer) < max_memory_size:
+            f = AsyncBytesIO(buffer)
+            self._read = f.read
+            return self
+
+        # create a temporary file
+        while True:
+            tmpname = "".join([
+                choice('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
+                for _ in range(12)
+            ])
+            try:
+                f = open(tmpname, 'x+b')
+            except OSError as e:  # pragma: no cover
+                if e.errno == 17:
+                    # EEXIST
+                    continue
+                elif e.errno == 2:
+                    # ENOENT
+                    # some MicroPython platforms do not support mode "x"
+                    f = open(tmpname, 'w+b')
+                    if f.read(1) != b'':
+                        f.close()
+                        continue
+                else:
+                    raise
+            break
+        f.write(buffer)
+        await self.save(f)
+        f.seek(0)
+
+        async def read(n=-1):
+            return f.read(n)
+
+        async def close():
+            f.close()
+            os.remove(tmpname)
+
+        self._read = read
+        self._close = close
+        return self
+
+    async def close(self):
+        """Close an open file.
+
+        This method must be called to free memory or temporary files created by
+        the ``copy()`` method.
+
+        Note that when using the ``@with_form_data`` decorator this method is
+        called automatically when the request ends.
+        """
+        if self._close:
+            await self._close()
+            self._close = None
+
+
+def with_form_data(f):
+    """Decorator that parses a ``multipart/form-data`` body and updates the
+    request object with the parsed form fields and files.
+
+    Example usage::
+
+        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)
+
+    Note: this decorator calls the :meth:`FileUpload.copy()
+    <microdot.multipart.FileUpload.copy>` method on all uploaded files, so that
+    the request can be parsed in its entirety. The files are either copied to
+    memory or a temporary file, depending on their size. The temporary files
+    are automatically deleted when the request ends.
+    """
+    @wraps(f)
+    async def wrapper(request, *args, **kwargs):
+        form = {}
+        files = {}
+        async for name, value in FormDataIter(request):
+            if isinstance(value, FileUpload):
+                files[name] = await value.copy()
+            else:
+                form[name] = value
+        if form or files:
+            request._form = form
+            request._files = files
+        try:
+            ret = f(request, *args, **kwargs)
+            if iscoroutine(ret):
+                ret = await ret
+        finally:
+            if request.files:
+                for file in request.files.values():
+                    await file.close()
+        return ret
+    return wrapper

tests/__init__.py

@@ -4,6 +4,7 @@ from tests.test_request import *  # noqa: F401, F403
 from tests.test_response import *  # noqa: F401, F403
 from tests.test_urlencode import *  # noqa: F401, F403
 from tests.test_url_pattern import *  # noqa: F401, F403
+from tests.test_multipart import *  # noqa: F401, F403
 from tests.test_websocket import *  # noqa: F401, F403
 from tests.test_sse import *  # noqa: F401, F403
 from tests.test_cors import *  # noqa: F401, F403

