florimondmanca: Looks like we've got some unrelated type checking breakage here, issued #865 to fix it. :-)
florimondmanca: Merged `master` in here, should resolve the build. :-)
diff --git a/httpx/_content_streams.py b/httpx/_content_streams.py
index 5f3237e..afffed3 100644
--- a/httpx/_content_streams.py
+++ b/httpx/_content_streams.py
@@ -323,7 +323,7 @@ def encode(
     Handles encoding the given `data`, `files`, and `json`, returning
     a `ContentStream` implementation.
     """
-    if data is None:
+    if not data:
         if json is not None:
             return JSONStream(json=json)
         elif files:
@@ -331,7 +331,7 @@ def encode(
         else:
             return ByteStream(body=b"")
     elif isinstance(data, dict):
-        if files is not None:
+        if files:
             return MultipartStream(data=data, files=files, boundary=boundary)
         else:
             return URLEncodedStream(data=data)

Redundant `boundary` if files/data is empty
If you try to send a post request with empty data and files — you will create a body with one `--boundary--` string, which can break the server.

It's because httpx create MultipartStream for `data={}, files={}`:
https://github.com/encode/httpx/blob/a82adcc933345c6b8cb1623b031eb85723e7665b/httpx/_content_streams.py#L332-L334

And this MultipartStream doesn't have special behavior for empty data/files:
https://github.com/encode/httpx/blob/a82adcc933345c6b8cb1623b031eb85723e7665b/httpx/_content_streams.py#L277-L283

Reproducible example:

```
from httpx.content_streams import encode

stream = encode(data={}, files={}, boundary=b"+++")
print(b"".join([part for part in stream]))
# b'--+++--\r\n'
```

I see two ways to solve it:
1. Check files not only for None but also for emptiness in `_content_streams.decode`
2. Check the count of fields in `MultipartStream.__init__` and doesn't write anything if fields are empty.

I already opened PR (#861) with a test example. If someone tells me which of these options is better, I will be happy to implement it  🙌
diff --git a/tests/test_content_streams.py b/tests/test_content_streams.py
index 6aa91f4..c5eb961 100644
--- a/tests/test_content_streams.py
+++ b/tests/test_content_streams.py
@@ -189,6 +189,18 @@ async def test_multipart_data_and_files_content():
     )
 
 
+@pytest.mark.asyncio
+async def test_empty_request():
+    stream = encode(data={}, files={})
+    sync_content = b"".join([part for part in stream])
+    async_content = b"".join([part async for part in stream])
+
+    assert stream.can_replay()
+    assert stream.get_headers() == {}
+    assert sync_content == b""
+    assert async_content == b""
+
+
 def test_invalid_argument():
     with pytest.raises(TypeError):
         encode(123)

pip install -e .[dev]
parse_log_pytest
requirements.txt
apt-get update apt-get install -y gcc
3.9
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
aspy.refactor-imports==3.0.2
attrs==25.3.0
autoflake==2.3.1
babel==2.17.0
backrefs==5.8
black==25.1.0
brotlipy==0.7.0
certifi==2025.1.31
cffi==1.17.1
chardet==3.0.4
charset-normalizer==3.4.1
click==8.1.8
colorama==0.4.6
coverage==7.8.0
cryptography==44.0.2
exceptiongroup==1.2.2
flake8==7.2.0
flake8-bugbear==24.12.12
flake8-pie==0.16.0
ghp-import==2.1.0
h11==0.9.0
h2==3.2.0
hpack==3.0.0
hstspreload==2025.1.1
-e git+https://github.com/encode/httpx.git@43ec09c3cbb089edd2e83ccc717fb95beef0c189#egg=httpx
hyperframe==5.2.0
idna==2.10
importlib_metadata==8.6.1
iniconfig==2.1.0
isort==6.0.1
Jinja2==3.1.6
Markdown==3.7
MarkupSafe==3.0.2
mccabe==0.7.0
mergedeep==1.3.4
mkautodoc==0.2.0
mkdocs==1.6.1
mkdocs-get-deps==0.2.0
mkdocs-material==9.6.10
mkdocs-material-extensions==1.3.1
mypy==1.15.0
mypy-extensions==1.0.0
outcome==1.3.0.post0
packaging==24.2
paginate==0.5.7
pathspec==0.12.1
platformdirs==4.3.7
pluggy==1.5.0
pycodestyle==2.13.0
pycparser==2.22
pyflakes==3.3.1
Pygments==2.19.1
pymdown-extensions==10.14.3
pytest==8.3.5
pytest-asyncio==0.26.0
pytest-cov==6.0.0
pytest-trio==0.8.0
python-dateutil==2.9.0.post0
PyYAML==6.0.2
pyyaml_env_tag==0.1
requests==2.32.3
rfc3986==1.5.0
seed-isort-config==2.2.0
six==1.17.0
sniffio==1.3.1
sortedcontainers==2.4.0
tomli==2.2.1
trio==0.29.0
trustme==1.2.1
typing_extensions==4.13.0
urllib3==1.26.20
uvicorn==0.34.0
watchdog==6.0.0
zipp==3.21.0

