Fix read/write order in AsyncBytesProvider (#421)

Author: alextwoods

packages/smithy-core/src/smithy_core/aio/types.py

@@ -2,6 +2,7 @@
 #  SPDX-License-Identifier: Apache-2.0
 import asyncio
 from asyncio import iscoroutinefunction
+from collections import deque
 from collections.abc import AsyncIterable, AsyncIterator, Awaitable, Callable
 from io import BytesIO
 from typing import Any, Self, cast
@@ -297,10 +298,9 @@ def __init__(
             Calls to ``write`` will block until the number of chunks is less than this
             number. Default is 16.
         """
+        self._data = deque[bytes]()
         if intial_data is not None:
-            self._data = [intial_data]
-        else:
-            self._data = []
+            self._data.append(intial_data)
 
         if max_buffered_chunks < 1:
             raise ValueError(
@@ -419,7 +419,7 @@ async def __anext__(self) -> bytes:
 
             # Pop the next chunk of data from the buffer, then notify any waiting
             # coroutines, returning immediately after.
-            result = self._data.pop()
+            result = self._data.popleft()
             self._data_condition.notify()
             return result
 

packages/smithy-core/tests/unit/aio/test_types.py

@@ -359,12 +359,13 @@ async def test_provider_reads_written_data() -> None:
     # Start the read task in the background.
     read_task = asyncio.create_task(drain_provider(provider, result))
     await provider.write(b"foo")
+    await provider.write(b"bar")
 
     # Wait for the buffer to drain. At that point all the data should
     # be read, but the read task won't actually be complete yet
     # because it's still waiting on future data.
     await provider.flush()
-    assert result == [b"foo"]
+    assert result == [b"foo", b"bar"]
     assert not read_task.done()
 
     # Now actually close the provider, which will let the read task
@@ -373,7 +374,7 @@ async def test_provider_reads_written_data() -> None:
     await read_task
 
     # The result should not have changed
-    assert result == [b"foo"]
+    assert result == [b"foo", b"bar"]
 
 
 async def test_close_stops_writes() -> None:
@@ -393,7 +394,7 @@ async def test_close_without_flush_deletes_buffered_data() -> None:
     # We weren't able to read data, which is what we want. But here we dig into
     # the internals to be sure that the buffer is clear and no data is haning
     # around.
-    assert provider._data == []  # type: ignore
+    assert len(provider._data) == 0  # type: ignore
 
 
 async def test_only_max_chunks_buffered() -> None: