Fix handling of multipart/form-data (#8280)

https://datatracker.ietf.org/doc/html/rfc7578

CHANGES/8280.bugfix.rst

@@ -0,0 +1 @@
+Fixed ``multipart/form-data`` compliance with :rfc:`7578` -- by :user:`Dreamsorcerer`.

CHANGES/8280.deprecation.rst

@@ -0,0 +1,2 @@
+Deprecated ``content_transfer_encoding`` parameter in :py:meth:`FormData.add_field()
+<aiohttp.FormData.add_field>` -- by :user:`Dreamsorcerer`.

aiohttp/formdata.py

@@ -1,4 +1,5 @@
 import io
+import warnings
 from typing import Any, Iterable, List, Optional
 from urllib.parse import urlencode
 
@@ -54,7 +55,12 @@ def add_field(
         if isinstance(value, io.IOBase):
             self._is_multipart = True
         elif isinstance(value, (bytes, bytearray, memoryview)):
+            msg = (
+                "In v4, passing bytes will no longer create a file field. "
+                "Please explicitly use the filename parameter or pass a BytesIO object."
+            )
             if filename is None and content_transfer_encoding is None:
+                warnings.warn(msg, DeprecationWarning)
                 filename = name
 
         type_options: MultiDict[str] = MultiDict({"name": name})
@@ -82,7 +88,11 @@ def add_field(
                     "content_transfer_encoding must be an instance"
                     " of str. Got: %s" % content_transfer_encoding
                 )
-            headers[hdrs.CONTENT_TRANSFER_ENCODING] = content_transfer_encoding
+            msg = (
+                "content_transfer_encoding is deprecated. "
+                "To maintain compatibility with v4 please pass a BytesPayload."
+            )
+            warnings.warn(msg, DeprecationWarning)
             self._is_multipart = True
 
         self._fields.append((type_options, headers, value))

aiohttp/multipart.py

@@ -260,12 +260,18 @@ def __init__(
         boundary: bytes,
         headers: "CIMultiDictProxy[str]",
         content: StreamReader,
+        *,
+        subtype: str = "mixed",
+        default_charset: Optional[str] = None,
     ) -> None:
         self.headers = headers
         self._boundary = boundary
         self._content = content
+        self._default_charset = default_charset
         self._at_eof = False
-        length = self.headers.get(CONTENT_LENGTH, None)
+        self._is_form_data = subtype == "form-data"
+        # https://datatracker.ietf.org/doc/html/rfc7578#section-4.8
+        length = None if self._is_form_data else self.headers.get(CONTENT_LENGTH, None)
         self._length = int(length) if length is not None else None
         self._read_bytes = 0
         self._unread: Deque[bytes] = deque()
@@ -357,6 +363,8 @@ async def _read_chunk_from_length(self, size: int) -> bytes:
         assert self._length is not None, "Content-Length required for chunked read"
         chunk_size = min(size, self._length - self._read_bytes)
         chunk = await self._content.read(chunk_size)
+        if self._content.at_eof():
+            self._at_eof = True
         return chunk
 
     async def _read_chunk_from_stream(self, size: int) -> bytes:
@@ -477,7 +485,8 @@ def decode(self, data: bytes) -> bytes:
         """
         if CONTENT_TRANSFER_ENCODING in self.headers:
             data = self._decode_content_transfer(data)
-        if CONTENT_ENCODING in self.headers:
+        # https://datatracker.ietf.org/doc/html/rfc7578#section-4.8
+        if not self._is_form_data and CONTENT_ENCODING in self.headers:
             return self._decode_content(data)
         return data
 
@@ -511,7 +520,7 @@ def get_charset(self, default: str) -> str:
         """Returns charset parameter from Content-Type header or default."""
         ctype = self.headers.get(CONTENT_TYPE, "")
         mimetype = parse_mimetype(ctype)
-        return mimetype.parameters.get("charset", default)
+        return mimetype.parameters.get("charset", self._default_charset or default)
 