tests/test_multipart.py

@@ -0,0 +1,192 @@
+import asyncio
+import os
+import unittest
+from microdot import Microdot
+from microdot.multipart import with_form_data, FileUpload, FormDataIter
+from microdot.test_client import TestClient
+
+
+class TestMultipart(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        if hasattr(asyncio, 'set_event_loop'):
+            asyncio.set_event_loop(asyncio.new_event_loop())
+        cls.loop = asyncio.get_event_loop()
+
+    def _run(self, coro):
+        return self.loop.run_until_complete(coro)
+
+    def test_simple_form(self):
+        app = Microdot()
+
+        @app.post('/sync')
+        @with_form_data
+        def sync_route(req):
+            return dict(req.form)
+
+        @app.post('/async')
+        @with_form_data
+        async def async_route(req):
+            return dict(req.form)
+
+        client = TestClient(app)
+
+        res = self._run(client.post(
+            '/sync', headers={
+                'Content-Type': 'multipart/form-data; boundary=boundary',
+            },
+            body=(
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="foo"\r\n\r\nbar\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="baz"\r\n\r\nbaz\r\n'
+                b'--boundary--\r\n')
+        ))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json, {'foo': 'bar', 'baz': 'baz'})
+
+        res = self._run(client.post(
+            '/async', headers={
+                'Content-Type': 'multipart/form-data; boundary=boundary',
+            },
+            body=(
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="foo"\r\n\r\nbar\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="baz"\r\n\r\nbaz\r\n'
+                b'--boundary--\r\n')
+        ))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json, {'foo': 'bar', 'baz': 'baz'})
+
+    def test_form_with_files(self):
+        saved_max_memory_size = FileUpload.max_memory_size
+        FileUpload.max_memory_size = 5
+
+        app = Microdot()
+
+        @app.post('/async')
+        @with_form_data
+        async def async_route(req):
+            d = dict(req.form)
+            for name, file in req.files.items():
+                d[name] = '{}|{}|{}'.format(file.filename, file.content_type,
+                                            (await file.read()).decode())
+            return d
+
+        client = TestClient(app)
+
+        res = self._run(client.post(
+            '/async', headers={
+                'Content-Type': 'multipart/form-data; boundary=boundary',
+            },
+            body=(
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="foo"\r\n\r\nbar\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="f"; filename="f"\r\n'
+                b'Content-Type: text/plain\r\n\r\nbaz\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="g"; filename="g"\r\n'
+                b'Content-Type: text/html\r\n\r\n<p>hello</p>\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="x"\r\n\r\ny\r\n'
+                b'--boundary--\r\n')
+        ))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json, {'foo': 'bar', 'x': 'y',
+                                    'f': 'f|text/plain|baz',
+                                    'g': 'g|text/html|<p>hello</p>'})
+        FileUpload.max_memory_size = saved_max_memory_size
+
+    def test_file_save(self):
+        app = Microdot()
+
+        @app.post('/async')
+        @with_form_data
+        async def async_route(req):
+            for _, file in req.files.items():
+                await file.save('_x.txt')
+
+        client = TestClient(app)
+
+        res = self._run(client.post(
+            '/async', headers={
+                'Content-Type': 'multipart/form-data; boundary=boundary',
+            },
+            body=(
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="foo"\r\n\r\nbar\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="f"; filename="f"\r\n'
+                b'Content-Type: text/plain\r\n\r\nbaz\r\n'
+                b'--boundary--\r\n')
+        ))
+        self.assertEqual(res.status_code, 204)
+        with open('_x.txt', 'rb') as f:
+            self.assertEqual(f.read(), b'baz')
+        os.unlink('_x.txt')
+
+    def test_no_form(self):
+        app = Microdot()
+
+        @app.post('/async')
+        @with_form_data
+        async def async_route(req):
+            return str(req.form)
+
+        client = TestClient(app)
+
+        res = self._run(client.post('/async', body={'foo': 'bar'}))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.text, 'None')
+
+    def test_upload_iterator(self):
+        app = Microdot()
+
+        @app.post('/async')
+        async def async_route(req):
+            d = {}
+            async for name, value in FormDataIter(req):
+                if isinstance(value, FileUpload):
+                    d[name] = '{}|{}|{}'.format(value.filename,
+                                                value.content_type,
+                                                (await value.read(4)).decode())
+                else:
+                    d[name] = value
+            return d
+
+        client = TestClient(app)
+
+        res = self._run(client.post(
+            '/async', headers={
+                'Content-Type': 'multipart/form-data; boundary=boundary',
+            },
+            body=(
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="foo"\r\n\r\nbar\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="f"; filename="f"\r\n'
+                b'Content-Type: text/plain\r\n\r\nbaz\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="g"; filename="g.h"\r\n'
+                b'Content-Type: text/html\r\n\r\n<p>hello</p>\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="x"\r\n\r\ny\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="h"; filename="hh"\r\n'
+                b'Content-Type: text/plain\r\n\r\nyy' + (b'z' * 500) + b'\r\n'
+                b'--boundary\r\n'
+                b'Content-Disposition: form-data; name="i"; filename="i.1"\r\n'
+                b'Content-Type: text/plain\r\n\r\n1234\r\n'
+                b'--boundary--\r\n')
+        ))
+        self.assertEqual(res.status_code, 200)
+        self.assertEqual(res.json, {
+            'foo': 'bar',
+            'f': 'f|text/plain|baz',
+            'g': 'g.h|text/html|<p>h',
+            'x': 'y',
+            'h': 'hh|text/plain|yyzz',
+            'i': 'i.1|text/plain|1234',
+        })