httpcore/backends/trio: map OSError exceptions (#543)

The underlying socket implementations can raise OSError for situations
such as `getaddrinfo` failing to resolve an address.

Previously, these errors would not be mapped to httpcore exception types
for the trio backend.

Now, map OSError exceptions in the trio backend to ConnectError.

This will make trio consistent with the asyncio backend.

Signed-off-by: Vincent Fazio <vfazio@xes-inc.com>

Author: vfazio

httpcore/backends/trio.py

@@ -111,6 +111,7 @@ async def connect_tcp(
         exc_map = {
             trio.TooSlowError: ConnectTimeout,
             trio.BrokenResourceError: ConnectError,
+            OSError: ConnectError,
         }
         # Trio supports 'local_address' from 0.16.1 onwards.
         # We only include the keyword argument if a local_address
@@ -130,6 +131,7 @@ async def connect_unix_socket(
         exc_map = {
             trio.TooSlowError: ConnectTimeout,
             trio.BrokenResourceError: ConnectError,
+            OSError: ConnectError,
         }
         with map_exceptions(exc_map):
             with trio.fail_after(timeout_or_inf):