Trying to make use of the new ClientResponse.output_size attribute

[mib1185]

Hi 👋

with 3.14 the new output_size and upload_complete ClientResponse attributes (#12452) were introduced to allow the consumer to track the upload progress. Therefore the following example code has been documented:

async with session.post(url, data=mpwriter) as resp:
    while not resp.upload_complete.done():
        print(f"uploaded {resp.output_size} bytes")
        await asyncio.sleep(0.5)
    print(f"upload complete: {resp.output_size} bytes")

But when using this, where mpwriter is an instance of MultipartWriter, we only get the final "upload complete: nnn bytes" message printed, but never the progress messages "uploaded nnn bytes". It seems that the context manager only enters after the post itself is completed 🤔

[Dreamsorcerer]

I messed up. Once the async with has been entered, that means the server has sent the headers in response. Most servers don't begin any response until they've read the entire request...

[Dreamsorcerer]

Going to need to deprecate that and come up with a new design.

[mib1185]

You mean deprecate these two new attributes?

[Dreamsorcerer]

Yeah, they fundamentally can't be useful in most cases, so going to need a completely new design. Currently thinking this:

  async def report(p: aiohttp.Payload) -> None:                                                                                                                                                                      
      while not p.upload_complete.done():                                                                                                                                                                            
          print(f"uploaded {p.bytes_written} bytes")                                                                                                                                                                 
          await asyncio.sleep(1)          # app picks the cadence                                                                                                                                                    
      print(f"upload complete: {p.bytes_written} bytes")                                                                                                                                                             
                                                                                                                                                                                                                     
  progress = asyncio.create_task(report(mpwriter))                                                                                                                                                                   
  async with session.post(url, data=mpwriter) as resp:

Which does require that you create a Payload object to pass to data first, as that's where the upload progress would live.

[Dreamsorcerer]

#13427 should be in the next patch release