Improve typings in multipart

CHANGES/3621.bugfix

@@ -0,0 +1,4 @@
+Improve typing annotations for multipart.
+
+Use `async for` instead of `while` loop for
+reading full multipart data in `web_request.Request#post` functionality.

aiohttp/multipart.py

@@ -240,7 +240,7 @@ class BodyPartReader:
     def __init__(
         self,
         boundary: bytes,
-        headers: Mapping[str, Optional[str]],
+        headers: Mapping[str, str],
         content: StreamReader,
         *,
         _newline: bytes = b'\r\n'
@@ -443,7 +443,7 @@ def decode(self, data: bytes) -> bytes:
         return data
 
     def _decode_content(self, data: bytes) -> bytes:
-        encoding = cast(str, self.headers[CONTENT_ENCODING]).lower()
+        encoding = self.headers[CONTENT_ENCODING].lower()
 
         if encoding == 'deflate':
             return zlib.decompress(data, -zlib.MAX_WBITS)
@@ -455,7 +455,7 @@ def _decode_content(self, data: bytes) -> bytes:
             raise RuntimeError('unknown content encoding: {}'.format(encoding))
 
     def _decode_content_transfer(self, data: bytes) -> bytes:
-        encoding = cast(str, self.headers[CONTENT_TRANSFER_ENCODING]).lower()
+        encoding = self.headers[CONTENT_TRANSFER_ENCODING].lower()
 
         if encoding == 'base64':
             return base64.b64decode(data)
@@ -547,7 +547,7 @@ def __init__(
     def __aiter__(self) -> 'MultipartReader':
         return self
 
-    async def __anext__(self) -> Any:
+    async def __anext__(self) -> Union['MultipartReader', BodyPartReader]:
         part = await self.next()
         if part is None:
             raise StopAsyncIteration  # NOQA
@@ -569,19 +569,19 @@ def at_eof(self) -> bool:
         """
         return self._at_eof
 
-    async def next(self) -> Any:
+    async def next(self) -> Optional[Union['MultipartReader', BodyPartReader]]:
         """Emits the next multipart body part."""
         # So, if we're at BOF, we need to skip till the boundary.
         if self._at_eof:
-            return
+            return None
         await self._maybe_release_last_part()
         if self._at_bof:
             await self._read_until_first_boundary()
             self._at_bof = False
         else:
             await self._read_boundary()
         if self._at_eof:  # we just read the last boundary, nothing to do there
-            return
+            return None
         self._last_part = await self.fetch_next_part()
         return self._last_part
 
@@ -598,7 +598,10 @@ async def fetch_next_part(self) -> Any:
         headers = await self._read_headers()
         return self._get_part_reader(headers)
 
-    def _get_part_reader(self, headers: 'CIMultiDictProxy[str]') -> Any:
+    def _get_part_reader(
+        self,
+        headers: 'CIMultiDictProxy[str]',
+    ) -> Union['MultipartReader', BodyPartReader]:
         """Dispatches the response by the `Content-Type` header, returning
         suitable reader instance.
 

aiohttp/web_request.py

@@ -32,7 +32,7 @@
 from .abc import AbstractStreamWriter
 from .helpers import DEBUG, ChainMapProxy, HeadersMixin, reify, sentinel
 from .http_parser import RawRequestMessage
-from .multipart import MultipartReader
+from .multipart import BodyPartReader, MultipartReader
 from .streams import EmptyStreamReader, StreamReader
 from .typedefs import (
     DEFAULT_JSON_DECODER,
@@ -608,46 +608,50 @@ async def post(self) -> 'MultiDictProxy[Union[str, bytes, FileField]]':
             multipart = await self.multipart()
             max_size = self._client_max_size
 
-            field = await multipart.next()
-            while field is not None:
+            async for field in multipart:
                 size = 0
-                content_type = field.headers.get(hdrs.CONTENT_TYPE)
-
-                if field.filename:
-                    # store file in temp file
-                    tmp = tempfile.TemporaryFile()
-                    chunk = await field.read_chunk(size=2**16)
-                    while chunk:
-                        chunk = field.decode(chunk)
-                        tmp.write(chunk)
-                        size += len(chunk)
+                field_content_type = field.headers.get(hdrs.CONTENT_TYPE)
+
+                if isinstance(field, BodyPartReader):
+                    if field.filename:
+                        assert field_content_type is not None, \
+                            'Cannot read file without knowing what it is'
+                        # store file in temp file
+                        tmp = tempfile.TemporaryFile()
+                        chunk = await field.read_chunk(size=2**16)
+                        while chunk:
+                            chunk = field.decode(chunk)
+                            tmp.write(chunk)
+                            size += len(chunk)
+                            if 0 < max_size < size:
+                                raise HTTPRequestEntityTooLarge(
+                                    max_size=max_size,
+                                    actual_size=size
+                                )
+                            chunk = await field.read_chunk(size=2**16)
+                        tmp.seek(0)
+
+                        ff = FileField(
+                            field.name,
+                            field.filename,
+                            cast(io.BufferedReader, tmp),
+                            field_content_type,
+                            CIMultiDictProxy(CIMultiDict(**field.headers)),
+                        )
+                        out.add(field.name, ff)
+                    else:
+                        value = await field.read(decode=True)
+                        if content_type is None or \
+                                content_type.startswith('text/'):
+                            charset = field.get_charset(default='utf-8')
+                            value = value.decode(charset)
+                        out.add(field.name, value)
+                        size += len(value)
                         if 0 < max_size < size:
                             raise HTTPRequestEntityTooLarge(
                                 max_size=max_size,
                                 actual_size=size
                             )
-                        chunk = await field.read_chunk(size=2**16)
-                    tmp.seek(0)
-
-                    ff = FileField(field.name, field.filename,
-                                   cast(io.BufferedReader, tmp),
-                                   content_type, field.headers)
-                    out.add(field.name, ff)
-                else:
-                    value = await field.read(decode=True)
-                    if content_type is None or \
-                            content_type.startswith('text/'):
-                        charset = field.get_charset(default='utf-8')
-                        value = value.decode(charset)
-                    out.add(field.name, value)
-                    size += len(value)
-                    if 0 < max_size < size:
-                        raise HTTPRequestEntityTooLarge(
-                            max_size=max_size,
-                            actual_size=size
-                        )
-
-                field = await multipart.next()
         else:
             data = await self.read()
             if data: