bpo-46487: Add `get_write_buffer_limits` to Write and _SSLProtocol transports (GH-30958)

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

Lib/asyncio/sslproto.py

@@ -367,6 +367,12 @@ class _SSLProtocolTransport(transports._FlowControlMixin,
         """Return the current size of the write buffer."""
         return self._ssl_protocol._transport.get_write_buffer_size()
 
+    def get_write_buffer_limits(self):
+        """Get the high and low watermarks for write flow control. 
+        Return a tuple (low, high) where low and high are 
+        positive number of bytes."""
+        return self._ssl_protocol._transport.get_write_buffer_limits()
+
     @property
     def _protocol_paused(self):
         # Required for sendfile fallback pause_writing/resume_writing logic

Lib/asyncio/transports.py

@@ -99,6 +99,12 @@ class WriteTransport(BaseTransport):
         """Return the current size of the write buffer."""
         raise NotImplementedError
 
+    def get_write_buffer_limits(self):
+        """Get the high and low watermarks for write flow control. 
+        Return a tuple (low, high) where low and high are 
+        positive number of bytes."""
+        raise NotImplementedError
+
     def write(self, data):
         """Write some data bytes to the transport.
 

Misc/NEWS.d/next/Library/2022-01-27-12-24-38.bpo-46487.UDkN2z.rst

@@ -0,0 +1 @@
+Add the ``get_write_buffer_limits`` method to :class:`asyncio.transports.WriteTransport` and to the SSL transport.