Unclosed client session asyncio ERROR logs from internal aiohttp sessions

[sunayana]

What happened?

When using cdsapi.Client() to retrieve data, asyncio logs multiple ERROR-level messages about unclosed aiohttp client sessions. These
appear during garbage collection and create noise in application logs, even though data retrieval completes successfully.

Environment

• cdsapi version: [your version, e.g., 0.7.x]
• Python version: 3.12
• OS: Linux (AWS Batch container)

Steps to Reproduce

  import cdsapi                                                                                                                             
                                                                                                                                            
  client = cdsapi.Client()                                                                                                                  
  client.retrieve(                                                                                                                          
      'sis-agrometeorological-indicators',                                                                                                  
      {                                                                                                                                     
          'variable': '2m_temperature',                                                                                                     
          'year': '2024',                                                                                                                   
          'month': '01',                                                                                                                    
          'day': '01',                                                                                                                      
          'version': '2_0',                                                                                                                 
      },                                                                                                                                    
      'output.zip'                                                                                                                          
  )                                                                                                                                        

Observed Behavior

2026-01-19 06:37:54,906 - asyncio - ERROR - Unclosed client session                                                                       
  client_session: <aiohttp.client.ClientSession object at 0x7fcda4d5a9f0>                                                                   
  2026-01-19 06:37:54,906 - asyncio - ERROR - Unclosed connector                                                                            
  connections: ['deque([...])']                                                                                                             
  connector: <aiohttp.connector.TCPConnector object at 0x7fcda4b9c740>                                                                      

These errors appear:

1. Immediately after Client() initialization (before any API requests)
2. At the end of the process during garbage collection

Expected Behavior

The library should properly close its internal aiohttp sessions, either:

1. By exposing a close() method on the Client
2. By implementing context manager support (enter/exit)
3. By properly cleaning up sessions internally

Workaround

Currently, users can suppress these logs with a logging filter, but this isn't ideal:

import logging                                                                                                                            
                                                                                                                                          
class UnclosedSessionFilter(logging.Filter):                                                                                              
    def filter(self, record):                                                                                                             
        return "Unclosed client session" not in record.getMessage()                                                                       
                                                                                                                                          
logging.getLogger("asyncio").addFilter(UnclosedSessionFilter())                                                                           

Additional Context

The sessions appear to be created by ecmwf.datastores.legacy_client during initialization. The cdsapi.Client object has a session
attribute (requests.Session) and a client attribute (ecmwf.datastores.client.Client), but neither exposes the internal aiohttp sessions
for cleanup.

What are the steps to reproduce the bug?

import cdsapi                                                                                                                             
                                                                                                                                            
  client = cdsapi.Client()                                                                                                                  
  client.retrieve(                                                                                                                          
      'sis-agrometeorological-indicators',                                                                                                  
      {                                                                                                                                     
          'variable': '2m_temperature',                                                                                                     
          'year': '2024',                                                                                                                   
          'month': '01',                                                                                                                    
          'day': '01',                                                                                                                      
          'version': '2_0',                                                                                                                 
      },                                                                                                                                    
      'output.zip'                                                                                                                          
  )

Version

v0.7.x

Platform (OS and architecture)

Linux (AWS Batch container)

Relevant log output

2026-01-19 06:37:54,906 - asyncio - ERROR - Unclosed client session                                                                       
  client_session: <aiohttp.client.ClientSession object at 0x7fcda4d5a9f0>                                                                   
  2026-01-19 06:37:54,906 - asyncio - ERROR - Unclosed connector                                                                            
  connections: ['deque([...])']                                                                                                             
  connector: <aiohttp.connector.TCPConnector object at 0x7fcda4b9c740>

Accompanying data

No response

Organisation

CarbonSpace