Support stdin with asyncio (#71)

changelog.d/feature.0f8582b8.entry.yaml

@@ -0,0 +1,5 @@
+message: Add support for stdin with asyncio.
+pr_ids:
+- '71'
+timestamp: 1642946529
+type: feature

pytest_subprocess/fake_popen.py

@@ -284,6 +284,9 @@ def run_thread(self) -> None:
     def _finish_process(self) -> None:
         self.returncode = self.__returncode
 
+        self._finalize_streams()
+
+    def _finalize_streams(self) -> None:
         self._finalize_stream(self.stdout)
         self._finalize_stream(self.stderr)
 
@@ -301,13 +304,21 @@ def received_signals(self) -> Tuple[int, ...]:
 class AsyncFakePopen(FakePopen):
     """Class to handle async processes"""
 
-    stdout: asyncio.StreamReader
-    stderr: asyncio.StreamReader
+    stdout: Optional[asyncio.StreamReader]
+    stderr: Optional[asyncio.StreamReader]
 
     async def communicate(  # type: ignore
         self, input: OPTIONAL_TEXT = None, timeout: Optional[float] = None
     ) -> Tuple[AnyType, AnyType]:
-        self._handle_stdin(input)
+        if input:
+            # streams were fed with eof, need to be reopened
+            await self._reopen_streams()
+
+            self._handle_stdin(input)
+
+            # feed eof one more time as streams were opened
+            self._finalize_streams()
+
         self._finalize_thread(timeout)
 
         return (
@@ -320,3 +331,17 @@ async def wait(self, timeout: Optional[float] = None) -> int:  # type: ignore
 
     def _get_empty_buffer(self, _: bool) -> asyncio.StreamReader:
         return asyncio.StreamReader()
+
+    async def _reopen_streams(self) -> None:
+        self.stdout = await self._reopen_stream(self.stdout)
+        self.stderr = await self._reopen_stream(self.stderr)
+
+    async def _reopen_stream(
+        self, stream: Optional[asyncio.StreamReader]
+    ) -> Optional[asyncio.StreamReader]:
+        if stream:
+            data = await stream.read()
+            fresh_stream = self._get_empty_buffer(False)
+            fresh_stream.feed_data(data)
+            return fresh_stream
+        return None

tests/test_asyncio.py

@@ -275,6 +275,42 @@ async def _read_stream(stream: asyncio.StreamReader, output_list):
             output_list.append(line.decode())
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize("fake", [False, True])
+async def test_input(fake_process, fake):
+    fake_process.allow_unregistered(not fake)
+    if fake:
+
+        def stdin_callable(input):
+            return {
+                "stdout": "Provide an input: Provided: {data}".format(
+                    data=input.decode()
+                )
+            }
+
+        fake_process.register_subprocess(
+            ["python", "example_script.py", "input"],
+            stdout=[b"Stdout line 1", b"Stdout line 2"],
+            stdin_callable=stdin_callable,
+        )
+
+    process = await asyncio.create_subprocess_exec(
+        "python",
+        "example_script.py",
+        "input",
+        stdin=asyncio.subprocess.PIPE,
+        stdout=asyncio.subprocess.PIPE,
+    )
+    out, err = await process.communicate(input=b"test")
+
+    assert out.splitlines() == [
+        b"Stdout line 1",
+        b"Stdout line 2",
+        b"Provide an input: Provided: test",
+    ]
+    assert err is None
+
+
 @pytest.fixture(autouse=True)
 def skip_on_pypy():
     """Async test for some reason crash on pypy 3.6 on Windows"""