name: httpx
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.4.4=h6a678d5_1
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=3.0.16=h5eee18b_0
  - pip=25.0=py39h06a4308_0
  - python=3.9.21=he870216_1
  - readline=8.2=h5eee18b_0
  - setuptools=75.8.0=py39h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - tzdata=2025a=h04d1e81_0
  - wheel=0.45.1=py39h06a4308_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - aspy-refactor-imports==3.0.2
      - attrs==25.3.0
      - autoflake==2.3.1
      - babel==2.17.0
      - backrefs==5.8
      - black==25.1.0
      - brotlipy==0.7.0
      - certifi==2025.1.31
      - cffi==1.17.1
      - chardet==3.0.4
      - charset-normalizer==3.4.1
      - click==8.1.8
      - colorama==0.4.6
      - coverage==7.8.0
      - cryptography==44.0.2
      - exceptiongroup==1.2.2
      - flake8==7.2.0
      - flake8-bugbear==24.12.12
      - flake8-pie==0.16.0
      - ghp-import==2.1.0
      - h11==0.9.0
      - h2==3.2.0
      - hpack==3.0.0
      - hstspreload==2025.1.1
      - hyperframe==5.2.0
      - idna==2.10
      - importlib-metadata==8.6.1
      - iniconfig==2.1.0
      - isort==6.0.1
      - jinja2==3.1.6
      - markdown==3.7
      - markupsafe==3.0.2
      - mccabe==0.7.0
      - mergedeep==1.3.4
      - mkautodoc==0.2.0
      - mkdocs==1.6.1
      - mkdocs-get-deps==0.2.0
      - mkdocs-material==9.6.10
      - mkdocs-material-extensions==1.3.1
      - mypy==1.15.0
      - mypy-extensions==1.0.0
      - outcome==1.3.0.post0
      - packaging==24.2
      - paginate==0.5.7
      - pathspec==0.12.1
      - platformdirs==4.3.7
      - pluggy==1.5.0
      - pycodestyle==2.13.0
      - pycparser==2.22
      - pyflakes==3.3.1
      - pygments==2.19.1
      - pymdown-extensions==10.14.3
      - pytest==8.3.5
      - pytest-asyncio==0.26.0
      - pytest-cov==6.0.0
      - pytest-trio==0.8.0
      - python-dateutil==2.9.0.post0
      - pyyaml==6.0.2
      - pyyaml-env-tag==0.1
      - requests==2.32.3
      - rfc3986==1.5.0
      - seed-isort-config==2.2.0
      - six==1.17.0
      - sniffio==1.3.1
      - sortedcontainers==2.4.0
      - tomli==2.2.1
      - trio==0.29.0
      - trustme==1.2.1
      - typing-extensions==4.13.0
      - urllib3==1.26.20
      - uvicorn==0.34.0
      - watchdog==6.0.0
      - zipp==3.21.0
prefix: /opt/conda/envs/httpx

tests/test_content_streams.py::test_empty_request
tests/test_content_streams.py::test_base_content tests/test_content_streams.py::test_empty_content tests/test_content_streams.py::test_bytes_content tests/test_content_streams.py::test_iterator_content tests/test_content_streams.py::test_aiterator_content tests/test_content_streams.py::test_json_content tests/test_content_streams.py::test_urlencoded_content tests/test_content_streams.py::test_multipart_files_content tests/test_content_streams.py::test_multipart_data_and_files_content tests/test_content_streams.py::test_invalid_argument
httpx/_content_streams.py
httpx/_content_streams.py