skip ssl import if not available

`utils.py` has support for detecting whether the `ssl` module is available, and
we can use this to omit SSL-specific funcionality while still providing other
features (e.g. unencrypted connections).

Prior to this patch, the `connection.py` modules both triggered an `ImportError`
due to unconditional imports of the `ssl` module.  Now, we check
`utils.SSL_AVAILABLE` prior to attempting the import and only raise an error
later if (and only if) the application requests an encrypted connection.  This
helps support platforms such as `wasm32-wasi` where the `ssl` module is not
built by default.

Signed-off-by: Joel Dice <[email protected]>

Author: dicej

redis/asyncio/connection.py

@@ -3,7 +3,6 @@
 import enum
 import inspect
 import socket
-import ssl
 import sys
 import warnings
 import weakref
@@ -25,6 +24,16 @@
 )
 from urllib.parse import ParseResult, parse_qs, unquote, urlparse
 
+from ..utils import SSL_AVAILABLE
+
+if SSL_AVAILABLE:
+    import ssl
+    from ssl import SSLContext
+
+else:
+    ssl = None
+    SSLContext = None
+
 # the functionality is available in 3.11.x but has a major issue before
 # 3.11.3. See https://github.com/redis/redis-py/issues/2633
 if sys.version_info >= (3, 11, 3):
@@ -740,6 +749,9 @@ def __init__(
         ssl_check_hostname: bool = False,
         **kwargs,
     ):
+        if not SSL_AVAILABLE:
+            raise RedisError("Python wasn't built with SSL support")
+
         self.ssl_context: RedisSSLContext = RedisSSLContext(
             keyfile=ssl_keyfile,
             certfile=ssl_certfile,
@@ -800,6 +812,9 @@ def __init__(
         ca_data: Optional[str] = None,
         check_hostname: bool = False,
     ):
+        if not SSL_AVAILABLE:
+            raise RedisError("Python wasn't built with SSL support")
+
         self.keyfile = keyfile
         self.certfile = certfile
         if cert_reqs is None:
@@ -820,7 +835,7 @@ def __init__(
         self.check_hostname = check_hostname
         self.context: Optional[ssl.SSLContext] = None
 
-    def get(self) -> ssl.SSLContext:
+    def get(self) -> SSLContext:
         if not self.context:
             context = ssl.create_default_context()
             context.check_hostname = self.check_hostname

redis/connection.py

@@ -1,7 +1,6 @@
 import copy
 import os
 import socket
-import ssl
 import sys
 import threading
 import weakref
@@ -35,6 +34,12 @@
     str_if_bytes,
 )
 
+if SSL_AVAILABLE:
+    import ssl
+
+else:
+    ssl = None
+
 if HIREDIS_AVAILABLE:
     import hiredis