     @reify
     def name(self) -> Optional[str]:
@@ -570,9 +579,17 @@ def __init__(
         headers: Mapping[str, str],
         content: StreamReader,
     ) -> None:
+        self._mimetype = parse_mimetype(headers[CONTENT_TYPE])
+        assert self._mimetype.type == "multipart", "multipart/* content type expected"
+        if "boundary" not in self._mimetype.parameters:
+            raise ValueError(
+                "boundary missed for Content-Type: %s" % headers[CONTENT_TYPE]
+            )
+
         self.headers = headers
         self._boundary = ("--" + self._get_boundary()).encode()
         self._content = content
+        self._default_charset: Optional[str] = None
         self._last_part: Optional[Union["MultipartReader", BodyPartReader]] = None
         self._at_eof = False
         self._at_bof = True
@@ -624,7 +641,24 @@ async def next(
             await self._read_boundary()
         if self._at_eof:  # we just read the last boundary, nothing to do there
             return None
-        self._last_part = await self.fetch_next_part()
+
+        part = await self.fetch_next_part()
+        # https://datatracker.ietf.org/doc/html/rfc7578#section-4.6
+        if (
+            self._last_part is None
+            and self._mimetype.subtype == "form-data"
+            and isinstance(part, BodyPartReader)
+        ):
+            _, params = parse_content_disposition(part.headers.get(CONTENT_DISPOSITION))
+            if params.get("name") == "_charset_":
+                # Longest encoding in https://encoding.spec.whatwg.org/encodings.json
+                # is 19 characters, so 32 should be more than enough for any valid encoding.
+                charset = await part.read_chunk(32)
+                if len(charset) > 31:
+                    raise RuntimeError("Invalid default charset")
+                self._default_charset = charset.strip().decode()
+                part = await self.fetch_next_part()
+        self._last_part = part
         return self._last_part
 
     async def release(self) -> None:
@@ -660,19 +694,16 @@ def _get_part_reader(
                 return type(self)(headers, self._content)
             return self.multipart_reader_cls(headers, self._content)
         else:
-            return self.part_reader_cls(self._boundary, headers, self._content)
-
-    def _get_boundary(self) -> str:
-        mimetype = parse_mimetype(self.headers[CONTENT_TYPE])
-
-        assert mimetype.type == "multipart", "multipart/* content type expected"
-
-        if "boundary" not in mimetype.parameters:
-            raise ValueError(
-                "boundary missed for Content-Type: %s" % self.headers[CONTENT_TYPE]
+            return self.part_reader_cls(
+                self._boundary,
+                headers,
+                self._content,
+                subtype=self._mimetype.subtype,
+                default_charset=self._default_charset,
             )
 
-        boundary = mimetype.parameters["boundary"]
+    def _get_boundary(self) -> str:
+        boundary = self._mimetype.parameters["boundary"]
         if len(boundary) > 70:
             raise ValueError("boundary %r is too long (70 chars max)" % boundary)
 
@@ -765,6 +796,7 @@ def __init__(self, subtype: str = "mixed", boundary: Optional[str] = None) -> No
         super().__init__(None, content_type=ctype)
 
         self._parts: List[_Part] = []
+        self._is_form_data = subtype == "form-data"
 
     def __enter__(self) -> "MultipartWriter":
         return self
@@ -842,32 +874,36 @@ def append(self, obj: Any, headers: Optional[Mapping[str, str]] = None) -> Paylo
 
