When calling `get_write_buffer_limits` on a SSL transport the following exception is raised:

```py
Traceback (most recent call last):
  File "/home/mooncell/works/test.py", line 26, in <module>
    asyncio.run(main())
  File "/usr/lib/python3.10/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "/usr/lib/python3.10/asyncio/base_events.py", line 641, in run_until_complete
    return future.result()
  File "/home/mooncell/works/test.py", line 24, in main
    print(transport.get_write_buffer_limits())
  File "/usr/lib/python3.10/asyncio/transports.py", line 306, in get_write_buffer_limits
    return (self._low_water, self._high_water)
AttributeError: '_SSLProtocolTransport' object has no attribute '_low_water'. Did you mean: '_high_water'?
```

We looked into the implementation and found out that `_SSLProtocolTransport` didn't override the `_FlowControlMixin.get_write_buffer_limits`.

Technically it should not provide the method according to the current design.
get_write_buffer_limits() is not a part of public transports API, this method is defined by private class _FlowControlMixin only.

WriteTransport requires only get_write_buffer_size() and set_write_buffer_limits() *setter* but not get_write_buffer_limits() getter.

I agree, looks weird.
The best solution maybe is adding get_write_buffer_limits() to WriteTransport definition and documenting the change.

Would you prepare a pull request? I'm happy to review/merge it.

Forgot to write, after making the method public we can implement it in SSL transport easily.

Hey Andrew, thanks for the reply! 

> Would you prepare a pull request?

Sure.

> ... and documenting the change.

Apparently `WriteTransport.get_write_buffer_limits` is already documented 
(https://docs.python.org/3/library/asyncio-protocol.html#asyncio.WriteTransport.get_write_buffer_limits) 

so please can you clarify on what did you mean by that? 

I am sorry this is my first time here.

Sorry, I didn't look into docs before writing.
Now we have an interesting situation: the documentation reflects the desired state already but the code is not :)

The PR should contain fixes for transports.py and sslproto.py only (plus a blurb record for NEWs).

Sorry for misleading you.

New changeset 64568acbd88a88d54ac9b8215447f88280448dd5 by Emiya in branch 'main':
bpo-46487: Add `get_write_buffer_limits` to Write and _SSLProtocol transports (GH-30958)
https://github.com/python/cpython/commit/64568acbd88a88d54ac9b8215447f88280448dd5

New changeset e4a6e549027b33bbe87f49fcfccc880243e49834 by Miss Islington (bot) in branch '3.9':
bpo-46487: Add `get_write_buffer_limits` to Write and _SSLProtocol transports (GH-30958)
https://github.com/python/cpython/commit/e4a6e549027b33bbe87f49fcfccc880243e49834

New changeset e5e1441d41907f92cc3bb5de675a2c519068173d by Miss Islington (bot) in branch '3.10':
bpo-46487: Add `get_write_buffer_limits` to Write and _SSLProtocol transports (GH-30958)
https://github.com/python/cpython/commit/e5e1441d41907f92cc3bb5de675a2c519068173d

Done, thanks!