bpo-44011: New asyncio ssl implementation (#17975)

diff --git a/Lib/asyncio/constants.py b/Lib/asyncio/constants.py
index 33feed6..f171ead 100644
--- a/Lib/asyncio/constants.py
+++ b/Lib/asyncio/constants.py
@@ -15,10 +15,17 @@
 # The default timeout matches that of Nginx.
 SSL_HANDSHAKE_TIMEOUT = 60.0
 
+# Number of seconds to wait for SSL shutdown to complete
+# The default timeout mimics lingering_time
+SSL_SHUTDOWN_TIMEOUT = 30.0
+
 # Used in sendfile fallback code.  We use fallback for platforms
 # that don't support sendfile, or for TLS connections.
 SENDFILE_FALLBACK_READBUFFER_SIZE = 1024 * 256
 
+FLOW_CONTROL_HIGH_WATER_SSL_READ = 256  # KiB
+FLOW_CONTROL_HIGH_WATER_SSL_WRITE = 512  # KiB
+
 # The enum should be here to break circular dependencies between
 # base_events and sslproto
 class _SendfileMode(enum.Enum):