     def append_payload(self, payload: Payload) -> Payload:
         """Adds a new body part to multipart writer."""
-        # compression
-        encoding: Optional[str] = payload.headers.get(
-            CONTENT_ENCODING,
-            "",
-        ).lower()
-        if encoding and encoding not in ("deflate", "gzip", "identity"):
-            raise RuntimeError(f"unknown content encoding: {encoding}")
-        if encoding == "identity":
-            encoding = None
-
-        # te encoding
-        te_encoding: Optional[str] = payload.headers.get(
-            CONTENT_TRANSFER_ENCODING,
-            "",
-        ).lower()
-        if te_encoding not in ("", "base64", "quoted-printable", "binary"):
-            raise RuntimeError(
-                "unknown content transfer encoding: {}" "".format(te_encoding)
+        encoding: Optional[str] = None
+        te_encoding: Optional[str] = None
+        if self._is_form_data:
+            # https://datatracker.ietf.org/doc/html/rfc7578#section-4.7
+            # https://datatracker.ietf.org/doc/html/rfc7578#section-4.8
+            assert CONTENT_DISPOSITION in payload.headers
+            assert "name=" in payload.headers[CONTENT_DISPOSITION]
+            assert (
+                not {CONTENT_ENCODING, CONTENT_LENGTH, CONTENT_TRANSFER_ENCODING}
+                & payload.headers.keys()
             )
-        if te_encoding == "binary":
-            te_encoding = None
-
-        # size
-        size = payload.size
-        if size is not None and not (encoding or te_encoding):
-            payload.headers[CONTENT_LENGTH] = str(size)
+        else:
+            # compression
+            encoding = payload.headers.get(CONTENT_ENCODING, "").lower()
+            if encoding and encoding not in ("deflate", "gzip", "identity"):
+                raise RuntimeError(f"unknown content encoding: {encoding}")
+            if encoding == "identity":
+                encoding = None
+
+            # te encoding
+            te_encoding = payload.headers.get(CONTENT_TRANSFER_ENCODING, "").lower()
+            if te_encoding not in ("", "base64", "quoted-printable", "binary"):
+                raise RuntimeError(f"unknown content transfer encoding: {te_encoding}")
+            if te_encoding == "binary":
+                te_encoding = None
+
+            # size
+            size = payload.size
+            if size is not None and not (encoding or te_encoding):
+                payload.headers[CONTENT_LENGTH] = str(size)
 
         self._parts.append((payload, encoding, te_encoding))  # type: ignore[arg-type]
         return payload

tests/test_client_functional.py

@@ -1388,50 +1388,6 @@ async def handler(request):
     resp.close()
 
 
-async def test_POST_DATA_with_context_transfer_encoding(aiohttp_client: Any) -> None:
-    async def handler(request):
-        data = await request.post()
-        assert data["name"] == "text"
-        return web.Response(text=data["name"])
-
-    app = web.Application()
-    app.router.add_post("/", handler)
-    client = await aiohttp_client(app)
-
-    form = aiohttp.FormData()
-    form.add_field("name", "text", content_transfer_encoding="base64")
-
-    resp = await client.post("/", data=form)
-    assert 200 == resp.status
-    content = await resp.text()
-    assert content == "text"
-    resp.close()
-
-
-async def test_POST_DATA_with_content_type_context_transfer_encoding(
-    aiohttp_client: Any,
-):
-    async def handler(request):
-        data = await request.post()
-        assert data["name"] == "text"
-        return web.Response(body=data["name"])
-
-    app = web.Application()
-    app.router.add_post("/", handler)
-    client = await aiohttp_client(app)
-
-    form = aiohttp.FormData()
-    form.add_field(
-        "name", "text", content_type="text/plain", content_transfer_encoding="base64"
-    )
-
-    resp = await client.post("/", data=form)
-    assert 200 == resp.status
-    content = await resp.text()
-    assert content == "text"
-    resp.close()
-
-
 async def test_POST_MultiDict(aiohttp_client: Any) -> None:
     async def handler(request):
         data = await request.post()
@@ -1483,7 +1439,7 @@ async def handler(request):
 
     with fname.open("rb") as f:
         async with client.post(
-            "/", data={"some": f, "test": b"data"}, chunked=True
+            "/", data={"some": f, "test": io.BytesIO(b"data")}, chunked=True
         ) as resp:
             assert 200 == resp.status