Bug: ContainerClient.download_blob works once but not twice in windows

[PabloRuizCuevas]

• azure.storage.blob.aio:
• 18.3.1:
• Windows:
• 3.11:

Describe the bug

The code aio download_blob of the azure blob works once but not twice when run with asyncio.run, this looks like a bug related to aiohttp, but could not figure out how to solve it. (Windows)

The code i have to reproduce it is almost a copy from their original example at: https://github.com/Azure/azure-sdk-for-python/blob/main/sdk/storage/azure-storage-blob/samples/blob_samples_hello_world_async.py

To Reproduce

from azure.storage.blob.aio import ContainerClient
from azure.identity import DefaultAzureCredential
credentials = DefaultAzureCredential()

async def test(conn_client):
    async with conn_client as client_conn:
        stream = await client_conn.download_blob(my_path)
        data = await stream.readall()
    return data

if __name__ == "__main__":
    my_container_name = "Container name"
    my_client = ContainerClient.from_container_url(container_url=my_container_name, credential=credentials)
    my_path = 'test_path'

    data = asyncio.run(test(my_client)) # works and returns the file from blob storage
    data2 = asyncio.run(test(my_client)) # doesn't work

error:

DEBUG - asyncio: Using proactor: IocpProactor
...
    await self.open()
  File "C...\Cache\virtualenvs\transformer-wi-nHELc-py3.11\Lib\site-packages\azure\core\pipeline\transport\_aiohttp.py", line 127, in open
    await self.session.__aenter__()
          ^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute '__aenter__'. Did you mean: '__delattr__'?

Process finished with exit code 1

[PabloRuizCuevas]

For what I see the issue seems related to the not closing of TCP connection, but is not so straight forward as i can come up with a code that close the session, but still doesn't work :

async def test4(my_client):
    async with my_client as client:
        # this at least closes the session
        stream = await client.download_blob(my_path)
        data = await stream.readall()
        session = my_client._client._client._pipeline._transport.session
    return data, session

data, s = asyncio.run(test(my_client))
print(session.closed)

will return that the session is closed

the best work around i found is instantiate the class as many times as needed:

my_client = ContainerClient.from_container_url(container_url=my_container_name, credential=credentials)
data = asyncio.run(test(my_client))
my_client = ContainerClient.from_container_url(container_url=my_container_name, credential=credentials)
data2 = asyncio.run(test(my_client))

or even in the dowload blob:

  async def test():
    # best working alternative so far
    async with DefaultAzureCredential() as credential:
        async with ContainerClient.from_container_url(container_url=my_container_name, credential=credential) as client:
            stream = await client.download_blob(my_path)
            data = await stream.readall()
    return data

but honestly this is not a great solution for this bug.

note: i didn't see any difference using aio credential or normal credentials, they both work and don't avoid the issue, not sure why there is the choice in the first place.

[annatisch]

Thanks for the report @PabloRuizCuevas
I believe the reason you're seeing this is due to using the client within the context manager - which will close the client/session/connection on exiting the context - and which is then not re-openable.
You should be able to resolve this by either changing where you open the context, or manually closing the client when you have finished with it. For example:

from azure.storage.blob.aio import ContainerClient
from azure.identity import DefaultAzureCredential
credentials = DefaultAzureCredential()

async def test(conn_client):
    stream = await conn_client.download_blob(my_path)
    data = await stream.readall()
    return data

if __name__ == "__main__":
    my_container_name = "Container name"
    my_client = ContainerClient.from_container_url(container_url=my_container_name, credential=credentials)
    my_path = 'test_path'

    try:
        data = asyncio.run(test(my_client))
        data2 = asyncio.run(test(my_client))
    finally:
        asyncio.run(my_client.close())
        asyncio.run(credentials.close())

Let me know if this helps, or whether the problem is persisting :)