Allow str content for multipart upload files

[tomchristie]

Closes #2069.

Allow str for simple multipart uploads...

httpx.post(url, files={"upload": "some content"})

However we (continue to) explicitly disallow io.StringIO and files opened in text mode, since we can't upfront determine their byte-length.

I think this is probably a pretty okay middle-ground, supporting the simple text-use-case, while enforcing bytes for the file-like cases. Not a breaking change, since we're expanding our supported cases here.

---

Edit: This change enforces the constraint that upload files must be opened in binary mode. That's the right thing to do but I'm unclear why I hadn't called it out explicitly in this description.

[adriangb]

Makes sense to me! Do we just encode it as utf-8?

[tomchristie]

Makes sense to me! Do we just encode it as utf-8?

Yup.

[euri10]

I think this is probably a pretty okay middle-ground, supporting the simple text-use-case, while enforcing bytes for the file-like cases. Not a breaking change, since we're expanding our supported cases here.

I think this is a breaking change, at least it breaks my test suite with

        if "b" not in getattr(fileobj, "mode", "b"):
>           raise TypeError(
                "Multipart file uploads must be opened in binary mode, not text mode."
            )
E           TypeError: Multipart file uploads must be opened in binary mode, not text mode.

this is the snippet that was previously working:

    files: List[Tuple[str, IO]] = [
        ("files", (open(Path(__file__).parent / "data_upload" / "ls" / ls_file)))
        for ls_file in to_upload
    ]
    response = await client.post(
        "/uploads/ls",
        files=files,
        headers={"Authorization": f"Bearer {token}"},
    )

[tomchristie]

Okay. Error on my part - we shouldn't have issued that as a minor point release.
Still, we're here now.

Make sure to open upload files in binary mode.

We have that as a constraint since it ensures that you're uploading the actual binary file content, rather than decoding it into text and then re-encoding it into bytes when it goes out onto the wire. This also means we can correct determine the content length in advance.

    files: List[Tuple[str, IO]] = [
        ("files", (open(Path(__file__).parent / "data_upload" / "ls" / ls_file, "rb")))  # Added "rb" mode.
        for ls_file in to_upload
    ]
    response = await client.post(
        "/uploads/ls",
        files=files,
        headers={"Authorization": f"Bearer {token}"},
    )